Antibacterial copper-bearing titanium alloy prepared by laser powder bed fusion for superior mechanical performance

Copper element was added in pure titanium to produce a new biomedical titanium-copper alloy by laser powder bed fusion (LPBF). Addition of copper can eliminate the mismatch of high strength but poor duc-tility problem caused by lath alpha' martensite, which is the usual microstructure of near alpha titanium alloy fabricated by LPBF. Instead of by the usual trade-off relationship between strength and ductility, which is a long-standing challenge for martensitic titanium alloys, in this study, we proposed a boundary engineer-ing strategy and aim to synergistically enhance the strength and ductility of martensitic titanium alloy fabricated by LPBF. It is hypothesized that whilst both low-angle and high-angle grain boundaries are beneficial to the strength, high-angle grain boundary can simultaneously improve the ductility of materi-als. To test this strategy, a Ti-5Cu (wt.%) alloy is selected to compare against pure titanium and Ti-6Al-4V at the same laser processing conditions. EBSD, TEM and XRD analysis show that the as-fabricated LPBF Ti-5Cu alloy is comprised of partially tempered martensite with extraordinarily high number density of both high-angle and low-angle grain boundaries as well as low dislocation density. Such microstructure enables a high tensile strength of 940-1020 MPa, which is at a similar level as LPBF Ti-6Al-4V, and an excellent elongation of 13%-16%, twice as much as that of LPBF Ti-6Al-4V. The mechanism of microstruc-ture refinement in LPBF Ti-5Cu at different levels from prior-beta grains, martensitic packets, blocks to laths is also discussed. (C) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.