Non-uniform plastic deformation in additive friction stir deposited Ti-6Al-4V

Ti-6Al-4V (Ti-64) material deposited by additive friction stir deposition (AFSD) on a rolled Ti-64 base plate was evaluated. Extracted tensile coupons containing both base plate and AFSD regions showed different stress–strain responses in uniaxial tensile testing with digital image correlation. These differences were rationalized based on microstructure gradients observed by optical microscopy and spatially resolved laboratory X-ray powder diffraction (PXRD). The AFSD regions show characteristic basket weave α-Ti microstructure within the 25–50 μm prior β grains. The base plate shows a globular α+β microstructure typical of the rolled and annealed state. In one sample, plastic strain concentration occurred in the AFSD region where diffraction analysis indicates the 〈hki0〉 α-Ti directions were preferentially loaded. In the second sample, strain concentration occurred in the rolled base plate, but the textured domains were smaller than the area probed by PXRD. The control of prior β microstructure using targeted deposition temperature and shear rate and axial stress will be critical to achieving rapid volumetric control for targeted final properties using AFSD with titanium alloys.