Fumio Ono

Evaluation of the Accuracy of Young’s Moduli of Thermal Barrier Coatings Determined on the Basis of Composite Beam Theory

The Young’s modulus of thermal barrier coating (TBC) is an important mechanical property as it is required for calculating the parameters of material mechanics in the TBC system. In this study, we investigated the accuracy of the Young’s modulus of TBC calculated using the composite beam theory. Generally, both the Young’s modulus and the thickness of TBC are approximately one order of magnitude lower than those of the substrate. Consequently, the Young’s modulus of the TBC calculated on the basis of the composite beam theory is considerably sensitive to experimental errors. In order to improve the accuracy of the composite beam method, methods that make use of coating strain, substrate strain, or deflection were compared. The methods with low sensitivity to experimental errors were determined through sensitivity analysis. Further, the effectiveness of the methods with low sensitivity was confirmed experimentally.

Thermal Diffusivity Measurement for Thermal Spray Coating Attached to Substrate Using Laser Flash Method

Ceramic-based thermal barrier coatings are used as heat and wear shields of gas turbine blades. There is a strong need to evaluate the thermal conductivity of coating for thermal design and use. The thermal conductivity of a bulk material is obtained as the product of thermal diffusivity, specific heat capacity, and density above room temperature in many cases. Thermal diffusivity and thermal conductivity are unique for a given material because they are sensitive to the structure of the material. Therefore, it is important to measure them in each sample. However it is difficult to measure the thermal diffusivity and thermal conductivity of coatings because coatings are attached to substrates. In order to evaluate the thermal diffusivity of a coating attached to the substrate, we have examined the laser flash method with the multilayer model on the basis of the response function method. We carried out laser flash measurements in layered samples composed of a CoNiCrAlY bond coating and a 8YSZ top coating by thermal spraying on a Ni-based superalloy substrate. It was found that the procedure using laser flash method with the multilayer model is useful for the thermal diffusivity evaluation of a coating attached to a substrate. # 2011 The Japan Society of Applied Physics

Thermal Diffusivity Measurements of the Layered Materials by the Laser Flash Method

Ceramics-based thermal barrier coatings are used as heat and wear shields of blades of gas turbine. There are strong needs to evaluate thermophysical properties of coatings, such as thermal conductivity, thermal diffusivity and heat capacity of them. Since coatings are attached on substrates, it is not easy to measure these properties separately. In order to evaluate the thermal diffusivity of coating attached on substrate, we have tried to apply the multi-layer model based on the response function method and established a procedure for the measurement by the laser flash method. We verified the procedure by the measurements from room temperature to about 1000 K for two-layer ceramics sample prepared by the doctor blade tape casting method. The thermally sprayed CoNiCrAlY coating on the SUS304 substrate was also used for verification. The thermal diffusivity of coating attached on substrate approximately agreed with that of the single-layer coating removed from substrate. In the case of the ceramics sample, the thermal diffusivity of the coating including the interfacial thermal resistance determined within about 20 % uncertainty. We compared the laser flash measurement signals of the samples prepared by the thermal spraying with variant thickness and found the difference among them. It was found that the procedure has enough resolution to detect the heat shield effect caused by the change with about 200 m in thickness. The result shows that the procedure and analysis were practically effective for the thermal diffusivity estimation of coating attached on the substrate without remove from substrate.

Constitution of ISO and JIS for Method of Tensile Testing of Superplastic Materials

Method for tensile testing of superplastic materials had been standardized as ISO 20032: 2007, which is based on JIS, Japanese Industrial Standard, H 7501 and H 7505. These standards specify the test specimens of S-and R-types. Recently, the working group organized by Osaka Science and Technology Center, Japan, proposed a revised version of ISO 20032 with several corrections. After systematic review and voting at ISO/TC (Mechanical Testing of Metals) 164/SC2 (Ductility Testing), the second edition of ISO 20032 was published in 2013. Now, a working group has been set for proposing a revised version of JIS corresponding to ISO 20032: 2013. This paper reports the constitution process of these ISO and JIS standards.

Thermal Cycle Properties of Plasma Sprayed Oxidation-Resistant Metallic Coatings

Thermal cycle resistance of Ni-20Cr, Ni-50Cr and CoNiCrAlY coatings produced by air plasma spraying was investigated according to Japanese Industrial Standard Testing method for thermal cycle resistance of oxidation resistant metallic coatings (JIS H 8452: 2008). The specimens were exposed to a cyclic heating and cooling regimen comprised of up to 100 cycles of 10 hours heating to 1000 °C or 1093 °C in air followed by cooling. The thermal cycle resistance of oxidation-resistant metallic coatings was found to depend strongly on testing temperature and on the chemical composition of the coating materials. In thermal cycle testing at 1000 °C, no remarkable failure was observed in any specimen. However, in thermal cycle testing at 1093 °C, spalling was observed over the entire surface of the Ni-20Cr coating, although the Ni-50Cr and the CoNiCrAlY coatings exhibited excellent thermal cycle resistance even upon exposure to 100 thermal cycles. The CoNiCrAlY coating showed mass gain with increasing number of thermal cycles due to preferential oxidation between thermal spray particle splats. Furthermore, the failure behavior of specimens was investigated in detail by SEM, XRD, EPMA, etc.