Аңдатпа
This study investigates the effect of oxygen pressure on the structural-phase state, microstructure, mechanical properties and tribological behavior of Zr(C,N)-based coatings deposited on U8G tool steel by high-velocity oxygen fuel (HVOF) spraying. The coatings were produced at oxygen pressures of 4.0 × 10 5 , 4.3 × 10 5 and 4.5 × 10 5 Pa, while the spraying distance, propane pressure and air pressure were kept constant. Variation in oxygen pressure was found to affect the relative XRD peak intensities, Rietveld-refined phase fractions, diffraction-line broadening parameters, coating thickness, porosity and tribological response. However, since the coatings exhibited differences in thickness, the interpretation of XRD intensity variations was performed with consideration of possible thickness-related effects and substrate contribution. X-ray diffraction and Rietveld refinement indicated the formation of a multiphase Zr(C,N)-based system containing carbonitride, carbide, nitride, oxide and α-Fe phases. The coating deposited at 4.3 × 10 5 Pa showed the most favorable combination of Zr(C,N)-type phase retention, reduced oxide fraction, low apparent cross-sectional porosity and relatively uniform microstructure. Williamson–Hall analysis suggested the largest coherent scattering domain size of approximately 82 nm and the lowest microstrain of approximately 0.30% for this condition, although these values should be considered as comparative estimates due to partial overlap of Zr 2 CN, ZrC and ZrN reflections. SEM/EDS analysis showed that the coating obtained at 4.3 × 10 5 Pa had the most homogeneous distribution of Zr, C and N and relatively low oxygen content. This coating also exhibited the highest microhardness (1826 ± 38.4 HV 0.5 ), the highest apparent pull-off adhesion strength (18.4 MPa) and the lowest friction coefficient (μ ≈ 0.54 ± 0.01). Quantitative wear assessment according to ASTM G99 showed that this coating had the lowest wear volume and specific wear rate among the investigated samples. SEM examination of wear tracks suggested a correlation between oxygen pressure, coating morphology and wear-track features; however, direct post-wear chemical analysis of the tribofilm would be required to confirm the detailed wear mechanisms. Overall, the results indicate that an oxygen pressure of 4.3 × 10 5 Pa provides the most balanced coating characteristics under the investigated HVOF conditions.