Influence of Water Vapour on the Zircaloy-4 Oxidation at 700 °C: Stress Determination by In Situ X-ray Diffraction

Abstract

Zircaloy-4 was oxidized in dry and wet air (15 vol% H2O) at 700 °C. At high temperature and at room temperature, X-ray diffraction shows that the oxide scale is composed of monoclinic zirconia (m-ZrO2) and quadratic zirconia q-ZrO2. In dry and wet air, growth stress was determined in situ at 700 °C on the m-ZrO2. In dry air, results showed that the compressive growth stress in the oxide oscillates between −1300 ± 100 and −600 ± 100 MPa. In wet air, compressive growth stress varied from −1000 ± 100 to −400 ± 100 MPa during the 20 first hours of oxidation. Then, the stress level remained constant (−400 ± 100 MPa). In dry air, stress oscillations can be explained by successive growth stress increases in the growing scale and stress relaxation by perpendicular cracks propagation. The growth stress relaxation process in wet air is related to a higher zirconia grain size.