Effects of Bi on microstructure and corrosion behavior of Zr-1 Nb alloy in 500 °C/10.3 MPa superheated steam

The effects of Bi on the microstructure and corrosion behavior of Zr-1 Nb alloy in superheated steam at 500 °C/10.3 MPa were investigated. Results revealed that addition of trace amount of Bi improved the corrosion resistance of Zr-1 Nb alloy. Based on the experimental and DFT calculation results, we propose that the reduction of micro-pores and micro-cracks in the oxide film is mainly attributed to Bi3+ stabilizing the tetragonal phase and reducing the volume expansion of the tetragonal→monoclinic phase transition. Meanwhile, Bi can improve the proportion of columnar grains by delaying the microstructural evolution from columnar grains to equiaxed grains.