Effect of Heat Treatment on Microstructure Characteristics of Hot Worked Zr-2.5Nb Alloy Tubes

Abstract Characterization and analysis techniques including XRD, FEG-SEM with attached EBSD detector, TEM with attached EDS detector were employed to investigate the microstructure characteristics of a Zr-2.5Nb alloy tube. The samples as received from the hot worked tube were treated under 550°C/5.5h annealing, and 850°C/1h solution heat treatment followed by 550°C/5.5h aging (SAHT) respectively. Hardness test was also performed for predicting of the strength changes. Results show that there was residual β-Zr existed in the hot worked tube, and after annealing at 550°C, decomposition of the residual β-Zr in the hot worked tube happened and the low angle grain boundaries reduced. There is no obvious texture memory effect after solution at 850°C flowed by water quenching, however the effect can be well observed after aging at 550°C. Nb-rich second phase particles appeared during aging process, with their locations near the boundaries inside primary a grains. Hardness of the hot worked tube didn’t show obvious change after annealing, while after solid solution and aging treatment (SAHT), the hardness increased significantly both in LD and TD directions.