Influence of thermal history on Young's modulus of thermal barrier coating

In previous study, we developed the new method for measuring the in-plane Young's modulus at elevated temperatures of thermal barrier coatings (TBCs), which consist of metallic bond coats (BCs) and ceramic top coats (TCs) on formed on substrates, by flexural resonance. This fundamental procedures consist of the measurement of the resonance frequencies at elevated temperatures and of calculations according to the theory of flexural vibration for a composite beam. Using this method, the influence of the thermal history on the Young's modulus of TBC was investigated. BC and TBC specimens were prepared by thermal spraying and some specimens were heat-treated in air prior to the measurement. The Young's modulus was measured from room temperature up to 1000ºC in air. The measurement was repeated up to three times for some specimens. For another specimens, the change in the Young's modulus was measured while holding at 1000 ºC for 25 h. It was found that the Young's modulus of the TC in as-sprayed TBC increases with increasing the number of measurements. On the other hand, the TC in heat-treated TBC exhibited the stable Young's modulus.