Phase selection-oriented mechanical properties tailoring for β-type TiNbZrTaSi alloy fabricated by laser powder bed fusion
Xuan Luo, Tao Song, Feng Wang, H.Z. Lu, Limei Kang, Hongwei Ma, Dongdong Li, A. Gebert, Chao Yang
Abstract
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.