Low Thermal Conductivity Yttria-Stabilized Zirconia Thermal Barrier Coatings Using the Solution Precursor Plasma Spray P
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Eric H. Jordan, Chen Jiang, Jeffrey Roth, and Maurice Gell (Submitted November 27, 2013; in revised form January 14, 2014) The primary function of thermal barrier coatings (TBCs) is to insulate the underlying metal from high temperature gases in gas turbine engines. As a consequence, low thermal conductivity and high durability are the primary properties of interest. In this work, the solution precursor plasma spray (SPPS) process was used to create layered porosity, called inter-pass boundaries, in yttria-stabilized zirconia (YSZ) TBCs. IPBs have been shown to be effective in reducing thermal conductivity. Optimization of the IPB microstructure by the SPPS process produced YSZ TBCs with a thermal conductivity of 0.6 W/mK, an approximately 50% reduction compared to standard air plasma sprayed (APS) coatings. In preliminary tests, SPPS YSZ with IPBs exhibited equal or greater furnace thermal cycles and erosion resistance compared to regular SPPS and commercially made APS YSZ TBCs.
Keywords
erosion resistance, plasma spray, spray parameters, thermal barrier coatings, thermal conductivity, thermal cyclic durability
List of Symbols
k a cp q
Nomenclature
1. Introduction Thermal barrier coatings (TBCs) consist of a ceramic insulating top layer and an aluminum-rich bond-coat that promotes growth of a protective aluminum oxide layer. TBCs are applied to internally cooled metallic gas turbine components to reduce the metal temperature when the part is subjected to high temperature gases. TBCs can decrease the underlying component temperatures by 100300 C (Ref 1, 2). At present, most of commercial TBCs used in gas turbines are made of yttria-stabilized zirconia (YSZ) because of its relatively high thermal expansion coefficient and fracture toughness. There is a strong economic driving force to develop alternate TBCs with low thermal conductivity and increased use temperatures (Ref 1, 3-19). Reduced thermal conductivity provides a larger temperature drop for a given coating thickness, which translates to increased component durability and/or thermodynamic efficiency. Alternative TBC compositions involving expensive rare earth elements have been studied, the maximum use temperatures of which are considEric H. Jordan, Department of Mechanical Engineering, University of Connecticut, Storrs, CT and Institute of Materials Science, University of Connecticut, Storrs, CT; Chen Jiang and Maurice Gell, Department of Materials Science and Engineering, University of Connecticut, Storrs, CT and Institute of Materials Science, University of Connecticut, Storrs, CT; and Jeffrey Roth, Institute of Materials Science, University of Connecticut, Storrs, CT. Contact e-mail: [email protected].
Journal of Thermal Spray Technology
Thermal conductivity, W/mK Thermal diffusivity, m2/s Specific heat, J/gK Density, kg/m3
TBC SPPS IPB Y(F/P)SZ APS FOD OEM HVOF LPPS SEM FEA EB-PVD
Thermal barrier coatings Solution precursor plasma spray Inter-pass boundaries Yttria(-fully/partially)-stabilized zirconia Air plasma spray Foreign object dama
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