Achieving High Strength and Ductility of Ti₂AlNb Alloy Fabricated by Electron Beam Powder Bed Fusion

ABSTRACT: Ti₂AlNb alloy is a promising lightweight high-temperature structural material for aerospace. In this study, Ti₂AlNb alloys were fabricated by electron beam powder bed fusion (EB-PBF) using pre-alloyed Ti-22Al-25Nb (at,%) powders. This work optimizes the substrate preheating temperature and scanning speed of the EB-PBF process to achieve superior strength. The microstructure, tensile properties, and crack propagation mechanism of the as-deposited alloy were systematically studied. The EB-PBFed Ti₂AlNb alloy exhibits a typical refined basket-weave microstructure with uniformly fine lamellar O-phases and dispersed remnant B2 laths. The alloy achieves favorable strength-ductility synergy both at room temperature (ultimate tensile strength (UTS) of 1178 ± 10 MPa, yield strength (YS) of 1058 ± 7 MPa and elongation of 3 ± 0.6%) and at 650 °C (UTS of 933 ± 12 MPa, YS of 790 ± 5 MPa and elongation of 4 ± 1%). Fracture analysis indicates that boundaries of coarse primary O-phases are the main sites for crack initiation and propagation due to local stress concentration and dislocation tangling. The optimized process contributes to retarding the precipitation of coarse primary O-phases and restrains crack evolution, enabling simultaneous improvement of strength and ductility. This work provides an effective route to obtain high strength and ductility in EB-PBF-fabricated Ti₂AlNb alloy for aerospace high-temperature lightweight components.