| Abstract: |
Abstract: Gas thermal-shock experiment of thermal barrier coating (TBCs) was carried out in air up to 1250 in order to simulate the thermal cycling process of the engine blades during the start heating and shut cooling. The growth of thermal growth oxide layer (TGO) and microstructure evolution of YSZ layer was investigated systematically by impedance spectroscopy testing and SEM observation. Results indicated that the thickness of TGO layer raised when increased the frequency of thermal cycling, with the impedance response of middle frequencies were more and more remarkable. Meanwhile, initiation and growth of micro-cracks occurred in YSZ layer during the gas thermal-shock experiment. The corresponding impedance of micro-cracks in YSZ layer after 100 cycles was similar to the as-sprayed sample, meaning micro-cracks occurred in short time could be healing since the YSZ micro-cracks will be sintered in high temperature. But after 300 cycles, the impedance spectroscopy of YSZ layer were quite different to the as-sprayed sample, with the corresponding impedance of particle-gap of YSZ were more and more remarkable when prolong the thermal-shock times, indicating un-healing micro-cracks formed in the YSZ layer, which were maybe the main reason induce the failure of YSZ layer.
Key words: thermal cycling; impedance spectroscopy; thermal barrier coating; structure evolution
|
|
