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Face-centered cubic (FCC) high/medium entropy alloys (HEAs/MEAs), novel multi-principal element alloys, are known to exhibit exceptional mechanical properties at room temperature; however, the origin is still elusive. Here, we report the deformation microstructure evolutions in a tensile-deformed Co20Cr40Ni40 representative MEA and Co60Ni40 alloy, a conventional binary alloy for comparison. These FCC alloys have high/low friction stresses, fundamental resistance to dislocation glide in solid solutions, respectively, and share similar other material properties, including stacking fault energy. The Co20Cr40Ni40 MEA exhibited higher yield strength and workhardening ability than in the Co60Ni40 alloy. Deformation microstructures in the Co60Ni40 alloy were marked by the presence of coarse dislocation cells (DCs) regardless of grain orientation and a few deformation twins (DTs) in grains with the tensile axis (TA) near <1 1 1>. In contrast, the MEA developed three distinct deformation microstructures depending on grain orientations: fine DCs in grains with the TA near <1 0 0>, planar dislocation structure (PDS) in grains with other orientations, and a high density of DTs along with PDS in grains oriented <1 1 1>. Three-dimensional electron tomography revealed that PDS in the MEA confined dislocations within specific {1 1 1} planes, indicating suppression of cross-slip of screw dislocations and dynamic recovery. In-situ X-ray diffraction during tensile deformation showed a higher dislocation density in the MEA than in the Co60Ni40 alloy. These findings demonstrate that FCC HEAs/MEAs with high friction stresses naturally develop unique deformation microstructures which is beneficial for realizing superior mechanical properties compared to conventional materials.

権利情報:

• In Copyright
  

キーワード: High/medium entropy alloys, Dislocation structure, Deformation twinning, Strain hardening, 3D characterization

刊行年月日: 2024-10-21

出版者: Elsevier BV

掲載誌:

• Acta Materialia (ISSN: 13596454) vol. 283 120498

研究助成金:

• Government of Japan Ministry of Education Culture Sports Science and Technology
• National Natural Science Foundation of China
• Japan Society for the Promotion of Science

原稿種別: 査読前原稿 (Author's original)

MDR DOI: https://doi.org/10.48505/nims.5992

公開URL: https://doi.org/10.1016/j.actamat.2024.120498

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更新時刻: 2025-12-11 12:30:12 +0900

MDRでの公開時刻: 2025-12-11 12:24:32 +0900