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Martins, Vinicius. "Estudo das propriedades mecânicas dos compósitos WC-6Co, WC-10Co, WC-20Co, WC-6Co-6Ni, WC-6Co-12Ni obtidos por metalurgia do pó convencional para aplicação em anéis de selos mecânicos." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2010. http://hdl.handle.net/10183/31381.
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O presente trabalho tem como objetivo o estudo das propriedades mecânicas do metal duro nas composições WC-6Co, WC-10Co, WC-20Co, WC-6Co-6Ni, WC-6Co-12Ni, obtidos por metalurgia do pó convencional para aplicação em anéis de selos mecânicos. Estes compósitos foram obtidos a partir de uma composição comercial de WC-6Co, e adicionado cobalto e níquel para realização do balanço de massa. Determinou-se um procedimento de obtenção das composições, através de cálculos de balanceamento adicionando-se a quantidade de cobalto e níquel necessária para transformar um compósito comercial 94WC-6Co nos metais duros mencionados. Após este procedimento adicionou-se 1,5% de lubrificante, em um misturador em “Y”. Analisou-se no Microscópio eletrônico de varredura a homogeneidade das composições. Determinou-se a densidade aparente, a curva de compressibilidade e compactaram-se as amostras de metal duro obtendo-se as densidades a verde. Realizou-se a pré-sinterização e determinaram-se as densidades das peças présinterizadas, executou-se ensaio de compressão e obtiveram-se parâmetros de usinagem na operação de faceamento e furação dos corpos de prova pré-sinterizados. A sinterização foi realizada em diversas vezes, nos dois fornos resistivos e em três atmosferas de controle diferentes. Determinaram-se curvas rápidas de sinterização e utilizou as temperaturas de 1360, 1400, 1420, e 1450ºC para as várias composições de metal duro. Para analisar-se a eficiência da mistura foi realizado ensaio de densidade das amostras sinterizadas, dureza, microdureza, metalografia, micrografia, EDS, contração linear e contração volumétrica e compressão. Após a caracterização dos materiais foi projetado e fabricado um ferramental de compactação. Compactou-se, sinterizou-se e retificou-se um anel de selo mecânico.The aim of this work is to characterize to study the mechanical properties of carbide in the composition WC-6Co, WC-10Co, WC-20Co, WC-6Co-6Ni, WC-6Co-12Ni obtained by conventional powder metallurgy for application to rings of mechanical seals. These composites were obtained from a commercial composition of WC-6Co, and added cobalt and nickel to perform the mass balance. It was determined a procedure for obtaining the compositions, by calculation of balancing resulting in the amount of cobalt and nickel needed to transform a composite commercial 94WC-6Co in hard metals mentioned. After this procedure was added to 1.5% of lubricant, in a blender "Y". Analyzed in a scanning electron microscope the homogeneity of the compositions. It was determined the density, the compressibility curve and compress the samples carbide yielding green densities. We calculated the pre-sintering and determined the densities of pre-sintered parts, performed in compression test and it was obtained machining parameters in milling operation and drilling of the specimens pre-sintered. The sintering was performed at various times in the two resistive furnaces and atmospheres in three different control. Were determined fast corners and used sintering temperatures of 1360, 1400, 1420, and 1450 º C for various compositions of carbide. To analyze the efficiency of mixing was performed to test the samples sintered density, hardness, hardness, metallography, electron micrograph, EDS, linear and volumetric shrinkage and compression. After the characterization of materials was designed and manufactured tools of compaction, compacted, sintered and ground a ring of mechanical seal.
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Hashe, Nobom Gretta. "Characterization of WC-VC-Co and WC-VC-TiC-Co hardmetals." Thesis, Nelson Mandela Metropolitan University, 2007. http://hdl.handle.net/10948/522.
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This thesis contains the results of a study focused on cubic carbide and carbonitride grain growth retardation in hardmetals. Large additions of VC, or VC and TiC, or (W,V)C were made to the WC-Co hardmetal, which was then sintered in vacuum or nitrogen. The effectiveness of Ti as the grain growth inhibitor, and the influence of nitrogen sintering on grain coarsening were investigated using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffractrometry (XRD) and atom probe field ion microscope (APFIM). Analysis of vacuum-sintered WC-VC-Co revealed that the cubic carbide grains have a core-rim structure. Ti was found to be a core-rim inhibitor in vacuum-sintered WCVC- TiC-Co. The average cubic carbide grain size distribution for the vacuumsintered materials was narrowed in the Ti-containing hardmetal. The nitrogen-sintered WC-VC-TiC-Co consisted of two phases of cubic carbonitride, one with high Ti-content and the other with high (W,V)-content. The surface region of the nitrogen-sintered WC-VC-TiC-Co was covered with a cubic carbonitride phase. Similar phenomena was observed in nitrogen-sintered WC-VC-Co where two types of carbonitrides were found, those with high V-content and the others with low Vcontent. A gradient zone, consisting of fine WC grains in a Co-rich binder and free from cubic carbonitride grains, was created in the surface region. The nitrogensintered materials consisted of a narrow grain size distribution. The use of (W,V)C as a starting powder affected the mechanical properties of the material with the WC-(W,V)C-Co material being the hardest of those produced in this study. Addition of (W,V)C powder to WC-Co was shown to be the most effective way to limit the cubic carbide grain size during sintering and produce a hard material. The cubic carbide grain size in the material produced this way was the smallest of all studied.
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Lay, Dietrich-Sabine. "Approche microstructurale et comportement en fluage de materiaux wc et wc-co." Caen, 1985. http://www.theses.fr/1985CAEN2002.
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Rappel de resultats de metallographie quantitative et d'analyse fine permettant de considerer que des les premiers pourcents de liant, il existe un squelette continu de cobalt. Observations sur echantillons recuits a 1700 c puis deformes a 1450 c montrant que l'ensemble des mecanismes de deformation des carbures est gouverne par la montee des dislocations
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Gyllensvärd, Niklas. "WC-spolning med regnvatten." Thesis, Malmö högskola, Fakulteten för teknik och samhälle (TS), 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:mau:diva-21416.
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Idag spolar den stora majoriteten av alla invånare i Sverige med dricksvattnen itoaletten. Spolning med regnvatten i WC är något som på flera håll i världenanvänds flitigt främst i områden med någon slags vattenbrist. Men i Sverige harregnanvändande anläggningars popularitet inte riktigt slagit igenom ännu.Orsaken till detta kan härledas till flera faktorer. De viktigaste och de sompåverkar mest är; den goda tillgången och således låga priset på dricksvatten iSverige, samt begränsad konkurrens bland företag och återförsäljare vilket ger etthögt investeringspris på regnanvändande anläggningar för konsumenten.Fokus i detta examensarbete ligger på att göra en grundläggande analys avregnvatten och möjligheterna att genom en regnanvändande anläggning kunnaanvända regnvatten istället för dricksvatten för att spola i toaletten med.Tillvägagångssättet har varit att genom en studie av olika källor sammanställainformation relevant till ämnet regnvatten och regnvattenanvändning till WCspolning,följt av en analys och jämförelse av hur ekonomiskt hållbar enregnanvändande anläggning i ett standardhus beläget i Malmö är, i förhållande tillsamma standardhus med en traditionell dricksvattenförsörjning för WC-spolning.Resultatet av analysen visar tydligt att en regnvattenanvändande anläggning ifallet med standardhuset i dagsläget inte går att rättfärdiga ur ekonomisksynpunkt, men även att det finns möjlighet till en realistisk ekonomisk förtjänst iandra byggnader eller i framtiden.The vast majority of the Swedish population today flushes their toilet withdrinking water. Flushing the toilet with rain water is used diligently on multiplelocations around the world, typically where there is a shortage of fresh water. InSweden though, the popularity of rain water harvesting has not yet beensuccessful. The cause of this can be deducted to several factors, where the mostimportant and the most influential are the abundant source, and therefore low cost,of fresh water in Sweden and the lack of competition among retailers, whichresults in a high investment cost of rain water harvesting equipment for theconsumer.The focal point of this Bachelor’s Degree project is to make a fundamentalanalysis of rain water and the possibilities of using rain water instead of drinkingwater for flushing the toilet. The procedure of the project has consisted of a studyof sources, a compilation of information relevant to rain water and the use of rainwater as flushing water in the toilet and an analysis of a calculated average housein Malmo, Sweden, and a comparison between a traditional toilet flushing systemand a rain water toilet flushing system of the same average house.The result of the analysis clearly shows that a rain water toilet flushing systemcan not be justified from a economical standpoint in the case of the average house,but also that there is a realistic chance of an economical profit in the future or ifused with other building types.
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Ahmadian-Najafabadi, Mehdi. "Sintering, microstructure and properties of WC-FeAl-B and WC-Ni3Al-B composite materials." Access electronically, 2005. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20061121.154813/index.html.
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BALBINO, Nádia Alves Nery. "Caracterização Microestrutural e Mecânica dos Metais Duros WC-Ni-Mo e WC-Ni-Cr." reponame:Repositório Institucional da UNIFEI, 2016. http://repositorio.unifei.edu.br:8080/xmlui/handle/123456789/537.
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Os metais duros são materiais compósitos metal-cerâmica que apresentam uma combinação única de elevada dureza e boa tenacidade à fratura, encontrando diversas aplicações de engenharia, tais como: ferramentas para usinagem, corte industrial, moldes, matrizes de conformação, indústrias de minério e de petróleo, componentes resistentes ao desgaste entre outras. O cobalto é o ligante mais utilizado na produção de metais duros convencionais, porém, fatores econômicos tem motivado a busca por novas alternativas visando à substituição total ou parcial do cobalto por outros elementos como fase ligante. O níquel, por pertencer ao mesmo grupo do cobalto e ter um preço mais baixo, se comparado ao cobalto, tem recebido grande atenção. Contudo, a substituição do cobalto pelo níquel resulta em uma diminuição da dureza e da resistência mecânica do metal duro resultante. Para superar essa deficiência, tem sido estudada a adição de elementos, como molibdênio e cromo, que promovam o endurecimento do níquel por solução sólida. O principal objetivo desse trabalho é a caracterização mecânica e microestrutural dos metais duros 90%WC-8%Ni-2%Mo₂C e WC-8%Ni-2%Cr₃C₂, produzidos pela metalurgia do pó convencional, onde os pós foram misturados por 80 horas e sinterizados a 1460ºC. Os pós de partida foram caracterizados pelas técnicas de microscopia eletrônica de varredura (MEV), difração de raios X (DRX) e distribuição granulométrica. As amostras sinterizadas foram caracterizadas por microscopia óptica (MO), MEV, espectroscopia de raios X por dispersão de energia (EDS), fração volumétrica da porosidade, densidade, ensaios de microdureza Vickers e cálculo da tenacidade à fratura. As amostras do metal duro 90%WC-8%Ni-2%Mo₂C obtiveram resultados superiores ao do metal duro WC-8%Ni-2%Cr₃C₂, com propriedades mecânicas comparáveis as dos metais duros convencionais WC-Co.
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Roulon, Zoé. "Effet du liant sur le frittage et la microstructure de carbures cémentés." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAI061/document.
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Grâce à leurs excellentes propriétés de dureté et de résistance à l’usure, les carbures cémentés sont les meilleurs candidats pour la réalisation d’outillage de coupe. Elaborés par la métallurgie des poudres, ils sont majoritairement composés de carbure de tungstène, choisis pour ses propriétés de dureté et d’un liant métallique à haute ductilité, le plus souvent le cobalt. Néanmoins, l’utilisation du cobalt comme liant est remis en question depuis quelques années par la commission européenne REACH à cause de sa toxicité. En conséquence, des liants alternatifs tels que les alliages de Fe et Ni sont étudiés. Malgré les différents travaux menés, il subsiste un manque de compréhension fondamental sur l’effet spécifique du liant sur le frittage et le grossissement de grains des carbures cémentés. Le but de cette étude est la compréhension de l’effet de la composition du liant sur le frittage et le grossissement de grains. Dans cet objectif, différent liants WC-20vol%M (M=Fe, Ni or Co) et différent taux de carbone sont considérés. Le frittage et le grossissement de grains seront étudiés à l’aide de caractérisations macroscopiques et microstructurales, puis les résultats discutés en comparaison avec la littérature. Comme il a été déjà observé dans le cas d’alliages WC-Co, le retrait au cours du frittage survient plus tôt dans le cas d’alliages riches en W qu’en C, quelque soit le liant considéré. Concernant l’effet de la nature du liant, le frittage en phase solide est décalé vers les hautes températures pour WC-Fe en comparaison avec WC-Co et WC-Ni. Dans cette étude le retrait est directement corrélé avec la capacité d’étalement du liant dans la porosité, comme le confirme l’analyse de la microstructure. Quant au grossissement de grain, il est inhibé pour un faible ratio C/W, quelque soit la nature du liant. Néanmoins, pour un ratio C/W élevé, celui-ci augmente, ainsi que la tendance au grossissement anormal, en particulier dans le cas du liant nickel. Les mécanismes de grossissement de grains sont discutés en lien avec les observations structurales des interfacesThanks to their exceptional hardness and wear resistance, cemented carbides are the best candidates to make efficient cutting and drilling tools by the powder metallurgy route. Known as a very hard ceramic material, tungsten carbide is used as the major component of cemented carbides. A ductile metal binder is added as the matrix, which in most cases is cobalt. Nevertheless the use of cobalt as a binder is questioned by the new European regulation on chemicals (REACH). Therefore, new alternative binders are considered, especially Fe and Ni-alloys. Although a few studies exist for Fe-based and Ni-based WC cemented carbides, there is still a lack of fundamental understanding of the specific effect of the binder on sintering and grain growth. This work discusses the effect of binder composition on sintering and grain growth of cemented carbides. For this purpose, different binder compositions WC-20vol%M (M= Fe, Ni or Co) and different C/W ratio are considered. Sintering and grain growth behaviors are investigated using several macroscopic and microstructural characterizations, and results are discussed and compared to the literature. As already observed in previous works on WC-Co, shrinkage occurs earlier for W-rich than for C-rich alloys for the three binders. Regarding the influence of the binder nature, solid state sintering is delayed to higher temperature for WC-Fe in comparison to WC-Co and WC-Ni alloys. Shrinkage is directly related to the spreading efficiency of the binder into the porosity, as confirm by the microstructure analysis. Grain growth is inhibited for low C/W ratio whatever the binder nature. Nevertheless, for a high C/W ratio, grain growth is enhanced and the abnormal character of grain growth increases, especially in the case of a Ni binder. Grain growth mechanisms are discussed in relation with the observed structure of phase boundaries
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Hankey, S. E. "Cavitation erosion of WC-Co." Master's thesis, University of Cape Town, 1987. http://hdl.handle.net/11427/21135.
