Influence of Fe content on corrosion and hydrogen pick up behavior of Zr-2.5Nb pressure tube material

The effects of Fe addition in the range of 300-1250 ppm in cold worked stress-relieved Zr-2.5Nb pressure tube on oxidation and hydrogen pick up behavior have been studied after 415 °C steam autoclaving. Microstructure and micro-chemistry of second phase and precipitates were characterized using electron microscope. Addition of 800 ppm Fe in Zr-2.5Nb alloy led to better oxidation resistance. With further addition of Fe no significant improvement of oxidation resistance was observed but hydrogen-pickup was found to increase. Zr-Nb-Fe bearing precipitates were observed in Zr-2.5Nb alloy containing 800 ppm Fe. Further addition of Fe led to formation of Zr-Fe intermetallic. The chemical state of oxide has been determined by X-ray photo electron spectroscopy. Grazing Incidence X-ray Diffraction revealed that oxide in alloys with higher Fe, contained a higher fraction of tetragonal-Zirconia which is indicative of a protective oxide film and hence better oxidation resistance of the alloy.