EFFECT OF FINISHING ON THE CORROSION PROPERTIES OF FLAME SPRAYED Ni-5%Al AND Ni-5%Al-Al2O3 COATINGS
Journal Title: Journal of KONES - Year 2014, Vol 21, Issue 4
Abstract
The Ni-5%Al alloy and Ni-5% Al-Al2O3 composite coatings were obtained by a flame spraying method, “Casto-Dyn DS 8000” torch was used. The coatings onto a substrate made of austenitic stainless steel (X5CrNi18-10) were sprayed. The coatings were subjected to turning, burnishing and grinding. The evaluation of corrosion properties were based on the measurements of direct current (potentiodynamic method) and the alternating current (EIS method). Corrosion tests were performed in a 3.5% sodium chloride solution. On the basis of studies, the effect of finishing type on the corrosion properties of flame sprayed coatings has been demonstrated. The lowest corrosion current density was found for Ni-5%Al coatings after burnishing, icorr value equal to 0.76 µA/cm2, and the charge transfer resistance was 31063 Ω/cm2. The lowest resistance to corrosion of grinded Ni-5%Al-Al2O3 composite coatings was observed. These coatings were characterized by the following parameters of corrosion process: icorr = 14.01 µA/cm2, Rct = 3260 Ω/cm2. Burnishing caused increased corrosion resistance of both coatings. Due to reduced roughness and waviness are obtained reduction of the area of the actual burnished coatings compared to turned coatings. Thus, it is resulting in reduced values of corrosion current density. After finishing treatment, the thermally sprayed Ni-5%Al 15%Al2O3 coatings characterized by lower corrosion resistance compared to the alloy coating. The presence of the reinforcing phase in the coating promotes the increase of the porosity. Burnishing does not cause a significant change in porosity of the coating. The flame sprayed coatings on nickel-based have a tendency to localized corrosion in seawater environment.
Authors and Affiliations
Adam Charchalis, Robert Starosta
Keywords
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