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Effect of the microstructure of EB-PVD thermal barrier coatings on the thermal conductivity and the methods to reduce the thermal conductivity

Altun O., Boke Y.E.

Archives of Materials Science and Engineering

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2009

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Vol. 40, nr 1

47-52

EN

Purpose: The goal of the paper is to evaluate the effect of the microstructure of EB-PVD thermal barrier coatings on the thermal conductivity and the methods to reduce the thermal conductivity. Design/methodology/approach: In this study, the effect of microstructure of the coating to the thermal conductivity of EB-PVD TBCs and the methods to reduce the thermal conductivity of these coatings have been investigated. Findings: Microstructure of the EB-PVD coating - it is found that they are formed in two different structure and microstructural characteristics and they are different from each other. Practical implications: Nowadays, selection of materials for usage purpose is getting important because of new high technologic developments. Especially for the parts operating at high temperatures, materials which have low thermal conductivity and high mechanical resistance are preferred. Thermal Barrier Coatings (TBCs) are used in aerospace, diesel engine and power plant technologies due to porous structures and low thermal conductivity. Generally these coatings are applied by two methods, Electron Beam-Plasma Vapour Deposition (EB-PVD) and Atmospheric Plasma Spray (APS). Originality/value: This paper reviews the current status of EB-PVD thermal barrier coatings technology and investigation to reduce the thermal conductivity in future generations of EB-PVD thermal barrier coatings.

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Problems for determining the thermal conductivity of TBCs by laser-flash method

Altun O., Erhan Boke Y., Kalemtas A.

Journal of Achievements in Materials and Manufacturing Engineering

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2008

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Vol. 30, nr 2

115-120

EN

Purpose: The purpose of this paper was to investigate the parameters which effect the results of determining the thermal conductivity of thermal barrier coatings (TBCs) by laser-flash method. Design/methodology/approach: The air plasma-spray (APS) technique was used to deposition of two- and three-layered samples. Two-layered samples were composed of metal substrate (321 stainless steel), and ceramic top coat (8YSZ). Three-layered samples were composed of metal substrate (321 stainless steel), bond coat (NiCrAlY) and top coat (8YSZ). Thermal diffusivity of each layer have been measured in the temperature range from room temperature (RT) to 900° C by laser-flash method. The thermal conductivity was calculated with respect to density, specific heat and diffusivity of the materials. Findings: Obtained results show that the specific heat, density and thicknesses of metal substrate, bond coat and top coat play important role in the thermal conductivity measurement. Research limitations/implications: To obtain the correct results in laser-flash technique thickness, density, and cp of the materials are needed to be measured accurately and surface smoothness of samples should be provided sensitively. Errors in these parameters cause high deviations in measurements. Practical implications: It has been aimed offer an insight into the experimental determination of thermal conductivity of layered TBC system which are used in high technologic applications. Originality/value: Laser-flash method is the most widely used experimental technique to determine the thermal conductivity of APS TBCs at high temperatures. The research contributes to better understanding and recognition the importance of sample preparation in laser-flash method.

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Effect of the microstructure of EB-PVD thermal barrier coatings on the thermal conductivity and the methods to reduce the thermal conductivity

Altun O., Boke Y. E.

Archives of Materials Science

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2008

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Vol. 29, nr 1-2

7-15

EN

Nowadays, the selection of the materials for usage aim is getting important because of the new high technologic developments. Especially for the parts operating at high temperatures, the materials which have low thermal conductivity and high mechanical resistance are preferred. Thermal Barrier Coatings (TBCs) are used in aerospace, diesel engine and power plant technologies due to porous structures and low thermal conductivity. Generally these coatings are applied by two methods, Electron Beam-Plasma Vapor Deposition (EB-PVD) and Atmospheric Plasma Spray (APS). EBPVD method provides the advantages of superior strain and thermal shock tolerant due to its columnar microsturucture. However this columnar structure increases the thermal conductivity of the coating, so this is an undesired property with regard to heat transfer. In this study, the effect of microstructure of the coating to the thermal conductivity of EB-PVD TBCs and the methods to reduce the thermal conductivity of these coatings have been investigated.