Дисертації з теми "Tungstene carbide"
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1
Roure, Sophie. "Densification des mélanges de poudres WC-Co : de la compression au frittage." Grenoble INPG, 1996. http://www.theses.fr/1996INPG0222.
Анотація:
Ce travail a pour objectif de prevoir le comportement des melanges wc-co lors du compactage et leur evolution au cours du frittage, en s'interessant particulierement a l'influence de la geometrie des microstructures sur la densification du materiau. Lors de l'etude macroscopique de la compression a froid, un test de compressibilite est etabli pour caracteriser l'aptitude de ces melanges a se comprimer selon les parametres de la poudre et les conditions de l'essai. Ce test fournit une loi de compressibilite intrinseque du melange et un coefficient relatif a la fluidite de la poudre et a son frottement aux parois. Les resultats des essais effectues sont interpretes a l'aide d'une analyse micromecanique du comportement d'empilements composites de particules. Au cours du frittage, l'etude macroscopique de la densification par dilatometrie determine l'evolution du retrait en fonction des parametres du procede, des caracteristiques du melange et de la densite a vert. Un interet particulier est porte a la part de densification realisee en phase solide. On montre que celle-ci est reliee a un rearrangement des grains wc qui se poursuit jusqu'a la formation d'un empilement stable de ces grains. En parallele, une etude microscopique quantitative par analyse d'images caracterise les etats comprime et fritte et l'evolution d'un etat a un autre. Elle permet d'etablir qu'en phase solide l'ecoulement du liant et le rearrangement des grains wc sont deux phenomenes simultanes. Finalement, une modelisation de la densification des melanges wc-co est proposee, qui integre les caracteristiques geometriques instantanees de l'empilement, propres au systeme etudie, au sein d'une approche cinetique globale simple
2
Harry, Emmanuelle. "Stabilité mécanique et modes d'endommagement de revêtements multicouches à base de tungstène et de tungstène-carbone élaborés par PVD." Grenoble INPG, 1998. http://www.theses.fr/1998INPG0071.
Анотація:
Les revetements a base de tungstene et de tungstene-carbone sont utilises pour leurs proprietes de resistance a l'usure contre le frottement ou contre l'erosion par des particules solides. Ces revetements peuvent etre le siege de contraintes residuelles elevees. Seules ou associees a une sollicitation exterieure, elles peuvent etre a l'origine de nombreux mecanismes d'endommagement, alterant la fiabilite des revetements. L'objectif de notre travail est d'analyser la stabilite mecanique et les modes de rupture de ces revetements, en relation avec leurs proprietes microstructurales et mecaniques, afin d'optimiser leur architecture pour une application donnee. Les revetements ont ete elabores par pulverisation cathodique magnetron : monocouche w et w(c) (contenant 14 at. %c), revetement multicouches et revetement a gradient de concentration en carbone. La morphologie des couches evolue d'une structure colonnaire a une structure compacte par ajout de carbone dans le tungstene. La durete des depend majoritairement de la taille des grains. Les contraintes residuelles sont equivalentes quelques soit l'architecture du revetement. Les modules d'young ont ete determines par des essais de flexion trois points, et sont voisins du module du tungstene massif. Des essais micromecaniques (flexion trois points avec suivi acoustique, traction in situ dans un microscope electronique a balayage) ont permis de determiner leur contrainte critique de fissuration, leur densite de fissures transversales a saturation, dont sont deduites l'energie de fissuration en volume et la tenacite. Ces parametres, qui sont intrinseques au revetement, decrivent la stabilite mecanique du systeme revetement/substrat. Nous avons utilise un modele base sur la redistribution des contraintes dans un revetement fissure pour analyser son adherence au substrat. Par ailleurs, des essais de rayure (avec suivi acoustique, et analyse par microscopie optique et microscopie electronique a balayage) ont permis de degager les differents mecanismes d'endommagement des revetements (en volume, aux interfaces et en surface) en fonction de la charge appliquee et de caracteriser egalement leur adherence. L'ensemble des resultats montre l'influence determinante de l'architecture des revetements (epaisseur, morphologie, composition, sequence d'empilement des couches) et de la presence de defauts microstructuraux au sein des depots sur leur comportement mecanique. Ces facteurs de structure peuvent, suivant leur amplitude, modifier considerablement la tenue mecanique des revetements.
3
Lavergne, Olivier. "Mécanismes de dissolution et de précipitation dans les carbures cémentés WC/Co." Grenoble INPG, 1997. http://www.theses.fr/1997INPG0214.
Анотація:
Les carbures cementes wc/co sont des cermets prepares par metallurgie des poudres. L'evolution microstructurale au cours du frittage avec phase liquide se caracterise par le grossissement moyen de l'ensemble des grains de wc (croissance normale) et par l'apparition de tres gros grains (croissance anormale). Les proprietes mecaniques etant optimisees par une microstructure fine, industriellement, des inhibiteurs de grossissement, entre autres cr#3c#2 et vc, sont ajoutes en faible quantite (<1pds%) dans le melange de poudres de depart. Pour tenter d'expliquer l'evolution microstructurale de ces materiaux, nous avons etudie : - les mecanismes de dissolution de wc dans co en phase solide, a 1200c, par la technique des couples de diffusion, et en phase liquide, a 1450c, par la methode du cylindre tournant. Les resultats montrent qu'au cours de la dissolution, l'equilibre est realise aux interfaces. Les elements cr et v ont le meme effet qu'un petit exces de w : ils favorisent la formation des phases (m#6c) et '(m#1#2c). Dans tous les cas, la cinetique de dissolution de wc dans co est rapide, controlee par diffusion. - les mecanismes de precipitation de wc a partir d'un liquide sursature en w et c. Pour cela, nous avons analyse experimentalement : * l'evolution microstructurale dans des echantillons frittes prepares a partir de poudres de wc submicroniques. Cette etude a permis de definir plus clairement les phenomenes associes aux notions de croissance normale, anormale et inhibee. Les resultats montrent notamment que cr#3c#2 n'a pas pour effet d'inhiber la croissance mais seulement de la retarder ou de la ralentir. * les microstructures de solidification obtenues a partir de liquides sursatures en w et c. Les resultats montrent d'une part que la germination de wc est tres difficile et d'autre part que la croissance peut etre rapide en condition de fortes sursaturations. D'apres les resultats, l'evolution microstructurale des frittes est limitee par l'etape de precipitation. Les differences de tailles observees s'expliquent par des differences de sursaturation locale dans la phase liquide conduisant a un ou plusieurs mecanismes de germination-croissance. L'effet des elements cr ou v pourrait etre relie a un diminution de l'activite de c dans les phases liquides quaternaires.
4
Lindahl, Bonnie. "Equilibrium Study of Chromium Containing Cemented Carbides : Solubility of chromium in tungsten carbide and η-phase". Thesis, KTH, Materialvetenskap, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-49974.
Анотація:
This project treats the W-C-Co-Cr quaternary system at low carbon contents. The main goals with this project were to find a four phase equilibrium between WC, Co-binder phase, η-phase (M6C) and a fourth unknown phase, to discover which the fourth phase is and to establish whether or not WC dissolves any chromium. In order to answer these questions a number of alloys were prepared, the compositions were chosen using thermodynamic calculations and observations from previous alloys. The samples were prepared using a powder metallurgical route and they were sintered at 1410oC. The samples were prepared for analysis via grinding and polishing and then analyzed using LOM, SEM, EDS, WDS and XRD. The results showed that no four phase equilibrium could be found in the analyzed spectra and therefore neither could the fourth phase. However other interesting phenomena were found. The η-phase showed a much higher solubility of chromium than previously thought. According to the current Sandvik-Seco database the η-phase should dissolve a maximum of 0.21 wt% and the maximum value detected using WDS was 8.42 wt%. The solubility of chromium in WC was found to be approximately 5 wt%. The most important conclusion that could be drawn from this project was that the Sandvik-Seco database for the W-C-Co-Cr system still needs to be improved, especially concerning the solubility of chromium in the η-phase.
5
Guiz, Robin. "Influence d’additions de titane/tungstène et de vanadium sur la précipitation de carbures secondaires au sein d’alliages modèles de type HP." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEM011/document.
Анотація:
Les alliages de type HP constituent un matériau de choix pour l'élaboration des tubes de vaporeformage et de vapocraquage dans l'industrie pétrochimique. Exposés à des températures comprises entre 700°C et 1000°C sous des pressions gazeuses de plusieurs MPa, leur microstructure initiale associée à une fine précipitation secondaire, intervenant en cours de service, leur confèrent une excellente résistance aux mécanismes de fluage auxquels ils sont sujets. Néanmoins, à terme, la coalescence des précipités conduit à la dégradation rapide des tubes.Les effets de certains éléments d'alliages (V, Ti/W) sur la précipitation secondaire des carbures M23C6 et NbC ont été étudiés au travers de simulations via le logiciel TC-PRISMA. Sur la base de résultats prometteurs en termes d'optimisation des caractéristiques de la précipitation, deux alliages modèles ont été coulés au laboratoire et soumis à divers vieillissements dans la gamme de température correspondant aux conditions de service. Les microstructures de ces alliages ont d'abord été comparées à celle d'un alliage HP industriel de composition standard à l'état brut de coulée. La précipitation secondaire a par la suite été caractérisée au sein des trois alliages dans les différents états vieillis. Les investigations microstructurales ont permis de mettre en avant certains effets bénéfiques d'un ajout de vanadium et d'ajouts combinés de titane et de tungstène sur les caractéristiques de la précipitation secondaireHP alloys are typically used as steam methane reforming tubes in the petrochemical industry. During service, they are exposed to temperatures between 700°C and 1000°C under gaz pressure of several MPa. Their as-cast microstructure, together with fine in-situ secondary precipitation, provide these alloys with an excellent resistance to creep deformation. Nevertheless, after long-time ageing, coarsening of secondary carbides leads to the weakening of the tubes and therefore to an accelerated damaging.The effects of some alloying elements (V, Ti/W) on secondary precipitation of M23C6 and NbC carbides were investigated through numerical simulations performed with TC-PRISMA software. On the basis of encouraging results in terms of precipitation optimization, two model HP-type alloys were cast at the laboratory and aged in the range of temperatures corresponding to service conditions. As-cast microstructures were first compared with an industrial "standard" alloy. Then, secondary precipitation were characterized for all the alloys and all ageing temperatures. Microstructural investigation highlighted the beneficial effect of vanadium and titanium/tungsten additions on secondary precipitation characteristics
6
Agode, Kofi Edoh. "Analyse et modélisation du comportement à l’usure des outils de coupe en carbure de tungstène pour différentes teneurs en cobalt lors de l’usinage de l’alliage de titane Ti-6Al-4V." Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0141.
