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Phase Structure-Mechanical Property Relationships in HVOF-Sprayed WC-12Co Coatings


 Rietveld analysis was used to measure the phase content of twenty-four coatings sprayed with a multimodal WC-12Co feedstock using three HVOF spray guns. Different correlations were investigated involving, on the one hand, the thermal spray history (particle temperature and velocity) and the mechanical properties of the deposits (microhardness and abrasion resistance), and, on the other, the phase structure of the tested coatings. The results show an inherent effect of the spraying temperature, regardless of the HVOF process used, on the generation of sub-carbide species, mainly W2C, W and an amorphous-nanocrystalline phase. In particular, it was found that decarburization of the WC to produce the amorphous/nanocrystalline and tungsten phases is beneficial in enhancing the mechanical properties as long as there is no large amount of tungsten present in the coating. A linear relationship relates this phase with the presence of the amorphous-nanocrystalline phase, independently of the spraying process used in this study. It was also shown that metallic tungsten precipitated in a nanocrystalline structure only with the Diamond Jet HVOF process.