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2227 |
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Wednesday, May 05, 2010, Olivia Room 2:40 PM Gas Turbines 3 |
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Next generation thermal barrier coatings for the gas turbine industry |
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Nicholas Curry* / University West Production Technology Centre, Sweden Nicolaie Markocsan / University West, Sweden Xin Hi Li/ Siemens Turbomachinery, Sweden Aurelien Tricoire/ Volvo Aero Corporation, Sweden Mitchell Dorfman/ Sulzer Metco, USA |
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The Thermal Barrier Coating (TBC) was developed to protect gas turbine components and make it possible to use an operating temperature above the softening temperature of the component material. Present TBC systems consist of a metallic bond coat and usually a Yittria Partially Stabilised Zirconia (YPSZ) top coat that provides the temperature drop across the coating. YPSZ has become the material of choice due to its exceptionally low thermal conductivity and high stability under the operating conditions. Development of the TBC top coat is concentrated on increasing lifetime and lowering thermal conductivity. The aim of the project was to develop the next generation of production ready air plasma sprayed thermal barrier coating with a low conductivity and long lifetime. In order to achieve these goals; a number of coating architectures were produced using F4 and Triplex plasma spray guns. Modifications were made to chemistry including; high purity powders for sintering resistance, Dysprosia stabilised Zirconia powders and powders containing porosity formers. Agglomerated & Sintered (A&S) and Hollow Oxide Spherical Powder (HOSP) morphologies were used to attain beneficial microstructures. Finally, dual layer coatings were produced using the different powder morphologies. Evaluation of the thermal conductivity of the coating systems from room temperature to 1200ºC was conducted using Laser Flash Technique. Tests were done on as-sprayed samples and samples heat treated for 50 hours at 1150ºC in order to evaluate the first stage sintering resistance of the coating systems. Thermal conductivity results were correlated to coating microstructure using image analysis of porosity and crack content. The results show the influence of beneficial porosity on reducing the thermal conductivity of the produced coatings. |