IWPDF2023

Delamination behaviour of elastic surface coatings subjected to ther mal shock

M. N. Balcı ∗ , M. A. Yalçın

Department of Mechanical Engineering, Hacettepe University, Ankara 06800, Turkey

∗ mehmetbalci@hacettepe.edu.tr

Keywords: Elastic coating delamination, Hot shock, Cold shock, Displacement Correlation Tech nique, Finite Element Method.

Elastic surface coatings, especially, Thermal barrier coatings (TBCs) are recognized as essential key materials for high-performance aero-engine and heavy-duty gas turbine blades due to their excellent thermal protection properties [1-3]. When the surface of the metallic substrate is deposited by these coatings with a thickness of 100-400 µm , it was reported that the substrate temperature could effectively be reduced by 100-200 ◦ C [4-7]. Moreover, they protect metallic substrate from severe chemical corrosion and high temperature oxidation. Thus, utilization of these coatings leads to increase in the efficiency of engines and gas turbine blades. This papers examines the effect of transient thermal loading and the thermal shock on delamination behavior of the thermal barrier coatings (TBCs). The coating-substrate system is considered to consist of three layers which are ceramic coating, bond coating and the metallic substrate. In order to analyze the problem, finite element method (FEM) is used. Boundary conditions and loads are determined in thermal and mechanical fields. Delamination behavior of TBCs is investigated based on two different crack configurations, which are crack at the interface of the surface coating and crack at the interface of the bond coating. Cracks are modeled using singular finite elements and mixed mode I/II stress intensity factors (SIFs) are calculated through the use displacement correlation technique (DCT). Energy release rate and dimensional phase angle values are also determined for different conditions. Parametric analyses are carried out to reveal the influences of crack configuration, material properties, thermal shock time and its type either hot or cold, thickness of coating materials and crack length. Fracture analysis of TBC delamination under cold thermal shock loading was examined by Ping-wei [8]. However, authors examined coating system subjected to cold shock, crack at the bond coating was not analyzed and presented results were limited since effects of aforementioned parameters on delamination were not thoroughly presented. Hence, results presented in this study fill this gap and it is found that the crack tip stress field is shear dominant, energy release rate and SIFs for crack configurations are different from each other due to the utilized materials. Possible delamination due to unstable propagation of the crack is also presented for different parameters. References [1] Clarke, D.R., Phillpot, S.R. (2005). Thermal barrier coating materials. Mater. Today, 8, 22–29. [2] Padture, N.P., Gell, M. Jordan, E.H. (2002). Thermal barrier coatings for gas-turbine engine applications. Science, 296, 280–284. [3] Clarke, D.R., Oechsner, M., Padture, N.P. (2012). Thermal-barrier coatings for more efficient gas-turbine engines. MRS Bull., 37, 891–898.

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