The damage mechanisms of several plasma-sprayed ceramic coatings in controlled scratching

The damage mechanisms of several widely used plasma-sprayed ceramic coating s were studied by single point scratch tests using diamond indenters. The c eramic coatings investigated were Al2O3, Al2O3/13% TiO2 and Cr2O3. Single s cratching on polished virgin surface, repeated scratching over the same tra ck and parallel interacting scratching were investigated. Microstructures o f the coatings, their surface and subsurface damage patterns due to the scr atching, and the morphology of wear debris were examined. It was found that the unique microstructure of the coatings determined their wear and relate d damage mechanisms. The predominant mechanism of material removal in the s cratching of Al2O3 and Al2O3/13% TiO2 coatings was microfracture within the plastic region, which takes place preferentially at pre-existing microcrac ks and micropores and is driven by plastic strain. The mechanism of materia l removal in the scratching of the Cr2O3 coating depended on contact load a nd contact geometry. When the contact load was less than a critical value t hat was related to contact geometry, the predominant mechanism of material removal was the same as that of Al2O3 and Al2O3/13% TiO2 coatings. When the contact load exceeded the critical value, the predominant mechanism of mat erial removal was macro-fracture controlled by lateral cracking. (C) 1999 E lsevier Science S.A. All rights reserved.