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.

Influences of Microstructure Defect Size and Distribution for Performance Optimization of Thermal Barrier Coatings

2016 ◽  
Author(s):  
Stephanie A. Wimmer ◽  
Virginia G. DeGiorgi ◽  
Edward P. Gorzkowski
Keyword(s):  
Mechanical Properties ◽  
Thermal Barrier Coatings ◽  
Material Properties ◽  
Performance Optimization ◽  
Thermal Protection ◽  
Bulk Material ◽  
Turbine Blades ◽  
Heat Radiation ◽  
Thermal Barrier ◽  
Barrier Coatings

Thermal barrier coatings are often used to protect a component by reducing temperature excursions. Such coatings are in use on engineered products such as turbine blades. The work presented is part of a broader effort that is focusing on new and novel processing techniques for thermal barrier coatings. Manufacturing methods are being developed to create microstructures that optimize thermal protection while not degrading the mechanical properties of the coating. Sufficient mechanical properties are necessary so the coatings do not fail as a result of loadings associated with the operation of the component. One fabrication method investigated is the inclusion of spherical micron-sized pores to reflect heat radiation at high temperatures along with nano-sized grains to reflect phonons thus providing thermal protection. Pores are sized and distributed so that sufficient mechanical strength is maintained. In the current work the model material used is a yttria-stabilized zirconia (YSZ). Two-dimensional microstructures representing YSZ are computationally generated. The size and distribution of defects that have been experimentally observed to develop during bulk processing are incorporated into the computationally generated microstructural models. Heat transfer and stress-displacement analyses are performed to determine effective bulk material properties. Comparisons are made to experimental measurements available in the literature as appropriate. The influence that defect dimensions and distributions have on the effective bulk material properties are quantified as a first step understanding the impacts that micron sized pores, voids and cracks have on thermal and mechanical characteristics which will facilitate optimizing the microstructure for thermal protection and strength retention.

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.

scholarly journals Mechanisms Controlling the Performance and Durability of Thermal Barrier Coatings

2000 ◽  
Author(s):  
Daniel R. Mumm ◽  
Anthony G. Evans
Keyword(s):  
Thermal Cycling ◽  
Thermal Barrier Coatings ◽  
Bond Coat ◽  
Large Scale ◽  
Mechanical Performance ◽  
Thermal Protection ◽  
Crack Nucleation ◽  
Ceramic Coatings ◽  
Thermal Barrier ◽  
Barrier Coatings

Abstract Thermal protection systems based on ceramic thermal barrier coatings (TBCs) are used extensively to protect hot-section components in gas turbine engines. They comprise thermally insulating ceramic coatings, deposited on an aluminum-containing intermetallic bond coat (BC) that provides oxidation protection. A thin thermally-grown oxide (TGO layer forms between the TBC and BC during cyclic thermal exposure. Each of the system constituents evolves in service and all interact during thermal cycling to control the thermo-mechanical performance of the system. Exposed to thermal cycling conditions, TBC systems are susceptible to loss of adhesion and spalling failures. Multiple failure mechanisms exist, dependent upon differing thermal histoiy and processing approach for various coating systems. Coating failure is ultimately controlled by the large residual compression in the TGO and its role in amplifying the effects of imperfections in the vicinity of the TGO. The failure occurs through a process involving crack nucleation, propagation and coalescence events. For a particular commercial system, it is found that the TGO ‘ratchets’ into the bond coat with each thermal cycle, at an array of interfacial sites. The displacements induce strains in the superposed TBC that cause it to crack. The cracks extend laterally as the TGO ratcheting process proceeds, until the cracks from neighboring sites coalesce. Once this happens, the system fails by large scale buckling. It is shown that the displacements are ‘vectored’ by a lateral component of the growth strain in the TGO. The relative roles of bond coat visco-plasticity, initial interface morphology, and phase evolution are discuss. The behavior observed for this system is compared with predictions of a ratcheting model, as well as with the behavior observed for other commercial coating systems.

Three-Dimensional Modeling of Reduced Material Properties in Ceramics With Added Porosity

2019 ◽  
Author(s):  
Stephanie A. Wimmer ◽  
Virginia G. DeGiorgi ◽  
Edward P. Gorzkowski ◽  
Heonjune Ryou
Keyword(s):  
Mechanical Properties ◽  
Thermal Conductivity ◽  
Finite Element ◽  
Computational Modeling ◽  
Computational Models ◽  
Thermal Protection ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Ceramic Coatings ◽  
Grain Structure

