Zr–Nb Alloys and Its Hot Deformation Analysis Approaches

Abstract

Zr and its alloys are considered as strategic materials for nuclear industry. In nuclear industries, zirconium and its alloys are mostly used to manufacture the tubes for reactors. The properties of the end component i.e. tube is fully dependent on the material processing route and the final microstructure. Therefore, in the present review paper, brief description of zirconium and its alloys is provided, bringing in the effect of various phase stabilizers and the microstructures after processing. Additionally, the processing route of Zr and Zr–Nb alloys are explained in terms of primary and secondary processing. In primary processing, the production of usable shapes is obtained through ingot melting followed by secondary operations such hot rolling or forging. Further, optimization of mechanical properties can be done by controlling the microstructure using various thermo-mechanical processes. The secondary processing such as cold working and/or annealing also helps to control the final microstructure to large extent. The microstructure control is fully dependent on the dominant deformation mechanism during the hot deformation. The dominant deformation mechanism depends on relative ease with which following processes occur; dislocation generation and glide, cross slip and climb and, diffusion. The possible restoration mechanisms for different Zr-alloys are discontinuous dynamic recrystallization (DDRX), continuous dynamic recrystallization (CDRX), rotational recrystallization (RRX), geometric dynamic recrystallization (GDX), dynamic recovery (DRV) accompanied by grain growth (GG). There are various techniques which helps to understand the hot deformation behaviour of any material. These techniques are; analysis of stress–strain data, development of processing maps, development of constitute equation. At the end, present paper summarises the work related to processing map, findings of processing map in terms of safe processing parameter, dominant deformation mechanism, role of activation energies during deformation of Zr–Nb alloys and their different phases (i.e. single α or β phase, or two phase α + β).