Mechanisms of ceramic coating deposition in solution-precursor plasma spray
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Alper Ozturk Department of Mechanical Engineering, Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269-3136
Liangde Xie Department of Metallurgy and Materials Engineering, Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269-3136
Eric H. Jordan and Baki M. Cetegen Department of Mechanical Engineering, Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269-3136
Maurice Gell Department of Metallurgy and Materials Engineering, Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269-3136
Xinqin Ma Inframat Corporation, Farmington, Connecticut 06032
Nitin P. Padtureb) Department of Metallurgy and Materials Engineering, Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269-3136 (Received 17 April 2002; accepted 13 June 2002)
The solution-precursor plasma spray (SPPS) method is a new process for depositing thick ceramic coatings, where solution feedstock (liquid) is injected into a plasma. This versatile method has several advantages over the conventional plasma spray method, and it can be used to deposit nanostructured, porous coatings of a wide variety of oxide and non-oxide ceramics for a myriad of possible applications. In an effort to understand the SPPS deposition process, key diagnostic and characterization experiments were performed on SPPS coatings in the Y2O3-stabilized ZrO2 (YSZ) system. The results from these experiments show that there are multiple pathways to SPPS coating formation. The atomized precursor droplets undergo rapid evaporation and breakup in the plasma. This is followed by precipitation, gelation, pyrolysis, and sintering. The different types of particles reach the substrate and are bonded to the substrate or the coating by sintering in the heat of the plasma. The precursor also reaches the substrate or the coating. This precursor pyrolyzes in situ on the substrate, either after it reaches a “cold” substrate or upon contact on a “hot” substrate and helps bond the particles. The coating microstructure evolves during SPPS deposition as the coating temperature reaches approximately 770 °C. I. INTRODUCTION
Although the plasma spray process is more commonly used for depositing metallic coatings, this process has found widespread use for the deposition of thick ceramic coatings. In this process, ceramic-powder feedstock is
a)
Present address: United Technologies Center, East Hartford, CT 06108. b) Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 17, No. 9, Sep 2002
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injected into the plasma, causing powder particles to melt into droplets that are propelled toward a substrate, typically a metal.1,2 Solidification of the droplet stream onto the substrate as “splats” results in the buildup of thick ceramic coatings, which are widely used to protect metallic structural components from corrosion, wear, and erosion and to provide lubrication and
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