The activation energies for plastic flow in a superplastic copper alloy

Abstract

A superplastic copper alloy, which is nominally single phase, exhibits a sigmoidal relationship between strain rate and stress dividing the behavior into three regions. Only a very small amount of primary creep occurs in the low stress region I and the intermediate stress region II, and temperature cycling experiments show that the activation energies are independent of the total strain within the extended steady-state region. The activation energies are ∼ 179 kJ mol −1 in region I and ∼ 144 kJ mol −1 in region II, and these values are similar to those anticipated for lattice and grain boundary diffusion, respectively. The activation energy in the high stress region III is ∼ 159 kJ mol −1, suggesting that grain boundary sliding occurs to an appreciable extent in this region in addition to an intragranular dislocation creep process.