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1994 |
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Wednesday, May 05, 2010, Moor Room 12:00 PM Modeling and Simulation 2 |
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In situ observation of impact phenomena of zirconia molten drops in millimeter scale via aerodynamic levitator |
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Kentaro Shinoda / Center for Thermal Spray Research
Stony Brook University, USA Kosuke Nagashio/ The University of Tokyo, Japan Hideyuki Murakami/ National Institute for Materials Science (NIMS), Japan Seiji Kuroda*/ National Insititute for Materials Science (NIMS), Japan Kazuhiko Kuribayashi/ Shibaura Institute of Technology, Japan |
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The impact experiment of millimeter-scale drops gives us a deep insight into the deposition process of plasma spraying, which is difficult to observe. Recent developments in the experiments have enabled not only observation of impact of metal drops but also that of oxide molten drops such as alumina and yttrium-aluminum garnet. However, no studies have been reported on that of yttria-stabilized zirconia (YSZ) drops, even though YSZ is widely sprayed as a thermal barrier coating. In this study, we present a novel method to observe the impact phenomena of YSZ molten drops in millimeter scale utilizing an aerodynamic levitator (ADL). This ADL nozzle was designed to split into two parts by an electromagnetic coil so that a levitated sample could be dropped downward through the nozzle. YSZ spheres approximately 2 mm in diameter were made from commercially available 8 wt. % YSZ powder. The YSZ sphere was levitated in the ADL nozzle with oxygen gas, and melted with a carbon dioxide gas laser. After the sample temperature reached to a target temperature, the ADL nozzle was split and the sample was dropped onto a stainless steel substrate at the speed of 1.7 m/s. The spreading and solidification behavior of the YSZ molten drops was observed with a high-speed video camera. The effect of drop undercoolings as well as those of substrate temperature and roughness was examined. When a drop impacted at a super heated state, the solidification occurred after the completion of the drop spread. Meanwhile, when a drop impacted at the undercooled state, the solidification occurred just after the impact and suppressed the spread. The substrate surface roughness and temperature affected the roundness of splats as well as the degree of flattening. Some implications on the deposition process of plasma spraying will be discussed. |