Thermal barrier

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A physics-based life prediction methodology for thermal barrier coating systems

A physics-based life prediction methodology for thermal barrier coating systems

• National Physical Laboratory, UK ABSTRACT A novel mechanistic approach is proposed to predict the life of thermal barrier coating (TBC) systems. The life prediction methodology is based on a criterion linked directly to the dominant failure mechanism. It relies on a statistical treatment of the TBC’s morphological characteristics, non-destructive stress measurements and on a continuum mechanics framework to quantify the stresses that promote the nucleation and growth of microcracks within the TBC. The latter accounts for the effects of TBC constituents’ elasto-visco-plastic properties, the stiffening of the ceramic due to sintering and the oxidation at the interface between the thermally insulating yttria stabilized zirconia layer and the metallic bond coat. The mechanistic approach is used to investigate the effects on TBC life of the properties and morphology of the top YSZ coating, metallic low-pressure plasma sprayed bond coat and the thermally grown oxide. Its calibration is based on TBC damage inferred from non-destructive fluorescence measurements using piezo-spectroscopy and on the numerically predicted local TBC stresses responsible for the initiation of such damage. The potential applicability of the methodology to other types of TBC coatings and thermal loading conditions is also discussed.
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Processing thermal barrier coatings via sol-gel route: crack network control and durability

Processing thermal barrier coatings via sol-gel route: crack network control and durability

formulation of the composite sol (previously described) remained un- changed: 1-propanol, acetylacetone, ultra-pure water, zirconium prop- oxide, yttrium nitrate hexahydrate. The criterion to de fine the optimal percentages for each dispersant (based on their ability to disperse), is relative to their rheological properties (Fig. 1). The chosen dispersant must have a viscosity approaching that of the C213 dispersant which is the case of all the selected dispersant (10 –25 mPa·s at 100 s − 1 ). An- other parameter to take into account is the stability of the suspension, that was evaluated from the hysteresis area between the values of viscosities taken with increasing shear rates and those taken with de- creasing shear rates (the lowest the hysteresis the highest the stability). Following this preliminary step, the chosen dispersant as a function of the viscosity criterion, was PVP 3500 M w corresponding to 1% wt because of the lack of hysteresis, which means that the composite sol is stable. The absence of hysteresis is also a signature of the lack of large aggregates that could be broken at high shear rates, thus smaller ag- gregation is expected in PVP dispersion as compared to C213 disper- sions. PVP dispersant is made up of a long carbon chain and a vinyl group on the rami fications. These groups allow a steric hindrance in the solution that causes the particles to repel each other. Note that PVP percentage is ten times lower than for the C213 (10%wt) so that the particle volume fraction is higher for PVP based material as compared to C213 ones. According to [16,17] works, the increase in particle vo- lume fraction will have a huge impact on material fracture toughness since elastic modulus and energy release for the creation of crack sur- face depend on the particle volume fraction to the fourth power. In order to evaluate such effect PVP and C213 were selected for devel- oping the thermal barrier coatings investigated in this paper.
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Thermal cycling and reactivity of a MoSi2/ZrO2 composite designed for self-healing thermal barrier coatings

Thermal cycling and reactivity of a MoSi2/ZrO2 composite designed for self-healing thermal barrier coatings

[7] Z. Derelioglu, A.L. Carabat, G.M. Song, S. van der Zwaag, W.G. Sloof, On the use of B- alloyed MoSi 2 particles as crack healing agents in yttria stabilized zirconia thermal barrier coatings, J. Eur. Ceram. Soc. 35 (16) (2015) 4507–4511. [8] D.A. Berztiss, R.R. Cerchiara, E.A. Gulbransen, F.S. Pettit, G.H. Meier, Proceedings of the First High Temperature Structural Silicides Workshop Oxidation of MoSi 2 and

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Self-healing thermal barrier coating systems fabricated by spark plasma sintering

Self-healing thermal barrier coating systems fabricated by spark plasma sintering

