THE FORMATION OF ANTI-CORROSIVE STRUCTURES AND THIN FILMS ON METAL SURFACES BY APPLYING EDM

Abstract

The methods of formation anti-corrosive strata and thin films on metal surfaces by applying electric discharge machining (EDM) are presented in this chapter. It has been demonstrated the increase of anti-corrosion resistance of metal surfaces by the formation ofpalladium depositions, carbon films and oxide and hydroxide films. Corrosion and electrochemical behavior 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 2 orders (from 18.7 down to 0.3 g·m-2·h-1), 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 107times, the potential of corrosion increased from -0.44 mV to +0.4 V, the resistance to corrosion has increased by about 2 times in 1% NaCl water solution, and by about 10 times in 30% H2SO4water solution. The less pronounced increase of anti-corrosion properties is possessed by 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

• carbon
• corrosion
• electric discharge machining
• microhardness
• thin films