Strain Heterogeneity and Damage Nucleation at Grain Boundaries during Monotonic Deformation in Commercial Purity Titanium

Heterogeneous strain was analyzed in polycrystalline, commercial-purity titanium using many experimental techniques that provide information about microstructure, dislocation arrangement, grain orientation, orientation gradients, surface topography. and local strain gradients. The recrystallized microstructure with 50-200 mu m grains was extensively characterized before and after deformation using 4-point bending to strains between 2% and 15%. Extremely heterogeneous deformation occurred along some grain boundaries, leading to orientation gradients exceeding 10 degrees over 10-20 mu m. Patches of highly characterized microstructure were modeled using crystal plasticity element (CPFE) analysis to simulate the de,formation to evaluate the ability of the CPFE model to capture local deformation processes. Damage nucleation events were identified that are associated with livin interactions with grain boundaries. Progress toward identifying fracture initiation criteria based upon slip and twin interactions with grain boundaries is illustrated with related CPFE simulations of deformation in a TiAl alloy.