1. Introduction Thermal Barrier Coatings (TBCs) made of Yttria Partially Stabilized Zirconia (YPSZ), deposited by Electron Beam Physical Vapour Deposi- tion (EBPVD) or plasma-spraying techniques onto metallic superalloy turbine blades, are widely used to increase the durability of internally cooled hot-section metal components in advanced gas-turbines for air- crafts and power generation [ 1–4 ]. The role of such a ceramic coating is to act as a thermal insulator by decreasing the temperature of the un- derlying Ni-based superalloy blade material. The TBC is deposited on a bond coating that promotes and maintains the adhesion of the TBC and provides oxidation resistance to the system due to the formation of a Thermally Grown Oxide (TGO) consisting mainly of α-Al 2 O 3 . The
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Influence of embedded MoSi2 particles on the high temperature thermal conductivity of SPS produced yttria-stabilised zirconia model thermal barrier coatings

Influence of embedded MoSi2 particles on the high temperature thermal conductivity of SPS produced yttria-stabilised zirconia model thermal barrier coatings

1. Introduction Yttria-stabilised zirconia (YSZ) has one of the lowest thermal conductivity values among ceramic materials, and therefore is widely used as the base material in thermally protective coatings for gas turbine components in aircraft engines and power generators. These thermal barrier coatings (TBCs) are generally deposited onto the metallic components by atmospheric plasma spraying (APS) or electron beam physical vapour deposition (EB-PVD) methods. The coated systems experience high stresses that develop due to the mismatch of

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Self-healing thermal barrier coating systems fabricated by spark plasma sintering

Self-healing thermal barrier coating systems fabricated by spark plasma sintering

1. Introduction Thermal Barrier Coatings (TBCs) made of Yttria Partially Stabilized Zirconia (YPSZ), deposited by Electron Beam Physical Vapour Deposi- tion (EBPVD) or plasma-spraying techniques onto metallic superalloy turbine blades, are widely used to increase the durability of internally cooled hot-section metal components in advanced gas-turbines for air- crafts and power generation [ 1–4 ]. The role of such a ceramic coating is to act as a thermal insulator by decreasing the temperature of the un- derlying Ni-based superalloy blade material. The TBC is deposited on a bond coating that promotes and maintains the adhesion of the TBC and provides oxidation resistance to the system due to the formation of a Thermally Grown Oxide (TGO) consisting mainly of α-Al 2 O 3 . The
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Processing thermal barrier coatings via sol-gel route: crack network control and durability

Processing thermal barrier coatings via sol-gel route: crack network control and durability

A B S T R A C T Thermal barrier coatings (TBC) processed by sol –gel route are deposited onto NiPtAl bond coated superalloy substrates. A crack microstructure, if well controlled, is adequate to get satisfactory thermo-mechanical beha- viour when the TBC is cyclically oxidized. This paper deals with the adjustment of the properties of the micro- cracked network which is inherent to the process by changing the formulation of the sol and by adding a reinforcement step. The objective is to reduce the size and depth of the surface cracks network. This network controls the release of thermo-mechanical stress in the layers and reduces detrimental propagation of cracks that could result in the spallation of the coatings during engine operation. Several physico-chemical characterizations were performed, associated to image analyses to (i) evaluate the cracks distribution (depth, length and width), in
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Characterisation of thermal barrier sensor coatings synthesised by sol–gel route

Characterisation of thermal barrier sensor coatings synthesised by sol–gel route

E-mail address: lisa.pin@mines-albi.fr (L. Pin). on the coated surface and at the substrate interface to safely achieve efficiency increases. Conventional temperature measure- ment methods, such as pyrometry or thermocouples, have intrinsic disadvantages when employed to measure coating temperatures. Changes in emissivity of the coating, reflections from the combus- tion environment and glowing particles in the gas flow all cause errors in pyrometer measurements. Thermocouples and fibre optic sensors have limited applicability due to their intrusive nature, par- ticularly for rotating components. Thermal barrier sensor coatings (TBsCs) have been conceived to overcome these disadvantages [5] . These coatings integrate optically active material into the TBC to perform phosphor thermometry using a functional TBC, allowing remote temperature measurements inside the coating. Further- more the sensor layer can be placed at different positions through the thickness of the coating enabling temperature and heat flux measurements in the coatings [6,7] .
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Reinforced sol–gel thermal barrier coatings and their cyclic oxidation life

