A Comparative Study on Microstructure and Mechanical Properties of Ti-6Al-4V Fabricated by Laser/Electron Beam Powder Bed Fusion

To address the strength–ductility trade-off in titanium alloys, a comparative study was conducted on Ti-6Al-4V (TC4) alloys fabricated by laser powder bed fusion (L-PBF) and electron beam powder bed fusion (EB-PBF). The L-PBF specimen primarily consisted of acicular α′ martensite with high residual stress. In contrast, the EB-PBF specimens, owing to a substrate preheating temperature of 740 °C and a reduced cooling rate (103~105 K/s), exhibited a stable and coarse α + β lamellar structure. Combined with the high oxygen content (0.24 wt.%) that provided solid-solution strengthening, this morphology enabled simultaneous attainment of a yield strength of 1120 ± 12 MPa and an elongation at fracture of 11.1 ± 1.3%. Notably, deformation-induced HCP→FCC phase transformation occurred in EB-PBF alloys, generating a dual-phase HCP/FCC structure that effectively accommodated plastic strain. These results highlight the superior potential of EB-PBF over L-PBF for fabricating titanium alloys with an exceptional strength–ductility synergy.