Transient Residual Stresses in Thermal Barrier Coatings: Analytical and Numerical Results

1998 ◽  
Vol 65 (2) ◽  
pp. 346-353 ◽  
Author(s):  
S. Q. Nusier ◽  
G. M. Newaz
Keyword(s):  
Finite Element ◽  
Steady State ◽  
Residual Stresses ◽  
Thermal Barrier Coatings ◽  
Bond Coat ◽  
Biaxial Stress ◽  
Thermal Barrier ◽  
Processing Temperature ◽  
Barrier Coatings ◽  
State Case

Thermal barrier coatings (TBCs) provide thermal insulation to high-temperature superalloys. Residual stresses develop in TBCs during cool-down from processing temperatures due to the thermal expansion mismatch between the different layers (substrate, bond coat, and the ceramic TBC). These residual stresses can initiate microcracks at the bond coat/TBC interface which can lead to debonding at the bond coat/TBC interface. Elasticity-based modeling was used to determine the transient stresses in the TBC, bond coat, and the superalloy substrate with specific attention to the interfaces. For the steady-state case, finite element modeling was undertaken as well. Closed-form elasticity solutions correlated well with the finite element results for the steady-state case. The highest residual stresses occurred at the interface between the bond coat and the TBC. An important result of this investigation was that the TBC/bond coat interface was under biaxial stress field. An important result was that the residual stresses developed in the substrate are higher for the case of partly cooled specimen compared to the fully cooled specimen which can be rationalized due to the presence of higher temperature gradients at earlier times during cool-down from processing temperature.

Investigation about Thermal Shock Property of Plasma-Spraying Sm2Zr2O7 Thermal Barrier Coatings with Different Substrate Condictions

2011 ◽  
Vol 354-355 ◽  
pp. 145-148
Author(s):  
Hong Song Zhang ◽  
Hong Chan Sun
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Thermal Expansion ◽  
Residual Stresses ◽  
Plasma Spraying ◽  
Thermal Barrier Coatings ◽  
Thermal Barrier ◽  
Shear Stresses ◽  
Substrate Thickness ◽  
Barrier Coatings

Effect of substrate conditions, including material type, thickness and radius of substrate, on thermal-shocking stresses of plasma spraying Sm2Zr2O7/ NiCrCoAlY TBCs was analyzed through finite element method. Results show that radial stresses decrease with time increasing, and they decrease with the increasing of distance from center to edge along radius. However, axial residual stresses increse abruptly at the edge of specimen. All residual stresses increse with incresing of thermal expansion coefficient of substrate. Radial stresses increase with substrate thickness increasing, however, they are not effectd by substrate thickness if it is great than 20mm.and axial residual stresses and shear stresses are not effected by the substrate thickness. The maximum values of axial stresses and shear stresses were not effected by sustrate radius. and values of radial stresses remian invariable when substrate radius is over 18mm.

Modeling Effects of Material Properties and Three-Dimensional Surface Roughness on Thermal Barrier Coatings

2000 ◽  
Vol 645 ◽  
Author(s):  
Michael L. Glynn ◽  
K.T. Ramesh ◽  
P.K. Wright ◽  
K.J. Hemker
Keyword(s):  
Surface Roughness ◽  
Residual Stresses ◽  
Thermal Barrier Coatings ◽  
Material Properties ◽  
Bond Coat ◽  
Coefficient Of Thermal Expansion ◽  
Three Dimensional ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Dimensional Surface

ABSTRACTThermal barrier coatings (TBCs) are known to spall as a result of the residual stresses that develop during thermal cycling. TBC's are multi-layered coatings comprised of a metallic bond coat, thermally grown oxide and the ceramic top coat, all on top of a Ni-base superalloy substrate. The development of residual stresses is related to the generation of thermal, elastic and plastic strains in each of the layers. The focus of the current study is the development of a finite element analysis (FEA) that will model the development of residual stresses in these layers. Both interfacial roughness and material parameters (e.g., modulus of elasticity, coefficient of thermal expansion and stress relaxation of the bond coat) play a significant role in the development of residual stresses. The FEA developed in this work incorporates both of these effects and will be used to study the consequence of interface roughness, as measured in SEM micrographs, and material properties, that are being measured in a parallel project, on the development of these stresses. In this paper, the effect of an idealized three-dimensional surface roughness is compared to residual stresses resulting from a grooved surface formed by revolving a sinusoidal wave about an axis of symmetry. It is shown that cylindrical and flat button models give similar results, while the 3-D model results in stresses that are significantly larger than the stresses predicted in 2-D.