Reinforced sol–gel thermal barrier coatings and their cyclic oxidation life

Keywords: Sol–gel; Oxidation; Reinforcement; Thermal barrier coating 1. Introduction Improving turbojet engine performances requires to con- tinuously increase the turbine inlet temperature. Nickel base superalloys, main materials used for the application, show supe- rior creep and fatigue strength. However, superalloy turbine blades cannot sustain the high temperature imposed to modern engines without thermal protection and internal cooling. Ther- mal barrier coatings (TBCs) are deposited on hollow turbine blades in order to establish a thermal gradient prone to protect against the detrimental effects of long-term high temperature exposure. Thicker TBCs are also beneficially used to coat and thermally insulate the internal parts of the combustion chambers. Currently, TBCs – consisted of yttria-stabilised- zirconia (YSZ) – are manufactured using the so-called Electron Beam – Physical Vapour Deposition (EB-PVD), typically for turbine blades, or Plasma Spraying (PS), for combustion chambers. The thermal and mechanical properties of TBCs strongly depend on their
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Thermal Spray Coatings Engineered from Nanostructured Ceramic Agglomerated Powders for Structural, Thermal Barrier and Biomedical Applications

Thermal Spray Coatings Engineered from Nanostructured Ceramic Agglomerated Powders for Structural, Thermal Barrier and Biomedical Applications

https://doi.org/10.1007/s11666-006-9010-7 Access and use of this website and the material on it are subject to the Terms and Conditions set forth at Thermal Spray Coatings Engineered from Nanostructured Ceramic Agglomerated Powders for Structural, Thermal Barrier and Biomedical Applications

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Optimized sol–gel thermal barrier coatings for long-term cyclic oxidation life

Optimized sol–gel thermal barrier coatings for long-term cyclic oxidation life

b Université de Toulouse, UPS-INP-CNRS, Institut Carnot CIRIMAT, 118 Route de Narbonne, 31062 Toulouse Cedex 09, France Abstract New promising thermal barrier coatings (TBCs) processed by the sol–gel route are deposited onto NiPtAl bond coated superalloy substrates using the dip and/or spray coating technique. In this study, the optimization of the process, including an appropriate heat treatment prone to densify the yttria-stabilized-zirconia (YSZ) top-coat and leading to the sintering and the development of a resulting crack network, is investigated. In particular, relevant information on internal strain evolution during the heat treatment are obtained using in situ synchrotron X-rays diffraction and confirm a stabilization of the TBC through the occurrence of the micro-cracks that beneficially releases the in-plane sintering stress. Such TBCs are subsequently reinforced using additional material brought within the cracks using sol–gel spray coating. The effect of various process parameters, such as the pre-oxidation of the bond-coat, on the sol gel TBCs consolidation and their cyclic oxidation resistance enhancement, is presented. Reinforced sol–gel TBCs are successfully oxidized up to more than one thousand 1 h-cycles at 1100 ◦ C, without any detrimental spallation.
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Residual Stress Analysis of Laser-Drilled Thermal Barrier Coatings Involving Various Bond Coats

Residual Stress Analysis of Laser-Drilled Thermal Barrier Coatings Involving Various Bond Coats

The gas turbine combustion chamber of aero-engines requires a thermal barrier coating (TBC) by thermal spraying. Further heat protection is achieved by laser drilling of cooling holes. The residual stresses play an important role in the mechanical behaviour of TBC. It could also affect the TBC response to delamination during laser drilling. In this work, studies of the cracking behaviour after laser drilling and residual stress distribution have been achieved for different bond coats by plasma spray or cold spray. From interface crack length measured pulse-by-pulse after laser percussion drilling at 20! angle, the role of the various bond coats on crack initiation and propagation are investigated. It is shown that the bond coat drastically influences the cracking behaviour. The residual stresses profiles were also determined by the incremental hole-drilling method involving speckle interferometry. An original method was also developed to measure the residual stress profiles around a pre-drilled zone with a laser beam at 90!. The results are discussed to highlight the influence of TBCs interfaces on the resulting residual stresses distribution before laser drilling, and also to investigate the modification around the hole after laser drilling. It is shown that laser drilling could affect the residual stress state.
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Hot corrosion of lanthanum zirconate and partially stabilized zirconia thermal barrier coatings

Hot corrosion of lanthanum zirconate and partially stabilized zirconia thermal barrier coatings

