Correlation between microstructure and corrosion behavior of Zr–Nb binary alloy

To investigate the correlation between microstructure and corrosion characteristics of Zr–Nb alloy, the microstructural observation and corrosion test with the change of cooling rate from beta temperature and the variation of Nb content were performed. The oxide characterization was also carried out by synchrotron XRD and TEM. When the Nb is contained less than solid solution limit (0.6 wt%) in Zr matrix, the difference of corrosion rate was not observed in spite of showing the significant changes of microstructures with cooling rate. While, when the Nb content in the alloy is more than 0.6 wt%, the corrosion properties were deteriorated with increasing the supersaturated Nb concentration in matrix and increasing the area fraction of βZr. Also it was observed that the supersaturated Nb in matrix was more effective to decrease the corrosion resistance than the βZr phase in the same Nb containing alloy, while the equilibrium Nb concentration below solubility limit in the matrix played an important role to enhance the corrosion resistance. During the corrosion testing in steam at 400 °C, the formation of βNb phase in water-quenched specimen would result in the reduction of Nb concentration in matrix. Thus, the corrosion resistance is enhanced with the formation of βNb phase. It is suggested from this study that the equilibrium Nb concentration below solubility limit in α matrix would be a more dominant factor in the enhancement of corrosion resistance than β phase (βNb or βZr), supersaturated Nb, precipitate, and internal microstructure such as twin, dislocation and plate.