Residual stress and microstructural uniformity in large-scale Ti-6Al-4V fabricated via Additive Friction Stir Deposition (AFSD)

Additive Friction Stir Deposition (AFSD) is a solid-state additive manufacturing process with significant potential for titanium alloys, yet its applicability to large-scale Ti-6Al-4V builds has remained largely unexplored. This work presents an assessment of residual stresses along with the characterization of microstructure and mechanical properties in a 200 × 35 × 67 mm3 AFSD Ti-6Al-4V block. The comprehensive characterization includes scanning electron microscopy, electron backscatter diffraction, hardness mapping, tensile testing, and full-field contour method residual stress analysis. It demonstrates that AFSD produces a uniform basket-weave α+β microstructure from the substrate/first-layer interface to the top and along the edges of the block. The deposited block without post-heat treatment exhibits consistent hardness and reproducible tensile behaviour, matching or exceeding wrought standards. Most critically, this is the first report of residual stress in AFSD Ti-6Al-4V, revealing exceptionally low magnitudes with longitudinal stresses limited to +100–150 MPa in the core and −100 to −150 MPa at the top surface, while build-direction stresses remain negligible (−40 to +40 MPa), corresponding to ∼13% of yield strength compared to fusion-based additive manufacturing processes, where residual stresses often reach 30–50% of yield. AFSD uniquely achieves large-scale, defect-free, and stress-minimized deposits without any post-processing. These results establish AFSD as a robust and industrially viable route for near-net-shape fabrication and repair of aerospace-grade titanium structures.