Evolution of phase, microstructure and mechanical properties of as-cast Al0.3CoCrFeNiTix high entropy alloys

Al0.3CoCrFeNi high entropy alloy (HEA), as a widely studied alloy with excellent plasticity and low strength has received a widespread attention. In this work, the strength of this alloy could be improved by addition of Ti for satisfying its engineering application. And then the effect of Ti on the evolutions of phase, microstructure and corresponding mechanical properties of as-cast Al0.3CoCrFeNiTix HEAs were investigated. The results demon-strated that addition of Ti could promote the microstructure of the alloys transforming from a single-phase structure to a typical dendritic structure. Simultaneously, minor Ti content caused formation of the (Al, Ni, Ti)-rich L12 phase in alloys, and then further addition of Ti content promoted formation of the (Co, Ti)-rich Laves, (Ni, Ti)-rich gamma and (Fe, Cr)-rich a phases in the Ti-0.3, Ti-0.4 and Ti-0.5 alloys. The volume fraction of these phases increased with Ti content increasing. The evolutions of the phase and microstructure greatly modified the mechanical properties of the alloys. With the increase of Ti content, the hardness of the alloys increases from 124 (Ti0) to 448 (Ti-0.5) HV, and the yield strength from 167 (Ti0) to 698 (Ti-0.4) MPa. Based on the correlation between microstructure and strength, the strengthening mechanisms of current HEAs were analyzed, confirming that the precipitation strengthening is the dominant strengthening mechanism.