Strain-influenced hydrogen segregation in polycrystalline nickel

Abstract

Interstitial hydrogen at grain boundaries (GBs) can significantly compromise material strength, leading to catastrophic intergranular fracture. However, the intricate interaction between hydrogen and GBs remains inadequately understood, particularly under complex external loading conditions. In this study, we use atomistic simulations and a geometrical algorithm to elucidate the hydrogen segregation energy spectrum at the GBs of polycrystalline nickel under various loading strategies. Three distinct peaks are identified in all spectra, with segregation energy decreasing under increasing tensile loading. Four types of loading—triaxial compression, uniaxial tension, uniaxial straining, and triaxial tension—are applied, with triaxial tension causing the most dramatic spectrum shift. Notably, a linear relationship between hydrogen segregation energy and local volume change is established for the first time. This relationship reveals that hydrogen solution is almost exclusively determined by local volume change, irrespective of the loading conditions. Uniquely in the spectrum of the uniaxial tension case, a fourth peak emerges, signifying a group of super-trapping sites formed through early-stage dislocation-GB interactions. These findings underscore the distinguishable impact of both elastic and plastic deformation on hydrogen distribution in polycrystals. Furthermore, hydrogen diffusion coefficients are derived through mean square displacement analysis, revealing the hydrogen diffusivity in the lattice and GBs under various loading conditions. This study provides critical insights into hydrogen embrittlement in polycrystalline materials, essential for developing more resilient hydrogen storage and transport systems.