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David R. Clarke - One of the best experts on this subject based on the ideXlab platform.

  • Enhanced zirconia Thermal Barrier Coating systems
    Proceedings of the Institution of Mechanical Engineers Part A: Journal of Power and Energy, 2006
    Co-Authors: David R. Clarke, Carlos G Levi, A G Evans
    Abstract:

    The results of a research programme sponsored by the Department of Energy and directed at establishing some of the scientific issues underpinning the development of enhanced zirconia Thermal Barrier Coatings (TBCs) are reviewed. Our studies have established the stability ranges for both yttria stabilized and codoped zirconia Coating materials and identified the mechanisms responsible for failure of current Coating systems. These reveal that it is likely that present EB-PVD Coatings systems are limited by the performance of current bond-coats and their oxidation behaviour, especially under Thermal cycle conditions, rather than the zirconia Coating material itself These studies provide the scientific framework for the development of enhanced zirconia-based Thermal Barrier Coating systems for advanced industrial gas turbine engine applications.

  • Spalling failure of a Thermal Barrier Coating associated with aluminum depletion in the bond-coat
    Acta Materialia, 1999
    Co-Authors: E. A.g. Shillington, David R. Clarke
    Abstract:

    A plasma-sprayed Thermal Barrier Coating is observed to spall after oxidation at 1121 °C from a CoNiCrAlY bond-coated superalloy at the interface between the Thermally grown oxide (TGO) and the zirconia Thermal Barrier Coating (TBC). Phase characterization by photostimulated luminescence and X-ray diffraction, as well as microstructural characterization by scanning electron microscopy, indicates that the spalling is associated with the conversion of the initially formed α-alumina Thermally grown oxide to α-chromia and a (CoNi)(CrAl) spinel. It is proposed that the phase conversion occurs after the alumina TGO has cracked on Thermal cycling and the underlying bond-coat alloy is depleted of aluminum with concurrent enrichment of the oxide by Cr, Co and Ni. The observations suggest that monitoring the luminescence intensity as a function of oxidation time might form the basis of a nondestructive tool for detecting the onset of failure based on the disappearance of α-alumina.

  • observation of subcritical spall propagation of a Thermal Barrier Coating
    Journal of the American Ceramic Society, 1998
    Co-Authors: Valter Sergo, David R. Clarke
    Abstract:

    Observations are reported of the room-temperature propagation of a spalling failure mode of a Thermal Barrier Coating (TBC) from its bond coat after oxidation. The Coating is a Y2O3-stabilized ZrO2 Coating formed by electron-beam deposition on a Ni-Co-Cr-Al-Y bond coat. The spall shape evolution and stress redistribution as the spall propagates are reported. The failure propagates primarily as an interface crack between the bond coat and the Thermally grown aluminum oxide (TGO) formed on the underside of the TBC during oxidation. The observations are consistent with subcritical propagation of an interface crack between the TGO and bond coat assisted by the presence of moisture. An estimate of 9 J/m2 is made of the fracture resistance in air of the interface.

  • Observation of subcritical spall propagation of a Thermal Barrier Coating
    Journal of the American Ceramic Society, 1998
    Co-Authors: Valter Sergo, David R. Clarke
    Abstract:

    Observations are reported of the room-temperature propagation of a spalling failure mode of a Thermal Barrier Coating (TBC) from its bond coat after oxidation. The Coating is a Y2O3-stabilized ZrO2 Coating formed by electron-beam deposition on a Ni-Co-Cr-Al-Y bond coat. The spall shape evolution and stress redistribution as the spall propagates are reported. The failure propagates primarily as an interface crack between the bond coat and the Thermally grown aluminum oxide (TGO) formed on the underside of the TBC during oxidation. The observations are consistent with subcritical propagation of an interface crack between the TGO and bond coat assisted by the presence of moisture. An estimate of 9 J/m2 is made of the fracture resistance in air of the interface. Reprinted by permission of the American Ceramic Society.

Huibin Xu - One of the best experts on this subject based on the ideXlab platform.

