Characterization of Staggered Twin Formation in HCP Magnesium

Twins in hexagonal close-packed polycrystals, most often nucleate at grain-boundaries (GBs), propagate into the grain and terminate at opposing GBs. Regularly, multiple parallel twins of the same variant form inside the same grain. When twins terminate inside the grains, rather than the grain boundary, they tend to form a staggered structure. Whether a staggered twin structure or the more common grain spanning twin structure forms can greatly affect mechanical behavior. In this work, the underlying mechanism for the formation of staggered twins is studied using an elasto-visco-plastic fast Fourier transform model, which quantifies the local stresses associated with {10 (1) over bar2}-type staggered twins in magnesium for different configurations. The model results suggest that when a twin tip is close to the lateral side of another twin, the driving force for twin propagation is significantly reduced. As a result, the staggered twin structure forms.