Effect of Nb on He segregation behavior in NiΣ5 grain boundary: First-principles study

摘要

The segregation of He at the grain boundary (GB) significantly affects the application of Ni-based alloys in the nuclear industry. However, the influence mechanism of other elements on the segregation of He at Ni GB is still unclear. Therefore, first-principles calculation was used to investigate the segregation behavior of He at Ni Sigma 5 GB with various Nb segregation concentration. We found that Nb atoms tend to replace the site "1" at Ni Sigma 5 GB, and Nb atoms can weaken the segregation tendency of He atoms at the Ni Sigma 5 GB gap. The charge density results show that the segregation of He atoms causes the Ni Sigma 5 GB to expand, and the Ni(2)-Ni(-2) bonds weaken so that the tensile strength decreases significantly. When Nb atoms are at Ni GB, strong Nb-Ni(4) bonds and Nb-Ni(-4) bonds are formed. Therefore, the GB remains strong enough when the Ni(2)-Ni(-2) bonds break. The results are helpful to the optimum design of Ni-based alloy.