Controlling microstructure with tailorable mesoscale spatial heterogeneity in additively manufactured Ti-6Al-4V via laser powder bed fusion

Additive manufacturing (AM) via laser-based powder bed fusion of metals (PBF-LB/M) enables the fabrication of intricate metallic parts but often lacks precise local microstructural control due to its highly dynamic thermal history. By integrating optimised PBF-LB/M process parameters (“processing recipes”) with its inherent design flexibility, here we demonstrate the ability to achieve controllable microstructural variations in the widely used dual-phase Ti-6Al-4V alloy through spatially tuning the local thermal environment. Specifically, two representative microstructures, α′ martensite (hard domain) and lamellar α+β (soft & tough domain), are intentionally formed in situ during PBF-LB/M, one as alternating stacked bands along the build direction and another as vertically aligned core-shell structures. The spatial orientation and length scale of these domains govern the resulting microstructure and mechanical response, enabling tunable strength-ductility combinations. Post-deformation microstructural analyses reveal localised deformation behaviour and highlight the critical role of transition zones between microstructural domains. Quasi- in situ heat treatments that replicate local thermal conditions further reveal the formation of crystallographically distinct α/α intervariant interfaces as a reliable microstructural feature, allowing a clearer distinction between slow-cooling and martensite-decomposition pathways responsible for the in-situ development of lamellar α+β. This strategy for achieving controllable microstructural variation paves the way for precise local property control in PBF-LB/M-produced multi-phase materials like Ti-6Al-4V.