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Bibliography: pages 68-70.An investigation involving the vibratory cavitation erosion of WC-Co alloys was undertaken in order to determine the mechanisms of material removal. Nineteen grades of WC-Co alloys were studied. These alloys had been previously characterised according to microstructural and mechanical properties. Further characterisation by way of Young's modulus and density of the materials was undertaken. An investigation of the i nfluence of various parameters on cavitation erosion established a binder content dependence on erosion. For two grain sizes, erosion was found to increase to a maximum at 12 vo1-% binder content (1.8 μm grain size) and 23 vol-% binder (2.8 μm grain size). The main mode of material removal was found to be cobalt removal followed by WC grain pull-out. In high binder content alloys, cobalt removal was predominant with little loss of WC grains. X-ray diffraction showed that the allotropic phase transformation of the binder under cavitational attack was beneficial to the erosion resistance of these alloys. The erosion of low binder content alloys was controlled by the contiguity of the WC skeleton. Maximum erosion occurred at binder contents which corresponded to the combination of a fragile WC skeleton and a small volume of available cobalt for strain induced transformation.
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Holmgren, Jonna. "Growth of TiN on WC surfaces." Thesis, Uppsala universitet, Institutionen för kemi - Ångström, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-188243.
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The growth of TiN on cemented carbide, deposited by chemical vapour deposition (CVD), was studied. Today TiN is used as a seeding layer between the cemented carbide and the following layer. Previous experiments have shown that the coverage is uneven on the cemented carbide surface showing pits with a different growth than the main part of the surface. These pits most likely occur on some of the WC surfaces. Therefore the growth and orientation relation between the two phases were examined. Cemented carbide specimens were deposited with TiN under two different pressures and with different deposition time to give a layer as thick as the seeding layer used in the production and one about ten times thicker to study growth after the whole surface had been covered. Two pre-treatments where used on the specimens; one which were polishing with diamond and the other where the specimens were boiled in acid to remove the binder phase and expose the WC surfaces. The specimens were studied using XRD and a SEM equipped with EDS and EBSD detectors. The pictures taken with SEM showed that initial growth occurred at grain boundaries and polishing scratches. It also showed that growth occurred on all surfaces, which were confirmed by EDS. Both processes showed about the same appearance in the thinner layers but very different appearance in the thicker. This was confirmed by XRD were the thinner layers showed about the same result while the thicker ones differ from one another. Thus further growth is dependent on the parameters of the CVD process and not the surface beneath. EBSD showed an orientation relation between TiN and WC crystals in both processes. The process at lower pressure gave much finer grains which were difficult to index with EBSD, giving results in only three points. The process at higher pressure gave coarser grains which were more easily indexed. The relations WC{0001}-TiN{110}, giving WC{101̅0}-TiN{100}, and WC{0001}-TiN{111}, giving WC{101̅0}-TiN{211}, could be seen in more than one point. These results are consistent with previous studies of the growth of TiC on WC. This comparison between TiC and TiN makes it possible to draw the conclusion that also Ti(C,N) should behave the same. It also shows an orientation relation that is consistent no matter what WC plane is on the surface. The poor growth and the pits depend on the growth orientation of TiN on each specific WC surface.
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Andersson, Karin M. "Aqueous Processing of WC-Co Powders." Doctoral thesis, KTH, Chemistry, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3725.
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The object of this work is to obtain a fundamentalunderstanding of the principal issues concerning the handlingof an aqueous WC-Co powder suspension.
The WO3 surface layer on the oxidised tungsten carbidepowder dissolves at pH>3 with the tungsten concentrationincreasing linearly with time. Adding cobalt powder to thetungsten carbide suspension resulted in a significant reductionof the dissolution rate at pH<10. Electrokinetic studiesindicated that the reduced dissolution rate may be related tothe formation of surface complexes; the experiments showed thatCo species in solution adsorb on the oxidised tungsten carbidepowder.
The surface forces of oxidised tungsten and cobalt surfaceswere investigated using the atomic force microscope (AFM)colloidal probe technique. The interactions at various ionicstrengths and pH values are well described by DLVO theory. Theadsorption of cobalt ions to tungsten oxide surfaces resultedin an additional non-DLVO force and a reduced absolute value ofthe surface potential. It was shown that the adsorption ofpoly(ethylene imine) (PEI) to the WO3 surfaces induces anelectrosteric repulsion.
The properties of spray-dried WC-Co granules were related tothe WC primary particle size, and the poly(ethylene glycol)(PEG) binder and PEI dispersant content in aqueous WC-Cosuspensions. The granule characterisation includes a new methodfor measuring the density of single granules. The increase inthe fracture strength of granules produced from suspensionsthat were stabilised with PEI was related to a more densepacking of the WC-Co particles.
The AFM was used to study the friction and adhesion ofsingle spray-dried WC-Co granules containing various amounts ofPEG binder. The adhesion and friction force between two singlegranules (intergranular friction) and between a granule and ahard metal substrate (die-wall friction) have been determinedas a function of relative humidity. The granule-wall frictionincreases with binder content and relative humidity, whereasthe granule-granule friction is essentially independent of therelative humidity and substantially lower than the granule-wallfriction at all PEG contents.
Key words:Hard Metal, Cemented Carbide, WC-Co, TungstenCarbide, Cobalt, Oxidation, Dissolution, Surface Complexation,XPS, AFM, Colloidal Probe, Hamaker Constant, Cauchy, WO3,CoOOH, ESCA, Zeta-Potential, Surface Potential, Poly(ethyleneimine), PEI, Suspension, van der Waals, Steric, Spray-Dried,Poly(ethylene glycol), Strength, Density, Friction, Adhesion,Granule, PEG, Pressing, FFM.
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Ndlovu, Siphilisiwe Nompumelelo. "The erosion of WC-Co coatings." Master's thesis, University of Cape Town, 2002. http://hdl.handle.net/11427/4959.
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Includes bibliographical references.A study has been conducted on both the particle and slurry erosive wear behaviour of WC-Co hard metal coatings. The coating compositions were WC-12%Co and WC-10%Co-4%Cr and were produced using both the TAFA JP5000 and the METCO Diamond Jet (DJ) thermal spray systems.
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Pugsley, Victoria Antonietta. "The erosion of ultrafine WC-Co." Master's thesis, University of Cape Town, 1999. http://hdl.handle.net/11427/19805.
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A series of four ultrafine WC-Co alloys of varying cobalt contents has been sintered from powder produced through the spray conversion process. The materials have been characterised and subjected to slurry erosion and cavitation erosion. A further twelve WC-Co alloys of varying grain sizes and cobalt contents have been produced through conventional processes and subjected to the same tests in order to provide data for comparison. The erosion resistance of all the grades tested was found to increase with decreasing grain size, both under cavitation erosion and slurry erosion conditions. Furthermore, a transition from a localised material removal mechanism to a bulk material removal mechanism was observed in both erosive systems as the WC grain size of the material decreased below about lμm. The erosion resistance of sub-micron materials was found to be considerably more sensitive to bulk deformation parameters than that of coarser materials. As a result, ultrafine grades subjected to slurry erosion or cavitation erosion were found to exhibit lifetimes up to seven times greater than those of the best-performing materials with grain sizes above 1 μm. This increase in erosion resistance was achieved without any significant drop in fracture toupness. Significant differences were observed between the response of WC-Co to the two erosive systems, particularly in those materials exhibiting a localised erosion response. Under slurry erosion conditions, these materials displayed increasing erosion resistance with decreasing cobalt content, and both the cobalt and WC phases responded to erosive attack. Under cavitation erosion conditions, however, the opposite trend was observed, and only the cobalt phase responded to erosive attack. Materials exhibiting a bulk erosion response responded in a similar fashion to both forms of erosive attack, although cavitation erosion produced damage to a greater depth. The effect of defects on material performance was found to depend critically on the erosive system.
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Pereira, de Magalhaes e. Couto Miguel. "Cold Spray Deposition of WC-Co Cermets." Doctoral thesis, Universitat de Barcelona, 2014. http://hdl.handle.net/10803/285313.
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The main subject of this Thesis is the production of hard, wear and corrosion resistant cermets tungsten carbide and cobalt cermets (WC-Co) with different contents in cobalt matrix, onto low carbon steels and aluminum alloy Al7075-T6 substrates, by means of Cold Gas Spray (CGS). The current state of the art for the deposition of WC-Co uses High Velocity Oxy-Fuel (HVOF) as the main technique. Understanding both techniques was also one of the keys points in this work.
A deep theoretical approach about the CGS process, in which no melting of the particles occurs, was made at first to gain a better comprehension about the behaviour of the powder particles when sprayed onto different substrates and therefore being able to produce good quality coatings.
The starting purpose of this doctoral Thesis was to produce WC-25, 17 and 12%Co coatings onto low carbon steel and Al7075-T6 substrates. Until the day, using nitrogen as the process gas, such coatings could not be produced with enough adhesion, thickness and wear and corrosion properties. These are the main characteristics sought by the industry in these coatings. In the end of this doctorate WC-Co coatings were obtained with excellent mechanical and electrochemical properties, adhesion to both low carbon steel and Al7075-T6 substrates. Besides, these properties were increased and improved when compared to the same WC-Co coatings obtained by HVOF conventional deposition technique.
Initial problems such as flowability of the powders, bad adherence to the substrate, poor coating quality and extremely low deposition efficiencies were resolved during the period of the Thesis.
Also, and taking advantage of the novel coatings and excellent properties obtained using the referred feedstock powders and substrates, the knowledge was transferred to the industry as a trade secret.En primer lugar, el objetivo principal de este trabajo de investigación fue proporcionar un nuevo método de deposición para depositar cermets de WC-Co. Esta nueva tecnología proporcionó nuevos recubrimientos sin ninguna descomposición de la microestructura del polvo inicial y por lo tanto la mejora de las presentes aplicaciones de WC-Co en la gran industria. La deposición de cermets de WC-Co resistentes al desgaste ha sido siempre una de las principales aplicaciones de las técnicas de proyección térmica convencionales como por ejemplo High Velocity Oxy-Fuel (HVOF). Las demandas de la industria en términos de producción y la necesidad y constante búsqueda de mejores propiedades mecánicas y electroquímicas conducen al objetivo principal y la motivación de esta tesis: la producción de nuevos y mejores recubrimientos de WC-Co sobre varios sustratos utilizando una técnica de deposición nueva, Cold Gas Spraying (CGS). El hecho de que antes de la publicación del primer artículo que nació de este trabajo de investigación no se había depositado previamente con éxito este tipo de materiales por CGS fue también uno de los principales puntos de motivación. Por esta razón, el lector encontrará, en la integridad del documento, los trabajos de investigación que fueron publicados durante estos años de programa de doctorado y cumplen los objetivos principales de esta tesis titulada "Deposición de cermets de WC-Co por Proyección Fría".
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Bocarro, R. A. "Water conserving WC design for developing countries." Thesis, Brunel University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379757.
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Liu, Chunxin. "Alternative binder phases for WC cemented carbides." Thesis, KTH, Materialvetenskap, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-168229.
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WC cemented carbides are composites consisting of WC and a binder phase. WC/Co is widely used as cutting tools due to its excellent combination of hardness and toughness. This thesis work was performed at the R&D department of Sandvik Coromant and aimed to find the alternative binder phase to substitute cobalt. Several compositions of Fe-Ni and Fe-Ni-Co binder have been investigated in this study. The WC/Co reference samples were also prepared. The initial compositions were decided by the CALPHAD method. The samples were then produced by the means of powder metallurgy. The producing conditions, especially the sintering conditions, were manipulated to achieve full dense and uniform samples. The samples were analyzed by XRD, LOM, SEM, and EDS. Mechanical properties test has also been performed.The results showed that adjustment on carbon content is necessary to attain desirable structure. Increasing Fe content in the binder tends to make the materials harder. For Fe-Ni and Fe-Ni-Co, the martensitic transformation is essential to the mechanical performance. The induced “transformation toughening” in 72Fe28Ni and 82Fe18Ni binders significantly promoted the toughness. Furthermore, the grain growth inhibition by Fe was confirmed. The relations between sintering temperature, grain size and mechanical properties have been discussed. Compared with the WC/Co references, several compositions showed close and even superior mechanical performance which might provide solutions for the future alternative binder phase.
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Zuñega, Jonee. "High temperature indentation of WC/Co hardmetals." Thesis, University of Southampton, 2013. https://eprints.soton.ac.uk/352190/.
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WC/Co is the material of choice for most high wear applications such as hot forming operations, drilling, cutting, machining and wire drawing due to its superior wear properties. In the evaluation of its material properties to withstand wear, particularly that of its hardness, most of the available information is based on room temperature investigations. However, when WC/Co is used in the actual applications, it also experiences very high contact temperatures and this localized heating has a detrimental effect on the WC/Co material causing microstructural changes on the surface and sub-micron surface that affect its wear resistance properties. Creep also plays an important role in the damage mechanisms at elevated temperatures especially in prolonged contact to heat such as those used in hot metal forming operations. However, the current information on these high temperature properties is not complete and has contradictory results. Moreover, creep studies of WC/Co have been done at temperatures >800°C and information below this temperature is also lacking. Therefore, the primary goal of this thesis is to obtain a first time in-depth understanding of its high temperature property–composition–microstructure interaction that affects its wear properties from room temperature up to 800°C using comprehensive scratch tests, high temperature indentation hardness tests and indentation creep tests. These tests are supplemented with advanced 3D imaging, microstructural and composition analysis using SEM, EBSD, FIB, EDX, SIMS and laser confocal microscopy. Moreover, due to the lack of a commercially available high temperature microindentation test system, this thesis also aims to design, build and commission a high temperature and high vacuum microindentation test system to carry out these investigations. The results of the scratch tests showed new information on the damage mechanisms, particularly on the formation of a tribo-layer on the scratched surfaces and the evolution of surface damages incurred on the indenter tip which is found to affect the coefficient of friction. These provide baseline information on the damage mechanisms occurring at room temperature and were instrumental in the development of the methodology used in the high temperature indentation tests. The results of the high temperature indentation tests showed that the behaviour of the WC/Co hardmetals were categorised according to two temperature regimes. In the low temperature regime (20°C→500°C), the controlling factor is dominated by the WC grain size and that the damage mechanisms are characterised by plastic deformation of the WC grains via slip, intragranular fracture of the WC grains within the surface of the indent and intergranular fracture along the edges of the indent. In the high temperature regime (>500°C), the controlling factor was dominated by the Co binder and the damage mechanism showed first time observation of severe plastic flow accompanied by shape change on the WC grains. A tribo-layer was also found to exist on the room temperature indents but not on the high temperature indents. In addition, pitting of the indenter tip occurred at test temperatures >700°C and its contribution to the measured hardness were determined. These results provide significant information on the best combination of WC grain size and Co content that are suitable for applications requiring high hardness retention and creep resistance. In addition, the thorough investigation of the damage mechanisms ensuing at these temperatures is beneficial in the design of WC/Co with better wear properties at elevated temperatures.
