CHARACTERIZATION OF HOT DEFORMATION-BEHAVIOR OF ZR-2.5NB-0.5CU USING PROCESSING MAPS

The characteristics of hot deformation of beta-quenched Zr-2.5Nb-0.5Cu in the temperature range 650-1050 degrees C and in the strain rate ra nge 0.001-100 s(-1) have been studied using hot compression testing. F or this study, the approach of processing maps has been adopted and th eir interpretation done using the Dynamic Materials Model. The efficie ncy of power dissipation given by [2m/(m + 1)], where m is strain rate sensitivity, is plotted as a function of temperature and strain rate to obtain a processing map. The processing map for Zr-2.5Nb-0.5Cu with in (alpha + beta) phase field showed a domain of dynamic recrystalliza tion, occurring by shearing of alpha-platelets followed by spheroidiza tion, with a peak efficiency of 48% at 750 degrees C and 0.001 s(-1). The stress-strain curves in this domain had features of continuous flo w softening and all these are similar to that in Zr-2.5Nb alloy. In th e beta-phase field, a second domain with a peak efficiency of 47% occu rred at 1050 degrees C and 0.001 s(-1) and this domain is correlated w ith the superplasticity of beta-phase. The beta-deformation characteri stics of this alloy are similar to that observed in pure beta-zirconiu m with large grain size. Analysis of flow instabilities using a contin uum criterion revealed that the Zr-2.5Nb-0.5Cu exhibits flow localizat ion at temperatures higher than 800 degrees C and strain rates higher than about 30 s(-1) and that the addition of copper to Zr-2.5Nb reduce s its susceptibility to flow instability, particularly in the (alpha beta) phase field.