INVESTIGATION OF STRUCTURE AND PROPERTIES OF THERMAL COATINGS OF WC-Co-Cr SYSTEM PRODUCED BY HIGH-VELOCITY METHODS OF SPRAYING

摘要

Spraying of coatings of WC-9Co-4Cr powder was performed by high-velocity procedures of thermal spraying, using the methods of detonation, supersonic air-gas plasma (SAGP) and oxy-fuel HVOF spraying. Microstructure and properties of produced coatings were investigated. Analysis of results of the coating structure examination showed that during spraying with these methods the dense coatings are formed, consisting of inclusions of tungsten carbide, uniformly distributed in Co-Cr matrix. Porosity of coatings is less than 1%. Microhardness of SAGP- and HVOF-sprayed coatings is 11.0-11.7 GPa. As to the values of microhardness these coatings are superior to those of the galvanic chromium (10 GPa). Microhardness of the detonation coating is 8.5 GPa. The cause of decrease in hardness of the detonation coating is a partial loss of carbon and appearance of oxide inclusions in it, that is caused by the oxidizing medium of the detonation products. By the complex of characteristics of hardness, adhesion strength (more than 50 MPa) and porosity the coatings of WC-9Co-4Cr system, sprayed by SAGP and HVOF methods, are advantageous as compared with the galvanic chrome-plating. Among the investigated methods of high-velocity thermal spraying of coatings of WC-9Co-4Cr system the SAGP method is characterized by the highest efficiency (15 kg/h).