scholarly journals Thermal conductivity of EB-PVD thermal barrier coatings evaluated by a steady-state laser heat flux technique

2001 ◽  
Vol 138 (1) ◽  
pp. 1-8 ◽  
Author(s):  
Dongming Zhu ◽  
Robert A. Miller ◽  
Ben A. Nagaraj ◽  
Robert W. Bruce
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Steady State ◽  
Thermal Barrier Coatings ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
State Laser ◽  
Laser Heat

The Fabrication, High Heat Flux Testing, and Failure Analysis of Thermal Barrier Coatings for Power Generation Gas Turbines

2017 ◽  
Author(s):  
Mary Helen McCay ◽  
Pei-feng Hsu ◽  
D. Edward Croy ◽  
David Moreno ◽  
Mengqi Zhang
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Thermal Barrier Coatings ◽  
Gas Turbines ◽  
High Heat ◽  
Compressed Air ◽  
Thermal Barrier ◽  
High Heat Flux ◽  
Test Cases ◽  
Barrier Coatings

Thermal barrier coatings (TBC) are used to protect the hot components of gas turbines engines to enhance thermal efficiency and component service life. The coating, based on yttria stabilized zirconia, is used in this study. In this paper high heat flux testing with a temperature gradient across the coating thickness of TBC coated coupons is presented. These buttons are subject to precisely-controlled laser heating on the top side and compressed air cooling on the bottom side. Analysis of the thermal conductivity change with respect to heating time and peak temperature, failure assessment, and metallurgical examination are also presented. Some important results of using this method of testing are: definition of the service time vs temperature relationship for TBC lifetime; improved durability of TBCs under severe environmental conditions; determination of effective steady-state sintering conductivity; identification of onset of coating cracking and delamination; adjustable peak temperature, automated and accelerated thermal cycling, etc. This leads to faster testing turn-around for TBC development. Two different types of heating modes can be employed: soak test and cycle test. In soak tests, coated coupons are subjected to steady laser heat flux for up to 12 hr. In cycle tests, the laser heat flux is on for one hour and then off to cool the coated coupons for three minutes. Coupon top surface temperatures from 1200 to 1528°C are maintained in various test cases. At the highest temperature test cases, delamination of TBC (cycle test) and surface crack (soak test) are observed. All key measurements (temperatures, laser power to coupon, compressed air flow rate, etc.) are recorded per second. The normalized thermal conductivity can be computed in real time or processed after the test. It is found that the normalized thermal conductivity increases in the first few hours or cycles of heating and it either reaches a near steady state value or decreases due to surface cracking or delamination in the later state of testing.

Development of Operating Temperature Prediction Method Using Thermophysical Properties Change of Thermal Barrier Coatings

2004 ◽  
Vol 126 (1) ◽  
pp. 102-106 ◽  
Author(s):  
T. Fujii ◽  
T. Takahashi
Keyword(s):  
Thermal Conductivity ◽  
Thermal Barrier Coatings ◽  
Operating Temperature ◽  
Thermal Barrier ◽  
Conductivity Measurements ◽  
Barrier Coatings ◽  
Barrier Performance ◽  
Very High ◽  
General Method ◽  
Exposure Conditions

Thermal barrier coatings (TBCs) have become an indispensable technology as the temperature of turbine inlet gas has increased. TBCs reduce the temperature of the base metal, but a reduction of internal pores by sintering occurs when using TBCs, and so the thermal barrier performance of TBCs is deteriorated. This in turn increases the temperature of the base metal and could shorten its lifespan. The authors have already clarified by laboratory acceleration tests that the deterioration of the thermal barrier performance of TBCs is caused by a decrease in the noncontact area that exists inside TBCs. This noncontact area is a slit space that exists between thin layers and is formed when TBCs are coated. This paper examines the relations between the decrease of the noncontact area and the exposure conditions, by measuring the thermal conductivity and the porosity of TBCs exposed to the temperatures that exist in an actual gas turbine, and derives the correlation with exposure conditions. As a result, very high correlations were found between the thermal conductivity and exposure conditions of TBCs, and between the porosity and exposure conditions. A very high correlation was also found between the thermal conductivity and porosity of TBCs. In addition, techniques for predicting TBC operating temperature were examined by using these three correlations. The correlation of diameter and exposure conditions of the gamma prime phase, which exists in nickel base super alloys, is used as a general method for predicting the temperature of parts in hot gas paths. This paper proposes two kinds of operating temperature prediction methods, which are similar to this general method. The first predicts the operating temperature from thermal conductivity measurements of TBCs before and after use, and the second predicts the operating temperature from thermal conductivity measurements of TBCs after use and porosity measurements before use. The TBC operating temperatures of a combustor that had been used for 12,000 hours with an actual E-class gas turbine were predicted by these two methods. The advantage of these methods is that the temperature of all parts with TBC can be predicted.

