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Selected Works

Thermal Barrier Coatings

Articles 1 - 13 of 13

Full-Text Articles in Mechanical Engineering

On The Microstructural Development In Platinum-Modified Nickel-Aluminide Bond Coats, S. Darzens, Anette M. Karlsson Jan 2013

On The Microstructural Development In Platinum-Modified Nickel-Aluminide Bond Coats, S. Darzens, Anette M. Karlsson

Anette M Karlsson

A numerical procedure for simulating the distortions exhibited by a thermally grown oxide (TGO) upon temperature cycling has been adapted to incorporate the microstructure of the bond coat. The focus is on the dual phase β/γ′ microstructure that develops upon oxidation of a system with a Pt-aluminide bond coat. The results reveal that the presence of the γ′-phase next to the TGO reduces its distortion locally, because of the superior high-temperature strength of γ′, relative to β. Conversely, in regions where the β-phase exists adjacent to the TGO, it distorts and the TGO propagates downward, while simultaneously lengthening ...


The Effect Of The Thermal Barrier Coating On The Displacement Instability In Thermal Barrier Systems, Anette M. Karlsson, T. Xu, A. G. Evans Jan 2013

The Effect Of The Thermal Barrier Coating On The Displacement Instability In Thermal Barrier Systems, Anette M. Karlsson, T. Xu, A. G. Evans

Anette M Karlsson

Thermal barrier systems are susceptible to instability of the thermally grown oxide (TGO) at the interface between the bond coat and the thermal barrier coating (TBC). The instabilities have been linked to thermal cycling and initial geometrical imperfections, as well as to misfit strains due to both oxide growth and thermal expansion misfit. Numerical simulations are used to investigate the role of the thermo-mechanical properties of the TBC in this instability. It is found that the TBC constrains the deformation, whereupon instabilities develop preferentially in regions where crack-like imperfections either pre-exist in the TBC or are created because of the ...


A Numerical Model For The Cyclic Instability Of Thermally Grown Oxides In Thermal Barrier Systems, Anette M. Karlsson, A. G. Evans Jan 2013

A Numerical Model For The Cyclic Instability Of Thermally Grown Oxides In Thermal Barrier Systems, Anette M. Karlsson, A. G. Evans

Anette M Karlsson

Morphological instability of the thermally grown oxide (TGO) is a fundamental source of failure in some thermal barrier systems. The instabilities occur when initial non-planarity in the TGO grows in amplitude as the system experiences thermal cycling. By numerical means, this study explores how these instabilities are linked to constituent properties. The associated phenomena involve oxidation of the TGO, plastic flow of the bond coat, thermal expansion misfit between the TGO, bond coat and substrate, and stress relaxation in the TGO at high temperature. A key implication of the simulations is that the incidence of reverse yielding upon reheating differentiates ...


On Tgo Creep And The Initiation Of A Class Of Fatigue Cracks In Thermal Barrier Coatings, Mercedes T. Hernandez, Anette M. Karlsson, Marion Bartsch Jan 2013

On Tgo Creep And The Initiation Of A Class Of Fatigue Cracks In Thermal Barrier Coatings, Mercedes T. Hernandez, Anette M. Karlsson, Marion Bartsch

Anette M Karlsson

The initiation of a class of fatigue cracks observed in thermal barrier coatings (TBCs) subjected to thermal gradient mechanical fatigue testing is investigated. The coating system is based on a NiCoCrAlY bond coat and a partially yttria stabilized zirconia top coat. To explain the development of the cracks of interest, the thermo-mechanical response of the bond coat and the thermally grown oxide (TGO) is examined and quantified through finite element analyses. The models include non-linear and time-dependent behavior such as creep, TGO growth stress, and thermo-mechanical cyclic loading. The simulations suggest that stress-redistribution due to creep can lead to tensile ...


