Demands, Potentials, and Economic Aspects of Thermal Spraying with Suspensions: A Critical Review
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ilofteia-Laura Toma, Annegret Potthoff, Lutz-Michael Berger, and Christoph Leyens (Submitted January 28, 2015; in revised form June 22, 2015) Research and development work for about one decade have demonstrated many unique thermal spray coating properties, particularly for oxide ceramic coatings by using suspensions of fine powders as feedstock in APS and HVOF processes. Some particular advantages are direct feeding of fine nano- and submicron-scale particles avoiding special feedstock powder preparation, ability to produce coating thicknesses ranging from 10 to 50 lm, homogeneous microstructure with less anisotropy and lower surface roughness compared to conventional coatings, possibility of retention of the initial crystalline phases, and others. This paper discusses the main aspects of thermal spraying with suspensions which have been taken into account in order to produce these coatings on an economical way. The economic efficiency of the process depends on the availability of suitable additional system components (suspension feeder, injectors), on the development and handling of stable suspensions, as well as on the high process stability for acceptance at industrial scale. Special focus is made on the development and processability of highly concentrated water-based suspensions. While costs and operational safety clearly speak for use of water as a liquid media for preparing suspensions on an industrial scale, its use is often critically discussed due to the required higher heat input during spraying compared to alcoholic suspensions.
Keywords
concentrated suspension, economic aspects, hardware development, process stability, suspension thermal spraying
1. Introduction For about one decade, modified thermal spraying processes using suspensions of fine submicron- and nanosizedpowders as feedstock materials have continuously gained increasing interest in the scientific world. Extensive development efforts reflected by an important number of papers and reviews made over the last years have uncovered the potential of thermal spraying with suspensions, e.g., Ref 1-6. Compared with conventional thermal spray methods, the suspension spraying technique presents some advantages: direct feeding of fine nano- and submicronscale particles; tailored coating architecture that can be adapted to the given application; less anisotropy and lower surface roughness of the coating; retention of the initial Filofteia-Laura Toma, Fraunhofer Institute for Material and Beam Technology (IWS), Winterbergstrasse 28, 01277 Dresden, Germany; Annegret Potthoff and Lutz-Michael Berger, Fraunhofer Institute for Ceramic Materials and Systems (IKTS), Winterbergstrasse 28, 01277 Dresden, Germany; and Christoph Leyens, Fraunhofer Institute for Material and Beam Technology (IWS), Winterbergstrasse 28, 01277 Dresden, Germany and Technische Universita´t Dresden (TUD), Helmholtzstrabe 10, 01069 Dresden, Germany. Contact e-mail: [email protected].
Journal of Thermal Spray Technology
crystalline phases (i.e., a-Al2O3, anatase m
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