[PDF] Evaluation Of Oxidation Damage In Thermal Barrier Coating Systems eBook

Author : Dongming Zhu
Publisher :
Page : 19 pages
File Size : 10,62 MB
Release : 1996
Category : Oxidation
ISBN :

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A method based on the technique of dilatometry has been established to quantitatively evaluate the interfacial damage due to the oxidation in a thermal barrier coating system. Strain isolation and adhesion coefficients have been proposed to characterize the thermal barrier coating (TBC) performance based on its thermal expansion behavior. It has been found that, for a thermal barrier coating system consisting of ZrO2-8%Y2O3/FeCrAlY/4140 steel substrate, the oxidation of the bond coat and substrate significantly reduced the ceramic coating adherence, as inferred from the dilatometry measurements. The in-situ thermal expansion measurements under 30 deg C to 700 deg C thermal cycling in air showed that the adhesion coefficient, A sub i decreased by 25% during the first 35 oxidation cycles. Metallography showed that delamination occurred at both the ceramic/bond coat and bond coat/substrate interfaces. In addition, the strain isolation effect has been improved by increasing the FeCrAlY bond coat thickness. The strain isolation coefficient, Si, increased from about 0.04 to 0.25, as the bond coat thickness changed from 0.1 mm to 1.0 mm. It may be possible to design optimum values of strain isolation and interface adhesion coefficients to achieve the best TBC performance.

Author : Yichun Zhou
Publisher : Springer Nature
Page : 943 pages
File Size : 42,1 MB
Release : 2022-10-08
Category : Science
ISBN : 9811927235

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This book highlights the failure theories and evaluation techniques of thermal barrier coatings, covering the thermal-mechanical–chemical coupling theories, performance and damage characterization techniques, and related evaluations. Thermal barrier coatings are the key thermal protection materials for high-temperature components in advanced aeroengines. Coating spallation is a major technical bottleneck faced by researchers. The extremely complex microstructure, diverse service environments, and failure behaviors bring challenges to the spallation analysis in terms of the selective use of mechanical theories, experimental methods, and testing platforms. In the book, the authors provide a systematic summary of the latest research and technological advances and present their insights and findings in the past couple of decades. This book is not only suitable for researchers and engineers in thermal barrier coatings and related fields but also a good reference for upper-undergraduate and postgraduate students of materials science and mechanics majors.

Author : Kang N. Lee
Publisher : MDPI
Page : 168 pages
File Size : 25,22 MB
Release : 2020-12-29
Category : Science
ISBN : 3039365177

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The global increase in air travel will require commercial vehicles to be more efficient than ever before. Advanced engine hot section materials are a key technology required to keep fuel consumption and emission to a minimum in next-generation gas turbines. Ceramic matrix composites (CMCs) are the most promising material to revolutionize gas turbine hot section materials technology because of their excellent high‐temperature properties. Rapid surface recession due to volatilization by water vapor is the Achilles heel of CMCs. Environmental barrier coatings (EBCs) is an enabling technology for CMCs, since it protects CMCs from water vapor. The first CMC component entered into service in 2016 in a commercial engine, and more CMC components are scheduled to follow within the next few years. One of the most difficult challenges to CMC components is EBC durability, because failure of EBC leads to a rapid reduction in CMC component life. Key contributors to EBC failure include recession, oxidation, degradation by calcium‐aluminum‐magnesium silicates (CMAS) deposits, thermal and thermo‐mechanical strains, particle erosion, and foreign object damage (FOD). Novel EBC chemistries, creative EBC designs, and robust processes are required to meet EBC durability challenges. Engine-relevant testing, characterization, and lifing methods need to be developed to improve EBC reliability. The aim of this Special Issue is to present recent advances in EBC technology to address these issues. In particular, topics of interest include but are not limited to the following: • Novel EBC chemistries and designs; • Processing including plasma spray, suspension plasma spray, solution precursor plasma spray, slurry process, PS-PVD, EB-PVD, and CVD; • Testing, characterization, and modeling; • Lifing.

Author : National Research Council
Publisher : National Academies Press
Page : 102 pages
File Size : 25,75 MB
Release : 1996-05-13
Category : Technology & Engineering
ISBN : 0309176026

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This book assesses the state of the art of coatings materials and processes for gas-turbine blades and vanes, determines potential applications of coatings in high-temperature environments, identifies needs for improved coatings in terms of performance enhancements, design considerations, and fabrication processes, assesses durability of advanced coating systems in expected service environments, and discusses the required inspection, repair, and maintenance methods. The promising areas for research and development of materials and processes for improved coating systems and the approaches to increased coating standardization are identified, with an emphasis on materials and processes with the potential for improved performance, quality, reproducibility, or manufacturing cost reduction.

