Age hardening of the Al0.3CoCrFeNiC0.1 high entropy alloy

In this study, an Al0.3CoCrFeNiC0.1 high entropy alloy was synthesized by induction melting in air. The as-cast alloy was heat treated for 5–72 h at 600–1000 °C to investigate the effects of age treatments on the hardness and microstructure. The microstructure of the as-cast alloy consisted of a FCC solid solution matrix and an eutectic k1 carbide. This k1 carbide decomposed to a k2 carbide after being aged at 800–1000 °C. The optimal age hardening occurred at 700 °C, and the hardening effect decreased with further increase in temperature. The precipitation of fine k2 carbides in the matrix during 700–1000 °C aging is the main age hardening mechanism. In addition, the precipitation of a Ni–Al rich phase at 800 °C and 900 °C provides a secondary hardening effect.