Fundamental approach to superior trade-off between strength and ductility of TiB/Ti64 composites via additive manufacturing: From phase diagram to microstructural design

Reinforcement distribution tailoring has been proven effective in strengthening and toughening titanium matrix composites (TMCs). In this work, the analysis of the Ti64 (Ti-6Al-4V)-B phase diagram indicated that B content dominates the TiB distribution. With this philosophy, B content regulation was applied to tailor homogeneous and network structures in Ti64-B composites fabricated via laser-directed energy deposition additive manufacturing (AM). The unique plate-like TiB attends inhomogeneous composites (Ti64-0.05B). However, in network composite (Ti64-0.25B), the TiB whisker (TiBw) arranges along prior β-Ti grains with the same orientation. Moreover, the synergistic improvement of strength (988 MPa → 1202 MPa), stiffness (106 GPa → 116 GPa), hardness (325 HV → 362 HV), and uniform elongation (5 % → 7.8 %) were achieved. This work exhibited a balanced strength/ductility trade-off, which provides a good guide on microstructure tailoring.