| Title |
Damage Behavior and Creep-Rupture Characteristics of a Service-Exposed First-Stage Gas Turbine Blade Operated under Flexible Operating Conditions |
| Authors |
김영대(Youngdae Kim) ; 송인환(Inhwan Song) ; 정진성(Jinesung Jung) ; 김윤진(Yunjin Kim) ; 강병연(Byeongyeon Kang) |
| DOI |
https://doi.org/10.3365/KJMM.2026.64.10.928 |
| ISSN |
1738-8228(ISSN), 2288-8241(eISSN) |
| Keywords |
Creep; Gas turbine blade; Ni-based superalloy; Service degradation; Thermal barrier coating |
| Abstract |
Recently, the operating pattern of industrial gas turbines has increasingly shifted from conventional base-load operation toward cyclic start-stop operation due to the growing penetration of renewable energy into the power grid. Under such flexible operating conditions, localized damage modes associated with repeated thermal and mechanical loading may become increasingly important in addition to conventional creep-dominant degradation. In this study, the degradation and damage characteristics of service-exposed first-stage blades from an F-class gas turbine, manufactured from a single-crystal Ni-based superalloy, were investigated. The blades experienced approximately 17,462 equivalent operating hours (EOH) and 851 equivalent starts (ES). Visual inspection, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), coating characterization, microstructural analysis, and stress-rupture testing were conducted to evaluate the service-induced degradation. Multiple radial and tangential cracks were observed in the fillet region, whereas coating delamination was mainly found near the trailing-edge regions at the airfoil tip and bottom. SEM-EDS mapping revealed Al-rich oxide layers near the crack surface and Cr- and Ti-rich oxides inside the cracks, indicating that internal oxidation occurred during crack development under cyclic start-stop operating conditions. In contrast, severe creep-dominant degradation such as extensive γ' rafting and creep void formation was not observed in the fillet crack region. The thermal barrier coating (TBC) system remained relatively stable at the examined locations, with TGO thicknesses below approximately 3.5 μm. The Larson-Miller parameter (LMP)-based stress-rupture evaluation indicated that the blades retained substantial creep-rupture resistance without evidence of severe creep-dominant degradation. In contrast, localized cracking accompanied by internal oxidation was prominently observed in the fillet region under ES-dominant cyclic start-stop operation. These results suggest that integrity assessment of service-exposed gas turbine blades operated under flexible operating conditions should consider localized crack-related damage in addition to conventional creep-dominant degradation. |