Phase composition, microstructure, mechanical properties, and wear performance of nanostructured Al2O3 and Al2O3-Y2O3 coatings deposited by plasma spraying

In this study, conventional and nanostructured Al2O3 and Al2O3-Y2O3 coatings were produced by atmospheric plasma spraying. Phase composition, microstructure and chemical composition studies were performed on the coatings. Microhardness, crack propagation resistance and bonding strength of the coatings were evaluated. Wear testing was also carried out by a pin-on-disc machine at loads of 2, 10 and 20 N. The results showed that the coatings obtained from nano-agglomerated powders had a Bi-modal microstructure. The addition of Y2O3 resulted in stabilizing desired alpha-Al2O3 phase. Nanostructured coatings displayed more increase in I alpha/I gamma than conventional types. Composite coatings showed higher bonding strength than individual Al2O3 coatings, due to the better adhesion of the splats, chemical bonding of Y2O3 and Al2O3, and the better melting and wetting of Y2O3 in the composite coatings. Nanostructured alumina coating had about twice crack propagation resistance more than conventional type. Despite the lower crack propagation resistance, conventional coatings showed higher wear resistance than nanostructured coatings due to their higher adhesion strength and hardness and denser microstructure.