Effects of precipitation characteristics on the out-of-pile corrosion behavior of niobium-containing zirconium alloys

Abstract

The effects of intermediate annealing temperature on the corrosion behavior of Zr−0.4Nb−0.8Sn−0.3Fe−0.2Cr−0.1Mn and Zr−1.5Nb−0.4Sn−0.1Fe alloys intermediate-annealed at various temperatures were investigated. The relationship between the corrosion behavior and the precipitation characteristics was discussed. A desirable microstructure containing a fine dispersion of second phase particles was obtained by intermediate annealing at a low temperature. Intermediate annealing at higher temperatures resulted in undesirable microstructural features including the precipitation of β-Zr and the coarsening of precipitates. The corrosion resistance of the alloys was apparently degraded with increasing size of the precipitated intermetallic compounds, especially in Zr−1.5Nb−0.4Sn−0.1Fe where β-Zr precipitated on higher-temperature annealing. The corrosion behavior of Zr−1.5Nb−0.4Sn−0.1Fe was more sensitive to intermediate annealing temperature than was that of Zr−0.4Nb−0.8Sn−0.3Fe−0.2Cr−0.1Mn. An examination of particle size distribution revealed that the corrosion behavior of the alloys was dominantly affected by β-Zr larger than the specific size, which is responsible for the difference in corrosion resistance between Zr−0.4Nb−0.8Sn−0.3Fe−0.2Cr−0.1Mn and Zr−1.5Nb−0.4Sn−0.1Fe. It is implied from these results that the optimum corrosion performance of niobium-containing zirconium alloys is achieved by maintaining a uniform distribution of fine second phase particles.