Design, Preparation and Thermal Properties of (La0.4Sm0.5Yb0.1)2Zr2O7 Ceramic for Thermal Barrier Coatings

2012 ◽  
Vol 512-515 ◽  
pp. 469-473 ◽  
Author(s):  
L. Liu ◽  
Z. Ma ◽  
F.C. Wang ◽  
Q. Xu
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Thermal Properties ◽  
Rare Earth ◽  
Thermal Expansion Coefficient ◽  
Thermal Barrier Coatings ◽  
Expansion Coefficient ◽  
Phonon Transport ◽  
Thermal Barrier ◽  
Barrier Coatings

According to the theory of phonon transport and thermal expansion, a new complex rare-earth zirconate ceramic (La0.4Sm0.5Yb0.1)2Zr2O7, with low thermal conductivity and high thermal expansion coefficient, has been designed by doping proper ions at A sites. The complex rare-earth zirconate (La0.4Sm0.5Yb0.1)2Zr2O7 powder for thermal barrier coatings (TBCs) was synthesized by coprecipitation-calcination method. The phase, microstructure and thermal properties of the new material were investigated. The results revealed that single phase (La0.4Sm0.5Yb0.1)2Zr2O7 with pyrochlore structure was synthesized. The thermal conductivity and the thermal expansion coefficient of the designed complex rare-earth zirconate ceramic is about 1.3W/m•K and 10.5×10-6/K, respectively. These results imply that (La0.4Sm0.5Yb0.1)2Zr2O7 can be explored as the candidate material for the ceramic layer in TBCs system.

Evaluation of CeSZ Thermal Barrier Coatings for Diesels

2000 ◽  
Author(s):  
P.J. Huang ◽  
J.J. Swab ◽  
P.J. Patel ◽  
W.S. Chu
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Thermal Barrier Coatings ◽  
Coefficient Of Thermal Expansion ◽  
Fuel Efficiency ◽  
Atmospheric Plasma ◽  
Thermal Barrier ◽  
Mechanical And Thermal Properties ◽  
Barrier Coatings ◽  
Spray Process

Abstract The development of thermal barrier coatings (TBCs) for diesel engines has been driven by the potential improvements in engine power and fuel efficiency that TBCs represent. TBCs have been employed for many years to reduce corrosion of valves and pistons because of their high temperature durability and thermal insulative properties. There are research programs to improve TBCs wear resistance to allow for its use in tribologically intensive areas of the engine. This paper will present results from tribological tests of ceria stabilized zirconia (CeSZ). The CeSZ was applied by atmospheric plasma spray process. Various mechanical and thermal properties were measured including wear, coefficient of thermal expansion, thermal conductivity, and microhardness. The results show the potential use of CeSZ in wear sensitive applications in diesel applications. Keywords: Thermal Barrier Coating, Diesel Engine, Wear, Thermal Conductivity, and Thermal Expansion

scholarly journals Analysis of the energetic/environmental performances of gas turbine plant: Effect of thermal barrier coatings and mass of cooling air

2009 ◽  
Vol 13 (1) ◽  
pp. 147-164 ◽  
Author(s):  
Ion Ion ◽  
Anibal Portinha ◽  
Jorge Martins ◽  
Vasco Teixeira ◽  
Joaquim Carneiro
Keyword(s):  
Thermal Conductivity ◽  
Gas Turbine ◽  
Thermal Barrier Coatings ◽  
Turbine Blades ◽  
Heat Transfer Analysis ◽  
Thermal Barrier ◽  
Inlet Temperature ◽  
Barrier Coatings ◽  
Cooling Air Flow ◽  
Cooling Air

Zirconia stabilized with 8 wt.% Y2O3 is the most common material to be applied in thermal barrier coatings owing to its excellent properties: low thermal conductivity, high toughness and thermal expansion coefficient as ceramic material. Calculation has been made to evaluate the gains of thermal barrier coatings applied on gas turbine blades. The study considers a top ceramic coating Zirconia stabilized with 8 wt.% Y2O3 on a NiCoCrAlY bond coat and Inconel 738LC as substrate. For different thickness and different cooling air flow rates, a thermodynamic analysis has been performed and pollutants emissions (CO, NOx) have been estimated to analyze the effect of rising the gas inlet temperature. The effect of thickness and thermal conductivity of top coating and the mass flow rate of cooling air have been analyzed. The model for heat transfer analysis gives the temperature reduction through the wall blade for the considered conditions and the results presented in this contribution are restricted to a two considered limits: (1) maximum allowable temperature for top layer (1200?C) and (2) for blade material (1000?C). The model can be used to analyze other materials that support higher temperatures helping in the development of new materials for thermal barrier coatings.

Two-channel model for ultralow thermal conductivity of crystalline Tl3VSe4

Science ◽  
2018 ◽  
Vol 360 (6396) ◽  
pp. 1455-1458 ◽  
Author(s):  
Saikat Mukhopadhyay ◽  
David S. Parker ◽  
Brian C. Sales ◽  
Alexander A. Puretzky ◽  
Michael A. McGuire ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Random Walk ◽  
Specific Heat ◽  
Thermal Barrier Coatings ◽  
Lattice Thermal Conductivity ◽  
Channel Model ◽  
Disordered Materials ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Transport Component

Solids with ultralow thermal conductivity are of great interest as thermal barrier coatings for insulation or thermoelectrics for energy conversion. However, the theoretical limits of lattice thermal conductivity (κ) are unclear. In typical crystals a phonon picture is valid, whereas lowest κ values occur in highly disordered materials where this picture fails and heat is supposedly carried by random walk among uncorrelated oscillators. Here we identify a simple crystal, Tl3VSe4, with a calculated phonon κ [0.16 Watts per meter-Kelvin (W/m-K)] one-half that of our measured κ (0.30 W/m-K) at 300 K, approaching disorder κ values, although Raman spectra, specific heat, and temperature dependence of κ reveal typical phonon characteristics. Adding a transport component based on uncorrelated oscillators explains the measured κ and suggests that a two-channel model is necessary for crystals with ultralow κ.

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