Abstract Scope |
A micro-structurally informed crystal plasticity model was developed for polycrystalline alloy René 88DT (R88DT) at a high temperature (650 oC). R88DT is a precipitation strengthened Ni-based superalloy used in gas turbine engine disks due to high tensile strength, superior creep resistance, and high resistance to fatigue crack growth. It was experimentally observed [1] that crack initiation in polycrystalline superalloys is highly dependent on the grain size, orientation and microstructure, as well as on the inelastic sub-grain properties. Thus, understanding the fundamental deformation mechanisms at the sub-grain level is a necessary step for development of fatigue life models. For this purpose, single crystals with microstructures representative of R88DT were first created by the investment casting process. Specific crystallographic orientations were mechanically tested in tension and compression to investigate dominant deformation mechanisms as activation of various slip systems, stacking faults/micro twin formation and precipitate shearing. These mechanisms were incorporated into a physics - based viscoplastic constitutive model. The model was calibrated using data from tests on single crystals and it was then applied for each grain in polycrystalline R88DT to predict the macroscopic stress-strain response as well as heterogeneous local stress and strain fields. |