Experimental Study of the Impact of Substrate Shape and Tilting on Particle Velocity in Suspension Plasma Spraying

Suspension plasma spraying has shown its capacity to deposit finely structured coatings with a wide range of microstructures including columnar microstructures that are generally sought in thermal barrier coating applications for gas turbines. However, some challenges are still to be taken up before the application of the technology at an industrial scale. One deals with the deposition of a uniform and reliable coating on a complex substrate shape. This work offers an experimental observation of submicron particle streams close to the substrate in order to understand mechanisms of deposition. Effects of the substrate shape and tilting were investigated on particle velocity, direction and coating growth. It was shown that particle velocities and directions are disrupted by the substrate presence up to 10 mm upstream. When the substrate is a cylinder or in a tilted orientation to the plasma jet, particles kinetic behavior is less affected. Finally, submicron particle velocity vectors orientation near impact greatly shape the coating morphology. When impacting with a 40° angle of incidence, columns appeared on beads, contrary to submicron particle streams impacting orthogonally to the substrate surface.