Quantitative estimation method of the effect of segregated solute on hydrogen-enhanced decohesion at a grain boundary

Hydrogen-enhanced decohesion (HEDE) is a proposed mechanism of hydrogen-induced grain boundary (GB) fracture in metals and has been widely calculated from first principles over the past decade. However, the effect of GB-segregated solutes on HEDE is complex and rarely quantified. This study presents a quantitative numerical estimation method based on statistical thermodynamics using first-principles calculations of multiple hydrogen trappings at a GB and its fracture surfaces with segregated solutes. This method accurately estimates the lattice-dissolution-hydrogen-dependent HEDE, including the interactions caused by the segregated solute: the decohering or cohesion-enhancing effect of the solute itself, solute-hydrogen interaction, solute-affected hydrogen-hydrogen interaction, and mobile hydrogen effect. We present a trial calculation to examine how the attractive interaction between solute and hydrogen influences HEDE, showing that HEDE can be induced at lower hydrogen concentrations if not canceled by other interactions.