THE LINEAR HARDENING OF CADMIUM

Abstract

It has been observed that in polycrystalline cadmium regions of linear hardening insensitive to temperature and strain rate occur at temperatures below 150 °K. The extent of this region increases as the temperature decreases. The hardening coefficients of single crystals are also independent of temperature below 150 °K.The rate of hardening at 77 °K is a function of the grain size and has been shown to vary linearly with the inverse square root of the grain size. The hardening rate obtained on extrapolating [Formula: see text] to zero is that of the tensile hardening rate during stage B deformation of single crystals when the latter is associated with a heavily twinned structure. The grain-size dependence of hardening is due mainly to the amount of [Formula: see text][Formula: see text] slip. It was observed that the Cottrell–Stokes Law is obeyed only in the linear hardening regions. The rate-controlling process is probably one of dislocation intersection with the force–distance curve being independent of grain size. A grain-size dependence of the value of Δσ/σ is interpreted in terms of a change in the relative contributions of the components of the athermal stress τG.