Hydrogen induced microstructure evolution and cracking mechanism in a metastable dual-phase high-entropy alloy

Metastable Fe₅₀Mn₃₀Cr₁₀Co₁₀ high-entropy alloys show outstanding mechanical properties, which are likely to be exposed to the hydrogen environment for many potential applications. However, the effects of hydrogen on mechanical properties and embrittlement behavior of this alloy are still unclear. In the present work, the influence of hydrogen on the microstructure evolution, mechanical properties, and embrittlement behavior of the metastable Fe₅₀Mn₃₀Cr₁₀Co₁₀ high-entropy alloy (HEA) is observed. Hydrogen-assisted cracking initiation and propagation are observed via electron backscatter diffraction analysis and electron channelling contrast imaging. A high hydrogen flux is observed in the FCC phase, indicating the diffusible hydrogen is preferred desorbed from this phase compared to the HCP phase. Fracture of the hydrogen-charged specimens is dominated by localized plastic deformation. Microstructural observations confirmed that cracks mainly initiated in austenite grain boundaries, propagated along austenite grain boundaries aided by the impingement of HCP laths and in a minor fraction propagated along FCC/HCP interfaces or inclusion interfaces. The failure mode under tensile deformation in the presence of hydrogen is a mainly intergranular and partial transgranular fracture.