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This study clarified the grain size dependence of the deformation microstructure evolution and work-hardening behavior in CoCrNi medium entropy alloy. We fabricated fully recrystallized specimens with coarse-grained (CG)
and ultrafine-grained (UFG) specimens by severe plastic deformation and subsequent annealing processes. Tensile deformation was applied to the specimens at room temperature. The UFG specimen exhibited both high strength and high ductility compared to conventional UFG metals due to the high work-hardening ability. In the CG specimen, three distinct types of deformation microstructures consisting of dislocations and deformation twins developed depending on grain orientations, similar to the single-crystalline specimens. In the UFG specimen, widely-extended stacking faults and randomly-tangled dislocations were found to coexist in most grains. Deformation twins were found to nucleate without evidence of dislocation reactions regardless of grain orientations, implying abnormal nucleation mechanisms of deformation twins in the UFG specimen. Dislocation
densities quantified by in-situ synchrotron XRD measurements during tensile deformation were higher in the UFG specimen than those in the CG specimen and conventional UFG metals. Our analysis showed that the workhardening behavior of the specimens was primarily controlled by increases in dislocation density as well as the introduction of planar defects during deformation. Through comparisons with the CG specimen and conventional UFG metals, we concluded that the excellent work-hardening ability of the UFG specimen was mainly due to the evolution of unique deformation microstructures and rapid increase in dislocation density, which could be due to inhibited dynamic recovery in the MEA.

権利情報:

• Creative Commons BY Attribution 4.0 International
  

キーワード: Ultrafine-grained metals, High/medium entropy alloys, Deformation microstructure, Deformation twins, Grain boundary-mediated plasticity

刊行年月日: 2024-11-03

出版者: Elsevier BV

掲載誌:

• Journal of Alloys and Metallurgical Systems (ISSN: 29499178) vol. 8 100123

研究助成金:

原稿種別: 出版者版 (Version of record)

MDR DOI:

公開URL: https://doi.org/10.1016/j.jalmes.2024.100123

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更新時刻: 2024-11-23 16:30:14 +0900

MDRでの公開時刻: 2024-11-23 16:30:16 +0900