Effect of Cr Addition on Microstructure and Corrosion Behavior of Zr-0.3Nb Alloy in 400 C/10.3 MPa Superheated Steam

Zr-0.3Nb-xCr(x=0.2, 0.5, 1.0, wt%) alloys were prepared and then corroded in 400 degrees C/10.3 MPa superheated steam in an autoclave. 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. Results show that the second phase particles in the Zr-0.3Nb-xCr alloys are face centered cubic and hexagonal close-packed ZrCr2 phase with a size in a range of 10 similar to 100 nm. With increasing the Cr content, the size of second phase particles is nearly unchanged, but their number is 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 is relatively better when 0.5wt% Cr is 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.