**4. Conclusions and future directions**

Up to now, many testing techniques and characterization methods for stress among APS-prepared TBCs have been developed. The stress in the ceramic top coat, TGO and bond coat under various operating conditions were obtained. However, some topics, such as the measurement of the stress deep inside TBCs, the in-situ evaluation of the stress among TBCs applied on the profiled blade, and the real-time monitoring of the stress among TBCs under the complicated service environments have yet to be further studied. Thus, for the testing of stress among APS-prepared TBCs, the following aspects should be considered in the future:

