Flow behaviour and microstructural evolution in cold worked 70∶30 α -brass

Abstract

Deformation behaviour and microstructures at failure were investigated in a mill cold worked 70∶30 α-brass over the test temperature range of 298–973 K and strain rate range of 10⁻⁵–5×10⁻³ s⁻¹. Tensile properties as a function of temperature revealed three distinct regions, with their temperature sensitivity being maximum at intermediate temperatures (553–673 K) and much less towards the lower and higher temperature ranges. Two values of activation energy for high temperature deformation Q were obtained to be 117·5 kJ mol⁻¹ below 623 K and 196·4 kJ mol⁻¹ above this critical temperature. In the respective temperature range the values of stress exponent n were 5·6 and 3·8. Based on the values of Q and n, the deformation mechanism was suggested to be dislocation climb creep with a probable contribution from dislocation pipe diffusion on lowering the temperature. Both grain size and cavity size were found to increase with increasing test temperature, suggesting them to be interrelated and act as an alternative steps for accommodating grain boundary sliding. Static grain growth study, over the temperature range of 773 to 1073 K, led to activation energy for grain growth to be 71 kJ mol⁻¹, with the time exponent of 0·37.