Auswahl der wissenschaftlichen Literatur zum Thema „Cobalt-based alloy“

A magnetorheological material containing iron alloy particles demonstrates magnetorheological strength dependent upon the elements of the alloy and relative concentration of the alloy elements. Selected iron/cobalt alloys demonstrate improved yield strength over traditional carbonyl iron based MR materials when the iron-cobalt alloy has an iron-cobalt ratio ranging from about 30:70 to 95:5. The iron-nickel alloys which have an iron-nickel ratio ranging from about 90:10 to 99:1 maintains superior strength over iron-nickel alloys outside that range.

Cobalt-based alloy materials, widely used for laser cladding, are difficult to process. To address this problem, and based on the analysis of the physicochemical properties of cobalt and its compounds, a method for removing cobalt-based alloy materials under photocatalytic conditions was proposed under the effect of ultraviolet photocatalysis and chemical corrosion. In this study, a material removal model under photocatalytic conditions was established, and the reaction principle of cobalt-based alloys under ultraviolet photocatalysis and chemical corrosion conditions was described. We designed a corrosion solution configuration test and established a cobalt-based alloy processing test based on a pneumatic wheel test platform. The processing test proved that the combination of ultraviolet (UV) photocatalysis and Basic Yellow 40 + TiO2 chemical corrosion pretreatment can significantly increase the mechanical material removal rate of cobalt-based alloy materials and effectively reduce surface roughness. At the same time, processing efficiency can be increased over 40%. This showed that the new method is capable of performing well in the field of mold cobalt-based alloy coating processing in the future.

Laser cladding, as an effective method of metal surface modification, is to fuse an alloy coating of enhanced mechanical and chemical properties on the surface of a substrate. Therefore, laser cladding has been attracting continuous and extensive research for years. In this paper, the research progress in laser clad cobalt-based alloys is summarized. The preparing processes, microstructures, properties and influence factors of laser clad cobalt-based alloys coatings and their ceramic particles strengthened composites coatings are analyzed systematically. And the existing problems, some solving measures, the development tendencies and industral uses are presented.

This article presents the results of an X-ray spectral microanalysis of cobalt-chromium alloys based on particles of the of the tungsten nickel iron alloy dispersed by electric erosion, obtained in alcohol. It has been experimentally proved that a part of oxygen is present in the cobalt-chromium alloy of particles of the cobalt-chromium-molybdenum alloy dispersed by electric erosion. All other elements are distributed relatively evenly over the volume of particles. It is shown that Co, Cr and Mo are the main elements of the (CoCrMo) alloy dispersed by electric erosion.

The effectiveness of complex orthopedic treatment of partial loss of teeth in inflammatory periodontal disease is a very serious problem. Of particular importance is the choice of materials for removable dentures, as it can contribute to the adsorption of periodontal pathogens. This paper studied the tolerance of dental alloys (cobalt alloy ‘Gialloy PA Co/Cr’, gold-based ‘CASDEN-B’ cobalt alloy ‘Gialloy PA Co/Cr’ with zircon gold plated ‘Kamadan’) to parodontoceras microflora (Staphylococcus aureus, Escherichia coli, Streptococcus pyogenes, Pseudomonasa eroginosa, Candida albicans). It is established that all the studied samples of dental alloys are subject to colonization by periodontal microorganisms in the oral cavity, while the degree of colonization depends on the chemical composition of the alloys and the type of bacterial cultures. Cobalt-chromium alloy with gold-zirconium coating, which is recommended as a structural material in periodontal pathology, has the lowest tolerance indicators of dental structural alloys to periodontal microflora. Based on the analysis of clinical studies, we have established a high efficiency of the use of prostheses made of cobalt-chromium alloy with gold-zirconium coating in the treatment of chronic generalized periodontitis of moderate severity against the background of tooth loss in comparison with the traditional alloy.

The research presents the atomic structure investigation of amorphous rapidly quenched Co58Ni10Fe5Si11B16 at.% alloys. The alloys were quenched with linear velocity of cooper wheel surface from 22 to 38 m/s. We found a nonlinear dependence of local atomic ordering from linear velocity of cooling wheel. The average lateral density of ordered atomic clusters of 5 nm size changes from 4% to 8%. The amorphous alloy with metastable disordered structure with lower level of free energy is more stable against the external conditions. This approach can be used to determine the best technological parameters for preparing amorphous metallic alloy with metastable structure.

