Abstract No.:
2655

 Title:
Stress analysis in the vicinity of TGO in TBC systems with cold sprayed and LPPS bond coatings

 Authors:
Ismail Ozdemir / Bartin University,Faculty of Eng.,Met. and Mater.Science Eng, Turkey
Ismail Tirtom / Department of Mechanical Science and Bioengineering, Osaka University, Japan
Kazuhiro Ogawa/ Fracture and Reliability Research Institute, Tohoku University, Japan
Tetsuo Shoji/ Fracture and Reliability Research Institute, Tohoku University, Japan

 Abstract:
The thermal and residual stress/strain distribution was numerically investigated in vicinity of the TGO for the TBC coatings. For TBC systems, the bond coat was produced by cold spray (CS) and low pressure plasma spray (LPPS) methods while both systems have Atmospheric Plasma Sprayed (APS) yttria-stabilized zirconia (YSZ) top coating. FEM calculation shown that the shape, size and thickness of TGO had an significant influence on localization of stress and strain which might cause cracking and thus failure of TBC system. In order to obtain more reliable results, cross section microstructure images from both types of coating samples were imported and meshed to prepare Numerical FEM model. Simulation results shown similarities with in-situ measurement of residual stress close to the interface between bond coat and top coat. When the samples subjected to thermal loading from room temperature to 1000 oC, in situ residual stress measurement showed that the cold sprayed sample posses less compressive residual stresses than that of the sample produced by LPPS, which is in agreement with FEM simulation. Based on the FEM calculation, the relation between several failures and high stress components at sharp and convex locations close to the interfaces between bond coat-TGO and TGO-top coat were scrutinized. Because of dense and smoother shape of the TGO in CS system, internal (residual) stresses are lower than LPPS and therefore CS coated system has longer lifetime.

Keywords: Cold spray, LPPS, TGO, Residual stress, FEM, Thermal expansion misfit, TBC


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