Influences of Nb on Impurity C Distribution in Surface and Oxide Film of Zirconium Alloys

Abstract:

Zr-0.75Sn-0.35Fe-0.15Cr-xNb alloys were investigated, and static autoclave tests were conducted in deionized water at 360 ℃ and 18.6 MPa for 580 d. Secondary ion mass spectrometry was employed to characterize the concentration gradient distribution of carbon from the oxide film surface to the oxide/matrix interface, and X-ray photoelectron spectroscope was used to analyze the valence states of carbon on the substrate surface. The experimental results show that the C concentration in the oxide film on the rolling surface (S_N) of the Zr-0.75Sn-0.35Fe-0.15Cr alloy was significantly higher than that on the surface perpendicular to the transversal direction (S_T). Adding 0.15wt% Nb can considerably decrease the C concentration in the oxide film and reduce the difference in carbon concentration distribution among oxide films on different surfaces. The C/Zr ratio on the S_N surface of the Nb-free alloy increases more obviously with the rise of temperature, suggesting a potential competitive relationship between Nb and Zr in C binding. In conjunction with experimental observations of corrosion anisotropy of the Zr-0.75Sn-0.35Fe-0.15Cr alloy, this study explored the relationship between C and anisotropic corrosion from the perspective of the effects of Nb on impurity C distribution.