Characterization of alumina–3 wt.% titania coating prepared by plasma spraying of nanostructured powders

Nanostructured and conventional alumina–3 wt.% titania coatings were deposited by air plasma spraying (APS). The microstructure and phase composition of the coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Mechanical properties including hardness, adhesion strength, crack extension force (GC) and sliding wear rate were measured. Equiaxed α-Al2O3 grains were observed in the nanostructured Al2O3–3 wt.% TiO2 coating and the diameter of α-Al2O3 grains were about 150 to 700 nm in size. The microhardness of both kinds of coating was similar and about 820 HV0.2. However, the adhesion strength and crack extension force of the nanostructured coating increased by 33 and 80%, respectively, as compared with those of the conventional coating. The wear rate of the nanostructured coating was lower than that of the conventional coating. The results were explained in terms of characteristics of the powders and microstructure of the coatings.