Анотація:
En raison de sa grande dureté et sa résistance à l'usure, le carbure de tungstène avec liant cobalt (WC-Co) est le matériau incontournable pour la fabrication des outils d’usinage, des outillages de découpe et de formage, ainsi que des pièces d'usure nécessitant une dureté importante et une grande précision. La modification de la microstructure du carbure de tungstène, et plus particulièrement sa teneur en cobalt suscite aujourd’hui le plus grand intérêt de la part des fabricants pour développer de nouvelles nuances plus performantes et ainsi gagner de nouveaux parts de marché. Cette thèse propose d’étudier l’effet de la teneur en cobalt des outils carbure sur les grandeurs mesurées et les mécanismes d’usure lors de l’usinage des superalliages durs à base de titane (Ti-6Al-4V). Le travail de recherche, à la fois expérimental et numérique, est consacré d’une part à la compréhension des mécanismes microscopiques d’endommagement conduisant à l’usure macroscopique du composite WC-Co, et d’autre part à l’influence de la teneur en cobalt sur le comportement du WC-Co en tenant compte du couplage mécanique-microstructure-endommagement. Sur la base d’une analyse expérimentale, l’identification des phénomènes physiques macroscopiques et microscopiques mis en jeu aux niveaux des interfaces de contact outil/copeau et outil/pièce a été conduite. A cet effet, des essais d’usinage ont été réalisés dans un premier temps sur le couple outil-matière WC-Co/Ti-6Al-4V avec différentes teneurs en cobalt pour les outils. Dans un deuxième temps, une caractérisation tribologique, du même couple outil-matière, a été menée afin d’évaluer l’influence de la teneur en cobalt et les conditions de contact (vitesse de glissement, effort appliqué) sur le coefficient de frottement et l’usure. Toutefois, l’inaccessibilité des zones de contact pendant l’usinage et les essais tribologiques n’ont pas permis une description complète des mécanismes d’usure observés qu’ils soient macroscopiques (collage, abrasion, déformation, ...), ou microscopique (fissuration, endommagement des phases WC, Co). La simulation numérique par éléments finis s’est avérée alors un outil complémentaire intéressant pour l’analyse de ces mécanismes d’usure. Notre stratégie de modélisation s’est intéressée à la réponse du WC-Co à l’échelle de la microstructure sous un chargement thermomécanique représentatif de l’usinage. Le modèle proposé tient compte du comportement des phases WC et Co séparément et celui des interfaces WC-WC et WC-Co. Cette stratégie a permis d’étudier et identifier les paramètres influant sur le comportement de la microstructure depuis la phase élastique jusqu’à l’initiation de l’endommagement. Un bon accord a été obtenu entre les résultats du comportement numérique à l’initiation de l’endommagement dans la microstructure et ceux des observations expérimentales en termes d’effets de la teneur en cobalt dans le carbure de tungstène et des conditions d’usinage appliquéesDue to their high hardness and wear resistance, cemented carbide (WC-Co) is the main material used to manufacture machining tools and forming tooling, as well as wear parts requiring high hardness and high precision. The modification of tungsten carbide microstructure, and more particularly its cobalt content, is currently attracting the greatest interest from manufacturers to develop new grades tools with high performance, and then expand new markets.This thesis aims to study the effect of the cobalt content of carbide tools on the measured values and wear mechanisms when machining hard superalloys such as the aeronautical titanium alloys Ti-6Al-4V. Both experimental and numerical research work are devoted on one hand to the understanding of the microscopic damage mechanisms leading to the macroscopic wear of the WC-Co composite and on the other hand, to the influence of the cobalt content on the behavior of the WC-Co taking into account the mechanical-microstructure-damage coupling.On the basis of an experimental analysis, the identification of the macroscopic and microscopic physical phenomena involved at the tool/chip and tool/workpiece contact interfaces was conducted. Machining tests were firstly carried out on the tool-material couple WC-Co/Ti-6Al-4V with different cobalt contents for the tools (from 6 to 15%). In a second step, a tribological characterization of the same tool-material couple was carried out to evaluate the influence of the cobalt content and the contact conditions (sliding speed, applied force) on the friction coefficient and wear. However, the inaccessibility of the contact zones during machining and the tribological tests did not allow a complete description of the wear mechanisms observed, whether macroscopic mechanisms (adhesion, abrasion, deformation, ...), or microscopic mechanisms (cracking, damage of the WC and Co phases). The numerical simulation using finite elements (FE) proved to be a very interesting complementary tool for the analysis of these wear mechanisms.Our modeling strategy focused on the response of WC-Co at the microstructure scale for the thermomechanical loading close to that obtained by machining. The proposed model takes into account the behavior of the WC and Co phases separately and that of the interfaces WC-WC and WC-Co of the composite. This strategy allowed to study and identify parameters influencing the behavior of the microstructure from the elastic stage to the damage initiation. A good agreement was obtained between the results of the numerical behavior at the initiation of damage in the microstructure and those of the experimental observations in terms of the effects of the cobalt content in the tungsten carbide and of the applied machining conditions
7
Gianni, Lorenzo. "Electrodialytic recovery of tungsten and cobalt from tungsten carbide scrap." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2022.
Анотація:
Critical raw materials (CRMs) are essential for a wide range of European industrial ecosystems. Access to critical resources is necessary for Europe’s ambition to achieve climate neutrality and deliver the Green Deal. However, supply of material from primary sources is putting extreme pressure on the planet through greenhouse gas emissions, biodiversity loss and water stress. In this scenario, promoting circular economy by obtaining resources from secondary sources is therefore essential to reduce the environmental burden posed by raw material primary extraction and to secure the supply chain of CRMs. This work is a preliminary assessment on the potential of the electrodialytic (ED) treatment in alkaline condition on a tungsten carbide scrap powder obtained from end-of-life cutting tools industry for the recovery of two CRMs: Tungsten (W) and Cobalt (Co). Modular ED reactors with 2 or 3 cell compartments have been used to perform eleven ED experiments (each lasting 24 h), with either NaOH or NH4OH and at 100, 150 or 200 mA to individuate the best reactor configuration, alkaline reagent, and current intensity.
The alkaline reagents were placed at different concentrations in the anode compartment (in case
of 2-compartments reactor) or in the central compartment (in case of a 3-compartments reactor) along with 450 mL of deionized water and the solid matrix with a solid:liquid ratio of 1/50. Inductively coupled plasma-atomic emission spectroscopy was used to quantify the amount of W and
Co obtained in solution at the end of the experiments.
The experiments showed that the 2-compartments ED cell setup at 100 mA and with NaOH 0.1 M resulted in the highest W dissolution ( 651 mg), and that the 3-compartments ED cell setup at 100 mA and with NaOH 0.01 M resulted in the highest Co dissolution ( 372 mg) and electromigration (85%). Further investigation is needed to optimize the operational parameters.
8
Deshpande, Pranav Kishore. "Infrared Processed Copper-Tungsten Carbide Composites." University of Cincinnati / OhioLINK, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1025107651.
9
Kelley, Andrew III. "Tungsten carbide-cobalt by Three Dimensional Printing." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/32316.
Анотація:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1998.Includes bibliographical references (p. 69-70).
Three Dimensional Printing is an additive manufacturing process for rapid prototyping ceramic and metallic parts [Sachs, et al, 1990]. Green (not sintered) tungsten carbide-cobalt parts must have a density greater than 50% of the theoretical density, 14.9 g/cc, for proper sintering and post-processing. Two approaches were assessed for feasibility and robustness: printing slurry into tungsten carbide-cobalt spray dried powder and printing a solvent in spray dried tungsten carbide powder that readily dissolves. For slurry administered to a powder bed of solid, spherical particles, it has been found that the resulting packing primitive packing fraction increases almost linearly with the volume loading of the slurry over a range of powder size. The increase in density is approximately half what would be calculated by assuming that the slurry fills all the porosity in the powder bed. The maximum green density achieved by printing slurry into a spray dried tungsten carbide-cobalt bed was 41%, midway between the lower bound calculated by assuming the vehicle in the slurry infiltrates only the large pores between the spray dried power and the upper bound calculated by assuming that the vehicle of the slurry also infiltrates the find pores within a spray dried granule. A re-dispersible spray dried powder (38-53 micron size range) was fabricated using only the Duramax 3007 dispersant as the binder. This powder redisperses in water. Administering a drop of water to this powder resulted in primitives with 47% packing density, but which had significant quantities of 80 micron voids.
(cont.) Several lines of evidence pointed to the hypothesis that the voids were the result of trapped air. Two methods were successfully employed to nearly eliminate such voids. In one approach, the droplet of water wvas administered to the powder bed under a vacuum of between 25 and 40 torr and air was admitted to the chamber to 1 atmosphere after different intervals of time ranging from 30 seconds to 10 minutes. In another approach, the ability of water to absorb CO₂ was used to "getter" any trapped gas into the liquid. Water was administered to a powder bed under a CO₂ environment at room temperature. After a 2 minute period, intended to allow the spray dried powder to substantially re-disperse, the temperture of the powder bed was lowered to 0-5 degrees Centigrade in order to increase the amount of CO₂ which could be absorbed in the water and "switch on" the gettering of the trapped gas.Controls were run with the same procedure in air. The primitives made under CO₂ were nearly void free and had densities as high as 52%, while the controls were not significantly different than primitives made at room temperature in air.
by Andrew Kelley, III.
