Recrystallization kinetics within adiabatic shear bands

Small recrystallized grains (0.1-0.2 mu m diameter) are observed to form in adiabatic shear bands of shock-prestrained copper. However, the mechanism for recrystallization under the high strain, high-strain-rate conditions within shear bands is somewhat unclear. The kinetics of two classical mechanisms for recrystallization, high angle boundary migration and subgrain coalescence, are compared with the time-temperature profile determined for these adiabatic shear bands. It was found that the kinetics of the existing models are inadequate to explain the observed grain sizes, with the kinetics being several orders of magnitude slower than the deformation time and/or the cooling time of the shear bands. Tests conducted at liquid nitrogen temperature also demonstrated that temperature did not play a major role in dynamic recrystallization under these circumstances. A dynamic recrystallization model is suggested in which mechanically-driven subgrain relations assist the mechanism for recrystallization. This approach may enable dynamic recrystallization to proceed at very high strain rates, with only limited thermal assistance. Copyright (C) 1997 Acta Metallurgica Inc.