In-situ EBSD Observation on Slip-less Fragmentation of Irregular-shaped Primary a Grains of Ti-6Al-4V-0.55Fe Alloy before Rupture

Abstract

In-situ SEM/EBSD characterization techniques were employed to investigate the microstructural evolution and characteristic deformation behavior of slip-lees fragmentation of irregular-shaped α grains in Ti-6Al-4V-0.55Fe alloy. The as-forged Ti-6Al-4V-0.55Fe alloy exhibits multiscale synergistic evolution during in-situ tensile deformation, including the changes in the fraction of the high-angle grain boundaries (HAGBs), the rotation of the grains, stress concentrations and dislocation slips. With increase of strains, cross slips and multi slips are activated after the single slips occur at the small strains. The HAGB proportion decreases while that of low-angle grain boundaries continues to increase. This transformation originates from strain-induced dislocation slip and rearrangement. The uniform plastic deformation of as-forged Ti-6Al-4V-0.55Fe alloy is mainly achieved by the activation of the pyramidal <c+a> slips. Within grains in high-strain regions, stress concentration causes a dramatic accumulation of orientation differences, inducing slip-less fracture of irregular-shaped primary α grains along specific internal paths at relatively low strain. In terms of crystallographic evolution, the grain rotation path activated by prismatic slip prefers (0001) basal plane, and promotes a synergistic effect of (0001) texture strengthening and (10-10) texture weakening. Structural inhomogeneities in the size and shape of primary a grains cause abnormal slip-less fragmentation during tensile deformation.