Stress Distribution Measured by Raman Spectroscopy in Zirconia Films Formed by Oxidation of Zr-Based Alloys

摘要

Raman spectroscopy is used to characterize zirconia films formed on Zircaloy-4 and Zr-1percentNb-0.12percentO oxidized in pure water and in water containing 70 ppm of Li as LiOH at 360deg C in an autoclave. Raman spectra of monoclinic and tetragonal zirconia change across the thickness of the oxide films. The use of a high-pressure cell enabled us to calibrate the line frequency variation of monoclinic zirconia with pressure. Thus we obtained the distribution of compressive stress in the zirconia films. By developing a model, it was possible to use the Raman spectra to obtain the distribution of compressive stresses and of the fraction of the tetragonal phase in the oxide films. Using Raman imaging, we showed that tetragonal zirconia is formed in large quantities close to the metal/oxide interface. The distribution of the compressive stresses changes according to the oxidation stage. In the case of Zircaloy-4 oxidation in water containing 70 ppm of Li as LiOH, the appearance of Phase III correlates with the gradual decrease of compressive stresses close to the metal/oxide interface. The level and distribution of the stresses in the zirconia films depend on the chemical composition of the alloy and the oxidizing medium.