Influence of Microstructure on Thermal Properties of Axial Suspension Plasma-Sprayed YSZ Thermal Barrier Coatings
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JTTEE5 25:202–212 DOI: 10.1007/s11666-015-0355-7 1059-9630/$19.00 ASM International
Influence of Microstructure on Thermal Properties of Axial Suspension PlasmaSprayed YSZ Thermal Barrier Coatings Ashish Ganvir, Nicholas Curry, Nicolaie Markocsan, Per Nyle´n, Shrikant Joshi, Monika Vilemova, and Zdenek Pala (Submitted May 6, 2015; in revised form November 10, 2015) Suspension plasma spraying is a relatively new thermal spaying technique to produce advanced thermal barrier coatings (TBCs) and enables production of coatings with a variety of structures—highly dense, highly porous, segmented, or columnar. This work investigates suspension plasma-sprayed TBCs produced using axial injection with different process parameters. The influence of coating microstructure on thermal properties was of specific interest. Tests carried out included microstructural analysis, phase analysis, determination of porosity, and pore size distribution, as well as thermal diffusivity/conductivity measurements. Results showed that axial suspension plasma spraying process makes it possible to produce various columnar-type coatings under different processing conditions. Significant influence of microstructural features on thermal properties of the coatings was noted. In particular, the process parameter-dependent microstructural attributes, such as porosity, column density, and crystallite size, were shown to govern the thermal diffusivity and thermal conductivity of the coating.
Keywords
axial injection, columnar microstructure, porosity, suspension plasma spraying, thermal conductivity, thermal diffusivity
1. Introduction Thermal barrier coatings (TBCs) find increasing interest for various applications to protect high temperature metallic components. For example, the operating temperature in gas turbines has been continuously increased to enhance its thermal efficiency by applying TBCs on hot gas path components (Ref 1). Traditional techniques to generate TBCs for a long time were Atmospheric Plasma Spraying (APS) or Electron Beam Physical Vapor Deposition (EB-PVD) (Ref 2). In order to realize high performance TBCs, high coating lifetime and low thermal conductivity are among the two most important properties of the coating. This work is focused on achieving the latter. An advantage of APS is its higher process flexibility and lower cost, with the APS TBCs also showing lower assprayed thermal conductivity and acceptable lifetime (Ref This article is an invited paper selected from presentations at the 2015 International Thermal Spray Conference, held May 11-14, 2015, in Long Beach, California, USA, and has been expanded from the original presentation. Ashish Ganvir, Nicholas Curry, Nicolaie Markocsan, Per Nyle´n, and Shrikant Joshi, University West, 46186 Trollha¨ttan Sweden; and Monika Vilemova and Zdenek Pala, IPP, Prague, Czech Republic. Contact e-mail: gmashish19@gmail. com and [email protected].
202—Volume 25(1-2) January 2016
3). EB-PVD TBCs have been known to yield a columnartype microstructure which has been shown to prolong
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