The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Detlev Stoever - One of the best experts on this subject based on the ideXlab platform.
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new double ceramic layer Thermal Barrier coatings based on zirconia rare earth composite oxides
Journal of The European Ceramic Society, 2006Co-Authors: Xueqiang Cao, Robert Vaßen, Frank Tietz, Detlev StoeverAbstract:Abstract A series of La 2 O 3 –ZrO 2 –CeO 2 composite oxides were synthesized by solid-state reaction. The final product keeps fluorite structure when the molar ratio Ce/Zr ≥ 0.7/0.3, and below this ratio only mixtures of La 2 Zr 2 O 7 (pyrochlore) and La 2 O 3 –CeO 2 (fluorite) exist. Averagely speaking, the increase of CeO 2 content gives rise to the increase of Thermal expansion coefficient and the reduction of Thermal conductivity, but La 2 (Zr 0.7 Ce 0.3 ) 2 O 7 has the lowest sintering ability and the lowest Thermal conductivity which could be explained by the theory of phonon scattering. Based on the large Thermal expansion coefficient of La 2 Ce 3.25 O 9.5 , the low Thermal conductivities and low sintering abilities of La 2 Zr 2 O 7 and La 2 (Zr 0.7 Ce 0.3 ) 2 O 7 , double-ceramic-layer Thermal Barrier coatings were prepared. The Thermal cycling tests indicate that such a design can largely improve the Thermal cycling lives of the coatings. Since no single material that has been studied so far satisfies all the requirements for high temperature Thermal Barrier coatings, double-ceramic-layer coating may be an important development direction of Thermal Barrier coatings.
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characterization of Thermal Barrier coatings with a gradient in porosity
Surface & Coatings Technology, 2005Co-Authors: A Portinha, Robert Vaßen, V Teixeira, Joaquim A O Carneiro, Jorge Martins, Manuel F M Costa, Detlev StoeverAbstract:Abstract A major problem in Thermal Barrier coatings (TBC) applied to gas turbine components is the spallation of ceramic coating under Thermal cycling processes. In order to prevent spallation and improve the thermomechanical behaviour of the TBC, graded ceramic coatings can be produced. For this purpose we are developing a new concept of Thermal Barrier Coating (TBC) that consist of a conventional NiCoCrAlY bond coat and an atmospheric plasma sprayed ZrO2–8 wt.%Y2O3 top coat graded in porosity on an Inconel 738 LC substrates. The aim of this work is to produce coatings with low Thermal conductivity and better thermomechanical behaviour due to the gradient in porosity which reflects a gradient in the elastic properties. Absolute porosity was measured with a mercury porosimetry and by image analysis. The second technique was also used to estimate the porosity variation along the cross-section. Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) were used to observe the morphology and coating microstructure. The microhardness was measured with a Vickers indenter and 0.981 N load. The microhardness has been evaluated for coatings in as-sprayed condition and after annealing at 1100 °C during 100 h. The results show a fast increase of the hardness after annealing. After Thermal shock heating at 1000 °C, 1 h and quickly cooling in water no spallation was observed for 100 cycles.
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Ceramic materials for Thermal Barrier coatings
Journal of the European Ceramic Society, 2004Co-Authors: Xueqiang Cao, Robert Vaßen, Detlev StoeverAbstract:This paper summarizes the basic properties of ceramic materials for Thermal Barrier coatings. Ceramics, in contrast to metals, are often more resistant to oxidation, corrosion and wear, as well as being better Thermal insulators. Except yttria stabilized zirconia, other materials such as lanthanum zirconate and rare earth oxides are also promising materials for Thermal Barrier coatings.
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Zirconates as New Materials for Thermal Barrier Coatings
Journal of the American Ceramic Society, 2000Co-Authors: Robert Vaßen, Debabrata Basu, Xueqiang Cao, Frank Tietz, Detlev StoeverAbstract:Zirconates with high melting points were investigated for application as materials for Thermal Barrier coatings at operating temperatures >1300°C. SrZrO3, BaZrO3, and La2Zr2O7 powders were synthesized and sintered to compacts with various levels of porosity. The sintering results indicated a promising low-sintering activity of the investigated materials. Thermal properties of these dense materials were determined. Thermal expansion coefficients were slightly lower than those of Y2O3-stabilized ZrO2 (YSZ); Thermal conductivities of SrZrO3 and BaZrO3 were comparable or slightly higher than those of YSZ. La2Zr2O7 had a lower Thermal conductivity. SrZrO3 was not suitable for application as a Thermal Barrier coating because of a phase transition at temperatures between 700° and 800°C. Mechanical properties (hardness, fracture toughness, and Young's modulus) of dense BaZrO3 and La2Zr2O7 samples were determined by indentation techniques and showed lower hardness and Young's modulus compared to YSZ. BaZrO3 and La2Zr2O7 powders were optimized for application as powders for plasma spraying. Plasma-sprayed coatings were produced and characterized. Thermal cycling with a gas burner at 1200°C showed a massive attack of the BaZrO3 coating, with loss of BaO. On the other hand, the La2Zr2O7 coating showed excellent Thermal stability and Thermal shock behavior.
