Korean Journal of Materials Research (한국재료학회지)

Materials Research Society of Korea (한국재료학회)
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Hot Corrosion and Thermally Grown Oxide Formation on the Coating of Used IN738LC Gas Turbine Blade

사용된 IN738LC 가스 터빈 블레이드 코팅층의 고온 부식 및 Thermally Grown Oxide 형성 거동

  • Choe, Byung Hak (Department of Metal and Materials Engineering, Gangneung-Wonju National University) ;
  • Han, Sung Hee (Department of Metal and Materials Engineering, Gangneung-Wonju National University) ;
  • Kim, Dae Hyun (Department of Metal and Materials Engineering, Gangneung-Wonju National University) ;
  • Ahn, Jong Kee (Hanwha Aerospace) ;
  • Lee, Jae Hyun (School of Material Science & Engineering, Changwon National Univ.) ;
  • Choi, Kwang Su (Forensic Safety Division, National Forensic Service)
  • 최병학 (강릉원주대학교 신소재금속공학과) ;
  • 한성희 (강릉원주대학교 신소재금속공학과) ;
  • 김대현 (강릉원주대학교 신소재금속공학과) ;
  • 안종기 (한화에어로스페이스) ;
  • 이재현 (창원대학교 신소재공학부) ;
  • 최광수 (국립과학수사연구원 법공학부 안전과)
  • Received : 2022.01.26
  • Accepted : 2022.04.12
  • Published : 2022.04.27
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Abstract

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 ㎛ 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 ㎛ 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 high-temperature 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.

Keywords

Acknowledgement

This work was supported by "Power Generation & Electricity Delivery (No. 20193310100090)" of the Korea Institute of Energy Technology Evaluation and Planning from the Ministry of Trade, Industry and Energy, Republic of Korea.

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