Ex-reactor corrosion and oxide characteristics of Zr-Nb-Fe alloys with the Nb/Fe ratio

The effects of different Nb and Fe addition ratios on the microstructure, corrosion and oxide characteristics of Zr-based alloys were investigated. The Nb/Fe ratio was controlled to be 0.6, 1.0, 1.7, 3.0, and 7.0 with the same amount of Nb + Fe in each alloy. The microstructural analysis and precipitate characterization were performed to obtain the correlation between the corrosion and the microstructures. The grain size and the area fraction of the precipitate in all the tested alloys were almost the same even though the Nb/Fe ratio was considerably changed. But the mean diameter and the crystal structure of the precipitates were affected by the variation of the Nb/Fe ratio. In the alloy with a low Nb content, the FCC-(ZrNb)2Fe precipitate was mainly formed while the HCP-Zr(NbFe)2 precipitate was frequently observed in the alloy of with a high Nb content. The corrosion resistance of the Zr-xNb-yFe ternary alloys was improved by decreasing the Nb/Fe ratio. From the microstructure and corrosion studies, it seems that the corrosion resistance would be more closely related to the crystal structure of the precipitate rather than the other properties such as the size distribution and the density of the precipitates