Plasma spraying of sintered carbides using a compound powder

A WC-Co cemented compound containing 16.8 weight % Co was applied to the surfacing of steel and molybdenum by a plasma gun. A compound powder in which a polycrystalline core is surrounded by a cobalt layer was used. The density, hardness, tranverse rupture strength, adhesion, and shear strength as a function of the arc current were determined along with the oxygen and carbon balance in the alloy. The presence of the phases from the system W-CoC was revealed by metallographic and electron microscope and X-ray studies. Because of extreme temperature and cooling conditions, local nonequilibrium states occur in the coatings, which greatly affect the mechanical properties. These states can be eliminated by an annealing treatment, resulting in coatings with a structure analogous to that of the sintered alloy. The WC-Co compound powder is technologically superior, yeilding improved cemented carbide spray coatings, as compared with previously used powder mixtures.