Effects of heat treatment on the microstructure, mechanical properties and corrosion resistance of AlCoCrFeNiTi0.5 high-entropy alloy

Abstract AlCoCrFeNiTi0.5 high-entropy alloy was fabricated, and the effects of heat treatment on the microstructure, mechanical properties and corrosion resistance of this alloy were investigated. The results indicate that heat treatment can not only refine as-cast dendrites and change the morphology of precipitation from long strip to short rod-like structure but also control the ratio of BCC to FCC. The volume fraction of the BCC phase at 1100 °C is 34.8%, which is 9.2% higher than that under the as-cast conditions (25.6%). The highest compression fracture strength and fracture strain of 2785 MPa and 30.7%, respectively, are achieved when the heat treatment temperature and time are 1100 °C and 6 h, respectively. The highest Vickers hardness values of FCC and BCC are 687 HV0.5 and 782 HV0.5, respectively. The order of corrosion resistance is 800-2 h 900-2 h, as-cast, 1000-2 h, 1100-2 h, and 1200-2 h, which is contrary to the trend of the BCC volume fraction. The potential of dendritic FCC is higher than that of interdendritic BCC, and the potential difference is rising because of dendrite decomposition and atom diffusion. The corrosion mechanism is also discussed in this study. Corrosion occurs preferentially on the phase interface and interdendrites, and subsequently connects with each other. As the corrosion intensifies, dendritic FCC begins to be corroded and develops into a large corrosion area.