Microstructural evolution in adiabatic shear bands in Ta and Ta-W alloys

Microstructural evolution of adiabatic shear bands originated due to high s train, high strain rate deformation in Ta and Ta-W alloys has been examined . Tests were performed using a specially designed stepped specimen in a Hop kinson bar. Upon completion of the deformation, the region is cooled to bel ow one half of the temperature achieved during adiabatic heating in less th an one millisecond. Microstructural characterization of the shear bands was performed using optical microscopy as well as scanning and transmission el ectron microscopy. No evidence of recrystallization within the shear bands could be found. This is in contradiction with several recent reports, which claim that recrystallization may take place at these stringent time and te mperature conditions. These studies, however, do not take into account the kinetics of boundary refinement processes, which are a distinctive characte ristic of a recrystallized microstructure. It will be shown that the absenc e of recrystallization in Ta and Ta-W adiabatic shear bands can be predicte d by a progressive subgrain misorientation (PriSM) recrystallization model, applied successfully in previous studies to predict the microstructure evo lution in copper adiabatic shear bands. (C) 2001 Acta Materialia Inc. Publi shed by Elsevier Science Ltd. All rights reserved.