GOALI: Use Of Microsample Testing To Characterize and Model Bond Coat Performance and TBC Life

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9986752Hemker A key component of high temperature thermal barrier coatings (TBC's) is the bond coat since it provides both the thermally grown oxide layer critical to the attachment of TBC's, especially those deposited by physical vapor deposition, and the mechanical foundation upon which the coating sits. The collaboration in this GOALI grant joins the novel microsample tensile, creep and fatigue testing capabilities developed at Johns Hopkins with the expertise of aerospace engineers and scientists and the test capabilities at General Electric Aircraft Engines. The overall goal of this collaborative study is to characterize the deformation behavior of bond coat layers and relate their mechanical performance and failure processes to TBC life. The microsample testing approach adopted permits characterization of small-scale and highly scale-specific coatings and properties in a way not possible by conventional means. The use of microsamples provides a unique opportunity to measure the high temperature coefficient of thermal expansion, Young's modulus, and tensile, creep and fatigue strength of both as-deposited and thermally cycled bond coat layers. Detailed observations of the failure mechanisms and underlying microstructure will be used to assess the importance of strain accommodation, micro-cracking, void formation, elemental diffusion, grain boundary sliding, and other failure processes thought to affect TBC performance. The collaboration provides a mechanistic foundation for life prediction assessment using finite element modeling calculations in addition to generating much needed design data. The GOALI effort includes closely meshed research activities and yearly personnel exchanges, placing students and faculty in direct contact with engineers and scientists at GE-AE. Doing so broadens the education of the JHU students by providing invaluable technological and industrial experience. The benefits to GE-AE include the availability of unique experimental facilities and the ability to focus on fundamental research not otherwise undertaken in an industrial environment. The grant is jointly funded by the MPS Office of Multidisciplinary Activities and the Metals Research Program in the Division of Materials Research.%%%The performance and durability of aircraft engine turbines has become more closely linked to the capability and durability of TBC's that are placed on hot section components. TBC's are now widely used to increase durability of turbine components, but the use of TBC's to increase inlet temperatures, and thus performance, is currently inhibited by the possibility of spallation. If TBC's are to be used to increase engine performance, it is essential that these coatings be retained reliably on the metallic substrates they are designed to protect.***