Microstructure degradation and residual low cycle fatigue life of a serviced turbine blade

This paper was attempted to investigate the microstructure degradation and low cycle fatigue (LCF) performance of a serviced K465 Ni-based superalloy turbine blade. LCF tests were carried out with small-scale plate specimens sampled from the blades. Relationship between residual LCF life and microstructure state was estimated. The results indicate that the coarsening of gamma/gamma ' phases was the most significant microstructure degradation mode for the serviced blades. Both the gamma matrix width and the gamma ' precipitate diameter increased with the increase of service duration, while the gamma ' precipitate volume fraction slightly decreased. The most severe microstructure degradation occurred at the leading edge along the chord direction, particularly at 50-70 % airfoil spans. The residual LCF life exhibited an accelerated decrease characteristic as increases of microstructure degradation degree. The coarsened microstructure diminished shear resistance of the superalloy, which resulted in additional accumulated inelastic deformation and a corresponding reduction in LCF life. Service induced microstructure evolution and LCF life decay of a blade were investigated. Coarsening was identified as the main degradation form of gamma/gamma' phases in serviced blade. Accelerated decrease of residual LCF life was identified as increases of coarsening. Reduced plastic deformation resistance owing to coarsening is crucial to decay LCF life.