ICMCTF2010 Session A3-1: Thermal Barrier Coatings

Thursday, April 29, 2010 8:00 AM in Room Sunrise

Thursday Morning

Start	Invited?	Item
8:00 AM	Invited	A3-1-1 Models for Foreign Object Damage to Columnar Zirconia Thermal Barrier Coatings M.W. Crowell (University of California, Santa Barbara (now at Los Alamos National Lab)); Robert McMeeking, A.G. Evans (University of California, Santa Barbara) The columnar thermal barrier oxides typically relied upon to protect critical hot-section rotating parts from extreme temperatures in modern aero-turbines suffer from a number of damage mechanisms. These include thermal, chemical, and mechanical attack, each of which can limit the functional life of the thermal barrier coating (TBC), and hence the underlying component and the entire engine. Mechanical attack in the form of impacts due to particulates ingested in the engine’s hot gas path have proven to be particularly unpredictable. Engine designers are often forced to assume TBCs subject to these impacts will immediately spall and provide no thermal protection. However, there exists both engine and experimental evidence suggesting variations in the TBC’s columnar microstructure can help in resisting such foreign object damage (FOD). The engine operating environment is extremely complex and difficult to accurately reproduce experimentally, so dynamic finite element modeling has been employed, as well as model experiments. Automated parameter variation and 2-D modeling in ABAQUS have enabled high resolution parametric studies of varying FOD scenarios and TBC microstructures. Various figures of merit concerning simulated resistance to spallation have been explored via postprocessing in MATLAB, and validation has been obtained through the experiments. Such methods and results will be presented.
8:40 AM		A3-1-3 Lifetime of Thermal Barrier Coatings With MCrAlY-Bondcoats: Effects of Testing Procedure and Coatings Microstructure Dmitry Naumenko, Peng Song, Lorenz Singheiser, WillemJoe Quadakkers (Forschungszentrum Jülich GmbH, Germany) Yttria stabilized zirconia thermal barrier coatings (TBCs) produced by air plasma spraying on Ni-based superalloys with MCrAlY (M = Ni, Co) bondcoats were studied. The specimens were subjected to cyclic oxidation testing in laboratory air at temperatures between 1000 and 1100°C under various cyclic conditions. It was observed that the lifetime of the TBC-system was about 30% shorter when tested with hot-dwell times in the order of 2 hours than when tested with hot-dwells in the order of 20 hours. Analytical studies of the polished cross-sections of the exposed specimens by optical metallography and scanning electron microscopy (SEM) indicated that TBC-failure was initiated by delaminations at the alumina scale/bondcoat interface in the convex regions of the rough bondcoat surfaces, which then propagated through the TBC. Independent of the testing procedure the absolute values of the TBC lifetime were found to depend strongly on the TBC-microstructure and especially the morphology of the TBC/bondcoat interface. Comparison of two TBC systems with nominally the same base material, bondcoat and TBC chemical compositions revealed that these properties crucially determine the rate of crack propagation through the TBC.
9:00 AM	Invited	A3-1-5 Suspension Plasma Spray as a Route for Microstructural Design of New Thermal Barrier Coatings Rodney Trice (Purdue University) Suspension plasma spray is an emerging injection technology that adapts to existing plasma spray equipment; it affords the capability to form new coating microstructures for thermal barrier and other applications. In suspension plasma spray, powders are first dispersed in a solvent to form a stable suspension, then fed through a small nozzle into the plume. The enthalpy of the plume evaporates or combusts the solvent, and the powders are melted and propelled towards the substrate where they flatten to form lamella. Coatings are composed of stacked lamella, similar to conventional plasma spray with some important differences. First, powders as small as 50 nm have been plasma sprayed using this approach, much smaller than the 10 micron lower limit associated with conventional powder feed techniques. Also, it has recently been demonstrated that by changing the composition of the suspension the final composition of the coating can be varied. In this paper we will present some recent recent results that establish processing-property-microstructure relationships, with a focus on how porosity distribution and shape relate to thermal conductivity. Finally, we will present results that show that suspension plasma spray can be combined with a defect oxide clustering approach to fabricate ultralow thermal conductivity coatings that possess conductivities of 0.8 W/m/K after 50 hours at 1200^oC.
9:40 AM		A3-1-7 Proto-TGO Formation in TBC Systems Fabricated by Spark Plasma Sintering Mathieu Boidot, Serge Selezneff, Daniel Monceau, Djar Oquab, Claude Estournès (CIRIMAT, France) Complete thermal barrier systems were fabricated on single crystal Ni-based superalloy (AM1) in a one-step Spark Plasma Sintering process (SPS). The lifetime of such systems is highly dependent on its ability to form a dense, continuous, slow growing alumina layer (usually called Thermally Grown Oxide, TGO) between an underlying bond coat and a ceramic top coat. Then, TEM-EDS and Raman spectroscopy were used to determine the nature of the proto-TGO phases in the as-fabricated systems. The proto-TGO is determined as being amorphous-Al₂O₃ in the as-fabricated samples, transforming to α-Al₂O₃ during thermal treatment or cyclic oxidation under laboratory air at 1100°C. Oxidation kinetics calculations are presented and demonstrate the phase transformation from amorphous alumina to alpha alumina during thermal treatment. This paper investigates the mechanisms that lead to both the formation of the amorphous-alumina called proto-TGO and the reactive elements doping of the bond coat (Zr in the present case) during TBC processing.
