Alumina sol-gel coating on 316 stainless steel

Sol-gel derived alumina was used to coat 316 stainless steel substrates. The coating was applied via a drain technique. Substrate was prepared prior to coating. Single and multiple coated samples were studied. Multiple coated samples are analyzed in order to determine the effect of thickness increase and multiple firing on coating properties and densification.;Different ways to control crystallization of the coating were investigated as a part of our study of the effect of chemical and morphological interactions between the substrate and the coating. Addition of substrate elements separately into alumina sol illustrates the possible effect of substrate elements on the coating.;The alumina gel transformation follows the path: pseudoboehmite ;The pore size distribution of the coating was 10 to 200 A. Pores ;The coating thickness is 2-5 ;Surface analysis showed that the substrate surface consists of iron, chromium, oxygen and carbon. Trace amounts of manganese and nickel are also present.;Study of the effect of these substrate elements on alpha phase formation showed that iron is the most effective additive in the transformation of alpha-alumina.;Crystallization occurred when the coating was fired to temperatures above 1000;Experiments showed that the coating-substrate interface effect predominate. The crystallization of the coating is occurring faster than if due solely to the surface topography effect, when compared with the calculated transformation rate. Other mechanisms also enhance the crystallization of alpha-alumina.;The crystallization in the coating can be controlled by adding appropriate additives.