Cermet coatings of chromium carbide-nichrome system produced by supersonic plasma gas air spraying

Abstract

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 Cr7C3 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 Cr3C2 in comparison with coating from mechanical mixture Cr3C2 + NiCr. These coatings can be recommended for application as wear-resistant at increased temperatures. 6 Ref. Plasma coatings based on chromium carbides are characterized by combination of such properties as resistance to wear by abrasive particles and hard surfaces at high temperatures (540-840 °C), high resistance under conditions of fretting-corrosion and aggressive media (for example, in liquid sodium at 200-625 °C), heat resistance at temperatures to 980 °C, radiation resistance [1].Cr 3 C 2 mechanical mixtures (rarely its mixture with Cr 7 C 3 or Cr 23 C 6 carbide) with such metals as Ni, Co, Ni+Cr, NiCr at different combination of component content (amount of metallic binder can be from 6-8 to 45 wt.%) are used for spray deposition of cermet coatings with chromium carbide.Main methods, which are used for spray deposition of coatings with chromium carbides, are plasma, detonation and HVOF spraying [1][2][3].

Investigation of Upgraded Technology for Plasma Spraying of Bronze Powder Using the Combined Process with Hydrocarbon Additions

“…powder materials. These technologies use both hydrocarbon gases as heat carriers (including plasma mixtures of methane with CO 2 ) to improve the velocity and thermal conductivity of plasma jets and intensification of particle melting in them, and with feeding of particulates or droplets of organic additives to the plasma jet to control the porosity and microstructure of sprayed metal and composite functional coatings, including for thermally resistant blades of gas turbines (in particular, according to the data [6,[9][10][11][12][13][14]). At the same time, in recent years, in particular, in Theoretical and Applied Mechanics Institute (Siberian Branch of the Russian Academy of Sciences), an adjacent promising air plasma spraying technology is being developed for use with new medium-power plasma torches to spray powders from a number of alloys, oxides (including doped alumina) and cermet compositions [8,[15][16].…”