Effect of alloying active elements of powder on spreading behaviour of plasma spray splats

To understand the effect of active elements Cr and Al on droplet spreading, pure Ni, Ni-20Cr and Ni-5Al alloy powders with size of 45~63µm were plasma sprayed on mirror-polished 304stainless steel heated to different temperatures. Substrate heating resulted in very little change in surface roughness.  However, there was a measureable change in the surface chemistry of the outermost few nanometers, which became increasingly enriched in Fe at higher temperatures. Splat morphologies were characterised and transition temperatures estimated. The transition from splashed to disk splats was not solely dependent on the substrate temperature. In some cases, splashing still occurred to a measureable extent at relatively high substrate temperatures, even above temperatures at which adsorbates (water) should be removed from the surface. The splashing behaviour could be correlated to a combination of the surface chemistry change in the substrate and the presence of active elements in the coating materials. For publication.