Deformation induced nanoscale twinning improves strength and ductility in additively manufactured titanium alloys

The mechanical properties of aerospace-grade Ti–6Al–4V parts with varying microstructures fabricated via an electron beam melting (EBM) additive manufacturing method have been investigated. We find that α lath width in microstructure is significant to the deformation mechanisms in EBM-built Ti–6Al–4V specimens. The deformation-induced nanoscale twinning is observed due to a high work hardening rate at room temperature with an average α lath width of ∼ 0.6 μm, which results in high yield strength and ultimate tensile strength with extraordinary ductility. By contrast, the fine-microstructure specimens with an average α lath width of ∼ 0.2–0.3 μm where a low work hardening rate occurs, exhibit only the dislocation plasticity. These findings provide an in-depth understanding of the microstructure-dependent deformation mechanisms in additively manufactured Ti–6Al–4V. More importantly, this work sheds light on overcoming the strength-ductility trade-off in titanium alloy by additive manufacturing.