**4. Conclusions**

The microstructure, phase transformation and mechanical properties of PS–PVD YSZ TBCs have been examined before and after exposure at 1200–1600 ◦C for 24 h and at 1550 ◦C for 20–100 h in air. PS–PVD TBCs showed a typical columnar structure with porosity between the individual columns before thermal exposure. Conclusions are summarized as follows:

• After thermal exposure, the columnar structure degraded and micro pores were generated in the columns, resulting in a close contact of columns as a result of sintering effect.


**Author Contributions:** Conceptualization, Z.C. and S.T.; Data Curation, Z.C., X.Z., H.Z., Y.Z. and J.N.; Formal Analysis, Z.C. and F.S.; Writing—Original Draft Preparation, Z.C.; Writing—Review & Editing, J.Y. and S.T.

**Funding:** This research was funded by Fundamental Research of Aero-engine and Combustion Gas Turbine Major Special Project (No. 2017-VI-0010-0082), National Natural Science Foundation of China (NSFC) (No. 51701235), Science and Technology Innovation of Shanghai (No. 18511108702) and Natural Science Foundation of Shanghai (No. 17ZR1412200).

**Conflicts of Interest:** The authors declare no conflict of interest.
