Influence of alloying additions on grain boundary cohesion of transition metals: First-principles determination and its phenomenological extension - art. no. 165415

The toughness and ductility of ultrahigh-strength alloys is often limited b y intergranular embrittlement, particularly under conditions of unfavorable environmental interactions such as hydrogen embrittlement and stress corro sion cracking. Here we investigated the mechanism by which the segregated s ubstitutional additions cause intergranular embrittlement. An electronic le vel phenomenological theory is proposed to predict unambiguously the effect of a substitutional alloying addition on grain boundary cohesion of metall ic alloys, based on first-principles full-potential linearized augmented pl ane-wave method (FLAPW) calculations on the strengthening and embrittling e ffects of the metals Mo and Pd on the Fe grain boundary cohesion. With the bulk properties of substitutional alloying addition A and the matrix elemen t M as inputs, the strengthening or embrittling effect of A at the grain bo undary of M can be predicted without carrying out first-principles calculat ions once the atomic structure of the corresponding clean grain boundary is determined. Predictions of the embrittlement potency of a large number of metals, including the 3d, 4d, and 5d transition metals, are presented for t he Fe Sigma3 (111) and the Ni Sigma5 (210) grain boundaries. Rigorous FLAPW calculations on the effect of Co, Ru, W, and Re on the Fe Sigma3 (111) gra in boundary and Ca on the Ni Sigma5 (210) grain boundary cohesion confirm t he predictions of our model. This model is expected to be applicable to oth er high-angle boundaries in general and instructive in the quantum design o f ultrahigh-strength alloys with resistance to intergranular fracture.