COMPARISON OF PLASMA-SPRAYED ALUMINA COATINGS BY RF AND DC PLASMA SPRAYING

Splat size and shape-factor distributions for plasma-sprayed alumina particles on various substrates were studied using a setup derived from the line-scan test. Direct-current (dc) and radiofrequency (rf) plasma torches were used to study the influence of particle velocity at impact, The influence of substrate temperature prior to spraying also was studied, Splats collected on smooth substrates kept below 100 degrees C were extensively fingered and had poor substrate contact, When the substrates were heated to 300 degrees C before spraying, the splats became disk-shaped and their substrate contact was very good, Similar results were obtained for rough substrates, Coating adhesion decreased with particle velocity and was lower for the de plasma torch when using larger particles, which did not melt as well as smaller ones, Melting and adhesion were much improved with the rf torch.