Review of New Developments in Suspension and Solution Precursor Thermal Spray Processes
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Andreas Killinger, Rainer Gadow, Georg Mauer, Alexandre Guignard, Robert Vaßen, and Detlev Sto¨ver (Submitted December 23, 2010; in revised form February 21, 2011) Thermal spray coatings from liquid feedstock such as suspensions and solution precursors have received increasing interest due to the unique coating properties obtainable by these processes. Several research groups are working on the basis of plasma as well as on high-velocity oxy-fuel approaches to manufacture advanced nanostructured and nanophased materials. These activities are reflected in various recent publications and conference presentations about feedstock preparation, equipment and process design, modeling techniques, in-process diagnostics, coating characterization, and emerging applications. This article will review these recent developments to give an up-to-date overview and to trace the current trends.
Keywords
high-velocity flame spraying, high-velocity oxyfuel spraying, plasma spraying, solution precursor, suspension
1. Introduction In the field of coating technology atmospheric plasma spray (APS) as well as high-velocity oxy-fuel spray (HVOF) are well-established processes with many recent improvements. Although a fairly wide flexibility of coating morphologies can be obtained, the size of microstructural features within the coatings is typically governed by that of the feedstock. For conventional APS and HVOF processes, this is a well-flowable powder, which can be melted in a very short period of time (mainly less than 1 ms). Thus, the size range is usually about 10-100 lm. Moreover, in most cases the minimum thickness of the coatings is limited to about 40-50 lm, as at least several piled-up splats should form the coating. However, the use of liquid feedstock such as solutions (solution precursor plasma spraying, SPPS, and solution precursor HVOF) or suspensions (suspension plasma spraying, SPS, and highvelocity suspension flame spraying, HVSFS, or HVOF suspension spraying, respectively) yields higher flexibility, as even submicron- to nano-sized coatings can be produced or processed. The rapid development of thermal spray processes using liquid feedstock is reflected by a number of review
Andreas Killinger, and Rainer Gadow, Institut fu¨r Fertigungstechnologie keramischer Bauteile (IFKB), Universita¨t Stuttgart, Stuttgart, Germany; and Georg Mauer, Alexandre Guignard, Robert Vaßen, and Detlev Sto¨ver, Institut fu¨r Energie- und Klimaforschung (IEK-1), Forschungszentrum Ju¨lich GmbH, Ju¨lich, Germany. Contact e-mail: [email protected].
Journal of Thermal Spray Technology
papers published since 2006. Initially, suspensions or solutions were processed for the most part by plasma spraying as reflected in the relevant surveys of Fazilleau et al. (Ref 1), Delbos et al. (Ref 2), and Fauchais et al. (Ref 3, 4). Direct synthesis of oxide ceramic particles by feeding liquid precursors into an oxyfuel flame has been studied since the early 1970s. Special interest focused on the production of nanoparticles by flame spray pyrolysis. As a l
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