Thermophysikalische Charakterisierung von Wärmedämmschichten

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Kevin Knopp ◽  
Amir Shandy ◽  
Achim Winterstein ◽  
Mariacarla Arduini ◽  
Frank Hemberger ◽  
...  
Keyword(s):  
Thermal Barrier Coatings ◽  
Laser Flash ◽  
Thermal Barrier ◽  
Barrier Coatings

Zusammenfassung Die Effizienzsteigerung moderner Gasturbinen erfordert die stetige Anhebung der Betriebstemperatur. Die derzeitigen Brenngastemperaturen liegen mit über 1400 °C signifikant über der kritischen Temperatur der verwendeten Turbinenstähle. Zur Gewährleistung der Betriebssicherheit werden die Turbinenschaufeln neben Aktivkühlung durch Beschichtung mit thermischen Schutzschichten, sogenannten thermal barrier coatings (TBC), geschützt. Da es sich bei den TBC um Keramikschichten handelt, ist für die Erhöhung der Haftfestigkeit das Aufbringen eines Haftvermittlers (Verbindungsschicht) notwendig. Da die Eigenschaften dünner Schichten stark von den Eigenschaften des Bulkmaterials abweichen können und zudem von der Herstellungsmethode beeinflusst werden, ist eine Untersuchung der thermischen und infrarot-optischen Eigenschaften der tatsächlichen Schichtstrukturen unumgänglich, insbesondere im Hochtemperaturbereich. Hierfür wurden Proben des reinen Trägerstahls, des Trägerstahls mit Haftvermittlerschicht und des kompletten Schichtsystems aus Trägerstahl, Haftvermittlerschicht und Wärmedämmschicht verschiedener Dicken hergestellt und mittels Laser-Flash-Methode untersucht. Die Auswertung erfolgte dabei analytisch, ausgehend von der Trägerstahl-Einschichtprobe, über die Zweischicht- und Dreischichtsysteme. Vervollständigt wurden diese Untersuchungen durch infrarot-optische Charakterisierungen, mit denen sich die Wärmeausbreitung durch die Schichtsysteme beschreiben lässt. Zusammen mit den Laser-Flash Messungen erlaubt dies eine spätere Quantifizierung der einzelnen, bei Keramiken auftretenden, Wärmetransportmechanismen.

Thermal Conductivity Prediction for Thermal Barrier Coatings

2010 ◽  
Author(s):  
Monica B. Silva ◽  
S. M. Guo ◽  
Patrick F. Mensah ◽  
Ravinder Diwan
Keyword(s):  
Thermal Conductivity ◽  
Thermal Barrier Coatings ◽  
Volume Fraction ◽  
Mercury Porosimetry ◽  
Laser Flash ◽  
Atmospheric Plasma ◽  
Thermal Barrier ◽  
Interfacial Resistance ◽  
Barrier Coatings ◽  
Spray Process

Thermal barrier coatings (TBCs) are used in gas turbine engines to achieve a higher working temperature and thus lead to a better efficiency. Yttria-Stabilized-Zirconia (YSZ), a material with low thermal conductivity, is commonly used as the TBC top coat to provide the thermal barrier effect. In this paper, an analytical model is proposed to estimate the effective thermal conductivity of the TBCs based on the microstructures. This model includes the micro structure details, such as grain size, pore size, volume fraction of pores, and the interfacial resistance. To validate the model, two sets of TBC samples were fabricated and tested for thermal conductivity and associated microstructures. The first set of samples were disk shaped YSZ-Al2O3 samples fabricated using a pressing machine. The YSZ-Al2O3 powder mixture was 0, 1, 2, 3, 4 and 5 wt% Al2O3/YSZ powder ratio. The second set of samples were fabricated by Atmospheric Plasma Spray process for two different microstructure configurations, standard (STD) and vertically cracked (VC), at two different thicknesses, 400 and 700 urn respectively. A laser flash system was used to measure the thermal conductivity of the coatings. Experiments were performed over the temperature range from 100°C to 800°C. The porosity of the YSZ samples was measured using a mercury porosimetry analyzer, POREMASTER 33 system. A Scanning Electron Microscope (SEM) was used to study the microstructure of the samples. It is observed that the microstructure and the porosity are directly linked with the thermal conductivity values. The relationship of the properties to the real microstructure determines the validity of the proposed model.

