Search NASA⌕ Search

SEARCH · Search NASA

Results for “barrier coating”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Combined Mode I and Mode II Fracture of Plasma-Sprayed Thermal Barrier Coatings at Ambient and Elevated Temperatures

The mode I, mode II, and combined mode I-mode II fracture behavior of ZrO2- 8wt%Y2O3 thermal barrier coatings was determined in asymmetric flexure loading at both ambient and elevated temperatures. Precracks were introduced in test specimens using the single-edge-v-notched beam (SEVNB) method incorporated with final diamond polishing to achieve sharp crack tips. A fracture envelope of KI versus KII was determined for the coating material at ambient and elevated temperatures. Propagation angles of fracture as a function of K(sub I)/K(sub II) were also determined. The mixed-mode fracture behaviors of the coating material were compared with those of monolithic advanced ceramics determined previously. The mixed-mode fracture behavior of the plasma-sprayed thermal barrier coating material was predicted in terms of fracture envelope and propagation angle using mixed-mode fracture theories.

Choi, Sung R.↗
NASA NTRS1983

Development of strain tolerant thermal barrier coating systems, tasks 1 - 3

Insulating ceramic thermal barrier coatings can reduce gas turbine airfoil metal temperatures as much as 170 C (about 300 F), providing fuel efficiency improvements greater than one percent and durability improvements of 2 to 3X. The objective was to increase the spalling resistance of zirconia based ceramic turbine coatings. To accomplish this, two baseline and 30 candidate duplex (layered MCrAlY/zirconia based ceramic) coatings were iteratively evaluated microstructurally and in four series of laboratory burner rig tests. This led to the selection of two candidate optimized 0.25 mm (0.010 inch) thick plasma sprayed partially stabilized zirconia ceramics containing six weight percent yttria and applied with two different sets of process parameters over a 0.13 mm (0.005 inch) thick low pressure chamber sprayed MCrAlY bond coat. Both of these coatings demonstrated at least 3X laboratory cyclic spalling life improvement over the baseline systems, as well as cyclic oxidation life equivalent to 15,000 commercial engine flight hours.

Anderson, N. P.↗
NASA NTRS1986

Degradation mechanisms in thermal-barrier coatings

The degradation mechanism in a thermal barrier-coating system subjected to prolonged heating in air as well as to thermal cycling was studied. Bond-coat oxidation was found to be the most important reason for degradation. The oxidation produced NiO as well as Al2O3 in one set of samples, but the variation in initial coating structure made it difficult to resolve systematic differences between isothermally heated and thermally cycled samples. However, the contribution to degradation from changes in substrate composition seemed less in the cycled sample.

Shinde, S. L.↗
NASA NTRS1995

Thermal barrier coating experience in the gas turbine engine

Thermal Barrier Coatings (TBC), provide thermal insulation and oxidation resistance in an environment consisting of hot combustion gases. TBC's consist of a two layer system. The outer ceramic layer provides good thermal insulation due to the low thermal conductivity of the ceramic coatings used, while the inner metallic bond coat layer provides needed oxidation resistance to the underlying superalloy. Pratt & Whitney has over a decade of experience with several generations of TBC systems on turbine airfoils. This paper will focus on the latest TBC field experience along with a proposed durability model.

Bose, S.↗
NASA NTRS2004

Optical Diagnostics for Thermal Barrier Coatings

The translucent nature of ceramic oxide thermal barrier coatings (TBCs) provides an opportunity to employ optical probes to monitor temperature gradients and buried damage propagation within the coating. An important advantage of noncontact optical diagnostics is that they are amendable to health monitoring of TBCs in service. In this paper, two optical diagnostic approaches, operating in different wavelength regimes, are discussed. The first approach is the use of mid-infrared reflectance (MIR) to monitor the progression of TBC delamination produced by thermal cycling. This approach takes advantage of the maximum transparency of the TBCs at mid-infrared wavelengths, in particular, between 3 and 5 microns. Recent progress in extending the MIR method to a more practical visual inspection tool will be presented. A second approach, using visible wavelengths, is the embedding of thermographic phosphors within the TBC to add sensing functions to the coating that can provide depth-selective information about temperature gradients and TBC integrity. Emphasis will be given to the use of fluorescence decay time measurements to provide temperature readings from a thermographic phosphor layer residing beneath the TBC.