S.M.
10
Deshpande, Pranav K. "Copper-tungsten carbide composites with infrared processing." Cincinnati, Ohio : University of Cincinnati, 2002. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=ucin1025107651.
11
Björklund, Kajsa. "Microfabrication of Tungsten, Molybdenum and Tungsten Carbide Rods by Laser-Assisted CVD." Doctoral thesis, Uppsala University, Department of Materials Chemistry, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-1593.
Анотація:
Thin films of refractory metals and carbides have been studied extensively over many years because of their wide range of application. The two major techniques used are Chemical Vapour Deposition (CVD) and Physical Vapour Deposition (PVD). These can result in the deposition of two-dimensional blanket or patterned thin films. Laser-assisted Chemical Vapour Deposition (LCVD) can provide a maskless alternative for localised deposition in two and three dimensions. This thesis describes LCVD of micrometer-sized tungsten, molybdenum and tungsten carbide rods. The kinetics, phase composition and microstructure have been studied as a function of in situ measured laser induced deposition temperature.
Tungsten and molybdenum rods were deposited by hydrogen reduction of their corresponding hexafluorides, WF6 and MoF6, respectively. Single crystal and polycrystalline tungsten rods were obtained, depending on the H2/WF6 molar ratio and deposition temperature. The molybdenum rods were either single crystals or dendritic in form depending on experimental conditions. The field emission characteristics of the tungsten single crystals were investigated. The results showed LCVD to be a potential fabrication technique for field emitting cathodes.
Nanocrystalline tungsten carbide rods were deposited from WF6, C2H4 and H2. TEM analysis showed that the carbide rods exhibited a layered structure in terms of phase composition and grain size as a result of the temperature gradient induced by the laser beam. With decreasing WF6/C2H4 molar ratio, the carbon content in the rods increased and the phase composition changed from W/W2C to WC/WC1-x and finally to WC1-x/C.
12
Björklund, Kajsa. "Microfabrication of tungsten, molybdenum and tungsten carbide rods by laser-assisted CVD /." Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2001. http://publications.uu.se/theses/91-554-5197-7/.
13
Escolle, Bérenger. "Optimisation des outils de micro-fraisage destinés à l'usinage des aciers durs : cas des micro-fraises hémisphériques." Thesis, Besançon, 2015. http://www.theses.fr/2015BESA2023.
Анотація:
L’objectif de ces travaux de thèse est l’optimisation par une approche expérimentale d’un modèle de micro-fraise hémisphérique en carbure de tungstène revêtu, de diamètre 0,5 mm, destiné à l’usinage des aciers durs. Les données expérimentales obtenues résultent donc de l’usinage d’un acier 40NiCrMo16 à l’état trempé (54 HRC). Les résultats permettent de mettre en évidence certains phénomènes de coupe, d’usure et de comportement dynamique de l’outil liés au procédé, et leur évolution en fonction du type de fraise considéré et des conditions de coupe choisies. La géométrie de l’outil et son comportement dynamique sont ici principalement commentés. Dans un premier temps, l’étude de différentes nuances de carbure, préparation de surface ainsi que l’optimisation des géométries globale et locale des micro-fraises a permis de proposer un modèle optimisé pour notre partenaire outilleur Magafor. Dans un second temps, une approche numérique du micro-fraisage a été utilisée. Un premier modèle de calcul analytique des efforts de coupe a été testé et il a été mis en évidence les limites d’identification des coefficients spécifiques de coupe dans notre cas. Ensuite, une modélisation numérique par éléments finis du micro-fraisage a été réalisée afin d’appréhender l’étude du comportement dynamique des micro-fraises en fonction de la géométrie globale de l’outil développéThe aim of this PhD work is optimized by experimental approach with 0.5 mm diameter micro-ball-end mills made from micro-grain tungsten carbide and PVD coated for hardened tool steels machining. The experimental data are obtained on machining of hardened steel (54/55HRC), typically used for the production of plastic injection molds. Results permit to highlight some cutting phenomena of wear and dynamic behavior of the process related tool, and changes depending on the type of milling considered and selected cutting conditions. The geometry of the tool and dynamic behavior are primarily discussed here. As a first step, the study of different carbide grades, surface preparation and optimization of global and local geometries of micro-cutters helped provide an efficient model for our partner Magafor toolmaker. In a second step, the modelling of micro-milling is discussed and an analytical model for cutting forces calculation is introduced. It was demonstrated the identifying limits of the specific cutting coefficients in our case. Then, a test of finite element modelling of micro-milling is made in order to estimate the potential of such a method for the study of the dynamic behaviour of micro-mills
14
Durand, Corinne. "Atomisation de gouttes liquides sur une cible tournante microstructurée." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENI035.
Анотація:
L’objectif de ce travail est de concevoir un outil d’atomisation adapté à la production de poudres de carburede tungstène dans l’entreprise Technogenia, située à Saint-Jorioz (74). Plus généralement, nous avons étudiéune nouvelle conception d’atomiseur rotatif pour lequel les surfaces d’atomisation sont orientées selon un angled’incidence non nul. Une telle orientation permet alors d’exploiter de façon plus efficace la fréquence de rotationde l’atomiseur ainsi que les forces de centrifugation et de Coriolis. A partir de cette base de réflexion, troisgéométries de surface d’atomisation ont été étudiées : des surfaces lisses, des surfaces pourvues de structurationsde long de leur bord de fuite et des surfaces matricées de perforations.Les différents modes de déstabilisation des écoulements liquides ont été observés grâce à l’acquisition de vidéosultra-rapides des différentes étapes de l’impact d’une goutte unique sur les différentes géométries de surfacesd’atomisation étudiées. Les processus d’atomisation peuvent ainsi varier entre la rupture de jets liquides régulierscausée par des instabilités de type Rayleigh-Plateau et la rupture de nappes liquides causée par des instabilitésde type Rayleigh-Taylor et/ou l’initiation de perforations au coeur des nappes et films liquides. Les vidéos dessprays aqueux ainsi que l’observation au microscope des poudres métalliques nous permettent de caractériser lessprays produits. Sur l’ensemble de nos expériences nous observons que la finesse de l’atomisation s’améliore àmesure que la fréquence de rotation augmente ; ce qui constitue l’objectif prioritaire du procédé développé dans lathèse. Cependant, les surfaces texturées, certes compatibles avec les liquides classiques (aqueux ou organiques),ne le sont plus avec les contraintes induites par du métal à haute température de fusion, tel le carbure detungstène fondu objet de la thèse. En conséquence, seules les surfaces lisses sont aujourd’hui retenues et fontl’objet de développements dans le cadre de la production de poudres métalliques au sein de TechnogeniaThe aim of this work is to design a spray tool for the production of tungsten carbide powder for the companyTechnogenia, located in Saint-Jorioz (74). Thus, we have studied a new design of rotary atomizer based onatomization surface oriented at a non-zero incidence angle. Such an orientation can then allow to use moreeffectively the rotation frequency of the atomizer and the centrifugal and Coriolis forces. From this base reflection,three geometries of atomization surface were studied : smooth surfaces, surfaces with serrated structurationsalong their trailing edge and multi-perforated surfaces.The different destabilization modes of liquid flows were observed through high-speed videos of the different stagesof the single drop impact on each atomization surfaces. The atomization process can thus vary between liquid jetbreakup caused by Rayleigh-Plateau instabilities and liquid sheet breakup caused by Rayleigh-Taylor instabilitiesand/or initiating of holes in liquid films or sheets. Videos of aqueous sprays and microscopic observation of metalpowders allow us to characterize sprays. On all of our experiments, we observe that the atomisation gets better(producing finer spray), as the frequency of rotation increases. Although the textured surfaces are compatiblewith usual liquids (aqueous or organical), they can’t stand the constraints imposed by metal with a high meltingtemperature such as tungsten carbide, the object of this thesis. Therefore, only the smooth surfaces are nowthe subject of an industrial development to produce metallic powder with Technogenia company
15
Moche, Hélène. "Utilisation du carbure de tungstène-cobalt (WC-Co) comme témoin positif génotoxique nanoparticulaire et étude de la génotoxicité de candidats nanovecteurs de médicaments." Thesis, Lille 2, 2014. http://www.theses.fr/2014LIL2S024/document.
