Evaluation of oxidation behavior of laser clad CoWSi-WSi2 coating on pure Ni substrate at different temperatures

Microstructural aspects of CoWSi-WSi2 coating on pure Ni and its oxidation performance under cyclic heating and cooling conditions in air at 900, 1100 and 1300 °C have been studied. The coating was applied by laser cladding process. The microstructure evaluations demonstrated that a uniform free cracks coating formed which was metallurgically bonded to the substrate. XRD and EDS analysis results showed that the coating consisted of CoWSi, WSi2 and γ-Co. The mass gain/unit area versus oxidation time plot for all the samples was parabolic indicating that the oxidation process was diffusion-controlled. The structure of scales depended on oxidation temperatures; at 900 °C, a dense scale layer consisting of SiO2 and small amounts of WO3 and CoO, at 1100 °C, a characteristic scale structure, namely a mixed layer structure and at 1300 °C, the dense oxide scale enrichment of SiO2 and porous interdiffusion layer with low oxygen concentration was formed.