Study of the stabilization process of gas atomized Al0.5CoCrFeNi2Ti0.5 high-entropy alloy in phase transformation

•Characterization of Al0.5CoCrFeNi2Ti0.5 powders produced by the gas atomization method.•Phase constitution of Al0.5CoCrFeNi2Ti0.5 powders transferred from BCC to FCC-dominated structure on annealing treatment.•EBSD and EDS results indicate that precipitates were of (Al, Ti)-rich whereas the matrix was (Fe, Cr)-rich.•Average hardness improved due to precipitation strengthening brought about by Ti addition. The phase and microstructure evolution of a precipitation-hardening high entropy alloy (HEA), Al0.5CoCrFeNi2Ti0.5, were studied. In order to promote the applications in surface modification, the proposed HEA was made into powders by using a gas-atomization process. The as-obtained powders presented a spherical shape with uniform element distribution; moreover, their phase constitution transferred from BCC to FCC-dominated structure while particle size varied from several to 120 µm. Further annealing treatments were conducted with the metastable fine powders to investigate the size effect in the microstructure. Below 500 °C, the structure kept a major BCC phase, but the size of grains arranged along (110) plane were getting smaller with temperature. FCC crystal became the dominant structure while the temperature was higher than 550 °C, and the transitional sigma phase existed at 700–800 °C. After annealed at 900 °C, the metastable fine Al0.5CoCrFeNi2Ti0.5 powders fully transferred to a stable structure composed of a dominant FCC plus minor BCC phases. Elemental mappings showed that the Al0.5CoCrFeNi2Ti0.5 HEA transformed from a microstructure with uniform element distribution to a coarsened system comprised of (Fe, Cr)-rich FCC matrix and (Al, Ti)-rich order BCC precipitate. Furthermore, the hardness of the Al0.5CoCrFeNi2Ti0.5 HEA increased by more than 20% on annealing treatment, from 5.50 ± 0.75–6.91 ± 1.49 GPa due to the solid solution and the precipitation strengthening effect brought about by Ti addition.