(Fig. 3-b), it is observed that the cracks are perpendicular to the surface. It has been reported that these cracks increase thermal shocks resistance and are expected to be beneficial for accommodating the oxidation and the mismatch stresses [30].
Fig. 4 shows the XRD patterns of the APSed YSZ and the laser clad layer. Pattern (a) belongs to the YSZ which indicates the presence of t′-ZrO2 crystal structure, a common phenomenon after plasma spraying of YSZ. As seen in pattern (b) (The XRD pattern of the Al2O3 laser clad layer), the dense layer contained t′-ZrO2 and the rhombohedral phase of Al2O3. This pattern confirms the formation of in situ Al2O3-YSZ composite with the thickness of about 45 mm on the top of the sprayed YSZ. This composite probably is formed due to the partial melting of the YSZ layer and mixing with molten alumina during laser cladding. To prove formation of the Al2O3/ZrO2 composite layer, Grazing Incidence X-ray Diffraction was utilized (Fig. 4-c).