Effects of local stress on the stability of tetragonal phase in ZrO2 film

An in-depth understanding of the phase stability in ZrO2 film is very important for improving the corrosion resistance of zirconium alloys. ZrO2 film formed on Zr–2.5Nb alloys was characterized by grazing incidence X-ray diffraction. It is shown that in comparison to the monoclinic phase crystallites, the tetragonal phase crystallites undergo larger compressive strain, indicating that there are some regions of local stress concentration in ZrO2 film. These local stresses have an important influence on the phase stability in ZrO2 film. In this paper, the correlation among the macroscopic compressive stress, the grain size and the local stress was analyzed qualitatively from a thermodynamic viewpoint, showing that the tetragonal phase may be partly stabilized by the local stresses. The local stresses mainly come from three sources: the local transformation strain produced by the tetragonal → monoclinic phase transformation, the oxidization of intermetallic precipitates and the different matching degrees between the ZrO2 and Zr-based crystallites.