[PDF] Oxidation Studies Of Air Plasma Sprayed Bond Coats For Thermal Barrier Coatings eBook

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Page : pages
File Size : 20,50 MB
Release : 2001
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Thermogravimetric methods for evaluating bond coat oxidation in plasma-sprayed thermal barrier coating (TBC) systems were assessed by high-temperature testing of TBC systems with air plasma-sprayed (APS) Ni-22Cr-10Al-1Y bond coatings and yttria-stabilized zirconia top coatings. High-mass thermogravimetric analysis (at 1150[sup degrees]C) was used to measure bond coat oxidation kinetics. Furnace cycling was used to evaluate APS TBC durability. This paper describes the experimental methods and relative oxidation kinetics of the various specimen types. Characterization of the APS TBCs and their reaction products is discussed.

Author : National Aeronautics and Space Administration (NASA)
Publisher : Createspace Independent Publishing Platform
Page : 26 pages
File Size : 42,2 MB
Release : 2018-07-02
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ISBN : 9781722190873

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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...

Author : Patrick Richer
Publisher :
Page : 0 pages
File Size : 38,90 MB
Release : 2010
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Gas turbine engines are considered to be among the most hostile operating environments for conventional material systems. Increasing demands for higher engine performance and durability of components have led to the development of thermal barrier coating (TBC) systems. Typical TBC systems consist of two coating layers: an insulating ceramic top coat for thermal protection and an underlying metallic bond coat for improved adhesion of the top coat and better chemical protection against high temperature oxidation and hot corrosion. However, current use of these coating systems is limited due to their premature failure which is associated to cracking and delaminating of the ceramic top coat. It is generally accepted that the primary mechanism responsible for TBC failure is attributed to oxidation of the bond coat which results in the formation of an oxide scale at the interface between the bond coat and ceramic top coat and eventually causes cracking and delamination of the top coat. Better understanding and control of the bond coat oxidation dynamics is therefore of primary importance for the development of TBC systems with improved performance. The bond coat is commonly manufactured by thermal spray techniques: the bond coat material, initially in powder form, is heated beyond its melting point, projected onto the surface to be coated and finally re-solidified upon cooling to form a coating. It has been demonstrated that certain microstructural features of the bond coat that are detrimental to its oxidation behaviour originate from thermally induced effects encountered during thermal spraying. Therefore, it is expected that improved bond coat oxidation behaviour could be achieved if the deposition process did not involve significant heating of the material. Recent developments in the surface and coatings industry have given rise to a new coating technology known as Cold Gas Dynamic Spraying (CGDS). As its name implies, this process does not rely on thermal energy for the formation of coatings, but rather on kinetic energy: particles are accelerated above a critical velocity and plastically deform upon impact on the substrate to adhere and form a coating. Due to the absence of significant heating of the sprayed material, this work aims to manufacture bond coats using the CGDS deposition technique and investigate whether improved oxidation behaviour can be achieved. The present thesis provides a description of the experimental approaches considered for the development of CGDS bond coats with improved oxidation behaviour. Given the complexity of TBC systems due to the various interactions between the multiple coating layers, this work strictly concentrates on the bond coat layer without the presence of the superalloy substrate or ceramic top coat, thereby allowing the thorough characterization of the bond coat oxidation behaviour as a function of the initial powder microstructure and different deposition techniques. As such, the objectives of this work are to demonstrate the feasibility of manufacturing bond coats using the CGDS technique, optimize the deposition process for the materials considered, verify whether the CGDS process induces microstructural changes in the deposited material and finally evaluate and compare the oxidation behaviour of CGDS bond coats with those of thermal sprayed bond coats. Results of this work show that bond coatings with conventional and nanocrystalline microstructures were successfully manufactured by the CGDS system developed at the University of Ottawa Cold Spray Laboratory. Optimal spraying parameters were also identified and coatings with low levels of porosity were successfully deposited using this technique. Investigation of the original feedstock powder and resulting coating microstructures revealed that significant microstructural transformations had occurred throughout the CGDS deposition process as a result of extensive plastic deformation of the particles. Isothermal oxidation testing was also carried out on both the conventional and nanocrystalline CGDS coatings. For comparison purposes, thermal spray coatings were also manufactured (using the air plasma spray and high velocity oxy-fuel processes) and subjected to oxidation testing. Results showed that low temperature processing of bond coat materials is beneficial to their oxidation behaviour as it results in coatings with low porosity and limited oxide content, thereby leading to lower oxide growth rates. Furthermore, the CGDS process was observed to produce coatings characterized with fine grain structures (either by means of a grain refinement process of the conventional material or by preserving the fine grain structure of the nanocrystalline material) which was also shown to be beneficial to the oxidation behaviour. Results from this work therefore demonstrate that potentially significant improvements to TBC performance could be achieved by manufacturing bond coats using the CGDS deposition technique.

