Ab initio study of H, He, Li and Be impurity effect in tungsten Σ3{1 1 2} and Σ27{5 5 2} grain boundaries.

Density functional theory calculations were performed to investigate the effect of H, He, Li and Be impurities on the intergranular cohesion of W Σ3〈1 1 0〉{1 1 2} and Σ27〈1 1 0〉{5 5 2} grain boundaries (GBs). A rigorous search of unique interstices was performed to reveal a range of impurity behaviors. It was found that He exhibits the largest defect formation energy, however it is Li that shows the strongest tendency to segregate towards the GBs. The embrittling potency was studied using the ideal GB fracture energy (Rice-Wang) criterion (Rice and Wang 1989 Mater. Sci. Eng. A 107 23). The potency was found to depend significantly on the local atomic environment. A site-dependent concentration was used as the weighing factor to obtain an average potency as a function of temperature. It was found that the potency depends only weakly on temperature. In Σ3 H, He, Li and Be decrease fracture energy by 4%, 27%, 30% and 14%, respectively. In Σ27 H, He and Li also decrease cohesion, albeit less severely: 3%, 14% and 7%. On the other hand, Be increases cohesion in Σ27 by 3%.