Effect of strain rate and test temperature on superplasticity of a Zr-2.5 wt% Nb alloy

Tensile specimens of a Zr-2.5 wt% Nb pressure tube alloy were deformed at strain rates ((epsilon) over dot) of 3.2 x 10(-4)-2.9 x 10(-2) s(-1) and test temperatures (T) of 625-800 degrees C to investigate the nature of stress-strain curves and the optimum condition for superplasticity. The maximum ductility of 1384%;, was obtained at T=700 degrees C and intermediate strain rate of 3.4 x 10(-3) s(-1). The stress-strain curves were found to exhibit the dominance of flow hardening, especially in the early part of deformation, followed by how softening. The variation inductility and flow stress as a function of test condition is explained by the observed microstructural evolution and fracture behavior. (C) 1999 Elsevier Science B.V. All rights reserved.