Abstract
Abstract First-stage turbine blades and vanes were fractured after 18,420 h of operation at about 800 °C in a power station. Overheating was found to be the cause of failure as indicated by microstructural characterization using various electron-optical techniques. This was indicated by coarsening and rafting of the strengthening γ′-phase in the nickel-base blade material as well as the presence of a continuous network of grain boundary carbides. For the cobalt-base vane material, overheating was indicated by decomposition of MC-type carbides and formation of a cellular structure of Laves phase at grain boundaries. Fracture of both the blades and vanes was found to occur by a mixed mode involving intergranular cracking and fatigue. Most evidence pointed out that initial damage by creep resulting in intergranular cracking had shortened the fatigue life of blades and vanes.
Published Version
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