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 7 00-1100-degrees-C. ZrNb1 and Zircaloy-4 are oxidizing approximately ac cording to similar oxidation kinetics. The oxidation rate of ZrNb1 is somewhat lower. It can be described by the equation DELTAm = 0.4873 sq uare-root t exp(- 10261/T). However, remarkable differences are observ ed in respect to morphology of the oxide and the O-stabilized a-layer, hydrogen uptake, and both the fraction and distribution of the oxygen dissolved in the metal. Above all the rapid drop in ductility by expo sure to steam is of significance under safety aspects. Differences in the thermodynamic conditions for equilibrium of the ternary systems Zr -O-Nb and Zr-O-Sn may provide an appropriate explanation of these diff erences.