PLASMA SPRAYING OF ZIRCONIUM CARBIDE-HAFNIUM CARBIDE-TUNGSTEN CERMETS

摘要

Preparation of coatings and self-standing parts from materials with the highest melting points is allowed only by a limited number of techniques. Plasma torch WSPR with exit nozzle plasma temperature about 30 000 K, operating at 150 kW, enables treatment of such refractories with extreme melting points in an amount of tens of kilograms per hour [1] . A mixture of the W powder was prepared with 10 vol.% to 20 vol.% of ZrC or HfC. This feedstock having spheroidal character and micrometric size was fed into the plasma of the water stabilized plasma torch (WSPR) by means of inert gas carrying. Coatings thickened up to 2 mm were sprayed on various substrates, namely graphite. Self-standing bodies were obtained by substrate removal. Pure tungsten and pure zirconium carbide were sprayed at similar conditions. Various manners of coating improvement by shrouding and sample controlled cooling were tested. XRD, XRF, mercury porosimetry, dilatometry and various microscopic structural techniques were used for the coatings characterization. Resulting coatings are hard and can serve as a surface protection of graphite substrates with various shapes and grain orientations.