Hydrogen–Grain Boundary Interaction in Fe, Fe–C, and Fe–N Systems

Abstract

Highly accurate predictions of hydrogen’s influence on material strength and development of materials with minimal\rhydrogen effects are essential to prevent failure under various hydrogen environments. Here, we investigated the\rinfluence of misorientation angle and solute elements (carbon and nitrogen) on the cohesive energy of <110> symmetrical\rtilt grain boundaries (STGBs) in bcc Fe under a gaseous hydrogen environment by using density functional\rtheory. We found a good correlation among GB energy, GB free volume, and the hydrogen concentration at GBs under\rhydrogen environments: high-energy GBs have large gaps, and many hydrogen atoms are captured at these spaces.\rThus, higher-energy GBs are more influenced by hydrogen. It is also shown that the binding energy between hydrogen\rand a GB is negligible when nitrogen or carbon atoms exist at the GB at their solubility limit. Therefore, carbon\rand nitrogen atoms exclude hydrogen atoms from GBs and improve the cohesive energy of GBs under hydrogen environments.