Abstract

The methods of the formation of anticorrosive strata and thin films on metal surfaces by applying electric discharge machining (EDM) are presented in this chapter. The increase of anticorrosion resistance of metal surfaces by the formation of palladium depositions, carbon films and oxide and hydroxide films has been demonstrated. Corrosion and electrochemical behaviour of titanium with palladium powder coatings were investigated in sulfuric acid solutions at temperatures of 80 and 100°C. In order to increase the diffusion of palladium in the base material and to increase the layer homogeneity, after coating, the samples were annealed in vacuum at 1150°C for 1 hour. The proposed method allows to reduce the corrosion speed of titanium at least by two orders (from 18.7 to 0.3 g m<sup>2</sup> h<sup>1</sup> ); the corrosion potential is changed towards positive values (from 0.56 mV to +0.3 V). The research on surface electrical resistance and resistance to corrosion of oxide and hydroxide films formed on steel C45 surfaces by applying EDM have shown that the surface electrical resistance of the samples increased by 10<sup>7</sup> times, the potential of corrosion increased from 0.44 mV to +0.4 V and the resistance to corrosion has increased by about two times in 1% NaCl water solution and by about 10 times in 30% H2SO4 water solution. The less pronounced increase of anticorrosion properties has carbon films formed on the same steel C45 surface; instead they increase superficial microhardness, the functional durability and processing productivity of the active piece surfaces.

Keywords: electric discharge machining, corrosion, thin films, carbon, microhardness