Author : Hongbo Guo
Publisher : Woodhead Publishing
Page : 490 pages
File Size : 40,65 MB
Release : 2023-01-18
Category : Science
ISBN : 0128190280

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Thermal Barrier Coatings, Second Edition plays a critical role in counteracting the effects of corrosion and degradation of exposed materials in high-temperature environments such as gas turbine and aero-engines. This updated edition reviews recent advances in the processing and performance of thermal barrier coatings, as well as their failure mechanisms. Novel technologies for the manufacturing of thermal barrier coatings (TBCs) such as plasma spray-physical vapor deposition and suspension plasma spray, are covered, as well as severe degradation of TBCs caused by CMAS attack. In addition to discussions of new materials and technologies, an outlook about next generation TBCs, including T/EBCs is discussed.This edition will provide the fundamental science and engineering of thermal barrier coatings for researchers in the field of TBCs, as well as students looking for a tutorial. Includes coverage of emerging materials, such as rare-earth doped ceramics Presents the latest on plasma spray-physical vapor deposition and suspension (solution precursor) Discusses the degradation of TBCs caused by CMAS attack and its protection Looks at thermally environmental barrier coatings, interdiffusion and diffusion barrier

Author : Matthew J. Donachie
Publisher : ASM International
Page : 439 pages
File Size : 44,69 MB
Release : 2002
Category : Heat resistant alloys
ISBN : 1615030646

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This book covers virtually all technical aspects related to the selection, processing, use, and analysis of superalloys. The text of this new second edition has been completely revised and expanded with many new figures and tables added. In developing this new edition, the focus has been on providing comprehensive and practical coverage of superalloys technology. Some highlights include the most complete and up-to-date presentation available on alloy melting. Coverage of alloy selection provides many tips and guidelines that the reader can use in identifying an appropriate alloy for a specific application. The relation of properties and microstructure is covered in more detail than in previous books.

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Page : 59 pages
File Size : 45,26 MB
Release : 2001
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This program has been directed at determining the mechanisms by which oxidation causes failure of thermal barrier coatings (TBCs) and developing modified systems with improved resistance to Oxidation-induced failures. The thermal barrier coating was yttria stabilized zirconia (YSZ) deposited via electron beam vapor deposition (EBPVD). This TBC was deposited on both platinum aluminide and NiCoCrA1Y bond coats which in turn were deposited on superalloy substrates of Rare N5. The oxidation testing was performed at 1000 deg, 1100 deg and 1200 deg C in air using cyclic exposures. The approach consisted of initially examining state-of-the-art systems and based upon the results obtained to prepare modified TBCs. Emphasis was placed upon bond coat modifications. In the case of the NiCoCrA1Y bond coats it was found that defects in the as-processed coatings at the TBC-bond coat interface caused failures. Procedures to prevent the formation of such defects extended TBC lives. The lives of TBCs on platinum-aluminide bond coats were influenced by ratcheting of the bond coat at the bond coat-TBC interface. Polishing of bond coats prior to TBC deposition is proposed to inhibit ratcheting and extend TBC lives.