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2932 |
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Thursday, September 29, 2011, Saal B2.2 9:50 AM HVOF & Flame Spraying 2 |
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Influence of the suspension characteristics and spraying parameters on the properties of dense suspension-HVOF sprayed Al2O3 coatings |
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Filofteia-Laura Toma* / Fraunhofer IWS, Germany Lutz-Michael Berger / Fraunhofer Institute IWS, Germany Stefan Langner/ Fraunhofer Institute IWS, Germany Conny Rödel/ Fraunhofer Institute IKTS, Germany Annegrett Potthoff/ Fraunhofer Institute IKTS, Germany |
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In this work suspension-HVOF spraying (S-HVOF) was proposed to produce dense and mechanical stable Al2O3 sprayed coatings with high content of alpha-phase. Spray-available feedstock aqueous suspensions with various contents of solid (from 25 wt.% up to 50 wt.%) have been developed starting from two commercial sub-micron alpha-Al2O3 powders, characterized by different purity degree levels. The influence of the load content on the particles size distribution, stability, and rheological properties of the suspensions have been investigated. The suspensions have been internally injected in the modified combustion chamber of a HVOF-TopGun. The spray parameters have been carefully chosen in order to obtain dense Al2O3 coatings with high thicknesses. Coating microstructures, phase compositions, mechanical stabilities resulting from interactions between suspension characteristics and spray parameters are presented. Injection of a suspension with high solid load allows the preparation of thick and mechanically stable coatings with high rates of deposition. An increase content of the initial alpha-phase in the coating can be obtained by the injection of suspensions containing powders with very high purity level. |