In this study, the effects of bond coat compositions with and without 0.5 mass.% Y on oxidation behaviour were investigated. Oxidation behaviour was accessed in terms of The TGO structure and growth kinetics. After isothermal oxidation tests, the TGO formed on Y-free CoNiCrAl coatings was composed mainly of alumina without the presence of Y-rich oxide and showed lower growth kinetics than that formed on conventional CoNiCrAlY coating. This result indicates that potential improvements to the bond coat oxidation behaviour can be achieved using Y-free bond coat compositions.

The thermal shock resistance of plasma-sprayed thermal barrier coatings (TBCs) with different top coats was investigated according to the Japanese Industrial Standard "Testing methods for thermal cycle and thermal shock resistance of thermal barrier coatings" (JIS H 8451:2008). Three types of ceramics powders, namely, Al 2 O 3 , 8 mass % Y 2 O 3 -stabilized ZrO 2 (YSZ) and La 2 Zr 2 O 7 (LZ) were used in the top-coat spray. After the specimens were subjected to a thermal shock, the tensile adhesive strength of the TBCs was measured and the thermal shock resistance as defined in JIS H8451 was determined. The thermal shock properties of the TBCs were found to depend strongly on the chemical composition of the top-coat material. For TBCs with Al 2 O 3 and LZ, the adhesive strength decreased with increasing thermal shock temperature difference (ΔT). On the other hand, little change in the adhesive strength was observed with increasing ΔT for YSZ TBC. From these results, the thermal shock resistance, ΔTc, was determined to be 480 °C for Al 2 O 3 , 680 °C for LZ and more than 880 °C for YSZ TBC. Furthermore, the influence of thermal shock on the adhesive strength of TBCs was investigated in detail through observations of cross-sectional microstructures and fracture surfaces after adhesive testing.

Thermal cycle resistance of Ni-20Cr, Ni-50Cr and CoNiCrAlY coatings manufactured by air plasma spraying was investigated according to a Japanese Industrial Standard "Testing method for thermal cycle resistance of oxidation resistant metallic coatings (JIS H 8452)” established in 2008. The specimens were exposed at 1000 °C and 1093 °C in air under cyclic heating and cooling condition up to 100 times. The thermal cycle resistance of oxidation-resistant metallic coatings was found to depend strongly on the testing temperature and the chemical composition of the coating materials. In the thermal cycle test at 1000 °C, the remarkable failure was not observed in any specimen. However, in the thermal cycle test at 1093 °C, although the Ni-20Cr coating caused the spalling on the whole surface of coating, the Ni-50Cr and the CoNiCrAlY coatings exhibited the excellent thermal cycle resistance even after applying the thermal cycles of 100 times, The CoNiCrAlY coating showed the mass gain with increasing the numbers of thermal cycle due to the preferential oxidation between the splats of the thermal spray particles. Furthermore, the failure behavior of specimens was investigated in detail by SEM, XRD and EPMA etc.

“Testing Method for Thermal Cycle and Thermal Shock Resistance of Thermal Barrier Coating (TBC)” is a Japanese Industrial Standard (JIS) newly established by the Minister of Economy, Trade, and Industry in 2008, after deliberations by Japanese Industrial Standards Committee, in accordance with the Industrial Standardization Law. The standard specifies a testing method that evaluates the spalling resistance of TBCs based on operating conditions in gas turbines. This paper provides an overview of the standard along with examples of its use.