Plasma Sprayed Dense MgO-Y 2 O 3 Nanocomposite Coatings Using Sol-Gel Combustion Synthesized Powder
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Jiwen Wang, Eric H. Jordan, and Maurice Gell (Submitted July 13, 2009; in revised form March 8, 2010) MgO-Y2O3 nanostructured composite powder (volume ratio of 50:50) was synthesized by a sol-gel combustion process which generated crystal sizes in the 10-20 nm range. The MgO-Y2O3 nanopowder was plasma sprayed using a conventional, DC arc plasma spray system. X-ray diffraction analysis shows that the as-sprayed MgO-Y2O3 coating is composed of cubic MgO and Y2O3 phases and has ~95% density. Microstructure characterization by SEM reveals that the as-sprayed coating has fine grain sizes of 100-300 nm as a result of rapid solidification. The hardness of the coating, 7.5 ± 0.6 GPa, is higher than that of coarse-grained, dense MgO, and Y2O3 ceramics. This approach demonstrates the potential of plasma spray processes for making thick, dense MgO-Y2O3 nanocomposite performs for applications as durable, infrared windows.
Keywords
air plasma spray, magnesia, nanocomposite, plasma spray coatings, yttria
1. Introduction Plasma sprayed nanostructured and nanocomposite coatings have exhibited promising mechanical properties, such as hardness, strength, and wear resistance over conventional micrograined coatings and therefore have gained considerable attention (Ref 1-3). Different plasma spray technologies have been used to achieve nanostructured and nanocomposite coatings, which include air plasma spray (APS) (Ref 1-5), suspension plasma spray (SPS) (Ref 6-10), and solution precursor plasma spray (SPPS) (Ref 11, 12). In APS, nanoparticles cannot be thermally sprayed using conventional powder feeders. The powders must be agglomerated to sprayable sizes using a spray dry process (Ref 1, 2). Recently, MgO-Y2O3 nanocomposites were reported to have excellent mid-infrared transparency and improved mechanical properties for use as infrared window materials (Ref 13). In Ref 13, the powder was made by a combustion spray pyrolysis process and consolidated to bulk structures, using a series of powder classification, Jiwen Wang, Department of Chemical, Materials and Biomolecular Engineering, Institute of Materials Science, University of Connecticut, Storrs, CT and Navy Research Laboratory, Code 6364, Washington, DC 20375; Eric H. Jordan, Department of Mechanical Engineering, Institute of Materials Science, University of Connecticut, Storrs, CT; and Maurice Gell, Department of Chemical, Materials and Biomolecular Engineering, Institute of Materials Science, University of Connecticut, Storrs, CT. Contact e-mails: [email protected] and [email protected].
Journal of Thermal Spray Technology
purification, and sintering techniques. This study seeks to directly deposit a nanocomposite preform, with fewer consolidation steps, using APS. Limiting the phase domain size to the nanoscale is important to minimize the light scattering at the two-phase grain boundaries and to further improve the mechanical properties of MgO-Y2O3 nanocomposite ceramics. The rapid solidification characteristics of plasma spray may be a useful tool to achieve such req
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