Annealing studies on Zr-1Nb and Zr-1Nb-1Sn-0.1Fe alloys

Abstract

This paper summarizes the experimental results of microstructure development and mechanical properties of two types of zirconium alloys, namely, the quaternary Zr-1Nb-1Sn-0.1 Fe and the binary Zr-1Nb. Both these alloys and their derivatives are finding increasing applications as fuel tube materials and have the potential for meeting the requirement of high burn up fuel. This is reflected in the current international literature. It has been recognized that the level of tin required for imparting necessary corrosion resistance to zirconium based alloys can be brought down to about 1 % from the level of 1.5 % as in Zircaloy-2. The synergy of Sn and Nb additions is also known to be beneficial for both mechanical properties and aqueous corrosion behavior of zirconium alloys. Microstructural studies on these alloys after different thermomechanical processing have revealed the shape, size distribution and the nature of precipitate phases, the extent of recrystallization of the matrix hcp α grains the factors which are expected to have strong effects on both short term mechanical behavior and long term performance during service. The distribution of β _II particles in Zr-1Nb is of significance in the context of both mechanical and corrosion properties. The optimized fabrication condition has been found to generate the desired precipitate distribution in Zr-1Nb. Annealing studies on these alloys have been carried out. The annealed microstructure and morphology of constituent phases and precipitates have been studied in detail. Tensile properties of these alloys in different temperatures are also discussed. Microstructural features of hydrides formed in Zr-1Nb alloy are also reported.