The isothermal oxidation behavior and thermal stability of a cobalt base alloy was investigated up to a period of 312 hr in air from 1000 to 1200°C. A comparison of oxidation behavior of this alloy with a conventional nickel-base superalloy (Inconel 713C) has been conducted in detail. This experimental alloy oxidizes by forming layers of Al2O3, Cr2O3, TiO2, CoO and traces of SiO2 with WO2 oxides on the surface of the specimen in contact with air. Scanning electron microscopy (SEM) was used to study the microstructure, morphology and compositions of oxides formed after the exposure. Thermal stability of the alloy after extended periods of exposures to air at 1000, 1100 and 1200°C was studied using transmission electron microscopy (TEM).

The diploma thesis deals with the topic of machinability of materials. The theoretical part describes the aspects according to which machinability can be evaluated. The material side of the thesis is focused on various types of difficult-to-machine materials. The cobalt alloy UmCo50 belongs to the group of difficult-to-machine materials and it is the subject of the experimental part. UmCo50 is an alloy for high temperature use. The primary aim of the thesis was to monitor the wear of the selected cutting tool when turning this alloy. Other aspects of the selected machining process were also monitored, such as force effects or the quality of the machined surface. Despite the fact that machinability of tested materials cannot be expressed in terms of the absolute value of a quantity, it is necessary to compare the various aspects of the machining processes by reference materials. However, certain conditions of this comparison must be met. Based on this, a comparison of tested and reference material was performed.

