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

Abstract

• A boundary engineering strategy is proposed to improve the strength and ductility of materials simultaneously. • The addition of Cu successfully verified the feasibility of the boundary engineering strategy, and improved the comprehensive mechanical properties of LPBF martensitic titanium alloy. • The role of copper addition in microstructure development are clarified. • The strengthening mechanism of LPBF Ti, Ti-5Cu and Ti-6Al-4V is explained by calculation and fitting. 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 ductility problem caused by lath α' martensite, which is the usual microstructure of near α 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 engineering 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 materials. 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 microstructure refinement in LPBF Ti-5Cu at different levels from prior-β grains, martensitic packets, blocks to laths is also discussed.