2, The University of Alabama in Huntsville, Huntsville, Alabama, United States
Annealing twins can have a strong impact on the mechanical performance of Ni-base superalloys used in turbine disks. While they are recognized for helping to increase yield strength, annealing twins are also known to localize strain and initiate microcracks in high-cycle fatigue. Using a combination of in-situ deformation DIC and 3D crystal plasticity based computational modeling, we investigate the microstructural factors leading to strain localization and subsequent slip band initiation. The analysis focuses on the coupled role of elastic anisotropy, grain neighborhoods, and grain shape and size in determining the location of the exceptionally preferred points of high elastic strain concentration and localized slip, when the applied strain is under but near the macroscopic elastic-plastic transition. We find that the very few localized slip bands are correlated to the development of only the highest elastic strain concentrations. The latter develops in grains that have an outstandingly compliant orientation relative to all its neighbors. We discuss some important microstructural features responsible for microcrack initiation as revealed by the model calculations.