Enhancing strength-ductility synergy in laser directed energy deposited TiB/Ti6Al4V composites by ultrasonic vibration

Additively manufactured high-performance titanium matrix composites (TMCs) have attracted significant attention for their prospective applications in aerospace industry. However, the detrimental aggregation of reinforcement (e.g. TiB) along grain boundaries severely degrades their strength-ductility synergy. Herein, we propose a synchronized ultrasonic vibration (UV) strategy during laser directed energy deposition (LDED) that effectively resolves TiB agglomeration in TiB/Ti6Al4V composites. The results show that the as-deposited TMCs were densified by reducing porosity (0.250 % to 0.003 %) under ultrasonic effects. Furthermore, the use of UV effectively inhibited TiB aggregation and refined TiB whiskers in the TMCs, but exhibited a limited capability on the refinement of prior β-Ti grains. Acoustic cavitation-induced powerful shockwaves disrupted TiB aggregates and facilitated bubble escape, while acoustic streaming-driven homogenization of boron distribution promoted TiB nucleation. Consequently, the TMCs achieved synergistic strength-ductility enhancement under the influence of UV, with ultimate tensile strength increasing from 1104.8 MPa to 1198.1 MPa and the elongation rising from 3.5 % to 6.2 %. Compared with TMCs without UV, ultrasonic treatment provided a higher Hall-Petch strengthening level and introduced an extra Orowan strengthening mechanism by finer TiB. Crack propagation between adjacent TiB was also suppressed by preventing TiB agglomeration at grain boundaries, thereby improving ductility.