| 초록 |
The time-dependent degradation of first-stage blades for gas turbine was investigated. The specimens were prepared from the operating facilities in the combined-cycle plant. A microstructural investigation showed that the degradation condition in blade depends on position in airfoil region. In the case of TBC (Thermal Barrier Coating) showed that exposure to the environment increased thickness of TGO (Thermally Grown Oxide) and β depletion region, and then debonding and spallation of TBC (Thermal Barrier Coating) occurred finally. In the case of substrate, Ni-based superalloy, the shape and size of γ` were changed with increasing operating time. Especially, in the leading and trailing edges of blades, the size of γ` was bigger and the shape was more elliptic than other region. It can be thought that the leading and trailing edges of blades can be the starting point of degradation in first-stage blades. Creep tests were also carried out to know the effect of microstructural degradation such as γ ' coarsening, formation of TCP phase, carbide dissolution and misorientation angles with neighbouring grains. Finally, we tried to correlate creep lifetime with misorientation angles by EBSD. |
