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Élaboration et étude thermomécanique d'un Alliage à Mémoire de Forme Haute Température et à Haute entropie

Abstract : Conventional metal alloys are made up of a majority element, such as copper, iron, or nickel, associated with other elements present in smaller quantities. In 2004, Cantor et al. produced an alloy composed of 5 elements with an equiatomic distribution. These high entropy alloys (HEAs) are of growing interest for applications in extreme environments thanks to their good behavior at high temperatures and their high chemical stability. On the other hand, high-temperature shape memory alloys (HT-SMAs) are subject to a short lifetime due to phase precipitation at grain boundaries above 200°C. In this thesis, alloys combining the high temperature strength of HEAs and the high temperature shape memory effect (HT SMAs) have been developed in cold crucible and have been thoroughly investigated in terms of microstructure, metallurgical state and thermomechanical responses. The study of these new materials with high entropy and containing high melting point metals has obliged us to adapt our means of heat treatment and related analysis. The activation temperatures of these alloys as well as the phases present have been identified by coupling temperature bending tests. The lifetime of these new HE&HT-SMAs has been tested in stress bending and temperature fatigue tests. The behavior of the new AHEs is also compared to the behavior of the usual AMFs, in particular the binary alloys NiTi and TiNb. The microstructural evolutions at the origin of the high entropy optimization have been studied by X-ray diffraction, optical and electronic microscopy, DSC and mechanical tests. This work concludes with a study of the Ms temperature estimation for HE-SMAs as a function of the chemical composition of the alloy. The proposed equation is based on the study of the compositions of HE-SMAs from the scientific literature and the alloys produced for this thesis work.
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Submitted on : Monday, June 13, 2022 - 5:14:15 PM
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Laurent Peltier. Élaboration et étude thermomécanique d'un Alliage à Mémoire de Forme Haute Température et à Haute entropie. Mécanique des matériaux [physics.class-ph]. HESAM Université, 2022. Français. ⟨NNT : 2022HESAE028⟩. ⟨tel-03694503⟩

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