Microstructure Evolution and High Strength-Ductility Synergy of Ti-13Nb-13Zr-2Ta Alloy Fabricated by Laser Powder Bed Fusion

This work systematically investigates the densification, microstructure evolution and the attainment of high strength-ductility in Ti-13Nb-13Zr-2Ta alloy processed by laser powder bed fusion (LPBF). A narrow and viable process window (P_{laser power} = 175 W, v_{scanning speed} = 1000 mm/s, h_{scanning distance} = 0.1 mm and d_{layer thickness} = 0.03 mm) was accordingly determined and the relative density of Ti-13Nb-13Zr-2Ta alloy reaches 99.76%. The depth of molten pool increases gradually with the increase of energy density, and the relationship between the depth of molten pool and energy density has been quantitatively described. Three types of α′ martensites with average grain width less than 3 μm can be observed in the LPBF-fabricated Ti-13Nb-13Zr-2Ta alloys, attributed to the significantly high cooling rate and remelting process. The fine grain size, high density dislocations, nanotwins, ordered oxygen complexes and α + α″ heterostructure all contributed to the high strength (1037.75 ± 25.18 MPa) and ductility (20.32% ± 1.39%) of LPBF-fabricated Ti-13Nb-13Zr-2Ta alloy in this work.