Les maladies cardio-vasculaires sont la principale cause de mortalité dans le monde. Parmi celles-ci, et une des plus importantes, se trouve l'athérosclérose. Cette maladie se traduit par la formation d'une plaque sur les parois artérielles réduisant alors le diamètre luminal. La plaque d'athérome entrave la circulation du sang et peut se compliquer par la formation d'un thrombus artérielle pouvant provoquer un infarctus du myocarde. Une intervention capable de rétablir le flux (recanalisation) est alors nécessaire. Dans le cas des artères coronaires, l'intervention coronaire est percutanée (ICP) et consiste à amener et déployer jusqu'au site malade, une endoprothèse, appelé aussi stent. Un stent est un petit treillis métallique tubulaire qui permet de rouvrir la lumière de l'artère et de rétablir la circulation sanguine. Il sert aussi de support à l'artère malade pour empêcher son affaissement. Cependant, après implantation, certaines complications sont induites, telle que la resténose intra-stent (ISR) qui se caractérise par la réduction de la lumière de l'artère, reconduisant les problèmes créés par la plaque d'athérome. Ce phénomène est essentiellement dû à une prolifération excessive des cellules musculaires lisses, et qui résulte d'une lésion de l'endothélium lors de l'implantation. Afin de limiter cette complication, la première approche a été de changer les matériaux utilisés pour ces endoprothèses. Les principaux alliages utilisés pour fabriquer des stents sont l'acier inoxydable, les alliages de nitinol et ceux de chrome cobalt, plus particulièrement le L605. Ce dernier, dû à ses propriétés mécaniques, permet la fabrication de dispositifs plus minces, donc moins de métaux présents dans le corps humain, et a démontré induire moins de complications cliniques. Néanmoins, malgré la diminution des complications par rapport aux autres alliages, les endoprothèses nues en L605 ne s'intègrent que peu ou pas du tout dans le tissu artériel de l'hôte. Pour répondre aux exigences biologiques et cliniques, l'idéal serait d'avoir un dispositif qui favoriserait le recouvrement du dispositif par l'endothélium, ou « endothélialisation » et qui aurait un faible potentiel thrombotique et inflammatoire. L'approche couramment utilisée pour répondre à ces critères est de recourir à des dispositifs qui libèrent des médicaments anti-inflammatoires. Pour ce faire, il faut recouvrir les dispositifs métalliques avec des revêtements à base de polymères, en tant que couche intermédiaire, fonctionnalisée ensuite par des molécules bioactives. Toutefois, les dépôts de ces couches polymériques impliquent l'utilisation de chimie en solution incluant des solvants organiques. En outre, ces dernières démontrent avoir une faible adhésion au substrat métallique, dû au procédé utilisé, mais aussi un manque de cohésion. Lors de la procédure d'implantation, les stents subissent une déformation plastique, comme ces revêtements manquent de résistance, ils ont tendance à fissurer ou délaminer. Ce projet de recherche s'insère donc dans cette problématique générale, et propose une nouvelle approche qui permettrait d'éviter ce revêtement polymérique, tout en apportant les propriétés biologiques recherchées. Pour ce faire, la modification de surface proposée implique la fonctionnalisation directe des surfaces métalliques par un procédé plasma. Ce procédé permet de ne pas modifier les propriétés de cœur du matériau, et de créer des groupes fonctionnels en surface, ici des groupes amine réactifs (NH₂), qui servent de points d'ancrage pour le greffage ultérieur des molécules bioactives d'intérêt. En résumé, ce procédé original peut être divisé en 3 parties principales : a) préparation de la surface, b) fonctionnalisation par plasma et c) greffage de molécules bioactives. Tout au long de ce projet de recherche, l'optimisation de chaque partie a été réalisée en vue d'obtenir les propriétés adéquates et nécessaires pour l'application cardiovasculaire visée. Concernant la partie a), c'est-à-dire la préparation de la surface, les traitements suivants ont été testés : électropolissage, traitements thermiques et implantation ionique par immersion dans un plasma. Ces modifications ont été optimisées en vue d'obtenir une couche d'oxyde stable sous déformation présentant la meilleure résistance possible à la corrosion, tout en démontrant la plus haute efficacité d'amination directe par plasma pour la partie b). Enfin, en ce qui concerne le bloc c), le greffage de molécule bioactive, deux bras de liaison différents ont été étudiés pour évaluer leur impact sur la conformation et la performance biologique. Cette étude a été effectuée avec un peptide bioactif dérivé de la molécule d'adhésion des cellules endothéliales et des plaquettes (PECAM-1 ou CD31), en raison de ses propriétés anti-inflammatoire, anti-thrombotique et pro-endothélialisation. Les 2 bras d'ancrage testés sont un à chaine courte, l'anhydride glutarique (GA), contenant seulement 5 atomes de carbone, et un à longue chaine (600 atomes), le polyéthylène glycol (PEG) choisi aussi pour ses propriétés anti-adhérentes. Tout d'abord, cette stratégie a été développée sur des échantillons plats, qui facilitaient grandement les analyses de surface, telles que XPS et ToF-SIMS, et donc les processus d'optimisation de chaque étape, comme la résistance à la déformation, corrosion et l'analyse des propriétés biologiques. Ceci a permis de démontrer que le prétraitement de surface optimal pour les substrats L605 était l'électropolissage, agissant sur sa couche d'oxyde passive pour une efficacité maximale lors de l'étape d'amination. Le bras de liaison qui a démontré le plus grand potentiel pour immobiliser le peptide d'intérêt est le PEG, avec une augmentation significative de la migration et viabilité des cellules endothéliales, par rapport au substrat métallique nu. De plus, le greffage du peptide sur le PEG ajoutait des propriétés anti-thrombotique et anti-inflammatoire par rapport aux échantillons électropolis. Ce procédé a été ensuite adapté à des stents, dont la configuration 3D est très complexe. Après optimisation, les stents pegylées + peptides biomimétiques (Plasma-P8RI) ont été testés in vivo par implantation dans les coronaires de porc porcin pendant 7 jours et 28 jours et leur potentiel de ré-endothélialisation et anti-resténotique ont été évalués. Il a été constaté que la stratégie proposée