Eldridge, J. I.↗
NASA NTRS2004

Current Issues with Environmental Barrier Coatings for Ceramics and Ceramic Composites

The environmental barrier coating (EBC) for SiC/SiC ceramic matrix composites and Si3N4 ceramics is an emerging field as the application of silicon-based ceramics in the gas turbine engine hot section is on the horizon, both for aero and industrial gas turbines. EBC is an enabling technology for silicon-based ceramics because these materials without an EBC cannot be used in combustion environments due to rapid surface recession. Significant progress in EBC development has been made during the last decade through various government-sponsored programs. Current EBCs are based on silicon, mullite (3Al2O3-2SiO2) and BSAS (barium strontium aluminum silicate with celsian structure). Volatility of BSAS, BSAS-silica chemical reaction, and low melting point of silicon limit temperature capability of current EBCs to about 1350 C for long-term applications. There is a need for higher temperature EBCs as the temperature capability of silicon-based ceramics continue to increase. Therefore, research is underway to develop EBCs with improved temperature capability compared to current EBCs. The current status and issues with the advanced EBC development efforts will be discussed.

Lee, Kang N.↗
NASA NTRS2008

Failure Mechanisms and Life Prediction of Thermal and Environmental Barrier Coatings under Thermal Gradients

Ceramic thermal and environmental barrier coatings (TEBCs) will play an increasingly important role in gas turbine engines because of their ability to further raise engine temperatures. However, the issue of coating durability is of major concern under high-heat-flux conditions. In particular, the accelerated coating delamination crack growth under the engine high heat-flux conditions is not well understood. In this paper, a laser heat flux technique is used to investigate the coating delamination crack propagation under realistic temperature-stress gradients and thermal cyclic conditions. The coating delamination mechanisms are investigated under various thermal loading conditions, and are correlated with coating dynamic fatigue, sintering and interfacial adhesion test results. A coating life prediction framework may be realized by examining the crack initiation and propagation driving forces for coating failure under high-heat-flux test conditions.

Zju, Dongming↗
NASA NTRS2008

The Lattice and Thermal Radiation Conductivity of Thermal Barrier Coatings

The lattice and radiation conductivity of thermal barrier coatings was evaluated using a laser heat flux approach. A diffusion model has been established to correlate the apparent thermal conductivity of the coating to the lattice and radiation conductivity. The radiation conductivity component can be expressed as a function of temperature and the scattering and absorption properties of the coating material. High temperature scattering and absorption of the coating systems can also be derived based on the testing results using the modeling approach. The model prediction is found to have good agreement with experimental observations.

Zhu, Dongming↗
DOE OSTI2020

Advanced high temperature environmental barrier coating for SiC/SiC ceramic matrix composites

Advanced environmental barrier coating bond coat systems with higher temperature capabilities and environmental resistance are disclosed. These bond coat systems can be applied to ceramic substrates such as SiC/SiC ceramic matrix composite substrates, and can provide protection from extreme temperature, mechanical loading and environmental conditions, such as in high temperature gas turbines. Example bond coat systems can include either an advanced silicon/silicide component, an oxide/silicate component, or a combination thereof.

36 MATERIALS SCIENCE↗
NASA NTRS2024

Theoretical Prediction of Thermal Expansion Anisotropy for Y 2 Si 2 O 7 Environmental Barrier Coatings Using a Deep Neural Network Potential and Comparison to Experiment

Environmental barrier coatings (EBCs) are an enabling technology for silicon carbide (SiC)-based ceramic matrix composites (CMCs) in extreme environments such as gas turbine engines. However, development of new coating systems is hindered by the large design space and difficulty in predicting properties for these materials. Density Functional Theory (DFT) has successfully been used to model and predict some thermodynamic and thermo-mechanical properties of high-temperature ceramics for EBCs, although these calculations are challenging due to their high computational costs. In this work, we use machine learning to train a deep neural network potential (DNP) for Y 2 Si 2 O 7 , which is then applied to calculate thermodynamic and thermo-mechanical properties at near-DFT accuracy much faster and using less computational resources than DFT. We use this DNP to predict phonon-based thermodynamic properties of Y 2 Si 2 O 7 with good agreement to DFT and experiments. We also utilize the DNP to calculate the anisotropic, lattice direction-dependent coefficients of thermal expansion (CTEs) for Y 2 Si 2 O 7 . Molecular dynamics trajectories using the DNP correctly demonstrate accurate prediction of the anisotropy of the CTE in good agreement with diffraction experiments. In the future, this DNP could be applied to accelerate additional property calculations for Y 2 Si 2 O 7 compared to DFT or experiments.

rare earth silicates↗
DOE OSTI2024

Theoretical Prediction of Thermal Expansion Anisotropy for Y 2 Si 2 O 7 Environmental Barrier Coatings Using a Deep Neural Network Potential and Comparison to Experiment

