Plasma Spraying of Refractory Cermets by Water-Stabilized Spray System WSP®

Among important metal matrix composites we can find cemented carbides, predominantly tungsten carbide with cobalt binder. For high temperature applications metals with higher melting point, namely tungsten, are preferred. Tungsten carbides with decomposition temperature 2785°C should be also replaced by for example ZrC. Bulk parts can be produced by powder metallurgy techniques but plasma spraying of cermets could be an interesting alternative. A mixture of the W powder was prepared with 3 to 20 vol. % of ZrC. This feedstock having spheroidal character was fed into the plasma of the water-stabilized plasma generator (WSP^®) by means of inert gas carrying. Coatings thick about 1 mm were sprayed on various substrates, namely graphite. Pure tungsten was sprayed at similar conditions. Microhardness, surface roughness, XRD, XRF, dilatometry and microscopic techniques were used for the coatings characterization. Resulting coatings are hard and can serve as a surface protection of various graphite substrates.