Zonal dislocations mediating {101-bar1} 101-bar 2-bar twinning in magnesium

摘要

The twin boundary (TB) interfacial structure and the configuration of zonal twinning dislocations for {1 0 1-bar 1} twin growth in magnesium have been investigated by using molecular dynamics simulations and transmission electron microscopy (TEM). The simulation results show that twin growth is initially dominated by the motion of existing TB steps. After these steps, the twin growth is mediated by the nucleation and glide of new zonal dislocations at the TBs. The steps and the twinning dislocations have Burgers vectors of 1b_T, 2b_T and 4b_T, where b_T = 1/4 centre dot 1/2 is the Burgers vector of the elementary twinning dislocation. The favorable zonal dislocation is 2b_T, which can be viewed as the 1/2 centre dot 1/2 matrix dislocation spreading over two {1 0 1-bar 1} layers to accomplish the twinning relationship across the TB. The connection established between the twinning and the dislocation slip in the matrix is supported by TEM observations.