J. Cedelle, University of Limoges, 87060 LIMOGES Cedex, France; Y. Tanaka, University of Limoges, 87060 Limoges Cedex, France; M. Vardelle, P. Fauchais, University of Limoges, Limoges, France
Many properties (thermal, electrical, mechanical…) of thermal sprayed coatings are strongly linked to the real contacts between the “piled-up” splats. The quality of contact depends on the particle impact pressure, that varies drastically with droplet (size, velocity…) and substrate parameters (temperature, topography).
Two different techniques have been developed in order to study plasma sprayed particle behaviour at impact. The first one allows direct studying under dc plasma spray conditions, while the latter one, based on the millimetre sized free falling drop, enables the visualization of flattening phenomena, but at larger scale. These two techniques bring complementary approaches and results. Results show that flattening time and cooling rate of the lamellae (metallic and ceramic) are improved with stainless steel substrate surface modification at the nanoscale and preheating over the transition temperature. Experiments of wettability show that the presence of nanopics increases the contact angle of the liquid on the substrates and reduces thermal contact resistance at interface. Two phenomena seem to govern the behavior of the drop during its spreading and cooling. For zirconia substrates, preheating over Tt increases the substrate wettability due to the desorption of contaminants . for stainless steel substrate,the surface is modified with a formation of peaks resulting on positive skewness more increasing the wettability and thus the cooling rates