Simulation of the Effect of Sintering and Interface on the Failure Mechanism of Thermal Barrier Coatings

2015 ◽  
Vol 817 ◽  
pp. 764-771
Author(s):  
Wei Chen ◽  
Jian Guo Zhu ◽  
Gui Lan Chai
Keyword(s):  
Finite Element ◽  
Failure Mechanism ◽  
Thermal Barrier Coatings ◽  
Bond Coat ◽  
Great Influence ◽  
Element Model ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Cooling Stage ◽  
The Finite Element Model

Thermal barrier coatings (TBC) are mainly composed of four layers: top coat (TC), thermal barrier oxidation (TGO), bond coat (BC) and substrate (SUB). The finite element model is used to investigate the failure mechanism of TBC. The influences of sintering of TC and the properties of TGO/BC interface on the stress S22 were considered. The numerical results show that sintering of TC can change the tendency of the stress S22 within TC from peak to valley along the TC/TGO interface; When considering the cohesive behavior of TGO/BC interface, the TGO/BC interface may begin to crack in the heating stage, then in the swelling stage the interface crack in the TGO/BC interface may close, and in the cooling stage the interface will crack again along the TGO/BC interface. When considering TGO/BC interface and sintering of TC simultaneously, sintering of TC has great influence on the stress S22 of BC near the peak and valley of TGO/BC interface.

Process and In-Service Residual Stresses in Thermal Barrier Systems

1996 ◽  
Author(s):  
J. Wigren ◽  
L. Pejryd ◽  
B. Gudmundsson ◽  
R.T.R. McGrann ◽  
D.J. Greving ◽  
...  
Keyword(s):  
Residual Stresses ◽  
Thermal Barrier Coatings ◽  
Bond Coat ◽  
Substrate Material ◽  
Laboratory Method ◽  
Thermal Barrier ◽  
Application Process ◽  
Barrier Coatings ◽  
Coated Materials ◽  
Processing History

Abstract Thermal barrier coatings are used in several industries to improve thermal efficiency, for example, of gas turbine engines. The performance and life of thermal barrier coated components depend on many factors. One important factor is the residual stresses in the coating and substrate. Residual stresses can be influenced by the parameters of the application process. Parameters affecting residual stresses include the condition of the substrate, the type of spray application process, and the prespray heat treatment of the substrate. Residual stresses can also change significantly during the life of a thermal barrier coated material. The goal of this work is to quantitatively evaluate the changes in residual stresses of the thermal barrier coating and the substrate during the stages of processing and during simulated in-service testing. Through-thickness residual stresses distributions of the coating and the substrate material were determined using a destructive laboratory method, called the "Modified Layer Removal Method." Thin thermal barrier coatings (less than 0.5 mm) were evaluated in this work. Residual stresses in thermal barrier coated specimens were evaluated at three stages of the processing history: (1) after grit blasting of the Hastelloy substrate, (2) after application of the bond coat, and (3) after spraying the top coat. The effect on residual stresses of substrate temperature during spraying is examined. Changes in the residual stresses for thin thermal barrier coatings are shown at selected stages during the processing history of the coated materials. Differences between residual stresses at the selected stages are identified and discussed. Changes to residual stress distribution due to in-service conditions are examined. The effect of bond coat oxidation is examined by long-term, high-temperature exposure. Also, residual stresses are evaluated for thick thermal barrier coatings after thermal shock testing.

Analysis of the Stress State in Thermal Barrier Coatings during a Thermal Cycle

1996 ◽  
Author(s):  
G. Jönsson ◽  
C. Persson
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Stress State ◽  
Residual Stresses ◽  
Thermal Barrier Coatings ◽  
Thermal Cycle ◽  
Thermal Stresses ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Element Method

Abstract Thermal barriers made up by a ceramic top coating and a metallic bond coating are subjected to thermal cycles in service. The thermal stresses vary during the cycles and the residual stresses change as a result of plastic flow and creep. The stress state in thermal barrier coatings during a thermal cycle has been examined with a finite element method using temperature dependent material data. The calculated results were verified by measurements of the residual stresses with the layer removal technique before and after cycling of specimens heated in furnace with air environment. According to the simulation of a thermal cycle to 700 ° C, using a finite element method, the bond coat is approximately stress free after 1 hour dwell time. Thus, the residual stresses after a thermal cycle is a result of thermal expansion mismatch and temperature drop.

Effect of Substrate Condictions on Thermal Shock Property of Plasma-Spraying Sm2Zr2O7 /YSZ Thermal Barrier Coatings

2011 ◽  
Vol 332-334 ◽  
pp. 1799-1802
Author(s):  
Hong Song Zhang ◽  
Yuan Wei
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Thermal Expansion ◽  
Residual Stresses ◽  
Plasma Spraying ◽  
Thermal Barrier Coatings ◽  
Thermal Barrier ◽  
Shear Stresses ◽  
Substrate Thickness ◽  
Barrier Coatings

Effect of substrate conditions, including material type, thickness and radius of substrate, on thermal-shocking stresses of plasma spraying Sm2Zr2O7/YSZ TBCs was analyzed through finite element method. Results show that radial stresses decrease with time increasing, and they decrease with the increasing of distance from center to edge along radius. However, axial residual stresses increse abruptly at the edge of specimen. All residual stresses increse with incresing of thermal expansion coefficient of substrate. Radial stresses increase with substrate thickness increasing, however, they are not effectd by substrate thickness if it is great than 25mm.and axial residual stresses and shear stresses are not effected by the substrate thickness. The maximum values of axial stresses and shear stresses were not effected by sustrate radius. and values of radial stresses remian invariable when substrate radius is over 18mm.

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