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5380 |
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Thursday, June 08, 2017, Hall 12 11:20 AM Aviation & Power Generation Industry II |
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Performance of atmospherically plasma sprayed self-healing thermal barrier coatings |
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Robert Vaßen* / Forschungszentrum Jülich GmbH, Germany Denise Koch / Forschungszentrum Jülich GmbH, IEK-1, Germany Alexandra Lucia Carabat/ Delft University of Technology, The Netherlands Wim Sloof/ Delft University of Technology, The Netherlands |
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Thermal barrier coatings (TBC) are essential to gain high efficiencies in modern gas turbines. The state of the art material for the topcoat of such TBCs is yttria stabilized zirconia (YSZ). Due to induced stresses upon thermal cycling cracks develop in the topcoat near the thermally grown oxide layer (TGO), which forms on the bond coat layer, and these cracks can cause delamination of the topcoat. In the here described approach these cracks will be repaired by the oxidation of MoSi2 particles embedded in the topcoat. The oxidation and the accompanying volume expansion fills and heal these cracks, resulting in a self-healing TBC. By this the lifetime of TBCs will be improved. To avoid an early reaction of the embedded particles with the YSZ matrix resulting in a densification and a loss of strain tolerance the MoSi2 particles are coated by an alumina layer. The spraying parameters have been optimized with special respect to the highly different characteristics of MoSi2 and YSZ in terms of e.g. melting temperature, and oxidation behavior. The optimized coating systems have been applied on bond coated Ni-base substrates and cyclic oxidation tests (1100 °C, 2 hours dwell time, and 15 min cooling) were performed. The best self-healing TBC systems revealed lifetimes about a factor of three better than the YSZ reference system indicating the high potential of the used approach. Details on the microstructural changes of the self-healing coatings after thermal cycling will be presented and discussed. |