Carlos G Levi - One of the best experts on this subject based on the ideXlab platform.
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equilibrium relationships between Thermal Barrier oxides and silicate melts
Acta Materialia, 2016Co-Authors: David L Poerschke, Talia L Barth, Carlos G LeviAbstract:Abstract The phase equilibria between Thermal Barrier coating (TBC) materials and calcium–magnesium–aluminosilicate melts (CMAS, representing deposits formed when siliceous debris is ingested into modern turbine engines), were investigated at 1300 °C. The primary goal was to understand the influence of the deposit and Thermal Barrier oxide compositions on the melt solubility limits and reaction product constitution. Model deposit compositions with SiO 2 to CaO ratios from 1.4 to 4.7 and with or without MgO were reacted with yttria- and gadolinia-zirconia Thermal Barrier oxides ranging from pure ZrO 2 to the pure yttria and gadolinia. The reactions formed various crystalline silicate phases; rare earth–calcium–silicate apatite and zircon (ZrSiO 4 ) were observed most frequently. Following the reactions, the residual melts were depleted in SiO 2 and generally enriched in CaO, MgO, and Al 2 O 3 . The implications of the anticipated changes in the melt viscosity and the cation partitioning between the melt and various solid solution phases on the efficacy of degradation-mitigating crystallization reactions are discussed.
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environmental degradation of Thermal Barrier coatings by molten deposits
Mrs Bulletin, 2012Co-Authors: Carlos G Levi, J W Hutchinso, Mariehelene Vidalsetif, Curtis Ala JohnsoAbstract:Molten deposits based on calcium-magnesium alumino-silicates (CMAS), originating from siliceous debris ingested with the intake air, represent a fundamental threat to progress in gas turbine technology by limiting the operating surface temperature of coated components. The thermomechanical and thermochemical aspects of the CMAS interactions with Thermal-Barrier coatings, as well as the current status of mitigating strategies, are discussed in this article. Key challenges and research needs for developing adequate solutions are highlighted.
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shear band formation in columnar Thermal Barrier oxides
Acta Materialia, 2005Co-Authors: T Xu, Ashutosh S Gandhi, Carlos G Levi, A. G. EvansAbstract:Columnar Thermal Barrier oxides either impressed or impacted by projectiles at high temperature develop kink bands. The bands emanate from sub-surface sites adjacent to the contact zone and extend diagonally toward the substrate. At the boundaries, the columns are cracked, indicating that the material has been weakened, and rendering them preferred sites for material removal upon subsequent impact. In some cases, the bands reach the interface with the Thermally grown oxide and initiate a delamination crack. The experimental challenges in characterizing the bands and in relating their occurrence to constituent properties and microstructure are extreme. To address this limitation, the present article explores methods for numerical simulation of the bands. By modeling the material within the columns as a minimally porous Gurson solid and treating the inter-columnar material as a low density foam, it will be demonstrated that bands can be simulated consistent with those observed experimentally.
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emerging materials and processes for Thermal Barrier systems
Current Opinion in Solid State & Materials Science, 2004Co-Authors: Carlos G LeviAbstract:Thermal Barrier systems have been the subject of vigorous research and development activities over the past few years, driven by the demands for enhanced reliability and substantially higher operating temperatures envisaged for the next generations of gas turbine engines. The menu of candidate materials and architectures has expanded considerably, including numerous concepts based on zirconia as well as radically different materials, multilayers and modulated distributions of porosity and chemical composition. Advances in deposition processes enable increased flexibility for tailoring composition and microstructure to local requirements within the coating system, e.g. for Thermal insulation, control of interdiffusion, enhanced resistance against environmental degradation and condition monitoring. Many challenges remain but healthy and growing collaborations between the science and technology communities bode well for future progress in this area.
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materials design for the next generation Thermal Barrier coatings
Annual Review of Materials Research, 2003Co-Authors: David R Clarke, Carlos G LeviAbstract:▪ Abstract The emphasis in this short review is to describe the materials issues involved in the development of present Thermal Barrier coatings and the advances necessary for the next generation, higher temperature capability coatings.
Robert Vaßen - One of the best experts on this subject based on the ideXlab platform.
