Oxidation behaviour and properties of carbide ceramic reinforced Ni-based composite coatings at 700 °C

To improve the wear and corrosion properties of the coatings, WC-12Co and Cr3C2-25NiCr carbide ceramic reinforced Ni-based coatings were prepared, and pre-oxidation of the coatings was performed under 700 degrees C. Subsequently, the microstructure and properties of the coatings were analysed. The results demonstrated that the microstructure of the pre-oxidised coating was more uniform and denser than that of the as-sprayed raw coating, and the porosity was significantly decreased. Meanwhile, an oxide film was formed on the surface of the pre-oxidised coating, and its phases were mainly Cr2O3 and NiCr2O4. The corrosion rate of the pre-oxidation sample coating was approximately 83.18 mm/a, which was decreased by approximately 50 % over that of the as-sprayed raw sample coating (166.4 mm/a). This is because the formation of the oxide film prevents the corrosive medium from invading the interior of the material, and various atoms fully diffuse during the preoxidation heat treatment of the coating. Simultaneously, owing to the formation of the oxide film and the strengthening of the phase boundary, the wear damage of the pre-oxidised coating is mainly a fatiguing fracture due to the strengthening of the binder and the phase boundary, and the wear mechanism changes from bonding phase extrusion and rapid removal of the traditional coating to the slow expansion of fatigue cracks and the reduction in the wear loss of the coating owing to the formation of the oxide film.