Activation Analysis of Plastic Deformation of BCC Metals Using Stress and Temperature Jumps

Abstract

The activation volume, γ, and the enthalpy of activation, AH, for dislocation motion in bcc metals, were obtained using new indirect methods - stress jump (σ-jump) and temperature jump (T-jump) during dynamic loading on a testing machine. These methods are based on calculation of the ratios of the plastic strain rates when the samples undergo pulse loading (σ-jump method) and pulse heating (T-jump method). In these cases the mobile dislocation density ρ=const can be considered a good approximation and the ratios of plastic strain rates are equal to those of dislocation velocities. Pulse loading that can be obtained during T-jump due to thermal expansion makes it possible to get the enthalpy of activation at zero stress and the long range internal stress, σ-jump method is also used for dislocation velocity-stress exponent, m, determination. The experiments were performed at room temperature on Nb and V single crystals and Nb, V, Ta and Mo polycrystals. The parameters obtained are compared with those that were obtained from direct dislocation velocity measurements (Nb, Mo) and from other indirect methods.