The deformation and cooling of ceramic particles sprayed with a thermal radio-frequency plasma under atmospheric conditions |
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Authors: | B Dzur H Wilhelmi G Nutsch |
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Affiliation: | 1. Technische Universit?t Ilmenau, FG Plasma und Oberfl?chentechnik, Kirchhoffstra?e 1, D-98684, Ilmenau, Germany
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Abstract: | Common thermal-spray techniques use the strong acceleration of powder particles to produce dense ceramic coatings with high
bond strength. The residence time of the powder particles within the plasma jet is correspondingly low, and only relatively
small particles can be molten. In this work, on the contrary, an inductively coupled radio-frequency (RF) inductively coupled
plasma (ICP) torch was used to spray large oxide-ceramic powder particles under atmospheric conditions. The slow plasma flow
of a RF plasma leads to large residence times of the powder particles, so that the powder size of the feedstock can be 100
μm and more. It was observed that these particles will not be strongly accelerated in the plasma and that their velocity at
the moment of impact is in the range of 10 to 20 m/s. Ceramic coatings were ICP sprayed with a low porosity and a high bond
strength, similar to direct current (DC) or high-velocity-oxygen-fuel (HVOF) sprayed coatings. The morphology of ICP-sprayed
particles on smooth steel surfaces, as a function of the surface temperature, is described and compared with DC plasma-sprayed
splats. Furthermore, the degree of deformation was measured and determined by different models, and the pronounced contact
zones formed between the pancake and the substrate were investigated. The ICP-sprayed ceramic coatings show some special properties,
such as the absence of metastable crystalline phases, which are common in other spray technologies. |
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Keywords: | alumina coatings coating formation microstructure particle deformation plasma spraying RF inductively coupled plasma |
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