Microstructural characterization of plasma sprayed conventional and nanostructured coatings with nitrogen as primary plasma gas

Air plasma sprayed conventional and nanostructured Al2O3-13 wt.%TiO2, WC-12-17 wt.%Co, and ZrO2-7-8 wt.%Y2O3 coatings were deposited using nitrogen as the primary plasma gas. In nanostructured coatings, as critical plasma spray parameter (CPSP) - which is defined as the ratio of gun or arc power to the primary gas flow rate - controls the volume fraction of unmelted/partially melted regions, which in turn control the properties of coatings, coatings for all systems considered in this work were obtained as a function of CPSP. Coating properties, e.g. porosity, microhardness and percentage of partially melted/unmelted regions, for nanostructured coatings, were seen to be monotonic functions of CPSP. However, the effect of CPSP on percentage of partially melted/unmelted regions was significantly smaller for nitrogen as compared to argon as the primary plasma gas, particularly for nanostructured Al2O3-13 wt.%TiO2 coatings.