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The Degradation Of Environmental Barrier Coatings By Molten Silicates
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Book Synopsis The Degradation of Environmental Barrier Coatings by Molten Silicates by : Kendra Marie Grant
Download or read book The Degradation of Environmental Barrier Coatings by Molten Silicates written by Kendra Marie Grant and published by . This book was released on 2010 with total page 318 pages. Available in PDF, EPUB and Kindle. Book excerpt: The volatilization of Si-based ceramic matrix composites (CMCs) in moisture-laden combustion environments is alleviated by the application of an environmental barrier coating (EBC). In principle all current (e.g. BSAS) and prospective (e.g. Y2SiO5) EBC materials are susceptible to thermochemical degradation by calcium-magnesium alumino-silicate (CMAS) deposits. The mechanism involves dissolution of the parent EBC into the CMAS melt and the precipitation of silicate reaction products. For example, BSAS in contact with the melt dissolves and re-precipitates as modified Celsian. However, the CMAS attack of BSAS involves an additional and potentially more damaging mechanism, wherein CMAS penetrates along grain boundaries to depths typically of the order of a practical coating thickness. Yttrium silicate monoliths are not susceptible to grain boundary attack; however, the primary precipitated phase, calcium-yttrium apatite (Ca2Y8(SiO 4)6O2), is not fully effective as a diffusion barrier. The apatite is interpenetrated by thin amorphous grain boundary films that allows rapid transport of the glass species to the reaction front. The secondary products and morphological characteristics of the reaction zone depend on time, temperature and whether the environment is stagnant laboratory air or flowing H2O/O2. The degradation mechanisms and their implications to the durability of EBCs in potential gas turbine applications are discussed in light of experiments exploring the effect of these variables.
Book Synopsis Molten Silicate Reactivity with Environmental Barrier Coating Materials for Gas Turbine Engine Applications by : Jamesa Stokes
Download or read book Molten Silicate Reactivity with Environmental Barrier Coating Materials for Gas Turbine Engine Applications written by Jamesa Stokes and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Environmental barrier coatings (EBCs) are employed in gas turbine engines to protect silicon carbide (SiC)-based engine components from deleterious reactions with water vapor in the harsh combustion environment. Yttrium disilicate (YDS) and ytterbium disilicate (YbDS), the current state-of-the-art EBC topcoat materials, degrade when exposed to calcium-magnesium-aluminosilicates (CMAS) caused by the ingestion of dust particles during engine operation. This damage mechanism will be exacerbated as gas turbine engines continue to operate at temperatures much greater than the melting temperature of the ingested particulates. The degradation of EBC materials is largely thermochemically driven, resulting in dissolution of coatings via hot corrosion. After dissolution, various reaction products are precipitated based on the thermodynamic equilibria between the coating and molten deposit. Therefore, novel coating chemistries based on YDS and YbDS were formulated to utilize this thermochemical interaction advantageously to aid in crystallizing molten deposits at high temperature to prevent further degradation. The thermochemical behavior of EBCs was studied primarily through heat treatments of mixtures of EBC material and various CMAS compositions. The products of these interactions were evaluated using X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, and electron probe microanalysis. Four quaternary CaO-MgO-Al2O3-SiO2 silicates were investigated, having CaO:SiO2 ratios equal to terrestrial sources of ingested particles relevant to engine operating environments. The silicates exhibited a wide range of melting temperatures from ~1240C up to ~1500C, with most of the compositions exhibiting incongruent melting behavior. These CMAS compositions were mixed with YDS and YbDS and heat treated at 1200C, 1300C, and 1400C for 1 hour, 10 hours and 50 hours. Below the full melting temperatures of the CMAS compositions, reactions were kinetically limited due to intrinsic crystallization of CMAS, with YbDS exhibiting little to no interaction with the molten silicates up to 50 hours. Above glass melting temperatures, exposure of the disilicates resulted in full dissolution into the molten glass. Reaction products included reprecipitation of the disilicate phase and a Ca2RE8(SiO4)6O2 