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Mari, Daniele. "Déformation à haute température des composites WC-Co /." [S.l.] : [s.n.], 1991. http://library.epfl.ch/theses/?nr=938.
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Perry, Joan M. "Erosion-corrosion of WC-Co-Cr cermet coatings." Thesis, University of Glasgow, 2001. http://theses.gla.ac.uk/2845/.
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The erosion-corrosion characteristics of a WC-Co-Cr coating were assessed under an impinging jet of 3.5% NaCl solution at a velocity of 12 ms-1 both free from solids and containing solids up to 2500 mg/l at a range of impingement angles. The total weight loss increased with increasing solids in the liquid stream and maximum material loss occurred in the area directly under the jet where high impact angles occurred. The material loss tended to reduce as the impingement angle reduced. The mechanism and contribution to the overall material loss in erosions-corrosion processes were studied. Surface profiling revealed the erosions mechanism to be that of solid particles causing craters on the surface of the coating, not associated with any specific microstructural aspect of the coating. The total contribution to overall material loss from corrosion processes was substantial (up to 30%). While the impinging jet increased the corrosion rate, in the absence and presence of solids, these corrosive effects could be inhibited, particularly in the presence of solids, by the application of cathodic protection which reduced overall material loss by up to 50%. The synergistic component of material loss can be referred to as an indirect corrosion effect, and in this work, the synergistic effect was significant (up to 40%). However, more complex direct corrosion effects were found in the form of galvanic currents between the area directly under the impinging jet and the outer area which significantly increase the corrosion rate on the impinged area. This study, which focuses on the interactions between corrosion and erosion, has improved the understanding of erosion-corrosion processes on complex composite materials.
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Chabretou, Valérie. "Croissance de cristaux facettes : cas de WC-Co." Grenoble INPG, 2000. http://www.theses.fr/2000INPG0003.
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Les carbures cementes wc-co sont constitues de deux phases : une phase liante, solution solide a base de co, et une phase wc, majoritaire presentant generalement des grains facettes. Ils sont prepares par metallurgie des poudres et une densification quasi totale est obtenue par frittage avec phase liquide. Durant cette etape, une evolution microstructurale, nefaste pour les proprietes mecaniques, se produit. Cette evolution correspond a une croissance des grains de wc normale (augmentation uniforme de la taille) et anormale (apparition de tres gros grains), et apparait bloquee par l'ajout en faible quantite de certains elements dits inhibiteurs tels que v ou cr. Afin de cerner le(s) mecanisme(s) mis en jeu, l'influence de divers parametres sur la croissance est caracterisee par analyse qualitative (meb, met) et quantitative. Cette derniere est realisee par analyse d'images meb en mesurant les distributions de taille d'intercepts dans la phase wc. Les facteurs etudies sont : la granulometrie de la poudre wc, la composition du liant (rapport c/w), la presence de la phase graphite ou m 6c, un ajout de v ou cr, la fraction de liant, la densite a vert des comprimes, le broyage du melange de poudres, la temperature de frittage et la vitesse de refroidissement. Un minimum de deux temps de frittage (dont un de quelques minutes) est realise. A partir des resultats experimentaux, le grossissement parait produit principalement par dissolution-precipitation, la contribution de la coalescence restant limitee. L'analyse de l'enthalpie libre du liquide a base co montre une grande metastabilite, qui explique la croissance faible et limitee pour des particules microniques et la croissance anarchique dans les populations submicroniques, et une stabilite un peu moins grande pour les compositions riches en c, coherence avec la croissance plus reguliere pour de telles compositions. Cette analyse suggere en outre que la germination de graphite peut activer la germination 2d de wc.
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Pires, Filipe de Sousa. "Diamante nanocristalino CVD sobre graus WC-Co submicrométricos." Master's thesis, Universidade de Aveiro, 2011. http://hdl.handle.net/10773/7880.
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Mestrado em Engenharia de MateriaisO diamante possui propriedades mecânicas, térmicas e eléctricas excepcionais que o tornam um material de eleição para várias aplicações. A deposição de filmes finos de diamante CVD encontrou uma das suas mais promissoras aplicações na área das ferramentas de corte. Devido à elevada dureza, estes revestimentos são muito interessantes para aplicações tribológicas. O objectivo deste trabalho consistiu no estudo da adesão de revestimentos de diamante obtidos pela técnica de HFCVD em substratos de metal submicrométricos. Estudou-se o efeito de diferentes teores de cobalto e tamanhos de grão de WC. Foram realizados ataques químicos de modo a preparar a superfície de WC-Co para a deposição de diamante, minimizando assim o efeito prejudicial do cobalto e melhorando a ancoragem mecânica do diamante. Produziram-se assim amostras com vários tipos de revestimento, nomeadamente, diamante microcristalino (MCD) e diamante nanocristalino facetado (f-NCD). Através das técnicas de microscopia electrónica de varrimento, espectroscopia de Raman, perfilometria e microscopia de força atómica, foi possível caracterizar os diferentes substratos e filmes de diamante. Foi estudado o comportamento tribológico dos diversos filmes, na forma de pares homólogos do tipo movimento linear alternativo esfera-sobre-disco, na ausência de lubrificação. O revestimento MCD mostrou ter uma rugosidade superficial maior, proporcionando valores de atrito inicial superiores mas cargas críticas de delaminação maiores. O substrato MD22 (combinação do maior tamanho de grão WC e maior teor de cobalto) apresentou os melhores resultados na avaliação da adesão através de testes de indentação estática (cargas superiores a 1000 N) e apresentando os valores mais altos de cargas suportadas nos ensaios tribológicos (30N e 50N para os filmes f-NCD e MCD, respectivamente). Os coeficientes de desgaste obtidos nas placas em testes curtos (2 h) foram na ordem de grandeza de 10-7 mm3 N-1 m-1 para os filmes MCD e f-NCD sobre os diferentes graus de metal duro, denotando um regime de desgaste suave. Nos ensaios longos (16 horas), verificou-se uma tendência da diminuição dos valores de coeficiente de desgaste para uma ordem de grandeza de 10-8 mm3 N-1 m-1.
Diamond possesses mechanical, thermal and electrical properties that make it an elegible material for several applications. The deposition of of thin CVD diamond films has founded one of its most promising applications in the cutting tools field. Due to the high hardness, these coatings are very interesting for tribological applications. The objective of this work was to study the adhesion of diamond coatings, by the HFCVD technique on substrates with submicrometric degrees of WC-Co, i.e., with different cobalt content and WC grain sizes. Chemical attacks were made in order to prepare the WC-Co surface for the diamond deposition, therefore minimizing the harmful effect of cobalt and improving the mechanical anchoring of the diamond. Several samples with different coating types were produced, namely microcrystalline diamond (MCD) and faceted nanocrystalline diamond (f-NCD). The several coatings were characterized by SEM, Raman spectroscopy, perfilometry and AFM. Thus the tribological behavior of the different coating was studied in homologous pairs of the type linear alternative movement sphere-on-disc, in the absence of lubrication. The MCD coating revealed a higher surface roughness, which provided for higher initial friction but critical delamination load values. The MD22 substrate (combination with higher WC grain size and higher cobalt content) presented the best adhesion values by static indentation tests and the higher load bearing values on the tribological essays (30 N and 50 N for the f-NCD and MCD, respectively). The wear coefficient values obtained in the plates on short tests (2 h) were of the order of 10-7 mm3 N-1 m-1 for the films f-NCD and MCD about the different grades of carbide, therefore denoting a soft wear regime. On long tests (16 h), there was a trend of drecrease in Kd values for an order of magnitude of 10-8 mm3N-1m-1.
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Pinho, Carla Maria da Silva. "Desenvolvimento de compósitos de WC com ligantes intermetálicos." Master's thesis, Universidade de Aveiro, 2014. http://hdl.handle.net/10773/12559.
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Mestrado em Engenharia de MateriaisUma das vertentes de investigação na área dos compósitos à base de carboneto de tungsténio (WC) é a substituição, total ou parcial do ligante, normalmente utilizado, o cobalto. Os ligantes constituídos por aluminetos de ferro (FeAl) têm merecido uma atenção especial, devido à sua boa resistência à oxidação e à corrosão a temperaturas elevadas. Contudo, a dificuldade de obtenção de materiais densos no sistema WC-FeAl, por técnicas convencionais de sinterização, e a redução acentuada da dureza com o aumento do teor de FeAl, são aspectos que necessitam de ser ultrapassados para que estes compósitos se tornem interessantes sob o ponto de vista industrial. O principal objetivo do presente trabalho foi a obtenção de compósitos de WC e ligantes intermetálicos, do tipo FeAl, por sinterização reativa a partir de pós precursores de WC, aço e alumínio, utilizando o processamento convencional de pulverometalurgia. Para o efeito, a homogeneização de pós de WC, aço inoxidável AISI 304 (SS) e Al foi efetuada através de moagem convencional em meio húmido. A percentagem de fase ligante (SS+Al) variou entre 8 e 12% pp, sendo que a fração de Al adicionada ao SS se situou na gama entre 0 e 0.5. A avaliação da reatividade térmica em atmosfera de vazio indicou a expansão dos compósitos com Al na composição do ligante, correspondendo à formação de soluções sólidas de Fe(Al), na gama de temperaturas entre 500 e 1000ºC. Com o aumento da temperatura, formaram-se fases intermetálicas de estequiometria variável, do tipo FeAlx com x=1,2,3, consoante a fração de Al presente no ligante e a temperatura. Os compósitos foram obtidos a partir de compactos dos pós, sinterizados a 1450ºC, durante 125 min, em atmosfera de vazio (P= 20-40 Pa), e posteriormente submetidos a uma etapa de prensagem isostática a quente, a 1400ºC, 9h, e 60 MPa. Os compactos densificados foram avaliados em termos estruturais, microestruturais e também de desempenho mecânico e resistência à oxidação. Os resultados da avaliação estrutural e microestrutural mostraram que se conseguiram obter materiais bem densificados por sinterização reativa, tendo ocorrido a síntese de fases intermetálicas, predominantemente do tipo FeAl na gama de composições estudada. A avaliação das propriedades mecânicas revelou que o aumento da fração de Al no ligante diminui os valores de dureza e melhora a resistência à oxidação.
One side of research of materials based on tungsten carbide composites (WC) is the total or partial replacement of the binder usually used, cobalt. The iron aluminides binders (FeAl) have received attention due to their good resistance to oxidation and corrosion at high temperatures. However, the difficulty of obtaining dense materials in the WC-FeAl system, by conventional sintering techniques, and the marked decrease in hardness with the increase of FeAl content, are aspects that need to be overcome if these composites become popular under the industrial point of view. The main objective of this study was to obtain composites and intermetallic WC binders, of Feal type, by reactive sintering from precursor powders of WC, steel and aluminum, using the conventional powder metallurgy processing. To this end, the powders mixing of WC, AISI 304 (SS) Al and stainless steel was performed by conventional wet milling. The percentage of binding phase (SS + Al) varied between 8 and 12 wt%, and the fraction of Al added to the SS stood in the range between 0 and 0.5. The evaluation of the thermal reactivity in an atmosphere of vacuum indicated expansion of composites with Al in the binder composition, corresponding to the formation of solid solutions of Fe (Al) in the temperature range between 500 and 1000 ° C. With the increase of temperature intermetallic phases formed with variable stoichiometry, of type FeAlx with x = 1,2,3, depending on the fraction of Al binder present and temperature. The composites were obtained from compressed powders, sintered at 1450 ° C for 125 min in an atmosphere of vacuum (P = 20-40 Pa) and subsequently subjected to a step of hot isostatic pressing, at 1400 ° C, 9h, and 60 MPa. Structural and microstructural characteristics were evaluated on the densified compacts as well the mechanical performance and oxidation resistance. The results of structural and microstructural evaluation showed that good densified materials have been achieved by reactive sintering, ocurring intermetallic phases synthesis, predominantly Feal type in the range of the studied compositions. The evaluation showed that the mechanical properties by increasing the Al content in the binder reduces the hardness and improves oxidation resistance.
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Sacks, Natasha. "The fracture toughness of ultrafine WC-Co Alloys." Master's thesis, University of Cape Town, 1999. http://hdl.handle.net/11427/20181.
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Bibliography: pages 147-152.This thesis examines the fracture toughness behaviour of a series of cemented carbides having carbide grain sizes between 0.35f.Lm and 4f.Lm, cobalt contents ranging from 6 to 15wt%, and vanadium carbide contents from 0 to 0.8wt%. A series of twenty-four ultrafine WC-Co alloys were sintered from powders produced through three different production routes, namely, the spray conversion process and two variations of the conventional powder production methods. A further twelve WC-Co alloys with three different carbide grain size distributions were produced through conventional powder metallurgy processes. Two different fracture toughness test methods have been used to determine the toughness measurements, namely, the Palmqvist Indentation test and the Short Rod test. A Terra Tek Fractometer machine was used to automatically determine the Short Rod toughness values. The Palmqvist testing was carried out on a Vickers hardness machine using indenting loads of 20, 30 and 50kg. The Palmqvist crack lengths were measured by summing the individual crack lengths emanating from the corners of the hardness indentation. These crack lengths were used in a formula developed by Shetty et al., to calculate the Palmqvist fracture toughness. The influence of annealing at 800°C and 900°C on the Palmqvist crack lengths has also been assessed. Microstructural parameters have been determined using ASTM procedures and microscopy techniques and the influence of these parameters on the fracture toughness has also been assessed.
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Pennefather, RC. "The solid particle erosion of WC-Co alloys." Master's thesis, University of Cape Town, 1986. http://hdl.handle.net/11427/22199.
