Microstructure and corrosion characteristics of Zr–1.5Nb–0.4Sn–0.2Fe–0.1Cr alloy with a β-annealing

The corrosion characteristics of Zr-based alloys are very sensitive to their microstructures which are determined by the β-annealing conditions. Specimens of Zr–1.5Nb–0.4Sn–0.2Fe–0.1Cr alloy were investigated in order to obtain their optimized β-annealing conditions such as the β-annealing temperature and the cooling rate from the β-region. From the microstructural analysis, the prior β-grain size of this alloy was increased by increasing the β-annealing temperature. The martensitic structure was formed by a fast cooling rate of a water quenching from a range of 960–1200 °C and the Widmanstätten structure was formed by a slow cooling rate of an air cooling from 1050 °C. The corrosion behavior of the Zr–1.5Nb–0.4Sn–0.2Fe–0.1Cr alloy was not affected by the β-annealing temperature but it was changed by the cooling rate. The increased corrosion resistance was caused by a decreased the supersaturated Nb content in the matrix by a formation of the β-Zr phase. However, the formation of the β-Zr phase is not recommended in the β-solution annealing procedure of Nb-containing Zr-based alloy, because the aim of the β-solution annealing is to obtain a good homogeneity.