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 beta-annealing conditions. Specimens of Zr-1.5Nb-0.4Sn-0.2Fe-0.1Cr alloy were investigated in order to obtain their optimized beta-annealing conditions such as the beta-annealing temperature and the cooling rate from the beta-region. From the microstructural analysis, the prior beta-grain size of this alloy was increased by increasing the beta-annealing temperature. The martensitic structure was formed by a fast cooling rate of a water quenching from a range of 960-1200 degrees C and the Widmansatten structure was formed by a slow cooling rate of an air cooling from 1050 degrees C. The corrosion behavior of the Zr-1.5Nb-0.4Sn-0.2Fe-0.1Cr alloy was not affected by the beta-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 beta-Zr phase. However, the formation of the beta-Zr phase is not recommended in the P-solution annealing procedure of Nb-containing Zr-based alloy, because the aim of the P-solution annealing is to obtain a good homogeneity. (C) 2007 Elsevier B.V. All rights reserved.