Effect of annealing conditions on the microstructure and corrosion characteristics of Zr-xNb alloys

Most of the advanced Zr-based alloys contain Nb for improving the corrosion resistance. However, the Nb effect on the corrosion behavior of Zr alloys has not been established. For developing fuel cladding materials, it is essential to investigate the effect of the Nb-content and annealing conditions after beta quenching on the microstructure and the corrosion of Zr-xNb alloys. In this study, a systematic investigation to obtain the optimized annealing condition and Nb content were performed for Zr-xNb alloys (x = 0.1 similar to 2.0 wt.%). The corrosion resistance of 0.1 and 0.2 wt.% Nb alloys where Nb existed in an equilibrium soluble state in the matrix was excellent in the quenched and annealed conditions. For the high Nb-containing alloys, the corrosion rates were very sensitive to the annealing condition, and it took about 50 hours at 570 degrees C to reach the corrosion rates comparable to those of the low Nb wt.% alloys. The corrosion resistance was closely related to the stabilization of the tetragonal ZrO2 and the columnar oxide structure when the Nb concentration in the matrix was reduced to the equilibrium soluble limit.