Download or read book Monthly Catalog of United States Government Publications written by and published by . This book was released on 1999-07 with total page 1154 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Effect of Layer Graded Bond Coats on Edge Stress Concentration and Oxidation Behavior of Thermal Barrier Coatings written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-07-02 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt: Thermal barrier coating (TBC) durability is closely related to design, processing and microstructure of the coating Z, tn systems. Two important issues that must be considered during the design of a thermal barrier coating are thermal expansion and modulus mismatch between the substrate and the ceramic layer, and substrate oxidation. In many cases, both of these issues may be best addressed through the selection of an appropriate bond coat system. In this study, a low thermal expansion and layer-graded bond coat system, that consists of plasma-sprayed FeCoNiCrAl and FeCrAlY coatings, and a high velocity oxyfuel (HVOF) sprayed FeCrAlY coating, is developed to minimize the thermal stresses and provide oxidation resistance. The thermal expansion and oxidation behavior of the coating system are also characterized, and the strain isolation effect of the bond coat system is analyzed using the finite element method (FEM). Experiments and finite element results show that the layer-graded bond coat system possesses lower interfacial stresses. better strain isolation and excellent oxidation resistance. thus significantly improving the coating performance and durability. Zhu, Dongming and Ghosn, Louis J. and Miller, Robert A. Glenn Research Center RTOP 523-23-2U...

Download or read book The Effect of Interface Roughness and Oxide Film Thickness on the Inelastic Response of Thermal Barrier Coatings to Thermal Cycling written by National Aeronautics and Space Adm Nasa and published by Independently Published. This book was released on 2018-09-17 with total page 42 pages. Available in PDF, EPUB and Kindle. Book excerpt: The effects of interfacial roughness and oxide film thickness on thermally-induced stresses in plasma-sprayed thermal barrier coatings subjected to thermal cycling are investigated using the recently developed higher-order theory for functionally graded materials. The higher-order theory is shown to be a viable alternative to the finite-element approach, capable of modeling different interfacial roughness architectures in the presence of an aluminum oxide layer and capturing the high stress gradients that occur at the top coat/bond coat interface. The oxide layer thickness is demonstrated to have a substantially greater effect on the evolution of residual stresses than local variations in interfacial roughness. Further, the location of delamination initiation in the top coat is predicted to change with increasing oxide layer thickness. This result can be used to optimize the thickness of a pre-oxidized layer introduced at the top coat/bond coat interface in order to enhance TBC durability as suggested by some researchers. The results of our investigation also support a recently proposed hypothesis regarding delamination initiation and propagation in the presence of an evolving bond coat oxidation, while pointing to the importance of interfacial roughness details and specimen geometry in modeling this phenomenon.Pindera, Marek-Jerzy and Aboudi, Jacob and Arnold, Steven M.Glenn Research CenterINTERFACES; OXIDE FILMS; THICKNESS; SURFACE ROUGHNESS; TEMPERATURE EFFECTS; STRESS DISTRIBUTION; FILM THICKNESS; THERMAL CYCLING TESTS; THERMAL CONTROL COATINGS; SPRAYED COATINGS; SPECIMEN GEOMETRY; RESIDUAL STRESS; POSITION (LOCATION); PLASMA LAYERS; JOINTS (JUNCTIONS); FINITE ELEMENT METHOD; DURABILITY; ALUMINUM OXIDES

Download or read book Analysis of Plasma Sprayed Thermal Barrier Coatings with Homogeneous and Heterogeneous Bond Coats Under Spatially Uniform Cyclic Thermal Loading written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-05-29 with total page 68 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report summarizes the results of a numerical investigation into the spallation mechanism in plasma-sprayed thermal barrier coatings observed under spatially-uniform cyclic thermal loading. The analysis focuses on the evolution of local stress and inelastic strain fields in the vicinity of the rough top/bond coat interface during thermal cycling, and how these fields are influenced by the presence of an oxide film and spatially uniform and graded distributions of alumina particles in the metallic bond coat aimed at reducing the top/bond coat thermal expansion mismatch. The impact of these factors on the potential growth of a local horizontal delamination at the rough interface's crest is included. The analysis is conducted using the Higher-Order Theory for Functionally Graded Materials with creep/relaxation constituent modeling capabilities. For two-phase bond coat microstructures, both the actual and homogenized properties are employed in the analysis. The results reveal the important contributions of both the normal and shear stress components to the delamination growth potential in the presence of an oxide film, and suggest mixed-mode crack propagation. The use of bond coats with uniform or graded microstructures is shown to increase the potential for delamination growth by increasing the magnitude of the crack-tip shear stress component.Arnold, Steven M. and Pindera, Marek-Jerzy and Aboudi, JacobGlenn Research CenterSPRAYED COATINGS; THERMAL CONTROL COATINGS; STRESS-STRAIN RELATIONSHIPS; PLASMAS (PHYSICS); SPALLATION; CYCLIC LOADS; OXIDE FILMS; ALUMINUM OXIDES; METAL COATINGS; DELAMINATING; FUNCTIONALLY GRADIENT MATERIALS; CREEP PROPERTIES; MICROSTRUCTURE; HETEROGENEITY; HOMOGENEITY; SHEAR STRESS; CRACK PROPAGATION

