3D in situ observations of stress redistribution in Ti-6Al-4V within rogue grain neighborhoods during monotonic and cyclic loading

Abstract

Grain-scale stress redistribution events are characterized within the Ti-6Al-4V (Ti64) hexagonal close-packed $\alpha$ phase using far-field high-energy X-ray diffraction microscopy. Specimens were deformed in monotonic uniaxial tension and under cyclic tensile loading with approximately 7000 grains probed in each specimen. Analyses focused on the evolution of the resolved shear stresses applied to the basal $〈a〉$, prismatic $〈a〉$, and pyramidal $〈c+a〉$ slip systems, as well as normal stresses applied to basal planes, within individual grains. Slip system softening is observed in the basal $〈a〉$ and prismatic $〈a〉$ slip systems across the ensemble, while hardening is observed for the pyramidal $〈c+a〉$ slip systems during both monotonic and cyclic loading. In addition, discrete stress redistribution events in which increases of normal stresses in grains not favorably oriented for slip that may lead to crack initiation are analyzed. It is observed that these increases in normal stresses are correlated to crystallographic slip in multiple neighboring grains favorably oriented for slip.