THE MICROSTRUCTURAL DEPENDENCE OF WEAR AND INDENTATION BEHAVIOR OF SOME PLASMA-SPRAYED ALUMINA COATINGS

Plasma-sprayed coatings are built up from individual overlapping solid ified droplets, and the nature of boundaries between these ''splats'' influences their mechanical and wear characteristics. This work aims t o elucidate the correlation between these characteristics and microstr uctural features of model coatings produced under well-controlled proc essing conditions. A series of coatings with different average splat s ize 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 fr actured surfaces was used to evaluate coating microstructures, and ind entation 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 reve al the role of microstructural features on the material performance, p articularly the critical influence of porosity, splat (grain) size and inter-splat cohesion, on the multiple-splat scale wear and indentatio n behaviour of the coatings. (C) 1997 Elsevier Science S.A.