Wear resistant alumina-titania plasma sprayed coatings from nanostructured powders

The development of engineering components for harsh operating conditions, such as increasingly high velocity and operating contact loads, requires continuous improvement in the reliability and service life of mating surfaces, thus justifying the massive interest put in the optimization of protective coatings in the last decades. Wear resistant coatings, in particular, are used to reduce the damage caused by abrasion, erosion, cavitation and fretting, also potentially associated with corrosion, and in some cases to reduce friction. Oxide ceramics, such as alumina, titania, zirconia, chromia, yttria and mixtures therein, have been widely used in force of their wear resistance (1-3) as well as for their protective role in the presence of thermal loads, and the fabrication processes for this kind of coatings are today technologically consolidated, being APS the most efficient and economical deposition technique. Particular attention has been devoted in the very recent past to the possibility of depositing nanostructured oxide ceramic coatings (1), anticipating potential exceptional improvements of tribological properties associated with the extremely high density of grain boundaries of these materials, provided that the nanocrystalline structure of the starting materials can be preserved during the deposition and reproduced within the coating. While presenting evident shortcomings correlated to the risk of grain coarsening, thermal spray of nanostructured powders appears however as a very attractive route to nanostructured coatings, due to the very short time of residence of starting materials at high temperature. Very limited literature is available as of today on the particular subject (4-9). In the present communication, preliminary results of the fabrication and characterization of coatings produced by air plasma spray deposition of commercially available nanostructured alumina-titania powders are presented.