On the ability of additive friction stir deposition to print homogeneous large blocks of Ti–6Al–4V

This study presents a comprehensive multi-scale investigation of the microstructural and mechanical properties of a large Ti–6Al–4V block fabricated via Additive Friction Stir Deposition (AFSD). AFSD is a solid-state additive manufacturing process with growing industrial relevance. While AFSD has been widely studied for small deposited blocks, its scalability and ability to maintain uniform properties across large build volumes remain underexplored. To address this, a large (250 × 30 × 80 mm3) Ti–6Al–4V block was deposited and systematically characterized through optical microscopy, SEM, EBSD, XRD, EDS, and full-field measurement using Digital Image Correlation (DIC)-assisted tensile testing. Alternating bands were observed across the deposited block; however, no elemental segregation, microstructural, or mechanical differences were observed across layers. The build demonstrated a consistent lamellar α+β microstructure with minimal retained β-phase with no defects or porosity. An isotropic and weak texture was seen throughout the deposition. Mechanical testing revealed uniform hardness (346–358 HV0.5), yield strength (∼906 MPa), and elongation (∼13 %) across both longitudinal and transverse directions. Full-field measurements revealed deformation to be homogeneous. Fractographic analysis confirmed ductile failure with a complete absence of porosity. When compared to prior AFSD and fusion-based studies, this work establishes the largest reported defect-free AFSD Ti–6Al–4V build to date with homogenous microstructure and consistent mechanical properties, achieved without post-processing or heat treatment. These findings validate AFSD's scalability and process stability for manufacturing large-scale components with microstructure and properties on par or above those of wrought or fusion-based AM.