FRACTURE CHARACTERISTICS OF A SUPERPLASTIC SINGLE-PHASE COPPER ALLOY

A superplastic single phase copper alloy exhibits a sigmoidal relationship between strain rate and stress at 823 K, dividing the behaviour into three regions. Maximum elongation to fracture (∼380%) occurs at intermediate strain rates at the lower end of region II, and there is a decrease in total elongation at both low (region I) and high (region III) strain rates. No necking is observed in regions I and II, and there is only very slight necking in region III. Internal cavities are formed at all strain rates, but the appearance of the cavities depends critically on the imposed strain rate. At high strain rates, the cavities are small and lie in strings parallel to the tensile axis; but as the strain rate is reduced the cavities become larger, more rounded, and essentially randomly distributed. The mode of failure is ductile rupture in region III, but void growth and interlinkage become increasingly important with decreasing strain rate. © 1978 Chapman and Hall Ltd.