Slip band-grain boundary interactions in commercial-purity titanium: A statistical study

Grain boundaries (GBs) critically influence the deformation and fracture behavior of polycrystalline metals, yet a comprehensive understanding of their strain localization and failure mechanisms across various types remains elusive. This study employs high-resolution digital image correlation (HR-DIC) coupled with in-situ scanning electron microscopy to statistically analyze slip band-GB interactions in commercial-purity titanium (CP-Ti) during tensile deformation up to 25% strain. By tracking 164 GBs, we found 14 types of grain boundaries based on the types of slip band interactions across the GB as parameterized by the Luster-Morris parameter m′, within which 4 types constitute the majority of GBs: prismatic-basal, prismatic-prismatic, prismatic-<a> pyramidal, and prismatic-<c+a> pyramidal. The prismatic-prismatic GBs exhibit homogeneous deformation with normal strain distributions and minimal localization, conferring high ductility; the prismatic-basal and prismatic-<c+a> pyramidal GBs show high strain localization and high fracture susceptibility, with skewed strain distributions due to the influences of the surrounding grains. In contrast, the prismatic-<a> pyramidal GBs display localized strain reflection into the slip-active grain, enabling fracture resistance through secondary dislocation emission despite comparable strain magnitudes with the <c+a> pyramidal boundaries. A novel Schmid ratio—defined as the ratio of the Schmid factors for the m′ max slip system in the adjacent grain to that of the incident system—predicts fracture timing for fracture-prone grain boundaries: ratios >1 trigger early failure (10–15% strain) via synergistic stress alignment, while <1 delays it to higher strains. These findings provide mechanistic insights for GB deformation and serve as steppingstone for advancing bottom-up design strategies for enhanced mechanical performance.