Achieving high strain hardening and strength in an additively manufactured titanium alloy

Strain hardening is a crucial property of metals and alloys that directly affects their mechanical processability, safe usage, and durability throughout their service life. However, titanium alloys traditionally used in structural applications often exhibit limited strain hardening, restricting their broader use. In this work, we demonstrate that by employing additive manufacturing (AM), strong strain hardening with high strength can be simultaneously achieved in a commercially available titanium alloy. These remarkable properties arise from a martensitic microstructure originated from the AM process. The microstructure is characterized by nanosized martensite plates with extremely fine triple-twinned substructures. During tensile deformation, detwinning rather than dislocation slip gradually transforms this microstructure into single-twinned lamellae with ~10 nm twin boundary spacing and internal stacking faults, necessitating progressively higher stresses and resulting in significant strain hardening.