The microstructures of the oxide layers formed on near(0001) plane of Zircaloy-4 were investigated by autoclave tests at 360 °C in lithiated aqueous solution. Oxygen-rich regions with hcp structure were observed at the undulating O/M interface, and the inner surface morphology of the oxide layers formed on(0001) was only concave–convex. Monoclinic, tetragonal and cubic phases and a kind of zirconium sub-oxide with bcc structure were detected in the oxide layer near the metal matrix. This zirconium sub-oxide layer had a coherent relationship with α-Zr matrix, and the growth direction of the zirconium sub-oxide layer was nearly parallel to the [0001] direction of α-Zr regardless of the orientation of metal matrix. The orientations scattering of columnar grains formed on near(0001) plane differ from that formed on near(10ī0) plane.
