Twin Related Domains in Polycrystalline Nickel-Base Superalloys: 3D Structure and Fatigue
Fatigue is the life limiting property of polycrystalline nickel-base superalloys used in turbine disks in the hot section of turbine engines for aerospace and power generation applications. Fabricating components through a powder metallurgy route provides enhanced properties and removes many extrinsic defects associated with fatigue crack formation, driving cracks to initiate at intrinsic microstructrual extremes. Fatigue cracks in the powder metallurgy alloy René 88DT frequently initiate in large grains that are in the tail of the size distribution and contain favorably oriented annealing twin boundaries. Fully characterizing twin boundaries and twin related domains requires 3D microstructural volumes. Datasets of 3D microstructure for René 88DT were collected by TriBeam tomography across a range of resolutions and volumes to characterize microstructure and annealing twins. Algorithms developed to analyze these datasets allow identification of strain localizing sites from 2D cross sections and the frequency of microstructural features amenable to fatigue crack initiation is statistically assessed. Twin related domain structure is quantified via network analysis and leveraged to propose a criterion for identifying fatal fatigue crack sites.