Metastable Ti-Fe-Ge alloys with high elastic admissible strain

Abstract

Iron is employed as an alloying element in powder metallurgy Ti alloys for healthcare applications owing to its fast diffusion which aids sintering, excellent biocompatibility, and cost-effectiveness. In this study, we assess the use of Ge to enhance the sintering and mechanical properties of a Ti-7Fe based powder metallurgy alloy (Ge = 0, 2, and 4 wt.%). Germanium is an α-stabilising element with good solubility in the Ti matrix and possesses better biocompatibility than the commonly used aluminium α-stabiliser. After sintering, all alloys exhibited dual-phase microstructures (α and β phase), while an intermetallic Ti5Ge3 also formed in Ti-7Fe-4Ge. Despite being an α-stabilising element, germanium primarily segregated to the β phase regions in the Ti-7Fe-xGe alloys. Gradual increments of the sintered density of the alloys were observed with increasing Ge additions. The sintered Ti-7Fe-xGe alloys were solution treated to exploit the metastability of the retained β phase. After solution treatment at 1000 °C, the alloys predominantly exhibited β phase with minor traces of martensitic athermal ω-phase. Germanium suppressed the formation of the athermal ω-phase and reduced the stability of the β phase. The solution-treated Ti-7Fe-2Ge alloy is most promising for implant applications with a relatively low compressive Young's modulus (∼ 70 GPa) and high yield strength (∼ 1450 MPa), which leads to an outstanding elastic admissible strain of ∼ 2.2%.