Development of Novel Functionally Graded Al2O3-Lanthanum Hexaaluminate Ceramics for Thermal Barrier Coatings

2009 ◽  
Vol 631-632 ◽  
pp. 97-102 ◽  
Author(s):  
Zahra Negahdari ◽  
Monika Willert-Porada ◽  
Florian Scherm
Keyword(s):  
Mechanical Properties ◽  
Thermal Conductivity ◽  
Thermal Barrier Coatings ◽  
Structural Reliability ◽  
Functionally Graded ◽  
Thermal Barrier ◽  
Composite Ceramics ◽  
Barrier Coatings ◽  
The One ◽  
Lanthanum Hexaaluminate

Lanthanum hexaaluminate (LHA) has superior thermo-chemical stability at temperatures higher than 1000 °C and is a promising competitor to Y-ZrO2-based thermal barrier coatings (TBCs). The yet unresolved problem is control of microstructure of high LHA content ceramics and adjustment of porosity upon, to arrive at a material exhibiting low thermal conductivity at high temperature combined with structural reliability. Therefore, a functionally graded alumina/lanthanum hexaaluminate (FGLHA) with a gradient in composition was developed. The thermal diffusivity and thermal conductivity of FGLHA were compared with the one of the monolithic composite ceramics. The alumina-rich composites showed excellent mechanical properties whereas the LHA-rich composites presented lower thermal conductivity.

scholarly journals High-entropy Rare-earth Zirconate Ceramics With Low Thermal Conductivity for Advanced Thermal Barrier Coatings

2021 ◽  
Author(s):  
Baosehng Xu ◽  
Debao LIU ◽  
Baolu SHI ◽  
Liyan GENG ◽  
Yiguang WANG ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Thermal Conductivity ◽  
Rare Earth ◽  
Thermal Barrier Coatings ◽  
High Speed ◽  
Solid State Reaction Method ◽  
Thermal Barrier ◽  
Excellent Thermal Stability ◽  
Barrier Coatings ◽  
High Entropy

Abstract In this work, we have successfully fabricated a novel high-entropy rare-earth zirconate (La0.2Nd0.2Sm0.2Gd0.2Yb0.2)2Zr2O7 (5RE2Zr2O7) ceramics and its counterparts by using a new high-speed grinding strategy combined with typical solid-state reaction method. The X-ray diffraction (XRD) and Raman spectroscopy analysis indicated that the as-prepared 5RE2Zr2O7 ceramics performed single-phase defect fluorite-type structures with highly sintering resistant and excellent thermal stability. The possibility of formation of 5RE2Zr2O7 was verified via first-principles calculations. Meanwhile, the phase structure, thermophysical and mechanical properties of the samples were systematically investigated. The results showed that the 5RE2Zr2O7 ceramics demonstrated lower thermal conductivity (0.9-1.72 W·m-1·K-1) and higher thermal expansion coefficients (10.9 × 10-6 K-1 at 1273 K) than its counterparts. Furthermore, the 5RE2Zr2O7 ceramics presented outstanding mechanical properties including large Young’s modulus (186-257 GPa), higher fracture toughness and lower brittleness index than that of YSZ. Therefore, in view of various excellent properties, the as-prepared 5RE2Zr2O7 ceramics possess great potential for applications in the field of thermal barrier coatings.

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.

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