Grain size dependence of the deformation behaviour of cadmium

Abstract

The grain size dependence of the yield and flow stresses of cadmium in the temperature range 77–298 K has been investigated by combining Hall-Petch analysis with thermal activation strain rate analysis. Results from temperature cycling tests showed that the Hall-Petch intercept σ 0 ε is essentially athermal in nature, while the Hall-Petch slope K ε contains in addition to the thermal component of flow stress a contribution from the athermal component also. Activation areas were determined from strain rate change tests and were found to vary linearly with the square root of the grain size. σ 0 ε was found to increase with strain at all temperatures. At 77 and 196 K, the Hall-Petch slope K ε was found to first increase with strain, pass through a maximum at 7 per cent strain at 77 K and at 4 per cent strain at 196 K and then decrease with strain. At 255 and 298 K, K g3 was found to decrease continuously with strain. Both σ 0 ε and K ε were found to decrease with increase in temperature. The variations in σ 0 ε and K ε with strain and temperature have been examined in the light of the various physical models for the Hall-Petch equation.