Enhanced strength-ductility synergy in laser additive manufactured TC4 titanium alloy by grain refinement

• The columnar grains of TC4 alloy was remarkably refined by the addition of ZrB 2 during laser additive manufacturing. • Fine basket-weave structure was obtained in the microstructure with ZrB 2 addition. • TC4+0.5ZrB 2 alloy exhibited good balance of strength and ductility. In this study, a significant refinement of prior-β grains was achieved in the TC4 (Ti-6Al-4V) titanium alloy through the addition of zirconium diboride (ZrB 2 ), made additively by laser melting deposition (LMD). With the increase of ZrB 2 content, the fine basket-weave structure was obtained instead of α-Widmanstätten laths. The tensile results shown that the mechanical anisotropy of modified-TC4 alloys was decreasing in comparison with the as-deposited TC4 alloy. The higher content of forming eutectoid TiB phase resulted in the higher strength by precipitation strengthening but poorer elongation in the vertical direction. TC4+0.5ZrB 2 (TC4 with 0.5 wt.% ZrB 2 addition) alloy exhibited the excellent combination of strength and ductility and presented isotropic characteristics, which could be related to the synergetic effect of refinement of prior-β grains and α phase and the trace formation of TiB phase.