Effect of Droplet Characteristics and Substrate Surface Topography on the Final Morphology of Plasma-Sprayed Zirconia Si
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.R. Salimijazi, L. Pershin, T.W. Coyle, J. Mostaghimi, S. Chandra, Y.C. Lau, L. Rosenzweig, and E. Moran (Submitted November 21, 2006; in revised form January 24, 2007) The morphology of atmospheric plasma-sprayed yttria-stabilized zirconia single splats has been studied. Single splats of plasma-sprayed ZrO2-7%Y2O3 powder have been collected on polished stainless steel substrates kept at three different temperatures (room temperature, 300 °C, and 600 °C). The effect of heating on the substrates surface topography was evaluated. The effects of spray process parameters such as substrate temperature, particle temperature, and velocity on the morphology of single splats was studied. Variation of splat shape with location within the footprint of plasma spray was investigated. Pore and microcrack formation, splashing behavior, splat/substrate, and splat/splat interfaces were analyzed. Splat morphology and diameter, satellite particles, and splashing behavior were recorded using both scanning electron microscopy and image analysis. Splat/substrate and splat/splat interfaces were studied from cross sections prepared by focused ion beam milling. Results showed primarily disk-shape morphology and no evidence of delamination along the splat/substrate interface at 600 °C substrate temperature. Overlapped splats showed evidence of melting (microwelding) at splat boundaries. Splat thickness was measured to be less than 1 lm for all spray conditions.
Keywords
coatings for engine components, influence of process parameters, coatings for gas turbine components, splat morphology, surface and interface characterization
1. Introduction Yttria-stabilized zirconia plasma spray coatings are widely used for thermal, oxidation, and hot corrosion protection applications in gas turbine and diesel engines. The most common thermal barrier coating material is 7%Y2O3-ZrO2 because of its high temperature phase stability, low thermal diffusivity, and high coefficient of thermal expansion (CTE). It is known that plasma-sprayed deposits consist of individual splat lamellae formed from molten and resolidified particles which are connected together by mechanical and chemical bonding. Pores are also found at inter-lamellae boundaries, the significance of which depends on the thermal spray process parameters. Thus, the final physical and mechanical properties of such deposits depend on the morphology of individual splats, adhesion H.R. Salimijazi, L. Pershin, T.W. Coyle, J. Mostaghimi, and S. Chandra, Centre for Advanced Coating Technologies, University of Toronto, Toronto, Canada; Y.C. Lau, L. Rosenzweig, and E. Moran, GE Global Research, Niskayuna, NY, USA. Contact e-mail: [email protected].
Journal of Thermal Spray Technology
between the deposited structure and substrate, cohesive strength within individual splats, the size and morphology of pores, cracks, and defects, and also on the microstructure of the splats themselves (Ref 1-5). It was shown that the in-flight temperature and velocity of the particle upon impact influence the flattening
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