High temperature tribological behavior of nanostructured and conventional plasma sprayed alumina-titania coatings

Alumina-titania coatings are used where a high wear and oxidation resistances are required. These coatings are usually deposited by thermal spraying. The use of nanoparticles as feeding powders can lead to improved properties if some technological problems are solved. The small size of the nanoparticles makes necessary to prepare agglomerates able to be sprayed by conventional equipments. The plasma spray parameters should be chosen to maintain the starting nanostructure in the final coating. This can be achieved if the coating contains partially melted particles. In this work the mechanical and high temperature wear behaviour of Al2O3-13%TiO2 nanostructured coatings was compared to that of the conventional ones. Microstructural characterization was performed using scanning and transmission electron microscopy and X-rays diffraction techniques. Mechanical properties such as Young's modulus, hardness and fracture toughness were determined by depth sensing indentation. Wear rates and friction coefficients were measured by means of a Pin on disc machine in which both counterparts were made of Al2O3-13%TiO2. Experiments at different loads under unlubricated conditions, without elimination of the wear debris were carried out. Although the mechanical properties are slightly higher in the nanostructured coatings, they exhibit a much better wear behaviour under all the testing conditions.

► Wear behavior at different temperatures was studied in alumina-titania coatings.
► Nanostructured coating presents lower wear rates than conventional one.
► Brittle fracture is the main wear mechanism at room temperature.
► Plastic deformation is the main wear mechanism at high temperature.
► Nanocoating better wear behavior is due to its hierarchical microstructure.