EVALUATION OF MECHANICAL PROPERTIES OF PLASMA SPRAYED MIXTURE OF PARTIALLY STABILIZED ZIRCONIA AND TUNGSTEN CARBIDE ON LOW CARBON STEEL

摘要

Industries such as aerospace, automotive, oil and gas utilize various chemical, thermal, and mechanical techniques to improve the surface properties of engineering components. Deposition of metallic or nonmetallic materials on the surface of engineering components using different thermal spraying techniques is a common method to improve the mechanical properties of the surface of the components working at severe conditions. Thermal spraying techniques are capable of deposition of a coating layer with high corrosion, wear, erosion, and high temperature resistance. This technology can also be used for surface repair and treatment. Zirconia (ZrO_2) based coatings are excellent candidates to serve at high temperature due to their tribological and insulation properties, and also high stiffness. ZrO_2-based coatings are usually used in aircraft and gas-turbine engines as thermal barrier coatings. However, the relatively low wear and erosion resistance of Zirconia-based coatings limits their application. Among all coating materials, Tungsten Carbide (WC) based materials are commonly used to improve wear and corrosion resistance of the surface. It is speculated that combination of ZrO_2 and WC follows by generating a coating with desirable thermal and mechanical properties, particularly at high temperature conditions. In the presented work, an innovative thermally sprayed coating material was proposed by depositing mixture of ZrO_2-Y_2O_3 and WC-Ni (YPSZ/WC-Ni) powders on a low carbon steel substrate using Atmospheric Plasma Spraying (APS). As thermo-mechanical properties of coatings are under the influence of the microstrucrural features such as porosity, micro cracks, voids, and possible oxides, in this study microstructure and phase consistency of the resultant coating was briefly evaluated. To this end, Optical Microscopy, Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDX) were used. The results indicated that deposited coating was well-bonded to the substrate with minimum observed separation line. Porosity amount of APS deposited YPSZ/WC-Ni measured by image analysis of the cross-sectional area Moreover, mechanical properties including hardness and elastic modulus of the coating were evaluated. Since thermally sprayed coatings exhibit anisotropic behavior, the Knoop hardness in the longitudinal and transverse directions were analyzed in this study. Elastic modulus of the coating was also evaluated, based on the measurement of elastic recovery of Knoop indentation in both directions using Marshal analytical model. Wear resistance of the coating was also investigated by pin-on-disk method, at room temperature. The friction coefficient of the consecutive coating was calculated and had a value lower than that of reported for APS deposited YPSZ.