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2142 |
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Tuesday, May 04, 2010, Sophia Room 2:00 PM Young Scientists |
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Flattening and cooling of millimetre and micrometre sized alumina drops |
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Simon Goutier* / University of Limoges, France Michel Vardelle / SPCTS Laboratory, University of limoges, France Jean Claude Labbe/ SPCTS Laboratory, University of limoges, France Pierre Fauchais/ SPCTS Laboratory, University of limoges, France |
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Coating adhesion-cohesion is strongly linked to the real contact between splats and substrate and between themselves. Unfortunately, the study of a single micrometer sized splat interface, resulting from flattening and solidification processes and dynamic behaviors, all occurring in a few microseconds, is extremely complex. In order to overcome problems due to time and dimension scales, many previous works were devoted to the flattening of millimetre-sized drops. But, because of difficulties in producing millimetre sized ceramic fully melted drops, most works deal with metals or alloys. The aim of this work is to compare the flattening and the cooling at two different scales. The first study concerns the millimetre-sized scale. A set-up has been developed, at the SPCTS Laboratory, to produce fully melted, millimetre-sized, ceramic or metallic drops with impact velocities up to 10 m/s. Such impact velocities allow reaching impact Weber numbers, close to those of the plasma spray process (We=2300 for alumina). A fast camera (4000 image/s) follows the drop flattening and, combined with temperature evolution measured with a fast pyrometer (4000 Hz), it allows understanding the coupling between flattening and solidification. The second study is related to the micrometre-sized scale. A direct current plasma torch is used to melt alumina particles (with sizes between 10 and 45 µm). The experimental set-up is composed of a fast (50ns) two-color pyrometer and an imaging system, i.e., two fast CCD cameras triggered by the velocity signal. The experimental investigation of the splashing phenomenon when a single particle hits the substrate is carried out using an imaging technique with a fast CCD camera aimed either parallel to the substrate for impact splashing or almost orthogonal to it for flattening splashing. The cooling rate of the splat is estimated from the time- temperature evolution of the lamella. Results obtained at both scales are compared. |