Microstructural and tribological characterization of air plasma sprayed nanostructured alumina-titania coatings deposited with nitrogen and argon as primary plasma gases

Air plasma sprayed nanostructured Al2O3-13wt%TiO2 coatings were deposited as a function of critical plasma spray parameter (CPSP), defined as the ratio of arc power to primary gas flow rate, using nitrogen and argon as the primary plasma gases. Microstructural features including percentage of α-Al2O3 phase, percentage of partially melted/unmelted regions, microhardness, and wear characteristics were evaluated for the deposited coatings. Effect of CPSP on microstructural and wear characteristics of coatings deposited with nitrogen was found to be relatively small. In contrast, significant effect of CPSP on coating characteristics was found for coatings deposited with argon. In wear tests, while strong effect of normal load on weight loss was observed for coatings deposited with nitrogen, weight loss for coatings deposited with argon was nearly independent of applied normal load, at least for coatings deposited at the highest CPSP.