Анотація:
Les nanomatériaux sont utilisés dans de nombreux secteurs industriels, et plusieurs produits de consommation contenant des nanomatériaux sont d’ores et déjà commercialisés. Dans ce contexte d’exposition humaine croissante aux nanomatériaux, l’évaluation de leur potentiel génotoxique est d’une importance significative. Cependant, la pertinence des tests classiques de génotoxicité, développés pour des produits non nanoparticulaires, est fréquemment remise en question pour l’évaluation des nanomatériaux. Un témoin positif de référence sous forme nanoparticulaire pourrait donc constituer une avancée importante pour l’évaluation de la génotoxicité des nanomatériaux, permettant de s’assurer que les systèmes d’essais sont appropriés et/ou d’en valider de nouveaux.Dans un premier temps, nous avons étudié la possibilité d’utiliser des nanoparticules de carbure de tungstène – cobalt (WC-Co) commerciales, préalablement caractérisées sur le plan physico-chimique (distribution de taille et charge dans les milieux utilisés), comme témoin positif dans trois essais de génotoxicité in vitro. Le test de mutations géniques au locus thymidine kinase sur cellules de lymphome de souris, le test des micronoyaux étudiant les dommages chromosomiques et le test des comètes détectant les dommages primaires à l’ADN ont ainsi été réalisés, les deux derniers essais dans deux types cellulaires, la lignée de lymphome de souris L5178Y et des cultures primaires de lymphocytes humains. Nos résultats montrent que les nanoparticules de WC-Co pourraient être utilisées comme témoin positif dans ces essais de génotoxicité in vitro, selon le type cellulaire et le schéma de traitement.Nous avons ensuite étudié les mécanismes d’action impliqués dans la génotoxicité des nanoparticules de WC-Co. Le marquage des centromères dans les micronoyaux grâce à la technique d’hybridation in situ en fluorescence (FISH) montre l’implication d’évènements clastogènes et aneugènes. Ces résultats ont été confirmés par un essai d’aberrations chromosomiques sur lymphocytes humains bloqués en métaphase, avec l’observation de cassures de chromatides et de cellules polyploïdes. Par ailleurs, les mécanismes oxydants étant les plus décrits pour les nanomatériaux, nous avons étudié les lésions oxydatives à l’ADN en utilisant le test des comètes in vitro modifié avec l’enzyme de réparation de l’ADN formamidopyrimidine DNA glycosylase (FPG). Nous avons également détecté par résonance paramagnétique électronique une production de radicaux hydroxyles après mise en suspension des nanoparticules de WC-Co en présence et en absence de cellules. Dans le cadre d’études haut-débit des nanoparticules de WC-Co réalisées dans trois lignées cellulaires humaines correspondant aux principaux organes cibles pour les nanomatériaux (la lignée pulmonaire A549, la lignée hépatique Hep3B et la lignée rénale Caki-1), il a été confirmé que le stress oxydant joue un rôle important dans la toxicité des nanoparticules de WC-Co. En effet, la production d’espèces réactives de l’oxygène dans les cellules traitées avec les nanoparticules de WC-Co était corrélée avec l’observation d’une cytotoxicité et de génotoxicité, étudiée à l’aide du test de détection des foyers γH2AX.Finalement, nous avons appliqué les tests de génotoxicité les plus pertinents à l’étude de nanodiamants et de nanocapsules lipidiques, qui constituent des candidats prometteurs pour la vectorisation de principes actifs. Les tests des comètes et des micronoyaux in vitro ont ainsi été réalisés sur d’autres types cellulaires mimant des organes cibles : la lignée intestinale T84 et la lignée bronchique 16-HBE exposées à des nanodiamants de trois tailles différentes et des lymphocytes humains exposés à des nanocapsules lipidiques de 3 tailles et 3 charges différentesNanomaterials are used in many industrial sectors, and many nanomaterial-containing consumer products are already available. In this context of increasing human exposure to nanomaterials, the evaluation of their genotoxicity is of significant importance. However, the relevance of routinely used genotoxicity assays, developed for non-nanoparticular products, is often questioned for the evaluation of nanomaterials. A nanoparticulate reference positive control would therefore constitute an important step to a better testing of nanomaterials genotoxicity, ensuring that test systems are actually appropriate and/or allowing the validation of new ones.Firstly, we studied the possibility of using commercially-available tungsten carbide-cobalt (WC-Co) nanoparticles, previously characterized for physicochemical properties (size distribution and charge in used media), as positive control in three in vitro genotoxicity assays. The mouse lymphoma thymidine kinase gene mutation assay, the micronucleus assay studying chromosomal aberrations and the comet assay detecting primary DNA damage were performed. The last two assays were realized in two cell types, the mouse lymphoma cell line L5178Y and primary cultures of human lymphocytes. Our results show that WC-Co nanoparticles could be used as positive control in these in vitro genotoxicity assays, according to cell type and treatment schedule.Secondly, we investigated the mechanisms of action involved in WC-Co nanoparticles genotoxicity. Detection of centromeres in micronuclei using fluorescence in situ hybridization (FISH) show the involvement of both clastogenic and aneugenic activities. This was correlated with the results of a chromosome aberration assay on human lymphocytes blocked in metaphase, showing chromatid breaks and polyploid cells. Moreover, as oxidative mechanisms are the most described for nanomaterials, we studied oxidative DNA damage using the modified in vitro comet assay with the DNA repair enzyme formamidopyrimidine DNA glycosylase (FPG). We also detected a production of hydroxyl radicals using electron paramagnetic resonance in suspensions of WC-Co nanoparticles with and without cells. While performing high-throughput assays on WC-Co nanoparticles in three human cell lines corresponding to the main target organs for nanomaterials (A549 lung cell line, Hep3B liver cell line and Caki-1 kidney cell line) it was confirmed that oxidative stress play a significant role in the toxicity of WC-Co nanoparticles. Indeed, the production of reactive oxygen species in cells exposed to WC-Co nanoparticles was correlated to the observation of cytotoxicity and genotoxicity, studied using the detection of γH2AX foci.Finally, we carried out the most relevant genotoxicity assays to study nanodiamonds and lipid nanocapsules, which constitute promising nanovectors for drug delivery. The in vitro comet and micronucleus assays were performed on other cell types mimicking target organs: the T84 intestinal epithelial cell line and the 16-HBE bronchial epithelial cell line exposed to nanodiamonds of three different sizes, and human lymphocytes exposed to lipid nanocapsules of three different sizes and three different charges
16
Fernandes, Cristina Maria da Silva. "Sputtering on the production of tungsten carbide based composites." Doctoral thesis, Universidade de Aveiro, 2008. http://hdl.handle.net/10773/2316.
Анотація:
Doutoramento em Ciência e Engenharia de MateriaisO principal objectivo deste trabalho é estudar a viabilidade do revestimento de partículas de carboneto de tungsténio (WC), como etapa alternativa à mistura convencional de componentes. Para tal, revestiram-se pós de WC com aço inoxidável 304 (AISI), por uma técnica de deposição física em fase de vapor, denominada pulverização catódica. O outro objectivo deste trabalho incide na investigação das potencialidades das ligas de Fe/Cr/Ni como ligantes nos compósitos à base de WC. Para estudar a viabilidade da técnica de deposição como alternativa à mistura de componentes, depositaram-se quantidades variáveis de aço inoxidável (entre 1 e 10%) nas partículas de pó de WC. Alternativamente, e para efeitos de comparação, prepararam-se composições similares por mistura convencional. Os resultados da caracterização de pós revestidos foram motivadores, uma vez que indicaram que as partículas de WC possuíam revestimentos nanocristalinos bastante uniformes e que todos os elementos constituintes do aço foram depositados nas proporções existentes no alvo. Estes pós apresentam ainda boa escoabilidade e prensabilidade, uma resistência à oxidação acrescida e elevada estabilidade em soluções aquosas a pH ácido e neutro. A investigação do aço inoxidável como ligante de sinterização mostrou que os elementos constituintes do aço são eficazes na promoção da densificação dos compactos à base de WC. Os pós revestidos apresentaram uma sinterabilidade e reactividade superiores às das misturas convencionais. Atingiram-se valores superiores de densificação nos pós revestidos, sobretudo com as perdas de peso controladas através do ciclo térmico ou atmosfera de sinterização. A cinética de formação de fases, designadamente de M6C, é mais rápida nestes pós, mas a quantidade formada pode ser reduzida ou mesmo eliminada, aumentando o teor de níquel no ligante e com pequenas adições de carbono. Os resultados da caracterização mecânica de compósitos preparados com os pós revestidos evidenciaram um bom compromisso entre a tenacidade e dureza, superior ao observado em amostras preparadas convencionalmente. Por outro lado, os ligantes à base de aço inoxidável mostraram uma relação de tenacidade versus dureza superior à existente em dados publicados para compósitos de Co. A presença de M6C aumentou a dureza dos compósitos, sem degradar a sua tenacidade, enquanto que o aumento do teor de níquel reduziu substancialmente a dureza do material.
The main objective of this work is to study the feasibility of the tungsten carbide (WC) particle covering as an alternative to the conventional mixture of components. For such purpose, WC powders were coated with stainless steel 304 (AISI) by a physical vapour deposition technique, called sputtering. The other objective of this work is to study the potentiality of Fe/Cr/Ni alloys as binders in WC based composites. To study the viability of the deposition technique as an alternative to the mixture process, different amounts of stainless steel (between 1 and 10 wt.%) were deposited on WC powder particles. Alternatively, similar compositions have been prepared by conventional mixture, for comparison. The results of the characterization of coated powders are very promising, since they indicated that the WC particles have very uniform nanocrystalline coatings and that all the elements were deposited in the same proportions of the target. These powders present good flowability and prensability, an increased oxidation resistance and high stability in aqueous solutions, at acid and neutral pH values. The study of the stainless steel as a sintering binder demonstrated that the steel constituent elements are efficient in the promotion of densification of the WC based composites. Coated powders present higher reactivity and sinterability than conventional mixtures, especially when weight losses are controlled through the thermal cycle or sintering atmosphere. The kinetic of phase formation, namely M6C, is faster in these powders, but the amount formed can be reduced, or eliminated, by increasing the Ni amount in the binder and by small carbon additions. The results of the mechanical characterization of composites prepared with coated powders evidenced a good compromise between hardness and toughness, higher than the one observed in conventionally prepared composites. On the other hand, the composites with stainless steel based binders show superior values of toughness versus hardness than the ones reported in literature for composites with cobalt. The presence of M6C increases the composites hardness, without degrading its toughness, while the increase of Ni substantially reduces the hardness of the material.
17
Crause, Chantelle. "Synthesis and application of carbene complexes with heteroaromatic substituents /." Access to E-Thesis, 2004. http://upetd.up.ac.za/thesis/available/etd-05252005-145146/.
18
Henon, Albin. "Étude du frittage par résistance de matériaux composites : cas du système Ag-WC." Grenoble INPG, 1997. http://www.theses.fr/1997INPG0136.
