The adhesion of plasma-sprayed coating is to a large extent controlled by the cleanness and roughness of the surface on which the coating is deposited. So, most of the plasma spray procedures involve surface pretreatment by grit-blasting to adapt the roughness of the surface to the size of the impacting particles. This preparation process brings about compressive stresses that make it inappropriate for thin substrates. The present works aims to elaborate a ceramic coating on a thin metal substrate with a smooth surface. The coating system is intended for use in a generation–IV nuclear energy system. It must exhibit a good adhesion between the ceramic topcoat (about 0.5-mm thick) and the smooth metal substrate (1-mm thick) to meet the specifications of the application. Our approach has consisted in depositing the ceramic layer on a few micrometers thick ceramic layer made by suspension spraying. We have observed the interface between both ceramic layers by transmission electronic microscope and studied the adhesion of the nanostructured layer by the Vickers Indentation Cracking technique and that of the coating system by tensile test.

The gas-cooled fast reactor is a 4th generation nuclear reactor currently under development. Its design concept requires protective coatings able to operate at 850°C and protect the underlying structure in case of extreme cases, where the functional temperature can increase up to 1250°C and there is depressurization from 70 bars to atmospheric pressure. The parts to be covered are made in 1-mm thick materials resistant to heat and erosion with high mechanical properties at high temperatures, such as the Haynes 230 nickel-based alloy. In this study, the potential of the suspension plasma spraying technique for forming the first layers of a ceramic coating on smooth 1-mm thick Haynes substrate was explored. In order to meet these specifications, the coating material selected was partially stabilized zirconia of standard composition (8 mol.% Y 2 O 3 -ZrO 2 ).

In this study, micro and nanostructured alumina coatings were plasma sprayed on steel substrates using different combinations of spraying parameters. Test results show that the nanostructured coatings have lower hardness, a lower friction coefficient, and higher wear resistance than microstructured alumina coatings.