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overview in the field of Thermal Barrier coatings including burner rig testing in the european union
Ceramics Japan, 2008Co-Authors: Robert Vaßen, Nicolaie Markocsan, Federico Cernuschi, Gabriele Rizzi, Lars Ostergren, Arien Kloosterman, Remy Mevrel, J P Feist, J R NichollsAbstract:Overview in the field of Thermal Barrier coatings including burner rig testing in the European Union
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new double ceramic layer Thermal Barrier coatings based on zirconia rare earth composite oxides
Journal of The European Ceramic Society, 2006Co-Authors: Xueqiang Cao, Robert Vaßen, Frank Tietz, Detlev StoeverAbstract:Abstract A series of La 2 O 3 –ZrO 2 –CeO 2 composite oxides were synthesized by solid-state reaction. The final product keeps fluorite structure when the molar ratio Ce/Zr ≥ 0.7/0.3, and below this ratio only mixtures of La 2 Zr 2 O 7 (pyrochlore) and La 2 O 3 –CeO 2 (fluorite) exist. Averagely speaking, the increase of CeO 2 content gives rise to the increase of Thermal expansion coefficient and the reduction of Thermal conductivity, but La 2 (Zr 0.7 Ce 0.3 ) 2 O 7 has the lowest sintering ability and the lowest Thermal conductivity which could be explained by the theory of phonon scattering. Based on the large Thermal expansion coefficient of La 2 Ce 3.25 O 9.5 , the low Thermal conductivities and low sintering abilities of La 2 Zr 2 O 7 and La 2 (Zr 0.7 Ce 0.3 ) 2 O 7 , double-ceramic-layer Thermal Barrier coatings were prepared. The Thermal cycling tests indicate that such a design can largely improve the Thermal cycling lives of the coatings. Since no single material that has been studied so far satisfies all the requirements for high temperature Thermal Barrier coatings, double-ceramic-layer coating may be an important development direction of Thermal Barrier coatings.
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characterization of Thermal Barrier coatings with a gradient in porosity
Surface & Coatings Technology, 2005Co-Authors: A Portinha, Robert Vaßen, V Teixeira, Joaquim A O Carneiro, Jorge Martins, Manuel F M Costa, Detlev StoeverAbstract:Abstract A major problem in Thermal Barrier coatings (TBC) applied to gas turbine components is the spallation of ceramic coating under Thermal cycling processes. In order to prevent spallation and improve the thermomechanical behaviour of the TBC, graded ceramic coatings can be produced. For this purpose we are developing a new concept of Thermal Barrier Coating (TBC) that consist of a conventional NiCoCrAlY bond coat and an atmospheric plasma sprayed ZrO2–8 wt.%Y2O3 top coat graded in porosity on an Inconel 738 LC substrates. The aim of this work is to produce coatings with low Thermal conductivity and better thermomechanical behaviour due to the gradient in porosity which reflects a gradient in the elastic properties. Absolute porosity was measured with a mercury porosimetry and by image analysis. The second technique was also used to estimate the porosity variation along the cross-section. Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) were used to observe the morphology and coating microstructure. The microhardness was measured with a Vickers indenter and 0.981 N load. The microhardness has been evaluated for coatings in as-sprayed condition and after annealing at 1100 °C during 100 h. The results show a fast increase of the hardness after annealing. After Thermal shock heating at 1000 °C, 1 h and quickly cooling in water no spallation was observed for 100 cycles.
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Ceramic materials for Thermal Barrier coatings
Journal of the European Ceramic Society, 2004Co-Authors: Xueqiang Cao, Robert Vaßen, Detlev StoeverAbstract:This paper summarizes the basic properties of ceramic materials for Thermal Barrier coatings. Ceramics, in contrast to metals, are often more resistant to oxidation, corrosion and wear, as well as being better Thermal insulators. Except yttria stabilized zirconia, other materials such as lanthanum zirconate and rare earth oxides are also promising materials for Thermal Barrier coatings.
