Corrosion behavior of Zr alloys with a high Nb content

The corrosion behavior of the Zr alloy with a high Nb content was evaluated in the water loop system containing 2.2 wppm Li and 650 wppm B. The characteristics of the precipitates were analyzed by transmission electron microscopy (TEM) and the oxide was characterized by an X-ray diffraction method using a synchrotron radiation source. On the basis of the results obtained by these measurements, the relationship among the oxidation behavior, the precipitate characteristics and the oxide properties was discussed. It was shown that the Cu addition was of benefit to the corrosion resistance of the Zr alloy with a high Nb content and the corrosion resistance of the Cu-containing alloy (Zr-1.5Nb-0.5Sn-0.2Fe-0.1Cu) was superior to that of the Cr-containing alloy (Zr-1.5Nb-0.5Sn-0.2Fe-0.1Cr). The fine β-Nb precipitates were found more frequently in the Cu-containing alloy than the Cr-containing alloy when heat-treated in the same condition. The fraction of the tetragonal zirconia in the region of the metal/oxide interface was higher in the Cu-containing alloy than the Cr-containing alloy, suggesting that the stabilization of the tetragonal phase in the oxide was promoted more when the smaller precipitates are incorporated into the oxide. It is concluded that the fine distribution of β-Nb is desirable for stabilizing the tetragonal phase in the oxide, thereby increasing the corrosion resistance of the Zr alloy with a high Nb content.