Influence of laser power on microstructure and performance of Ti6Al4V fabricated through coaxial wire-laser directed energy deposition using six laser beams

Wire-based directional energy deposition (DED) technology offers high deposition efficiency. However, the inherent melting and solidification conditions can result in uneven deposition and the formation of coarse columnar β grains with distinct solidification textures, leading to significant mechanical anisotropy. Coaxial wire-laser directed energy deposition (CWL-DED) employs a coaxial laser head featuring a ring arrangement of six laser beams, which facilitates vertical wire feeding and effectively mitigates challenges related to deposition direction and microstructure. Building on single bead experiments, a study was conducted to investigate the effects of laser power (ranging from 700 W to 1000 W) on the microstructure and mechanical properties of the three-dimensional blocks. The matrix primarily consists of an acicular α phase. As laser power increases, the length of the α phase extends from 11.0 μm to 18.0 μm. At lower laser power settings, a basketweave structure is observed, while higher laser power induces the formation of Widmanstätten side plates. This transition is attributed to a reduced thermal gradient and the nucleation of heterogeneous particles, resulting in a shift of the matrix from columnar to equiaxed β grains. The region of columnar grains expands with increasing laser power, and the grain size increases from 210-498 μm to 437–742 μm. The ultimate tensile strength of Ti6Al4V reaches a maximum of 947 MPa with an elongation of 18.4 % at 800 W, demonstrating relatively low mechanical anisotropy. This study establishes a foundational process for the preparation of titanium alloys using CWL-DED with six laser beams, addressing the existing gap in research regarding the microstructure and mechanical properties of Ti6Al4V produced using this technology.