The Non-Destructive And Nano-Microstructural Characterization Of Thermal-Barrier Coatings, Y. H. Sohn, B. Jayaraj, S. Laxman, B. Franke, J. W. Byeon, Anette M. Karlsson Jan 2013

The Non-Destructive And Nano-Microstructural Characterization Of Thermal-Barrier Coatings, Y. H. Sohn, B. Jayaraj, S. Laxman, B. Franke, J. W. Byeon, Anette M. Karlsson

Anette M Karlsson

The durability of thermal barrier coatings (TBCs) plays an important role in the service reliability and maintainability of hot-section components in advanced turbine engines for aerospace and utility applications. Photostimulated luminescence spectroscopy (PSLS) and electrochemical impedance spectroscopy (EIS) are being concurrently developed as complimentary nondestructive evaluation (NDE) techniques for quality control and liferemain assessment of TBCs. This paper discusses recent achievements in understanding the residual stress, phase constituents, and electrochemical resistance (or capacitance) of TBC constituents—with an emphasis on the thermally grown oxide. Results from NDE by PSLS and EIS are correlated to the nano- and microstructural development of ...


Measurement Of Interfacial Shear Mechanical Properties In Thermal Barrier Coating Systems By A Barb Pullout Method, S. Q. Guo, D. R. Mumm, Anette M. Karlsson, Y. Kagawa Jan 2013

Measurement Of Interfacial Shear Mechanical Properties In Thermal Barrier Coating Systems By A Barb Pullout Method, S. Q. Guo, D. R. Mumm, Anette M. Karlsson, Y. Kagawa

Anette M Karlsson

A test technique has been developed to facilitate evaluation of the fracture characteristics of coatings and interfaces in thermal barrier coating (TBC) systems. The methodology has particular application in analyzing delamination crack growth, where crack propagation occurs under predominantly mode II loading. The technique has been demonstrated by quantitatively measuring the effective delamination fracture resistance of an electron-beam physical vapor deposition TBC.


On The Opening Of A Class Of Fatigue Cracks Due To Thermo-Mechanical Fatigue Testing Of Thermal Barrier Coatings, M. T. Hernandez, D. Cojocaru, M. Bartsch, Anette M. Karlsson Jan 2013

On The Opening Of A Class Of Fatigue Cracks Due To Thermo-Mechanical Fatigue Testing Of Thermal Barrier Coatings, M. T. Hernandez, D. Cojocaru, M. Bartsch, Anette M. Karlsson

Anette M Karlsson

The evolution of fatigue cracks observed in thermal barrier coatings (TBCs) subjected to an accelerated test scheme is investigated via numerical simulations. The TBC system consists of a NiCoCrAlY bond coat and partially yttria stabilized zirconia top coat with a thermally grown oxide (TGO) between these two coatings. The cracks of interest evolve in the bond coat parallel and near the interface with the TGO during thermo-mechanical fatigue testing. In their final stage, the cracks lead to partial spallation of the TBC. This study focuses on why the cracks open to their characteristic shape. To this end, finite element simulations ...


A Simple Numerical Method Of Cycle Jumps For Cyclically Loaded Structures, D. Cojocaru, Anette M. Karlsson Jan 2013

A Simple Numerical Method Of Cycle Jumps For Cyclically Loaded Structures, D. Cojocaru, Anette M. Karlsson

Anette M Karlsson

A method for accelerated numerical simulations of structures subjected to cyclic loading is investigated. Of particular interest is a class of structures where the structural properties evolve with time. The proposed method is based on conducting detailed finite element analysis for a set of cycles to establish a trend line, extrapolating the trend line spanning many cycles, and use the extrapolated state as initial state for additional FEA simulations. This includes a control function that automatically monitors the length of the cycle jump to ensure a realistic solution. We compare the proposed method to a reference calculation, where all incremental ...


Evolution Of Surface Morphology Of Thermo-Mechanically Cycled Nicocraly Bond Coats, J. Shi, Anette M. Karlsson, B. Baufeld, M. Bartsch Jan 2013

Evolution Of Surface Morphology Of Thermo-Mechanically Cycled Nicocraly Bond Coats, J. Shi, Anette M. Karlsson, B. Baufeld, M. Bartsch

Anette M Karlsson

We investigate morphological surface instabilities on bond coat surfaces of thermal barrier coatings, induced due to thermo-mechanical loading. Experimental results of hollow circular cylindrical specimens, consisting of a directionally solidified superalloy (IN 100 DS) coated with a NiCoCrAlY bond coat, show that the morphological instabilities are strongly dependent on the load conditions. In particular, the morphological instabilities develop during thermal cycling with a thermal gradient over the cylinder wall, whereas the surface remains smooth for thermal cyclic conditions without a gradient. Furthermore, if a cyclic, axial tensile force is applied (synchronized with the thermal cycling), the morphological instabilities become aligned ...


