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RESEARCH PRODUCT

Development of high entropy tungsten-based alloys by powder metallurgy processes

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Although metallurgy is a very old research domain, many innovations are still being considered, such as the emergence of high-entropy alloys. These alloys, composed of at least three elements, are characterized by a chemical composition without a majority element and most of the time equimolar. Research in this field is very recent since the first studies concerning these alloys are from the early 2000s. The original chemical compositions of these alloys open the way to many possibilities to obtain unusual properties.In conjunction with these developments, powder metallurgy processes are expanding quickly because of the advantages they offer over more traditional techniques (foundry and forging). Spark Plasma Sintering technology is widely used to develop new materials with a fine and controlled microstructure. This technique is characterized by a high heating rate through Joule effect and by its great versatility. Indeed, it allows to shape a large variety of materials and many efforts are currently made to industrialize this process.This technique can be used to reach both high ductility and mechanical strength, mechanical properties highly looked for by the industry.The objective of this thesis is to develop a high entropy alloy composed of refractory metals: tungsten, molybdenum, tantalum and niobium, to achieve high densities. Sintered samples from a mixture of pure metal powders were characterized to study the influence of the microstructure on the properties of the alloy. The effect of the preparation method of these WMoTaNb powders was investigated on sintering and microstructure, highlighting the turbula mixing approach with balls versus mechanical activation with short duration milling and mechanosynthesis with high energy milling. The scale-up highlighted many obstacles to industrialization. As a result, several optimization routes have been developed to bring foreward sintering in the presence of a liquid phase.