Atomistic Simulation Study of Cohesive Energy of Grain Boundaries in Alpha Iron under Gaseous Hydrogen Environment

Abstract

Highly accurate prediction of material strength under a practical hydrogen environment and development of materials with minimal hydrogen effect are essential for safe use of hydrogen energy. Here, we estimated the relationship between grain boundary (GB) properties and GB cohesive energy under gaseous hydrogen environment for <110> symmetrical tilt GBs and <001> twist GBs in alpha iron using atomistic simulations. We employed the embedded-atom-method (EAM) potential developed by Wen et al. and conjugate gradient (CG) method for structure relaxation. First, we estimated the relationship between GB energy and GB free volume for various misorientation angles. After the estimation of GB properties, we incorporated a hydrogen atom into various occupation sites and obtained the distribution of hydrogen trap energy around the GBs. We found a good correlation among GB energy, GB free volume, and the number of trapped hydrogen atoms: high energy GBs have large gaps, and many hydrogen atoms are trapped in those spaces. Finally, we estimated the GB cohesive energy and found that there is negligible hydrogen influence on the low energy GBs. The reduction of the GB cohesive energy of Σ3{112} boundary was estimated to be only 6.61% under high-pressure hydrogen environment (T = 300K, p = 70MPa).