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.