On Cracks And Delaminations Of Thermal Barrier Coatings Due To Indentation Testing: Experimental Investigations, Jin Yan, Thorsten Leist, Marion Bartsch, Anette M. Karlsson Jan 2013

On Cracks And Delaminations Of Thermal Barrier Coatings Due To Indentation Testing: Experimental Investigations, Jin Yan, Thorsten Leist, Marion Bartsch, Anette M. Karlsson

Anette M Karlsson

Rockwell indentation testing as a method of establishing the interfacial fracture toughness of thermal barrier coatings is investigated. To this end, indentation tests have been systematically performed on coatings with yttria-stabilized zirconia top coat deposited by electron beam physical vapor deposition. Specimens in “as-coated” condition and after heat treatment in air have been studied. Unexpectedly, indentation of the heat-treated samples resulted in smaller delaminations than the as-coated samples, suggesting an increase in fracture toughness for coatings subjected to elevated temperatures. Careful image analyses of the cross-section of the indented area show that the ceramic top coat undergoes a complex damage ...


On Stresses Induced In A Thermal Barrier Coating Due To Indentation Testing, Jin Yan, Anette M. Karlsson, Marion Bartsch, Xi Chen Jan 2013

On Stresses Induced In A Thermal Barrier Coating Due To Indentation Testing, Jin Yan, Anette M. Karlsson, Marion Bartsch, Xi Chen

Anette M Karlsson

Instrumented indentation has been suggested as a method to determine interfacial fracture toughness of thermal barrier coatings. However, in a previous experimental study we showed that the results are ambiguous. In this work, we investigate the experimental results by numerical simulations incorporating the material microstructure. In the numerical simulations, based on finite element analyses, the stress fields that are associated with the loading and unloading of the indenter are investigated. By comparing these stress fields to the damage observed in the experimental study, including crack path and interfacial delaminations, we explain key findings from the experimental observations. Our results suggest ...


Aspects Of The Morphological Evolution In Thermal Barrier Coatings And The Intrinsic Thermal Mismatch Therein, J. Shi, S. Darzens, Anette M. Karlsson Jan 2013

Aspects Of The Morphological Evolution In Thermal Barrier Coatings And The Intrinsic Thermal Mismatch Therein, J. Shi, S. Darzens, Anette M. Karlsson

Anette M Karlsson

The evolution of interfacial deformations and stresses in thermal barrier coatings due to the formation of the thermally grown oxide and the intrinsic thermal mismatch is investigated. The study focuses on systems that are prone to displacement instabilities of the thermally grown oxide and numerical models spanning a range of properties are investigated. Material changes in the Pt-modified aluminide bond-coat, such as martensitic transformation and the change from β- to γ′-grains, are considered. The numerical simulations show that when the mismatch is large enough to cause overall yielding in the bond-coat, the thermal expansion of the substrate (the superalloy ...


The Displacement Of The Thermally Grown Oxide In Thermal Barrier Systems Upon Temperature Cycling, Anette M. Karlsson, J. W. Hutchinson, A. G. Evans Jan 2013

The Displacement Of The Thermally Grown Oxide In Thermal Barrier Systems Upon Temperature Cycling, Anette M. Karlsson, J. W. Hutchinson, A. G. Evans

Anette M Karlsson

Models that characterize the displacement instability of the thermally grown oxide (TGO) found in some thermal barrier systems are reviewed, consolidated and extended. It is demonstrated that the simulations are only consistent with the observations whenever the bond coat and TGO both undergo plastic deformation. The TGO yields at the peak temperature, during growth, while the bond coat yields on thermal cycling. The trends oppose. Namely, the TGO displacement is diminished by increasing the high temperature strength of the bond coat, but is increased upon increasing the TGO strength. The model rationalizes certain experimental trends, particularly the decrease in durability ...