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1557 |
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Wednesday, June 04, 2008, Room 04 12:20 PM Gasturbines 4 Coatings for mobile and stationary turbines, protection against wear, high temperature corrosion and thermal stresses, clearance control coatings for a better efficiency |
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Influence of thermal cycling on residual stresses in a thermal barrier coating with a kinetic metallization sprayed bond coating |
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Takahiro Niki* / Graduate School of Engineering, Tohoku University / Fracture and Reliability Research Institute
, Japan Kazuhiro Ogawa / Graduate School of Engineering, Tohoku University / Fracture and Reliability Research Institute, Japan Tetsuo Shoji/ Graduate School of Engineering, Tohoku University / Fracture and Reliability Research Institute, Japan |
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Kinetic Metallization (KM), which is one of the spraying systems for particle deposition, has been studied as a new technique for applying metallic bond coating of Thermal Barrier Coatings (TBCs). In this system, the coating powder is not melted prior to impingement on the substrate. The conversion of particle?s kinetic energy into thermal and strain energies upon striking the substrate leads to a relatively well-adherent and low porosity coating. In this study, in-situ residual stress in Atmospheric Plasma Sprayed (APS) YSZ top coating with two different bond coatings, namely Low pressure plasma sprayed (LPPS) and KM sprayed coatings, were compared under thermal cycle conditions. From the results of 1st thermal cycle, in the case of the TBC with the LPPS bond coating, tensile residual stress was observed at elevated temperature up to 400oC. Relaxation of the residual stress was promoted from 400oC to 1000oC. And then, residual stress drastically transforms to compression with cooling down to 800 oC. At last, approximately 80MPa compression stress was observed. On the other hand, in the case of the TBC with the KM sprayed bond coating, gradual increase of tensile residual stress was observed up to 1000oC. Moreover, during cooling down, residual stress did not transform to compression until 400 oC. At the room temperature, difference of both residual stresses was approximately 40MPa. Compressive stress causes detrimental effects with respect to delamination. As a result, it is believed that the TBC with KM bond coating, which has lower residual stress, is superior to that of the TBC with LPPS bond coating. After 2nd and 3rd thermal cycles, both specimens had tendency to be similar residual stress behavior. |