Achieving strength-ductility combination and anisotropy elimination in additively manufactured TiB/Ti6Al4V by in-situ synthesized network architecture with fine grains

It is of significance, but still remains a key challenge to overcome the strength–ductility trade-off, and homogenize the mechanical performance of the additively manufactured titanium alloy. Here, we provided a new strategy of multi-scale architecture design to overcome this issue through in-situ synthesizing TiB-reinforced titanium matrix composites manufactured by laser-directed energy deposition (LDED). The β grains were remarkably refined from ∼200 μm to ∼70 μm and the aspect ratio of α-Ti reduced from ∼16.3 to ∼4.8 by planting TiB (≥2.5 vol%). The 2.5 vol%TiB/Ti6Al4V composite exhibited the significant transition of columnar to equiaxed grains and presented the multi-scale columnar and equiaxed network structure with favorable continuity, and achieved the good combination of strength (1153 MPa) and ductility (6.2%) thanks to the grain refinement and structure strengthening afforded by the network structure with different strain domains. The 5 vol%TiB/Ti6Al4V obtained the excellent ultimate tensile strength of 1174 MPa while maintaining good ductility. Both the apparent columnar to equiaxed grain transition which led to the reduction of the texture intensity and Schmid factor, and the special distribution of TiB with <010> texture along the building direction achieved the isotropic strength in 2.5 vol%TiB/Ti6Al4V composite.