Investigation by 3D FE simulations of delamination crack initiation in TBC caused by alumina growth |
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| Affiliation: | 1. Department of Mechanical Engineering, Linköping University, SE-581 83 Linköping, Sweden;2. Alstom Power Sweden, SE-612 82 Finspång, Sweden;1. Rolls-Royce plc, PO Box 31, Derby DE24 8BJ, UK;2. ISIS Neutron and Muon Source, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell, Oxford, Didcot OX11 0QX, UK;3. School of Metallurgy and Materials, University of Birmingham, Birmingham B15 2TT, UK;1. Institute of General Mechanics, RWTH Aachen University, Germany;2. Institute of Materials Research, Materials Mechanics, Helmholtz-Zentrum, Geesthacht, Germany;3. Chair of Solid Mechanics, University of Wuppertal, Germany;1. School of Materials Science and Engineering, Shenyang University of Technology, Shenyang 110870, People’s Republic of China;2. School of Energy and Power Engineering, Shenyang University of Chemical Technology, Shenyang 110142, People’s Republic of China;3. Beijing Key Laboratory of Aeronautical Materials Testing and Evaluation, Science and Technology on Advanced High Temperature Structural Materials Laboratory, AVIC Beijing Institute of Aeronautical Materials, Beijing 100095, People’s Republic of China;1. School of Materials Science and Engineering, Tongji University, Shanghai 201804, China;2. Shanghai Key Laboratory for Engineering Materials Application Evaluation, Shanghai Research Institute of Materials, Shanghai 200437, China |
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| Abstract: | In gas turbines, thermal barrier coatings (TBCs) applied by air plasma spraying are widely used to reduce the temperature in hot components. The TBC allows higher gas temperature and/or reduces the need for internal cooling in the hot components, thus increasing the efficiency of the gas turbine. Spallation is a common failure mechanism of TBC and occurs after a critical number of thermal cycles, when the alumina layer has grown to a critical thickness. The influence of the growing alumina layer and the top/bond-coat interface roughness in the TBC has been investigated. The primary goal was to identify failure mechanisms that can be incorporated into a life model of the TBC, and to increase the understanding of the delamination process in the TBC. A new formulation of alumina growth is proposed, in which the swelling strains caused by the volumetric increase during alumina growth depends on the stress state. The alumina growth model is used in 3D FE thermal cycling simulations of a TBC in which the thermal cycle time is long enough to characterize a typical cycle of a gas turbine. From the simulations, the growing alumina layer is observed to be one failure mechanism of the TBC. Without an alumina layer in the model, high delamination stress is observed at room temperature, above ridges of the top/bond-coat interface in the top coat. When the alumina is growing, the point of maximum delamination stress is moved towards the valleys. When the thickness of the alumina layer has grown to approximately 8–10 μm, positive delamination stress is found above the valleys in the top coat. The movement of the positive delamination stress region can explain why a delamination crack develops, which will cause spallation of the TBC during shutdown to room temperature. |
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