Microstructure and enhanced strength-ductility of TiNbCu alloys produced by laser powder bed fusion.

The β-type Ti35NbxCu alloys (x = 0, 1, 3, 5, and 7 wt%) were produced by laser powder bed fusion (LPBF) and the influence of Cu content on the microstructure and mechanical properties was studied. The results indicate that when the content of Cu is less than 3 wt%, Cu can diffuse completely into the Ti matrix to form solid solution without element segregation. Moreover, the elastic modulus of Ti35Nb1Cu alloy (49.1 ± 1.6 GPa) is reduced by 33 % compared to that of Ti35Nb alloy (73.2 ± 1.4 GPa). When the content of Cu exceeds 3 wt%, the eutectoid reaction is activated during the cyclic heating and rapid cooling of LPBF, and the partially supersaturated β phase is transformed into nano-scale α and Ti 2 Cu phases (β→α+Ti 2 Cu). Nano-scale Ti 2 Cu particles precipitated along β grain boundary results in a pinning effect, which inhibits the growth of β grain, hinders dislocation movement, and improves the strength of the alloy. However, when the content of Cu is 7 wt%, the dislocation density (4.179 × 1015 m−2) and the ratio of brittle phase Ti 2 Cu (8.5 %) are too high, and the stress concentration caused by the initiation of inherent micro-cracks are the main reason for the tensile brittle fracture of Ti35Nb7Cu alloy. As such, the Ti35Nb5Cu alloy has the highest tensile strength of 867.3 ± 24 MPa and the elongation reaches 11.7 ± 0.5 %. Therefore, solution strengthening of Cu, fine grain strengthening of β, dislocation strengthening, and precipitation strengthening of Ti 2 Cu are the main reasons for the excellent comprehensive mechanical properties of Ti35Nb5Cu alloy. • LPBF-produced Ti35NbxCu alloys have uniform distribution of elements. • Adding Cu to Ti–Nb alloy can refine grains and reduce elastic modulus. • LPBF-produced Ti35NbxCu alloys have only half the elastic modulus of Ti6Al4V alloy. • Ti35Nb5Cu alloy exhibits an enhanced strength-ductility synergy. [ABSTRACT FROM AUTHOR]