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Bibliography: pages 76-82.An investigation involving the erosion of WC-Co alloys by solid particle impact erosion was undertaken to determine the mechanism by which material is removed. For this purpose a simple particle-gas stream erosion apparatus was employed. The nineteen different WC-Co alloys studied were initially characterised according to mi crostructural and mechanical properties. An investigation of the influence of various parameters on erosion was conducted to establish the manner by which the WC-Co alloys were eroded. A limit in erosion rate occurred with increasing particle size for all samples, which is associated with ductile erosion. The variation of erosion rate with the angle of impact was found to be dependent on the binder content. A maximum in erosion occurred at a 90u angle of incidence for the low cobalt content alloys and in the region of a SOU angle of incidence for high cobalt content alloys. Thus suggesting a predominantly brittle mode of erosion, with a ductile mode becoming more important with increasing binder content. The erosion rate was found to increase with decreasing hardness. For impact angles of 45u and greater, the hardness effect was masked by microstructural influences. Examination of the steady state eroded surface and the single particle impact event, using the scanning electron microscope revealed three modes of material removal. These may occur simultaneously, the predominant mode, however, changes with binder content. For WC-Co alloys containing less than 10 wt-% cobalt, cobalt extrusion was observed as being the controlling mode of material removal. Maximum carbide grain cracking was associated with a cobalt content of 10 wt-%. Above this binder level ductile cutting of the matrix became an increasingly important mode of material removal.
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Delanoë, Aurélie. "Carbures cémentés WC-Co : effet de la composition et de la température sur la morphologie et les interfaces des cristaux WC." Grenoble INPG, 2004. http://www.theses.fr/2004INPG0103.
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L'ajout de Cr et la maîtrise du potentiel de C permettent de ralentir l'évolution microstructurale des carbures cémentés WC-Co obtenus à partir de poudres submicroniques et ainsi de conserver les propriétés mécaniques intéressantes de ces alliages. Le but de notre travail est d'étudier les effets de Cr et du potentiel de C sur la microstructure au cours du frittage. Des alliages WC-Co dopés ou non en Cr et présentant à haute température soit du carbone graphite (C/W>1) soit de la phase ? (C/W<1) ont été élaborés. Plusieurs travaux ont été menés de façon à étudier ces alliages de la plus grande échelle, macroscopique, à la plus fine, atomique. L'anisotropie d'énergie interfaciale, mise en évidence par l'étude de la morphologie des grains de WC, évolue avec la composition des alliages. En fin de frittage, l'anisotropie d'énergie interfaciale entre plans de base et prismatique est diminuée en présence de W et/ ou de Cr, la baisse étant plus marquée dans les alliages dopés. Le suivi de la densification des alliages a mis en évidence une cinétique de retrait plus forte en début de frittage dans les alliages riches en W, indiquant un étalement du liant en surface des grains de WC plus rapide. En présence d'un excès de C et de Cr, une modification de la structure des plans de WC en contact avec Co est l'hypothèse la plus probable pouvant expliquer le ralentissement de la densification. La présence d'une couche interfaciale riche en Cr et la détection de Cr dans des grains de WC d'alliages modèles indiqueraient une ségrégation en Cr dans le liant liquide et dans les premières couches atomiques de WC, en accord avec la modification d'anisotropie d'énergie interfaciale observéeIn WC-Co alloys obtained with submicron powders, grain growth is limited by addition of Cr and control of C during the sintering process and so the good mechanical properties of these alloys are kept. In this work, we study the effect of Cr addition and C potential on the microstructure during sintering. We elaborate at different temperatures alloys located in the fields {WC+Co+Cg} (C excess) et {WC+Co+?} (W excess) doped or not with Cr. Macroscopic to nanometric caracterisations were made. The interfacial energy anisotropy, detected by morphology observations of WC grains, depends on the composition. At the end of sintering, interfacial energy anisotropy between basal and prismatic planes is lowered by W excess and/or Cr addition but the reduction is more important in Cr doped alloys. Between prismatic planes, W excess and Cr addition have opposite effect : W lowers the interfacial energy anisotropy whereas Cr addition increases it. Densification study of these alloys underlines an effect of the composition at the beginning of the sintering : densification rate is increased by W excess, which indicates a faster Co spreading on WC grains surfaces. In C rich alloys doped or not, a structural modification of WC planes which are in contact of Co is the more realistic hypothesis which could explain the slowing down of the densification. The detection of Cr rich interfacial layer and of Cr in WC grains would indicate a Cr segregation in the Co liquid phase and in the first atomic layers of WC grains in model alloys, in aggreement with the interfacial anisotropy energy modification
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Elo, Robin. "Evaluation of HVAF sprayed STR coatings." Thesis, Uppsala universitet, Tillämpad materialvetenskap, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-176954.
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The Seamless Stressometer® roll (Seamless STR) is used to measure the flatness of aluminum and steel strip when there is an extreme demand on the surface finish. To protect the roll and strip, the roll is coated with two layers deposited by high velocity oxygen fueled spraying (HVOF), Cr-Ni(Si,B) closest to the roll and WC-Co on top. This solution has several disadvantages; high cost and complicated logistics, corrosion sensitivity and high residual stresses creates the need for two coatings which in turn complicates the process. Cobalt is, in addition, sensitive to low pH coolants and environmentally unfriendly. These problems have given rise to the idea of switching both the method and material of the coating. In the first part of this work, high velocity air fueled spraying (HVAF) was evaluated as an alternative deposition method. Three materials, Cr3C2-NiCr, WC-Co and WC-CrC-Ni were deposited on steel coupons with varying chamber pressure, powder feed rate and distance from the nozzle, in order to evaluate if HVAF can be a valid technique for use in this application and to optimize the spraying recipe. The objectives were to get a sufficiently high thickness per sweep, to be able to make the depositions in a manageable number of sweeps, and to get low porosity, since the coatings need to be dense to be hard and possible to polish smooth. The tests showed that all three materials can be sprayed with the high settings on the parameters to obtain coatings that exceeded the set limits of the objectives. In the second part of this work, the recipe obtained from the first part was used to deposit samples for further analysis. The coatings were compared regarding cost, hardness, friction, wear and pick-up properties to evaluate if a switch in material from WC-Co was possible. The coatings showed both similarities and differences. The friction was very similar for the three materials. Cr3C2-NiCr was substantially cheaper than the other two, had lower hardness and higher porosity, but still probably acceptable values, and was satisfactory regarding wear and pick-up. WC-Co and WC-CrC-Ni were very similar to each other regarding cost, hardness and porosity but WC-Co was the best regarding wear and pick-up, where WC-CrC-Ni was the worst. The only clear advantage of WC-CrC-Ni over WC-Co is the lack of cobalt. Taking everything into consideration, including the fact that the wear and pick-up tests in this work was quite exaggerated, Cr3C2-NiCr is an interesting option for this application due to its low cost and acceptable test results, WC-Co had the best results but is expensive and contains cobalt and WC-CrC-Ni had as good results as WC-Co except for the wear and pick-up tests and does not contain cobalt.
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Teixeira, Wendel Anderson Dantas. "Estudo das brasagens de WC-Co/AgCu/a?o H13 e WC-Co/AgCUNi/a?o H13 utilizando metaliza??o mec?nica." PROGRAMA DE P?S-GRADUA??O EM CI?NCIA E ENGENHARIA DE MATERIAIS, 2016. https://repositorio.ufrn.br/jspui/handle/123456789/22372.
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Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES)
Interfaces Metal-WC-Co est?o presentes em opera??es de perfura??o de po?os de petr?leo, onde se utilizam brocas tric?nicas de insertos cer?micos duros. A a??o combinada de corte, esmagamento e desagrega??o de rochas causa a degrada??o das brocas de perfura??o. A degrada??o est? relacionada com o desgaste, fratura total ou parcial do corpo da broca ou dos insertos, choque t?rmico e corros?o. Tamb?m o deficiente encaixe mec?nico dos insertos cer?micos nos cones da broca pode originar o seu destacamento provocando uma s?rie de danos ? broca. O aprimoramento no processo de produ??o de interfaces metal-cer?mica pode eliminar ou minimizar algumas das falhas acima mencionadas nas brocas tric?nicas, otimizando o seu tempo de vida ?til, e portanto, reduzindo o custo m?trico de perfura??o. A brasagem ? uma t?cnica extensivamente utilizada para uni?o de metais e cer?micos, podendo ser uma excelente alternativa ao processo comum de encaixe mec?nico de ?pressfitting? dos insertos cer?micos no corpo de a?o da broca. A metaliza??o das superf?cies WC-Co ? utilizada para melhorar a molhabilidade e ades?o de sistemas M/C. Neste trabalho, pretendeu-se avaliar o efeito da temperatura de brasagem em uni?es de insertos WC-6Co com a?o H13 utilizando ligas de adi??o com base no eut?tico 72Ag28Cu, em um forno com uma condi??o de alto v?cuo. A caracteriza??o mec?nica, microestrutural e morfol?gica das uni?es geradas foi avaliada em ensaios de flex?o de 3 pontos, MEV-EDS e DRX. Os melhores resultados de resist?ncia mec?nica foram encontrados para os sistemas brasados a 880?C com liga de adi??o eut?tica AgCu.
Metal-WC-Co interfaces are present in oil well drilling operations, where tricone drill bits with hard ceramic inserts play an important role. The combination of cutting, crushing and breaking up of rocks results in the degradation of tricone drill bits by wear, total or partial rupture of the drill bit body or the ceramic inserts, thermal shock and corrosion. In addition, the improper pressfitting of the ceramic inserts on the bit body may cause its total detachment, and promote serious damages to the drill bit. The improvement on the production process of metal-ceramic interfaces can eliminate or minimize some of above-mentioned failures presented in tricone drill bits, optimizing their lifetime and so reducing drilling metric cost. Brazing is a widely established technique to join metal-ceramic materials, and may be an excellent alternative to the common mechanical press fitting process of hard ceramic inserts on the steel bit body for tricone drill bit. The metallization of WC-Co surfaces is used to improve the wetting and adhesion of the M/C system, when a liquid phase is present during the brazing process. In this work, the effect of brazing temperature was studied on WC-6Co and H13 steel couples, using 72Ag28Cu eutectic based brazing alloys inside a furnace under high vacuum. Mechanical and microstructure caracterization of the interfaces produced was analysed by 3 point flexural tests, SEM-EDX and XRD techinques.d, and the interfaces produced were analysed by SEM-EDX. Better results for mechanical strenght were found for the systems brazed at 880?C using AgCu eutectic braze alloy.
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Zhang, Zongyin. "Processing of Nanostructured WC-Co Powders and Sintered Steels." Doctoral thesis, KTH, Materials Science and Engineering, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3530.
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Processing of nanostructured WC-Co and W-Co powders,modelling of Fe-Mn-Si alloy, swelling of Fe-Cu alloy, andmechanical properties and sintering of Fe-Mn-Si steels havebeen studied in the present thesis.
W-Co precursors made by chemical synthesis were used toproduce nanostructured WCCo and W-Co powders by calcination,reduction and carburization. The phase constituents in thecalcined powders depend on temperature and atmospheres. Cobaltcan accelerate the reduction rate of the W-Co precursors as acatalyst, and cobalt influences the formation of intermediatephases during the reduction of the precursors.
The ratio of carbon monoxide to carbon dioxide controlscarburization process, gives different intermediate phases andcarburization rates. There exist several intermediate phases: W6Co6C, W3Co3C, W2C due to varying carbon monoxide content in thecarburization gases. Nanostructured WC-Co powders with aparticle size of 20-50 nm have been obtained.
The effect of silicon content on the particle sizedistribution of milled Fe-Mn-Si master alloy powders is muchmore significant than that of manganese content. A finer finalparticle size can be obtained in the alloy powders with highersilicon compositions. Long time milling results in theagglomeration of small particles. The grinding process can bedescribed using classic batch grinding equation based on thepopulation balance model. A swelling model for Fe-Cu alloyssintered at the temperatures above the melting point of copperhas been established based on the penetration mechanism. In themodel, the particle coordination number and heating rate wereused to express the porosity and the thickness of the diffusionlayers between iron and copper particles respectively.
The effects of sintering temperature and time on theproperties of sintered steels have been studied. Fe-Mn-Simaster alloys made by cast-milling, atomizing, and acombination of atomization and milling have been covered. Themilled, and atomizationmilled alloy steels showed goodmechanical properties with small dimensional change. Transientliquid phase of the Fe-Mn-Si alloys accelerates densification,and offer fast diffusion of alloying elements. The addition ofa small amount of Fe-Mn-Si master alloy to Astaloy 85Mo powdercan lead to high strength with zero dimensional change.
Key words:Processing; Modelling; Nanostructured powder;WC-Co; W-Co; Calcination; Reduction; Carburization; Particlesize; Sintered steel; Fe-Cu alloy; Swelling; Fe-Mn-Si masteralloy; Mechanical properties; Sintering parameters.
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Hewitt, Stephen A. "Consolidation of WC-Co nanocomposites synthesised by mechanical alloying." Thesis, University of Wolverhampton, 2009. http://hdl.handle.net/2436/106834.
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The influence of mechanical alloying (MA) milling time, temperature, sintering method and microstructure on the mechanical properties of a tungsten carbide-cobalt (WC-Co) hardmetal, based on 10wt% Co, has been established. The effects of high-energy milling for 30, 60, 180 and 300 min and the interrelation between milling time and powder properties, and the resultant effects on the mechanical properties of the consolidated WC-10Co material, has been obtained for a horizontally designed ball mill. Nanostructured WC-10Co powder was synthesised after 60 min cyclic milling at room temperature with an average WC domain size of 21 nm. In direct comparison, a WC-10Co composition MA at -30°C for 60 min produced an average WC domain size of 26 nm with a higher lattice strain. WC domain size showed a slight increase with milling time, measured at 27 nm after 300 min ball milling. Extended ball milling (300 min) reduced the mean particle size from 0.148 μm for 60 min milling to 0.117 μm. Thermal analysis showed that the onset temperature of the WC-Co eutectic was related to particle size with increased milling time reducing the onset temperature from 1344°C after 60 min milling to 1312°C after 300 min milling. Onset temperature was further reduced by the addition of vanadium carbide (VC), reducing the onset temperature to 1283°C after 300 min milling. Powder contamination increased with increased milling time with Fe content measured at ~ 3wt% after 300 min ball milling. Milling at -30°C reduced Fe contamination to an almost undetectable level. Increased ball milling time resulted in decreased levels of green density with the powders milled for 30 and 300 min achieving 62.5% and 59.5% TD, respectively. Relative density increased for the powder milled at -30°C compared to the RT milled powder due to its flattened, slightly rounded morphology. A large difference in VC starting particle size compared to WC and Co led to non-uniform dispersion of the inhibitor during milling. Densification and hardness reached optimum levels for the 60 min milled powder for both pressureless sintering and sinter-HIP. Both properties decreased with increased milling time, regardless of the sintering method. Low temperature milling resulted in a higher hardness value of 1390 HV30 compared to 1326 HV30 for the 60 min, RT milled material after pressureless sintering. Densification levels of the doped materials were restricted to < 90% TD for both sintering methods due to inhomogeneity in the microstructures. Palmqvist fracture toughness (WK) of the RT milled powders increased with increased milling time and increasing WC grain size for both sintering methods. WK reached 11.6 MN.m3/2 with 300 min milling after pressureless sintering but reached 16.1 MN.m32 for the same material after sinter-HIP due to the effect of mean WC grain size and binder phase mean free path. The -30°C milled powder exhibited higher fracture toughness for both sintering methods than the 60 min, RT milled material. Spark plasma sintering (SPS) showed that the onset of densification was dependent upon particle size with the powder from 300 min milling showing an onset temperature of ~ 800°C compared to ~ 1000°C for the 60 min milled powder. The low temperature milled powder showed an onset temperature of ~ 980°C, which suggested that low temperature milling provided enhanced densification kinetics.
