Hydrogen-enhanced compatibility constraint for intergranular failure in FCC FeNiCoCrMn high-entropy alloy

Highlights: • Hydrogen induced intergranular failure in FeNiCoCrMn high-entropy alloy. • Hydrogen caused changes to evolution of deformation across length scales. • Hydrogen-dislocation interactions caused "locking-in" of evolved microstructure. • Hydrogen effects on plasticity enhanced grain boundary compatibility constraints. • Hydrogen enhanced decohesion and effects on plasticity caused intergranular failure. The fundamental mechanism of hydrogen embrittlement was investigated in the high-entropy alloy FeNiCoCrMn using slow strain rate tensile tests with and without internal hydrogen. Hydrogen induced intergranular failure and reduced the average grain elongation parallel to the tensile axis, but also increased the local plasticity within grains. The influence of hydrogen on plasticity establishes a compatibility constraint across grain boundaries, which results in failure along the hydrogen-weakened grain boundaries. This study is the first to directly confirm the presence of the hydrogen-enhanced compatibility constraint in a high-entropy alloy and highlights the importance of developing a physical understanding of grain-scale interactions.