Effects of the morphology of grain boundary α-phase on the anisotropic deformation behaviors of additive manufactured Ti–6Al–4V

Abstract

Grain boundary α-phase (GB-α) in titanium alloys is the vulnerable site for failure, while the correlation between deformation behavior and local dislocation motion is still ambiguous. In this study, we made a detailed investigation into the deformation behavior of GB-α with different morphologies in a laser powder bed fusion (LPBF) fabricated Ti-6Al-4V (Ti-64) by using in-situ and interrupted tensile testing, and discussed the underlying mechanisms of dislocation motion. The deformation-induced dislocations were found severely accumulated within the continuous GB-α with the transverse loading direction, which corresponds to the strain localization, while uniformly distributed between the continuous GB-α and surrounding grains with the perpendicular tensile loading. In contrast, discontinuous GB-α could fully accommodate uniform deformation with the matrix microstructure under both loading directions. The new understanding of dislocation motions in GB-α provides a novel perspective to effectively eliminate the tensile property anisotropy with the columnar microstructure present in LPBF Ti-64.