The potentiodynamic tests of dispersed nickel matrix composite coatings obtained by flame spraying
Robert Starosta Akademia Morska w Gdyni, Wydział Mechaniczny, Katedra Materiałów Okrętowych i Technologii Remontów, ul. Morska 83, 81-225 Gdynia, Poland
Quarterly No. 2, 2008 pages 195-200
DOI:
keywords: dispersed composite coatings, corrosion, flame spraying
abstract The progress in technology is often determined by increase in reliability of constructions and machines. Therefore, new materials are permanently looked for, what has resulted in the past in development of composite materials. The dispersed coatings consist of metallic matrix (metals and their alloys) and small non-metallic particles. The deposition of ceramic particles simultaneously with metallic matrix leads often to composite coatings possessing properties much better than those of metallic coating. The nickel and, less often, other iron group elements are usually used as a matrix, and SiC and Al2O3 as tough particles. The metallic alloy Ni-5%Al and composite Ni-5%Al-Al2O3 coatings were investigated. These coatings were obtained by flame spraying. The coatings were prepared on the carbon steel C45. The volumetric contents of aluminium oxide in composite coatings numbered 15, 30 and 45%. The corrosion tests were performed by potentiodynamic technique. The specimen of 1 cm2 surface was rinsed with acetone, and then put into the cell, in which the anode made of platinised titanium and reference saturated calomel electrode were also immersed in 0.01 M H2SO4 at ambient temperature. The solution was constantly stirred. The polarization curves were obtained at a 10 mV/min rate of potential shift, within the region from stationary potential after 0.5 hour of pre-exposure in the electrolyte. As the first the cathodic curve, and then anodic curve were recorded. The corrosion current was determined. Positive effects of presence of alumina particles on corrosion behaviour of such coatings have been observed. The increasing corrosion resistance in presence of Al2O3 has been observed and attributed to the barrier effect of ceramics, which does not conduct the electrical current. The composite coatings Ni-5%Al-Al2O3 can be used as corrosion resistant.