Impact of grain boundary character on grain rotation

The capillarity-driven shrinkage of isolated cylindrical grains with structurally different grain boundaries in aluminum was studied by molecular dynamics simulations. Three pairs of grains with 〈1 0 0〉 tilt and mixed tilt-twist boundaries with the misorientation angles θ0 = 5.45°, 16.26° and 22.61° were examined. The simulation results showed that the shrinkage of grains with pure tilt boundaries was accompanied by their rotation towards higher misorientation angles. On the contrary, grains with the mixed boundaries did not rotate significantly during their shrinkage. An analysis revealed that for the observed rotational behavior the grain boundary structure is crucial. In contrast to pure tilt boundaries composed of edge dislocations, for mixed tilt-twist boundaries, which are composed of intersecting dislocations with the mixed edge-screw character, the effective mechanisms of dislocation annihilation are available, which allow the respective grains to shrink without rotation.