Abstract
A metallographic study is performed on a turbine blade from a land-based gas turbine in an industrial environment. The aim of the present work is to study the degradation of the turbine blade. The gas turbine has been running for about a month before shut down, which has established steady-state temperature gradients around the cooling holes, causing tensile stresses as a result of cold spots. The tensile stresses cause creep damage, which, in turn, plastically deformed the material, generating substructures and twins near the crack. Furthermore, by comparing substructures from the turbine blade formed during service with substructure from test bars subjected to thermal mechanical fatigue testing gives a strong indication that the damage of the turbine blade is not caused by thermal mechanical fatigue. The turbine blade is also exposed to chemical degradation by type I hot corrosion and internal corrosion/nitridation. Type I hot corrosion has formed Ti-sulfides in grain boundaries and nearby surroundings. Ti-sulfides are also found ahead of the crack tip region. The internal corrosion/nitridation has established TiN, AlN and simultaneously formed a depletion zone near the crack.
Published Version
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