Tribological behaviour of plasma sprayed Al<inf>2</inf>O<inf>3</inf> and TiO<inf>2</inf> ceramic hard coatings under dry contact

Plasma sprayed ceramic coatings a e used in a number of industries in which surface modification of components to compare tribological properties is important: so hence, are evaluations of their tribological properties. This paper presents a study on the wear behaviour of three ceramic coatings - Al2O3, TiO2 and Al2O3-TiO2 combination - in the load and speed ranges of 5 to 50 N, and 0.3 to 10 m/s, respectively, on which few data are available in the literature. The tests were carried out using a standard dry sand rubber wheel abrasion test and a pin-on-disc machine under dry sliding conditions. It was found that a stick-slip effect seems to occur at low sliding speeds, and transition takes place at a sliding speed of around 4 m/s. Of the three ceramic coatings, TiO2 was found to be the most wear resistant, with the least friction coefficient, although it is less hard than the Al2O3 coatings. Scanning electron microscopy of the surface shows evidence of wear mechanisms such as plastic deformation, transfer-film formation, micro cracks, and grain pull-out in the coatings.