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

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 3(111), 3(112), 5(210) and 5(310) 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 5(210) GB most and that of the 3(111) least. Detailed analyses of solute-GB chemical interactions are conducted using electron localiza-tion 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. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

Thermal annealing or radiation induced segregation of solute and impurity elements to grain boundaries in metallic alloys changes GB chemistry, affecting the cohesive strength. Solute elements show varying effects on GB strength, with C and P causing embrittlement while Cr and Ti strengthening GBs. Detailed chemical interactions between solutes and Ni atoms at GBs play a significant role in determining GB strength.