Tribological Behavior of High-Velocity Oxygen-Fuel-Sprayed NiCrBSi Coatings at Elevated Temperatures

Abstract:

A NiCrBSi coating was fabricated on 304 stainless steel substrate using high-velocity oxygen-fuel (HVOF) spraying. The tribological behavior of the coating was investigated at room temperature (RT), 200 °C, 400 °C, and 600 °C to reveal the effect of elevated temperatures on its wear mechanisms. The effects of temperature on the microstructure and mechanical properties of the coating were analyzed by scanning electron microscope and high-temperature microhardness tester, respectively. The morphology and chemical composition of the wear tracks were characterized using white light interferometer and Raman spectroscope. The results show that the NiCrBSi coating exhibits a distinct crystallization exothermic peak at approximately 505 °C. Above this temperature, the crystallinity and microstructure of the coating are significantly improved. As the temperature increases, both the porosity and microhardness of the coating generally decrease, with a relatively gentle decrease below 505 °C and a sharp drop beyond it. The combined effect of mechanical action between the coating and the counterpart ball and the high-temperature environment induces oxidation during friction, generating oxides such as NiO, Cr₂O₃, and NiCr₂O₄. At temperatures below 505 °C, the high-temperature environment leads to a certain reduction in friction coefficient. With a further increase in temperature, the lubricating effect of the oxides further contributes to the decrease in friction coefficient. Meanwhile, the wear rate of the coating continuously increases with temperature, rising from 2.0×10^-5 mm³/(N·m) at RT to 11.3×10^-5 mm³/(N·m) at 600 °C. At RT, the dominant wear mechanism is fatigue wear. As the temperature increases to 600 °C, the marked decrease in coating microhardness leads to the generation of substantial debris, making abrasive wear the predominant mechanism. In engineering applications, the determination of the amorphous transition temperature of NiCrBSi coatings provides essential data for the design of coating service temperatures and the formulation of heat treatment processes.