Effect of annealing heat treatment on microstructure and mechanical properties of nonequiatomic CoCrFeNiMo medium-entropy alloys prepared by hot isostatic pressing

Abstract

In this study, nonequiatomic Co28.5Cr21.5Fe20Ni26Mo4 medium-entropy alloys (MEAs) were prepared using hot isostatic pressing. The effect of annealing heat treatment on microstructure and mechanical properties of MEAs was investigated. The results showed that the microstructure of as-sintered alloys was mainly composed of the face-centered cubic (FCC) phase and μ phase. The presence of the μ phase could improve the compressive strength of Co28.5Cr21.5Fe20Ni26Mo4 MEAs. Meanwhile, the ductile FCC phase matrix could effectively suppress the propagation of cracks to improve its ductility. Hence, as-sintered MEAs possessed excellent compression properties, and the average compressive strength value was 2,606 MPa when the strain was 50%. Compared with as-sintered MEAs, the phase composition of as-annealed MEAs did not change. The micro-hardness of annealed MEAs was stable compared to as-sintered MEAs (342 HV), and its fluctuation was about ±30 HV. The compressive strength of the annealed MEAs did not alter greatly, and the maximum fluctuation value was only about 6.5%. Hence, Co28.5Cr21.5Fe20Ni26Mo4 MEAs had excellent thermal stability.