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.

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.

scholarly journals Surface-Roughness Induced Residual Stresses in Thermal Barrier Coatings: Computer Simulations

1999 ◽  
Vol 308-311 ◽  
pp. 442-449 ◽  
Author(s):  
C.H. Hsueh ◽  
Paul F. Becher ◽  
Edwin R. Fuller ◽  
S.A. Langer ◽  
W.C. Carter
Keyword(s):  
Surface Roughness ◽  
Residual Stresses ◽  
Thermal Barrier Coatings ◽  
Computer Simulations ◽  
Thermal Barrier ◽  
Barrier Coatings

Computational Three-Dimensional Microstructure Defect Distributions in Thermal Barrier Coatings

2017 ◽  
Author(s):  
Stephanie A. Wimmer ◽  
Virginia G. DeGiorgi ◽  
Edward P. Gorzkowski ◽  
John Drazin
Keyword(s):  
Mechanical Properties ◽  
Thermal Barrier Coatings ◽  
Material Properties ◽  
Thermal Protection ◽  
Bulk Material ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Ceramic Coatings ◽  
Thermal Barrier ◽  
Barrier Coatings

Thermal protection of components such as turbine blades is often done with thermal barrier coatings which are typically ceramic materials. Methods to manufacture ceramic coatings are being developed to create microstructures that optimize thermal protection without degrading mechanical properties of the coating. The coating requires sufficient mechanical properties to remain in place during loads associated with the operation of the component. The work presented in this paper is part of a broader effort that focuses on novel processing techniques. A fabrication method of interest is the inclusion of spherical micron-sized pores to scatter photons at high temperatures along with nano-sized grains to scatter phonons. Pores are sized and distributed so that mechanical strength is maintained. In the current work, yttria-stabilized zirconia (YSZ) is modeled. Three-dimensional microstructures representing YSZ are computationally generated. The defect sizes and orientations are generated to match an experimentally observed distribution. The defects are either randomly or regularly placed in the microstructural models. Stress-displacement analysis is used to determine effective bulk material properties. Comparisons are made to prior two-dimensional work and to experimental measurements available in the literature as appropriate. The influences that defect distributions and three dimensional effects have on the effective bulk material properties are quantified. This work is a preliminary step toward understanding the impacts that micron sized pores, voids and cracks have on thermal and mechanical characteristics. The goal is to facilitate optimizing the microstructure for thermal protection and strength retention.

scholarly journals The Evaluation of Durability of Plasma-Sprayed Thermal Barrier Coatings with Double-layer Bond Coat

Coatings ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 241 ◽  
Author(s):  
Li ◽  
Peng ◽  
Dong ◽  
Zhou ◽  
Wang ◽  
...  
Keyword(s):  
Thermal Barrier Coatings ◽  
Double Layer ◽  
Bond Coat ◽  
Coefficient Of Thermal Expansion ◽  
Type A ◽  
Thermal Barrier ◽  
Type B ◽  
Barrier Coatings ◽  
Oxidation Layer ◽  
Plasma Sprayed

The durability of atmospheric plasma-sprayed thermal barrier coatings (APS TBCs) with a double-layer bond coat was evaluated via isothermal cycling tests under 1120 °C. The bond coat consisted of a porosity layer deposited on the substrate and an oxidation layer deposited on the porosity layer. Two types of double-layer bond coats with different thickness ratios of the porosity layer to the oxidation layer (type A: 1:2 and type B: 2:1, respectively) were prepared. The results show that the porosity layer was oxidation free, the oxidation layer included a fraction of well-distributed α-Al2O3. The coefficient of thermal expansion of the oxidation layer was about 11.2 × 10−6 K−1, which was rather lower than that of the porosity layer. Thus, the oxidation layer can be regards as a secondary bond coat between ceramic topcoat and traditional bond coat. The thermal cyclic lifetime of type A TBCs was about 60 cycles, which exceeded 1.2 times the durability of type B TBCs. The delamination cracks in both TBCs all propagated in the ceramic topcoat, which were all identical to those in traditional TBCs. Therefore, the design of the double-layer bond coat affected the stress level rather than the stress distribution in TBCs.

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.

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