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Klymov, Oleksiy [Verfasser]. "Magnetabrasive Bearbeitung von Werkzeugen aus WC-Hartmetall / Oleksiy Klymov." Aachen : Shaker, 2014. http://d-nb.info/1051574404/34.
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Wu, Jianhui. "Tribological behavior of WC-DLC-WS2 (WCS) nanocomposite coatings." Connect to this title online, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1094675462.
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Thesis (Ph. D.)--Ohio State University, 2004.Title from first page of PDF file. Document formatted into pages; contains xix, 188 p.; also includes graphics. Includes bibliographical references (p. 179-188).
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Haslam, Gareth Eric. "Ni-C and WC materials as fuel cell electrocatalysts." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610113.
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Puga, Joel Bento. "WC-(Cu, Fe, Cr, Ni) composites attained by mechanosynthesis." Master's thesis, Universidade de Aveiro, 2013. http://hdl.handle.net/10773/12263.
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Mestrado em Engenharia de MateriaisThis work aims to study the feasibility of replacing cobalt by copper and stainless steel in tungsten carbide composite. The composites were prepared with a binder content of 12 wt% using the powder metallurgy method in which the conventional milling was replaced by high energy ball milling. To obtain a composite with high density, good microstructure uniformity and controlled phase composition, suitable for a good mechanical performance, the processing conditions of the high energy ball milling (HEBM) and sintering methods were enhanced. Within the studied parameters, the prime milling conditions were found at the rotation speed of 350 rpm and ball-to-powder weight ratio of 20:1, varying the milling times between 8-10 hours for the studied compositions. The HEBM process was able to reduce the particle size of the composite powders down to the nanoscale and a good binder homogenization was reached. After compacting, the powders were submitted to vacuum sintering, in a temperature range of 1300 – 1500ºC followed by HIP (hot isotactic pressing). This procedure allowed attaining dense compacts and introduce efficiently copper in the stainless steel binder up to 30%, without substantial decrease of the sintered relative density. The WC-SS composite powders show a significant amount of M6C phase formed during sintering, endorsed by the high reactivity of the small powder particles and the appearing of the M6C phase. Adding copper to the WC-SS composite allowed the decrease of the M6C phase formation. The WC-Cu sintered samples revealed two distinct major phases, W2C and Cu0.4W0.6 and their appearance depends on the applied sintering technique, in the case of being conventional or two stages sintering, respectively. The mechanical characterization revealed that the hardness of the WC-SS compacts is equivalent to the reported values in the literature for WC-Co. On the other hand, the fracture toughness remains below the reference values. Nevertheless, it was possible to attain a good balance between hardness and fracture toughness in the WC-(SSCu) composites, which make them promising candidates for substituting the traditional WC-Co composite.
Este trabalho tem como objetivo estudar a viabilidade da substituição do ligante cobalto por cobre e aço inoxidável em compósitos de carboneto de tungsténio. Estes compósitos foram preparados com um teor de ligante de 12% pp, utilizando o método de pulverometalurgia no qual a moagem convencional foi substituída pela moagem de alta energia (MAE). Por forma a obter compósitos de elevada densidade, boa uniformidade microestrutural, e composição de fases adequada a um bom desempenho mecânico, foram otimizadas as condições de processamento das etapas de moagem de alta energia e da sinterização. As melhores condições de moagem foram verificadas com uma velocidade de rotação de 350 rpm, um rácio de peso bolas:material de 20:1 e, dependendo da composição estudada, um tempo de moagem variável entre 8 – 10 horas. Utilizando o processo de MAE foi possível reduzir o tamanho de partícula dos pós compósitos até à nanoescala e ainda obter uma boa uniformidade da distribuição da fase ligante. Após compactação, os pós foram submetidos a uma etapa de sinterização em vácuo num intervalo de temperaturas entre 1300 - 1500 °C, seguindo-se uma etapa de prensagem isostática a quente. Este método permitiu obter compactos de densidade elevada e introduzir de forma eficiente até 30% de cobre na fase ligante de aço inoxidável sem se verificarem reduções substanciais da densidade dos compactos sinterizados. Os compósitos de WC-SS apresentam uma composição de fases com uma quantidade elevada de fase M6C, formada durante a sinterização e que é favorecida nestes materiais, devido à elevada reatividade dos pós nanométricos. Contudo, a adição de cobre ao compósito WC-SS permitiu a diminuição da formação de fase M6C. As amostras sinterizadas de WC-Cu apresentam maioritariamente duas fases distintas, W2C e Cu0.4W0.6 e o aparecimento desta última fase depende da técnica de sinterização utilizada, convencional e sinterização em duas etapas respetivamente. A caracterização mecânica revelou que a dureza dos compósitos de WC-SS é equivalente aos valores indicados na literatura para os compósitos de WC-Co, enquanto a tenacidade permanece abaixo dos valores de referência. No entanto, foi possível alcançar um bom equilíbrio entre a dureza e tenacidade nos compósitos de WC-(SSCu), o que poderá permitir a sua utilização em algumas aplicações dos tradicionais carbonetos cementados de WC-Co.
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Bartzakos, Peter. "On the binary frequency of a complete sample of magellanic, WC Wolf-Rayet stars and a spectroscopic study of WC binary colliding winds." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0009/NQ39720.pdf.
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Reddiar, Dona. "Regulatory B and T cells in Helicobacter pylori infection." Thesis, University of Nottingham, 2018. http://eprints.nottingham.ac.uk/51220/.
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In the human gastric mucosa, an inflammatory response stimulated by H. pylori infection can lead to gastric cancer and peptic ulcer disease. Expression of the i1 active variant of Vacuolating Cytotoxin A (VacA) by the colonising bacterial strain has been identified as an independent risk factor for disease. VacA skews the adaptive immune response towards a regulatory phenotype to promote persistent H. pylori colonisation. In H. pylori-infected individuals, regulatory T cells (Tregs), which suppress inflammation through mechanisms including interleukin-10 (IL-10) production, are thought to play a role in protection against extra-gastric diseases such as multiple sclerosis and oesophageal cancer. IL-10 is an immunomodulatory cytokine which is expressed by several immune cell types including regulatory B cells (Bregs), whose role in H. pylori infection is unclear. Blood was donated by uninfected and infected patients, and those who underwent successful eradication of their H. pylori infection. A flow cytometry antibody panel was developed to quantify the relative frequencies of peripheral blood Bregs and Tregs, and investigate differences according to H. pylori status. Mice were also infected with H. pylori to determine VacA i1 versus i2 differences in the induced regulatory B and T cell frequencies. Stool samples were collected from patients to develop a VacA i-region PCR-based diagnostic test. Results showed that compared to during H. pylori infection, the proportion of IL-10-producing Tregs in the peripheral blood of patients declined after successful eradication therapy. A pilot study in mice revealed B lymphocytes to be another important source of IL-10, and the population expanded after H. pylori infection. In a study of H. pylori-positive, H. pylori-negative and H. pylori-eradicated patients, there were no significant differences in peripheral blood Breg or IL-10+ Breg frequencies. Data from an expanded mouse study using blood and spleen showed that VacA variants in a colonising H. pylori strain did not induce differences in Breg or Treg frequencies 9 weeks after wildtype or mutant H. pylori SS1 infection. The H. pylori 16S gene was successfully detected in stool DNA samples and could be used to determine infection status, but the development of a vacA i-region PCR-based typing stool test was unsuccessful. Previous work in the research group has identified how Treg frequencies are associated with H. pylori infection and disease. While Bregs are capable of producing IL-10 after stimulation, their role in H. pylori infection in mice and humans appears to be limited. The consistency of peripheral blood Treg frequencies in patients from their infected state until two years post-eradication is a start to understanding whether H. pylori-induced extra-gastric protection may also be maintained after eradication. While stool remains a promising resource for non-invasively diagnosing H. pylori infection worldwide, there are strong concerns about contamination and reproducibility which are unlikely to be overcome for use in a clinical setting.
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Pinder, Leila. "An international study of the use of pandemic vaccines during the 2009-10 influenza A(H1N1) pandemic : a qualitative methodological study." Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/40590/.
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Background: The 2009-10 influenza A(H1N1) pandemic was the first pandemic influenza of the twenty-first century and presented the first major opportunity for the use of influenza vaccines en-masse during a pandemic scenario. National anticipatory policies of pandemic influenza vaccine preparedness were implemented, and vaccine guarantee agreements were activated. Large quantities of vaccines were purchased and made available to identified citizens over the course of the pandemic. The use of pandemic influenza vaccines has been examined in this research. Methods: A comparative health policy approach in five study countries (Sweden, New Zealand, Japan, Singapore, and Canada) was conducted. Qualitative interviews (n= 36) were undertaken in each country with key pandemic influenza response personnel (n = 39). Participants included public health officials, policy makers and clinicians engaged at national country response level. Interviews facilitated discussions surrounding the 2009-10 influenza A(H1N1) pandemic response and use of vaccines. Documentary examination of available records supplemented the analysis of the interview data. Results: Several interview themes were identified following data analysis of the use of pandemic vaccines in the study countries. Themes of the vaccine use included: single or multiple vaccine supplier routes; hemisphere variation; historical pandemic legacy; targeted populations; setting vaccination priorities; side effect concerns; perceived effectiveness of vaccines during the pandemic influenza response. The themes which were most prominent comprised the sourcing and distribution of the vaccines during the response and the associated communication challenges. The necessary prioritisation of vaccines caused extensive discussions and uneasiness by the pandemic influenza response personnel as the initial vaccines arrived in small quantities and required allocation, especially in circumstances where country’s intended for all/most citizens to eventually have access to the vaccine. The variation in timing of the vaccination campaigns and disease activity would suggest that subsequent influenza wave morbidities and mortalities could have been reduced if vaccines had been available more promptly. The southern hemisphere country, New Zealand, exemplified the circumvention of vaccine safety concerns through the use of a trivalent vaccine inclusive of H1N1. Conclusions: Pandemic vaccines were the cornerstone of two countries responses and were associated with high uptake rates. Vaccine discussions, such as prioritisation and essential workers estimates, can be established during interpandemic phases by pandemic influenza response personnel. The use of annual seasonal influenza vaccines that are inclusive of the novel pandemic influenza strain should play a greater role in future pandemic influenzas, should the vaccination campaign timing be appropriate, as this may reduce public anxiety concerning the perceived safety of novel vaccines. The use of the 2009-10 influenza A(H1N1) pandemic vaccines had varied in success and the lessons learnt from this event have important implications for future policy. Pandemic influenza response personnel are recommended to prepare as fully as possible during this interpandemic period.
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Morandi, Elena. "The viral hypothesis in multiple sclerosis : role of Epstein-Barr virus and human endogenous retroviruses." Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/45125/.
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Epstein Barr Virus (EBV) is a major risk factor in Multiple Sclerosis (MS), via as yet unclear mechanisms. Several hypotheses have been proposed to explain how EBV infection could cause MS and the aim of this thesis was to better understand the mechanisms of action of EBV in the context of MS studying a) the role of EBV in myelin antigen presentation by B cells and b) the association of HERVs with MS. In a non-human primate experimental autoimmune encephalomyelitis (EAE) model, an EBV-related lymphocryptovirus enables B cells to protect a proteolysis-sensitive immunodominant myelin oligodendrocyte glycoprotein (MOG) peptide (residues 35- 55) against destructive processing. This facilitates its cross-presentation to autoaggressive cytotoxic MHC-E-restricted cytotoxic T cells. The present study extends these observations to human B cells and identifies a key role of autophagy. EBV infection upregulated antigen presentation-related markers on B cells and activated the cross-presentation machinery. Although human MOG protein was degraded less in EBV-immortalized B-lymphoblastoid cell lines (LCL) than in uninfected B cells, induction of cathepsin G activity by EBV led to total degradation of the immunodominant peptides. Inhibition of cathepsin G or citrullination of the arginine residue within a LC3-interacting regions (LIR) motif of immunodominant MOG peptides abrogated their degradation. Internalized MOG co-localized with autophagosomes, which may protect it from destructive processing. Thus, EBV infection switched MOG processing in B cells from destructive to productive possibly facilitating cross-presentation of disease-relevant epitopes to CD8+ T cells. This mechanism could facilitate presentation of myelin autoantigens that may be involved in MS induction and progression. The first part of this thesis shows a possible EBV-mediated mechanism involved in MS pathogenesis, but it is likely that different mechanisms act alternatively or cumulatively in different individuals based on environmental and genetic differences. A further mode of action of EBV is through the activation of Human Endogenous Retroviruses (HERVs). In normal conditions HERVs are silenced or expressed at low levels, but in some pathological cases, like MS, their expression is higher than in the healthy population. We performed a systematic review and meta-analysis of the literature on the association between HERVs and MS. The systematic review suggested a strong association between HERV expression and MS, in particular with the HERV-W family. The meta-analysis showed odds ratios of 22, 44, and 6 for the expression of MSRVpol in serum/plasma, MSRVenv in PBMC and MSRVpol in CSF respectively. Furthermore, we confirmed the association experimentally. An increased expression of MSRV/HERV-Wenv and TLR4 RNA was detected in blood of MS patients compared with control groups and the viral protein Env was expressed mainly by B cells and monocytes, but not by T cells. Our finding that EBV infection can induce the expression of MSRV/HERV-Wenv is consistent with previous reports in the literature. We also established that such increased expression was not due to a repression of retroviral restriction factors in LCL. A further connection between HERVs and MS is supported by the observation that people infected by HIV may have a lower risk of developing MS than the HIV non- infected, healthy population. We found that the expression of MSRV/HERV-Wenv RNA in HIV-infected people was lower than in MS patients and similar to healthy controls. Nevertheless, there was no difference in MSRV/HERV-Wenv expression between antiretroviral drug -treated and -untreated HIV patients. The expression of MSRV/HERV-Wenv was also detected in vitro in LCL treated with different classes of antiretroviral treatments (ART) and only Efavirenz (NNRI) reduced MSRV/HERV- Wenv expression. In conclusion, taking in consideration the multifactorial aetiology of MS, it is likely that EBV infection and increased expression of MSRV/HERV-W are significant contributing factors in genetically predisposed individuals. This thesis helps to better understand the mechanisms of action of EBV and HERVs in the context of MS.