Анотація:
Le frittage par resistance permet de densifier des materiaux dans des temps d'environ une seconde. Un comprime a vert est fritte sous contrainte entre deux electrodes ; un courant electrique traverse l'ensemble et la chaleur degagee par effet joule permet la densification du materiau. Ce travail a pour objectif de determiner le role des differents parametres du procede et d'identifier les mecanismes de densification dans le cas de melanges de poudres d'argent et de carbure de tungstene. Un interet particulier est porte a l'influence du rapport de taille entre les poudres constitutives du materiau et a la teneur en wc. L'etude de la compression a froid a consiste a caracteriser l'aptitude des melanges a se densifier a temperature ambiante et a mesurer la conductivite electrique des comprimes fabriques. Les resultats des essais sont interpretes d'une part a l'aide du modele micromecanique de turner, et d'autre part, a l'aide de modeles decrivant la conductivite de materiaux biphases et de resultats sur la percolation dans les milieux granulaires. Un dispositif experimental a ete concu pour suivre l'evolution de la temperature et du retrait du materiau en cours de frittage. Parallelement, une simulation thermoelectrique par la methode des elements finis a ete utilisee. Les experiences ont montre l'importance de la temperature atteinte en cours de frittage sur la densification, qui depend aussi de la contrainte appliquee et des caracteristiques du melange : dans certains cas, il apparait un phenomene d'extrusion du materiau accompagne d'une limite en densification pour des temperatures trop elevees. Les processus de densification possibles sont analyses et discutes. Un processus de deformation plastique des particules d'argent est propose comme principal mecanisme de la densification des melanges ag-wc frittes par resistance.
19
Bernard, D'arbigny Julien. "Synthèse, caractérisation et mise en forme d'électrodes nanocomposites platine / carbure de tungstène pour les piles à combustibles à membrane haute température." Thesis, Montpellier 2, 2012. http://www.theses.fr/2012MON20144/document.
Анотація:
Ces travaux de thèse s'inscrivent dans le contexte des efforts de recherches menés pour proposer des matériaux susceptibles de lever les verrous technologiques au développement des piles à combustible à membrane. L'un de ces enjeux est l'augmentation de la température de fonctionnement (150 - 250 °C) afin d'améliorer les cinétiques réactionnelles permettant une diminution de la quantité de catalyseur ainsi qu'une simplification de la gestion de l'eau, une réduction du système de refroidissement et une meilleure résistance à l'empoisonnement au monoxyde de carbone du platine. La motivation de cette étude a été de substituer au carbone un matériau support de catalyseur avec une plus grande résistance électrochimique.Notre choix s'est porté sur le carbure de tungstène qui, en plus d'une conductivité électronique élevée, présente une activité catalytique pour l'oxydation de l'hydrogène et la réduction de l'oxygène en milieu acide. La mise au point d'une méthode de synthèse innovante par voie hydrothermale a permis l'élaboration de microsphères de carbure de tungstène (MCT) de surface spécifique élevée (68 m2.g-1 avec 4 % de carbone résiduel) et d'architecture inusuelle. Des nanoparticules de platine de taille contrôlée ont été préparées par méthode polyol afin d'être déposées en surface des MCT. Après caractérisations électrochimiques ex-situ couplées à des analyses de surface (XPS) de ces catalyseurs Pt/WC, la mise en forme d'électrodes par enduction et transfert sur la membrane a permis la réalisation d'assemblages membrane - électrode et leurs caractérisations en pile à combustible. Des membranes polybenzimidazole dopé acide phosphorique (PBI-H3PO4) ont été utilisées pour remplacer les membranes Nafion afin d'augmenter la température de fonctionnementThe objective of this work was to develop alternative suitable materials to increase operating temperature of a Proton Exchange Membrane Fuel Cell. The increase of the operating temperature (150 - 250 °C) is attractive for cost reduction and reliability in terms of reaction kinetics, catalyst tolerance, heat rejection and water management. Our work was focused on tungsten carbide which has an high electrical conductivity and exhibits a significant catalytic activity for hydrogen oxidation and oxygen reduction in acidic environment. We have reported a novel approach to produce tungsten carbide microspheres (TCM) with an high surface area (68 m2.g-1 including only 4 % of residual carbon) and an unusual architecture. Platinum nanoparticles were prepared by polyol method and were then deposited on TCM. Physical, chemical as well as electrochemical characterisations of WC supported platinum nanoparticles Pt/WC are described and discussed in comparison with a platinum electrocatalyst on a commercial carbon support (Vulcan XC-72R). Membrane Electrode Assembly was then prepared by coating - decal process, and characterised by single cell test and compared to conventional Pt/C assembly. Phosphoric acid doped polybenzimidazole PBI(H3PO4) was used as electrolyte to replace Nafion membrane in order to carry out fuel cell testing at higher temperature
20
Zhuang, Yipping. "Mechanisms of alkane reactions over platinum and tungsten carbide catalysts." Doctoral thesis, Universite Libre de Bruxelles, 1995. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/212599.
21
Puzz, Travis Earl. "DEVELOPMENT OF A TUNGSTEN CARBIDE-NICKEL BRAZE ALLOY HARDFACE COATING." MSSTATE, 2008. http://sun.library.msstate.edu/ETD-db/theses/available/etd-11082007-141548/.
Анотація:
If an expensive part such a turbine blade or high quality tool needed to be refurbished instead of discarded, the part would have be coated in a way that would resemble or even exceed its previous surface properties. In this regard, this work studies a tungsten carbide-nickel braze alloy hardface composite prepared by liquid infiltration. A unique polymeric binder system was used to form the brazing cloth which formed the carrier for the tungsten carbide and nickel braze alloy particles. After thermal pyrolysis of the binder, the nickel braze alloy would infiltrate into a porous tungsten carbide layer becoming a hard surface coating or hardfacing. These brazing cloths were formulated to achieve a theoretical full density coating after the infiltration process. The hardface would also be brazed to its base substrate. In this study, infiltration of a porous material and brazing are mated in one continuous process. The goal of this research is the measure of hardfacing in relations to powder-polymer processing, infiltration of porous materials and brazing cycles to achieve superior hardness and braze interface quality.
22
Tran-Nguyen, Diem-Hang. "Direct production of tungsten carbide via the FFC-Cambridge process." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610280.
23
Humbert, Michael P. "Catalytic properties of platinum and tungsten carbide-based bimetallic surfaces." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 167 p, 2010. http://proquest.umi.com/pqdweb?did=1992441341&sid=11&Fmt=2&clientId=8331&RQT=309&VName=PQD.
24
Dyson, Glynn. "The low-temperature chemical vapour deposition of tungsten carbide coatings utilising the pyrolysis of tungsten hexacarbonyl." Thesis, Loughborough University, 1998. https://dspace.lboro.ac.uk/2134/33243.
Анотація:
A detailed study has been made of the atmospheric pressure chemical vapour deposition (CVD) of tungsten carbide coatings onto powder metallurgy (PM) BT42 grade high speed steel (HSS) indexable cutting tool inserts. The pyrolysis of tungsten hexacarbonyl (W(CO)6) deposition route was utilised in conjunction with a laboratory-scale hot-wall CVD reactor. After numerous coating runs, deposition conditions were established under which rudimentary tungsten carbide coatings could be deposited at 350°C. The characteristics of these coatings were determined using an established characterisation procedure. This involved the following techniques: X-ray diffraction, ball cratering, Auger electron spectroscopy (AES), optical microscopy, fractography/scanning electron microscopy (SEM), profilometry, scratch adhesion testing and micro-indentation hardness testing.
25
Sallom, Zuhair Kamil. "Evolution of particle characteristics in sintered hard metal." Thesis, University of Leeds, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.236236.
26
Vatry, Aude. "Mise en suspension par laser de poussières générées lors du fonctionnement des réacteurs de fusion." Thesis, Aix-Marseille 2, 2010. http://www.theses.fr/2010AIX22105/document.
Анотація:
Lors du fonctionnement d’une machine de fusion, les interactions plasma-parois conduisent à des processus d’érosion des matériaux et à la production de particules. Ces poussières sont principalement composées de carbone et de tungstène. Pour des raisons de sureté et afin de garantir un fonctionnement optimum du réacteur, il est important de garder en quantité raisonnable les poussières dont la taille varie entre 10 nm et 100 $m. La mise en suspension de ces poussières est une étape préliminaire à leur récupération, et le laser est une technique prometteuse pour cette application. Afin d’optimiser le nettoyage, les mécanismes physiques à l’origine de l’éjection induite par laser de ces poussières ont été identifiés. Les agrégats sont directement ablatés par le laser et les gouttelettes métalliques sont éjectées intactes par une force électrostatique induite par les photoélectrons. Nous avons également caractérisé l’éjection des particules pour choisir un système de récupération adaptéDuring tokamak operation, plasma-wall interactions lead to material erosion processand dusts production. These dusts are mainly composed by carbon and tungsten, with sizesranging from 10 nm to 100 $m. For safety reasons and to guarantee an optimum reactorfunctioning, the dusts have to be kept in reasonable quantity. The dusts mobilization is a firststep to collect them, and the laser is a promising technique for this application. To optimizethe cleaning, physical mechanisms responsible for dust ejection induced by laser have beenidentified. Some particles, such as aggregates, are directly ablated by the laser. The metaldroplets are ejected intact by an electrostatic force, induced by the photoelectrons. We alsocharacterized the particles ejection to choose an appropriate collection device
27
Zellner, Michael. "Tungsten carbides as potential alternative direct methanol fuel cell anode electrocatalysts." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 213 p, 2006. http://proquest.umi.com/pqdweb?did=1172119451&sid=5&Fmt=2&clientId=8331&RQT=309&VName=PQD.
28
Di, Maio Davide. "Characterisation of tungsten carbide-based coatings produced by chemical vapour deposition." Thesis, University of Oxford, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.418634.