The requirement for increased insulation to protect components from hotter combustion gases will necessitate a change in the TBC system to achieve a higher temperature drop across the coat- ing. Thicker ceramic coatings are one possible approach to im- proving the insulating value of the TBC 关3,4兴. However, produc- ing thicker coatings presents challenges, particularly when deposited using plasma spraying, because of the build up of stresses that can cause the coating to spall. There are also con- cerns associated with the increased weight of thicker coatings and the possibility of creep at higher temperatures when the coatings are being employed on rotating components. And even if thicker coatings can be produced and employed on rotating components, there is a question concerning the ability of the most widely used top coat composition, 8 wt. % Y 2 O 3 – ZrO 2 , to resist sintering at the higher temperatures to which it will be exposed. Sintering and densification can degrade the coating 关5兴 and raise the thermal conductivity, making it a less effective thermal barrier.
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Optimizing Compliance and Thermal Conductivity of Plasma Sprayed Thermal Barrier Coatings via Controlled Powders and Processing Strategies

Optimizing Compliance and Thermal Conductivity of Plasma Sprayed Thermal Barrier Coatings via Controlled Powders and Processing Strategies

Yang Tan, Vasudevan Srinivasan, Toshio Nakamura, Sanjay Sampath, Pierre Bertrand, and Ghislaine Bertrand The properties and performance of plasma-sprayed thermal barrier coatings (TBCs) are strongly dependent on the microstructural defects, which are affected by starting powder morphology and pro- cessing conditions. Of particular interest is the use of hollow powders which not only allow for efficient melting of zirconia ceramics but also produce lower conductivity and more compliant coatings. Typical industrial hollow spray powders have an assortment of densities resulting in masking potential advan- tages of the hollow morphology. In this study, we have conducted process mapping strategies using a novel uniform shell thickness hollow powder to control the defect microstructure and properties. Cor- relations among coating properties, microstructure, and processing reveal feasibility to produce highly compliant and low conductivity TBC through a combination of optimized feedstock and processing conditions. The results are presented through the framework of process maps establishing correlations among process, microstructure, and properties and providing opportunities for optimization of TBCs.
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Reinforced sol-gel thermal barrier coatings and their cyclic oxidation life

Reinforced sol-gel thermal barrier coatings and their cyclic oxidation life

Keywords: Sol– gel; Oxidation; Reinforcement; Thermal barrier coating 1. Introduction Improving turbojet engine performances requires to con- tinuously increase the turbine inlet temperature. Nickel base superalloys, main materials used for the application, show supe- rior creep and fatigue strength. However, superalloy turbine blades cannot sustain the high temperature imposed to modern engines without thermal protection and internal cooling. Ther- mal barrier coatings (TBCs) are deposited on hollow turbine blades in order to establish a thermal gradient prone to protect against the detrimental effects of long-term high temperature exposure. Thicker TBCs are also beneficially used to coat and thermally insulate the internal parts of the combustion chambers. Currently, TBCs – consisted of yttria-stabilised- zirconia (YSZ) – are manufactured using the so-called Electron Beam – Physical Vapour Deposition (EB-PVD), typically for turbine blades, or Plasma Spraying (PS), for combustion chambers. The thermal and mechanical properties of TBCs strongly depend on their
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Outstanding durability of sol-gel thermal barrier coatings reinforced by YSZ-fibers

Outstanding durability of sol-gel thermal barrier coatings reinforced by YSZ-fibers

In order to identify the system with the optimum composition, the mass loss was compared to the surface spalling. Both spalling mea surements must be analyzed in order to conclude on a system. When the mass of the sample is measured, the obtained value takes into account the delamination of the thermal barrier, but also the mass gain due to oxidation. The mass change due to the formation and spalling of the oxide scale on the metallic substrate could cause variations in the ob tained mass values up to nearly 10% of the total mass variation. Furthermore, both faces of the substrate have not been treated in the same way, thus causing preferential delamination of the thermal barrier on the rear face of the substrate rather than that located on the front face. Moreover, a small part of the substrate, a metallic rod used to hold the sample, although cut at the edge of the substrate before cyclic oxidation, is responsible of a loss of mass that can reach 30% of the total mass variation. Thus, it is not uncommon for the percentage of mass loss to fall sharply as the ceramic coating on the rear face has under gone a complete delamination causing a sudden decrease in the value of the total mass. Moreover, it is not uncommon to obtain a coating with a greater thickness at the edges of the substrate. Because of this accu mulation of material, the thermal barrier is preferentially delaminated at the edges. It is therefore very di fficult to conclude on the analysis of mass loss alone. As for mass loss, the analysis of the percentage of surface spalling cannot conclude with certainty the suitability of a system. Indeed, this analysis is done from photographs taken at regular intervals of the samples. This method is less sensitive than a weighing (sensitivity about 10 μg for the mass versus 0.1 mm² for the surface). It is therefore interesting to combine the two analyzes in order to con clude on a system.
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Characterisation of thermal barrier sensor coatings synthesised by sol–gel route

