Rietveld analysis for studying the decarburisation in HVOF WC–CO coatings

Quantitative X-Ray analysis was used to quantify the phase content generated by the High Velocity Oxygen Fuel (HVOF) process following the decarburisation of WC–Co coatings. Rietveld analysis was used to quantify the different phases present. Particular attention has been made to identifying the sequence of formation of the different species, namely: during flight of the powders towards the substrate and/or during the solidification and cooling step on the substrate. The results show that decarburisation is influenced by the thermal history of the particles in flight. In particular, more W2C and W are generated with increasing spray distance indicating an increase WC decarburisation. During the coating building-up, new nanosized compounds (W3Co3C and W6Co6C) were generated. These compounds, at the reverse of W2C and W phases, decrease with the stand-off distance. Correlations are established between the mechanical properties (microhardness and crack propagation resistance) and the content of the phases determined from the Rietveld analysis.