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Conception and development of a novel grade of high resistance High Entropy Alloy from the CrFeMnNi family

Abstract : This PhD dissertation presents the design and evaluation of new compositions from the CoCrFeMnNi family focusing on low-Co or Co-free compositions. Three grades characterised by a large single phased domain were selected based on thermodynamic simulations. Alloys were prepared both in the academic laboratory of EMSE and in the industrial laboratory (APERAM). The study focused on one composition, the so called Y3 CrFeMnNi, a cobalt free grade. Microstructural optimisation of Y3-CrFeMnNi grade was based on mechanical testing combined with principal techniques of microscopic observations to be able to describe the finest microstructures at the origin of mechanical properties. Multiple strengthening mechanisms were identified. Secondary precipitation, as a possible source of additional hardening, was proposed. High efficiency of strain hardening, already found in similar HEAs, was confirmed in the selected material. Hot transformation of the alloy leads to creation of high density of dislocations that are surprisingly stable as for a metallic alloy. Their presence leads to eased formation of nanostructures and slows down the recrystallization process. Furthermore, the recrystallisation results in only slightly decreased dislocations density in the matrix. Dislocations forest hardening together with solid solution hardening where shown to be major contributors to materials hardening and plastic deformation behavior, they stay predominant even at cryogenic temperature. Finally, it was shown that the Y3 composition obeys the macroscopic deformation laws as proposed by the Kocks-Mecking model, with behavior close to other fcc materials with low stacking fault energy.
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Submitted on : Wednesday, January 19, 2022 - 12:43:14 PM
Last modification on : Friday, January 21, 2022 - 3:05:37 AM
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  • HAL Id : tel-03534289, version 1



Julia Olszewska. Conception and development of a novel grade of high resistance High Entropy Alloy from the CrFeMnNi family. Other. Université de Lyon, 2019. English. ⟨NNT : 2019LYSEM007⟩. ⟨tel-03534289⟩



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