Effects of annealing treatment on microstructure and hardness of bulk AlCrFeNiMo0.2 eutectic high-entropy alloy

Bulk AlCrFeNiMo0.2 (in molar ratio) alloy ingot was prepared by vacuum induction melting and casting methods. The effects of annealing temperature variations (550-1050 degrees C) on the crystal structure, microstructure, and hardness were investigated. The hardness of the as-cast alloy was HV467, and the alloy exhibited a typical eutectic cell microstructure consisting of FeCrMo-rich solid solution (BCC structure) and NiAl-rich intermetallic compound (B2 structure). After annealing at 750-950 degrees C, a Mo-rich sigma phase precipitated from the FeCrMo-rich solid solution, and apparent annealing hardening appeared. The hardness increased from HV479 to HV542. The hardening of this alloy was attributed to the transformation of the BCC phase to the sigma phase. The sigma phase changed back to the BCC phase at 1050 degrees C and the hardness decreased to HV478 which was nearly equal to that of the as-cast alloy. Overall, the AlCrFeNiMo0.2 alloy exhibited excellent annealing softening resistance. (C) 2015 Elsevier Ltd. All rights reserved.