Microstructure and Protertise of Self-Lubricative Ceramic Coatings on Carbon Steel by PEO in Aluminate Electrolyte Containing Graphite

Abstract

Self-lubricative ceramic coatings were prepared on Q235 carbon steel by plasma electrolytic oxidation (PEO) in aluminate electrolyte containing graphite. The microstructure of the PEO coatings were examined. Influence of graphite in electrolyte on the coating growth properties was analyzed according to the voltage vs. time plots. Effect of graphite concentration on the properties of the coatings such as bonding strength, surface roughness and thickness were studied. The tribological behavior of the coating was primarily evaluated.The results showed that the self-lubricative coatings consisted of FeAl2O4, Fe3O4 and a certain amount of graphite. With increasing the concentration of graphite in the electrolyte, the coating growth gradually became stable with lower breakdown voltage and end voltage. The bonding strength and the thickness of the coating were not strongly affected by the graphite concentration whose value remained approximately 19Mpa and 110μm, respectively. With increasing the graphite concentration, the surface roughness first decreased and then increased a little. The friction coefficient of the coatings also varied with the concentration of graphite. When the concentration of graphite was 8 g/l, the tribological property of the coatings was the most excellent with the friction coefficient bellow 0.1.