Effect of substrates on the microstructure of thermally sprayed WC-4.88 wt% Co coatings

Aluminium, 304L stainless steel, super-invar and brass substrates were coated with WC-4.88wt%Co using the High Velocity Oxyl-Fuel (HVOF) technique. Microstructure and phase identification studies were done using optical microscopy, scanning electron microscopy, X-ray diffraction and atomic force microscopy. X-ray residual stress and microhardness measurements were also undertaken. Porosity and grain sizes were determined. From the X-ray diffraction spectra of the sprayed coatings, differences in the phases present for each coated substrate were observed. The coatings had similar microhardnesses within experimental error. The residual stress results were different for each coating sprayed onto different substrates. These differences were interpreted as originating from the different specific heat capacities and coefficients of linear thermal expansion of the substrates.