Abstract Tungsten carbide-cobalt powder is pressed before sintering into a compacted form using punches and a die cavity. After the powder has been pressed to a specific shape, it is sintered and shrinks a certain amount to a final size. To accommodate this shrinkage, the pressing tools are designed to a certain “shrinkage percentage” and thus the pressed component or compact is larger than the sintered component by that percentage amount. During the pressing process, there is a large amount of friction between the powder being compacted and the die cavity wall. To counter pressing friction, a lubricant is pre-mixed with the tungsten carbide powder. In the past at Powder Industries, the powder was mixed with wax and all of the tools were designed to a 20% shrinkage. In recent times, the wax in the powder has been replaced by PEG (polyethylene glycol) by most manufacturers as this increases the quality of the final product and is easier to remove in the furnaces. As a result of the new PEG lubricant, the tool wear rate at Powder Industries increased and because a higher pressure had been necessary to achieve powder pressing to the same shape and form, often the pressed components exhibited cracks or were not pressed ideally. On account of the problems introduced by PEG, correct tool design for the shrinkage was obtained by a ‘trial & error’ process. This project has been motivated by the need of establishing pressing and/or design ‘rules’ that would do away with trial and error when designing compaction tooling. The project has consisted of investigating the physical properties of 23 grades of WC-Co powder (with or without TiC and TaC) and of performing a series of pressing tests for each grade. A relationship between the apparent density of a powder and the ideal green density of the green compact pressed from the same powder has been found. Using this relationship, an equation has been derived between ideal shrinkage, powder apparent density, component sintered density and powder volatile content. Since the last three parameters are known to the tool designer, this equation can be used to calculate the ideal shrinkage when designing new compaction tooling. This method of calculating shrinkage is now in general use at Powder Industries and many successful sets of compaction tooling have already been manufactured

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This work is a preliminary attempt to study the effect between thermal shock and abrasive wear in WC-Co alloys. This was done by evaluating the thermal shock resistance of a WC-12wt%Co mining grade as a function of temperature, number of thermal shock cycles and making comparisons between the abrasive wear responses of samples subjected to thermal shock and samples not subjected to thermal shock. A furnace was designed for the thermal shock treatments. Abrasive wear tests were performed on a 2-body sliding wear apparatus using 80-grit SiC abrasive paper as a counter-face. Stereo and electron microscopy as well as microprobe techniques were used to analyse the effects of thermal shock. It is confirmed that thermal shock has a negative effect on the wear rate of WC-12wt%Co. The results showed an initial high mass loss rate during abrasive wear testing, which increased with increasing temperature and a decrease in wear rate with time until the wear rates converged for all samples. The surface analysis after thermal shock indicated voids on and below the surface, stained surfaces, a thin oxide layer and the possibility of WC decarburization which accelerated the wear response.

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 différentes. / Nanomaterials 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.

The Seamless Stressometer® roll (Seamless STR) is used to measure the flatness of aluminum and steel strip when there is an extreme demand on the surface finish. To protect the roll and strip, the roll is coated with two layers deposited by high velocity oxygen fueled spraying (HVOF), Cr-Ni(Si,B) closest to the roll and WC-Co on top. This solution has several disadvantages; high cost and complicated logistics, corrosion sensitivity and high residual stresses creates the need for two coatings which in turn complicates the process. Cobalt is, in addition, sensitive to low pH coolants and environmentally unfriendly. These problems have given rise to the idea of switching both the method and material of the coating. In the first part of this work, high velocity air fueled spraying (HVAF) was evaluated as an alternative deposition method. Three materials, Cr3C2-NiCr, WC-Co and WC-CrC-Ni were deposited on steel coupons with varying chamber pressure, powder feed rate and distance from the nozzle, in order to evaluate if HVAF can be a valid technique for use in this application and to optimize the spraying recipe. The objectives were to get a sufficiently high thickness per sweep, to be able to make the depositions in a manageable number of sweeps, and to get low porosity, since the coatings need to be dense to be hard and possible to polish smooth. The tests showed that all three materials can be sprayed with the high settings on the parameters to obtain coatings that exceeded the set limits of the objectives. In the second part of this work, the recipe obtained from the first part was used to deposit samples for further analysis. The coatings were compared regarding cost, hardness, friction, wear and pick-up properties to evaluate if a switch in material from WC-Co was possible. The coatings showed both similarities and differences. The friction was very similar for the three materials. Cr3C2-NiCr was substantially cheaper than the other two, had lower hardness and higher porosity, but still probably acceptable values, and was satisfactory regarding wear and pick-up. WC-Co and WC-CrC-Ni were very similar to each other regarding cost, hardness and porosity but WC-Co was the best regarding wear and pick-up, where WC-CrC-Ni was the worst. The only clear advantage of WC-CrC-Ni over WC-Co is the lack of cobalt. Taking everything into consideration, including the fact that the wear and pick-up tests in this work was quite exaggerated, Cr3C2-NiCr is an interesting option for this application due to its low cost and acceptable test results, WC-Co had the best results but is expensive and contains cobalt and WC-CrC-Ni had as good results as WC-Co except for the wear and pick-up tests and does not contain cobalt.