Abstract Manufacturing methods to create ceramic coatings with tailored thermal conductivity are crucial to the development of thermal protection systems for many components including turbine blades in high temperature engines. A designed microstructure of grains, pores, and other defects can reduce the thermal conductivity of the ceramic. However, the same microstructure characteristics can reduce mechanical properties to the point of failure. This work is part of a larger program with the goal of optimizing ceramic coating microstructure for thermal protection while retaining sufficient mechanical strength for the intended application. Processing parameters have been examined to identify methods designed to maintain a nano-sized grain structure of yttria-stabilized zirconia while controlling the added porosity with a specific shape and size. In this paper computational modeling is used to evaluate the effects of porosity on coating performance, both thermal and structural. Coating porosity is incorporated in the computational models by randomly placing empty spaces or defects in the shape of spherical voids, oblate pores, or penny cracks. In addition to computational modeling, prototype coatings are developed in the laboratory with specific porosity. The size and orientation of defects in the computational modeling effort are statistically generated to match experiments. The locations of the defects are totally random. Finite element models are created which include various levels of porosity to calculate effective thermal and mechanical properties. Comparisons are made between three-dimensional finite-element simulations and measured data. The influences of pore size as well as three dimensional computational modeling artifacts are examined.

Parametric Studies of Nonlinear Damping Behavior of APS Thermal Barrier Coatings Based on Cohesive Interface Model

2012 ◽  
Author(s):  
Yong Chen ◽  
Wei Dong
Keyword(s):  
Thermal Barrier Coatings ◽  
Turbine Blades ◽  
Ceramic Coatings ◽  
Nonlinear Damping ◽  
Contact Friction ◽  
Thermal Barrier ◽  
Interface Model ◽  
Damping Properties ◽  
Barrier Coatings ◽  
Cohesive Interface

Thermal barrier coatings (TBCs) could reduce the temperature of the turbine blades and allow them working at higher temperatures, which leads to higher durability and reliability of turbine blades, and improves engine performance and fuel efficiency. Recent researches shown that thermal barrier coatings have very good damping properties, which means it could also improve the high cycle fatigue (HCF) life of the turbine blades. Previous studies found that damping of air plasma spray (APS) thermal barrier coatings exhibit non-linearities (amplitude-dependent) due to its microstructures, which consists of several layers of splats with inter- and intra-microstructural micro-cracks. The main purpose of this paper is on the application of a bilinear cohesive interface model to simulate the microstructural features, the damage process and the contact friction between the interfaces of microstructural faults in APS ceramic topcoat. A representative volume element (RVE) model which coupled with the cohesive interface model is built and parametric relations, in terms of interface strength and stiffness, vibration amplitude and vibration cycles, are computed in this paper for understanding the effect of interfacial degradation, de-bonding, sliding, and contact friction between the interfaces of microstructural faults on the nonlinear damping properties. The calculation results could provide a fundamental understanding of the mechanisms responsible for the observed nonlinear energy dissipation and damping properties in APS ceramic coatings.

Numerical Simulation for Surface Modification of Thermal Barrier Coatings by High-Current Pulse Electron Beam

2010 ◽  
Vol 654-656 ◽  
pp. 1807-1810
Author(s):  
Ying Qin ◽  
Wei Qu ◽  
Xian Xiu Mei ◽  
Sheng Zhi Hao ◽  
Ji Jun Zhao ◽  
...  
Keyword(s):  
Electron Beam ◽  
Thermal Barrier Coatings ◽  
Physical Vapor Deposition ◽  
Turbine Blades ◽  
Ceramic Coatings ◽  
Pulse Electron Beam ◽  
Thermal Barrier ◽  
High Current ◽  
Barrier Coatings ◽  
Pulsed Electron Beam

High current pulsed electron beam is an effective technique for surface sealing of ceramic thermal barrier coatings prepared by electron beam physical vapor deposition. Due to the rapid remelting and solidification, the outer layers of ceramic coatings become smooth and dense, and the protective performance for turbine blades is effectively improved. Because of the complex multi-layered structures in the coatings, a high-current pulsed electron beam treatment requires specific parameter inputs which are related to the temperature field induced by electron energy deposition in the coatings. In this paper, a two-dimensional temperature simulation was performed to demonstrate the melting depth and temperature evolution in ceramic coatings treated by high-current pulsed electron beam. Different energy densities and pulses were studied and discussed for obtaining optimized parameters.