Download or read book Oxidation behaviour of MCrAlX coatings written by Pimin Zhang and published by Linköping University Electronic Press. This book was released on 2018-02-12 with total page 79 pages. Available in PDF, EPUB and Kindle. Book excerpt: MCrAlY coatings (M=Ni and/or Co) have been widely used for the protection of superalloy components against oxidation and hot corrosion in the hot sections of gas turbines. The drive to improve engine combustion efficiency while reducing emissions by increasing the operation temperature brings a big challenge for coating design. As a result, the need for improvement of MCrAlY coatings for better oxidation resistance is essential. Formation of a stable, dense, continuous, and slow-growing ?-Al2O3 layer, on the MCrAlY coating surface, is the key to oxidation protection, since the protective ?-Al2O3 scale offers superior oxidation resistance due to its lower oxygen-diffusion rate as compared with other oxides. The ability of a MCrAlY coating to form and maintain such a protective scale depends on the coating composition and microstructure, and can be improved through optimization of deposition parameters, modification of coating surface conditions, and so on. Part of this thesis work focuses on studying the effect of post-deposition surface treatments on the oxidation behavior of MCrAlX coatings (X can be yttrium and/or other minor alloying elements). The aim is to gain fundamental understanding of alumina scale evolution during oxidation which is important for achieving improved oxidation resistance of MCrAlX coatings. Oxide scale formed on coatings at initial oxidation stage and the effect of surface treatment were investigated by a multi-approach study combining photo-stimulated luminescence, microstructural observation and weight gain. Results showed that both mechanically polished and shot-peened coatings exhibited superior performance due to rapid formation of ?-Al2O3 fully covering the coating and suppressing growth of transient alumina, assisted by the high density of ?-Al2O3 nuclei on surface treatment induced defects. The early development of a two-layer alumina scale, consisting of an inward-grown inner ?-Al2O3 layer and an outer layer transformed from outward-grown transient alumina, resulted in a higher oxide growth rate of the as-sprayed coating. The positive effect of the surface treatments on retarding oxide scale growth and suppressing formation of spinel was also observed in oxidation test up to 1000 hrs. As the oxidation proceeds to the close-to-end stage, a reliable criterion to estimate the capability of coating to form ?-Al2O3 is of great importance to accurately evaluate coating lifetime, which is the aim of the other part of the thesis work. Survey of published results on a number of binary Ni-Al and ternary Ni-Cr-Al, Ni-Al-Si systems shows that the empirical Al-concentration based criterion is inadequate to properly predict the formation of a continuous ?-Al2O3 scale. On the other hand, correlating the corresponding Al-activity data, calculated from measured chemical compositions using the Thermo-Calc software, to the experimental oxidation results has revealed a temperature dependent, critical Al-activity value for forming continuous ?-Al2O3 scale. To validate the criterion, long-term oxidation tests were performed on five MCrAlX coatings with varying compositions and the implementation of the Al-activity based criterion on these coatings successfully predicted ?-Al2O3 formation, showing a good agreement with experiment results.

Download or read book Thermal Barrier Coatings written by and published by Elsevier. This book was released on 2011-01-14 with total page 358 pages. Available in PDF, EPUB and Kindle. Book excerpt: Effective coatings are essential to counteract the effects of corrosion and degradation of exposed materials in high-temperature environments such as gas turbine engines. Thermal barrier coatings reviews the latest advances in processing and performance of thermal barrier coatings, as well as their failure mechanisms. Part one reviews the materials and structures of thermal barrier coatings. Chapters cover both metallic and ceramic coating materials as well as nanostructured coatings. Part two covers established and advanced processing and spraying techniques, with chapters on the latest advances in plasma spraying and plasma vapour deposition as well as detonation gun spraying. Part three discusses the performance and failure of thermal barrier coatings, including oxidation and hot-corrosion, non-destructive evaluation and new materials, technologies and processes. With its distinguished editors and international team of contributors, Thermal barrier coatings is an essential reference for professional engineers in such industries as energy production, aerospace and chemical engineering as well as academic researchers in materials. Reviews the latest advances in processing and performance of thermal barrier coatings, as well as their failure mechanisms Explores the materials and structures of thermal barrier coatings incorporating cover both metallic and ceramic coating materials as well as nanostructured coating Assesses established and advanced processing and spraying techniques, including plasma vapour deposition and detonation gun spraying

Download or read book Furnace Cyclic Oxidation Behavior of Multi Component Low Conductivity Thermal Barrier Coatings written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-06-21 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt: Ceramic thermal barrier coatings will play an increasingly important role in advanced gas turbine engines because of their ability to further increase engine operating temperatures and reduce cooling, thus helping achieve future engine low emission, high efficiency and improved reliability goals. Advanced multi-component zirconia-based thermal barrier coatings are being developed using an oxide defect clustering design approach to achieve the required coating low thermal conductivity and high temperature stability. Although the new composition coatings were not yet optimized for cyclic durability, an initial durability screening of the candidate coating materials was conducted using conventional furnace cyclic oxidation tests. In this paper, furnace cyclic oxidation behavior of plasma-sprayed zirconia-based defect cluster thermal barrier coatings was investigated at 1163 C using 45 min hot cycles. The ceramic coating failure mechanisms were studied using scanning electron microscopy (SEM) combined with X-ray diffraction (XRD) phase analysis after the furnace tests. The coating cyclic lifetime is also discussed in relation to coating processing, phase structures, dopant concentration, and other thermo-physical properties. Zhu, Dong-Ming and Nesbitt, James A. and Barrett, Charles A. and McCue, Terry R. and Miller, Robert A. Glenn Research Center NASA/TM-2004-212962, ARL-TR-3260, E-14434