Cermet plasma coatings deposited from mechanically alloyed W-TiAl-C-Co powder
Cermet powder with triple (W 0.6Ti 0.2Al 0.2)C 0.7 carbide particles distributed uniformly in a Co matrix has been synthesized by means of mechanical alloying of initials powders of W, Co, C, and TiAl intermetallide. Wetting of carbide particles with molten matrix and its uniform distribution in the melt during plasma spraying are took place owing to a certain chemical interaction of carbides with matrix phase in the process of mechanical alloying. Microhardness of plasma sprayed cermet coatings is 18 GPa under 20 g indentation load and 11 GPa under the load of 200 g. This difference is explained by poor cohesion, the value of which can be enhanced by thermomechanical treatment of coating. Phase composition of powders for spraying is found to be changed after mechanical alloying and following vacuum annealing at 700-1150°C while the annealing temperature for coating sprayed is 900°C. As-sprayed cermet coating has an amorphous-crystalline structure as well as high wear- and corrosion resistance.