Study of the Influence of Detonation Spraying Parameters on the Structure and Properties of Self-Fluxing Coatings of the Ni–Cr–Fe–Si–B–C System

This study investigates the influence of detonation spraying parameters on the microstructure, mechanical properties and tribological performance of self-fluxing Ni–Cr–Fe–Si–B–C coatings deposited on AISI 321 stainless steel substrates. The effects of the barrel filling ratio (48–68%), the oxygen-to-fuel molar ratio (O/C = 1.026–1.856), and the delay time between detonation shots (0–1 s) were systematically evaluated. The coatings were characterized using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), microhardness measurements, instrumented indentation, and ball-on-disk tribological testing. Microstructural investigations revealed that the spraying parameters significantly influence coating thickness, porosity and defect formation. The lowest porosity (0.306 per cent) and the most homogeneous microstructure were obtained at a barrel filling ratio of 48 per cent, an O/C ratio of 1.026 and a shot delay of 1 s. XRD analysis identified a multiphase structure consisting of a Ni3Fe matrix reinforced by Cr7C3 carbides, Ni3B and CrB borides, and Ni31Si12 silicides. Tribological tests demonstrated that increasing the delay between shots significantly improved wear resistance, reducing the wear rate to 1.89 × 10−4 mm3/(N × m). The optimised coating exhibited an average coefficient of friction of 0.578 ± 0.093 and a wear rate of 1.03 × 10−4 mm3/(N × m). Instrumented indentation revealed a hardness of 1049.1 ± 43.4 HV and a Young’s modulus of 215.9 ± 8.5 GPa. The wear mechanism was predominantly abrasive–adhesive, whilst the wear rate of the 100Cr6 counter-body remained low at 1.20 × 10−5 mm3/(N × m). The results obtained demonstrate that appropriate optimisation of detonation spraying parameters enables the formation of dense Ni–Cr–Fe–B–Si–C coatings with superior mechanical and tribological properties, making them promising candidates for wear-resistant engineering applications.