Microstructure and Dry-Sliding Tribology of Thermal-Spray Coatings on Cu for Continuous Casting Molds

The low hardness of copper alloys, which are the substrate material used for continuous casting molds, makes them prone to plastic deformation, wear, and high-temperature oxidation, leading to premature failure and the formation of surface defects on billets. In this work, the microstructure, phase composition, mechanical, and tribological properties of Cr3C2–NiCr coatings deposited by high-velocity oxy-fuel (HVOF) spraying onto copper substrates used in molds were investigated. This research was driven by the need to extend the service life of copper molds in continuous steel casting processes. It was established that spraying parameters have a decisive influence on porosity, coating thickness, microhardness, and friction behavior under conditions simulating billet contact with the working surface of the mold. Among the investigated regimes, the coating deposited at a powder feed rate of 11.39 m/s exhibited a dense lamellar structure and the highest level of microhardness. Tribological tests confirmed that this coating exhibited the lowest coefficient of friction, whereas the other coatings were characterized by higher porosity and poorer wear resistance. Thus, the results emphasize the necessity of optimizing spraying parameters to develop highly effective HVOF protective coatings for copper molds operating under extreme thermomechanical loads during steel casting.