29
Kausar, Rehana. "Surface studies of silicon carbide deposition on carbon and tungsten substrates." Thesis, University of Salford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314000.
30
Brunet, Pierre. "Fusion en creuset froid et pulvérisation de carbure de tungstène." Grenoble INPG, 1987. http://www.theses.fr/1987INPG0110.
31
Beadle, Kendra A. "Chemical vapor deposition of tungsten carbide films on silicon and carbon substrates." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 55 p, 2007. http://proquest.umi.com/pqdweb?did=1338918711&sid=5&Fmt=2&clientId=8331&RQT=309&VName=PQD.
32
Meliani, Hasnaa. "Fonctionnalisation d'outils de décolletage de précision par micro-structuration de surface." Thesis, Bourgogne Franche-Comté, 2020. http://www.theses.fr/2020UBFCD022.
Анотація:
L’usure des outils de coupe représente un problème majeur qui compromet la productivité et la capacité à réaliser des pièces de haute qualité. L’objectif de ces travaux de thèse est d’améliorer la durée de vie des outils coupants en carbure de tungstène, revêtus ou non, et destinés à l’usinage de l’acier inoxydable et de l’aluminium. La méthode de fonctionnalisation adoptée est la structuration de surface par laser femtoseconde.Dans un premier temps, une étude expérimentale qui traite de l’interaction entre le laser et le carbure de tungstène a été réalisée. Pour la première fois, tous les paramètres d’interaction laser/carbure de tungstène ont été déterminés, comprenant les conditions de génération des ripples et de structuration en régime d’ablation athermique.Des structures à différentes échelles dimensionnelles ont été réalisées et testées sur un tribomètre de laboratoire de type fermé. Le but étant d’étudier le comportement au frottement et à l’usure de surfaces structurées en milieu lubrifié et de les comparer à une surface de référence. La mouillabilité des surfaces structurées a également été mesurée et les énergies de surfaces correspondantes ont été déterminées.Dans la deuxième partie expérimentale, des essais d’usinage, en coupe orthogonale et en chariotage, ont été effectués avec des outils structurés. Un panel de structures a été testé afin d’identifier les structures géométriques favorisant la performance de l’outil.L’étude fait clairement apparaître le rôle de la fonctionnalisation de surface par structuration laser femtoseconde dans l’amélioration de la durée de vie des outils coupants de l’ordre de 30% dans certains casTool wear is a major issue which compromises productivity and the ability of manufacturing high quality components. The main objective of this thesis is to improve the lifetime of coated or non-coated tools made of tungsten carbide and intended for stainless steel and aluminum machining. The functionalization method used in this work is surface structuring by femtosecond laser.At first, experimental study is conducted to investigate the interaction between femtosecond laser and tungsten carbide material. For the first time, all laser-matter parameters for generating ripples or athermal ablation structures on tungsten carbide is determined.Several structures at different dimensional scales are produced and tested on a closed-type tribometer. The purpose is to study tribological performances, both friction and wear, using structured surfaces in wet environment and to compare them to a reference surface. Wettability of structured surfaces is also measured and corresponding surface energies are determined.In the second experimental part, machining tests are conducted with various structured tools in orthogonal cutting and longitudinal turning configurations. A panel of structures is tested in order to identify the best geometrical structure which improves cutting tool performance.This study clearly shows the role of surface functionalization via femtosecond laser structuring in improving the lifetime of cutting tools by 30% in some cases
33
Kamdi, Zakiah. "Characterisation, wear and corrosion of tungsten carbide based HVOF and PTAW coating." Thesis, University of Nottingham, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.659208.
Анотація:
In this study, three types of WC based coating were characterised in terms of both microstructure and performance in abrasive wear, corrosion and a combination of both. The coating types were high velocity oxy-fuel (HVOF) sprayed WC-Co and WC-CoCr and a tungsten carbide-nickel alloy weld-overlay plasma transferred arc welded (PTAW) coating . For the PTAW deposit, the nominal carbide content was varied. All coatings were characterised using x-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) analysis. The abrasive wear behaviour of the coatings was examined using micro-scale abrasion and dry sand rubber wheel (DSRW) abrasive testing. Corrosion behaviour of the coatings in sulphuric acid and alkaline drilling fluid were assessed through potentiodynamic testing. In addition, the combined effect of abrasion and corrosion was assessed through the use of micro-scale abrasion. Both HVOF coatings contained angular carbides with size of N 0.5 to 5 ~lm. The main carbide is WC in both HVOF sprayed coatings. In contrast, the carbides in the PTAW coating are a combination of WC and W2C, are spherical in shape and are much larger than those in the HVOF-sprayed coatings, being N 40 to 150 f.lm in diameter. Due to variation of carbide distribution through the coating resulting from carbide sinking during solidification in PTAW coatings, the local carbide content is considered when discussing the coating behaviour. It has been shown that the wear behaviour is strongly dependent on the relative size of the carbide and the abrasive employed in the test. The wear rate was shown to decrease with increasing local carbide content in the PTAW coatings. The precipitates in the matrix phase of the PTAW coating actively contribute to increasing the wear resistance of these materials. Both HVOF coatings have similar wear resistances to each other when abraded with either alumina or silica abrasive in both the micro-scale abrasion and DSRW test. In micro-scale abrasion, the wear rate of PTAW with the largest fraction of carbides (65 wt%) was approximately 1.5 times that of the HVOF-sprayed coatings when abraded with alumina, but was more than ten times that of the HVOF-sprayed coatings when abraded with silica. In contrast, in DSRW abrasion, the wear rate of PTAW with the largest fraction of carbides (65 wt%) was approximately twice that of the HVOF-sprayed coatings when abraded with alumina, but was only around half of that of the HVOFsprayed coatings when abraded with silica.
34
Oliveira, Mark A. (Mark Anthony) 1977. "Slurry based Three Dimensional Printing (S-3DP tm) of tungsten carbide cobalt." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/109638.
35
Deshpande, Pranav K. "Wear Resistance and Electrical Property of Infrared Processed Copper/Tungsten Carbide Composites." University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1147536455.
36
Wentzel, Eduard John. "Erosion-corrosion resistance of tungsten carbide hard metals with different binder compositions." Master's thesis, University of Cape Town, 1995. http://hdl.handle.net/11427/18212.
Анотація:
A study has been made of the slurry erosion resistance of a series of cemented tungsten carbides with different binder compositions consisting of combinations of cobalt, nickel and chromium. Testing was carried out on a specially designed laboratory rig in both tap and salt water using silica sand as an erodent. The synergistic action of erosion and corrosion on WC hard metals results in greatly enhanced wear rates compared to either erosion or corrosion processes alone. Cemented carbides with a 1 0 wt% binder were found to have a better slurry erosion resistance than the corresponding 6 wt% binder grades or the pure metal binder alloys alone. The performance of all the materials was found to be much worse in a salt water medium compared to tap water. The alloying of either pure Nickel or Cobalt binders was found to influence the fracture properties and corrosion resistance and lead to an improvement in the slurry erosion resistance of the cemented carbides. However any improvement in the corrosion resistance of the binder did not directly enhance the slurry erosion resistance of the cermet. Explanations are advanced to explain these differences in behaviour linked to chemical composition, mechanical properties of the binder phase and the dynamic nature of the slurry erosion system. Comparisons are also made between the performance of the Ni-Cr-Co based cermets and the pure alloyed metal binder grades. The acceptability of modelling the slurry erosion and corrosion resistance of cermets based on the behaviour of the binder phase materials is discussed.
37
Sabor, Said. "Contribution à l'étude quantique du carbure de tungstène neutre (WC) et ionisé (WCq+, q=1, 2)." Thesis, Paris Est, 2015. http://www.theses.fr/2015PEST1066/document.
Анотація:
Les carbures et oxydes des métaux de transition sont d'une importance capitale dans le domaine industriel voir catalytique. Le carbure de tungstène WC a été identifié comme un bon substituant des métaux nobles tel que le platine dans le domaine catalytique. Le but de ce travail de thèse est d'appliquer des méthodes de chimie quantique les plus poussées pour déterminer la structure électronique, la stabilité et la nature de liaison chimique des diatomiques WC et WC2+. Notre recherche préliminaire est motivée par les données spectroscopiques disponibles sur W, W+, W2+, WC et WC2+. La méthodologie adoptée, CASSCF/MRCI/MRCI+Q/aug-cc-pV5Z(-PP) implémentée dans le code MOLPRO, consiste à réaliser des calculs quantique tenant en compte des effets de corrélation et relativistes avec un traitement spécifique du couplage spin−orbite pour la recherche des courbes d'énergie potentielle de l'état fondamental et des états excités de plus basses énergies de WCn+ (n=0-2) tout en utilisant une base suffisamment étendue. Les résultats de ce travail sont en bon accord avec ceux disponibles dans la littérature. En outre, dans ce travail nous avons confirmé pour la première fois que le carbure diatomique dicationique WC2+ est thermodynamiquement stableMetal carbides and oxides are more interesting in catalytic and industrial domains. Tungsten carbide WC has been detected as serious substituent of platinum Pt catalytic. The ultimate goal of this thesis is theoretical studies of electronic structure, stability and the bound nature on WC, WO and its cations. Our preliminary research were motiving by the available spectroscopic data on W, W+, W2+, WC et WC2+. We used the methodology (CASSCF/MRCI/MRCI+Q/aug-cc-pV5Z(-PP)) implemented on MOLPRO package to perform quantum calculations with high accuracy taking into account the correlation and relativistic effects with a specific treatment of spin orbit coupling for some low lying excited electronic states of WCn+, (n=0, 1 et 2). Our results are shown in good agreement with those available in the literature. Furthermore, in this work for the first time we demonstrated that a carbide dication (WC2+) is thermodynamically stable
38
Ren, Qiao. "Tungsten carbides as anode electrocatalyst of direct methanol fuel cell." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 97 p, 2007. http://proquest.umi.com/pqdweb?did=1400426011&sid=12&Fmt=2&clientId=8331&RQT=309&VName=PQD.