Environmental barrier coatings (EBCs) are an enabling technology for silicon carbide (SiC)-based ceramic matrix composites (CMCs) in extreme environments such as gas turbine engines. However, the development of new coating systems is hindered by the large design space and difficulty in predicting the properties for these materials. Density Functional Theory (DFT) has successfully been used to model and predict some thermodynamic and thermo-mechanical properties of high-temperature ceramics for EBCs, although these calculations are challenging due to their high computational costs. In this work, we use machine learning to train a deep neural network potential (DNP) for Y 2 Si 2 O 7 , which is then applied to calculate the thermodynamic and thermo-mechanical properties at near-DFT accuracy much faster and using less computational resources than DFT. We use this DNP to predict the phonon-based thermodynamic properties of Y 2 Si 2 O 7 with good agreement to DFT and experiments. We also utilize the DNP to calculate the anisotropic, lattice direction-dependent coefficients of thermal expansion (CTEs) for Y 2 Si 2 O 7 . Molecular dynamics trajectories using the DNP correctly demonstrate the accurate prediction of the anisotropy of the CTE in good agreement with the diffraction experiments. In the future, this DNP could be applied to accelerate additional property calculations for Y 2 Si 2 O 7 compared to DFT or experiments.

36 MATERIALS SCIENCE↗
NASA NTRS1982

Further industrial tests of ceramic thermal barrier coatings

The NASA Lewis Research Center made technical assistance arrangements (contracts) with several commercial organizations under which Lewis designed plasma-sprayed thermal-barrier coatings (TBC) for their products. Lewis was then furnished with the test conditions and evaluations of coating usefulness. The coating systems were developed and sprayed at Lewis. All of the systems incorporated a two-layer, ceramic-bond coating concept. Coating thickness and chemical composition were varied to fit three applications: the leading edges of first-stage turbine vanes for an advanced gas turbine engine; the flame impingement surfaces of a combustor transition section; and diesel engine valves and head surfaces. The TBC incorporated yytria-stabilized zirconia, which lowered metal temperatures, protected metal parts, and increased metal part life. In some cases metal burning, melting, and warping were eliminated. Additional benefits were realized from these endeavors: hands-on experience with thermal-barrier coatings was provided to industry; the success of these endeavors encourages these and other organizations to accelerate the implementation of TBC technology.

Liebert, C. H.↗
NASA NTRS1986

Thermal barrier coating life-prediction model development

The program focuses on predicting the lives of two types of strain-tolerant and oxidation-resistant thermal barrier coating (TBC) systems that are produced by commercial coating suppliers to the gas turbine industry. The plasma-sprayed TBC system, composed of a low-pressure plasma-spray (LPPS) or an argon shrouded plasma-spray (ASPS) applied oxidation resistant NiCrAlY or (CoNiCrAlY) bond coating and an air-plasma-sprayed yttria partially stabilized zirconia insulative layer, is applied by both Chromalloy, Klock, and Union Carbide. The second type of TBS is applied by the electron beam-physical vapor deposition (EB-PVD) process by Temescal. The second year of the program was focused on specimen procurement, TMC system characterization, nondestructive evaluation methods, life prediction model development, and TFE731 engine testing of thermal barrier coated blades. Materials testing is approaching completion. Thermomechanical characterization of the TBC systems, with toughness, and spalling strain tests, was completed. Thermochemical testing is approximately two-thirds complete. Preliminary materials life models for the bond coating oxidation and zirconia sintering failure modes were developed. Integration of these life models with airfoil component analysis methods is in progress. Testing of high pressure turbine blades coated with the program TBS systems is in progress in a TFE731 turbofan engine. Eddy current technology feasibility was established with respect to nondestructively measuring zirconia layer thickness of a TBC system.

Strangman, T. E.↗
NASA NTRS1984

Degradation mechanisms of ceramic thermal barrier coatings in corrosive environments

Chemical as well as thermal-mechanical interactions between the ceramics and gas turbine combustion gases/condensates are found to play critical roles in the degradation of porous plasma-sprayed ceramic thermal barrier coatings. The detailed degradation mechanisms of several state-of-the-art ceramic thermal barrier coatings, including several zirconia compositions and a calcium silicate, in corrosive environments are examined in this paper. Approaches to extend coating lifetime are also described.

