Precipitation of BCC and sigma phases via heat treatment enhances the room temperature compressive properties and micro-hardness of Al₀.₂₈CoCr₀.₆NiV₀.₆ high entropy alloy

In this study, the effect of heat treatment on the microstructure and mechanical properties of Al_0.28CoCr_0.6NiV_0.6 high entropy alloy was investigated. By adjusting the heat treatment temperature, the contents and distributions of the FCC matrix, BCC phase, and Sigma phase in the alloy can be regulated. The microstructure and mechanical properties were influenced. Research revealed that within the heat treatment temperature range of 1000 °C to 1150 °C, the Sigma phase in the samples predominantly existed as particles within the BCC phase interface. Upon elevating the heat treatment temperature to 1200 °C, the Sigma phase tended to align along the BCC phase boundaries. The volume fraction of the brittle Sigma phase rose firstly and then declined with the increase of heat treatment temperature, reaching a maximum at 1050 °C. Tensile tests, compression tests, and microhardness tests were carried out on specimens with different heat treatments. The results of mechanical property tests indicate that the HT1150 specimen exhibits an excellent combination of strength and ductility. Its compressive yield strength reaches 850 MPa, which is approximately 49% higher than that of the as cast specimen (571 MPa). The micro hardness is 491 HV, approximately 32% higher than that of the as cast specimen (372 HV). The above-mentioned strengthening effects are mainly attributed to the second phase strengthening mechanism resulting from the dispersed distribution of the brittle σ phase.