Effect of heat treatment on microstructural evolution and mechanical properties of the TiAlV_0.5CrMo refractory complex concentrated alloy

Ultra-fine grain TiAlV_0.5CrMo refractory complex concentrated alloy (RCCA) was prepared by using mechanical alloying (MA) and spark plasma sintering (SPS), and the effects of heat treatment temperature on phase composition, microstructural evolution and mechanical properties were investigated. The results indicate that the phase composition of as-SPSed alloy comprises disordered BCC1 and BCC2 solid solution phases, along with a minor amount of Al₂O₃ phase. The system demonstrates exceptional microstructural and phase stability after the heat treatment at 1200 °C for 6 h, with only a slight decrease in hardness to a value of 9.86 GPa. With the increase in heat treatment temperature, the volume fraction of recrystallized grains gradually increases, leading to an initial growth and subsequent refinement in grain size. Under heat treatment at 800 °C and 1000 °C, the increase in volume fraction of Al₂O₃ was found to enhance the room temperature compressive yield strength of the alloy while deteriorating the plasticity. Specifically, the strength-plasticity trade-off was achieved after heat-treated at 1200 °C for 2 h, with a compressive yield strength of 2667 MPa and a plastic strain of 10.7% at room temperature. The excellent mechanical properties were attributed to the synergistic effects of lattice distortions, reduced dislocation density, weakened texture and refined grain structure. Furthermore, this alloy demonstrated a compressive yield strength of 153 MPa at a temperature of 1100 °C without fracturing at a strain of 50%. The flow stresses exhibited typical dynamic recrystallization (DRX) characteristics at elevated temperatures.