Synthesis and Properties of Muitimodal WC-12 Co Coatings

WC-Co has been extensively investigated for use in wear resistant coatings for engineering applications. In principal, when the WC particle size decreases in the starting powder, the decomposition of WC increases, and therefore, significant amounts of W₂C and W₃C, and even metallic phases, are observed in nanocrystalline WC-Co coatings. The reported increase in hardness of nanostructured materials is generally attributed to the significant decrease in grain size or particle size. However, the presence of brittle, non-WC phases in nanostructured WC-Co coatings leads to sliding and abrasive wear by removal of large plates of the coating. Concurrently, the greater degree of decomposition suffered by the nanostructured powder during spraying leads to a reduction in the volume fraction of the wear-resistant primary WC phase. For the reasons presented above, the present efforts are directed towards the synthesis of a wear-resistant coating using a multimodal WC size distribution of particles in the starting powder. The multimodal distribution is characterized by small WC particle(~50 nm) and coarse WC particles (1.7µm). In addition, the distribution of Co also spanned an order of grain size, hence the name multimodal. The coatings were deposited using HVOF technology.