Анотація:
Thesis (M.S.)--University of Delaware, 2007.Principal faculty advisors: Jingguang G. Chen, Dept. of Chemical Engineering; and Thomas P. Beebe, Jr., Dept. of Chemistry & Biochemistry. Includes bibliographical references.
39
Papy, Kévin. "Compréhension et maîtrise de la mise en oeuvre des cermets par procédé de fusion laser sur lit de poudre pour la réalisation de pièces anti-usure." Electronic Thesis or Diss., Ecully, Ecole centrale de Lyon, 2023. http://www.theses.fr/2023ECDL0025.
Анотація:
Technogenia® est une entreprise française, créée en 1979 et est spécialisée dans les revêtements soudés anti-usure en carbure de tungstène (WC). Dans le cadre de la thèse, Technogenia® souhaite évaluer la pertinence de réaliser des pièces anti-usure à base de carbure de tungstène par technologie de fabrication additive. L’objectif premier de l’entreprise est d’utiliser la technologie de fusion laser sur lit de poudre (L-PBF), afin de produire des pièces à base de carbure de tungstène se rapprochant des caractéristiques mécaniques des pièces en WC monobloc qui sont réalisées par procédé conventionnel. Cette thèse a pour objectif d’étudier la faisabilité de réalisation des pièces à base de carbure de tungstène et de caractériser les microstructures et les propriétés mécaniques et d’usure des pièces réalisées par fabrication additive. Les propriétés des matériaux obtenus par procédé L-PBF seront comparées aux propriétés connues de pièces conçues par procédé conventionnel. Dans un premier temps, deux poudres à base de carbure de tungstène avec des liants métalliques (carbures cémentés) sont sélectionnées afin de réaliser une optimisation paramétrique pour le procédé L-PBF. Cette étape est réalisée en analysant l’influence des principaux paramètres du procédé (puissance laser, vitesse de balayage, stratégie de balayage, écart vecteur, épaisseur de couche, …) sur les matériaux. Un plan d’expérience est défini en plusieurs étapes, comme la réalisation de cordons, de surfaces et de cubes dans le but de déterminer les principaux paramètres. Deux types de post-traitement thermique sont réalisés afin d’étudier l’influence sur les matériaux et d’éliminer certains défauts structurels. Les différences microstructurales entre les deux liants sont analysées et étudiées. De nombreux phénomènes dû au procédé laser sont observés et commentés lors de l’analyse des échantillons. Dans un deuxième temps, une étape de caractérisation mécanique et tribologique est réalisée sur les échantillons fabriqués avec succès. Différents tests mécaniques (dureté, ténacité, résilience) sont réalisés en vue de caractériser et de comparer les matériaux obtenus par L-PBF avec un matériau de référence réalisé par procédé conventionnel. Pour terminer, la résistance à l’usure des matériaux obtenus est étudiée et comparée lors de deux différents tests tribologiquesTechnogenia® is a French company, founded in 1979, specialized in hardfacing solutions based on tungsten carbide welding overlays. As part of the thesis, Technogenia® wishes to assess the suitability of using Additive Manufacturing technology to produce wear-resistant parts based on tungsten carbide. The company's primary objective is to use laser-powder bed fusion (L-PBF) technology to produce tungsten carbide-based parts that approach the mechanical characteristics of tungsten carbide-based parts made by conventional processes. The aim of this thesis is to study the feasibility of producing tungsten carbide-based parts, and to characterize the microstructures and mechanical and wear properties of parts produced by Additive Manufacturing. The properties of materials obtained using the L-PBF process will be compared with the known properties of parts produced by conventional processes. Firstly, two tungsten carbide-based powders with metal binders (cemented carbides) are selected for parametric optimization in the L-PBF process. This step is carried out by analyzing the influence of the main process parameters (laser power, scanning speed, scanning strategy, vector deviation, layer thickness, etc.) on the materials. An experimental design is defined in several steps, such as the production of beads, surfaces and cubes, in order to determine the main parameters. Two types of thermal post-treatment are carried out to study the influence on the materials and to eliminate certain structural defects. Microstructural differences between the two binders are analyzed and studied. Numerous phenomena due to the laser process are observed and commented on during sample analysis. Secondly, the samples successfully manufactured are subjected to mechanical and tribological characterization. Various mechanical tests (hardness, toughness, impact strength) are carried out to characterize and compare L-PBF materials with a reference material produced by conventional methods
40
Woolmore, Nicola J. "The failure of a tungsten carbide-cobalt cored projectile penetrating a hard target." Thesis, Cranfield University, 2010. http://dspace.lib.cranfield.ac.uk/handle/1826/4657.
Анотація:
Experimental results are presented from an investigation of the parameters of a ceramic-faced armour system that are required to induce damage in a tungsten carbide - cobalt (WC-Co) penetrator. A WC-Co material model has been successfully developed and implemented within the numerical hydrocode AUTODYN 2D. The understanding of penetration mechanisms was used to guide a parametric investigation, validating the WC-Co material failure model with experimental results. A series of experiments has been conducted firing the Russian 14.5 mm BS41 WC-Co cored projectile into various thicknesses and types of alumina (Al2O3) and silicon carbide (SiC), backed by aluminium alloy or mild steel semi-infinite witness blocks. Results demonstrated that SiC B out-performed standard monolithic armours and a selection of other armour ceramics including PS 5000 SiC and Sintox-CL. After comminution, the SiC B consisted of particles of closely interlocked grains. These appeared to provide considerable resistance to deviatoric stresses. Results suggest that it is not only increased hardness but also the nature of the fracture of the ceramic ahead of the penetrator that improves the armour’s ballistic performance at defeating WC-Co penetrators. If such superior ballistic response can be controlled and incorporated into practical armour systems, it will provide the basis for an advance in armour protective capability against WC-Co penetrators. In addition, a numerical material model derived from experimental data was developed to provide a preliminary tool to study the WC-Co failure. It was demonstrated that the numerical estimation of WC-Co behaviour using a shock Equation Of State (EOS), a piecewise linear strength model and a principle stress failure model provides a good method to estimate spall behaviour under dynamic loading in AUTODYN 2D. Successful numerical simulation of the material model used demonstrated the future potential of the technique.
41
Woolmore, N. J. "The failure of a tungsten carbide-cobalt cored projectile penetrating a hard target." Thesis, Engineering Systems Department, 2010. http://dspace.lib.cranfield.ac.uk/handle/1826/4657.
Анотація:
Experimental results are presented from an investigation of the parameters of a ceramic-faced armour system that are required to induce damage in a tungsten carbide - cobalt (WC-Co) penetrator. A WC-Co material model has been successfully developed and implemented within the numerical hydrocode AUTODYN 2D. The understanding of penetration mechanisms was used to guide a parametric investigation, validating the WC-Co material failure model with experimental results.
A series of experiments has been conducted firing the Russian 14.5 mm BS41 WC-Co cored projectile into various thicknesses and types of alumina (Al2O3) and silicon carbide (SiC), backed by aluminium alloy or mild steel semi-infinite witness blocks. Results demonstrated that SiC B out-performed standard monolithic armours and a selection of other armour ceramics including PS 5000 SiC and Sintox-CL. After comminution, the SiC B consisted of particles of closely interlocked grains. These appeared to provide considerable resistance to deviatoric stresses. Results suggest that it is not only increased hardness but also the nature of the fracture of the ceramic ahead of the penetrator that improves the armour’s ballistic performance at defeating WC-Co penetrators. If such superior ballistic response can be controlled and incorporated into practical armour systems, it will provide the basis for an advance in armour protective capability against WC-Co penetrators.
In addition, a numerical material model derived from experimental data was developed to provide a preliminary tool to study the WC-Co failure. It was demonstrated that the numerical estimation of WC-Co behaviour using a shock Equation Of State (EOS), a piecewise linear strength model and a principle stress failure model provides a good method to estimate spall behaviour under dynamic loading in AUTODYN 2D. Successful numerical simulation of the material model used demonstrated the future potential of the technique.
42
Bretzler, Patrick [Verfasser]. "Tungsten Carbide as Alternative for Precious Metal Based Hydrogenation- and Electrocatalysts / Patrick Bretzler." München : Verlag Dr. Hut, 2020. http://d-nb.info/1219476544/34.
43
Olivier, Andrew John. "Novel carbene complexes with pyrrole ligands." Diss., Pretoria : [s.n, 2001. http://upetd.up.ac.za/thesis/available/etd-02242006-125303/.
44
Marou, Alzouma Ousseini. "Durabilité tribologique de matériaux pour insert de dents de tunnelier." Thesis, Ecully, Ecole centrale de Lyon, 2015. http://www.theses.fr/2015ECDL0042.