  • lanthanum titanium aluminum oxide a novel Thermal Barrier Coating material for applications at 1300 c
    Journal of The European Ceramic Society, 2011
    Co-Authors: Shengkai Gong, Huibin Xu
    Abstract:

    Abstract Considerable efforts are being invested to explore new Thermal Barrier Coating (TBC) materials with higher temperature capability to meet the demand of advanced turbine engines. In this work, LaTi2Al9O19 (LTA) is proposed and investigated as a novel TBC material for application at 1300 °C. LTA showed excellent phase stability up to 1600 °C. The Thermal conductivities for LTA Coating are in a range of 1.0–1.3 W m−1 K−1 (300–1500 °C) and the values of Thermal expansion coefficients increase from 8.0 to 11.2 × 10−6 K−1 (200–1400 °C), which are comparable to those of yttria stabilized zirconia (YSZ). The microhardness of LTA and YSZ Coatings were in the similar level of ∼7 GPa, however, the fracture toughness value was relatively lower than that of YSZ. The lower fracture toughness was compensated by the double-ceramic LTA/YSZ layer design, and the LTA/YSZ TBC exhibited desirable Thermal cycling life of nearly 700 h at 1300 °C.

  • the Thermal cycling behavior of lanthanum cerium oxide Thermal Barrier Coating prepared by eb pvd
    Surface & Coatings Technology, 2006
    Co-Authors: Shengkai Gong, Huibin Xu
    Abstract:

    Abstract Bulk material and Coatings of Lanthanum–Cerium Oxide (La2Ce2O7) with a fluorite structure were studied as a candidate material for Thermal Barrier Coating (TBC). It has been showed that such material has the properties of low Thermal conductivity about four times lower than YSZ, the difference in the Thermal expansion coefficient between La2Ce2O7 and bond coat is smaller than that of YSZ in TBC systems, high phase stability between room temperature and 1673 K, about 300 K higher than that of the YSZ. The Coating prepared by electron beam physical vapor deposition (EB–PVD) showed that it has good Thermal cycling behavior, implying that such material can be a promising Thermal Barrier Coating material. The deviation of Coating composition from ingot can be overcome by the addition of excess La2O3 during ingot preparation and/or by adjusting the process parameters.

  • The Thermal cycling behavior of Lanthanum-Cerium Oxide Thermal Barrier Coating prepared by EB-PVD
    Surface and Coatings Technology, 2006
    Co-Authors: Wen Ma, Huibin Xu, Shengkai Gong, Xueqiang Cao
    Abstract:

    Bulk material and Coatings of Lanthanum-Cerium Oxide (La2Ce2O7) with a fluorite structure were studied as a candidate material for Thermal Barrier Coating (TBC). It has been showed that such material has the properties of low Thermal conductivity about four times lower than YSZ, the difference in the Thermal expansion coefficient between La2Ce2O7and bond coat is smaller than that of YSZ in TBC systems, high phase stability between room temperature and 1673 K, about 300 K higher than that of the YSZ. The Coating prepared by electron beam physical vapor deposition (EB-PVD) showed that it has good Thermal cycling behavior, implying that such material can be a promising Thermal Barrier Coating material. The deviation of Coating composition from ingot can be overcome by the addition of excess La2O3during ingot preparation and/or by adjusting the process parameters. © 2005 Elsevier B.V. All rights reserved.

P. C. Patnaik - One of the best experts on this subject based on the ideXlab platform.

  • Pre-oxidation and TGO growth behaviour of an air-plasma-sprayed Thermal Barrier Coating
    Surface and Coatings Technology, 2008
    Co-Authors: Weijie R. Chen, R S Lima, Basil R. Marple, X. Wu, P. C. Patnaik
    Abstract:

    In Thermal Barrier Coating (TBC) systems, spinel and nickel oxide formed in an oxidizing environment are believed to be detrimental to TBC durability during service at high temperatures. The present study shows that in an air-plasma-sprayed (APS) TBC with Co-32Ni-21Cr-8Al-0.5Y (wt.%) bond coat, pre-oxidation treatments in low-pressure oxygen environments can suppress the formation of the detrimental oxides by promoting the formation of an Al2O3layer at the ceramic topcoat/bond coat interface. The development of the Thermally grown oxide (TGO) layer generally exhibits a three-stage growth phenomenon that resembles high temperature creep. The pre-oxidation treatments reduce the growth rate and extend the steady-state growth stage, leading to an improved durability. Crack propagation in the TBC proceeds via opening and growth of pre-existing discontinuities in the ceramic topcoat, assisted by crack nucleation and growth associated with the TGO. Crack propagation during Thermal cycling appeared to be controlled by TGO growth, and the maximum crack length and TGO thickness generally have a power law relationship. Crown Copyright © 2008.

