FEASIBILITY OF FLUIDIZED-BED CVD FOR THE FORMATION OF PROTECTIVE COATINGS

Attempts have been made to clarify the feasibility of a fluidized bed CVD (FBCVD) process as another method for the formation of cementing a nd diffusion coatings in order to improve wear, oxidation and corrosio n resistance of metals. Treating agent powders consist of a donator, u sually a powder of the metal, an alloy or a metal carbide or nitride o f the coating forming metal, an activator, usually a halide or alkali metal halides, and a filler oxide, usually Al2O3, SiO2 etc. The precur sors of the coating forming metal are formed ''in situ'' the fluidized bed reactor by the reaction of the donator with the activator. The be d can be fluidized by inert or reactive gas or gas mixtures like Ar, N -2, Ar + H-2 etc. As the parts can be charged and withdrawn while the furnace is at treating temperature, this process can be integrated int o the heat treatment cycles. The FBCVD process was applied for the for mation of Ti-, V-, Cr-, Al-, and Si-bearing coatings. The produced coa tings were dense and uniform over the whole specimen surface. Accordin g to the results, the use of the FBCVD process is promising since it c an lead to a clean, flexible surface modification technology, combinin g adaptability with relatively low capital and operational costs.