The mechanical properties of a superplastic quasi-single phase copper alloy

The mechanical properties of a superplastic quasi-single phase copper alloy, containing a cobalt-rich dispersion, are essentially identical to those of superplastic eutectic and eutectoid alloys. Points of similarity include a sigmoidal relationship between stress and strain rate dividing the behavior into three regions, activation energies which are similar to lattice and grain boundary diffusion in the low stress region I and the intermediate stress region II, respectively, and an inverse dependence on grain size raised to the power ~ 2.2–2.6 in regions I and II. In addition, experiments in the high stress region III indicate an approximately inverse dependence on grain size and activation energy which is intermediate between the values obtained in regions I and II. The results suggest that region III is due to an intragranular dislocation process with a concomitant contribution from grain boundary sliding. Identical creep curves are obtained in regions I and II with a very brief primary stage and an extended steady-state behavior, whereas the creep curves in region III exhibit a significantly longer primary stage.