CERMET COATINGS OF CHROMIUM CARBIDE-NICHROME SYSTEM PRODUCED BY SUPERSONIC PLASMA GAS AIR SPRAYING

摘要

It is a well-known fact that application of supersonic methods of thermal spray deposition results in significant increase of service properties of parts. However, up to moment no trails were made on producing of carbide or cermet coatings with the help of supersonic methods of plasma spraying. Present work is dedicated to production of cermet coatings from chromium carbide-nichrome compositions using a method of supersonic plasma gas air spraying (SPGAS). SPGAS technology has series of advantages in comparison with well-known technology of HVOF spraying. First of all, it concerns efficiency, economy and characteristics (temperature, speed) of gas jet. Structure and phase composition of produced coatings were investigated. It is shown that spraying using supersonic gas jets promotes for increase of content of Cr_7C_3 carbide and reduction of NiCr in the coatings as a result of oxidation and formation of oxides. Coating from composite powder differs by higher level of density and homogeneity, has layered fine-laminated structure with inclusions of fine carbides, contains lower amount of oxide phase, but larger quantity of chromium carbide Cr_3C_2 in comparison with coating from mechanical mixture Cr_3C_2 + NiCr. These coatings can be recommended for application as wear-resistant at increased temperatures.