Age Hardening of the Al0.5CoCrNiTi0.5 High-Entropy Alloy

Al0.5CoCrNiTi0.5 high-entropy alloy was synthesized by vacuum arc melting in a copper mold. This alloy was aged at 773 K to 1473 K (500 degrees C to 1200 degrees C) for 24 hours to investigate the microstructure and hardness. The hardness of the as-cast alloy is HV743, and it exhibits a dendritic structure, in which dendrite is composed of body-centered cubic (bcc), face-centered cubic (fcc), and sigma phases, and interdendrite is an eutectic structure consisting of bcc and order bcc phases. Apparent age hardening appears at 873 K to 1173 K (600 degrees C to 900 degrees C), and no age softening occurs even after 1473 K (1200 degrees C) aging. The age hardening of this alloy is attributed to the transformation of the bcc phase to sigma phase. Detailed variations of hardness and the microstructure of aged alloys are reported in this article.