Finite element simulation of residual stress of double-ceramic-layer La2Zr2O7/8YSZ thermal barrier coatings using birth and death element technique
TL;DR: In this paper, the residual stress of double-ceramic-layer (DCL) La2Zr2O7/8YSZ thermal barrier coatings (TBCs) fabricated by atmospheric plasma spraying (APS) was calculated by finite element simulation using birth and death element technique.
About: This article is published in Computational Materials Science.The article was published on 2012-02-01. It has received 90 citations till now. The article focuses on the topics: Residual stress & Stress concentration.
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TL;DR: In this paper, the authors investigated the thermal shock behavior of three as-sprayed TBCs at 1000°C and 1200°C with NiCrAlY as the bond coat, and the results indicated that the thermal cycling lifetime of the double-ceramic-layer (DCL) TBC is longer than that of SCL 8YSZ TBC due to the fact that the DCL LZ/8YSZ further enhance the thermal insulation effect, improve the sintering resistance ability and relieve the thermal mismatch between the ceramic layer and the metallic layer at
166 citations
TL;DR: In this article, the authors reviewed the research progress of the finite element modeling (FEM) on the study of the thermal insulation and associated failure problems of the TBCs and proposed a solution method based on the thermal-mechanical coupled technique.
Abstract: To understand the thermal insulation and failure problems of the thermal barrier coatings (TBCs) deeply is vital to evaluate the reliability and durability of the TBCs. Actually, experimental methods can not reflect the real case of the TBCs during its fabrication and service process. Finite element modeling (FEM) play an important role in studying these problems. Especially, FEM is very effective in calculating the thermal insulation and the fracture failure problems of the TBCs. In this paper, the research progress of the FEM on the study of the thermal insulation and associated failure problems of the TBCs has been reviewed. Firstly, from the aspect of the investigation of the heat insulation of the TBCs, the thermal analysis via FEM is widely used. The effective thermal conductivity, insulation temperature at different temperatures of the coating surface considering the thermal conduct, convection between the coating and the environment, heat radiation at high temperature and interfacial thermal resistance effect can be calculated by FEM. Secondly, the residual stress which is induced in the process of plasma spraying or caused by the thermal expansion coefficient mismatch between the coating and substrate and the temperature gradient variation under the actual service conditions can be also calculated via FEM. The solution method is based on the thermal–mechanical coupled technique. Thirdly, the failure problems of the TBCs under the actual service conditions can be calculated or simulated via FEM. The basic thought is using the fracture mechanic method. Previous investigation focused on the location of the maximum residual stress and try to find the possible failure positions of the TBCs, and to predict the possible failure modes of the TBCs. It belonged to static analysis. With the development of the FEM techniques, the virtual crack closure technique (VCCT), extended finite element method (XFEM) and cohesive zone model (CZM) have been used to simulate the crack propagation behavior of the TBCs. The failure patterns of the TBCs can be monitored timely and dynamically using these methods and the life prediction of the TBCs under the actual service conditions is expected to be realized eventually.
135 citations
TL;DR: In this article, double-layered TBCs with YSZ as intermediate layer and pyrochlore as the top ceramic layer have been proposed, and the results showed that the double and triple layers had a longer thermal cyclic life compared to the single layer TBC.
Abstract: 7–8 wt.% yttria stabilized zirconia (YSZ) is the standard ceramic top coat material used in gas turbines to insulate the underlying metallic substrate. However, at higher temperatures (> 1200 °C), phase stability and sintering becomes an issue for YSZ. At these temperatures, YSZ is also susceptible to CMAS (calcium magnesium alumino silicates) infiltration. New ceramic materials such as pyrochlores have thus been proposed due to their excellent properties such as lower thermal conductivity and better CMAS attack resistance compared to YSZ. However, pyrochlores have inferior thermo mechanical properties compared to YSZ. Therefore, double-layered TBCs with YSZ as the intermediate layer and pyrochlore as the top ceramic layer have been proposed. In this study, double layer TBC comprising gadolinium zirconate (GZ)/YSZ and triple layer TBC (GZdense/GZ/YSZ) comprising relatively denser GZ top layer on GZ/YSZ were deposited by suspension plasma spray. Also, single layer 8YSZ TBC was suspension plasma sprayed to compare its functional performance with the multi-layered TBCs. Cross sections and top surface morphology of as sprayed TBCs were analyzed by scanning electron microscopy (SEM). XRD analysis was done to identify phases formed in the top surface of as sprayed TBCs. Porosity measurements were made using water intrusion and image analysis methods. Thermal diffusivity of the as sprayed TBCs was measured using laser flash analysis and thermal conductivity of the TBCs was calculated. The multi-layered GZ/YSZ TBCs were shown to have lower thermal conductivity than the single layer YSZ. The as sprayed TBCs were also subjected to thermal cyclic testing at 1300 °C. The double and triple layer TBCs had a longer thermal cyclic life compared to YSZ. The thermo cycled samples were analyzed by SEM.
