Influence of process parameters on microstructure–property relationships in additive friction stir deposition of Ti-6Al-4V

Additive Friction Stir Deposition (AFSD) is a promising solid-state additive manufacturing process for Ti-6Al-4V, but its robustness across different process parameters remains underexplored. This work systematically varies four key parameters, namely tool temperature (825–925 °C), layer thickness (0.5–1.5 mm), feed rate (55.9–111.8 mm/min), and traverse speed (169–504 mm/min) to deposit nine large (250 × 38 × 67 mm³) Ti-6Al-4V blocks using closed-loop temperature control. All deposited builds were fully dense and defect-free, exhibiting a uniform lamellar α + β (Widmanstätten) microstructure with fine α-laths (∼2 μm) and a weak, near-random crystallographic texture. A homogeneous, equiaxed microstructure free of martensitic α' was observed across all the deposited blocks. Among the varied parameters, temperature and traverse speed had a modest influence on α-lath thickness and α-colony size, while feed rate and layer thickness showed negligible effects. Despite these local variations, the α/β phase balance, geometrically necessary dislocation density, and grain morphology remained largely unchanged, resulting in mechanical properties that differed by less than 5% across all conditions. All specimens achieved yield strengths ∼0.9 GPa, UTS ∼1.0 GPa, and elongation of 10–15%, meeting or exceeding wrought Ti-6Al-4V standards without any post-processing. These findings demonstrate, that AFSD can reliably produce Ti-6Al-4V components with uniform microstructure and wrought-equivalent properties across a wide parameter space. They also highlight the potential of AFSD as a robust, scalable alternative to fusion-based AM for critical titanium applications.