The effect of twin–twin interactions on the nucleation and propagation of {101¯2} twinning in magnesium

Electron backscattered diffraction serial image analyses on AM30 magnesium alloy compressed under profuse {101¯2} twinning conditions at different strain levels suggest that twin nucleation and twin propagation rates strongly depend on the number of activated twins in a given grain. This behavior was identified by comparing the twin growth evolution in two grains with roughly the same high Schmid factors for twinning. One grain deformed by a single twin variant, while in the other grain, two intersecting twin variants grew at approximately the same rate. The twin thickening rate was higher in the predominant twinning condition, but the nucleation rate was substantially faster in the two variant twinning condition. The overall volume fraction of twins, however, was approximately the same in both grains, despite the difference in twin microstructure. According to the theory by Christian and Mahajan, there is a higher stress for nucleation than for propagation, and because of the Hall–Petch effect associated with twin segmentation, it is suggested that the grain with two variants should undergo a higher hardening rate than that with a single variant. These observations correspond to some of the most important characteristics of twin–twin hardening, which must be addressed in crystal plasticity simulations.