First-principles study of grain boundary embrittlement in Fe–Ni–S alloy

Grain boundary embrittlement due to grain boundary co-segregation of Ni and S atoms in face-centered cubic iron is examined for the (2 2 ¯ 1)Σ9[1 1 0] grain boundary by first-principles calculation. The phenomenon whereby the addition of Ni accelerates grain boundary embrittlement is reproduced for different concentrations of S at the grain boundary. With low concentrations of S, the cohesive energy of the grain boundary is reduced by Ni addition, while Ni addition leads to a steep reduction in binding energy as grain boundary separation increases with high concentrations of S. The mechanism of the embrittlement is related to repulsive interaction between S atoms induced by occupation of anti-bonding states between S atoms.