Estimation of Thermophysical Properties and Microstructure of Aged Thermal Barrier Coatings

2001 ◽  
Author(s):  
Tomoharu Fujii ◽  
Takeshi Takahashi
Keyword(s):  
Thermal Conductivity ◽  
Crystalline Structure ◽  
Plasma Spray ◽  
Thermophysical Properties ◽  
Thermal Barrier ◽  
Powder Size ◽  
Gas Temperature ◽  
Hot Gas ◽  
Heat Treated ◽  
Barrier Performance

A thermal barrier coating (TBC) is used for protecting hot gas path parts, and is useful for allowing the turbine inlet gas temperature to be increased. In order to quantitatively evaluate the performance of TBCs, the thermal conductivity of TBCs on the combustor of a gas turbine were measured. The results indicate that the thermal conductivity of age-deteriorated TBCs were higher than that of the as-sprayed TBC. This finding suggested that the thermal barrier performance of the TBC had deteriorated. When the thermal barrier performance of a TBC deteriorates, the temperature of the metal substrate rises, shortening the service life of hot gas path components. Accordingly, using experimental TBCs, laboratory-scale studies were performed to identify the causes of the deterioration of thermal barrier performance in TBCs. Six types of TBCs, prepared from six grades of plasma spray powder of yttria stabilized zirconia (YSZ), were tested. Average powder size, powder configuration, and percentage of yttria were the parameters of plasma spray powder taken to measure the thermophysical properties and carry out microstructural analyses on the as-sprayed TBCs and heat-treated TBCs. The results of the thermophysical property measurements indicate that the thermal barrier performance of heat-treated TBCs were two to three times greater than that of the as-sprayed TBCs. The results of the microstructural analyses revealed that the deterioration in performance was caused by changes occurring in the crystalline structure and the reduction of the non-contact area as in TBCs. The changes in thermal conductivity of TBCs were expressed as coefficients of porosity, crystalline structure, and heating time and temperature.

Development of Actual TBC Exposure Temperature Prediction Method

2004 ◽  
Author(s):  
Masahiko Morinaga ◽  
Tomoharu Fujii ◽  
Takeshi Takahashi
Keyword(s):  
Thermal Conductivity ◽  
Substrate Temperature ◽  
Gas Turbine ◽  
Co2 Laser ◽  
Infrared Camera ◽  
Thermal Barrier ◽  
Remaining Life ◽  
Hot Gas ◽  
Exposure Temperature ◽  
Barrier Performance

Gas turbines are being operated at ever-higher temperatures in order to increase their efficiency. As a result, thermal barrier technology to protect the gas turbine hot gas path parts from high-temperature combustion gas is becoming increasingly important, making it necessary to evaluate the thermal barrier performance of the thermal barrier coating (TBC) coated on these gas turbine hot gas path parts. Thermal barrier performance of the TBC deteriorates with the number of operating hours of the gas turbine. The degradation of TBC thermal barrier performance raises substrate temperature, and this rise in substrate temperature reduces the remaining life of the substrate. We proposed an effective nondestructive inspection (NDI) method to evaluate the thermal barrier performance of the TBC by infrared transient heating of the TBC surface. The temperature behavior closely correlated with the thermal barrier performance of the TBC. The results of numerical analysis and laboratory tests showed that the proposed NDI method was effective for evaluating the thermal barrier performance of TBC. So we developed NDI apparatus to inspect the thermal barrier performance of actual combustion liner TBC. In this NDI apparatus, the surface of the TBC was heated using a CO2 laser, and the temperature of the heated surface measured using an infrared camera. The CO2 laser and infrared camera were fixed, while the measured combustion liner was traversed continuously. The NDI apparatus developed enabled us to inspect the whole inner surface of an actual gas turbine combustion liner. We also showed the correlation with thermal conductivity of a virgin TBC, thermal conductivity of an inspected TBC, operating hours and TBC exposure temperature in our TBC thermophysical property study. The combination of this method and the NDI apparatus developed proved an effective way of clarifying the operating temperature of the hot gas path parts of the gas turbine. In this paper, we show a method for predicting actual gas turbine TBC exposure temperature, important when evaluating the remaining life of gas turbine substrate by the NDI apparatus developed and method of predicting TBC exposure temperature.

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.

Development of Operating Temperature Prediction Method Using Thermophysical Properties Change of TBC

2002 ◽  
Author(s):  
Tomoharu Fujii ◽  
Takeshi Takahashi
Keyword(s):  
Thermal Conductivity ◽  
Contact Area ◽  
Operating Temperature ◽  
Thermal Barrier ◽  
Conductivity Measurements ◽  
Temperature Prediction ◽  
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 non-contact area that exists inside TBCs [1]. This non-contact 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 non-contact 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 [2]. 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.

