Phase Transformation and Aging Behavior of Al0.5CoCrFeNiSi0.2 High-Entropy Alloy

An Al0.5CoCrFeNiSi0.2 high-entropy alloy was prepared by vacuum arc melting. The alloy was aged from 700 to 1100 degrees C. The effects of aging on the phase transformation and mechanical performances were explored. The as-cast alloy showed a dendritic (DR) microstructure. The DR region was an Fe,Cr-rich FCC phase, while the interdendritic (ID) region was a spinodal structure composed of Fe, Cr-rich BCC (A2) and Ni,Al-rich BCC (B2) phases. At aging temperatures between 700 and 900 degrees C, the Fe,Cr-rich BCC (A2) phase in the ID region transformed into sigma and Fe,Cr-rich FCC phases. Meanwhile, some Ni,Al-rich FCC phase particles precipitated from the DR region. During aging at 1100 degrees C, the DR microstructure disappeared, and a microstructure composed of Fe,Cr-rich FCC and Ni,Al-rich BCC (B2) phases both possessing a lamellar shape was developed. The alloy exhibited evident hardening and lower tensile strain when the aging temperature was lower than 1000 degrees C, which was mainly attributed to the generation of the sigma phase in the ID region. However, a contrasting behavior was observed when the aging temperature was higher than 1000 degrees C, which was attributed to the redissolution of the sigma phase and the microstructure coarsening.