Strain gradient crystal plasticity of hydrogen pressure assisted deformation and dislocation evolution in micro porous high entropy alloys

Abstract Hydrogen embrittlement constitutes one of the primary challenges to the safe service of CrMnFeCoNi high entropy alloys in hydrogen-bearing environments. As a key mechanistic contributor to hydrogen embrittlement, the mesoscale evolutionary behavior arising from the coupling between hydrogen pressure and microscopic defects remains insufficiently understood in a systematic and quantitative manner. Conventional crystal plasticity generally does not explicitly describe dislocation evolution associated with strain gradients. In the present work, a finite element model grounded in strain gradient crystal plasticity theory was established, incorporating a two-dimensional polycrystalline representative volume element comprising 50 randomly oriented grains, to systematically examine the void size effect and the associated mesoscale mechanical responses under hydrogen pressure conditions. Three representative loading scenarios were considered: pure mechanical uniaxial tension, pure hydrogen internal pressure loading, and combined tension hydrogen pressure loading. A void-free baseline model was further introduced under the pure mechanical condition to facilitate systematic comparison of the mesoscale mechanical characteristics among models containing circular voids of different diameters subjected to all three loading cases. Here we use a strain-gradient crystal plasticity framework to investigate how pore size, tensile loading, and pre-imposed internal hydrogen pressure affect the local mechanical response and dislocation density evolution of high-entropy alloys.