apatite-type silicate. However, the formation of the apatite phase was also dependent on cation size and CaO content in the molten deposit. Apatite formation decreased linearly with a decrease in CaO:SiO2 ratio below 0.635 in CMAS, because of the decreased stability of smaller RE cations like Yb3+ or Y3+ in the apatite structure. With high CaO:SiO2 ratio CMAS compositions, YDS formed ~50% more apatite than YbDS, indicating that apatite stability increases with increasing RE cation size. Investigations with additional RE disilicates (RE = Er, Dy, Gd, Nd) with CMAS were carried out at 1400C. With larger RE cations like Dy3+, Gd3+, and Nd3+, additional stoichiometries of apatite were stabilized (Ca2+yRE8+x(SiO4)6O2+3x/2+y). As the CaO:SiO2 ratio decreased, apatite formation remained consistent for ratios above 0.277, although the apatite precipitates became deficient in CaO and rich in REO1.5 content. Below CaO:SiO2 ratios of 0.277, GdDS reacted with CMAS to form the apatite, and no apatite was observed for DyDS or NdDS. From these studies, it was concluded that GdDS is in an optimum cation size range in which the Gd3+ cation, which is ~2% larger than Dy3+, stabilized apatite at very low CaO:SiO2 ratios. Because Nd3+ is ~5% larger than Gd3+, however, CMAS reactions with NdDS promoted ~20% greater liquid formation in the system due to its larger size. GdDS was incorporated into YDS and YbDS by synthesis of Y2-2xGd2xSi2O7 and Yb2-2xGd2xSi2O7 solutions via solid state reaction method at 1580C. YDS formed a complete solid solution series with GdDS, with the resulting single phase compounds exhibiting an orthorhombic crystal structure with a very high coefficient of thermal expansion (CTE) (>~810-6/K), not recommended for use as EBC materials. In the YbDS-GdDS system, 20 mol% GdDS was soluble in YbDS before the phase transformation occurred, making this material potentially useful as an EBC. Additionally, incorporation of 30 mol% GdDS resulted in a monoclinic single phase compound. Above 30 mol% GdDS, phase segregation was observed between a Yb-rich monoclinic compound and a Gd-rich orthorhombic compound, with results indicating that there is a maximum solubility of ~40 mol% GdDS in YbDS. Baseline YDS and YbDS pellets were tested alongside 5 mol% GdDS, 20 mol% GdDS and 30 mol% GdDS Yb2-2xGd2xSi2O7 samples in diffusion couple experiments with CMAS to determine extent of melt infiltration. Additions of GdDS to YbDS promoted more apatite formation over baseline YbDS and reduced CMAS infiltration on short time scales by ~60%. However, the formed apatite layer was observed to diffuse inwards at longer times at high temperature, in addition to CMAS infiltration occurring along grain boundaries. Thus, these materials were found not suitable for CMAS mitigation in EBCs.
Book Synopsis Environmental Barrier Coatings by : Kang N. Lee
Download or read book Environmental Barrier Coatings written by Kang N. Lee and published by MDPI. This book was released on 2020-12-29 with total page 168 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Novel Environmental Barrier Coatings for Resistance Against Degradation by Molten Glassy Deposits in the Presence of Water Vapor by : Caitlin Maureen Toohey
Download or read book Novel Environmental Barrier Coatings for Resistance Against Degradation by Molten Glassy Deposits in the Presence of Water Vapor written by Caitlin Maureen Toohey and published by . This book was released on 2011 with total page 40 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: Environmental barrier coatings (EBCs) are used to prevent oxidation of underlying ceramic-matrix composite (CMC) structural components in aircraft gas-turbine engines. As operating temperatures increase, ingested airborne sand poses a serious threat to the stability of these coatings, because the sand adheres to the hot EBC surfaces and melts, forming calcium--magnesium--aluminosilicate (CMAS) glass. The reaction of EBCs with molten CMAS can lead to EBC delamination. Additionally, the interaction of water vapor with the CMAS--reacted EBCs can result in the formation of undesirable phases. Yb2Si2O-- has been identified as a promising EBC ceramic, based on its desirable properties: phase stability up to 1600°C, low thermal expansion coefficient mismatch with common CMCs, and potential resistance against degradation by CMAS and water vapor. As--sintered Yb2Si2O-- and CMAS--coated Yb2Si2O-- are tested in an air environment and in a water vapor environment, at a temperature of 1300°C in both cases. The behavior of these ceramics is compared to that of reference materials. Results from oxidation and chemical stability studies and analyses are presented.
