The evaluation of corrosion resistance of protective and functional coatings using corrosion-ratemeter
Using device R5035 the corrosion rate, expressed as current units (A/sm<sup>2</sup>), of different protective and functional coatings, deposited on steel 12H18N9T was assessed. Samples with galvanic nickel, nickel-cobalt, tin and zinc coatings were investigated. Measurements of polarization resistance were carried out in a 3% aqueous solution of NaCl with the addition of 1 ml of HCl per 100 ml of solution. Polarization resistance of pairs of samples with similar coatings was defined for forward and reverse polarization current, amounting to 800 Ω for nickel, 700 Ω for nickel-cobalt, 96 Ω for tin, 6 Ω for zinc and550 Ω for steel without coating. From the values of polarization resistance the corrosion rate of coatings in the current units was calculated and the comparison of obtained values with the sample mass loss per surface unit was given. Using «Olympus» microscope the depth of the pits formed on the surface of coatings was assessed. Work is executed within implementation of the complex scientific direction 17.1 «Eco-friendly, plasma electrolytic coatings for light alloys» («The strategic directions of development of materials and technologies of their processing for the period till 2030»)