Анотація:
La fréquence des opérations de maintenance lors de l’excavation du sol par les tunneliers est problématique pour les entreprises de travaux publics. Ces opérations de maintenance engendrent des temps morts onéreux et nécessitent l'intervention d'opérateurs dans des conditions de travail hyperbares. Une des raisons aux nombreuses interventions humaines pour la maintenance est l’endommagement des outils racleurs du sol excavé (dents) qui sont placés sur la tête du tunnelier. Ces outils sont sujets à l’usure compte tenu de l’abrasivité des différents milieux qu’ils rencontrent. Le but de cette thèse est de contribuer à augmenter d’au moins 20% la durée de vie des matériaux constitutifs de ces outils, afin de réduire les différentes opérations de maintenance qui exposent les opérateurs à des risques importants. Pour atteindre cet objectif, les investigations menées dans ce travail ont porté sur plusieurs axes. Dans un premier temps, une expertise est menée pour identifier les modes d’endommagement prédominants sur les inserts à base de carbure de tungstène placés sur les dents ; ensuite, de nouveaux matériaux avec des propriétés mécaniques et des microstructures optimisées, développés dans le cadre du projet européen NeTTUN, sont caractérisés sur des bancs d’essais représentatifs. Ces essais ont permis de bien comprendre les mécanismes d’usure des nouveaux matériaux à base de carbure de tungstène. Les résultats de ce travail peuvent ensuite donner lieu à de nouvelles orientations en matière de choix de matériaux pour renforcer les dents de tunnelierThe frequency of maintenance operations during the excavation of the ground by the tunnel boring machines (TBM) is problematic for civil engineering companies. These maintenance operations provoke expensive timeouts and they bring in excavation operators in risky hyperbaric work conditions. One of the reasons which leads to the numerous human interventions for the maintenance is the damage of drag bits located on the cutting wheel of the TBM. These drag bits undergo wear due to the abrasiveness of the various media they meet. The purpose of this thesis is to contribute to increase by 20 % at least the lifetime of the materials of the dag bits, in order to reduce the various maintenance operations which expose the operators to important risks. To achieve this goal, the investigations led in this work concerned several axes. At first, an expertise is led to identify the wear modes prevailing on the carbide inserts located on the drag bits; then, new materials with enhanced mechanical properties and optimized microstructures, developed in the framework of the European project NeTTUN, are characterized on representative lab testing devices. These tests allowed us to understand well the wear mechanisms of the newly developed grades of tungsten carbides. The results of this work can lead to new strategies for the selection of materials to reinforce the drag bits
45
Stewart, David. "Studies on the abrasive wear behaviour of HVOF WC-Co coatings." Thesis, University of Nottingham, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287076.
46
Pretorius, René. "Fischer and N-heterocyclic carbene complexes of tungsten(0)." Diss., University of Pretoria, 2012. http://hdl.handle.net/2263/31515.
Анотація:
The synthesis of novel Fischer and N-heterocyclic tungsten(0) carbene complexes was endeavoured in this study and resulted in the synthesis, isolation and characterisation of eighteen new complexes.
Sixteen novel Fischer carbene complexes were synthesised. In these complexes, both carbene ligand substituents were varied. Ethoxy as well as amino heteroatom substituents were used. Heteroaryl compounds thiophene and furan were employed as the second substituents on the carbene ligand. Complexes with combinations of these different substituents were synthesised and investigated to assess the influence the various substituents of the carbene ligand may have on the carbene complex itself. In addition, the metal ligand sphere was altered by substitution of one or two carbonyl ligands for either an amine or a phosphine ligand/s. These substitutions resulted in the formation of metal pentacarbonyl, metal tetracarbonyl as well as metal tricarbonyl systems. The complexes were successfully characterised by means of NMR and IR spectroscopy, and in selected cases X-ray diffraction and mass spectrometry.
Synthesis of N-heterocyclic carbene complexes derived from isopropyl and mesityl imidazolium chlorides was attempted. The products were obtained in crude form, but could not be isolated due to decomposition during purification. Two novel decomposition products, which point towards a unique decomposition route, were isolated.
Theoretical models of both the novel Fischer carbene complexes and the N-heterocyclic carbene complexes were calculated. This allowed for identification of infrared modes observed in experimental data. Furthermore, the HOMO and LUMO distributions and the HOMO-LUMO energy gaps were calculated, along with electrostatic potential maps. In all the Fischer carbene complexes the HOMOs were located on the metal centre and the LUMOs on the carbene ligand. In contrast, the HOMO and the LUMO were both located on the metal centre for the N-heterocyclic carbenes. The HOMO-LUMO energy gap decreased as follows:
NHC complexes > Amino Fischer carbene complexes > Ethoxy Fischer carbene complexes
Lastly, in all the complexes studied, the electrostatic potential maps indicated that the highest amount of electron density was found on the carbonyl ligands of these complexes.
Both experimental and theoretical data indicated marked differences in the various classes of compounds, suggesting that these complexes would not only have different reactivities but also be suited to different applications. Experimental studies on reactivity and applications are thus future avenues of study which are made available from these results.Dissertation (MSc)--University of Pretoria, 2012.
Chemistry
MSc
Unrestricted
47
Abioye, Taiwo E. "Laser deposition of Inconel 625/tungsten carbide composite coatings by powder and wire feedstock." Thesis, University of Nottingham, 2014. http://eprints.nottingham.ac.uk/14253/.
Анотація:
There is an increasing global demand to extend the life span of down-hole drilling tools in order to improve operation effectiveness and efficiency of oil and gas production. Laser cladding of tungsten carbide/Ni-based alloy metal matrix composite (MMC) coatings is currently being utilised for this purpose. However, the effect of tungsten carbide dissolution on the corrosion performance of the MMC coatings has not been completely understood. In this work, a study was carried out in which laser cladding of a stainless steel substrate using (i) Inconel 625 wire and (ii) tungsten carbide powder (Spherotene)/Inconel 625 wire was undertaken. This work was performed using a fibre laser system and has examined the process characteristics, the microstructure and the corrosion performance of the clad layers. Process characteristics studies were carried out by visual observation of the cladding process within a process window (laser power: 1-1.8 kW, traverse speed: 100-300 mm min-1, wire feed rate: 400-1000 mm min-1, powder feed rate: 25 g min-1). The microstructures were investigated using a combination of optical microscopy, scanning electron microscopy (with energy dispersive X-ray analysis) and X-ray diffraction. The volume fraction of tungsten carbide retained in the composite coatings was determined using image processing software. Corrosion performance was assessed using electrochemical corrosion testing in de-aerated 3.5 wt.% NaCl solution. Well bonded, minimally diluted, pore- and crack-free Inconel 625 wire and Spherotene (WC/W2C) powder/Inconel 625 wire composite coatings were successfully deposited. Cladding process characteristics were categorised into wire dripping, smooth wire deposition and wire stubbing within the range of parameters used in this work. Process maps which predict the characteristic of Inconel 625 wire and Spherotene (WC/W2C)/Inconel 625 wire fibre laser cladding at varying cladding conditions within the process window were developed. The volume fraction of tungsten carbide (WC/W2C) retained in the composite coatings was found to decrease with increasing laser power, traverse speed and wire feed rate. Tungsten carbide dissolution was found to result in the precipitation of intermetallic compounds including M6C and M23C6 in the γ-Ni matrix, which is rich in W and C. The increase in tungsten carbide dissolution was also found to increase the propensity for corrosion in the MMC coatings compared to the Inconel 625 wire coatings. As a result, the corrosion performance of the tungsten carbide/Ni based alloy MMC coatings can be improved by reducing the level of tungsten carbide dissolution through process control.
48
Cook, Grant O. III. "Joining Polycrystalline Cubic Boron Nitride and Tungsten Carbide by Partial Transient Liquid Phase Bonding." BYU ScholarsArchive, 2010. https://scholarsarchive.byu.edu/etd/2366.
Анотація:
Friction stir welding (FSW) of steel is often performed with an insert made of polycrystalline cubic boron nitride (PCBN). Specifically, MS80 is a grade of PCBN made by Smith MegaDiamond that has been optimized for the FSW process. The PCBN insert is attached to a tungsten carbide (WC) shank by a compression fitting. However, FSW tools manufactured by this method inevitably fail by fracture in the PCBN. Permanently bonding PCBN to WC would likely solve the fracturing problem and increase the life of PCBN FSW tools to be economically viable. Partial transient liquid phase (PTLP) bonding, a process used to join ceramics with thin metallic interlayers, was proposed as a method to permanently bond PCBN to WC. PTLP bonding is often performed using three layers of pure elements. On heating, the two thin outer interlayers melt and bond to the ceramics. Concurrently, these liquid layers diffuse into the thicker refractory core until solidification has occurred isothermally. A procedure was developed to reduce the number of possible three-layer PTLP bonding setups to a small set of ideal setups using logical filters. Steps in this filtering method include a database of all existing binary systems, sessile drop testing of 20 elements, and a routine that calculates maximum interlayer thicknesses. Results of sessile drop testing showed that the PCBN grade required for this research could only be bonded with an alloy of Ti, Cu, Mg, and Sb. Two PTLP bond setups were tested using this special coating on the PCBN, but a successful bond could not be achieved. However, a PTLP bond of WC to WC was successful and proved the usefulness of the filtering procedure for determining PTLP bond setups. This filtering procedure is then set forth in generalized terms that can be used to PTLP bond any material. Also, recommendations for future research to bond this grade of PCBN, or some other grade, to WC are presented.
49
Trueman, Anthony Roger. "Characterization and corrosion studies of high carbon tool steel/tungsten carbide metal matrix composites." Thesis, Queensland University of Technology, 1999.
50
Archer, M., RI McCrindle, and ER Rohwer. "Analysis of cobalt, tantalum, titanium, vanadium and chromium in tungsten carbide by inductively coupled plasma-optical emission spectrometry." The Royal Society of Chemistry, 2003. http://encore.tut.ac.za/iii/cpro/DigitalItemViewPage.external?sp=1001953.
Анотація:
Summary
Inductively coupled plasma optical emission spectroscopy (ICP-OES) was used to measure the concentrations
of cobalt, tantalum, titanium, vanadium and chromium in solutions of tungsten carbide. The main advantage
of the method described here lies in the speed, convenience and effectiveness of the dissolution procedure.
Aliquots of powdered tungsten carbide were dissolved in a solution of 5% aqua regia in 30% hydrogen
peroxide. Complete dissolution was usually achieved within 10 min. The accuracy of the method was assessed
by the analysis of certified reference materials, secondary reference materials and matrix spiking. The method
was successfully applied to commercial type samples with differing compositions. Slightly more emphasis was
placed on the measurement of vanadium, since no information on the measurement of this element in solutions
of tungsten carbide, by ICP-OES, has been published. Investigation of the interference effects of the elements in
the sample matrix on each other was essential for accurate results comparable to other published analytical
methods.