The microstructural dependence of wear and indentation behaviour of some plasma-sprayed alumina coatings

Plasma-sprayed coatings are built up from individual overlapping solidified droplets, and the nature of boundaries between these ''splats'' influences their mechanical and wear characteristics. This work aims to elucidate the correlation between these characteristics and microstructural features of model coatings produced under well-controlled processing conditions. A series of coatings with different average splat size were sprayed from pure alumina powders of different particle size using an axial-injection plasma-spray torch under conditions optimized to obtain the best microstructures. Phase composition was determined by X-ray diffraction, while SEM with image analysis of polished and fractured surfaces was used to evaluate coating microstructures, and indentation and wear damage. Coatings were characterized by depth-sensing indentation (DSI) at the sub-splat scale and by DSI, micro- and macro-indentation at multiple splat scales. Both abrasion and dry-particle erosion behaviour of the coatings were also investigated. Results reveal the role of microstructural features on the material performance, particularly the critical influence of porosity, splat (grain) size and inter-splat cohesion, on the multiple-splat scale wear and indentation behaviour of the coatings. (C) 1997 Elsevier Science S.A.