Tribological properties of thermal-sprayed Magneli-type coatings with different stoichiometries (TinO2n-1)

This paper summarizes results on the possibility of coating aluminium with titania-based Magneli-type coatings by thermal spraying, as well as the tribological properties of these coatings. For this purpose, a spray powder with a defined phase composition was applied on AlMg substrates by atmospheric plasma spraying. Crystalline Magneli phases of the type TinO2n-1 with a crystallographic shear structure could be identified after spraying in the coating by means of X-ray diffraction. Dry sliding experiments were conducted on a high-temperature pin-on-disc test rig against polycrystalline alumina at 23 and 400 degreesC up to a sliding distance of 2000 m at 1 m/s. The coefficient of friction (COF) remains high, at between 0.7 and 0.8 for all tests. The best wear results are achieved for the Ti6O11 coatings, showing wear rates down to 1.2 x 10(-6) mm(3)/N m. The tribological behaviour of the sprayed coatings indicates strong anti-wear properties under dry sliding conditions. Under mixed/boundary-lubricated conditions, the interaction of a low-additive polyalkyleneglycol (PAC100) with Magneli-type phases results in very low friction and wear coefficients in the range of 10(-10) mm(3)/N m. (C) 2001 Elsevier Science B.V. All rights reserved.