Microstructural characteristics of high-velocity oxygen-fuel (HVOF) sprayed nickel-based alloy coating

A NiCrBSiWFeCoC alloy coating was prepared by means of high-velocity oxygen-fuel (HVOF) thermal spraying process and analyzed with regard to their detailed microstructures and phase composition. Systematic characterization of the coating was carried out using X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), differential scanning calorimeter (DSC) and high-resolution transmission electron microscope (HRTEM). Amorphous phase and nanoclusters were obtained in the coating and the major crystalline phases were compounds Cr23C6, Cr7C3, Ni3B, WC, and solid solution γ-Ni. It was found that microtwinning was highly localized within the Cr7C3 phase. The crystallization temperature of the amorphous phase was about 500 °C. The formation of the amorphous phase was attributed to the high cooling rates of molted droplets and the multicomponent alloy system of feedstock powder. The nanoclusters were formed by homogeneous nucleation.