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DEVELOPMENT OF EXPERIMENTAL SET-UPS ALLOWING CHARACTERIZING THE INFLUENCE OF NANO-SCALE SUBSTRATE TOPOGRAPHY ONTO THE FLATTENING AND SOLIDIFICATION OF MICROMETER AND MILLIMETER SIZED MOLTEN DROPLET

DOI: 10.1615/IHTC13.p8.300
13 pages

Michel Vardelle
LMCTS-URA 320, University of Limoges, 123 Avenue Albert Thomas -87060 Limoges Cedex - France

J. Cedelle
SPCTS Laboratory, University of Limoges, France

Y. Tanaka
Ariake National College, Fukuoka, Japan

Pierre Fauchais
Laboratoire Sciences des Procedes Ceramiques et de Traitements de Surface UMR CNRS 6638 University of Limoges 123 avenue Albert Thomas, 87060 LIMOGES - France

Abstrakt

Plasma sprayed coating thermo mechanical properties depend strongly upon the contact between the layered splats forming the coating. These contacts are linked to the flattening and the solidification of the impacting molten particles. This paper describes experiments performed on micrometer sized zirconia particles (spraying) with flattening time in the μs range and millimeter sized ones (falling drops) with flattening timein the ms range. They consist in measuring the parameters for a single particle prior to its impact (temperature, velocity, diameter), its temperature and surface time evolution during its flattening. Such measurements allow following flattening velocity links to its wettability an dits cooling rate and also evaluating the thermal contact resistance RTC between the flattening paticle and the substrate. These experiments performed on a smooth stainless steel (304 L) and plasma sprayed zirconia substrates have shown that the flattening velocity and cooling rate increase when preheating substrate over a so-called transition temperature Tt. With the ZrO2 substrate preheating allows eliminating the contaminants at the surface while with 304 L besides this elimination, the skewness parameter of the surface becomes positive improving the contact flattening particle-substrate. For preheated substrates over Tt the thermal contact resistance RTC mean value decreases significantly relatively to a room temperature substrate. At last RTC varies with time probably in connection with impacting pressure strong decrease with flattening time in the millisecond range.

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