Experimental investigation and multi-scale modelling of the behavior of mechanically activated metallic powders : from binary systems to High Entropy Alloys. ; Étude expérimentale et modélisation multi-échelle du comportement de poudres métalliques mécaniquement activées : des systèmes binaires aux alliages à haute entropie.

Generally, metal alloys consist of a main element associated with other elements present in smaller quantities such as iron, nickel, aluminum or copper alloys. The precise composition of an alloy is adjusted according to the required performance: high temperature behavior, corrosion resistance, mechanical properties, durability . In 2004, a Taiwanese scientist, JW Yeh, had the idea of making an alloy base of several elements, at least 5, whose composition in the alloy varies between 5% and 30% at. Yeh invented the high entropy alloy (HEA). Mixed on a microscopic scale, the metals form a remarkably stable solid solution. The explanation is thermodynamic. An alloy is all the more stable as the mixing Gibbs free energy is low. Unlike traditional alloys, in an HEA, it is the entropy term of Gibbs energy that prevails over the enthalpic term. This discovery revolutionizes the design of metallic materials and opens up impressive perspectives for innovation. The study of Alloys with High Entropy (HEAs) is one of the most dynamic fields of research in materials science. One of the main challenges is understanding the relationship between development method / microstructure / properties. Most HEAs are produced by arc fusion, via a liquid phase to obtain the mixture. In the present work, we propose to study another innovative method based on powder metallurgy. The elaboration of HEAs has been carried out by a solid-state process, combining mechanical activation and SPS (Spark Plasma Sintering). Mechanical activation is a crucial first step that takes place during the high energy milling of the elementary powders. During this step, the chemical mixing and the lattice defects of the different powders increase. In practice, the subsequent reactivity of the powders is improved. This particular reactivity results in a homogeneous material after sintering. In order to have a better understanding of the progress and of the role of this mechanical activation, a molecular dynamics study in the simplified framework of binary ...