Instead of using 2 semi-infinite crystals when calculating the grain-boundary energy (Read-Shockley approach) and the driving force for untwisting, equally spaced grain-boundary dislocations were used which moved on the (001) boundary plane; with the dislocations closest to the surface being pulled out by the image force. Experimental results on crystallite rotation in face-centered cubic Au were used to investigate the mobility of grain-boundary dislocations. Two types of grain-boundary dislocation motion (viscous, thermally activated) were tested. The observed motions of the grain-boundary dislocations during untwisting could be described only as being thermally activated. The Hirth-Lothe approach, which involved a thermally activated process that overcame the Peierls barrier, was used to describe the mobility of grain-boundary dislocations during untwisting into the 5 cusp minimum, and the mobility of lattice dislocations {100}<110> during untwisting into the 1 cusp minimum. The Peierls barrier, to grain-boundary dislocation motion that was confined to the glide plane of the (001) boundary, was significantly higher than that for lattice dislocation glide on {111} planes. On the basis of the untwisting rates, the energy barriers to grain-boundary dislocation motion were estimated to be 1.69eV for 1 and 1.84eV for 5 [001] twist boundaries. The results explained the high yield stress, and associated sharp temperature dependence, which were observed during the plastic deformation of nano-particle compacts of face-centered cubic metals.

Mobility of Grain Boundary Dislocations during the Untwisting of Twist Boundaries. S.W.Chan, V.S.Boyko: Physical Review B, 1996, 53[24], 16579-86