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Zirconates as New Materials for Thermal Barrier Coatings
Journal of the American Ceramic Society, 2000Co-Authors: Robert Vaßen, Debabrata Basu, Xueqiang Cao, Frank Tietz, Detlev StoeverAbstract:Zirconates with high melting points were investigated for application as materials for Thermal Barrier coatings at operating temperatures >1300°C. SrZrO3, BaZrO3, and La2Zr2O7 powders were synthesized and sintered to compacts with various levels of porosity. The sintering results indicated a promising low-sintering activity of the investigated materials. Thermal properties of these dense materials were determined. Thermal expansion coefficients were slightly lower than those of Y2O3-stabilized ZrO2 (YSZ); Thermal conductivities of SrZrO3 and BaZrO3 were comparable or slightly higher than those of YSZ. La2Zr2O7 had a lower Thermal conductivity. SrZrO3 was not suitable for application as a Thermal Barrier coating because of a phase transition at temperatures between 700° and 800°C. Mechanical properties (hardness, fracture toughness, and Young's modulus) of dense BaZrO3 and La2Zr2O7 samples were determined by indentation techniques and showed lower hardness and Young's modulus compared to YSZ. BaZrO3 and La2Zr2O7 powders were optimized for application as powders for plasma spraying. Plasma-sprayed coatings were produced and characterized. Thermal cycling with a gas burner at 1200°C showed a massive attack of the BaZrO3 coating, with loss of BaO. On the other hand, the La2Zr2O7 coating showed excellent Thermal stability and Thermal shock behavior.
Nicolaie Markocsan - One of the best experts on this subject based on the ideXlab platform.
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comparative study of suspension plasma sprayed and suspension high velocity oxy fuel sprayed ysz Thermal Barrier coatings
Surface & Coatings Technology, 2015Co-Authors: Ashish Ganvir, Nicholas Curry, Nicolaie Markocsan, Per Nylen, Filofteialaura TomaAbstract:Suspension Thermal Spraying is a relatively new Thermal spaying technique to produce advanced Thermal Barrier coatings. This technique enables the production of much different performance Thermal b ...
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Thermal conductivity analysis and lifetime testing of suspension plasma sprayed Thermal Barrier coatings
THE Coatings, 2014Co-Authors: Nicholas Curry, Kent Vanevery, Todd Snyder, Nicolaie MarkocsanAbstract:Suspension plasma spraying (SPS) has become an interesting method for the production of Thermal Barrier coatings for gas turbine components. The development of the SPS process has led to structures ...
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impact of impurity content on the sintering resistance of dysprosia and yttria stabilised zirconia Thermal Barrier coatings
International Thermal Spray Conference and Exposition: Innovative Coating Solutions for the Global Economy ITSC 2013; Busan; South Korea; 13 May 2013 , 2013Co-Authors: Nicholas Curry, Wyszomir Janikowski, Nicolaie MarkocsanAbstract:Dysprosia stabilised zirconia (DySZ) is a promising candidate to replace yttria stabilised zirconia (YSZ) as a Thermal Barrier coating due to its lower inherent Thermal conductivity. It is also sug ...
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solid particle erosion of Thermal spray and physical vapour deposition Thermal Barrier coatings
Wear, 2011Co-Authors: F Cernuschi, Robert Vasen, Nicolaie Markocsan, L Lorenzoni, S Capelli, C Guardamagna, M Karger, K Von Niessen, J Menuey, C GiolliAbstract:Thermal Barrier coatings (TBC) are used to protect hot path components of gas turbines from hot combustion gases. For a number of decades, in the case of aero engines TBCs are usually deposited by ...
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recent activities in the field of Thermal Barrier coatings including burner rig testing in the european union
Advanced Engineering Materials, 2008Co-Authors: Robert Vasen, Nicolaie Markocsan, F Cernuschi, Gabriele Rizzi, Lars Ostergren, Arien Kloosterman, Remy Mevrel, J P Feist, A Scrivani, J R NichollsAbstract:Although Thermal Barrier coatings are used in industry for several decades there is still considerable demand for a further improvement of this coating system. Present research projects are for example dealing with the improvement of temperature capability and lifetime, developing of lifetime models, new processing technologies, or incorporating of additional functional properties in the coating. The present paper tries to give an overview on these recent research activities. In addition, it will also try to describe the different burner rig test facilities in Europe, which serve as an important test bed of Thermal Barrier coating systems.
Huibin Xu - One of the best experts on this subject based on the ideXlab platform.
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the Thermal cycling behavior of lanthanum cerium oxide Thermal Barrier coating prepared by eb pvd
Surface & Coatings Technology, 2006Co-Authors: Shengkai Gong, Huibin XuAbstract: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.
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Thermal cycling life and Thermal diffusivity of a plasma-sprayed nanostructured Thermal Barrier coating
Scripta Materialia, 2004Co-Authors: Chungen Zhou, Shengkai Gong, Na Wang, Zhen-bo Wang, Huibin XuAbstract:Abstract The nanostructured Thermal Barrier coatings exhibited excellent Thermal cyclic resistance and low Thermal diffusivity. The Thermal cyclic life of the coating is about 600 h for 1-h cycles at 1050 °C. The Thermal diffusivity of the coating is 90% of that of conventional Thermal Barrier coatings.
