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Research Papers: Gas Turbines: Structures and Dynamics

Finite Element Analysis of the Effects of Thermally Grown Oxide Thickness and Interface Asperity on the Cracking Behavior Between the Thermally Grown Oxide and the Bond Coat

[+] Author and Article Information
Jishen Jiang

Key Laboratory of Power
Machinery and Engineering,
Gas Turbine Research Institute,
School of Mechanical Engineering,
Shanghai Jiao Tong University,
800 Dongchuan Road,
Shanghai 200240, China
e-mail: 1130209247@sjtu.edu.cn

Bingqian Xu

Key Laboratory of Advanced High-Temperature
Materials and Precision Forming,
School of Material Science and Engineering,
Shanghai Jiao Tong University,
800 Dongchuan Road,
Shanghai 200240, China
e-mail: xbqdoris@sjtu.edu.cn

Weizhe Wang

Key Laboratory of Power
Machinery and Engineering,
Gas Turbine Research Institute,
School of Mechanical Engineering,
Shanghai Jiao Tong University,
800 Dongchuan Road,
Shanghai 200240, China
e-mail: wangwz0214@sjtu.edu.cn

Richard Amankwa Adjei

Key Laboratory of Power
Machinery and Engineering,
Gas Turbine Research Institute,
School of Mechanical Engineering,
Shanghai Jiao Tong University,
800 Dongchuan Road,
Shanghai 200240, China
e-mail: Richard_x29a@sjtu.edu.cn

Xiaofeng Zhao

Key Laboratory of Advanced High-Temperature
Materials and Precision Forming,
School of Material Science and Engineering,
Shanghai Jiao Tong University,
800 Dongchuan Road,
Shanghai 200240, China
e-mail: xiaofengzhao@sjtu.edu.cn

Yingzheng Liu

Key Laboratory of Power
Machinery and Engineering,
Gas Turbine Research Institute,
School of Mechanical Engineering,
Shanghai Jiao Tong University,
800 Dongchuan Road,
Shanghai 200240, China
e-mail: yzliu@sjtu.edu.cn

1Corresponding author.

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 19, 2016; final manuscript received July 3, 2016; published online September 13, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(2), 022504 (Sep 13, 2016) (9 pages) Paper No: GTP-16-1236; doi: 10.1115/1.4034259 History: Received June 19, 2016; Revised July 03, 2016

Finite element simulations based on an interface cohesive zone model (CZM) have been developed to mimic the interfacial cracking behavior between the αAl2O3 thermally grown oxide (TGO) and the aluminum-rich Pt–Al metallic bond coat (BC) during cooling from high temperature to ambient temperature. A two-dimensional half-periodic sinusoidal geometry corresponding to interface undulation is modeled. The effects of TGO thickness and interface asperity on the stress distribution and the cracking behavior are examined by parametric studies. The simulation results show that cracking behavior due to residual stress and interface asperity during cooling process leads to stress redistribution around the rough interface. The TGO thickness has strong influence on the maximum tensile stress of TGO and the interfacial crack development. For the sinusoidal asperities, there exists a critical amplitude above which the interfacial cracking is energetically favored. For any specific TGO thickness, crack initiation is dominated by the amplitude while crack propagation is restricted to the combine actions of the wavelength and the amplitude of the sinusoidal asperity.

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References

Figures

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Fig. 1

Surface morphology of the TGO layer showing spallation from the BC in some areas. The arrows show the locations of the spallation.

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Fig. 2

SEM images of the microstructure of TGO and BC: (a) the rough surface of TGO and (b) cross-sectional morphology of BC showing a convoluted oxide layer on it

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Fig. 3

Schematic of an idealized sinusoidal geometry and the boundary conditions used in the FE simulation

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Fig. 4

Meshing applied to the FE model. Different positions on the interface have been defined for narrative convenience.

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Fig. 5

Schematic of the pure-mode bilinear traction–separation law used to model the cohesive zone interface

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Fig. 6

Stress components and equivalent plastic strain (PEEQ) at the ambient temperature without considering the interface crack: (a) Mises stress, (b) S11, stress in x direction, (c) S22, stress in y direction, and (d) PEEQ, equivalent plastic strain

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Fig. 7

Stress components and equivalent plastic strain (PEEQ) at the ambient temperature considering the interface crack: (a) Mises stress, (b) S11, stress in x direction, (c) S22, stress in y direction, and (d) PEEQ, equivalent plastic strain

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Fig. 8

The S22 stresses of BC without (a) and with (b) the interfacial crack

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Fig. 9

The evolutions of S22 stresses of at the peak of the sinusoidal interface during cooling process. Points A and B are located in the peak of TGO and BC, respectively.

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Fig. 10

The evolutions of the maximum S22 stress of TGO (a) and the interfacial crack length (b) during cooling period for different TGO thicknesses (L=10 μm ; A=0.75 μm)

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Fig. 11

(a) Cross-sectional SEM photograph showing the interfacial delamination (marked in rectangle) between the nonuniform TGO layer and the BC layer. (b) FE models (cases 1–3) for the cases with different kinds of nonuniform TGO thicknesses.

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Fig. 12

The interfacial crack length and maximum S22 stress of TGO as functions of the wavelength of sinusoidal geometry at ambient temperature (t=3 μm; A=0.75 μm)

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Fig. 13

The maximum S22 stress of TGO as a function of the amplitude of sinusoidal geometry with different wavelengths at ambient temperature. The TGO thickness t=4 μm.

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Fig. 14

The interfacial crack length (a) and time for crack initiation (b) as a function of the amplitude of sinusoidal geometry with different wavelengths L at ambient temperature. The TGO thickness t=4 μm.

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Fig. 15

(a) Schematic diagram showing two different cracking mechanisms in TGO–BC system. (b) Cross-sectional SEM photograph showing the two cracking mechanisms.

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