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

• Published in: Fusion engineering and design 2020-05, Vol.154, p.111549, Article 111549
• Main Authors: Wang, Shen, Xiong, Jun, Zeng, Qiang, Xiong, Min, Chai, Xiaosong, Li, Da
• Format: Article
• Language: English
• Subjects: Bonding strength; Charge density; First principles; First-principles study; Grain boundaries; Grain boundary; Ni-based alloy; Nickel base alloys; Niobium; Segregation of He; Tensile strength
• ISSN: 0920-3796; 1873-7196
• DOI: 10.1016/j.fusengdes.2020.111549

•With the increase of Nb atoms at NiΣ5 GB, the segregation energy of He atoms increases.•The Nb atom causes a slight expansion of the GB, but the Nb-Ni(4/-4) bonds are significantly strengthened.•When the Ni(2)-Ni(-2) bond breaks, the Nb-Ni(4/-4) bonds remain connected. 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 NiΣ5 GB with various Nb segregation concentration. We found that Nb atoms tend to replace the site “1” at NiΣ5 GB, and Nb atoms can weaken the segregation tendency of He atoms at the NiΣ5 GB gap. The charge density results show that the segregation of He atoms causes the NiΣ5 GB to expand, and the Ni(2)-Ni(-2) bonds weaken so that the tensile strength decreases significantly. When Nb atoms are doped 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.