Achieving highly promising strength-ductility synergy of powder bed fusion additively manufactured titanium alloy components at ultra-low temperatures

For the first time, electron beam powder bed fusion (EB-PBF) is verified to be feasible to additively manufacture high-performance titanium alloy components for ultra-low temperature application. Cryogenic strength and ductility of the EB-PBF-built trace yttrium modified Ti− 3Al− 3Mo− 3Zr alloy were found to be closely dependent on characteristics of lamellar structures. A breakthrough in cryogenic ductility of titanium alloys was achieved in the EB-PBF-built samples consisting of coarse columnar lamellar colonies, with elongation to fracture (EI) being up to 20.0% at 20 K and 29.0% at 77 K, without significantly sacrificing strength. The highly promising cryogenic ductility was ascribed to large-scale twinning which effectively relieved local stress concentration and enhanced the strain hardening capability. By contrast, interwoven structures of fine α-Ti laths strongly hindered dislocation slide/transferring and twins growing up, resulting in a superhigh ultimate tensile strength (UTS) being up to 1500 MPa at 20 K, but a moderate EI of ≦ 13.5%. The columnar lamellar colonies dominated sample mainly deformed by basal and prismatic slipping at 77 K and by prismatic and pyramidal slipping plus {101̅2}<101̅1̅> and {112̅1}<1̅1̅26> twinning at 20 K. Cryogenic strengthening and toughening mechanism was also discussed in detail.