Microstructure of alumina–3wt.% titania coatings by plasma spraying with nanostructured powders

The microstructure of plasma-sprayed alumina–3wt.% titania coatings with the nanostructured powders was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that the nanostructured coating exhibited a bimodal microstructure: splat lamellae similar to the conventional coating and equiaxed grains originating from the starting feedstock. The splat lamellae consisted of γ-Al2O3 grains and most of them were less than 200 nm in diameter. Equiaxed grains took the modification of α-Al2O3 and ranged from 150 to 800 nm in size. In addition, the modifications of TiO2 disappeared and Ti element was dissolved in γ-Al2O3 grains. The bimodal microstructure contributed to the improvement in mechanical properties of the nanostructured coating.