Effects of interstitial C and N on hydrogen embrittlement behavior of non-equiatomic metastable FeMnCoCr high-entropy alloys

The hydrogen embrittlement behavior of C-doped and C-N co-doped non-equiatomic FeMnCoCr high-entropy alloys were investigated by slow strain rate tensile tests (1 × 10−5 s−1) under in-situ electrochemical hydrogen charging. Multi-scale microstructural analysis suggests that appropriate phase stability and stacking fault energy adjusted by C-doping provide the alloy with slightly greater resistance to hydrogen embrittlement with the formation of abundant deformation-induced twins and ε-martensite during deformation. The C-N free alloy shows grain boundary and ε/γ interface cracking even though the γ and ε phases have high deformability. C-N co-doping promotes planar dislocation slip, assisting grain- and twin-boundary cracking under deformation in hydrogen.