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1 Journal of Achievements in Materials and Manufacturing Engineering

1 2008

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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

2008

Vol. 30, nr 2

115-120

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.