77 citations
TL;DR: In this article, a finite element model was developed for a turbine blade with thermal barrier coatings to investigate its failure behavior under cyclic thermal loading, and dangerous regions in ceramic coating were determined in terms of the maximum principal stress criterion.
70 citations
TL;DR: In this article, a multilayered coating approach is attempted in order to overcome these drawbacks at higher temperatures, and compared with the single layer yttria stabilized zirconia (YSZ) at temperatures above 1200 °C.
Abstract: Rare earth zirconates have lower thermal conductivity, better phase stability, improved sintering resistance and CMAS (calcium magnesium alumino silicates) infiltration resistance than yttria stabilized zirconia (YSZ) at temperatures above 1200 °C. However, their lower fracture toughness and lower coefficient of thermal expansion (CTE) compared to YSZ lead to premature coating failure. In order to overcome these drawbacks at higher temperatures, a multilayered coating approach is attempted in this study and compared with the single layer YSZ. Suspension plasma spray of single layer YSZ, single layer gadolinium zirconate (GZ) and double layer GZ/YSZ was carried out. Additionally, a triple layer coating system, with denser gadolinium zirconate on top of the GZ/YSZ system was sprayed to impart an added functionality of sealing the TBC from CMAS infiltration. Microstructural analysis was done using scanning electron microscopy and optical microscopy. Columnar microstructure with vertical cracks was observed. XRD analysis was used to identify phases formed in the as sprayed TBC samples. Porosity measurements were done using water impregnation method. Thermal diffusivity of single and multi-layered coatings was obtained by laser flash analysis and thermal conductivity of the coating systems was determined. It was found that the thermal conductivity of single layer gadolinium zirconate was lower than YSZ and that the thermal conductivity of multilayered systems were between their respective single layers. The single (YSZ), double (GZ/YSZ) and triple (GZ dense/GZ/YSZ) layer TBCs were subjected to thermal cyclic fatigue (TCF) test at 1100 °C and 1200 °C. It was observed that the single layer YSZ had lowest TCF life whereas the triple layer TBC had highest TCF life irrespective of test temperature.
69 citations
References
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TL;DR: In this article, the structure, properties, and failure mechanisms of thermal barrier coatings (TBCs) are reviewed, together with a discussion of current limitations and future opportunities.
Abstract: Hundreds of different types of coatings are used to protect a variety of structural engineering materials from corrosion, wear, and erosion, and to provide lubrication and thermal insulation. Of all these, thermal barrier coatings (TBCs) have the most complex structure and must operate in the most demanding high-temperature environment of aircraft and industrial gas-turbine engines. TBCs, which comprise metal and ceramic multilayers, insulate turbine and combustor engine components from the hot gas stream, and improve the durability and energy efficiency of these engines. Improvements in TBCs will require a better understanding of the complex changes in their structure and properties that occur under operating conditions that lead to their failure. The structure, properties, and failure mechanisms of TBCs are herein reviewed, together with a discussion of current limitations and future opportunities.
3,548 citations
TL;DR: In this paper, the authors present relationships between the durability, the governing material properties and salient morphological features of thermal barrier coatings and show that the failure is ultimately connected to the large residual compression in the thermally grown oxide through its roles in amplifying imperfections near the interface.
2,050 citations
TL;DR: In this article, the basic properties of ceramic materials for thermal barrier coatings are summarized, showing that they are more resistant to oxidation, corrosion and wear, as well as being better thermal insulators.
Abstract: This paper summarizes the basic properties of ceramic materials for thermal barrier coatings. Ceramics, in contrast to metals, are often more resistant to oxidation, corrosion and wear, as well as being better thermal insulators. Except yttria stabilized zirconia, other materials such as lanthanum zirconate and rare earth oxides are also promising materials for thermal barrier coatings.
1,789 citations
TL;DR: In this article, the double-layer concept, a method to overcome the limited toughness of new TBC materials, is discussed, and an overview is tried on different new materials covering especially doped zirconia, pyrochlores, perovskites, and aluminates.
Abstract: During the last decade a number of ceramic materials, mostly oxides have been suggested as new thermal barrier coating (TBC) materials. These new compositions have to compete with the state-of-the-art TBC material yttria stabilized zirconia (YSZ) which turns out to be difficult due to its unique properties. On the other hand YSZ has certain shortcomings especially its limited temperature capability above 1200 °C which necessitates its substitution in advanced gas turbines. In the paper an overview is tried on different new materials covering especially doped zirconia, pyrochlores, perovskites, and aluminates. Literature results and also results from our own investigations will be presented and compared to the requirements. Finally, the double-layer concept, a method to overcome the limited toughness of new TBC materials, will be discussed.
884 citations
TL;DR: In this paper, the authors highlight critical R&D needs for advanced TBC systems with a special focus on reduced thermal conductivity and life prediction needs, and highlight the need for reliable and predictable TBC performance.
443 citations