In this study, defects generated in the YSZ coating layer of the IN738LC turbine blade are investigated using an optical microscope and SEM/EDS. The blade YSZ coating layer is composed of a Y-Zr component top coat layer and a Co component bond coat layer. A large amount of Cr/Ni component that diffused from the base is also measured in the bond coat. The blade hot corrosion is concentrated on the surface of the concave part, accompanied by separation of the coating layer due to the concentration of combustion gas collisions here. In the top coating layer of the blade, cracks occur in the vertical and horizontal directions, along with pits in the top coating layer. Combustion gas components such as Na and S are contained inside the pits and cracks, so it is considered that the pits/cracks are caused by the corrosion of the combustion gases. Also, a thermally grown oxide (TGO) layer of several μm thick composed of Al oxide is observed between the top coat and the bond coat, and a similar inner TGO with a thickness of several μm is also observed between the bond coat and the matrix. A PFZ (precipitate free zone) deficient in γ' (Ni3Al) forms as a band around the TGO, in which the Al component is integrated. Although TGO can resist high temperature corrosion of the top coat, it should also be considered that if its shape is irregular and contains pore defects, it may degrade the blade high temperature creep properties. Compositional and microstructural analysis results for hightemperature corrosion and TGO defects in the blade coating layer used at high temperatures are expected to be applied to sound YSZ coating and blade design technology.

Abstract
1. 서 론
2. 실험 방법
3. 결과 및 고찰
    3.1. 블레이드 팁 및 코팅층 구조
    3.2. Top Coat 결함
    3.3. TGO (thermally grown oxide) 생성
    3.4. Inner TGO 생성
4. 결 론
Acknowledgment
References

• 최병학(강릉원주대학교 신소재금속공학과) | Byung Hak Choe (Department of Metal and Materials Engineering, Gangneung-Wonju National University, Gangneung 25457, Republic of Korea) Corresponding author
• 한성희(강릉원주대학교 신소재금속공학과) | Sung Hee Han (Department of Metal and Materials Engineering, Gangneung-Wonju National University, Gangneung 25457, Republic of Korea)
• 김대현(강릉원주대학교 신소재금속공학과) | Dae Hyun Kim (Department of Metal and Materials Engineering, Gangneung-Wonju National University, Gangneung 25457, Republic of Korea)
• 안종기(한화에어로스페이스) | Jong Kee Ahn (Hanwha Aerospace, Sungnam 13488, Republic of Korea)
• 이재현(창원대학교 신소재공학부) | Jae Hyun Lee (School of Material Science & Engineering, Changwon National Univ., Changwon 51140, Republic of Korea)
• 최광수(국립과학수사연구원 법공학부 안전과) | Kwang Su Choi (Forensic Safety Division, National Forensic Service, Wonju 26460, Republic of Korea)