Formation of intracrystalline deformation twins in austenitic Mn-steel at the early stage of plastic deformation

In austenitic Mn-steels with low stacking fault energy, the deformation twin is known to play an important role in plastic deformation. Usually, the position grain boundary is preferred to observe and investigate the formation process of the deformation twin, while other suitable formation positions may be neglected. Here, high-resolution transmission electron microscopy is used to observe and characterize the formation of intracrystalline twins in 120Mn13 steel at the early stage of tensile plastic deformation at the atomic scale. The result shows that intracrystalline twins nucleate through overlapping stacking faults generated by three different perfect dislocations dissociating on consecutive {111}-type planes, which is different from twin nucleation mechanisms that have been proposed. Subsequently, they become large-sized intracrystalline twins or twin bands throughout the whole grain by twin nuclei growing themselves and connecting to adjacent twin nuclei or existing twins in the same growth direction. Intracrystalline twins are mainly formed in three positions, namely near the grain boundary, at the end or side of existing twins. The stacking fault sources of intracrystalline twins at different positions are different.