Nucleation and growth mechanisms of nanoscale deformation twins in hexagonal-close-packed metal magnesium

A theoretical model is suggested to describe the dislocation-mediated mechanisms for the nucleation and growth of nanoscale deformation twins in hexagonal-close-packed materials. In the framework of the model, the nanoscale deformation twins nucleate and grow through the glide of glissile Shockley partial dislocations which are generated due to the nonplanar dissociation of the leading dislocation in a pile-up of 〈a〉 slip dislocations on the basal plane. Here, the pile-up of 〈a〉 dislocations on the basal plane was produced by preceding plastic deformation processes. The energy and stress conditions of the nanoscale deformation twin nucleation and growth through the dislocation-mediated mechanisms are calculated and discussed in detail. The results indicate that, when the pre-existent pile-up on the basal plane is 10-5, the nanoscale deformation {1¯012} twin nucleation stress is about 466.97-519.51 MPa. If take the shear stress applied to the pre-existent dislocation pile-up into account, the results are consistent with the experimental and molecular dynamic simulation results in literature. Besides, the twin is connected to grain boundary, and the longitudinal section of the twin is an approximately rectangular shape.