Impurity effect on recrystallization and grain growth in severe plastically deformed copper

The impurity effect on commercial purity copper (4 N and 3 N) was investigated by comparing their annealing induced recrystallization and grain growth behavior after severe plastic deformation. Equal channel angular pressing (ECAP) with additional cryogenic rolling was applied to produce equiaxed ultra-fine grained (UFG) and nano-laminated (NL) coppers with high stored excess energy. The stored excess energy increased with decreasing purity from 4 N to 3 N, whereas the grain boundary velocity and recrystallized grain size decreased for both UFG and NL Cu. In particular, the NL structures were found to be more sensitive to impurities than equiaxed ultra-fine grained ones, and consequently the abnormal grain growth at the early stages of recrystallization in NL 4 N Cu was effectively suppressed in NL 3 N Cu. The analysis of the grain growth rate during recrystallization, using the microstructural path methodology (MPM), demonstrates that the correlation between the abnormal grain growth and the significantly enhanced grain boundary mobility cannot be solely explained by the high stored excess energy. Under all conditions, the impurity drag effect poses a kinetic constraint on the rate-controlling mechanism for grain boundary migration.