Studying the Hot Deformation Behavior of Zr-1Nb Alloy Using Processing Map and Kinetic Analysis

The hot deformation process significantly affects the performance of the manufactured Zr alloy components in nuclear reactors. The hot deformation behavior of the Zr-1wt.% Nb alloy with an initial β -quenched microstructure was evaluated using hot compression test at the temperature range of 600-950 °C and the strain rate range of 0.001-0.8 s −1 . The constitutive equation was determined using kinetic analysis. The strong effect of Nb on decreasing self-diffusion in Zr was the reason for the obtained large activation energy of 390 kJ/mol in the Zr-1Nb alloy. Based on the dynamic material model, the processing map was constructed at the strain of 0.8 to show the stable and unstable hot deformation regions. The microstructural features of the hot deformed samples were observed using optical and scanning electron microscopes. The results indicated that the hot deformed microstructures were fully recrystallized so that the grain size of the as-received microstructure of the Zr-1Nb alloy was reduced from 1 mm to less than 4 μm after hot deformation at 800 °C. The optimum region in the hot deformation of the Zr-1Nb alloy with dynamic recrystallized microstructure and the peak efficiency of 40% was located at the temperature range of 675-775 °C and the strain rate range of 0.001-0.01 s −1 . On the other hand, flow localization and macro-surface cracking occurred within the strain rate range of 0.1-0.8 s −1 .