Comparative Studies on High-temperature Corrosion of ZrNb1 and Zircaloy-4

A comparative study of the oxidation behaviour of ZrNb1 and Zircaloy-4 was carried out in a steam atmosphere in the temperature range from 700-1100 °C. ZrNb1 and Zircaloy-4 are oxidizing approximately according to similar oxidation kinetics. The oxidation rate of ZrNb1 is somewhat lower. It can be described by the equation m = 0.4873 t exp(-10261/T). However, remarkable differences are observed in respect to morphology of the oxide and the O-stabilized -layer, hydrogen uptake, and both the fraction and distribution of the oxygen dissolved in the metal. Above all the rapid drop in ductility by exposure to steam is of significance under safety aspects. Differences in the thermodynamic conditions for equilibrium of the ternary systems Zr-0-Nb and Zr-0-Sn may provide an appropriate explanation of these differences.