ALUMINA COATINGS BY ATMOSPHERIC DC PLASMA SPRAYING OF ALUMINIUM HYDROXIDE POWDERS

Boehmite (-50+5 µm) and α fused and crushed (FC) alumina (-45+22 µm) powders have been sprayed with same plasma generation conditions at different spraying distances. The microstructural observations of the powders sprayed in water, those of the splats and the characterization of the coatings through their Vickers hardness, α phase content, microstructural observation indicate no significant differences between both type of coatings. However it was noticed that the boehmite powder characteristics were not well adapted for plasma spraying (size range and particule porosity) resulting in an enhanced heat propagation phenomenon. Moreover at short distances it seems that the thermal deshydratation of the boehmite leads to a poor melting state resulting in a more extensively fingered splat morphology than that obtained with FC α alumina powder.