Book Synopsis Thermal Barrier Coatings by : Hongbo Guo
Download or read book Thermal Barrier Coatings written by Hongbo Guo and published by Woodhead Publishing. This book was released on 2023-01-18 with total page 490 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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
Book Synopsis Upper Temperature Limit of Environmental Barrier Coatings Based on Mullite and BSAS by :
Download or read book Upper Temperature Limit of Environmental Barrier Coatings Based on Mullite and BSAS written by and published by . This book was released on 2002 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Environmental Degradation of Oxidation Resistant and Thermal Barrier Coatings for Fuel-flexible Gas Turbine Applications by : Prabhakar Mohan
Download or read book Environmental Degradation of Oxidation Resistant and Thermal Barrier Coatings for Fuel-flexible Gas Turbine Applications written by Prabhakar Mohan and published by . This book was released on 2010 with total page 218 pages. Available in PDF, EPUB and Kindle. Book excerpt: The development of thermal barrier coatings (TBCs) has been undoubtedly the most critical advancement in materials technology for modern gas turbine engines. TBCs are widely used in gas turbine engines for both power-generation and propulsion applications. Metallic oxidation-resistant coatings (ORCs) are also widely employed as a stand-alone protective coating or bond coat for TBCs in many high-temperature applications. Among the widely studied durability issues in these high-temperature protective coatings, one critical challenge that received greater attention in recent years is their resistance to high-temperature degradation due to corrosive deposits arising from fuel impurities and CMAS (calcium-magnesium-alumino-silicate) sand deposits from air ingestion. The presence of vanadium, sulfur, phosphorus, sodium and calcium impurities in alternative fuels warrants a clear understanding of high-temperature materials degradation for the development of fuel-flexible gas turbine engines. Degradation due to CMAS is a critical problem for gas turbine components operating in a dust-laden environment. In this study, high-temperature degradation due to aggressive deposits such as V2O5, P2O5, Na2SO4, NaVO3, CaSO4 and a laboratory-synthesized CMAS sand for free-standing air plasma sprayed (APS) yttria stabilized zirconia (YSZ), the topcoat of the TBC system, and APS CoNiCrAlY, the bond coat of the TBC system or a stand-alone ORC, is examined. Phase transformations and microstructural development were examined by using x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. This study demonstrated that the V2O5 melt degrades the APS YSZ through the formation of ZrV2O-- and YVO4 at temperatures below 747°C and above 747°C, respectively. Formation of YVO4 leads to the depletion of the Y2O3 stabilizer and the deleterious transformation of the YSZ to the monoclinic ZrO2 phase. The investigation on the YSZ degradation by Na2SO4 and a Na2SO4 + V2O5 mixture (50-50 mol. %) demonstrated that Na2SO4 itself did not degrade the YSZ, however, in the presence of V2O5, Na2SO4 formed vanadates such as NaVO3 that degraded the YSZ through YVO4 formation at temperature as low as 700°C. The APS YSZ was found to react with the P2O5 melt by forming ZrP2O-- at all temperatures. This interaction led to the depletion of ZrO2 in the YSZ (i.e., enrichment of Y2O3 in t'-YSZ) and promoted the formation of the fluorite-cubic ZrO2 phase. Above 1250°C, CMAS deposits were observed to readily infiltrate and significantly dissolve the YSZ coating via thermochemical interactions. Upon cooling, zirconia reprecipitated with a spherical morphology and a composition that depended on the local melt chemistry. The molten CMAS attack destabilized the YSZ through the detrimental phase transformation (t'[right arrow] t[right arrow]f + m). Free standing APS CoNiCrAlY was also prone to degradation by corrosive molten deposits. The V2O5 melt degraded the APS CoNiCrAlY through various reactions involving acidic dissolution of the protective oxide scale, which yielded substitutional-solid solution vanadates such as (Co, Ni)3(VO4)2 and (Cr, Al)VO4. The molten P2O5, on the other hand, was found to consume the bond coat constituents significantly via