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Daniel, Priya. "A study on epidemiological trends in community acquired pneumonia and associated outcomes in the UK." Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/46813/.
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Background Community acquired pneumonia (CAP) is a common illness in patients admitted to hospital, accounting for nearly 10% of acute medical admissions. Despite widespread use of antimicrobial therapy, morbidity and mortality from this disease remains high. In recent years in the UK, there have been significant developments in both preventative and treatment strategies for this illness. To understand the impact of these changes and direct future management strategies, it is important that the epidemiology of this disease is fully understood. This thesis investigates changes in epidemiology and outcomes in adult patients admitted to UK hospitals with a primary diagnosis of CAP, in recent years and with reference to the herd protection effect of the conjugate Streptococcus pneumoniae vaccine. Methods There are 3 study populations presented in this thesis. Data were derived from (a) the British Thoracic Society national CAP audit database, (b) a longitudinal cohort study of adults hospitalised with CAP, within the Greater Nottingham area, and (c) an observational study of adults admitted to four hospitals within the East Midlands area with a diagnosis of CAP. The specific methods used for the identification of study participants, laboratory and statistical analysis are described in detail in ensuing chapters. Results Across the UK, there was a significant reduction in 30-day mortality between 2009 and 2014; this improvement in outcome may be attributable in some part to improved processes of care. Whilst data derived from coding databases have previously been used to report CAP related mortality trends, this thesis has demonstrated significant variation in coding accuracy across UK institutions and that miscoded cases of pneumonia had lower odds of 30 day mortality compared to those individuals with CAP. Consequent to herd effects from national infant vaccination programmes and changes in nasopharyngeal carriage of S pneumoniae, this thesis shows that (a) school holiday periods were associated with increased incidence of pneumococcal CAP in hospitalised adults, (b) older adults at high risk of pneumococcal disease were less likely to be hospitalised with vaccine serotype CAP compared to non-vaccine-serotype pneumococcal CAP, and (c) there was a decrease in the overall burden of vaccine-serotype pneumococcal CAP compared to non-vaccine-serotype pneumococcal CAP. Conclusion Important changes in the epidemiology of adult CAP in the UK over recent years are reported in this thesis. This includes temporal decreases in mortality rates of all cause CAP, as well as a significant ongoing burden of non-vaccine serotype pneumococcal CAP. This data on the current burden of disease and associated outcomes should help inform future CAP management strategies.
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Elimian, Osezele Kelly. "Evaluation of early diagnostic approaches for malaria and pneumonia in children under-five presenting at the primary healthcare level in Benin City, Nigeria : a mixed methods study." Thesis, University of Nottingham, 2018. http://eprints.nottingham.ac.uk/48409/.
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Background Malaria and pneumonia are the leading causes of under-five mortality in sub-Saharan Africa especially in Nigeria. The Integrated Management of Childhood Illness (IMCI) guidelines were developed by the World Health Organisation (WHO)/United Nations Children’s Fund (UNICEF) as a strategy to reduce the burden of these and other preventable childhood diseases. However, there appears to be a paucity of evidence on the diagnostic performance of the revised IMCI guidelines and whether they offer an advantage over lay diagnosis (caregiver) for malaria and pneumonia management in Nigeria. Aim and specific objectives This study evaluates early diagnostic approaches (IMCI guidelines and lay diagnosis) for malaria and pneumonia in children under-five at the primary healthcare level. To address the overarching aim of the study, the following four specific objectives were studied: I. To assess the diagnostic accuracy of the IMCI guidelines and lay diagnosis (caregiver) for malaria and pneumonia in comparison to reference diagnostic approaches (microscopy and chest X-ray for malaria and pneumonia respectively). The extent of agreement between caregivers’ and health workers’ diagnosis of malaria and pneumonia is also assessed. II. To estimate the burden of malaria and pneumonia among children under-five presenting to study primary healthcare centres (PHCs) according to various diagnostic approaches. III. To determine the clinical outcomes in children diagnosed with malaria and pneumonia according to the IMCI guidelines and risk factors for severe outcomes. IV. To qualitatively explore caregivers’ and health professionals’ perspectives on lay diagnosis and IMCI guidelines as diagnostic approaches for childhood malaria and pneumonia. Methods A mixed methods approach was used for this study. The quantitative component used a consecutive sampling approach to recruit 903 children aged 2–59 months who met study eligibility criteria for malaria and pneumonia assessment according to the IMCI guidelines at presentation to five study PHCs in Benin City, Nigeria. Caregivers of these children were also asked what they thought the diagnosis was (lay diagnosis). Diagnostic accuracy was assessed in terms of sensitivity, specificity, positive and negative predictive values, Area under the Receiver Operating Characteristic Curves (AUROC) values and 95% Confidence Intervals (C.I). The extent of agreement was assessed in terms of Cohen’s kappa statistic (k) and 95% CI. The estimated burden of malaria and pneumonia during the study period was assessed using proportions and 95% C.I. Clinical outcomes in children diagnosed with malaria and pneumonia by the IMCI guidelines were described in terms of frequency and percentages, while the potential risk factors associated with clinical outcomes were assessed using odds ratios (ORs) and 95% C.I. For the qualitative component, health stakeholders (17 health professionals and 13 caregivers) who met the study eligibility criteria were purposively recruited and interviewed using semi-structured interviews. An inductive approach to thematic analysis was used for data analysis. Results Compared to microscopy, the diagnosis of malaria by health workers using the IMCI guidelines was poorly accurate with an AUROC value of 0.57 (with sensitivity and specificity of 51.8% and 61.3% respectively). Similarly, caregivers’ diagnosis of malaria was poor with an AUROC value of 0.55 (with sensitivity and specificity of 31.1% and 79.5% respectively) as compared to microscopy. Using the IMCI guidelines as the reference diagnostic test, caregivers’ diagnosis of malaria was more accurate (AUROC 0.60) in comparison to that of pneumonia (AUROC 0.54). There was a slight or minimal level of agreement (k=0.14; 95% CI: 0.09-0.19) between caregivers and health workers in the diagnosis of malaria and pneumonia. The estimated burden of malaria and pneumonia was relatively low, varying by the study local government areas, PHCs and seasonality, irrespective of the diagnostic approach. Where follow-up data were available, approximately 57% (172/304) and 78% (81/104) of the children diagnosed with malaria and pneumonia, respectively, recovered without complications within 30 days. Self-medication prior to presenting to study PHCs and use of preventive measures against malaria were independently and significantly associated with improved clinical outcomes. In contrast, exposure to solid fuels increased the odds of severe illness following malaria or pneumonia diagnosis. The qualitative component of the study found that caregivers rely on lay diagnosis despite the awareness of its limitations. The perceptions of malaria and pneumonia appeared to influence caregivers’ home management practices and health seeking behaviours. Caregivers showed willingness to be trained in the IMCI guidelines for improved home-based management of malaria and pneumonia. Health professionals believed that the IMCI guidelines were useful for managing both malaria and pneumonia. However, there are some recurring challenges to the wide-scale and sustainable implementation of the IMCI strategy in Nigeria. These include inaccurate diagnosis of malaria and inadequate funding. Conclusion The IMCI guidelines are crucial in the effective management (diagnosis and treatment) of malaria and pneumonia at the primary healthcare level in Nigeria. Although not perfect, lay diagnosis has an important contribution in the early detection and management of malaria and pneumonia at the community level in Nigeria. However, there is need for further investment in the training of both health professionals and caregivers in the IMCI guidelines for better health outcomes in under-five population. The training of caregivers in the IMCI guidelines and potential for a scale-up will benefit from careful design, piloting, implementation, and monitoring.
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Vieira, Luiz Fábio dos Santos [UNESP]. "Comportamento mecânico do aço AISI 4340 revestido com WC-CrCNi; WC-10Ni; Ni-20Cr; Ni-Cr-B-Si-Fe; Cr3C2-NiCr pelo processo HVOF." Universidade Estadual Paulista (UNESP), 2012. http://hdl.handle.net/11449/103748.
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vieira_lfs_dr_guara.pdf: 12571289 bytes, checksum: 0784fba14c816c566b5f3385624070f4 (MD5)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
O aço AISI 4340 tem sido utilizado largamente devido as suas propriedades físicas, químicas, mecânicas e resistência à fadiga, atendendo ao rigoroso e crescente aumento das exigências para aplicações na engenharia. Revestimentos superficiais são aplicados objetivando proteção contra corrosão e desgaste, por exemplo, a eletrodeposição de Cromo, pois apresenta resistência à corrosão, alta dureza, resistência ao desgaste abrasivo e adesivo, soldabilidade e baixo coeficiente de atrito. Por outro lado, microtrincas derivadas da camada de Cromo diminuem a resistência à fadiga, com isso o componente é submetido ao tratamento superficial para deformação plástica, shot peening, criando tensões residuais compressivas na superfície, que retardam ou eliminam a propagação de trincas, tendendo a aumentar sua vida em fadiga. Entretanto, durante o processo de deposição do Cromo duro é liberada uma substância cancerígena, o Cromo hexavalente. Por essa razão, estuda-se a substituição do Cromo por outros revestimentos que apresentem propriedades mecânicas similares, mas que não tenham restrições ambientais. O processo HVOF (High-Velocity-Oxigen-Fuel) para deposição de revestimentos alternativos, como carbeto de tungstênio, é considerado uma técnica promissora, pois fornece alta dureza e boa resistência ao desgaste e uma menor redução da resistência à fadiga do substrato quando comparado à redução fornecida pelo revestimento de Cromo duro aplicado ao aço AISI 4340. Portanto, o objetivo deste estudo é avaliar o comportamento mecânico do aço AISI 4340 com alta resistência mecânica (50 HRC), revestido com WC-CrC-Ni, WC-10Ni, Ni-20Cr, Ni-Cr-B-Si- Fe, e Cr3C2-NiCr, depositados através do processo HVOF; revestimentos alternativos à camada de Cromo duro. Os dados de fadiga axial são representados por curvas σ x N...
AISI 4340 steel is being used in the aeronautical industry because its good physical, chemical, mechanical and fatigue properties. Chromium coatings are used in applications to guarantee protection against wear and corrosion, combined with chemical resistance and good lubricity. The reduction in the fatigue strength of base material and since this technology presents detrimental environmental and health effects, resulted in the search on coatings viewed as being capable of replacing hard chrome plating. Thermally sprayed HVOF coatings are being considered to replace galvanic chromium deposits in industrial applications with comparable performance for wear and corrosion resistance. With respect to fatigue life, the HVOF technique induces tensile residual stress on the interface. In this case, the initiation and propagation phases of fatigue process are accelerated because the coating; on the other hand, compressive residual stresses close to the surface increases fatigue life. The technique to improve the coated materials fatigue strength is the shot peening process, which induces compressive residual stress in the surface, which delay nucleation and propagation process In the present research is verified the influence of WC-CrC-Ni; WC-10Ni; Ni-20Cr; Ni-Cr-B-Si-Fe; Cr3C2-NiCr HVOF process, coated high strength AISI 4340 with and without shot peening on the axial fatigue strength, in comparison with EHC. Corrosion resistance is also conducted by salt spray tests. S-N curves are obtained in axial fatigue tests. In order to study the influence of residual stresses on fatigue life, the stress field is measured by X-ray tensometry. Scanning electron microscopy and optical metallographic are used to investigate the fatigue source appearance. Experimental data show lower axial fatigue resistance for HVOF coated specimens in comparison to base material...(Complete abstract click electronic access below)
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Vieira, Luiz Fábio dos Santos. "Comportamento mecânico do aço AISI 4340 revestido com WC-CrCNi; WC-10Ni; Ni-20Cr; Ni-Cr-B-Si-Fe; Cr3C2-NiCr pelo processo HVOF /." Guaratinguetá : [s.n.], 2012. http://hdl.handle.net/11449/103748.
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Resumo: O aço AISI 4340 tem sido utilizado largamente devido as suas propriedades físicas, químicas, mecânicas e resistência à fadiga, atendendo ao rigoroso e crescente aumento das exigências para aplicações na engenharia. Revestimentos superficiais são aplicados objetivando proteção contra corrosão e desgaste, por exemplo, a eletrodeposição de Cromo, pois apresenta resistência à corrosão, alta dureza, resistência ao desgaste abrasivo e adesivo, soldabilidade e baixo coeficiente de atrito. Por outro lado, microtrincas derivadas da camada de Cromo diminuem a resistência à fadiga, com isso o componente é submetido ao tratamento superficial para deformação plástica, shot peening, criando tensões residuais compressivas na superfície, que retardam ou eliminam a propagação de trincas, tendendo a aumentar sua vida em fadiga. Entretanto, durante o processo de deposição do Cromo duro é liberada uma substância cancerígena, o Cromo hexavalente. Por essa razão, estuda-se a substituição do Cromo por outros revestimentos que apresentem propriedades mecânicas similares, mas que não tenham restrições ambientais. O processo HVOF (High-Velocity-Oxigen-Fuel) para deposição de revestimentos alternativos, como carbeto de tungstênio, é considerado uma técnica promissora, pois fornece alta dureza e boa resistência ao desgaste e uma menor redução da resistência à fadiga do substrato quando comparado à redução fornecida pelo revestimento de Cromo duro aplicado ao aço AISI 4340. Portanto, o objetivo deste estudo é avaliar o comportamento mecânico do aço AISI 4340 com alta resistência mecânica (50 HRC), revestido com WC-CrC-Ni, WC-10Ni, Ni-20Cr, Ni-Cr-B-Si- Fe, e Cr3C2-NiCr, depositados através do processo HVOF; revestimentos alternativos à camada de Cromo duro. Os dados de fadiga axial são representados por curvas σ x N ...(Resumo completo, clicar acesso eletrônico abaixo)Abstract: AISI 4340 steel is being used in the aeronautical industry because its good physical, chemical, mechanical and fatigue properties. Chromium coatings are used in applications to guarantee protection against wear and corrosion, combined with chemical resistance and good lubricity. The reduction in the fatigue strength of base material and since this technology presents detrimental environmental and health effects, resulted in the search on coatings viewed as being capable of replacing hard chrome plating. Thermally sprayed HVOF coatings are being considered to replace galvanic chromium deposits in industrial applications with comparable performance for wear and corrosion resistance. With respect to fatigue life, the HVOF technique induces tensile residual stress on the interface. In this case, the initiation and propagation phases of fatigue process are accelerated because the coating; on the other hand, compressive residual stresses close to the surface increases fatigue life. The technique to improve the coated materials fatigue strength is the shot peening process, which induces compressive residual stress in the surface, which delay nucleation and propagation process In the present research is verified the influence of WC-CrC-Ni; WC-10Ni; Ni-20Cr; Ni-Cr-B-Si-Fe; Cr3C2-NiCr HVOF process, coated high strength AISI 4340 with and without shot peening on the axial fatigue strength, in comparison with EHC. Corrosion resistance is also conducted by salt spray tests. S-N curves are obtained in axial fatigue tests. In order to study the influence of residual stresses on fatigue life, the stress field is measured by X-ray tensometry. Scanning electron microscopy and optical metallographic are used to investigate the fatigue source appearance. Experimental data show lower axial fatigue resistance for HVOF coated specimens in comparison to base material...(Complete abstract click electronic access below)
Orientador: Herman Jacobus Cornelis Voorwald
Coorientador: Maria Odila Hilário Cioffi
Banca: Marcelo dos Santos Pereira
Banca: Carlos de Moura Neto
Banca: Carlos Antonio Reis Pereira Baptista
Banca: Lindolfo Araujo Moreira Filho
Doutor
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Yan, Nicole. "Integrating point-of-care testing (POCT) for HIV, syphilis, malaria and anaemia into antenatal care services at dispensaries in western Kenya." Thesis, Liverpool School of Tropical Medicine, 2018. http://archive.lstmed.ac.uk/9471/.
