Characterization of hot deformation behaviour of Zr-2.5Nb in β phase

Hot deformation characteristics of beta Zr-2.5wt%Nb in the temperature range 1225-1425 K and in the constant true strain rate range of 0.002-10 s(-1) were studied by uniaxial compression testing in vacuum. A processing map using the strain rate sensitivity parameter was developed for beta Zr-2.5Nb on the basis of flow stress data as a function of temperature and strain rate for a given strain. A domain of high strain rate sensitivity of 0.5 at 1375 K and 0.002 s(-1), was obtained and the grain size in this domain was large and equiaxed, suggesting the occurrence of large grain superplasticity. Thermal activation analysis was employed to determine the experimental activation volume and enthalpy, from which it was suggested that the rate controlling mechanism involved the movement of dislocation jogs. A comparison of Zr-2.5Nb with Zr in beta phase suggested that Nb shifts the domain peak to higher temperatures. (C) 2002 Elsevier Science B.V. All rights reserved.