Achieving cryogenic strength-ductility synergy of near-α titanium alloy fabricated by laser direct energy deposition through multiscale deformation

• A novel cryogenic titanium alloy is fabricated via laser direct energy deposition. • The annealed alloy demonstrates an excellent strength-ductility synergy at 77 K. • Multiple twins accommodate dislocations and generate stress fields at interfaces. • Twins promote various slip systems activation and dislocations dissociation. A novel near-α titanium alloy designed for cryogenic applications was fabricated via laser direct energy deposition process. The microstructures and cryogenic mechanical properties of the alloy before and after heat treatment were analyzed. Both as-deposited and annealed alloys demonstrate remarkable strength-ductility synergy. Notably, the elongation of annealed alloy (∼17.5 %) is about 84.2 % higher than as-deposited alloy, while maintaining high ultimate tensile strength (∼1174 MPa). To comprehensively examine the impact of microstructure on cryogenic deformation, in-situ cryogenic TEM strain testing and other analytical techniques were employed, which offer new insights into the multiscale deformation mechanisms at cryogenic temperature. Larger α phase facilitates twin nucleation and effectively accommodates the strain gradient resulting from inhomogeneous deformation. Multiple twins promote non-basal dislocation slip and introduce additional heterogeneous interfaces, enhancing both twinning-induced plasticity and dynamic Hall-Petch effect. As flow stress increases, dislocations near twins dissociate into and dislocations, contributing to dislocation strengthening. The notable enlargement of grain size in annealed alloys facilitates more active dislocation behavior driven by extensive twinning, promoting sustained strain hardening. These findings not only elucidate the cryogenic deformation mechanism of near-α titanium alloy but also offer promising avenues for developing high-performance titanium alloys by additive manufacturing.