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HIV, syphilis, malaria, and anaemia are major causes of adverse pregnancy outcomes in sub-Saharan Africa (SSA). Despite global and national policies advocating for screening of these conditions, only HIV testing has achieved good coverage, precluding early detection and appropriate management in pregnancy. Rapid pointof-care tests (POCTs) provide an opportunity to integrate diagnosis and provide timely treatment of these conditions in rural antenatal care (ANC) settings. After an introductory chapter, a review of the literature on these four conditions in pregnancy is presented with a focus on SSA. The thesis then shifts attention to Kenya, a country that embodies many of the disease challenges and health system characteristics of the region. Kenyan ANC policy recommends testing for HIV, syphilis and anaemia and preventive strategies for malaria. The following chapters are comprised of three linked studies conducted in western Kenya, that use different methods to progressively investigate the implementation success of integrated point-of-care testing (POCT) for HIV, syphilis, malaria and anaemia at seven peripheral dispensaries. Baseline data confirmed that testing requirements for syphilis, malaria and anaemia are not currently met at dispensary level. We implemented an intervention where test kits were supplied and training plus supervision were provided to enable healthcare workers to conduct integrated POCT for pregnant women. Adoption and fidelity were measured quantitatively using exit interviews, antenatal registers and proficiency scores (Study 1: Integrating point-of-care testing (POCT) for HIV, syphilis, malaria and anaemia in antenatal care at dispensary level in western Kenya: an implementation study) while acceptability, appropriateness and feasibility were assessed qualitatively (Study 2: Exploring healthcare workers and pregnant women’s perspectives on appropriateness, acceptability and feasibility of integrating point-of care testing: A qualitative study). Our findings show that the innovation was highly adopted, meaning almost all pregnant women received the essential tests. This was supported by the qualitative findings where healthcare workers and pregnant women found the innovation acceptable and appropriate. However, fidelity to clinical management guidelines can still be improved. Our qualitative findings provide some explanation for these gaps. One common sentiment among interviews with healthcare workers was that workload was perceived to be a barrier to providing quality care. We explored this further with discrete-event simulation modelling (Study 3: Investigating the operational impact of integrating HIV, syphilis, malaria and anaemia point-of-care testing in antenatal care clinics in western Kenya: a discrete event simulation model) and found the healthcare workers were actually under-utilized. This suggests that nurses should, in theory, have sufficient time to deliver essential ANC services. While integrating POCT addresses one gap, additional interventions to support and supervise healthcare workers are needed to ensure appropriate and high quality of care. An integrated approach to health systems strengthening and more investment in implementation and translation research using multi-methods are needed.
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Gonçalves, André da Motta. "Retificação de ultraprecisão de carbeto de tungstênio-cobalto (WC-Co)." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/18/18146/tde-26072016-100144/.
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Este trabalho apresenta o estudo da Retificação de Ultraprecisão de ligas de carbeto de tungstênio-cobalto (WC-Co) com diferentes microestruturas. A motivação para este estudo foi o grande potencial desta liga para a fabricação de componentes que requerem materiais de alta dureza e resistência à fratura. Devido à combinação dessas características, esses materiais vêm sendo usados na fabricação de moldes para injeção de lentes ópticas de dispositivos eletrônicos e ópticos. Assim, amostras de carbeto de tungstênio-cobalto foram submetidas a vários testes para determinação da correlação entre os parâmetros de corte e parâmetros estruturais (tamanho de grão e teor de cobalto) com o regime de remoção de material. As amostras foram polidas e posteriormente microendentadas com cargas variadas para pré-avaliar a ocorrência de formação de microtrincas. Testes de usinagem foram conduzidos em uma retificadora de ultraprecisão, usando rebolos de diamante e posteriormente a rugosidade e os danos da superfície (microtrincas e crateras) foram avaliados. Para melhor entendimento da influência dos parâmetros estruturais e dos parâmetros de corte sobre os resultados de rugosidade foi realizado um teste ANOVA. As forças de usinagem foram medidas durante os ensaios usando um microdinamômetro piezelétrico com objetivo de estimar a temperatura na zona de retificação. Os resultados obtidos indicam que tanto os parâmetros estruturais como os parâmetros de corte influenciam na rugosidade, microdureza e temperatura na zona de retificação das ligas de carbeto de tungstênio-cobalto. Amostras com maior tamanho de grãos apresentam as menores rugosidades e altas temperaturas na zona de retificação. A velocidade de avanço (Vf) mostrou-se mais influente que a profundidade de corte (ap). Menores velocidades de avanço aumentam a temperatura na zona de retificação e a microdureza na camada superficial. Entretanto, verificou-se que as maiores temperaturas obtidas nos ensaios não foram suficientes para promover alteração metalúrgica no material. Algumas condições de corte combinadas com parâmetros estruturais levam a remoção de material em regime dúctil, resultando em superfícies com qualidade óptica. A porcentagem de cobalto e a velocidade de avanço (Vf) têm forte influência na alteração da microdureza da camada superficial das amostras retificadas. A diminuição da velocidade de avanço tende a aumentar a microdureza na camada. Há aumento de microdureza de até 200 kgf/mm2, sugerindo a ocorrência de encruamento por tensões compressivas. Com base nestes resultados, acredita-se que a retificação de ultraprecisão apresenta-se como uma opção viável para a manufatura de componentes de carbeto de tungstênio com acabamento submicrométrico, possibilitando a eliminação dos processos tradicionais de manufatura óptica, tais como a lapidação e o polimento.The ultraprecision grinding of different tungsten carbide-cobalt microstructures (WC-Co) were investigated. The motivation for this study is the materials high hardness and potential application for micromolds. These materials have been used as optical inserts in glass injection molding processes for optical and electric devices, due to their excellent combination of high hardness, ductility and fracture toughness. Tungsten carbide samples were subjected to tests to determine the correlation between cutting parameters and microstructures to achieve the ductile regime of material removal. Polished surfaces of carbide samples were indented using varying loads to evaluate the microcracks formation. The machining tests were conducted using an ultraprecision grinding and A V-shaped metal-bond was used. Surface roughness was investigated as functions of the grinding conditions by means Analysis of Variance (ANOVA). The tangential force was measured using a piezoelectric dynamometer to estimate the grinding zone temperature. The results indicate that structural parameters (grain size and cobalt content) and cutting parameters have a significant influence on surface roughness, micro-hardness and grinding zone temperature for tungsten carbide-cobalt alloys.Tungsten carbide-cobalt samples with the larger grain size presented lower surface finish results and high grinding temperatures. The feed rate (Vf) showed greater influence that the in-feed (ap). The grinding zone temperature and the hardness are increased when speed rate is reduced. However, it was found that the highest temperature achieved did not reach a critical temperature for phase transformation. Some cutting parameters combined with structural parameters lead to ductile mode grinding mechanism, and as consequence, high optical quality surfaces are obtained. The micro-hardness of layer is extremely influenced by cobalt content and speed rate. Lower feed rate tends to increase the micro-hardness up to 200 kgf/mm2, suggesting that the compressive stress occurs. Considering the results presented it is believed that the Ultraprecision grinding showed to be a viable option for the fabrication of components made of tungsten carbide-cobalt with nanometer surface finish possibly eliminating traditional optical manufacturing processes such as lapping and polishing.
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Santos, Thais da Silva. "Micro-nanocompósitos de Al2O3/ NbC/ WC e Al2O3/ NbC/ TaC." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-10022015-104122/.
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Cerâmicas à base de alumina pertencem à classe de materiais denominados estruturais, muito utilizados em ferramentas de corte. A alumina possui boas propriedades para uso como cerâmica estrutural e com o objetivo de melhorar suas tenacidade à fratura e resistência mecânica, são produzidos compósitos com diferentes aditivos. Novos estudos apontam para os micro-nanocompósitos, onde a adição de partículas micrométricas deve auxiliar no aumento da resistência mecânica, e de partículas nanométricas, no aumento da tenacidade à fratura. Neste trabalho foram obtidos micro-nanocompósitos à base de Al2O3 com inclusão de partículas nanométricas de NbC e micrométricas de WC com proporções de 2:1, 6:4, 10:5 e 15:10 e micro-nanocompósitos à base de Al2O3 com inclusão de partículas nanométricas de NbC e micrométricas de TaC com proporção de 2:1 em relação à alumina. Para o estudo de densificação, os micro-nanocompósitos foram sinterizados em dilatômetro com taxa de aquecimento de 20 °C / min até a temperatura de 1800 °C, em atmosfera de argônio. Com base nos resultados de dilatometria, corpos de prova foram sinterizados entre 1500°C e 1700°C, com patamar de 30 minutos, em forno resistivo de grafite e atmosfera de argônio. Foram determinadas as densidades, fases cristalinas formadas, durezas e tenacidades, e analisadas as microestruturas dos micro-nanocompósitos. As amostras Al2O3:NbC:TaC sinterizadas a 1700°C atingiram as maiores densidades aparentes (~95%DT) e a amostra sinterizada a 1600°C apresentou microestrutura homogênea e valor de dureza (15,8 GPa) em comparação à alumina pura. As composições com 3% de inclusões são as mais promissoras para aplicações futuras como ferramentas de corte.Alumina based ceramics belong to a class of materials designated as structural, which are widely used in cutting tools. Although alumina has good properties for application as a structural ceramics, composites with different additives have been produced with the aim of improving its fracture toughness and mechanical strength. New studies point out micro-nanocomposites, wherein the addition of micrometric particles should enhance mechanical strength, and nano-sized particles enhance fracture toughness. In this work, alumina based micro-nanocomposites were obtained by including nano-sized NbC and micrometer WC particles at 2:1, 6:4, 10:5 and 15:10 vol% proportions, and also with the inclusion of nano-sized NbC and micrometer TaC particles at 2:1 vol% proportion. For the study of densification, micro-nanocomposites were sintered in a dilatometer with a heating rate of 20°C/min until a temperature of 1800°C in argon atmosphere. Based on the dilatometry results, specimens were sintered in a resistive graphite furnace under argon atmosphere between 1500°C and 1700°C by holding the sintering temperature for 30 minutes. Densities, crystalline phases, hardness and tenacity were determined, and micro-nanocomposites microstructures were analyzed. The samples Al2O3: NbC: TaC sintered at 1700 ° C achieved the greater apparent density (~ 95% TD) and the sample sintered at 1600 ° C showed homogeneous microstructure and increased hardness value (15.8 GPa) compared to the pure alumina . The compositions with 3% inclusions are the most promising for future applications.
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SANTOS, THAIS da S. "Micro-nanocompósitos de Al2O3/ NbC/ WC e Al2O3/ NbC/ TaC." reponame:Repositório Institucional do IPEN, 2014. http://repositorio.ipen.br:8080/xmlui/handle/123456789/23599.
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Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Parker, Simon. "Towards carbon control in the manufacture of WC-Co hardmetal." Thesis, University of Surrey, 2017. http://epubs.surrey.ac.uk/813941/.
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WC-Co hardmetal, found in applications ranging from mining tools to valves in deep-sea gas pipelines, is valued for its hardness and toughness provided by the unique chemistry of the tungsten carbide – cobalt pairing. Properties of WC-Co hardmetal are very sensitive to carbon content, variation of 0.01 wt.% can lead to alteration of hardness yet carbon content is very difficult to control in manufacture of hardmetal, a powder metallurgical process involving high temperatures and interactions with different atmospheres. Accurate measurement of carbon content is difficult in hardmetal as the total carbon content is high compared to the sensitivity. Work has been reported on carbon measurement in hardmetals using x-ray diffraction (XRD) but attempts to replicate this work were unsuccessful due to limitations in accuracy of equipment. Examination of a commercial hardmetal production process sought to identify manufacturing variables that lead to changes in carbon content. The Vickers hardness, Palmqvist toughness, density and magnetic saturation of samples processed under different processed under different conditions found in commercial manufacture of hardmetal were compared. No clear correlation between any of the process variables examined and carbon content of sintered hardmetal could be found, motivating work to actively alter carbon content. An obvious solution to limited carbon control is to alter the balance of carbon and tungsten in powder blends to compensate for anticipated changes and work was undertaken to investigate this approach. In addition to mechanical and magnetic characterisation, the carbon content of samples was measured using the infra-red gas absorption method. Altering the carbon content of samples by adding carbon or tungsten did not appear to offer control of carbon content in sintered hardmetal as the amount of carbon added did not appear to correlate to the carbon content of sintered samples. Heat treatments in carbonaceous atmospheres has also been explored and was demonstrated to have potential as a method of controlling carbon content in the manufacture of WC-Co hardmetal. Pre-sintering, a heat treatment often applied to compacts before sintering, was replicated at laboratory scale using an atmosphere of nitrogen and hydrogen with various additions of methane at different temperatures. Samples were examined using Vickers microhardness and confocal light scanning microscopy (CLSM) to capture spatial variation in sample properties and by electron backscatter diffraction (EBSD) to obtain information on grain size distributions. It was found that carbon content increases with the amount of methane in the heat treatment atmosphere and with heat treatment temperature though the reliability and accurate control required to make the technique commercially viable were not achieved. Results demonstrate that with further refinement heat treatment of pressed compacts in carbonaceous atmosphere could be used to accurately control the carbon content of sintered hardmetal components.
