Special grain boundaries in zirconia corrosion films

Transmission electron microscopy (TEM) studies of the oxide film on the sur face of a zirconium alloy have been performed and the crystallography of in terfaces has been analysed. Regions of a peculiar microstructure consisting almost entirely of twins have been discovered in the zirconia film. The TE M results have been analysed in conjunction with the known texture data, an d the orientation relationships between monoclinic ZrO2 and the alpha-Zr su bstrate are discussed. Computer simulation has been performed to reveal the possible grain boundary character distributions in different regions of th e film. The relevance of the results obtained to the diffusion properties o f the surface zirconia layer is discussed in this paper. It is suggested th at a high concentration of special grain boundaries hinders transport throu gh the zirconia film.