Wear mechanism of plasma-sprayed alumina coating in sliding contacts with harder asperities

The wear mechanism of plasma-sprayed alumina was studied by scratching a model alumina coating using a diamond indenter. Single scratching on polished virgin surface, repeated scratching over the same track and parallel interacting scratching were investigated. The predominant mechanism of material removal was found to be microfracture within the quasi-plastic zone, which takes place preferentially at splat boundaries and pre-existing cracks and is driven by inelastic strain. When scratching was made on a virgin surface the wear rate was relatively low, but when parallel scratches interacted, subsequent scratching was made on already heavily strained material, thus, the wear rate was much higher. The wear debris produced during single and parallel interacting scratching was in the form of small angular particles whose dimensions were related to the splat structure and pre-existing cracks. In repeated scratching over the same track, surface material experienced repeated inelastic deformation and, thus, crack development at the splat boundaries, and this resulted in the production of thin platelet wear debris. (C) 1999 Elsevier Science S.A. All rights reserved.