Barrier Properties of Cr/Ta-Coated Zr-1Nb Alloy under High-Temperature Oxidation

In this paper, Cr (8 mu m)/Ta (3 mu m) bilayer coatings deposited on a Zr-1Nb alloy substrate were investigated and compared with a Cr-coated alloy under high-temperature steam oxidation at 1200-1400 degrees C. The bilayer coatings with alpha- and beta-Ta interlayers were obtained by magnetron sputtering. The Cr/Ta-coated samples were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), and optical microscopy (OM). The coating with an alpha-Ta interlayer can suppress the interdiffusion of chromium and zirconium more effectively up to 1330 degrees C in comparison with the coating having a beta-Ta interlayer. The weight gain of the alpha-Ta-coated samples after oxidation at 1200 degrees C for 2000 s was 5-6 times lower than that of the Cr-coated Zr alloy samples. Oxidation at 1400 degrees C for 120 s showed no significant difference in the weight gain of the Cr- and Cr/Ta-coated Zr-1Nb alloy samples. It was shown that the effect of suppression of Zr-Cr interdiffusion by the barrier coating (alpha- and beta-Ta) is only short-term.