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

Abstract

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.