No description available.

Grâce à leurs excellentes propriétés de dureté et de résistance à l’usure, les carbures cémentés sont les meilleurs candidats pour la réalisation d’outillage de coupe. Elaborés par la métallurgie des poudres, ils sont majoritairement composés de carbure de tungstène, choisis pour ses propriétés de dureté et d’un liant métallique à haute ductilité, le plus souvent le cobalt. Néanmoins, l’utilisation du cobalt comme liant est remis en question depuis quelques années par la commission européenne REACH à cause de sa toxicité. En conséquence, des liants alternatifs tels que les alliages de Fe et Ni sont étudiés. Malgré les différents travaux menés, il subsiste un manque de compréhension fondamental sur l’effet spécifique du liant sur le frittage et le grossissement de grains des carbures cémentés. Le but de cette étude est la compréhension de l’effet de la composition du liant sur le frittage et le grossissement de grains. Dans cet objectif, différent liants WC-20vol%M (M=Fe, Ni or Co) et différent taux de carbone sont considérés. Le frittage et le grossissement de grains seront étudiés à l’aide de caractérisations macroscopiques et microstructurales, puis les résultats discutés en comparaison avec la littérature. Comme il a été déjà observé dans le cas d’alliages WC-Co, le retrait au cours du frittage survient plus tôt dans le cas d’alliages riches en W qu’en C, quelque soit le liant considéré. Concernant l’effet de la nature du liant, le frittage en phase solide est décalé vers les hautes températures pour WC-Fe en comparaison avec WC-Co et WC-Ni. Dans cette étude le retrait est directement corrélé avec la capacité d’étalement du liant dans la porosité, comme le confirme l’analyse de la microstructure. Quant au grossissement de grain, il est inhibé pour un faible ratio C/W, quelque soit la nature du liant. Néanmoins, pour un ratio C/W élevé, celui-ci augmente, ainsi que la tendance au grossissement anormal, en particulier dans le cas du liant nickel. Les mécanismes de grossissement de grains sont discutés en lien avec les observations structurales des interfaces. / Thanks to their exceptional hardness and wear resistance, cemented carbides are the best candidates to make efficient cutting and drilling tools by the powder metallurgy route. Known as a very hard ceramic material, tungsten carbide is used as the major component of cemented carbides. A ductile metal binder is added as the matrix, which in most cases is cobalt. Nevertheless the use of cobalt as a binder is questioned by the new European regulation on chemicals (REACH). Therefore, new alternative binders are considered, especially Fe and Ni-alloys. Although a few studies exist for Fe-based and Ni-based WC cemented carbides, there is still a lack of fundamental understanding of the specific effect of the binder on sintering and grain growth. This work discusses the effect of binder composition on sintering and grain growth of cemented carbides. For this purpose, different binder compositions WC-20vol%M (M= Fe, Ni or Co) and different C/W ratio are considered. Sintering and grain growth behaviors are investigated using several macroscopic and microstructural characterizations, and results are discussed and compared to the literature. As already observed in previous works on WC-Co, shrinkage occurs earlier for W-rich than for C-rich alloys for the three binders. Regarding the influence of the binder nature, solid state sintering is delayed to higher temperature for WC-Fe in comparison to WC-Co and WC-Ni alloys. Shrinkage is directly related to the spreading efficiency of the binder into the porosity, as confirm by the microstructure analysis. Grain growth is inhibited for low C/W ratio whatever the binder nature. Nevertheless, for a high C/W ratio, grain growth is enhanced and the abnormal character of grain growth increases, especially in the case of a Ni binder. Grain growth mechanisms are discussed in relation with the observed structure of phase boundaries.

In dieser Arbeit wurden das feldaktivierte Sinterverhalten sowie das geschwindigkeitsabhängige Druckfestigkeitsverhalten von WC-Co-Hartstoffen mit variierenden Bindergehalten untersucht. Dazu wurde eine Herstellungsroute für kornwachstumshemmerfreie near-nanokristalline WC-Co-Hartstoffe mit der Field Assisted Sintering Technique (FAST) entwickelt und genutzt, um Materialien mit Co-Gehalten von 2 bis 12 Ma.-% zu erzeugen. Gezielte Werkstoffzustände und Probengeometrien sind durch Anpassung des Sinterprozesses herstellbar. Ausgewählte WC-Co-Materialien mit Co-Anteilen von 6 bis 12 Ma.-% wurden unter Einfluss von Beanspruchungsgeschwindigkeit, Spannungszustand und Beanspruchungshäufigkeit hinsichtlich der Druckfestigkeit und des Versagensverhaltens charakterisiert.

