Mechanisms of crack propagation in nanoscale single crystal, bicrystal and tricrystal nickels based on molecular dynamics simulation

Abstract

Molecular dynamics simulation was performed in order to investigate mechanisms of crack propagation in nanoscale single crystal, bicrystal and tricrystal nickels, respectively. The grain boundary plays a significant role in the initiation and propagation of crack. As for tricrystal, in particular, a void occurs at the triple junction of grain boundaries and contributes to accelerating the crack propagation. The existence of the grain boundary contributes to the increase of Shockley partial dislocations along with stacking faults. The orientation difference among the grains causes the dislocations to move along different directions in the different slip systems, which lays the foundation for the formation of the crossed or closed Lomer-Cottrell locks. The Lomer-Cottrell locks are able to impede the movement of dislocations and cause the pile-up of dislocations. Amorphous atoms are induced in the region near the Lomer-Cottrell lock. The deformation energy is relaxed when the amorphous atoms are separated one another, which consequently leads to the initiation and propagation of crack.