dans ce projet de recherche favorisait la ré-endothélialisation après 7 jours par rapport au DES (Drug Eluting Stent) commercial, et limitait l'adhérence des leucocytes et des plaquettes lorsque comparé au BMS (Bare Metal Stent). Après 28 jours d'implantation le diamètre luminal des artères n'était pas réduit sur le stent Plasma-P8RI, ce qui signifie que ces stents modifiés ne présentaient pas de risque de resténose, contrairement aux BMS. Ce projet de recherche a permis de développer et de valider une stratégie prometteuse consistant à immobiliser directement des molécules bioactives sur des dispositifs cardiovasculaires en L605, alliage de chrome-cobalt. A notre connaissance, cette approche n'a jamais été rapportée dans la littérature à notre connaissance. Cette stratégie originale, dépourvue des limites associées à l'usage des polymères et basée sur un procédé plasma, présente des avantages évidents et ouvre la voie vers le développement de dispositifs cardiovasculaires innovants.
Cardiovascular diseases represent the leading cause of death in the world. Among them is atherosclerosis that characterizes by the formation of a plaque on the arterial walls that narrows the lumen diameter. This atherosclerotic plaque disrupts the blood flow and can be complicated by thrombosis which can ultimately lead to myocardial infarction. Efficient revascularization is mandatory to treat this disease and a percutaneous coronary intervention (PCI) is performed complemented with the deployment of a stent. Stents are tiny wire mesh that reopens the artery, re-establishing the blood flow whilst supporting the artery avoiding its collapse. Nevertheless, complications after stent implantation exist and in-stent restenosis (ISR) is one of the major concerns. This complication is characterized by the reduction of the lumen diameter, similar to an atherosclerotic plaque, and it is associated to the wound caused on the endothelium by the stent implantation followed by the over-proliferation of smooth muscle cells. One of the first strategies to decrease ISR involved the manufacture of stents using different alloys such as stainless steel, nitinol and cobalt chromium alloys (L605). The latest alloy, L605, has generated significant interest because it allows the fabrication of thinner devices, which have decreased post-implantation clinical complications. Nonetheless, despite the decrease in ISR, when compared to other alloys, the integration of L605 bare metal stents in the host tissue is minimal or inexistent. Thus, enhanced biological properties, such as endothelialisation, low thrombosis activity and anti-inflammatory behaviour represent mandatory requirements for clinical applications. To confer these properties onto metallic devices, polymeric-based coatings, as an intermediate layer to further functionalize with bioactive molecules, are often deposited. Nonetheless, major techniques to deposit these polymeric coatings involve the use of wet-chemistry and do not ensure total resistance during the stent implantation procedure due to lack of cohesion and delamination of the polymeric layer. Thus, a novel approach that foregoes this previously mandatory coating step was developed in this research project. This novel approach involves the use of plasma-based techniques to create functional groups (reactive amine groups, -NH₂), directly onto the metallic surface without modifying the bulk properties, that can be used as anchor points for the further grafting of bioactive molecules of interest. Briefly, this novel approach can be divided in 3 blocks: a) Surface preparation, b) plasma functionalization and c) bioactive molecule grafting. Throughout this research project the optimization of these main blocks was performed aiming for the desired cardiovascular application. Concerning block a), surface preparation, electropolishing, thermal treatments and plasma immersion ion implantations were performed to obtain an oxide layer deformation and corrosion resistant whilst demonstrating the highest direct plasma amination efficiency, for block b). Finally, as regards block c), bioactive molecule grafting, two different linking arms were studied to assess their impact on conformation, and the biological performance of a bioactive peptide derived from the platelet endothelial cell adhesion molecule (PECAM-1 or CD31) due to its pro-endothelialization, anti-inflammatory and anti-thrombotic potential: Glutaric anhydride (GA), as a short chain spacer of 5 carbons, and polyethylene glycol (PEG), as a long chain spacer with antifouling properties. Initially, this strategy was developed on flat samples where using a combination of high-resolution surface characterizations techniques, such as XPS and ToF-SIMS, and corrosion, deformation and biological tests it was confirmed that the optimal surface pre-treatment for L605 was electropolishing, due to its passive oxide layer and that it further allowed to obtain the highest amination efficiency. Furthermore, the best linking arm to immobilize the peptide was PEG, which demonstrated a significantly increase on endothelial cell viability with a faster migration, when compared to the bare metallic substrate. Moreover, peptides immobilized by PEG demonstrated that endothelial cells attached to the surface presented an anti-thrombotic and anti-inflammatory phenotype, when compared to electropolished samples. Thus, this biomimetic surface was selected for an in vivo trial in porcine model to evaluate its potential re-endothelialization and anti-restenotic activity. It was found that by directly attaching a CD31 agonist onto the bare metal stent by this strategy improved re-endothelialization after 7 days when compared to commercial DES, with further, low adhesion of leukocytes and platelets when compared to BMS. Moreover, after 28 days of implantation, Plasma-P8RI did not present a significant decrease on the lumen diameter, which was not the case for BMS that presented in-stent restenosis after this period. Overall, this research project allowed the development and validation of a promising strategy to directly immobilize bioactive molecules onto L605 cobalt chromium cardiovascular devices, providing clear advantages of medical devices currently on the market. Furthermore, to the best of our knowledge, such plasma-based multi-step strategy has never been previously reported in literature.

