Effect of particle pre-oxidation on Ni and Ni20Cr splat formation during plasma spraying

During plasma spraying in air, molten metallic droplets can develop a surface oxide shell which is postulated to play a significant role on the subsequent impact and spreading on the substrate surface resulting in splat formation. In this work, oxide layers on Ni and Ni20Cr particles were formed through isothermal pre-oxidation prior to spraying and their influence on droplet spreading and splat-substrate interfacial interactions was investigated. The results showed that the presence of this oxide shell readily induced finger splashing, irrespective of the oxide shell thickness. In addition, small oxide nodules were frequently detected inside the splats. An oxygen-enriched interfacial interlayer was observed for the pre-oxidized-Ni splats. A mechanism is proposed to account for the inclusion of oxide fragments from the particle surface oxide shell, in the deposition of single plasma-sprayed Ni and Ni20Cr splats.