Microstructural characterisation and microhardness distribution of HVOF sprayed WC–10Co–4Cr coating

The aim of this work was to study the detailed microstructures, thermostability and microhardness distribution of high velocity oxygen fuel sprayed WC–10Co–4Cr coating using X-ray diffraction, scanning electron microscope, energy dispersive spectroscopy, differential scanning calorimeter and high resolution transmission electron microscope. The coating has a dense structure and is well bonded to the substrate. The coating is mainly composed of WC phase and W₂C phase. Owing to the high cooling rates of molten droplets and the multicomponent system of feedstock powder, amorphous phase is obtained in the coating. The crystallisation temperature of the amorphous phase is 651°C. The Weibull analysis of Vickers microhardness of the coating exhibits a bimodal distribution under indentation load of 300 g and a monomodal distribution under indentation load of 100 g. Such distribution is attributed to the presence of the poorly bonded splats and pores within the coating.