Distinct nitriding behaviors of γ and γ′ phases in Ni-based superalloys: A first-principles study

• Published in: Journal of alloys and compounds 2022-11, Vol.920, p.165996, Article 165996
• Main Authors: Hao, Lu-Yao, Wen, Xu-Zhong, Lei, Xiao-Wei, Yao, Wen-Jing, Wang, Nan
• Format: Article
• Language: English
• Subjects: Diffusion; First principles; Gamma-prime phase (crystals); Nickel; Nickel aluminides; Nickel base alloys; Nitriding; Nitrogen; Nitrogen atoms; Superalloys
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2022.165996

The diffusion of nitrogen through γ(Ni)/γ'(L12-Ni3Al) interface in Ni-based superalloys was investigated based on first-principles calculations and the different nitriding behaviors of γ matrix and γ' precipitate were determined. At the interface, nitrogen atoms prefer to occupy the 6-Ni octahedral interstitial site with a large physical volume rather than the octahedral site constituted by Ni and Al with good chemical affinity. This indicates that γ matrix can provide more trapping sites for nitrogen atom than γ' precipitate. Moreover, the migration energy barrier of N crossing the (002)γ/γ' coherent plane is higher than that in γ phase. Nitrogen atoms can move into γ' phase unless the diffusion front has higher nitrogen concentration and O4 * (5Ni-Al octahedral site) is occupied. Inside the γ' matrix, nitrogen atoms are also easily trapped by the 6-Ni octahedral interstitial site, but their escape rates are much lower. It is the potential barrier role of the (002)γ/γ' coherent plane and the low diffusion ability of N in γ' that are responsible for the unfavorable nitriding behavior of γ' phase in Ni-based superalloys.