A microstructural examination of the flow behaviour of a superplastic copper alloy

There are important differences in the microstructures of specimens of a superplastic Cu alloy (CDA 638, Cu--2.8Al--1.8Si--0.4Co) deformed in the three regions of flow associated with superplasticity. There is very extensive dislocation activity at high strain rates in Region III, whereas at intermediate and low strain rates in Regions II and I the dislocation density is low and many of the grains appear to be dislocation free. Measurements show that grain-boundary sliding is important in Region II but decreases in magnitude in the less superplastic Regions I and III. 27 ref.--AA