Iron as a microstructural architect in ATI 425 via DED-LB

Laser-based directed energy deposition (DED-LB) overcomes the long-standing barrier to iron alloying in titanium—β-fleck formation—unlocking new compositional space for alloy design. Here, we exploit this capability to engineer the α-β Ti alloy ATI 425 (≤1. 8 wt. % Fe) with Fe additions up to 4. 5 wt. %. Our findings reveal two previously unrecognised roles of Fe: (i) driving the development of a pronounced 10 1 ¯ 2 texture component with high Schmid factors across all primary slip systems, and (ii) promoting Type 2 α-variant misorientation (11 2 ¯ 0 / 60 ∘) that favour transformation strain self-accommodation. At total Fe contents ≥4. 5 wt. %, Fe additionally facilitates a columnar-to-equiaxed transition, notably without disrupting the 001‖Z texture. Across the composition range, Fe progressively refines both prior-β grains and α–β lamellae. Based on ω-phase formation and tensile response, a new practical limit of ∼3. 0 wt. % total Fe content is identified for DED-LB–processed ATI 425, which significantly enhances strength while preserving good ductility.