Formation mechanism of co-axial grain boundaries in a Mg alloy

Abstract

Due to the insufficient slip systems in hexagonal close-packed structure, twinning is frequently activated to support stable plastic deformation of Mg alloy. In this work, we found four typical twin-like interfaces with misorientations of 102°, 109°, 142° and 149°, respectively, which had not only a shared [11 2 ¯ 0] zone axis of neighboring grains, but also overlapped diffraction spots similar to twins. However, high-resolution transmission electron microscope (HRTEM) analysis revealed that the interfaces in real space deviated from the supposed twinning planes in reciprocal space, i.e. their overlapped diffraction spots. We clarified that the incoherent interfaces were co-axial grain boundaries (CGBs). Additionally, a special angle of θ , close to 90°, between the interface and one side of basal plane, was frequently formed in CGBs. We proposed that interaction of multiple twinning contributes to the formation of CGBs, and the θ is formed due to alternative tensile and compression twinning under a uniaxial loading.