First-principles investigation of grain boundary structure effects on hydrogen solubility and segregation in tungsten

Abstract

ABSTRACT Hydrogen (H) solubility, segregation, and hydrogen-induced intergranular fractures in eight symmetric tilt grain boundaries (GBs) in tungsten (W) are investigated through the first-principles calculations. The results show that there is an equilibrium distance, about 1.95 Å, between the H inserted in interstitial sites and its nearest W. Interactions between the inserted H and GBs are rather localized, thus the local environments of interstitial sites are responsible for the hydrogen solubility. The hydrogen solution energy decreases as the hard-sphere radius of the interstitial site increases. But the trend slows significantly down as the is larger than 0.57 Å, which is corresponding to the equilibrium H-W distance of 1.95 Å, due to the ignorable contributions from lattice distortions induced by the inserted H to the hydrogen solution energy. It is found out that the GBs with smaller interstitial site are more resistant to hydrogen segregation as well as the hydrogen-induced intergranular fractures. Among all GBs studied here, the twin GB ∑3(110)[111] has the smallest interstitial site; hence, it has the weakest capability to trap H and it is also the most resistant to hydrogen-induced intergranular fractures. Our results provide a sound guide to design GBs to suppress hydrogen-induced intergranular fractures.