Investigations of the yield region of concentrated CuGe and CuZn single crystals—I. Critical resolved shear stress, slip line formation and the true strain rate

Abstract

Measurements of the critical resolved shear stress τ and of formation times t B of slip bands for alloy single crystals of Cu containing 0.44–7.3% Ge and 30% Zn, respectively, at different deformation temperatures ( T= 77–400 K) and deformation rates ( i = 8 × 10 −5–3.5 × 10 −1 mm/s) are reported. The dependence of τ on solute concentration c varies between c 1 2 and c 2 3 depending on T and c; Basinski's ‘stress equivalence’ of alloy hardening appears to be fulfilled up to the high concentrations used, t B increases less than proportional to 1 i ; t B increases with decreasing T and decreasing c. The concepts of the true strain rate a ̇ and the active slip volume V a are outlined and connected with measurable quantities, a ̇ and V a are significant for determination of thermal activation parameters from strain rate and temperature changes.