3D ink-extrusion of elemental powders for high-compliance β-Ti microlattices

Two high-compliance β-Ti alloys – Ti-12Nb-12Zr-12Sn and Ti-6Nb-6Mo-12Zr-12Sn (wt.%) – are manufactured into microlattices via 3D ink-extrusion printing of elemental and hydride powders, followed by sintering and solutionizing at 1400 ºC. This study reveals that the formation of “oxygen-rich walls” plays a critical role in triggering embrittlement via intragranular cracking. In compression tests, the Ti-12Nb-12Zr-12Sn microlattices exhibit high compliance (2-6 GPa) and low collapse strength (25 - 115 MPa) along with semi-brittle behavior, even though stress-induced α'' martensite is triggered: stress-strain serrations are explained by the oxygen-rich walls decorated with α plates and athermal ω nanostructures. Nanostructures along these walls are caused by the formation of oxygen-enriched prior particle surfaces during sintering and solutionizing. In contrast, uniform plastic deformation and steady strain-hardening are observed in the Ti-6Nb-6Mo-12Zr-12Sn microlattices whose ductile behavior is consistent with observation of dislocation glide without phase transformation. Its microlattices exhibit very high compliance (6-15 GPa), high yield strength (98-365 MPa) and excellent compressive ductility (>40%), which are desirable properties for orthopedic implants. 1 This work demonstrates the first 3D ink-extrusion of elemental and hydride powders for high-compliance β-Ti microlattices. 2 The presence of “oxygen-rich wall” explains semi-brittle behavior of Ti-12Nb-12Zr-12Sn microlattices. 3 The nanostructure and origin of oxygen-rich wall is firstly elucidated in this study. 4 Ti-6Nb-6Mo-12Zr-12Sn microlattices with the higher stability of the β phase, showing excellent ductility and dislocation-based work hardening. 5 The microlattices of β-Ti alloys exhibit novel mechanical properties: very high compliance (6-15 GPa), high yield strength (98-365 MPa) and excellent compressive ductility. 6 This work is not only a new success in 3D ink-extrusion printing but metallurgical guideline for developments of ultra-low modulus Ti alloys for biomedical applications.