Influence of hydrogen charging on microstructure and mechanical properties in a single FCC Al0.35CoCrFeNi high-entropy alloy

The effect of hydrogen on the room-temperature mechanical behaviour of the Al 0.35 CoCrFeNi high-entropy alloy has been investigated. The studied alloy was prepared by vacuum induction melting and gravity casting, followed by three-step hot forging at a temperature of 1250 °С. Heat treatment at 1330 °C for 10 min resulted in a homogenized equiaxed grain structure with a face-centered cubic crystal structure. The samples were electrochemically charged at a constant current density. Hydrogen charging increased the yield strength from 210.8 ± 3.2 MPa to 218.8 ± 1.3 MPa, while reducing the ultimate tensile strength from 565.4 ± 3.7 MPa to 545 ± 4.0 MPa and elongation from 71.2 ± 1.9 % to 64.2 ± 0.6 %. The measured hydrogen concentration was 126 ± 15 wt ppm. Fractography analyses after tensile testing revealed that hydrogen induces localized embrittlement, particularly at the sample surface, where high hydrogen concentrations promote crack initiation along grain boundaries. The work hardening rate of hydrogen-charged and uncharged samples exhibits similar overall trends, indicating that hydrogen does not lead to an additional hardening effect. The studied Al 0.35 CoCrFeNi alloy exhibits relatively good immunity to hydrogen embrittlement, and hydrogen concentration does not lead to severe degradation of mechanical properties. • Al 0.35 CoCrFeNi HEA exhibits dual-phase fracture after hydrogen charging. • Hydrogen increases yield strength but decreases ductility and tensile strength. • Crack initiation occurs at grain boundaries, twins, and slip bands. • EBSD and SEM reveal stress localization and dislocation slip band activity. • Hydrogen-enhanced decohesion and twinning govern the embrittlement process.