WC-Co and WC-Co-Cr coatings were deposited on Q345 steel substrates by HVOF and plasma spraying. Coating hardness was measured and corrosion and wear tests were conducted. In terms of hardness and density, the HVOF sprayed WC-Co coating is shown to be superior to its plasma sprayed counterpart. The WC-Co-Cr coatings, on the other hand, exhibited better wear and corrosion resistance, especially the coating produced by HVOF spraying.

In this study, WC-CoWC coatings were produced by HVOF spraying using bimodal-structured WC-Co powder with both micro- and nano-sized WC particles. Due to the melting characteristics of the powder during spraying, the microsized particles are retained in the deposit, but the nanosized particles dissolve into the Co matrix, forming a Co-W-C ternary phase. Compared to coatings sprayed from conventional WC-CoWC powder, the bimodal coatings are more resistant to corrosion and wear and are comparable in microhardness.

Ti and Ti alloys can be applied to the steels as a protective coating in view of its excellent resistance to corrosive environment. Cold spraying as a new surface engineering technique has potential advantages in Ti coating manufacturing in comparison with conventional thermal spraying techniques. Ti coatings were prepared on a carbon steel substrate by cold spraying via controlling the process condition variables concluding carrying gas, temperature and pressure. The microstructure of coatings was observed by SEM. Potentiodynamic polarization experiments were performed to understand the corrosion behavior of the coatings. The SEM examination showed that the coatings become more compact with increase of molecular weight, pressure and temperature of carrier gas. Potentiodynamic polarization technique was used to measure the corrosion and electrochemical property of coatings deposited under different process conditions and surface conditions. The polarization curves indicated that the coatings which had lower porosity had lower corrosion current. The polishing treatment peeled the rough outer layer including the small pores as well as decreasing of the actual surface area of the coating, leading to the considerable improvement of corrosion resistance.

In the present paper, nanostructured, multimodal and conventional WC-12Co cermet coatings were deposited by HVOF and the properties and structures of the coatings such as microhardness, microstructure, phase composition and wear resistance were compared. Finally the wear failure mechanisms of WC-12Co coatings were explored by XRD and SEM analysis. Research results show that microstructures of nanostructured and multimodal WC-12Co coatings deposited by HVOF are dense with little porosity, and their microhardness values are obviously higher than conventional WC-12Co coating. As well, it was found that nanostructured and multimodal WC-12Co coatings exhibited better erosion and adhesive wear resistance in comparison with conventional coating, and nanostructured WC-12Co coatings possessed the best erosion resistance properties at large impact angles and adhesive wear resistance. At small impact angles, WC-12Co coatings deposited by HVOF demonstrate better erosion wear resistance than at large impact angles and the erosion wear performance at 30º is more than 1.7 times higher than at 90º. In comparison with conventional WC-12Co HVOF sprayed coating, the adhesive wear resistance of the nanostructured and multimodal coatings is respectively enhanced by above 70% and 50%. Testing results also show that although decarburization of WC occurred during spraying multimodal and nanostructured WC-12Co powders, the decarburization of WC for the nanostructured powder was more severe.

Several effective numerical techniques, based on finite element analysis, have been developed and computed independently in this paper. Results are presented describing the impacting process, and the subsequent temperature and residual stress fields of a molten nickel particle impacting onto a flat substrate. Problems of this type, especially the prediction of the thermal residual stresses, are of major practical interest in thermal spray operations as a pioneering approach.