K. Takagi, D. Kudo, A. Kawasaki, Tohoku university, Sendai, Japan; Y. Harada, Tocalo Co., Ltd., Akashi, Japan; M. Okazaki, Nagaoka University of Technology, Nagaoka, Japan
We are investigating the feasibility of measuring thermal expansion coefficient (CTE) of free-standing thermal barrier coatings with a practical thickness of several hundred micrometers by mean of a widespread thermomechanical analysis toward its industrial standardization. First of all, this study conducted the preliminary investigation for the accurate measurement of thin samples with dense yettria-stabilized zirconia (YSZ) ceramics. With a sample supporting jig and proper conditions, even the usual thermomechanical analysis could give the accurate CTE values of thin samples down to 0.3mm thick. Also it showed good reproducibility with small measurement error less than 5%. In actual, this modified method could provide the reasonable CTE values of plasma-sprayed YSZ samples with thickness of >0.3mm. Further investigation with this method found a slight monotonic decrease in the CTE with annealing. This decrease was estimated to arise from the continuous change of microstructure which still went on even after saturation of sintering shrinkage. All the results demonstrated the present method to be available for the industrial standard.
Summary: This study investigated the feasibility of thermal expansion evaluation of thin thermal barrier coatings utilizing a widespead method for its standardization. As a result, we demonstrated that the thermomechanical analysis with the sample supporting jig and the proper pushing load was able to accrately evaluate thermal expansion behavior of thin coating samples with a thickness larger than 0.3mm. In addition, by mean of this method, the CTE of plasma-sprayed coating was revealed to gradually decrease with anneling time.
