Enhanced strength-ductility synergy and mechanisms of heterostructured Ti6Al4V-Cu alloys produced by laser powder bed fusion

Limited slip systems of & alpha; structure always play a major role in hindering strength-ductility synergy improvement of titanium (Ti) alloys. To overcome the strength-ductility trade-off of Ti alloys, heterostructure is introduced into Ti6Al4V-xCu (x = 0, 1, 3, 5 wt.%) alloys produced by laser powder bed fusion (LPBF), and the formation mechanism and deformation behavior of heterostructures were investigated. The results showed that the monolithic & alpha;' in the LPBF-produced Ti6Al4V-xCu (wt%) alloys is decomposed into dual & alpha; and & alpha;" after heat treatment at 600-900 degrees C through & alpha;' & RARR; & alpha; + Ti2Cu & RARR; matastable phase & RARR; & alpha; + & alpha;". The multistage transformation of & alpha;' to & alpha; and & alpha;" is driven by thermal activation (temperature > 800 degrees C), Cu addition and rapid cooling of water quenching. The heterostructure with & alpha; and & alpha;" in the LPBF-produced Ti6Al4V-5Cu alloy after heat treatment at 800 degrees C results in high tensile strength (-1.3 GPa) and large elongation (-15%). The enhanced strength-ductility synergy is attributed to the decomposition of brittle & alpha;' and Ti2Cu, as well the soft-hard heterostructure of & alpha;" and & alpha;. Moreover, the deformation twins (DTs) in & alpha;" and the heterogeneous interfaces of & alpha; and & alpha;" can also improve the strength and ductility of the LPBF-produced Ti6Al4V-xCu alloys. These findings elucidate the influence of heterostructure (& alpha; and & alpha;") on strength and ductility, which is helpful for designing Ti alloys with excellent mechanical properties.