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Abstract
ABSTRACT
Air plasma spray process permits rapid application of high- performance coating materials, and is industrially the most common and technically the most important method to produce ceramic coatings. Ceramic coatings obtained by plasma spraying deposition often show porosity. These local defects can form a direct path between the corrosive environment and the substrate. Post treatment (sealing) by polyster resin can close these porosity and, improve the corrosion resistance of coatings.
In the present study, plasma spray coatings were applied to deposit pure alumina, alumina-3%titanina, and alumina-13% titanina ceramic coatings. Bond layer of Ni-5%A1 was used. Sealing using polyester resin was applied. The powders, coatings, and corroded coatings have been examined by means of X-Ray diffraction (XRD), scanning electron microscope examinations (SEM), and microhardness. Porosity was measured before and after sealing. Corrosion static immersion tests in 5% HCI and 10% HCl were carried out.
Results indicate that sealing improves the average hardness of all the coatings. The different ceramic coatings peel after 72h in 5%HCl. Adding bond layer (Ni-Al) increases the immersion time to 120 h and no peeling was observed. The Al2O3-13% TiO2 coating shows the lowest weight loss. This may be attributed to the porosity level (4.06%) in the coating. The sealed ceramic coatings with and without bond layer improves the corrosion resistance of the different coatings. Sealed Al2O3-13% Tio2 ceramic coating shows the highest corrosion resistance among the different sealed coatings in 5% HCl and 10%HCl respectively.