Session *BB2.3

2:15 PM *BB2.3
TRANSPORT PHENOMENA AND REACTION RATES IN THE IMPACT AND SOLIDIFICATION PROCESSES OF PLASMA-SPRAYED DROPLETS. Armelle Vardelle, Univ of Limoges, Laboratoire Matériaux Céramiques et Traitements de Surface, Limoges, FRANCE.

In the plasma spray process, when particles impinge on the substrate, they undergo severe deformation and rapid solidification. Particle spreading determine the geometry of the resulting splat and porosity formation while the cooling process conditions the cooling rate, selection of crystalline phases, crystal growth, and thus the microstructure. The transient behaviour of the molten droplet in the flattening and freezing processes controls the quality of the contact between the splat and the underlying layer, and the properties of the coating. The need for final products with closely controlled and reproducible properties requires that the design and control strategy of thermal spraying methods be based on a broad understanding of the transport and chemical reaction phenomena which occur during the residence of particles in the plasma jet and after impact on the substrate. This paper examines the role of the parameters of both particles at impact and substrate on splat formation and the properties of coating. This is done in light of transport phenomena theory and experimental evidence, by considering the formation of splats and the solidification and overlaying of splats that form the final coating.