Microstructural Characteristics of Y 2 O 3 -MgO Composite Coatings Deposited by Suspension Plasma Spray
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Chigozie K. Muoto, Eric H. Jordan, Maurice Gell, and Mark Aindow (Submitted May 2, 2012; in revised form July 17, 2012) Dense composite Y2O3-MgO coatings have been deposited by suspension plasma spray. Ethanol-based suspensions of powders synthesized by thermal decomposition of precursor solutions containing yttrium nitrate (Y[n]) and magnesium nitrate (Mg[n]) or magnesium acetate (Mg[a]) were selected as the feedstock; this gave powders with both phases in each particle, to inhibit phase segregation during solvent evaporation. The influence of powder characteristics on the microstructures of the coatings was investigated. The Y[n]Mg[a] suspension was more stable, with a better dispersion of the component phases than the Y[n]Mg[n] suspension. The coatings deposited using each suspension type exhibited lamellar structures comprising Y2O3 and MgO phases in wavy alternating streaks, with unmelted/semimelted particles entrapped in the lamellae; this indicates that phase segregation still occurred in the molten state. Eutectic structures were formed in the coating generated using the Y[n]Mg[a] suspension, resulting from improved mixing of the component phases in the suspension powder.
Keywords
microstructure, scanning electron microscopy, suspension plasma spray, transmission electron microscopy, yttria-magnesia composites
1. Introduction The plasma spray deposition of composites is potentially a useful way to create materials with a fine phase domain size that can exhibit improved resistance to grain coarsening and can yield improved properties such as hardness (Ref 1-3). The composite materials that resist coarsening and maintain their small phase domains the best are those that consist of immiscible phases. If submicron phase domain sizes are desired in such materials then the feed material needs to have small phase domains because there is insufficient time in the molten state during thermal spray for major rearrangements of the phase geometry. This research focuses on making nano-phase two-phase coatings by suspension plasma spray (SPS). Past efforts using suspension spray have shown that if separate powders of phases A and B are used, mixing is a challenge and phase separation of the powders tends to occur, probably in the suspension itself (Ref 4). To combat this, we have synthesized powders in which the two phases co-exist in the same solid suspended Chigozie K. Muoto, Maurice Gell, and Mark Aindow, Department of Chemical Materials and Biomolecular Engineering, Institute of Materials Science, University of Connecticut, Storrs, CT 06269; and Eric H. Jordan, Department of Mechanical Engineering, Institute of Materials Science, University of Connecticut, Storrs, CT 06269. Contact e-mail: [email protected].
Journal of Thermal Spray Technology
particle, and we have chosen the Y2O3-MgO system for this study. The Y2O3-MgO nano-composite system has attracted a great deal of research interest over the last decade due a combination of excellent mid-wave infrared transparency and enhanced mechanical properties that are
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