Influence of heat treatment on microstructure and mechanical behavior of biocompatible MoNbTaTiZr high-entropy alloy

This study investigates the effect of aging temperature (1000–1300°C for 5 h) on a homogenized MoNbTaTiZr refractory high-entropy alloy. The homogenized microstructure comprised two BCC phases: dendritic BCC1 (hardness 4.66 GPa) and interdendritic BCC2 (hardness 2.56 GPa). Aging at 1100°C increased the BCC1 fraction to 86.8%, but further heating to 1300°C reduced it to 80.5% due to the formation of Ti/Zr-rich HCP precipitates. This precipitation raised the macro-hardness from 513 HV at 1000°C to 592 HV at 1300°C, despite a decrease in BCC1 micro-hardness from 493 to 417 HV. The results demonstrate that aging temperature critically controls phase evolution and mechanical properties.