Effects of Grain Boundary Characteristics on Its Capability to Trap Point Defects in Tungsten

As recombination centers of vacancies (Vs) and self-interstitial atoms (SIAs), firstly grain boundaries (GBs) should have strong capability of trapping point defects. In this study, abilities to trap Vs and SIAs of eight symmetric tilt GBs in tungsten are investigated through first-principles calculations. On the one hand, vacancy formation energy E_\rm V^\rm f rapidly increases then slowly decreases as the hard-sphere radius r_0 of the vacancy increases. The value of E_\rm V^\rm f is the largest when r_0 is about 1.38 Å, which is half the distance between the nearest atoms in equilibrium single crystal tungsten. That is, any denser or looser atomic configuration around GBs than that in bulk is helpful to form a vacancy. On the other hand, SIA formation energy E_\rm SIA^\rm f at GBs decreases monotonically with increasing the hard-sphere radius of the interstitial sites, which indicates that GBs with larger interstitial sites have stronger ability to trap SIAs. Based on the data obtained for GBs investigated in this study, it is found that the ability to trap Vs increases as the GB energy increases, and the capability of trapping SIAs linearly increases as the excess volume of GB increases. Due to its lowest GB energy and smallest excess volume among all GBs studied, twin GB \sum3(110)111 has the weakest capability to trap both Vs and SIAs.