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1195 |
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Wednesday, June 04, 2008, Room 04 9:20 AM HVOF and Flame Spraying New very hard coatings and modern powder feeding for economic dense coatings against wear and corrosion |
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Microstructural and tribological investigation of high velocity suspension flame sprayed (HVSFS) Al2O3 coatings |
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Giovanni Bolelli / Department of Engineering "Enzo Ferrari", University of Modena and Reggio Emilia, Italy Johannes Rauch/ Universität Stuttgart, Institute for Manufacturing Technologies of Ceramic Components and Composites, Germany Valeria Cannillo/ Università di Modena e Reggio Emilia, Department of Materials and Environmental Engineering, Italy Andreas Killinger/ Universität Stuttgart, Institute for Manufacturing Technologies of Ceramic Components and Composites, Germany Luca Lusvarghi*/ Università di Modena e Reggio Emilia, Department of Materials and Environmental Engineering, Italy Rainer Gadow/ Universität Stuttgart, Institute for Manufacturing Technologies of Ceramic Components and Composites, Germany |
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The High-Velocity Suspension Flame Spraying (HVSFS) process has recently been introduced as a modification to the conventional HVOF technique, enabling the use of liquid suspension feedstock instead of dry powders. Thus, micrometric or nanometric particles, which could not be fed to the torch in dry form due to insufficient flowability, can now be thermally sprayed. The small particle size allows full melting and deposition of refractory ceramics. It also results in very small lamella size: thus, very low porosity (extremely small pores) is achieved. Moreover, this implies the ability to manufacture even thin (¡Ü50¦Ìm) deposits, preserving high layer quality. In this research, Al2O3 coatings have been manufactured by the HVSFS technique using a nanopowder suspension. Their structural and microstructural characteristics were investigated by XRD and SEM; hardness and elastic modulus were assessed by depth-sensing Berkovich microindentation; the tribological behaviour was studied by ball-on-disk testing at room temperature and at 400¡ãC. The results were compared to those obtained on conventional Al2O3 coatings manufactured by atmospheric plasma spraying and by HVOF using commercially available feedstock. The HVSFS coatings possess very low porosity, high hardness, smooth surface finish. The smaller lamellae possess grain size <100nm. The coatings undergo very low wear loss during tribological testing, regardless of the test temperature. |