High Temperature Oxidation Kinetics of Zr-Sn-Nb Alloy and the Effect of Its Oxide Film Growth On Corrosion Resistance

Abstract

Zirconium-based alloys are widely used for fuel claddings particularly in pressurized water reactor. The high temperature oxidation kinetics of Zr-Sn-Nb alloys in steam in the temperature range of 650°C∼1250°C are studied by a modified thermo-gravimetric analyzer. The oxidation rate exponents and oxidation correlation are calculated. The rate transition of kinetic oxidation for Zr-Sn-Nb occur at 1100°C. The microstructure characteristic of the oxide film formed at 1200°C indicated that the oxide layer is constituted of nanometer exquiaxed grains on the outer surface, columnar grains along perpendicular to the O/M interface and quaisi-equxiaxed grains near the O/M interface. The thickness, crystal distribution and grains size of each layer is measured and analyzed. Furthermore, the correlation among the tetragonal phase fraction, the stress, and the microstructural change of the oxide film is schematized and then analyzed. How to obtain the intact columnar grains structures in the oxide and uniform protective oxide film formation are the key to improve the corrosion resistance of zirconium alloys.