The aims of this study are: to prove the possibility that cobalt-based alloys can be produced with the addition of several alloying elements, such as chromium, molybdenum, nickel and tungsten; and to gain an understanding of the mechanism of electro-deoxidation. This study reports, for the first time, the successful production of metallic Co, Co-30Cr, Co-30Cr-7Mo, Co-27Cr-10Ni and Co-27Cr-12.5W. Preparatory work was conducted to construct some of the electrochemical equipment used and to determine reduction conditions. Mechanistic studies were performed through the use of constant voltage, and constant potential, chronoamperometry; as well as cyclic voltammetry. Fully and partially reduced samples were analysed using a variety of techniques, which included XRD, SEM, Electra oxygen analysis, and optical microscopy. This work also introduces constant current chronopotentiometry as a new technique to FFC investigations. This technique is used, for the first time, to determine mechanistic information about the electro-deoxidation of single and multiple oxide precursors. Electro-deoxidations are completed at a variety of constant currents and the resulting data is used to construct a novel type of Tafel plot.

Dans le domaine du forgeage à chaud de pièces aéronautiques, les matrices en acier sont couramment rechargées, sur quelques millimètres d’épaisseur, par un alliage base cobalt (Stellite 21) déposé par procédé de soudage à l’arc (MIG). Dans le cadre de ce travail de thèse, ce rechargement « classique» est comparé à des rechargements Stellite 21 et Stellite 6 déposés par deux procédés émergents dans ce domaine, le PTA et le LASER. L’objectif est d’apporter des éléments de compréhension aux mécanismes d’endommagement de surface, notamment par écoulement plastique, de ces différents rechargements afin de dégager des voies d’amélioration pour augmenter la durée de vie des matrices. Pour cela, des essais tribologiques (semi-industriels et laboratoire) ont été mis en œuvre pour créer des endommagements de surface comparables à ceux observés sur matrices industrielles. Associées à ces essais, des investigations microstructurales, structurales et mécaniques multi-échelles ont été réalisées (traction, flexion, microdureté, MO, MEB, MEB-STEM, DRX, EBSD). Selon les couples « nuance/procédé » de rechargement, des mécanismes de déformation plastique par glissement des dislocations parfaites et par transformation de phase CFC en HC ont été identifiés. L’activation de ce dernier a pu être reliée à la température de transformation allotropique CFC/HC du cobalt. Cette température dépend à la fois (i) des éléments d’addition, variant en fonction de la nuance déposée (Cr, C,...), (ii) de la dilution (variation de la teneur en Fe) liée aux paramètres de soudage et (iii) du nombre de couches déposées. De plus, une influence significative de la transformation de phase sur l’évolution du coefficient de frottement a été mise en évidence. En effet, dans le cas où la transformation de phase n’est pas observée, le coefficient de frottement est stable durant l'essai alors qu'une chute de la courbe de coefficient de frottement a été reliée avec la transformation de phase CFC en HC. Parallèlement, l'écoulement plastique des dendrites est observé en extrême surface sur quelques dizaines de micromètre d'épaisseur dans la direction de glissement. Cet écoulement est associé à une forte texturation morphologique et cristallographique de la phase identifiée (CFC ou HC), avec une orientation des plans de plus grande densité atomique parallèlement à la surface de glissement. Les résultats montrent également que sous sollicitations tribologiques, un important durcissement est observé en surface (jusqu'à 90%) et une corrélation a pu être établie entre l'augmentation de la microdureté et le taux de déformation plastique
In the field of hot forging of aeronautical parts, the steel dies are commonly hardfaced, on few millimeters thick, by a cobalt-based alloy (Stellite 21) deposited by arc welding (MIG). As part of this thesis, this "classic" hardfacing is compared to Stellite 21 and Stellite 6 hardfacings deposited by two emerging processes in this area, the PTA and the LASER one. The objective is to assess surface damage mechanisms, especially induced by plastic strain, of these various hardfacings. Tribological tests (laboratory and semi-industrial) were used to create surface damage comparable to those observed in industrial dies. Associated with these tests, multiscale microstructural, structural and mechanical investigations have been performed (tensile, bending, microhardness, OM, SEM, STEM, XRD, EBSD). According to the « material/process » couple, plastic strain mechanisms by perfect dislocation glide and by FCC to HCP phase transformation have been identified. The activation of the latter has been connected to the temperature of the allotropic phase transformation (FCC/HCP) in cobalt. This temperature depends on (i) the alloying elements, varying according to the deposited grade (Cr, C, ...), (ii) the dilution (Fe content evolution) connected to the welding parameters and (iii) the number of deposited layer. Moreover, a significant influence of the phase transformation on the evolution of the friction coefficient has been evidenced. Indeed, if the phase transformation is not observed, the friction coefficient is stable during the test, while a drop of the friction coefficient curve is connected with the FCC to HCP phase transformation. Moreover, the plastic flow of dendrites is observed at the extreme surface, on a few tens of micrometres in thickness, in the direction of sliding. It is associated with a high morphologic and crystallographic texturing of the identified phase (FCC or HCP), with the highest atomic density planes mostly oriented parallel to the sliding surface. The results also show that, under tribological laodings, a significant hardening is observed on the surface (up to 90%) and a correlation has been established between the increase in the microhardness and the plastic deformation ratio

