Misorientation effect of twist grain boundaries on crack nucleation from molecular dynamics

Abstract

Grain boundaries (GBs) have profound effects on the dislocation motion in materials so as to cause crack nucleation. However, the experimental observation on how the misorientation of twist GBs affects the crack nucleation is scarce. In this paper, we proposed a theoretical model to quantify the dislocation energy per unit length. With it, the critical resolved shear stress at GBs was calculated to assess the crack nucleation. It was found that crack nucleation is significantly influenced by the surface energy, grain boundary energy, system potential energy, boundary stress and misorientation. With the increase of the twist angle, high-angle GBs are more favorable for crack nucleation as general. Interestingly, some specific low-angle GBs possess comparable small critical resolved shear stress as the high-angle GBs and they are favorable for crack nucleation as well. Through the analysis of the resolved shear stress distribution of GBs, it is revealed that the crack nucleation mechanism of these specific low-angle GBs is similar to that of general high-angle GBs. It is inferred that the special low-angle GB systems could generate a crack under a relatively low resolved shear stress.