The effects of secondary elemental Mo or Ti addition in Al0.3CoCrFeNi high-entropy alloy on age hardening at 700 °C

Three FCC structured high-entropy alloys of Al0.3CoCrFeNi, Al0.3CoCrFeNiMo0.1, and Al0.3CoCrFeNiTi0.1 were synthesized in order to investigate the effects of secondary elemental Mo or Ti addition in Al0.3CoCrFeNi alloy on age hardening at 700 °C. All of the three alloys exhibited an apparent age hardening, especially when secondary elements were added. The hardness of the Al0.3CoCrFeNi alloy was increased by 65% after aging, whereas the other two alloys displayed an increase of over 80%. The Al0.3CoCrFeNi and Al0.3CoCrFeNiTi0.1 alloys were hardened by massive (Ni,Al)-rich and (Ni,Co,Ti)-rich B2 ordered precipitates, respectively. The large age hardening of the Al0.3CoCrFeNiMo0.1 alloy is attributed to the precipitation of both fine (Ni,Al)-rich phase and heavy blocky (Cr,Mo)(Co,Fe,Ni) σ phase.