Lau, S. K.↗
NASA NTRS2009

Thermal Residual Stress in Environmental Barrier Coated Silicon Nitride - Modeled

When exposed to combustion environments containing moisture both un-reinforced and fiber reinforced silicon based ceramic materials tend to undergo surface recession. To avoid surface recession environmental barrier coating systems are required. However, due to differences in the elastic and thermal properties of the substrate and the environmental barrier coating, thermal residual stresses can be generated in the coated substrate. Depending on their magnitude and nature thermal residual stresses can have significant influence on the strength and fracture behavior of coated substrates. To determine the maximum residual stresses developed during deposition of the coatings, a finite element model (FEM) was developed. Using this model, the thermal residual stresses were predicted in silicon nitride substrates coated with three environmental coating systems namely barium strontium aluminum silicate (BSAS), rare earth mono silicate (REMS) and earth mono di-silicate (REDS). A parametric study was also conducted to determine the influence of coating layer thickness and material parameters on thermal residual stress. Results indicate that z-direction stresses in all three systems are small and negligible, but maximum in-plane stresses can be significant depending on the composition of the constituent layer and the distance from the substrate. The BSAS and REDS systems show much lower thermal residual stresses than REMS system. Parametric analysis indicates that in each system, the thermal residual stresses can be decreased with decreasing the modulus and thickness of the coating.

Ali, Abdul-Aziz↗
DOE OSTI2023

Low-cost thermal/environmental barrier coatings: A first-principles study

Development of low-cost advanced thermal/environmental barrier coating (T/EBC) materials with acceptable thermal and mechanical properties is essential for safeguarding ceramic composites substrate against thermal and chemical degradation, thereby enhancing the efficiency of components in the high-temperature section of gas turbine engines. To this end, here we employed density functional theory-based approaches to predict the thermodynamic, mechanical, and thermal properties of rare earth disilicates based on abundant rare earth elements, namely La 2 Si 2 O 7 and Ce 2 Si 2 O 7 , as potential alternatives to the current-state-of-the-art ytterbium disilicate EBCs that uses expensive and scarce element Yb. The present study predicts that G-phase Ce 2 Si 2 O 7 has an ultralow thermal conductivity (0.26 W/m/K at 1500 K) and the apparent bulk coefficient of thermal expansion (ABCTE) (≈6.9x10 -6 K -1 ) slightly higher than SiC, demonstrating great potential as low-cost high-performance T/EBC. However, La 2 Si 2 O 7 and Ce 2 Si 2 O 7 undergo an A- to G-phase polymorphic transition at around 1470 K, resulting in significant changes to crystal structure and lattice parameters, and accordingly CTE and lattice thermal conductivity.

36 MATERIALS SCIENCE↗
NASA NTRSDate not supplied

The Development and Use of a Natural Gas / Oxygen Burner Rig for Environmental Barrier Coating and Ceramic Matrix Composite Technology Maturation

This work outlines the development of a new natural gas/oxygen (NG/O2) fueled combustion rig located at the NASA Glenn Research Center for high-temperature environmental durability studies of advanced materials and components at atmospheric pressure. The NG/O2 burner rig can simulate the high-temperature, high-heat flux, and high-velocity thermal environments encountered in gas turbine engines. It also provides the capability to study environmental effects such as water vapor and other foreign contaminants relevant to these applications. The rig is anticipated to bridge the gap between other laboratory methods such as furnaces, jet-fueled burner rigs, high-heat flux lasers, and more expensive engine rig testing. The NG/O2 rig is expected to have maximum sample temperature capabilities over 3,000°F (1,649°C) and result in higher water vapor content compared to our Mach 0.3 to Mach 1.0 jet-A burner rigs which is important for characterizing current and next-generation environmental barrier coatings. This paper will provide an overview of the development of the NG/O2 burner rig, initial characterization, and current research and development efforts on environmental barrier coated ceramic matrix composites.

Burner rig↗
NASA NTRS2023

The Development and Use of a Natural Gas / Oxygen Burner Rig for Environmental Barrier Coating and Ceramic Matrix Composite Technology Maturation

This work outlines the development of a new natural gas/oxygen (NG/O 2 ) fueled combustion rig located at the NASA Glenn Research Center for high-temperature environmental durability studies of advanced materials and components at atmospheric pressure. The NG/O 2 burner rig can simulate the high-temperature, high-heat flux, and high-velocity thermal environments encountered in gas turbine engines. It also provides the capability to study environmental effects such as water vapor and other foreign contaminants relevant to these applications. The rig is anticipated to bridge the gap between other laboratory methods such as furnaces, jet-fueled burner rigs, high-heat flux lasers, and more expensive engine rig testing. The NG/O 2 rig is expected to have maximum sample temperature capabilities over 3,000°F (1,649°C) and result in higher water vapor content compared to our Mach 0.3 to Mach 1.0 jet-A burner rigs which is important for characterizing current and next-generation environmental barrier coatings. This paper will provide an overview of the development of the NG/O 2 burner rig, initial characterization, and current research and development efforts on environmental barrier coated ceramic matrix composites.

Burner rig↗