Effect of Cr on microstructure and corrosion behavior of Zr-0.3Nb alloy in 400 ℃/10.3 MPa superheated steam

Abstract:

Zr-0.3Nb-xCr (x=0.2, 0.5, 1.0 wt.%) alloys were prepared and corroded in 400 ℃/10.3 MPa superheated steam in an autoclave, and the microstructures of the alloy matrix and oxide film were characterized using SEM and TEM, in order to investigate the effect of Cr on the microstructure and corrosion behavior of Zr-0.3Nb alloy. It was found that the second phase particles in the Zr-0.3Nb-xCr alloys were face centered cubic and hexagonal close-packed ZrCr₂ phase with a size in a range of 10~100 nm. By increasing the Cr content, the size of second phase particles was nearly unchanged, but their number was increased. Appropriate Cr addition to the Zr-0.3Nb alloy could promote the growth of columnar crystals in the oxide film and delay the transformation from columnar crystals to equiaxed crystals, thereby improving the corrosion resistance of the Zr-0.3Nb alloy. The corrosion resistance was relatively better when 0.5 wt.% Cr was added to the Zr-0.3Nb alloy. This may be due to the compact oxide film and the presence of a sub-oxide layer at the oxide/metal interface, which could delay the microstructure evolution of the oxide film and thus improve the corrosion resistance of the Zr-0.3Nb-0.5Cr alloy.

Key words:Zirconium;alloys, Cr;addition, super-heated;steam corrosion, oxide;film, microstructure