On migration and faceting of low-angle grain boundaries: Experimental and computational study

The motion and faceting behavior of low-angle 〈1 0 0〉 tilt and mixed tilt-twist boundaries was investigated. The experiments were conducted on high-purity (99.999%) aluminum bicrystals by utilizing an in situ technique for the observation and continuous recording of boundary migration. In contrast to pure tilt boundaries, the mixed boundaries were found to readily assume a curved shape and steadily move under the capillary driving force. This behavior is associated with the inclination dependence of boundary energy, which was determined for tilt and mixed boundaries by molecular statics simulations. The shape evolution and shrinkage kinetics of cylindrical grains with different tilt and mixed boundaries were studied by molecular dynamics simulations. The mobility of low-angle 〈1 0 0〉 boundaries with misorientation angle >10°, obtained by both the experiments and simulations, does not differ from that of the high-angle boundaries, but decreases essentially with the further decrease of misorientation. The shape evolution of the embedded grains was found to relate directly to results of the energy computations. Further simulation results revealed that the shrinkage of grains with pure tilt boundaries is accompanied by grain rotation. In contrast, grains with the tilt-twist boundaries composed of dislocations with the mixed edge-screw character do not rotate as they shrink.