10:00 AM		A3-1-8 Effect of Superalloy Substrate and Bond Coating on TBC Lifetime Bruce Pint, James Haynes (Oak Ridge National Laboratory); Ying Zhang (Tennessee Technological University) Several different single-crystal superalloys were coated with different bond coatings to study the effect of composition on the cyclic oxidation lifetime of an yttria-stabilized zirconia (YSZ) top coating. Three different superalloys were coated with a 7µm Pt layer that was diffused into the surface prior to YSZ deposition by physical vapor deposition from a commercial source. One of the superalloys was coated with a standard Pt-modified aluminide coating and Pt-diffusion coatings with 3 or 7µm of Pt. Three coatings of each type were cycled to failure in 1h cycles at 1150°C to get an average coating lifetime. The Pt-diffusion bond coating on the superalloy containing Ti exhibited the shortest YSZ coating lifetime. Initial characterization has been conducted to understand the role of Ti in the coating system.
10:20 AM	Invited	A3-1-9 On The Design of Industrial Sensor Thermal Barrier Coating Systems Jörg Feist (Southside Thermal Sciences); Andrew Heyes (Imperial College London, United Kingdom); R. Vaβen (Forschungszentrum Jülich GmbH, Germany); J.R. Nicholls (Cranfield University, United Kingdom) This paper will review the development and design aspects of Thermal Barrier Coating (TBC) Systems with intrinsic sensor properties. The sensor properties are introduced by embedding rare earth elements into the coatings which make these coatings phosphores. The concept of thermal–sensing and of phase detection utilising luminescence effects in TBCs was first introduced by Choy, Feist, Heyes et al. in 1998 (Choy et al US6974641; US2009226326). TBCs are ceramic protective coatings designed to withstand extreme environmental conditions such as high temperatures, thermal shock and possibly corrosion attack. Over the past decades a tremendous effort has been put into the development and understanding of thermal barrier coatings as their application in the gas turbine industry promises higher operational efficiency, longer life of components and hence lower fuel bills and maintenance bills. As the effort of the turbine industry is focused on lowering carbon emissions a drive for even higher operating temperatures is foreseen. This will require new approaches in regard to component monitoring to reduce maintenance costs and to permit maximum utilisation of engine components in the hot section. The paper looks into the design of materials suitable to manufacture EBPVD and APS sensor coating systems. Different aspect will be highlighted such as suitable dopants, two phase systems and layered coatings. Selected systems were manufactured and characterised using industrial standard coating techniques. These systems were studied on luminescence from room temperature to temperatures in excess of 1400oC. Further, some systems have shown very promising durability properties when tested alongside standard thermal barrier coatings. In addition to the thermal sensing properties the paper will demonstrate the potential to measure other properties such as ageing of the material or hot corrosion effects.
11:00 AM		A3-1-11 Microstructure Design and Mechanical Properties of Thermal Barrier Coatings with Layered Top and Bond Coats Yeon-Gil Jung, Sang-Won Myoung, Jae-Hyun Kim, Woo-Ram Lee (Changwon National University, Republic of Korea); Ungyu Paik (Hanyang University, Republic of Korea); Kee-Sung Lee (Kookmin Universiy, Republic of Korea) Thermal properties and failure mechanisms of thermal barrier coatings (TBCs) are closely related with its microstructure. Numerous factors, besides the thermo-mechanical properties, have to be considered in practical applications of TBCs, such as erosion and wear resistance. There is therefore a need to improve the adhesive strength and mechanical characteristics, which are essential to improving the reliability and lifetime performance of the air-plasma sprayed (APS) TBC system. In this study, the microstructures in the top and bond coats of TBCs have been designed as a new strategy for the advanced coatings, and we prepared the layered TBC with three coating layers in both the top and coats using a specialized coating system (TriplexPro-200). In order to determine and to understand the effects of the microstructure design on the fracture behavior and the mechanical properties, the adhesive strength and sharp indentation tests were conducted. Results were compared with the common TBC systems with single layer in each coat. In the layered TBCs, more dense coating could be possible due to an higher flame velocity compared to a conventional APS system (9MB), and semi-graded coating also possible using a multi-hopper system. The bond and top coats were coated with 100 and 200 mm for each feedstock, resulting in 300 and 600 mm in the bond and top coats, respectively. The microstructure of the top coat could be controlled by changing the feedstock—dense/intermediate/porous layers from surface to interface or reverse microstructure. The adhesive strength values of the bond and top coats were about 80 and 10 MPa, respectively, independent of microstructure, which are higher values than those of TBC system prepared by the 9MB system. The hardness and toughness values were gradually changed from surface to interface, indicating that the mechanical properties are well corresponded with the microstructure of TBCs.