Orientation-controlled Cu bicrystals, containing [001] symmetrical tilt boundaries aligned parallel to the loading axis, were deformed in tension at 923K at a strain rate of 4.2 x 10-4/s. The nucleation of dynamic recrystallization was investigated along the grain boundary. For this purpose, both optical and orientation imaging microscopy methods were used. After grain-boundary migration and bulging, nuclei appeared behind the most deeply indented grain boundary regions. The critical strain for nucleation was about one-quarter to one-half of the peak strain, and depended upon the misorientation angle. All of the nuclei were twin-related (Σ3) to the matrices. Moreover, all of the primary twin traces were parallel to those of the inactive slip planes of the parent single crystals. Crystallographic analysis revealed the important role of the direction of grain-boundary migration in twinning-plane variant selection. The characteristics of grain-boundary nucleation depended sensitively upon grain-boundary character and mobility. The observed dynamic recrystallization nucleation mechanism was considered with regard to the occurrence of grain-boundary migration and twinning.

Nucleation of Dynamic Recrystallization and Variant Selection in Copper Bicrystals. H.Miura, T.Sakai, R.Mogawa, J.J.Jonas: Philosophical Magazine, 2007, 87[27], 4197-209