  • The growth and influence of Thermally grown oxide in a Thermal Barrier Coating
    Surface and Coatings Technology, 2006
    Co-Authors: Weijie R. Chen, Basil R. Marple, X. Wu, P. C. Patnaik
    Abstract:

    The growth of a Thermally grown oxide (TGO) layer and its influence on cracking was studied in an air-plasma sprayed (APS) Thermal Barrier Coating (TBC) following Thermal cycling. The TGO that formed upon Thermal exposure in air was comprised predominantly of layered chromia and spinels, as well as some oxide clusters of chromia, spinel and nickel oxide. The increase in thickness of the TGO exhibited a three-stage growth phenomenon. Cracks formed mostly at oxide clusters as well as at the opening of discontinuities. Crack propagation during cyclic oxidation appeared to be related to TGO growth, with a nearly linear relationship between crack length and TGO thickness. Crown Copyright © 2006.

  • oxidation and crack nucleation growth in an air plasma sprayed Thermal Barrier Coating with nicraly bond coat
    Surface & Coatings Technology, 2005
    Co-Authors: W R Chen, X. Wu, Basil R. Marple, P. C. Patnaik
    Abstract:

    The oxidation behavior of an air-plasma-sprayed Thermal Barrier Coating (APS-TBC) system was investigated in both air and low-pressure oxygen environments. It was found that mixed oxides, in the form of (Cr,Al)2O3d Ni(Cr,Al)2O4d NiO, formed heterogeneously at a very early stage during oxidation in air, and in the meantime, a layer of predominantly Al2O3 grew rather uniformly along the rest of the ceramic/bond coat interface. The mixed oxides were practically absent in the TBC system when exposed in the low-pressure oxygen environment, where the TBC had a longer life. Through comparison of the microstructures of the APS-TBC exposed in air and low-pressure oxygen environment, it was concluded that the mixed oxides played a detrimental role in causing crack nucleation and growth, reducing the life of the TBC in air. The crack nucleation and growth mechanism in the air-plasma-sprayed TBC is further elucidated with emphasis on the Ni(Cr,Al)2O4 and NiO particles embedded in the chromia. D 2004 Elsevier B.V. All rights reserved.

Shengkai Gong - One of the best experts on this subject based on the ideXlab platform.

  • lanthanum titanium aluminum oxide a novel Thermal Barrier Coating material for applications at 1300 c
    Journal of The European Ceramic Society, 2011
    Co-Authors: Shengkai Gong, Huibin Xu
    Abstract:

    Abstract Considerable efforts are being invested to explore new Thermal Barrier Coating (TBC) materials with higher temperature capability to meet the demand of advanced turbine engines. In this work, LaTi2Al9O19 (LTA) is proposed and investigated as a novel TBC material for application at 1300 °C. LTA showed excellent phase stability up to 1600 °C. The Thermal conductivities for LTA Coating are in a range of 1.0–1.3 W m−1 K−1 (300–1500 °C) and the values of Thermal expansion coefficients increase from 8.0 to 11.2 × 10−6 K−1 (200–1400 °C), which are comparable to those of yttria stabilized zirconia (YSZ). The microhardness of LTA and YSZ Coatings were in the similar level of ∼7 GPa, however, the fracture toughness value was relatively lower than that of YSZ. The lower fracture toughness was compensated by the double-ceramic LTA/YSZ layer design, and the LTA/YSZ TBC exhibited desirable Thermal cycling life of nearly 700 h at 1300 °C.

