Volume 9, Issue 2 (February 2012)
Morphology of γ′ Precipitates in a First Stage Low Pressure Turbine Blade of a Ni-Based Superalloy after Service and after Following Aging
To estimate the temperature distribution, stress distribution, and stress direction in a blade in service, the morphology of γ′ precipitates in Ni-based superalloy serviced in the first stage low pressure turbine (1st LPT) blade of a jet engine was investigated before and after aging. Using a field emission scanning electron microscope, microstructures were observed in forty portions of the blade. Most of the γ′ precipitates remained cuboidal in the serviced blade. Many secondary γ′ precipitates were observed in the γ matrix at the root part. In contrast, there were no secondary γ′ precipitates at the leading edge of the tip part. After simple aging, low-completion rafted γ/γ′ structures appeared on the suction side of the 70 mm part, while in other portions, coarsening of the γ′ precipitates was observed. Therefore, the leading edge of the 1st LPT blade tip was exposed to the highest temperatures in service. However, the stresses were extremely low in all portions of the blade.