A comparative study on corrosion behavior of ceramic coatings via plasma spray process in 3.5% NaCl solution

Abstract

In the plasma spray process, material flows through a plasma arc and the molten particles are projected through an inert gas stream with high velocity on AISI 304L stainless steel sheet to give a coating with some degree of metallurgical bonding. This study discusses the effectiveness of particle size, type of coating and direction on the corrosion of ceramic coating in 3.5 % NaCl solution. Two approaches were used for preparing coated specimens. The first modification proposed to use coarse grain sized powder in spraying as the first layer followed by the fine one. The second trial assumes to change the coating direction of the top layer to be traversing the lower layer. WC-12% Co/Al2O3 coatings were deposited on AISI 304L stainless steel by means of a plasma spray process by different deposition techniques. For comparative purposes, a set of ceramics coatings via plasma spray process was employed on a substrate with Al2O3, and WC−12% Co. Potentiodynamic polarization measurements were carried out to determine the corrosion behavior of the plasma-sprayed-coatings in 3.5% NaCl. The results showed that the corrosion resistance depends strongly on the type of coating and on its direction of coating. The grain type combination showed a great influence on the corrosion behavior of the plasma coatings, the coarse WC-12% Co covered by fine Al2O3 showed a much better corrosion resistance than the fine WC-12% Co covered by coarse Al2O3.The parallel layers of coating specimen has the best corrosion resistance between the coated specimens with lowest corrosion rate 0.425 mm/year