scholarly journals Optimal parameterization in the measurements of the thermal diffusivity of thermal barrier coatings

2007 ◽  
Vol 11 (1) ◽  
pp. 137-156
Author(s):  
Nenad Milosevic
Keyword(s):  
Thermal Diffusivity ◽  
Thermal Barrier Coatings ◽  
Steel Substrate ◽  
Thermal Contact ◽  
Copper Substrate ◽  
Estimation Procedure ◽  
Laser Flash ◽  
Flash Method ◽  
Thermal Barrier ◽  
Barrier Coatings

The paper presents an estimation procedure for the measurement of the thermal diffusivity of thermal barrier coatings deposited on thermal conductive substrates using the laser flash method when the thermal contact resistance between the coating and substrate is unknown. The procedure is based on the application of the optimal parameterization technique and Gauss minimization algorithm. It has been applied on the experimental data obtained by using two different samples, one made of PTFE (polytetrafluoroethylene) coating deposited on a stainless steel substrate and the other made of PVC (polyvinylchloride) deposited on a copper substrate. .

scholarly journals Thermal Conductivity of Multi-Sized Porous Thermal Barrier Coatings at Micro and Nano Scales after Long-Term Service at High Temperatures

Coatings ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1183
Author(s):  
Pei-Hu Gao ◽  
Sheng-Cong Zeng ◽  
Can Jin ◽  
Bo Zhang ◽  
Bai-Yang Chen ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
High Temperature ◽  
Porous Structure ◽  
Thermal Barrier Coatings ◽  
Laser Flash ◽  
Physical Models ◽  
Atmospheric Plasma ◽  
Thermal Barrier ◽  
Barrier Coatings

Thermal barrier coatings with multi-sized porous structure at micro and nano scales were prepared with hollow spherical YSZ powders and polypropylene powders through atmospheric plasma spraying. The thermal conductivities of the multi-sized thermal barrier coatings after a long-term serving at high temperature were tested through laser flash heating method. Meanwhile, the physical models of thermal barrier coatings with multi-sized porous structure at micro and nano scales were constructed through Ansys Workbench. The evolutions of thermal conductivity of thermal barrier coatings with multi-sized pores after long-term service at 1100 °C were investigated through computation. It was found that the thermal conductivity of the coating increased with the extension of the serving time. When the serving time reached 60 days, the thermal conductivity of the coating tended to be stable and close to the compacted bulk. The computational results were consistent with the tested ones, which could be helpful to explain the thermal conducting evolution in thermal barrier coatings with multi-sized porous structure at nano and micro scales after long-term serving at high temperature.

Thermophysical and Mechanical Properties of PYZ Thick Thermal Barrier Coatings

1998 ◽  
Author(s):  
D. Schwingel ◽  
R. Taylor ◽  
T. Haubold ◽  
J. Wigren ◽  
C. Gualco ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Plasma Spraying ◽  
Thermal Barrier Coatings ◽  
Material Properties ◽  
Laser Flash ◽  
Thermal Barrier ◽  
Spray Parameters ◽  
Barrier Coatings ◽  
Point Bend

Abstract Within a Brite Euram project thick thermal barrier coatings for combustor applications were produced by plasma spraying of yttria partially stabilised zirconia (ZrO2 + 8 wt.% Y2O3). The material properties of such coatings strongly depend on their microstructure which can be altered by manipulating the parameters controlling the plasma spraying process. Covering a variation of possible microstructures, the coatings considered had a thickness of about 2 mm and were six to eight times thicker than the coatings currently in service. This investigation was concerned with an evaluation of the thermophysical and mechanical properties of these coatings and their correlation with the microstructure and the plasma spray parameters. Particular attention was paid to the influence of coating segmentation, microcracking and porosity. The experimental work included the measurement of the thermal diffusivity using the laser flash technique, thermal expansion measurements, and the determination of flexural strength and Young's modulus by means of a specially constructed four-point bend rig. Since some of the samples considered were sprayed according to a partially factorial test plan a statistical evaluation of the material data was possible yielding the correlation between process parameters and material properties.

