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Effects of Annealing on Microstructure and Mechanical Properties of Metastable Powder Metallurgy CoCrFeNiMo0.2 High Entropy Alloy

1
State Key Laboratory for Powder Metallurgy, Central South University, Changsha 410083, China
2
College of Mechanical and Vehicle Engineering, Hunan University, Changsha 410082, China
3
Yuanmeng Precision Technology (Shenzhen) Institute, Shenzhen 518055, China
*
Authors to whom correspondence should be addressed.
Entropy 2019, 21(5), 448; https://doi.org/10.3390/e21050448
Received: 15 February 2019 / Revised: 18 April 2019 / Accepted: 24 April 2019 / Published: 30 April 2019
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Abstract

A CoCrFeNiMo0.2 high entropy alloy (HEA) was prepared through powder metallurgy (P/M) process. The effects of annealing on microstructural evolution and mechanical properties of P/M HEAs were investigated. The results show that the P/M HEA exhibit a metastable FCC single-phase structure. Subsequently, annealing causes precipitation in the grains and at the grain boundaries simultaneously. As the temperature increases, the size of the precipitates grows, while the content of the precipitates tends to increase gradually first, and then decrease as the annealing temperature goes up to 1000 °C. As the annealing time is prolonged, the size and content of the precipitates gradually increases, eventually reaching a saturated stable value. The mechanical properties of the annealed alloys have a significant correspondence with the precipitation behavior. The larger the volume fraction and the size of the precipitates, the higher the strength and the lower the plasticity of the HEA. The CoCrFeNiMo0.2 high entropy alloy, which annealed at 800 °C for 72 h, exhibited the most excellent mechanical properties with the ultimate tensile strength of about 850 MPa and an elongation of about 30%. Nearly all of the annealed HEAs exhibit good strength–ductility combinations due to the significant precipitation enhancement and nanotwinning. The separation of the coarse precipitation phase and the matrix during the deformation process is the main reason for the formation of micropores. Formation of large volume fraction of micropores results in a decrease in the plasticity of the alloy. View Full-Text
Keywords: powder metallurgy; high entropy alloy; microstructure; precipitation strengthening; mechanical properties powder metallurgy; high entropy alloy; microstructure; precipitation strengthening; mechanical properties
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Zhang, C.; Liu, B.; Liu, Y.; Fang, Q.; Guo, W.; Yang, H. Effects of Annealing on Microstructure and Mechanical Properties of Metastable Powder Metallurgy CoCrFeNiMo0.2 High Entropy Alloy. Entropy 2019, 21, 448.

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