Microstructure of Zr-Nb Alloy Cladding Oxide Flim

The microstructure of the oxide film of Zr-Nb alloy cladding was studied by optical microscopy, X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM). The results showed that microcracks with different orientations were distributed on the surface of the oxide film of Zr-Nb alloy, including vertical and transverse cracks. The vertical cracks could provide a fast path for the diffusion of oxygen ions. TEM results showed that the oxide film was mainly composed of columnar and equiaxed monoclinic ZrO₂, The existence of equiaxed monoclinic ZrO₂ grains near the interface of zirconium alloy matrix/oxide film was closely related to cracks, large grain size and intragranular twinning. Due to the lattice expansion caused by residual stress, the interplanar spacing of monoclinic ZrO₂ increased about 0.4%.