Effect of deep cryogenic treatment on microstructure and mechanical properties of a CoCrFeNiMo medium-entropy alloy

Abstract The effects of different soaking times and cycles of deep cryogenic treatment on the microstructure and mechanical properties of Co 28.5 Cr 21.5 Fe 20 Ni 26 Mo 4 medium entropy alloys were studied. The results show that the maximum hardness and compress strength were 364 HV and 3153 MPa after cryogenic deep treatment for 8 h, which were increased by about 9.97% and 33.32%, respectively. The maximum hardness and compressive strength were 375 HV and 3039 MPa, which were increased by about 13.29% and 28.50%, respectively, after three deep cryogenic cyclic times. The reason is that μ phase is rich in Mo, and Mo element has high strength and hardness. After deep cryogenic treatment, the agglomeration of μ phase in the alloys was improved, the distribution of μ phase was more uniform, the content of μ phase was increased, and the content of Mo element in the μ phase was increased, so that the strengthening effect of μ phase was enhanced.