Age Heat Treatment of the CoCrFeNiTi0.3 High-Entropy Alloy

The hardness and microstructure of an as-cast CoCrFeNiTi0.3 high-entropy alloy after age heat treatment 24-144 h at 500-1000 degrees C are investigated. The as-cast alloy has a dendritic structure in which the dendrite is a Ti-lean face-centered cubic solid solution phase (FCC1) and the interdendrite consists of a Ti-rich face-centered cubic solid solution phase (FCC2), a mixture of (Cr, Fe)-rich sigma phase and (Ni, Ti)-rich eta phase. After a 144 h of age heat treatment, age hardening is observed at temperatures of 600-800 degrees C because the amount of sigma phase increases in the interdendrite. The optimum hardness is obtained at an aging temperature of 700 degrees C, which makes the hardness increase from HV366 to HV508. However, age softening occurs at 900-1000 degrees C. The vanishing sigma phase at 1000 degrees C brings the alloy hardness to the minimum, HV223.