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

Abstract

The damage mechanisms of several widely used plasma-sprayed ceramic coatings were studied by single point scratch tests using diamond indenters. The ceramic coatings investigated were Al 2O 3, Al 2O 3/13% TiO 2 and Cr 2O 3. Single scratching on polished virgin surface, repeated scratching over the same track and parallel interacting scratching were investigated. Microstructures of the coatings, their surface and subsurface damage patterns due to the scratching, and the morphology of wear debris were examined. It was found that the unique microstructure of the coatings determined their wear and related damage mechanisms. The predominant mechanism of material removal in the scratching of Al 2O 3 and Al 2O 3/13% TiO 2 coatings was microfracture within the plastic region, which takes place preferentially at pre-existing microcracks and micropores and is driven by plastic strain. The mechanism of material removal in the scratching of the Cr 2O 3 coating depended on contact load and contact geometry. When the contact load was less than a critical value that was related to contact geometry, the predominant mechanism of material removal was the same as that of Al 2O 3 and Al 2O 3/13% TiO 2 coatings. When the contact load exceeded the critical value, the predominant mechanism of material removal was macro-fracture controlled by lateral cracking.