  • the Thermal cycling behavior of lanthanum cerium oxide Thermal Barrier Coating prepared by eb pvd
    Surface & Coatings Technology, 2006
    Co-Authors: Shengkai Gong, Huibin Xu
    Abstract:

    Abstract Bulk material and Coatings of Lanthanum–Cerium Oxide (La2Ce2O7) with a fluorite structure were studied as a candidate material for Thermal Barrier Coating (TBC). It has been showed that such material has the properties of low Thermal conductivity about four times lower than YSZ, the difference in the Thermal expansion coefficient between La2Ce2O7 and bond coat is smaller than that of YSZ in TBC systems, high phase stability between room temperature and 1673 K, about 300 K higher than that of the YSZ. The Coating prepared by electron beam physical vapor deposition (EB–PVD) showed that it has good Thermal cycling behavior, implying that such material can be a promising Thermal Barrier Coating material. The deviation of Coating composition from ingot can be overcome by the addition of excess La2O3 during ingot preparation and/or by adjusting the process parameters.

  • The Thermal cycling behavior of Lanthanum-Cerium Oxide Thermal Barrier Coating prepared by EB-PVD
    Surface and Coatings Technology, 2006
    Co-Authors: Wen Ma, Huibin Xu, Shengkai Gong, Xueqiang Cao
    Abstract:

    Bulk material and Coatings of Lanthanum-Cerium Oxide (La2Ce2O7) with a fluorite structure were studied as a candidate material for Thermal Barrier Coating (TBC). It has been showed that such material has the properties of low Thermal conductivity about four times lower than YSZ, the difference in the Thermal expansion coefficient between La2Ce2O7and bond coat is smaller than that of YSZ in TBC systems, high phase stability between room temperature and 1673 K, about 300 K higher than that of the YSZ. The Coating prepared by electron beam physical vapor deposition (EB-PVD) showed that it has good Thermal cycling behavior, implying that such material can be a promising Thermal Barrier Coating material. The deviation of Coating composition from ingot can be overcome by the addition of excess La2O3during ingot preparation and/or by adjusting the process parameters. © 2005 Elsevier B.V. All rights reserved.

Maurice Gell - One of the best experts on this subject based on the ideXlab platform.

  • Low Thermal conductivity Thermal Barrier Coating deposited by the solution plasma spray process
    Surface and Coatings Technology, 2006
    Co-Authors: Fang Wu, Jeff Roth, Maurice Gell, Eric H Jordan
    Abstract:

    This work seeks to develop an innovative Thermal Barrier Coating (TBC) that will exhibit low Thermal conductivity and high durability compared with that of current TBCs. To achieve this objective, a multiple component co-doped zirconia chemistry was selected for the topcoat of the TBC system, and a new process - Solution Plasma Spray (SPS or SPPS) - was employed to produce desirable microstructural features: the co-doped zirconia TBC contains ultrafine splats, high volume porosity and vertical cracks, for lower Thermal conductivity and better durability, respectively. Test results verified a low Thermal conductivity of 0.55-0.66 W/K·m over a temperature range of R.T. to 1300 °C, 1/3X that of EB-PVD 8YSZ TBCs, and its Thermal cycling durability was 2.5X that of APS 8YSZ TBCs and 1.5X that of EB-PVD 8YSZ TBCs. © 2006 Elsevier B.V. All rights reserved.

  • Thermal residual stress in an electron beam physical vapor deposited Thermal Barrier Coating system
    Acta Materialia, 1998
    Co-Authors: Jiangtian Cheng, Eric H Jordan, Brent Barber, Maurice Gell
    Abstract:

    Abstract Elastic–plastic finite element models are used to define the Thermal/residual stress state responsible for the observed failure behavior of an electron beam physical vapor deposited yttria stabilized zirconia Thermal Barrier Coating on a Pt–Al bond coat. The failures were observed to start at grain boundary ridges, some of which evolved into oxide filled cavities. Finite element models are made of the actual interface geometries through the use of metallographic sectioning and image processing. There is a one to one correspondence of calculated tension in the oxide layer and the observed localized damage. Purely elastic analysis failed to show some important tensile regions associated with the observed failure.