This work describes novel mechanisms of interaction between dislocations and twin boundaries with nanoscale plate-shaped precipitates, with a thickness equivalent to a few atomic layers, in magnesium alloys. A combined approach including micromechanical testing of micropillars milled by focused ion beam within grains with selected orientations, and high resolution transmission electron microscopy, is put in place to unveil such mechanisms at the atomic scale.<br/><br/>It is shown, first, that basal dislocation movement leads to the dissolution of the ultrathin precipitates in the nearby regions (within 80 nm) and to room temperature solute diffusion resulting in microsegregation and hardening of the active slip planes, thus preventing slip localization and premature fracture. Second, this work demonstrates that twin-precipitate interactions are dependent on the twin boundary plane. In particular, the passage of coherent twin boundary segments across precipitates leads to elastic rotations of the former, while the interaction of prismatic-basal segments with precipitates leads to precipitate shearing.

Atomic interactions of dislocations and twin boundaries with nanoscale precipitates in magnesium alloys

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