## 3 Summary  
In this paper, a comprehensive review on superalloys and thermal barrier coating (TBC) used as gas turbine blade materials was performed. The manufacturing processes of superalloys have been developed in order of wrought process, conventional investment casting, directional solidification, and single crystal casting to cope with the improvement of the gas turbine inlet temperature. In case of single crystal alloys, Re and Ru were added to improve high temperature properties, and the generations are classified according to their amount of addition. However, considering the high cost of Re and Ru, recently, alloys having excellent high temperature properties with low Re and Ru are being developed. The composition and mechanical properties, especially tensile and creep properties  
Figure 17: (**a**) Zig-zag structured (reproduced with permission from [82], John Wiley and Sons, 2005) and (**b**) multilayered EB-PVD TBC (reproduced with permission from [83], Elsevier, 2000).  
of typical alloys in each casting process and generation were described. In order to improve creep property by reducing grain boundaries perpendicular to the stress axis, directional solidification in the [001] direction is induced by the Bridgman method. Only one grain remains while passing through the selector during directional solidification, which leads to single crystal. In addition, the applicability of various models to the life prediction of creep, which is a major cause of failure of blades, was examined. The TBC has a different microstructure depending on the manufacturing process (EB-PVD, CVD, APS), and the properties of each process and microstructure through SEM images were analyzed. The thermal barrier coating has a close relationship with durability and mechanical and thermal properties depending on the structure. As the thickness of the coating increases, the heat resistance performance increases, but due to the strong centrifugal force, there are limitations on the thickness that can be applied. The vertical crack inserted in the top coating reduces the stress caused by thermal expansion to improve the durability of the coating. The pores present in the coating play a role in reducing the thermal conductivity, but excessive amounts of pores may instead act as a cause of deteriorating mechanical properties. Phonons are the dominant factor in heat transfer of thermal barrier coating. Phonon scattering occurs due to cracks and pores, and the mean free path is shortened to lower thermal conductivity. If only the thermal conductivity is considered, the thermal barrier performance generated by the APS process is evaluated higher than that of the EB-PVD process. Since the thermal barrier coating has different structures and different mechanical and thermal properties, it is essential to select the appropriate process and to understand the coating structure when applying the thermal barrier coating or designing and developing a new thermal barrier coating. Overall, this review should serve as a reference for further enhancing the TET of the gas turbine for power plants or aviation in the future.  
Types of casting superalloys, properties, and manufacturing process, J.D. and B.-G.C.; Thermal barrier coating, S.W. and C.S.; Thermal properties of superalloy and thermal barrier coating, K.K. and W.K.; Creep life prediction model, C.L. and Y.C. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Agency for Defense Development (UD180043 GD).  
This work was supported by the UAV High Efficiency Turbine Research Center program of Defense Acquisition Program Administration and Agency for Defense Development.  
The authors declare no conflict of interest.