First principle studies of effects of solute segregation on grain boundary strength in Ni-based alloys

Abstract

Thermal annealing or radiation induced segregation of solute and impurity elements to grain boundaries (GBs) in metallic alloys changes GB chemistry and thus can alter the GB cohesive strength. In this work, first principles based density functional theory calculations are conducted to study how the segregation of substitutional solute and impurity elements (Al, C, Cr, Cu, P, Si, Ti, Fe, which are present in Ni-based X-750 alloys) influences the cohesive strength of Σ3111,Σ3112,Σ5210 and Σ5310 GBs in Ni. It is found that C and P show strong embrittlement potencies while Cr and Ti can strengthen GBs in most cases. Other solute elements, including Si, have mixed but insignificant effects on GB strength. In terms of GB character effect, these solute and impurity elements affect the GB strength of the Σ5210 GB most and that of the Σ3111 least. Detailed analyses of solute-GB chemical interactions are conducted using electron localization function, charge density map, partial density of states, and Bader charge analysis. The results suggest that the bond type and charge transfer between solutes and Ni atoms at GBs may play important roles on affecting the GB strength. For non-metallic solute elements (C, P, Si), their interstitial forms are also studied but their effects on GB strength are weaker than their substitutional counterparts.