reactions that formed both Ni/Co rich phosphates and Cr/Al rich phosphates. Sulfate deposits such as Na2SO4, when tested in encapsulation, damaged the CoNiCrAlY by Type I acidic fluxing hot corrosion mechanisms at 1000°C that resulted in accelerated oxidation and sulfidation. The formation of a protective continuous Al2O3 oxide scale by preoxidation treatment significantly delayed the hot corrosion of CoNiCrAlY by sulfates. However, CoNiCrAlY in both as-sprayed and preoxidized condition suffered a significant damage by CaSO4 deposits via a basic fluxing mechanism that yielded CaCrO4 and CaAl2O4. The CMAS melt also dissolved the protective Al2O3 oxide scale developed on CoNiCrAlY by forming anorthite platelets and spinel oxides. Based on the detailed investigation on degradation of the APS YSZ and CoNiCrAlY by various corrosive deposits, an experimental attempt was carried out to mitigate the melt-induced deposit attack. Experimental results from this study demonstrate, for the first time, that an oxide overlay produced by electrophoretic deposition (EPD) can effectively perform as an environmental barrier overlay for APS TBCs. The EPD protective overlay has a uniform and easily-controllable thickness, uniformly distributed closed pores and tailored chemistry. The EPD Al2O3 and MgO overlays were successful in protecting the APS YSZ TBCs against CMAS attack and hot corrosion attack (e.g., sulfate and vanadate), respectively. Furnace thermal cyclic oxidation testing of overlay-modified TBCs on bond-coated superalloy also demonstrated the good adhesive durability of the EPD Al2O3 overlay.
Book Synopsis Ceramic Coatings for High-Temperature Environments by : Amirhossein Pakseresht
Download or read book Ceramic Coatings for High-Temperature Environments written by Amirhossein Pakseresht and published by Springer Nature. This book was released on 2024-01-06 with total page 493 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book addresses the recent trends in thermal and environmental barrier coatings and their applications in extreme environments. It introduces the state of the art in coating materials and processes for high and ultrahigh-temperature environments and identifies areas for improvement in materials selection, performance upgrades, design considerations, and manufacturing methods. This book also covers fundamental studies involving modelling, creating coating architectures, coating preparation methods, and coating capability throughout a wide temperature range. The book examines a variety of high-temperature coatings prepared through various synthesis processes such as thermal spraying, electron beam evaporation, and sol–gel methods. This book also covers ultrahigh-temperature ceramic (UHTC) materials and provides a brief overview of the synthesis method, densification processes, and coating methods along with the properties and applications of emerging high entropy UHTCs. With contributions from international researchers active in the field, this edited book features the most recent and up-to-date literature references for a broad readership consisting of academic and industrial professionals. It is suitable for graduate students as well as materials scientists and engineers working in the area of high and ultrahigh-temperature ceramic materials.
Book Synopsis Proceedings of the 2nd International Conference on Advanced Surface Enhancement (INCASE 2021) by : Yuefan Wei
Download or read book Proceedings of the 2nd International Conference on Advanced Surface Enhancement (INCASE 2021) written by Yuefan Wei and published by Springer Nature. This book was released on 2021-08-21 with total page 261 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents the proceedings of the ‘2nd International Conference on Advanced Surface Enhancement’, INCASE 2021. It comprehensively reviews the state-of-the-arts in surface engineering related techniques and strategies, towards industrialization. The topics include ‘Advances in Surface Engineering’, ‘Surface and sub-surface Characterisation’, ‘Surface Coatings’ and ‘Modeling and Simulation’. With the opportunities and challenges discussed, this book identifies the gaps between research and manufacturing. The innovative ideas presented promote technology adoption in industry, for the future of manufacturing.
