Individual splats are the building blocks of any thermal spray coating. Near the coating-substrate interface, they affect coating properties like adhesion strength. This article examines the effect of substrate heating on droplet splashing. Nickel powder was plasma-sprayed onto a polished stainless steel substrate at various temperatures and the resulting splats were analyzed. Droplet splashing was observed experimentally for three different cases: low substrate temperature, high substrate temperature, and droplet-splat interaction. Mechanisms for splashing were explained with the help of computer-generated nickel droplet impacts. The article proposes that the jetting of molten metal is not triggered by the formation of a central splat but rather a solidified ring on the periphery of the splat. It was observed that, on substrates below 350 deg C, splashing is triggered by solidification at the edge of the spreading droplet. Interactions with previously deposited splats also cause droplets to splash.

This paper presents the experimental validation of a curvilinear novel nozzle design. Their effect on the speed and temperature of the particles in flight, on the porosity and adhesive force of the coatings is measured and compared with conventional conical nozzle devices. The nozzle testing is performed using a Miller SG100 dc plasma torch. It is observed that the curvilinear nozzle produced denser and more uniform coatings with lower porosity and higher adhesive force. This could be achieved by increasing the flight temperature of the particles and ensuring more complete melting of the particles. The velocity profile of the particles on the substrate remained unchanged. Paper includes a German-language abstract.