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
A indústria busca uma melhor otimização e performance de seus equipamentos, há muito notou-se a importância da contenção do desgaste para o aumento de vida útil dos componentes de máquinas. Em condições operacionais onde há o desgaste por abrasão, comumente faz-se o endurecimento da camada superficial ou a aplicação de uma liga mais nobre e de dureza mais elevada, visando conter este desgaste. A técnica também é chamada de revestimento. Entender melhor os parâmetros que influenciam nos resultados da aplicação destes revestimentos torna-se importante possibilitando menores perdas e uma maior economia, pois busca-se como alvo trabalhar com a melhor performance do revestimento. Objetivou-se neste trabalho o estudo das ligas a base de Cobalto que são aplicadas cada vez mais rotineiramente nas indústrias petroquímicas, onde os componentes e órgãos de máquinas estão expostos a condições severas de desgaste por abrasão e corrosão além da severidade dos trabalhos a altas temperaturas e pressão. Relacionando o desgaste, as ligas a base de Cobalto possuem uma posição destacada e a liga é conhecida comercialmente como “Stellite 6”. Em alguns trabalhos é chamada também de liga coringa por sua versatilidade e destaque em especial. Neste trabalho procurou-se variar as velocidades de resfriamento em cinco patamares, analisou-se a influência da diluição na micro-dureza e os efeitos da variação da velocidade de resfriamento no mecanismo de endurecimento. A aplicação do revestimento ocorreu em três camadas através do processo TIG. Verificamos ainda a interferência da diluição na dureza em cada camada de revestimento. A terceira e última camada foi a que apresentou maior dureza devido à menor diluição com o metal base principalmente no corpo de prova que possuía à menor velocidade de resfriamento devido ao tempo para a formação de precipitados e carbonetos na liga metálica.
The industry searchs a better optimization and performance of their equipment, long noted the importance of containment to increase the wear life of components of machines. In operating conditions where there is wear by abrasion, usually it is the hardening of the surface layer or the application of a more noble alloy and high hardness, wear it to contain. The technique also called hardfacing. Better understand the parameters that influence the results of applying these coatings becomes important because it enables lower losses and greater economy as it seeks to target work with the best performance of the coating. The objective of this research is complements the study of cobalt-based alloys that are applied more routinely in petrochemical industries, where the component units and machines are exposed to severe conditions of wear by abrasion and corrosion than the severity of the work at high temperatures and pressure. Relating the wear, the cobalt-based alloys have a prominent position and the league is known commercially as “Stellite 6”. Some work is also called the league wildcard for its versatility and highlight in particular. In this work we have tried to vary the speed of cooling in five steps, looked up the influence of dilution on micro hardness and the effects of variation in the rate of cooling in the hardening mechanism. The application of the coating occurred in three layers using the TIG process. We note also the interference of dilution in hardness in each layer of coating. The third and final layer was the one with higher hardness due to less dilution with the base metal mainly in the body of evidence that had the lowest rate of cooling due to the time for the formation of precipitates and carbides in the metal.

