Effect of annealing on mechanical properties of a nanocrystalline CoCrFeNiMn high-entropy alloy processed by high-pressure torsion

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING

卷:676

Article

Shahmir, Hamed¹  He, Junyang²  Lu, Zhaoping²  Kawasaki, Megumi^3,4  Langdon, Terence G.¹ 

[1] Univ Southampton, Fac Engn & Environm, Mat Res Grp, Southampton SO17 1BJ, Hants, England

[2] Univ Sci & Technol Beijing, State Key Lab Adv Met & Mat, Beijing 10083, Peoples R China

[3] Hanyang Univ, Div Mat Sci & Engn, Seoul 133791, South Korea

[4] Hanyang Univ, Res Inst Ind Sci, Seoul 133791, South Korea

关键词: CoCrFeNiMn;    High-entropy alloy;    High-pressure torsion;    Nanostructured materials;    Post deformation annealing;    Severe plastic deformation;   

DOI  :  10.1016/j.msea.2016.08.118

来源: Elsevier

【 摘 要 】

A CoCrFeNiMn high-entropy alloy (HEA) was processed by high-pressure torsion (HPT) under 6.0 GPa pressure up to 10 turns at room temperature. It is shown that there is a gradual evolution in hardness with increasing numbers of turns but full homogeneity is not achieved even after 10 turns. Micro hardness measurements reveal that the material reaches a saturation hardness value of similar to 4.41 GPa and in this condition the microstructure shows exceptional grain refinement with a grain size of similar to 10 nm. An ultimate strength value of similar to 1.75 GPa and an elongation to fracture of similar to 4% were obtained in a sample processed for 5 turns. The nanostructured HEA was subjected to post-deformation annealing (PDA) at 473-1173 K and it is shown that the hardness increases slightly to 773 K due to precipitation and then decreases up to 1173 K due to a combination of recrystallization, grain growth and a dissolution of the precipitates. The formation of brittle precipitates, especially sigma-phase, at 873 and 973 K significantly reduces the ductility. Short-term annealing for 10 min at 1073 K prevents grain growth and leads to a combination of high strength and good ductility including an ultimate tensile strength of similar to 830 MPa and an elongation to failure of similar to 65%. (C) 2016 Elsevier B.V. All rights reserved.

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