Phase selection-oriented mechanical properties tailoring for β-type TiNbZrTaSi alloy fabricated by laser powder bed fusion

The morphology and distribution of silicides in α/α+β type titanium alloys impress on their properties. Nevertheless, the types of silicide precipitates and their formation mechanisms remain unclear in β-type Ti–Nb–Zr–Ta alloys. In this study, we report the precipitation behavior of silicides formed upon aging treatment of a laser powder bed fusion (LPBF)-fabricated β-type Ti–34.5Nb–6.9Zr–4.9Ta–1.4Si (wt%, TNZTS) alloy. We further discuss their underlying formation mechanism and silicide selection-oriented mechanical properties tailoring for LPBF-fabricated TNZTS alloy. Two novel silicide precipitates were formed: a supersaturated Si–rich β–Ti matrix in the form of a network that can further transform into the (Ti, Zr)₂Si (S2) phase with the increase of aging temperature; and a short, rod-like S2 precipitate adjacent to pre-existing dot-shaped S2. The former results from the aggregation of Si solute atoms towards to the dislocation walls/microbands and the subsequent precipitation reaction, while the latter arises from the considerable micro-strain around the phase boundary between the dot-shaped S2 and β-Ti owing to the large difference in their thermal expansion coefficients. The aging-treated TNZTS alloy exhibits a good combination of tensile strength (1083 ​± ​5 ​MPa) and fracture strain (5.6% ​± ​1.0%), which is attributed to precipitation strengthening, grain-boundary strengthening, and discontinuous intergranular silicide derived from phase selection. The obtained results provide a basis for the design and fabrication of biomedical Si-containing β-type Ti alloys with excellent mechanical properties.