Assessment of Thermal Barrier Coatings by Plasma Deposition

1997 ◽  
Author(s):  
K.S. Ravichandran ◽  
K. An ◽  
R. Taylor
Keyword(s):  
Thermal Conductivity ◽  
Thermal Diffusivity ◽  
Specific Heat ◽  
Thermal Barrier Coatings ◽  
Laser Flash ◽  
Thermal Barrier ◽  
Conductivity Data ◽  
Barrier Coatings ◽  
Laser Flash Technique ◽  
Flash Technique

Abstract Thermal conductivity is an important design parameter for thermal barrier coatings. Accurate thermal conductivity data is therefore required to ensure proper design and reliability of gas turbine blades. In the present research, thermal conductivities of Al2O3 and 8wt.% Y2O3 stabilized ZrO2 (8YSZ) coatings, made by air plasma spray, were determined from the measurements of thermal diffusivity and specific heat as a function of temperature. Thermal diffusivity was determined by the laser flash technique. Specific heat was determined by a Differential Scanning Calorimeter (DSC). Detailed analyses of the results indicate that the thermal conductivity is sensitive to coating density (porosity), interfaces between splats as well as the interface between the coating and the substrate. Additionally, thermal conductivity evaluations of these coatings were also influenced by the accuracy and relevance of the data on bulk monolithic materials. Further, analyses of sensitivity of the laser flash technique to variations in the coating and the substrate parameters, for the coatings evaluated in this study, were also performed. The results are discussed in the context of coating characteristics, reference conductivity data for dense materials and the sensitivity of the measurement method to coating parameters.

Synthesis and Characterization of LaMgAl11O19 as Thermal Barrier Coatings Material

2016 ◽  
Vol 697 ◽  
pp. 390-394 ◽  
Author(s):  
Ze Ya Huang ◽  
Hao Ran Lu ◽  
Chang An Wang
Keyword(s):  
Thermal Barrier Coatings ◽  
Raw Materials ◽  
Laser Flash ◽  
Flash Method ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Heat Treated ◽  
Higher Temperature ◽  
Thermal Diffusivities ◽  
Thermal Conductivities

LaMgAl11O19 was synthesized at 1550 °C using La2O3, MgO and Al2O3 as raw materials. The samples were characterization by XRD and SEM. The tablet shaped crystals free of impurity phase formed under this condition. The thermal diffusivities were measured by laser flash method and the determined intrinsic thermal conductivities decreased as temperature increases from 25 °C to 1000 °C. As comparison, intrinsic thermal conductivities of LaMgAl11O19 are lower than that of 7YSZ. The synthesized LaMgAl11O19 was heat treated at higher temperature from 1600 °C to 1700 °C and no change in the phase indicates that the LaMgAl11O19 phase is stable under 1700 °C, which is very important for thermal barrier coatings (TBCs) serving at elevated temperature.

Characterization of thermal barrier coatings formed by electon-beam physical vapor deposition (EB-PVD)

1989 ◽  
Vol 47 ◽  
pp. 426-427
Author(s):  
Ozer Unal
Keyword(s):  
Thermal Barrier Coatings ◽  
Physical Vapor Deposition ◽  
Ceramic Coating ◽  
High Vacuum ◽  
Ceramic Coatings ◽  
High Energy ◽  
Thermal Barrier ◽  
Protective Oxide ◽  
Barrier Coatings ◽  
Energy Beam

Interest in ceramics as thermal barrier coatings for hot components of turbine engines has increased rapidly over the last decade. The primary reason for this is the significant reduction in heat load and increased chemical inertness against corrosive species with the ceramic coating materials. Among other candidates, partially-stabilized zirconia is the focus of attention mainly because ot its low thermal conductivity and high thermal expansion coefficient.The coatings were made by Garrett Turbine Engine Company. Ni-base super-alloy was used as the substrate and later a bond-coating with high Al activity was formed over it. The ceramic coatings, with a thickness of about 50 μm, were formed by EB-PVD in a high-vacuum chamber by heating the target material (ZrO2-20 w/0 Y2O3) above its evaporation temperaturef >3500 °C) with a high-energy beam and condensing the resulting vapor onto a rotating heated substrate. A heat treatment in an oxidizing environment was performed later on to form a protective oxide layer to improve the adhesion between the ceramic coating and substrate. Bulk samples were studied by utilizing a Scintag diffractometer and a JEOL JXA-840 SEM; examinations of cross-sectional thin-films of the interface region were performed in a Philips CM 30 TEM operating at 300 kV and for chemical analysis a KEVEX X-ray spectrometer (EDS) was used.

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