Effect of heat treatment on the phase evolution and mechanical properties of atomized AlCoCrFeNi high-entropy alloy powders

In this study, gas-atomized AlCoCrFeNi high-entropy alloy (HEA) powders were prepared by gas atomization process instead of ball milling method and the variations of annealing temperature on the crystal structure, microstructure, phase evolution and mechanical properties were investigated. This equatomic HEAs powder possesses an initial phase of BCC while the FCC and minor sigma phases could be adjusted via the annealing treatment. After the annealing process at 900 degrees C over 3 h, the phase constitution of gas-atomized AlCoCrFeNi gradually reached its stable state, composed of FCC + BCC phases. The BCC phase was identified as one kind of FeCo compound and served as the base of AlCoCrFeNi HEAs. During the annealing process, Cr element was separated and (Al, Ni)-rich phases were distributed in the uniform FeCo base. Based on such a microstructure, we found that the precipitated FCC and sigma phases can lead to a significant increase of the mechanical performance of AlCoCrFeNi HEA. In summary, our results suggest that the precipitation hardening is an important mechanism for obtaining a high strength AlCoCrFeNi HEA alloy. (C) 2019 Elsevier B.V. All rights reserved.