Improvements in HVOF Sprayed Cermet Coatings Produced from SHS Powders

It has been shown that high velocity oxy-fuel (HVOF) thermal spray coatings with good wear resistance can be produced from Ni(Cr)-TiC powders manufactured by self-propagating high temperature synthesis (SHS) reactions. In the present work the process was expanded to include additions of Mo and W with the objective of modifying the carbide phase in an attempt to increase the wear resistance further. The effect of changing the matrix, i.e. substituting Fe for Ni, and changing the ceramic phase from TiC to TiB₂ was also examined. The feedstock powder and resultant coatings are characterised in terms of x-ray diffraction analysis and scanning electron microscopy while the coating properties are measured by microhardness and dry sand rubber wheel (DSRW) abrasive wear testing. The results show that Fe(Cr)-TiB₂ and Ni(Cr)-(W, Ti)C coatings have wear rates comparable to that of conventional Cr₃C₂-NiCr coatings produced from sintered and crushed powder, but further improvements are needed to achieve the wear resistance of WC-Co coatings.