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. .

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.

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.

Oxidation Behavior of Thermal Barrier Coatings on Copper Substrates

2010 ◽  
Vol 66 ◽  
pp. 74-79
Author(s):  
Jana Schloesser ◽  
Martin Bäker ◽  
Joachim Rösler ◽  
Robert Pulz
Keyword(s):  
Thermal Cycling ◽  
Thermal Barrier Coatings ◽  
Bond Coat ◽  
Thermal Protection ◽  
Rocket Engine ◽  
Copper Substrate ◽  
Thermally Grown Oxide ◽  
Substrate Material ◽  
Thermal Barrier ◽  
Barrier Coatings

In rocket engine combustion chambers, the cooling channels experience extremely high temperatures and environmental attack. Thermal protection can be provided by Thermal Barrier Coatings. Due to the need of good heat conduction, the inner combustion liner is made of copper. The performance of a standard coating system for nickel based substrates is investigated on copper substrates. Thermal cycling experiments are performed on the coated samples. Due to temperature limitations of the copper substrate material, no thermally grown oxide forms at the interface of the thermal barrier coating and the bond coat. Delamination of the coatings occurs at the interface between the substrate and the bond coat due to oxide formation of the copper at uncoated edges. In real service a totally dense coating can probably not be assured which is the reason why this failure mode is of importance. Different parameters are used for thermal cycling to understand the underlying mechanisms of delamination. Furthermore, laser heating experiments account for the high thermal gradient in real service. Pilot tests which led to a delamination of the coating at the substrate interface were performed successfully.

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.

High-Temperature Performance of Self-Healing SiC-YSZ Thermal Barrier Coatings Deposited by Using Various Plasma Spray Concepts

2021 ◽  
Author(s):  
Mohammad Hassanzadeh ◽  
Paweł Sokołowski ◽  
Radek Musalek ◽  
Jan Medricky ◽  
Stefan Csaki
Keyword(s):  
High Temperature ◽  
Thermal Barrier Coatings ◽  
Plasma Spray ◽  
Gas Turbines ◽  
Isothermal Oxidation ◽  
Atmospheric Plasma ◽  
Flash Method ◽  
Thermal Barrier ◽  
Self Healing ◽  
Barrier Coatings

Abstract In this study; a novel self-healing concept is considered in order to increase the lifetime of thermal barrier coatings (TBCs) in modern gas turbines. For that purpose; SiC healing particles were introduced to conventional 8YSZ topcoats by using various plasma spray concepts; i.e.; composite or multilayered coatings. All topcoats were sprayed by SG-100 plasma torch on previously deposited NiCrAlY bondcoats produced by conventional atmospheric plasma spraying. Coatings were subjected to thermal conductivity measurements by laser flash method up to 1000°C; isothermal oxidation testing up to 200h at 1100°C and finally thermal cyclic fatigue (TCF) lifetime testing at 1100°C. Microstructural coating evaluation was performed by scanning electronic microscope (SEM); in the as-produced and post high-temperature tested states. This was done to analyze the self-healing phenomena and its influence on the hightemperature performance of the newly developed TBCs.

Sign in / Sign up

Export Citation Format

Share Document