Residual Stress and Microstructural Uniformity in Large-Scale Ti-6Al-4V Fabricated via Additive Friction Stir Deposition

Abstract

Abstract. 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 (SEM), electron backscatter diffraction (EBSD), 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 postheat treatment exhibits consistent hardness and reproducible tensile behavior, 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 postprocessing. These results establish AFSD as a robust and industrially viable route for both near-net-shape fabrication and repair of aerospace-grade titanium structures.