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TECHNICAL PAPERS

Optimization of Plasma Spray Processing Parameters for Deposition of Nanostructured Powders for Coating Formation

[+] Author and Article Information
I. Ahmed

Mechanical Engineering,Wichita State Universityikram.ahmed@wichita.edu

T. L. Bergman

Mechanical Engineering,The University of Connecticuttberg@engr.uconn.edu

J. Fluids Eng 128(2), 394-401 (Mar 01, 2006) (8 pages) doi:10.1115/1.2170131 History:

When nanostructured powder particles are used for thermal spray coatings, the retention of the original nanostructure that is engineered into the raw stock is a principal objective, along with production of some molten material in order to adhere the sprayed material to the surface being coated. Therefore, in contrast with spraying conventional powders, complete melting of the nanostructured raw stock is to be avoided. In this study, the melting and resolidification of sprayed material is correlated to a spray processing parameter that has been introduced in the literature by some of the spray processing practitioners. Using computer modeling, processing of zirconia agglomerates with plasma spraying has been simulated. Transition regions for the phase change response of the sprayed material to the thermal processing conditions are identified. The retained nanostructure content and liquid fraction of the sprayed material are correlated to particle diameters, injection velocities, as well as this thermal spray processing parameter. Finally, a novel method to produce desired coatings composed of partially molten material using a bimodal particle size distribution of the sprayed powder is suggested.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

A schematic representation of the plasma spray system modeled here: the nozzle diameter is 8mm; the standoff distance (between the nozzle exit and the substrate) is 100mm, and the disc shaped substrate has a diameter of 50mm and a thickness of 3mm. The powder injector diameter is 2mm, and it is positioned radially inward at a distance of 5mm from the nozzle exit as well as from the jet axis.

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Figure 2

Retained nanostructure in particles sprayed with three injection velocities and two plasma gas compositions: solid symbols: 80% argon, open symbols: 86.3% argon

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Figure 3

Instantaneous liquid fraction for the particles presented in Fig. 2, at a standoff distance of 100mm

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Figure 4

Retained nanostructure versus molten material fraction correlation as a function of injection velocity. Symbols represent different particle sizes as before (Fig. 2), but no differentiation is made regarding plasma composition. The dashed line represents Eq. 1.

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Figure 5

Retained nanostructure versus molten material fraction correlation as a function of CPSP* levels. The relative size of each symbol represents the injection velocity (5m∕s, 15m∕s, and 30m∕s) of the particle of particular size; see Fig. 2 for a legend for particle sizes).

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Figure 6

Aggregate retained nanostructure (top) and liquid fraction (bottom) in a powder batch consisting of equal numbers of 30μm and 70μm agglomerates sprayed with the same three injection velocities and various CPSP* values as in Fig. 5

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Figure 7

Aggregate retained nanostructure versus liquid fraction correlations. (a) For the powder batch presented in Fig. 6 (with a binary distribution, with 30μm and 70μm particles only). (b) For a batch of powder with a Gaussian mass distribution for particles sizes 30μm through 70μm with a mean diameter of 50μm and a standard deviation of 10μm. See the legend of Fig. 6 for particle injection velocity (Vinj) information.

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