Age-hardening of the CoCrFeNiMo0.85 high-entropy alloy

In this study, the effect of aging treatment for 24-144 h at 600-1000 degrees C on the hardness and microstructure of an as-cast CoCrFeNiMo0.85 high-entropy alloy was investigated. The microstructure of the as-cast alloy consists of three different phases that include an face-centered cubic solid solution matrix, a (Mo,Cr)-rich sigma phase, and a minor (Mo,Cr)-rich mu phase. The sigma phase can be completely transformed into the mu phase via aging at 900-1000 degrees C. The optimum hardness is obtained upon precipitation of fine needles of a sigma phase in the face-centered cubic matrix, which occurs at an aging temperature of 700 degrees C. The hardening effect is observed to decrease with any further increase in temperature beyond 700 degrees C. Comparison of the hardness of aged alloys and the as-cast alloy reveals that no obvious softening occurs after aging at temperatures of up to 1000 degrees C. (C) 2013 Elsevier Inc. All rights reserved.