Grain boundary decohesion by impurity segregation in a nickel-sulfur system

Yamaguchi, Masatake   ; Shiga, Motoyuki   ; Kaburaki, Hideo

Sulfur-induced embrittlement of nickel has long been wrapped in mysteries why and how sulfur weakens the grain boundaries of nickel and why a critical intergranular sulfur concentration is required. From first-principles calculations, we found that a large grain boundary expansion is caused by a short-range overlap repulsion among densely segregated and neighboring sulfur atoms. This expansion results in a drastic grain boundary decohesion that reduces the grain boundary tensile strength by one order of magnitude. This decohesion may directly causes the embrittlement since the critical sulfur concentration of this decohesion agrees well with experimental data of the embrittlement.