Properties of oxide layers on Zr alloys

The corrosion stability was studied of Zr alloys in water, water steam and carbon dioxide. The course of oxidation is described with regard to processes taking place at the oxide-metal interface. X-ray diffraction phase analysis of corrosion layers showed that the oxide layer is prevalently formed of monoclinic ZrO2 which sometimes contains traces of tetragonal ZrO2. The amount of tetragonal ZrO2 is higher in Zr-Al, Zr-Sn and Zr-Nb alloys than in Zr-Cu, Zr-Fe, Zr-Cr and Zr-Mo alloys. Electron microanalysis showed that Cu and Ni accumulate at the oxide-metal interface. In Zr-Cr, Zr-Fe and Zr-Mo the additions were present in the oxide in the form of inclusions, in Zr-Al, Zr-Nb and Zr-Sn the additions dissolve well in the oxide and their amount in the oxide corresponds to the initial addition content in the alloy. (J.B.)