Due to the tough working environments, wear damage to nuclear reactor components is frequent. Usually, nuclear elements run at 573 k to 873 k. The feed water controller valves, used for the thundering of coolant flow, wear out faster among the reactor components. Austenitic stainless steels, using different methods for hardfacing, improve wear resistance to the cobalt and nickel alloys. Nickel based hardfacing is more resistant to wear than cobalt based hardfacing at high temperatures thanks to the solid oxide layers. Austenitic stainless-steel substrates generally favor nickel-based hardfaced (Ni–Cr-Si–B-C) over cobalt-driven hardfacing because this reduces radiation-induced nuclear activity. A well-known surface method for depositing nickel hardfacing, minimal dilution, alloys is the Plasma Transfer Arc (PTAs) weld technique. In this study the Ni-based alloy is hardfaced over a 316 L (N) ASS substratum with PTA hardfacing, for a dense of approximately 4–4.5 mm. The substrates and deposits were tested at different temperatures with a pin on disc wear (room temperature, 150 and 250°C).When grinding with 1000 grain SiC abrasive paper, the wear test samples were polished to the roughness value (Ra) of less than 0,25 m.The deposit showed a variety of wear mechanisms regarding the test temperature. Using friction and wear values and wear analysis, the wear mechanisms were determined. There was a considerable wear loss at room temperature (RT).At 423 K operating heat, mild ploughing at short sliding distances and tribo-oxidation were carried out with increasing sliding time.The primary wear mechanism was adherence at the time of operating temperature at 623 K, but as the sliding distance widened, tribo-oxidation improved. In combination with a working hardened substrate, the formation of an oxide layer could significantly reduce the wear loss of nickel-based alloys.

The geometry of clusters with ligands and a polyhedral frame is considered by the methods of studying the geometry of higher-dimensional polytopes, developed in the author's monograph. It is shown that these methods allow us to establish important details of cluster geometry, which elude analysis based on the representations of three-dimensional geometry. It is established that the well-known Kuban cluster is a 4-cross-polytope, which allows different variants of the Kuban cluster. A cluster of gold with a tetrahedral backbone is a 5-cross-polytope. The cluster tetra anion of cobalt is a polytope of dimension 5 of a new type. Different types of ligands limit the cobalt skeleton from above and below.

Abstract Protective coatings adapted for titanium alloys which come into frictional contact with one another are described. Among the many coatings investigated, the best ones are cobalt based. The coatings are sprayed only on one of the rubbing surfaces. During rubbing, a small part of the coating transfers to the unprotected titanium alloy surface. The rubbing pair is thus essentially composed of two cobalt alloy-based surfaces. This leads to low coefficient of friction and little or no damage to the rubbing surfaces. The coatings find particular application in the protection from adhesive and fretting wear, galling and seizure of gas turbine and jet engine parts or the like made from titanium alloys.

Some cobalt based coatings have excellent antifretting properties when rubbed against titanium alloy hardware. The coatings are presently used in the gas turbine industry for specific antifretting applications. Their superior performance compared to the current art CuNiIn coatings has been demonstrated. This paper discusses the influence of coating structure on its mechanical properties and antifretting performance. The coating structure can be greatly modified by changing the coating application method (HVOF or plasma spraying). HVOF (High Velocity Oxygen-Fuel) and plasma spray equipment together with TriplexPro™ 200 gun configured to spray HVOF and plasma type coatings were used. The resulting coating properties can be tailored to specific application requirements encountered in aircraft engines and other industrial applications.

Abstract Austenitic stainless steel was cladded with Cobalt-based alloy by means of Tungsten inert gas (TIG) welding to improve the performance of the working parts such as the thrust bearing plates under dynamic loads and corrosive liquid. Specimens were prepared with different welding parameters, namely the cladding current, preheating temperature, inter-layer temperature and post heat treatment temperature, so as to investigate their influence on micro-hardness, as well as tensile and bending strength. It is revealed that the lower welding current coincides with higher micro-hardness as well as tensile and bending strength. The higher inter-layer temperature will result inhigher overlay micro-hardness. The post weld heat treatment temperature influences the bending strength of the overlay weld specimens. In addition, the accumulation of Cr and Ni compounds on weldment surface is found to coincide with higher corrosion resistance in over-layers by means of XRD.

Over the past five years the Liburdi Powder Metallurgy (LPM™) process for repair, overlay or joining of nickel and cobalt based alloys has been improved through the addition of new alloy combinations. In addition to the original IN738™ based LPM™, two MarM247™ based compositions have been used for repair and manufacture of turbine blades and vanes. These new compositions show improved properties over the original IN738™ material. The new LPM™ compositions can fill gaps up to 30 mm wide and 6.3mm deep per application. These new compositions can also be used for surface build-ups up to 0.25m2 at 6.3mm thick per application. This ability to fill large gaps and create large surface build-ups makes these new alloy compositions very flexible tools for manufacture and repair of turbine components. The structure of these new allow combinations along with stress rupture, and tensile properties are presented in this paper. Examples of typical LPM™ applications and performance are presented.