The Effect of Deposition Rate on Microstructural Evolution in WC-Co-Cr Coatings Deposited by High-Velocity Oxy-Fuel Thermal Spray Process

Tungsten carbide-reinforced cermet composites are widely used as wear- and erosion-resistant coatings due to their combination of hardness, strength, toughness and thermal properties. In this study, WC-Co-Cr coatings were deposited using high-velocity oxy-fuel thermal spray technology under different kinematic spray parameters. The microstructure of coatings was investigated using scanning electron microscopy and transmission electron microscopy techniques, and elemental/phase analysis was completed using x-ray diffraction, electron energy loss spectroscopy and x-ray energy-dispersive spectroscopy. The findings indicated the presence of W₂C and W₆Co₆C in addition to WC and chromium oxide (Cr₂O₃) in a nanocrystalline cobalt-rich matrix. The newly developed phases (W₂C and W₆Co₆C) were formed as a result of decarburization/oxidation of tungsten carbide (WC). They were found as individual particles (0.2-0.4 µm) embedded in the metallic binder phase as well as surrounding existing WC particles. Nonetheless, increasing the coating deposition rate, i.e., reduction of coating build-up per pass, increased the coating hardness from 1516 ± 124 to 1713 ± 106 HV_0.3 and led to a higher degree of phase transformation reactions in the coating.