On the role of flat-top beam in pore elimination and fatigue performance of Ti-6Al-4V fabricated by laser powder bed fusion

It's unavoidable to produce defects in the repeated layer-by-layer manufacturing process of laser powder bed fusion (LPBF). This limits the application of LPBF for safety–critical parts. The formation of defects is closely related to the interaction between the laser beam and material in the molten pool. In this paper, beam shaping was used to improve the building quality of LPBF. Process parameter optimization was performed to obtain samples with the fewest defects. Heat treatment was also employed to further improve the mechanical properties. The results showed that the obtained flat-top beam significantly reduced the propensity for keyhole pore formation and enlarged the process windows. In-situ heat treatment induced by high heat input led to the decomposition of martensite and improved the fatigue crack growth (FCG) threshold (∼3.7 MPa m0.5) of the as-built samples. After heat treatment (annealed and solution/aged), the FCG threshold further increased to 5.5/6.3 MPa m0.5, respectively. Reduced defects and high FCG resistance resulted in a fatigue limit above 600 MPa (N = 1e7, R = 0.1), which is comparable to wrought and aged Ti-6Al-4V parts. This study demonstrates the feasibility of improving molten pool stability and reducing defects through beam shaping, providing a new approach to manufacturing high-quality LPBF parts.