Microstructure Peculiarities of Intermetallic and Composite Coatings

Abstract

Coatings were obtained by the method of electrospark deposition (ESD), using Ni-Al intermetallic alloys, steel having been used as cathodes. The structure of samples preliminarily, coated with nickel aluminides of various phase compositions (NiAl, Ni3Al), was investigated. In addition to the indicated anode materials, a complex alloyed metal matrix alloy obtained by the method of self-propagating high-temperature synthesis, was used. It was established that the coating microstructure consisted of columnar crystallites, vertically oriented to the cathode surface. X-ray microanalysis of the transverse sections showed a change in the composition of crystallites along their height. It was found that the content of the cathode components decreased from the surface of the sample to the upper part of its coating, however, the content of the anode components increased. The revealed regularities indicate the fact that the coating structure obtained at ESD, was formed through the stage of liquid-phase mixing, which explained high coating adheasion. The mechanisms of structure formation of both single-layer and two-layer coatings proved to be identical.