Thermophysical Properties of Samarium-Cerium Oxide for Thermal Barrier Coatings Application

2007 ◽  
Vol 336-338 ◽  
pp. 1773-1775 ◽  
Author(s):  
Chun Lei Wan ◽  
Wei Pan ◽  
Zhi Xue Qu ◽  
Ye Xia Qin
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Thermal Barrier Coatings ◽  
Thermophysical Properties ◽  
Ceramic Coating ◽  
Fluorite Structure ◽  
Yttria Stabilized Zirconia ◽  
Thermal Barrier ◽  
Stabilized Zirconia ◽  
Barrier Coatings

Sm0.4Ce0.6O1.8 specimen with a defective fluorite structure was synthesized and its thermophysical properties were characterized for thermal barrier coatings (TBCs) application. At high temperature, Sm0.4Ce0.6O1.8 exhibited much lower thermal conductivity than 7wt% yttria-stabilized zirconia (7YSZ)-the commonly used composition in current TBCs. Sm0.4Ce0.6O1.8 also possessed large thermal expansion coefficient, which could help reduce the thermal mismatch between the ceramic coating and bond coat.

Preparation and Thermophysical Properties of (La0.4Sm0.5Yb0.1)2(Zr0.7Ce0.3)2O7 Ceramic for Thermal Barrier Coatings

2008 ◽  
Vol 368-372 ◽  
pp. 1334-1336
Author(s):  
Ling Liu ◽  
Qiang Xu ◽  
Fu Chi Wang ◽  
Hong Song Zhang
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Rare Earth ◽  
Phase Composition ◽  
Thermal Barrier Coatings ◽  
Thermophysical Properties ◽  
Single Phase ◽  
Pyrochlore Structure ◽  
Thermal Barrier ◽  
Barrier Coatings

A complex rare-earth zirconate (La0.4Sm0.5Yb0.1)2(Zr0.7Ce0.3)2O7 powder for thermal barrier coatings (TBCs) was synthesized by coprecipitation method. The phase composition, microstructure and the thermophysical properties were investigated. XRD results revealed that single phase (La0.4Sm0.5Yb0.1)2(Zr0.7Ce0.3)2O7 with pyrochlore structure was prepared and the SEM result showed that the microstructure of the product was dense and no other phases existed among the particles. With the temperature increasing, the thermal expansion coefficient (CTE) of the ceramic increased, while the thermal conductivity decreased. The results indicated that CTE of the ceramic was slightly higher than that of La2Zr2O7 and the thermal conductivity of the ceramic was lower than that of La2Zr2O7. These results imply that (La0.4Sm0.5Yb0.1)2(Zr0.7Ce0.3)2O7 can be explored as the candidate material for the ceramic layer in TBCs system.

scholarly journals Experimental investigation of the relationship between thermal barrier coating structured porosity and homogeneous charge compression ignition engine combustion

2019 ◽  
Vol 22 (1) ◽  
pp. 88-108 ◽  
Author(s):  
Tommy Powell ◽  
Ryan O’Donnell ◽  
Mark Hoffman ◽  
Zoran Filipi ◽  
Eric H Jordan ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Plasma Spray ◽  
Homogeneous Charge Compression Ignition ◽  
Thermal Barrier ◽  
Compression Ignition ◽  
Compression Ignition Engine ◽  
Spray Process ◽  
Plasma Spray Process ◽  
Temperature Swing ◽  
Homogeneous Charge

Heat transfer has a profound influence on homogeneous charge compression ignition combustion. When a thermal barrier coating is applied to the combustion chamber, the insulating effect magnifies the wall temperature swing, decreasing heat transfer during combustion. This enables improvements in both thermal and combustion efficiency without the detrimental impacts of intake charge heating. Increasing the temperature swing requires coatings with lower thermal conductivity and heat capacity. A promising avenue for simultaneously decreasing both thermal conductivity and capacity is to increase the porosity fraction. A proprietary solution precursor plasma spray process enables discrete organization of the porosity structure, called inter-pass boundaries, which in turn produces a step-reduction in thermal conductivity for a given porosity level. In this investigation, yttria-stabilized zirconia is used to create four different thermal barrier coatings to study the potential of structured porosity as means of improving the “temperature swing” behavior in a homogeneous charge compression ignition engine. The baseline coating is “dense YSZ,” applied using a standard air-plasma spray process. Next, significant reductions of the thermal conductivity are achieved by utilizing the solution precursor plasma spray process to create inter-pass boundaries with a moderate overall porosity. Performance, efficiency, and emissions are compared against both a baseline configuration with a metal piston and an air-plasma spray “dense YSZ” coating. Experiments are carried out in a single-cylinder gasoline homogeneous charge compression ignition engine with exhaust re-induction. Experiments indicate that incorporating structured porosity into thermal barrier coatings produces tangible gains in combustion and thermal efficiencies. However, there is an upper limit to porosity levels acceptable for homogeneous charge compression ignition engine application because an elevated porosity fraction leads to excessive surface roughness and undesirable fuel interactions. Comparison of the coatings showed the best results with coating thickness of up to 150  µm. Thicker coatings led to slower surface temperature response and attenuated swing temperature magnitude.

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