Effect of Al on characterization and properties of AlxCoCrFeNi high entropy alloy prepared via electro-deoxidization of the metal oxides and vacuum hot pressing sintering process

Highlights: • Direct conversion of metal oxide mixture into Al_xCoCrFeNi alloys via electro-deoxidization. • Research of the effects of Al addition on the crystal structure and microstructure of powder products. • Preparation of bulk Al_xCoCrFeNi alloys via vacuum hot pressing sintering process. • Evaluation of Al addition effects on mechanical property and corrosion behavior of Al_xCoCrFeNi alloys. -- Abstract: Al_xCoCrFeNi high-entropy alloys with different Al contents (x in molar ratio, x = 0 – 2.0) were prepared by electrochemical process using the mixed metal oxides as the precursor. The effects of Al addition on the crystal structure, microstructure, mechanical property and corrosion behavior were investigated by XRD, XPS, SEM, FE-EPMA, universal tensile testing machine, Vickers hardness tester and electrochemical workstation. With the increase of Al contents, the crystal structure of Al_xCoCrFeNi HEAs transformed from FCC to the mixed crystal structures of FCC and BCC, finally, to BCC + B2. The σ-phase was formed in Al_xCoCrFeNi (x = 0.8 – 1.5) HEAs during the electrolysis deoxidization. The bulk HEAs could be prepared successfully via vacuum hot pressing sintering process. The bulk HEAs exhibit excellent ultimate tensile strength (UTS) and hardness. The hardness of the Al₀ (245.2 HV) HEA and Al_0.3 (261.2 HV) HEA was twice high of the sample prepared by arc-melting method. Compared with 304 stainless steel (304SS) and Al_xCoCrFeNi HEAs prepared by other method, Al_xCoCrFeNi HEAs prepared by the united process shows a comparable corrosion resistance in acid, alkali and salt aqueous solutions.