Precipitate Microstructure as an Indicator of Stress and Temperature Distributions in a Serviced Gas Turbine Blade

Abstract

Superalloys are high temperature materials which are indispensable in many high temperature applications such as the gas turbines. IN738LC is a nickel-based superalloy that is extensively used in the hot sections of the gas turbines. The strengthening in this alloy is provided mainly by the γ′ precipitates. In this research, precipitate size and morphology of a serviced IN738LC polycrystalline turbine blade is investigated. Specimens from the trailing edge, middle, and leading edge positions of the tip, middle, and root sections on their hot (exterior) and cooled (interior) surfaces are analyzed for the precipitate size and morphology. The size and morphology are then linked to the temperature and stress/strain distribution in the blade. In general, the hot surfaces have larger precipitates that indicate a higher temperature exposure. In particular, the precipitate size is larger in the tip and middle sections than the root section, implying that the latter has a lower temperature. As the precipitates transforms to rafts at high temperature and stress/strain, the middle positions of the tip and middle sections, the trailing edge of the tip section, and the leading edge of the middle section are predicted to have high temperature–stress/strain coupling.