Alloying effects on sulphur embrittlement of the γ-γ′ interface of nickel-based single-crystal superalloys

Fully first-principles calculations have been performed to investigate the alloying effect on the sulphur embrittlement of the n - n ' interface of nickel-based single-crystal superalloys. The shear and cohesive strengths of the inter-face are calculated in terms of Mayer bond orders (BOs), and the ratio R BO of shear strength over cohesive strength is analysed as a function of alloying element substitution. The interface characteristics are also studied using the electron charge-density distribution. It is found that the interplay between shear and cohesive strengths has a significant influence on the interfacial embrittlement. Using the phenomenological theory of fracture as well as the calculated ratio R BO, we propose a new mechanism responsible for relieving sulphur embrittlement of the n - n ' interface through alloying substitution.