Author : Dong-ming Zhu
Publisher :
Page : 32 pages
File Size : 44,37 MB
Release : 1997
Category : Coatings
ISBN :

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In the present study, the mechanisms of fatigue crack initiation and propagation, and of coating failure, under thermal loads that simulate diesel engine conditions, are investigated. The surface cracks initiate early and grow continuously under thermal low cycle fatigue (LCF) and high cycle fatigue (HCF) stresses. It is found that, in the absence of interfacial oxidation, the failure associated with LCF is closely related to coating sintering and creep at high temperatures. Significant LCF and HCF interactions have been observed in the thermal fatigue tests. The fatigue crack growth rate in the ceramic coating strongly depends on the characteristic HCF cycle number, N̂ sub HCF, which is defined as the number of HCF cycles per LCF cycle. The crack growth rate is increased from 0.36 micrometer/LCF cycle for a pure LCF test to 2.8 micrometers/LCF cycle for a combined LCF and HCF test at NĤ sub HCF about 20,000. A surface wedging model has been proposed to account for the HCF crack growth in the coating systems. This mechanism predicts that HCF damage effect increases with increasing surface temperature swing, the thermal expansion coefficient and the elastic modulus of the ceramic coating, as well as with the HCF interacting depth. A good agreement has been found between the analysis and experimental evidence.

Author : Golam Newaz
Publisher :
Page : 46 pages
File Size : 34,48 MB
Release : 1998
Category :
ISBN :

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The primary focus of the investigation was to conduct a chronological evaluation of damage initiation and propagation in Electron Beam - Physical Vapor Deposition (EB-PVD) thermal barrier coated (partially stabilized zirconia) Rene N5 single crystal superalloy. Damage initiation and failure events due to thermal cycling were investigated. Early crack initiation was rationalized through interfacial asperity induced high stresses between the TBC and the PtAl bond coat . Analytical solution was forwarded for transient and steady-state residual stresses in the EB-PVD system. Oxide scale development as a function of time was predicted using Fick' S Law. The deviation of experimental results from Fick's Law was attributed to microcrack interaction and coalescence. Oxide scale induced internal pressure on crack surfaces was shown to be a plausible mechanism for microcrack growth. Buckling analysis was used to estimate the critical size of delamination necessary (sixteen times the TBC thickness) for spallation. It was shown that for various thermal cycles, spallation life can be estimated based on critical oxide layer thickness. Thermal wave imaging technique was used to track damage condition as a function of thermal cycles. It was found that saturation of thermal wave amplitude corresponds to spallation life of the sample. This work provides a mechanism-based framework for life prediction in TBC systems.

Author : Hyungjun Kim
Publisher :
Page : pages
File Size : 31,20 MB
Release : 2005
Category : Acoustic emission testing
ISBN :

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Abstract: To more fully understand microstructural evolution and the development of damage in thermal barrier coating (TBC) systems, thermocyclic experiments were conducted on TBC specimens with and without top coats. The degradation of a PtAl (platinum modified aluminide) bond coat and a CMSX superalloy substrate were investigated for cyclic and quasi-isothermal heating to 1200 0C. To accelerate the oxidation of the specimens, the thermally grown oxide (TGO) was removed at 10 hour intervals. Scanning electron microscopy (SEM) and instrumented indentation were employed to investigate microstructural evolution and material property changes of the bond coat. The microstructural evolution of a PtAl bond coat is strongly affected by the type of thermal exposure and the presence of TGO. The differences between cyclic and quasi-isothermal heating indicate that stresses associated with cooling and heating significantly alter microstructural evolution. Damage to TBC specimens with EB-PVD (electron beam physical vapor deposition) processed YSZ (yttria stabilized zirconia) top coats, PtAl bond coats, and René N5 superalloy substrates was assessed during thermal cycling to 1200 0C. Acoustic emission (AE) techniques were used to temporally identify damage to the TBC. For automated, continuous, and high temperature AE detection, a custom made experimental setup with either a nickel-chrome alloy wire wave guide or an alumina wave guide was used. It was found that there are four distinct regions of AE activity during the life of a TBC. Throughout the cooling cycles, images of the top coat were collected with darkfield-type lighting. These images showed how undulations developed in the top coat. In addition, digital image correlation (DIC) was used to identify regions with interfacial damage. Finally, the images were used to analyze the spallation of the top coat. Cycling of an additional specimen was interrupted periodically for analysis with profilometry and SEM. The profilometry and SEM images were used to further investigate the failure mechanisms in TBCs. The experiments and analysis performed in this dissertation work have elucidated how various failure mechanisms develop during the life of TBCs. This work has improved the scientific understanding of TBCs and could aid in the development of improved life prediction models.