Thermophysical and Mechanical Properties of PYZ Thick Thermal Barrier Coatings

1998 ◽  
Author(s):  
D. Schwingel ◽  
R. Taylor ◽  
T. Haubold ◽  
J. Wigren ◽  
C. Gualco ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Plasma Spraying ◽  
Thermal Barrier Coatings ◽  
Material Properties ◽  
Laser Flash ◽  
Thermal Barrier ◽  
Spray Parameters ◽  
Barrier Coatings ◽  
Point Bend

Abstract Within a Brite Euram project thick thermal barrier coatings for combustor applications were produced by plasma spraying of yttria partially stabilised zirconia (ZrO2 + 8 wt.% Y2O3). The material properties of such coatings strongly depend on their microstructure which can be altered by manipulating the parameters controlling the plasma spraying process. Covering a variation of possible microstructures, the coatings considered had a thickness of about 2 mm and were six to eight times thicker than the coatings currently in service. This investigation was concerned with an evaluation of the thermophysical and mechanical properties of these coatings and their correlation with the microstructure and the plasma spray parameters. Particular attention was paid to the influence of coating segmentation, microcracking and porosity. The experimental work included the measurement of the thermal diffusivity using the laser flash technique, thermal expansion measurements, and the determination of flexural strength and Young's modulus by means of a specially constructed four-point bend rig. Since some of the samples considered were sprayed according to a partially factorial test plan a statistical evaluation of the material data was possible yielding the correlation between process parameters and material properties.

scholarly journals Structural Analysis Applications

1989 ◽  
Vol 111 (2) ◽  
pp. 271-278 ◽  
Author(s):  
R. L. McKnight
Keyword(s):  
Structural Analysis ◽  
Thermal Barrier Coatings ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Turbine Engine ◽  
Inelastic Analysis ◽  
Breakthrough Technology ◽  
Computer Codes

The programs in the structural analysis area of the HOST program emphasized the generation of computer codes for performing three-dimensional inelastic analysis with more accuracy and less manpower. This paper presents the application of that technology to Aircraft Gas Turbine Engine (AGTE) components: combustors, turbine blades, and vanes. Previous limitations will be reviewed and the breakthrough technology highlighted. The synergism and spillover of the program will be demonstrated by reviewing applications to thermal barrier coatings analysis and the SSME HPFTP turbine blade. These applications show that this technology has increased the ability of the AGTE designer to be more innovative, productive, and accurate.

Influence of Impact Damage on the Thermal Stress Distribution within the EB-PVD Thermal Barrier Coatings

2016 ◽  
Vol 849 ◽  
pp. 683-688 ◽  
Author(s):  
Tai Hong Huang ◽  
Peng Song ◽  
Qiang Ji ◽  
Heng Luo ◽  
Jian Sheng Lu
Keyword(s):  
Thermal Stress ◽  
Stress Distribution ◽  
Thermal Barrier Coatings ◽  
Equivalent Stress ◽  
Turbine Blades ◽  
Ceramic Coatings ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Thermal Stress Distribution ◽  
The Impact

Macroscopic holes often form on gas turbine blades surface by high velocity gas stream with some foreign impact particles during service. The influence of the impact-holes on the thermal stress distribution was investigated in this paper. The thermal stress distribution within the TBCs after impact-damages at high temperature was intensively studied by using finite element method. Analyze equivalent stress and thermal stress, it was found that the macroscopic holes on the surface of ceramic coatings could change the original temperature gradient and it transform the thermal stress distribution in the TBCs without impacting, resulting in the maximum tensile stress area expanding at the crest and promoting the generation of cracks and reducing coatings life. The impact-holes at the edge of the blades changed the former thermal stress distribution completely. The maximum thermal stress region existed in the alumina scale, severely decreases the life of thermal barrier coatings.

Characterization of thermal barrier coatings formed by electon-beam physical vapor deposition (EB-PVD)

1989 ◽  
Vol 47 ◽  
pp. 426-427
Author(s):  
Ozer Unal
Keyword(s):  
Thermal Barrier Coatings ◽  
Physical Vapor Deposition ◽  
Ceramic Coating ◽  
High Vacuum ◽  
Ceramic Coatings ◽  
High Energy ◽  
Thermal Barrier ◽  
Protective Oxide ◽  
Barrier Coatings ◽  
Energy Beam

Interest in ceramics as thermal barrier coatings for hot components of turbine engines has increased rapidly over the last decade. The primary reason for this is the significant reduction in heat load and increased chemical inertness against corrosive species with the ceramic coating materials. Among other candidates, partially-stabilized zirconia is the focus of attention mainly because ot its low thermal conductivity and high thermal expansion coefficient.The coatings were made by Garrett Turbine Engine Company. Ni-base super-alloy was used as the substrate and later a bond-coating with high Al activity was formed over it. The ceramic coatings, with a thickness of about 50 μm, were formed by EB-PVD in a high-vacuum chamber by heating the target material (ZrO2-20 w/0 Y2O3) above its evaporation temperaturef >3500 °C) with a high-energy beam and condensing the resulting vapor onto a rotating heated substrate. A heat treatment in an oxidizing environment was performed later on to form a protective oxide layer to improve the adhesion between the ceramic coating and substrate. Bulk samples were studied by utilizing a Scintag diffractometer and a JEOL JXA-840 SEM; examinations of cross-sectional thin-films of the interface region were performed in a Philips CM 30 TEM operating at 300 kV and for chemical analysis a KEVEX X-ray spectrometer (EDS) was used.

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