Book Synopsis Ceramic Matrix Composites by : Composite Materials Handbook – 17 (CMH-17)
Download or read book Ceramic Matrix Composites written by Composite Materials Handbook – 17 (CMH-17) and published by SAE International. This book was released on 2017-06-29 with total page 491 pages. Available in PDF, EPUB and Kindle. Book excerpt: The fifth volume of this six-volume compendium publishes technical guidance and properties on ceramic matrix composite material systems. The selected guidance on technical topics related to this class of composites includes material selection, processing, characterization, testing, data reduction, design, analysis, quality control, application, case histories, and lessons learned of typical ceramic matrix composite materials. Volume 5, which covers ceramic matrix composites, supersedes MIL-HDBK-17-5 of June 17, 2002. The Composite Materials Handbook, referred to by industry groups as CMH-17, is an engineering reference tool that contains over 1,000 records of the latest test data for polymer matrix, metal matrix, ceramic matrix, and structural sandwich composites. CMH-17 provides information and guidance necessary to design and fabricate end items from composite materials. It includes properties of composite materials that meet specific data requirements as well as guidelines for design, analysis, material selection, manufacturing, quality control, and repair. The primary purpose of the handbook is to standardize engineering methodologies related to testing, data reduction, and reporting of property data for current and emerging composite materials. It is used by engineers worldwide in designing and fabricating products made from composite materials.
Book Synopsis "Plasma-sprayed Refractory Oxide Coatings on Silicon-base Ceramics" by : Surendra Tewari
Download or read book "Plasma-sprayed Refractory Oxide Coatings on Silicon-base Ceramics" written by Surendra Tewari and published by . This book was released on 1997 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "Silicon-base ceramics are promising candidate materials for high temperature structural applications such as heat exchangers, gas turbines and advanced internal combustion engines. Composites based on these materials are leading candidates for combustor materials for HSCT gas turbine engines. These materials possess a combination of excellent physical and mechanical properties at high temperatures, for example, high strength, high toughness, high thermal shock resistance, high thermal conductivity, light weight and excellent oxidation resistance. However, environmental durability can be significantly reduced in certain conditions such as when molten salts, H2 or water vapor are present. The oxidation resistance of silicon-base materials is provided by SiO2 protective layer. Molten salt reacts with SiO2 and forms a mixture of SiO2 and liquid silicate at temperatures above 800C. Oxygen diffuses more easily through the chemically altered layer, resulting in a catastrophic degradation of the substrate SiC and Si3N4 are not stable in pure I-t2 and decompose to silicon and gaseous species such as CH4, Sill, Sill4, N2, and NH3. Water vapor is known to slightly increase the oxidation rate of SiC and Si3N4. Refractory oxides such as alumina, yitria-stabilized zirconia, ytria and mullite (3A12032SIO2) possess excellent environmental durability in harsh conditions mentioned above. Therefore, refractory oxide coatings on silicon-base ceramics can substantially improve the environmental durability of these materials by acting as a chemical reaction barrier. These oxide coatings can also serve as a thermal barrier. The purpose of this research program has been to develop refractory oxide chemical/thermal barrier coatings on silicon-base ceramics to provide extended temperature range and lifetime to these materials in harsh environments."--Page 2.
Book Synopsis Coatings for High-Temperature Structural Materials by : National Research Council
Download or read book Coatings for High-Temperature Structural Materials written by National Research Council and published by National Academies Press. This book was released on 1996-05-13 with total page 102 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis High Temperature Coatings by : Sudhangshu Bose
Download or read book High Temperature Coatings written by Sudhangshu Bose and published by Butterworth-Heinemann. This book was released on 2017-11-27 with total page 418 pages. Available in PDF, EPUB and Kindle. Book excerpt: High Temperature Coatings, Second Edition, demonstrates how to counteract the thermal effects of rapid corrosion and degradation of exposed materials and equipment that can occur under high operating temperatures. This is the first true practical guide on the use of thermally protective coatings for high-temperature applications, including the latest developments in materials used for protective coatings. It covers the make-up and behavior of such materials under thermal stress and the methods used for applying them to specific types of substrates, as well as invaluable advice on inspection and repair of existing thermal coatings. With his long experience in the aerospace gas turbine industry, the author has compiled the very latest in coating materials and coating technologies, as well as hard-to-find guidance on maintaining and repairing thermal coatings, including appropriate inspection protocols. The book is supplemented with the latest reference information and additional support to help readers find more application- and industry-type coatings specifications and uses. - Offers an overview of the underlying fundamental concepts of thermally-protective coatings, including thermodynamics, energy kinetics, crystallography and equilibrium phases - Covers essential chemistry and physics of underlying substrates, including steels, nickel-iron alloys, nickel-cobalt alloys and titanium alloys - Provides detailed guidance on a wide variety of coating types, including those used against high temperature corrosion and oxidative degradation and thermal barrier coatings
