Analysis of the friction and wear mechanisms of multilayered plasma-sprayed ceramic coatings

Wear tests were conducted on a rotor-vane-disk adaptor where three rotating vanes were pressed against a disk. Vanes were coated by WC and used as the upper specimen while the disk was coated by Cr₂O₃ and used as the lower specimen. A buffer layer of various thicknesses and contents was placed between the top coating and the bulk steel of the disk to alleviate the effects of the large difference in thermal properties of the two materials. The experimental results reveal that correct placement of a buffer layer can indeed improve the wear resistance. Factors such as the temperature to which the specimen was heated before testing, the proportion by weight of each individual constituent in the buffer layer, and the thickness of each coating layer, were also important for the volume of wear of the lower specimen. As the specimens were heated to higher temperatures, the wear volume decreased with increasing proportions of Cr₂O₃ in the buffer layer. Elevating the preheating temperature of the specimens can diminish the wear volume but increases the friction coefficient. The steady-state wear rate is not much influenced by the constituents of the buffer layer and the coating thickness. Brittle fracture, abrasion, adhesion and oxidation were found to be the primary wear mechanisms in the tests.