Controlling the strength of Zr (10 [formula omitted] 2) grain boundary by nonmetallic impurities doping: A DFT study

Abstract

Impurity segregation even small amounts, can drastically change the cohesive properties of the grain boundaries (GB), eventually leading to intergranular embrittlement and failure of the materials, thereby effectively controlling the types and the concentrations of the impurity is very important. In this work, the nonmetallic impurities (C, H, O, N) segregation and their effects on the strength of Zr (10 1¯ 2) GB were thoroughly investigated using first-principles calculations based on density functional theory. A comprehensive analysis of the interstitial configurations and the relative site energies indicating that C, N and O overwhelmingly prefer the octahedral sites, only H, prefers to reside in the tetrahedral sites. Moreover, the strengthening/embrittlement potency of impurity atoms on the GB was estimated using both the Rice-Wang model and first-principles tensile test calculations. The results show that all impurities, exhibit a strong segregation tendency near the GB region. The segregation of C, N and O has a remarkable strengthening effect on strength of the GB, whereas the presence of impurity H weaken the GB. Most importantly, the underlying mechanism of the strength change of the GBs due to the segregation of impurities was profoundly discussed by charge density and the bond lengths analyses, revealing that the strengthening effect especially for C-doped GB, mainly comes from an enhancement of the charge density across the GB plane. In the end, we expect that our results will be certainly useful for future theoretical and experimental investigations on Zr and its alloys.