Book Synopsis Corrosion Mechanisms of Zirconia-yttria Thermal Barrier Coatings in the Presence of Molten Silicate Debris by : D. J. De Wet
Download or read book Corrosion Mechanisms of Zirconia-yttria Thermal Barrier Coatings in the Presence of Molten Silicate Debris written by D. J. De Wet and published by . This book was released on 1994 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Degradation of Thermal Barrier Coatings from Deposits and Its Mitigation by :
Download or read book Degradation of Thermal Barrier Coatings from Deposits and Its Mitigation written by and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Ceramic thermal barrier coatings (TBCs) used in gas-turbine engines afford higher operating temperatures, resulting in enhanced efficiencies and performance. However, in the case of syngas-fired engines, fly ash particulate impurities that may be present in syngas can melt on the hotter TBC surfaces and form glassy deposits. These deposits can penetrate the TBCs leading to their failure. In experiments using lignite fly ash to simulate these conditions we show that conventional TBCs of composition 93wt% ZrO2 + 7wt% Y2O3 (7YSZ) fabricated using the air plasma spray (APS) process are completely destroyed by the molten fly ash. The molten fly ash is found to penetrate the full thickness of the TBC. The mechanisms by which this occurs appear to be similar to those observed in degradation of 7YSZ TBCs by molten calcium-magnesium-aluminosilicate (CMAS) sand and by molten volcanic ash in aircraft engines. In contrast, APS TBCs of Gd{sub 2Zr2O-- composition are highly resistant to attack by molten lignite fly ash under identical conditions, where the molten ash penetrates ~25% of TBC thickness. This damage mitigation appears to be due to the formation of an impervious, stable crystalline layer at the fly ash/Gd2Zr2O-- TBC interface arresting the penetrating moltenfly- ash front. Additionally, these TBCs were tested using a rig with thermal gradient and simultaneous accumulation of ash. Modeling using an established mechanics model has been performed to illustrate the modes of delamination, as well as further opportunities to optimize coating microstructure. Transfer of the technology was developed in this program to all interested parties.
Book Synopsis Design of Thermal Barrier Coatings by : Mohit Gupta
Download or read book Design of Thermal Barrier Coatings written by Mohit Gupta and published by Springer. This book was released on 2015-05-05 with total page 93 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book details the relationships between microstructure, interface roughness, and properties of thermal barrier coatings. The author proposes a method for the reduction of the thermal conductivity of the ceramic layer in order to increase the lifetime of thermal barrier coatings. He includes models for the optimization of ceramic layer microstructure and interface roughness.
Book Synopsis Ceramic Matrix Composites by : Narottam P. Bansal
Download or read book Ceramic Matrix Composites written by Narottam P. Bansal and published by John Wiley & Sons. This book was released on 2014-11-24 with total page 725 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book is a comprehensive source of information on various aspects of ceramic matrix composites (CMC). It covers ceramic and carbon fibers; the fiber-matrix interface; processing, properties and industrial applications of various CMC systems; architecture, mechanical behavior at room and elevated temperatures, environmental effects and protective coatings, foreign object damage, modeling, life prediction, integration and joining. Each chapter in the book is written by specialists and internationally renowned researchers in the field. This book will provide state-of-the-art information on different aspects of CMCs. The book will be directed to researchers working in industry, academia, and national laboratories with interest and professional competence on CMCs. The book will also be useful to senior year and graduate students pursuing degrees in ceramic science and engineering, materials science and engineering, aeronautical, mechanical, and civil or aerospace engineering. Presents recent advances, new approaches and discusses new issues in the field, such as foreign object damage, life predictions, multiscale modeling based on probabilistic approaches, etc. Caters to the increasing interest in the application of ceramic matrix composites (CMC) materials in areas as diverse as aerospace, transport, energy, nuclear, and environment. CMCs are considered ans enabling technology for advanced aeropropulsion, space propulsion, space power, aerospace vehicles, space structures, as well as nuclear and chemical industries. Offers detailed descriptions of ceramic and carbon fibers; fiber-matrix interface; processing, properties and industrial applications of various CMC systems; architecture, mechanical behavior at room and elevated temperatures, environmental effects and protective coatings, foreign object damage, modeling, life prediction, integration/joining.