Characterisation of thermal barrier sensor coatings synthesised by sol–gel route

on the coated surface and at the substrate interface to safely achieve efficiency increases. Conventional temperature measure- ment methods, such as pyrometry or thermocouples, have intrinsic disadvantages when employed to measure coating temperatures. Changes in emissivity of the coating, reflections from the combus- tion environment and glowing particles in the gas flow all cause errors in pyrometer measurements. Thermocouples and fibre optic sensors have limited applicability due to their intrusive nature, par- ticularly for rotating components. Thermal barrier sensor coatings (TBsCs) have been conceived to overcome these disadvantages [5]. These coatings integrate optically active material into the TBC to perform phosphor thermometry using a functional TBC, allowing remote temperature measurements inside the coating. Further- more the sensor layer can be placed at different positions through the thickness of the coating enabling temperature and heat flux measurements in the coatings [6,7].
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Sol–gel processing and characterization of (RE-Y)-zirconia powders for thermal barrier coatings

Sol–gel processing and characterization of (RE-Y)-zirconia powders for thermal barrier coatings

process for thermal barrier applications. For each compound, structural and microstructural analyses were performed. LZ powders moves from a pure tetragonal structure for a low doping concentra- tion, to a pure pyrochlore phase for 30 LZ. Samarium and erbium doped zirconia powders crystallise mainly in the cubic form. The microscopic study suggests quite a similar behaviour between these rare earth doping elements. For each of them, the microstructure moves from compact monoliths (20 μm–50 μm) with heterogeneous size to agglomerates of thinner particles for an average doping amount of 20 mol%. This new structure can explain the higher specific surface areas of the compounds when increasing the doping content. The ceramics (heat treated at 950 °C) with a doping amount of 9.7 and 30 mol% were hot-pressed using the Spark Plasma Sintering method Table 4
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Optimizing Compliance and Thermal Conductivity of Plasma Sprayed Thermal Barrier Coatings via Controlled Powders and Processing Strategies

Optimizing Compliance and Thermal Conductivity of Plasma Sprayed Thermal Barrier Coatings via Controlled Powders and Processing Strategies

Yang Tan, Vasudevan Srinivasan, Toshio Nakamura, Sanjay Sampath, Pierre Bertrand, and Ghislaine Bertrand The properties and performance of plasma-sprayed thermal barrier coatings (TBCs) are strongly dependent on the microstructural defects, which are affected by starting powder morphology and pro- cessing conditions. Of particular interest is the use of hollow powders which not only allow for efficient melting of zirconia ceramics but also produce lower conductivity and more compliant coatings. Typical industrial hollow spray powders have an assortment of densities resulting in masking potential advan- tages of the hollow morphology. In this study, we have conducted process mapping strategies using a novel uniform shell thickness hollow powder to control the defect microstructure and properties. Cor- relations among coating properties, microstructure, and processing reveal feasibility to produce highly compliant and low conductivity TBC through a combination of optimized feedstock and processing conditions. The results are presented through the framework of process maps establishing correlations among process, microstructure, and properties and providing opportunities for optimization of TBCs.
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Mechanical and thermo-physical properties of plasma-sprayed thermal barrier coatings: a literature survey

Mechanical and thermo-physical properties of plasma-sprayed thermal barrier coatings: a literature survey

Philippe Lours 2 • Vincent Proton 3 • Fabrice Crabos 3 • Julitte Huez 1 • Bernard Viguier 1 Abstract Atmospheric plasma-sprayed thermal barrier coatings (APS TBCs) have been studied from an extensive review of the dedicated literature. A large number of data have been collected and compared, versus deposition parameters and/or measurement methods, and a comparison was made between two different microstructures: standard APS coatings and segmented coatings. Discussion is focused on the large scattering of results reported in the literature even for a given fabrication procedure. This scattering strongly depends on the methods of mea- surement as expected, but also—for a given method—on the specific conditions implemented for the considered experimental investigation. Despite the important scattering, general trends for the correlation of properties to microstructure and process parameters can be derived. The failure modes of TBC systems were approached through the evolution of cracking and spalling at various life fractions. Keywords Air plasma sprayed (APS)  Thermal barrier coatings (TBC) 
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