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Blandenet, Olivier. "Elaboration de revetements, dont WC-Co, par canon à détonation." Grenoble INPG, 1997. http://www.theses.fr/1997INPG0124.
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Lors de cette etude, nous avons mis au point et optimise les conditions d'elaboration de revetements ceramique oxyde et cermet a l'aide d'un procede de projection par canon a detonation : le korund. Les mesures experimentales de pression et de celerite de l'onde de detonation nous permettent de conclure a la validite de la representation de la detonation se propageant a l'interieur du fut du korund et de l'ecoulement des produits de detonation en aval de cette onde, respectivement a l'aide des modeles chapman-jouguet (c. J. ) et taylor zeldovich (t. Z. ). L'optimisation de la composition, de la microdurete, de la rugosite, de la porosite et de l'adherence-cohesion d'un certain nombre de revetements, dont l'alumine, la zircone-yttriee et le cermet carbure de tungstene-cobalt (wc-co), a ete rendue possible par l'etude des parametres de l'installation korund. Les revetements obtenus par ce procede sont generalement tres denses et tres adherents (a titre d'exemple : porosite = 1 a 2 % ; adherence cohesion 40 a 75 mpa). Leurs caracteristiques mecaniques ont ete etudiees par le biais d'essais de flexion 3 ou 4 points qui ont montre que la rupture interfaciale substrat-revetement est mixte adhesive-cohesive. La comparaison des proprietes, et notamment de la resistance a l'erosion des revetements obtenus par differents procedes de projection hypersonique, a mis en evidence le tres bon comportement des revetements optimises durant cette etude.
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Bewick, Thomas. "Improving outcomes in patients with community-acquired pneumonia." Thesis, University of Nottingham, 2012. http://eprints.nottingham.ac.uk/12432/.
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Community-acquired pneumonia (CAP) is a leading cause of adult morbidity and mortality worldwide despite decades of effective antibiotics and vaccination initiatives. There have been no recent significant improvements in outcomes, including 30-day mortality. The bacterium Streptococcus pneumoniae is the most prevalent causative pathogen in CAP, being found in up to half of cases. In September 2006 a childhood pneumococcal vaccine (PCV-7) was introduced, leading to reductions in vaccine-type (VT) pneumococcal disease in infants, with possible additional benefits reported in adults. However, the effect that infant PCV-7 vaccination has on adult disease has to date been inadequately described in a small fraction of patients with invasive CAP, almost exclusively in populations in the US. These issues are explored fully in the literature review, encompassing chapters 1, 2 and 3. New strategies for CAP are therefore required. The outcome of CAP can be improved by a) preventing the disease by vaccination and herd immunity, and b) ameliorating the course of the disease after it has been acquired. This thesis presents a collection of studies that aim to acquire observational data to investigate these two issues. The majority of the included studies are drawn from a two year prospective cohort study of consecutive adults with CAP admitted to a large UK teaching hospital trust between September 2008 and September 2010. After obtaining informed consent, the presence of pneumococcal disease in each participant was established by testing urine samples for pneumococcal capsular polysaccharide, a test which has a high sensitivity and specificity. The urine samples were subsequently tested for pneumococcal serotype. A full record of care processes, investigations, and clinical outcomes was made, and child contact in the month preceding admission was assessed. These methods are described more fully in chapter 4. Chapter 5 presents the data on the pneumococcal serotypes found in the cohort over a two year period, and links them to epidemiological characteristics in the study population. The most prevalent serotypes were 14, 1, 8, 3 and 19A, with VT serotypes less frequent in the second year of the study. Chapter 6 examines the association that infecting serotype has with disease manifestation and patient characteristics. Infection with a serotype not contained within PCV-7 (NVT) was associated with younger and fitter patients, a higher rate of complications such as para-pneumonic effusion, and hypotension at admission. The effect of child contact on pneumococcal disease is reported in chapter 7. Prior contact with a child aged ≤8 years was particularly associated with pneumococcal aetiology, and contact with a PCV-7 vaccinated child independently associated with NVT CAP. The findings from these three chapters are unique in that they relate individual pneumococcal serotype to specific clinical disease patterns, epidemiology and transmission in both invasive and non-invasive pneumococcal CAP for the first time. They show a change in serotype distribution in adults following the introduction of PCV-7 in infants, which is important to inform future vaccine development for both adults and children. Furthermore, different serotypes are associated with different clinical disease patterns, which may have a significant impact on the disease that clinicians see at the “front door” given that the serotype distribution of pneumococcal CAP may be changing. Finally, the link between child vaccination and adult disease provides more direct evidence for the transmission of pneumococci from children to adults as a mechanism for the development of CAP in adults. The second part of this thesis looks at current care processes, and how these might be improved. Chapters 8, 9 and 10 relate to efforts to better predict prognosis, and chapters 11 and 12 with how patents with CAP may be better managed at the “front door”. Symptoms are clearly important to patients, but the role of symptoms in management and outcome is unclear. Chapter 8 presents a study validating a symptom score that has not yet entered routine use, but which is shown to correlate with clinical outcomes, and may be useful in assessing outcome in low severity CAP. The influence that oxygenation status at admission has on outcome is poorly understood. Chapter 9 describes a study showing that whilst hypoxaemia does positively predict adverse outcome, it is not as predictive as existing severity scores. The presence of hypoxaemia may however identify a subset of patients who are classified as low severity by existing severity scoring, but are nevertheless at increased risk of adverse outcome. Severity scoring is the cornerstone of management in adult CAP, and is explored in chapter 10. Current severity scores adequately predict mortality in CAP, but often generate a group of “moderate severity” where appropriate management is often unclear. This study looked at the effect of pre-admission functional status on outcome in conjunction with existing severity scores in this difficult group, and validated a novel severity score for predicting need for escalation of care, SMART-COP. Incorporation of functional status does marginally improve the performance of existing severity scores, but may be of more use as a post-severity score test to identify sub-groups of patients with moderate severity CAP who are at increased risk of death. Chapter 11 looks at the influence that making a prompt diagnosis (rather than prompt treatment with antibiotics, as has previously been studied) has on outcome, using the time between admission and first chest radiograph as a surrogate measure. Whilst an early chest radiograph was not associated with an improvement in mortality, it was associated with a shorter length of hospital stay, and may therefore be regarded as a marker of good quality care. There is current debate as to the role of the speciality physician in the front-door early assessment of patients, and whether early review of patients with CAP may improve outcome compared with management by a non-specialty physician. Chapter 12 looks at the effect that early specialist senior respiratory review has on outcome for adults with CAP, showing a clear benefit on length of hospital stay to early consultant review. In conclusion, this thesis provides an up-to-date picture of the circulating pneumococcal serotypes in non-invasive adult CAP, and correlates infecting serotype to clinical and epidemiological parameters. It also identifies five areas of clinical care where management processes could be improved. By addressing of these aspects the outcome of CAP may be improved in the future.
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Lawson, Adam. "A study of the natural history of hepatitis C infection within a geographically determined population (Trent HCV study)." Thesis, University of Nottingham, 2012. http://eprints.nottingham.ac.uk/12477/.
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The epidemiology and natural history of Hepatitis C has been studied in a large geographically determined population (Trent HCV study). It has previously been suggested that patients with Hepatitis C and a persistently normal Alanine aminotransferase (PNALT) represent a group of patients with mild disease and at low risk of disease progression. Patients with PNALT were, therefore, compared to those with an elevated ALT. The majority of patients initially fulfilling the definition of a PNALT had an abnormal ALT within 3 years of follow-up. They also demonstrated similar rates of fibrosis progression as a sub-group of HCV infected patients with an elevated ALT who were re-biopsied prior to any institution of therapy. They, therefore, warrant the same consideration with regard to treatment. The morbidity and mortality associated with Hepatitis C with severe fibrosis was assessed in a group of patients with a liver biopsy demonstrating Ishak fibrosis stage 4. A worse prognosis than previously reported was observed for this patient population. Once decompensation develops, HCV infection is associated with a high mortality rate. Indicators of poor synthetic liver function and hypergammaglobulinaemia were important prognostic factors for mortality, while combination antiviral therapy was associated with improved survival. The majority of HCV infected patients (75%) diagnosed with hepatocellular carcinoma (HCC) were known to have cirrhosis at least 6 months prior to diagnosis of HCC and were, therefore, amenable to surveillance. There was a variable application of surveillance, however, and no significant improvement in survival was demonstrated. Age, duration of infection and immunoglobulin G levels were associated with an increased risk of HCC in cirrhotic patients in the univariate analysis. Achieving an SVR was associated with a reduced risk. No variable in cirrhotic patients was shown to be independently associated with HCC in the multivariate analysis. A comparison of disease progression and treatment outcome in White and Asian (Indian subcontinent) patients was made. Asian patients generally presented at an older age and with more severe disease on biopsy. The patient’s ethnic group was not associated with the likelihood of either an SVR or completion of therapy. Instead cirrhosis and a raised GGT were associated with a failure to achieve SVR in the multivariate analysis. The platelet count is a surrogate marker for the severity of liver fibrosis and correlates with the Ishak fibrosis stage. An analysis of factors associated with an SVR was performed. In the multivariate model, age at start of treatment was the only independent predictor of SVR in Genotype 1, while estimated duration of infection and Ishak stage were predictors in genotype 2/3 patients. The platelet count was not an independent predictor of SVR or completion of therapy.
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Killingley, Ben. "Investigations into human influenza transmission." Thesis, University of Nottingham, 2013. http://eprints.nottingham.ac.uk/13364/.
Full textAbstract:
Limited understanding of influenza transmission has been a frequent obstacle during the development of pandemic influenza infection prevention and mitigation strategies. The science is hotly debated, especially the relative importance of transmission via large droplets or aerosols. Clarification of the relative importance of different modes of transmission is critical for the refinement of evidence-based infection control advice and has been called for by the European Center for Disease Control (ECDC), the World Health Organization (WHO), and the US Institute of Medicine. The primary aims of this thesis were to investigate influenza transmission; i) by obtaining data concerning viral shedding and the presence of influenza virus in the near environment of infected individuals and ii) through the exploration of a human challenge model to study transmission. Two major clinical studies have been performed; • Shedding and environmental deposition of novel A (H1N1) pandemic influenza virus. The primary aims of the study were to correlate the amount of virus detected in a subject’s nose with that recovered from his/her immediate environment (on surfaces and in the air) and with symptom duration and severity. Adults and children, both in hospital and from the community, who had symptoms of influenza infection were enrolled. Information about symptoms was collected and samples were taken including nose swabs, swabs from surfaces and air samples. Forty two subjects infected with influenza A(H1N1)pdm09 were recruited and followed up. The mean duration of nasal viral shedding was 6.2 days (by PCR) and 4.6 days (by culture). Over 25% of cases remained potentially infectious for at least 5 days. Symptom scores and viral shedding were poorly correlated. From surface swabs collected in the vicinity of 40 subjects, 15 (38%) subject locations were contaminated with virus. Overall 36 of 662 (5.4%) surface swabs taken were positive for influenza, two (0.3%) yielded viable virus. Subjects yielding positive surface samples had significantly higher nasal viral loads on illness Day 3 and more prominent respiratory symptom scores. Room air was sampled in the vicinity of 12 subjects and PCR positive samples were obtained from five (42%). Particles small enough to reach the distal lung (≤4µm) were found to contain virus. • Use of a human influenza challenge model to assess person-to-person transmission: Proof-of-concept study. The primary aim of this study was to establish that an experimentally induced influenza infection is transmissible. Healthy subjects deemed sero-susceptible to influenza A/H3N2/Wisconsin/67/2005 were intranasally inoculated (Donors) and when symptoms began, further sero-susceptible subjects (Recipients) were exposed to Donors during an ‘Exposure Event’. Subjects were in close contact, e.g. playing games and eating meals together, for a total of 28 hours during a 2 day period. Samples were collected to confirm infection status. Among 24 healthy adult subjects, nine were randomised to the ‘Donor’ group and 15 to the ‘Recipient’ group. Following inoculation 5 out of 9 Donors (55%) developed illness and 7 out of 9 (78%) were proven to be infected. After exposure, 5 out of 15 Recipients developed symptoms and 3 out of 15 were proven to be infected. Three others were found to be non sero-susceptible prior to exposure. The overall attack rate in Recipients was 20% but was 25% after adjustment for pre-exposure immunity. The contact, droplet and aerosol routes of influenza transmission are all likely to have a role. This thesis shows that transmission of influenza via surfaces may be less important than current infection control policies and public guidance documents imply. Air sampling results add to the accumulating evidence that supports the potential for aerosol transmission of influenza. The human challenge model could be used to investigate routes of influenza transmission further and a study funded by the Centers for Disease Control (CDC) is planned.
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Stanczyk, Nina M. "An investigation of DEET-insensitivity in Aedes aegypti." Thesis, University of Nottingham, 2011. http://eprints.nottingham.ac.uk/11828/.
Full textAbstract:
N,N-Diethyl-m-toluamide (DEET) is one of the most effective and commonly used mosquito repellents. However, during laboratory trials a small proportion of mosquitoes are still attracted by human odours despite the presence of DEET. In this study behavioural assays identified Aedes aegypti females that were insensitive to DEET. The selection of either sensitive or insensitive groups of females with males of unknown sensitivity over several generations resulted in two populations with different proportions of insensitive females. Crossing experiments showed the ‘DEET-insensitivity’ trait to be dominant. In addition to the finding of heritable DEET-insensitivity, unselected culture mosquitoes were shown to change their sensitivity to DEET after brief pre-exposure to the repellent. Female mosquitoes that were sensitive to DEET when first tested became insensitive when retested. Electroantennography showed that mosquitoes that were insensitive to DEET had a reduced response to DEET compared with mosquitoes that were sensitive to it. This was the case both for culture mosquitoes displaying insensitivity to DEET after brief pre-exposure to it, and for the sensitive and insensitive lines selected for several generations. Single sensillum recordings of the selected lines identified DEET-sensitive sensilla in the sensitive line that did not respond to DEET in the insensitive line. This study suggests that behavioural insensitivity to DEET in Ae. aegypti is a genetically determined dominant trait, which can also be temporarily induced by pre-exposure, and resides in changes in sensillum function. These results highlight the necessity for careful monitoring of DEET-insensitivity in the field, and caution when designing laboratory methods for repellency assays.