Made available in DSpace on 2014-12-17T14:57:41Z (GMT). No. of bitstreams: 1 GislaineBP.pdf: 2931348 bytes, checksum: a3914c6b0349281b46081bda792536cc (MD5) Previous issue date: 2008-03-19 / Hard metals are the composite developed in 1923 by Karl Schr?ter, with wide application because high hardness, wear resistance and toughness. It is compound by a brittle phase WC and a ductile phase Co. Mechanical properties of hardmetals are strongly dependent on the microstructure of the WC Co, and additionally affected by the microstructure of WC powders before sintering. An important feature is that the toughness and the hardness increase simultaneously with the refining of WC. Therefore, development of nanostructured WC Co hardmetal has been extensively studied. There are many methods to manufacture WC-Co hard metals, including spraying conversion process, co-precipitation, displacement reaction process, mechanochemical synthesis and high energy ball milling. High energy ball milling is a simple and efficient way of manufacturing the fine powder with nanostructure. In this process, the continuous impacts on the powders promote pronounced changes and the brittle phase is refined until nanometric scale, bring into ductile matrix, and this ductile phase is deformed, re-welded and hardened. The goal of this work was investigate the effects of highenergy milling time in the micro structural changes in the WC-Co particulate composite, particularly in the refinement of the crystallite size and lattice strain. The starting powders were WC (average particle size D50 0.87 μm) supplied by Wolfram, Berglau-u. Hutten - GMBH and Co (average particle size D50 0.93 μm) supplied by H.C.Starck. Mixing 90% WC and 10% Co in planetary ball milling at 2, 10, 20, 50, 70, 100 and 150 hours, BPR 15:1, 400 rpm. The starting powders and the milled particulate composite samples were characterized by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) to identify phases and morphology. The crystallite size and lattice strain were measured by Rietveld s method. This procedure allowed obtaining more precise information about the influence of each one in the microstructure. The results show that high energy milling is efficient manufacturing process of WC-Co composite, and the milling time have great influence in the microstructure of the final particles, crushing and dispersing the finely WC nanometric order in the Co particles / O metal duro ? um comp?sito de matriz met?lica que tem grande aplica??o devido as suas propriedades, que aliam alta dureza e resist?ncia ao desgaste ? tenacidade. ? composto por uma fase fr?gil, o WC, e uma fase d?ctil, que pode ser o cobalto, o ferro ou o n?quel. Destes comp?sitos, o de maior destaque ? o WC-Co, que foi desenvolvido na d?cada de 20 e vem sendo estudado desde ent?o. As propriedades mec?nicas do comp?sito WC-Co, s?o dependentes das caracter?sticas microestruturais dos materiais de partida. Neste contexto, a obten??o do metal duro a partir de part?culas nanom?tricas vem sendo estudada. Existem v?rios m?todos de fabrica??o de metal duro WC-Co nanoparticulado, dentre as principais t?cnicas, a moagem de alta energia em moinho planet?rio, se mostra eficiente para este fim. Nesse processo, os p?s s?o submetidos a cont?nuos impactos, que provocam significativas altera??es em sua microestrutura. A fase fr?gil ? refinada at? a escala nanom?trica e a fase d?ctil ? deformada e soldada, formando placas, devido o excesso de deforma??o pl?stica, as placas tornam-se encruadas e sofrem fratura fr?gil. Simultaneamente as part?culas fr?geis s?o inseridas na fase d?ctil formando assim um comp?sito com matriz de cobalto pouco ou muito deformado e part?culas refinadas e dispersas de carbeto de tungst?nio. Estas caracter?sticas dependem das condi??es de moagem empregada. Neste trabalho foi realizada uma an?lise das caracter?sticas deste comp?sito quanto ao tamanho de cristalito, grau de encruamento, e morfologia. O principal objetivo deste trabalho ? investigar o efeito do tempo da moagem de alta energia nas altera??es microestruturais que ocorrem no comp?sito WC-Co, no que diz respeito ao refinamento das part?culas e a microdeforma??o da rede cristalina. Neste contexto foram utilizadas as t?cnicas de difra??o de raios X (DRX) e microscopia eletr?nica de varredura (MEV). A t?cnica utilizada para an?lise de tamanho de cristalito e microdeforma??o da rede cristalina foi o M?todo de Rietveld. Os resultados mostram que a moagem de alta energia foi eficiente na produ??o do comp?sito WC-Co com part?culas de WC nanom?tricas pouco ou muito encruadas

In dieser Arbeit wurden das feldaktivierte Sinterverhalten sowie das geschwindigkeitsabhängige Druckfestigkeitsverhalten von WC-Co-Hartstoffen mit variierenden Bindergehalten untersucht. Dazu wurde eine Herstellungsroute für kornwachstumshemmerfreie near-nanokristalline WC-Co-Hartstoffe mit der Field Assisted Sintering Technique (FAST) entwickelt und genutzt, um Materialien mit Co-Gehalten von 2 bis 12 Ma.-% zu erzeugen. Gezielte Werkstoffzustände und Probengeometrien sind durch Anpassung des Sinterprozesses herstellbar. Ausgewählte WC-Co-Materialien mit Co-Anteilen von 6 bis 12 Ma.-% wurden unter Einfluss von Beanspruchungsgeschwindigkeit, Spannungszustand und Beanspruchungshäufigkeit hinsichtlich der Druckfestigkeit und des Versagensverhaltens charakterisiert.