Microstructure, phase stability, and mechanical properties of binary Ti-Mo and ternary Ti-Mo-Fe alloys for biomedical applications

Metastable β-Ti alloys with non-toxic and low-cost alloying elements, with high biocompatibility and improved mechanical properties, are being developed globally for biomedical applications. Howerver, there is still limited published work on Ti-Mo and Ti-Mo-Fe alloys with high Mo content and low cost alloying element with high strength designed for biomedical applications such as vascular stents. Thus, the current study uniquely investigates the combined influence of Fe addition and theoretical methods on β stability and mechanical performance of Ti-Mo alloys with high Mo content vascular stents. Two metastable β-Ti alloys, namely, binary Ti-20Mo wt% (referred to as Alloy 1) and ternary Ti-16.5Mo-1.1Fe wt% (referred to as Alloy 2), were designed using the theoretical predictive methods such as the molybdenum equivalence (Moeq), the average Bo-Md method, and the electron-to-atom ratio (e/a). Microstructural characterization and tensile properties of the alloys after solution treatment at 1100 °C and quenched in ice-brine were analysed. The X-ray diffraction (XRD) patterns and optical micrographs showed stability of the β phase in both alloys due to similarity in e/a ratio value and a slight difference in Moeq. Alloy 1 showed a high ultimate tensile strength (UTS) of 920 MPa and yield strength (YS) of 906 MPa, whereas a much lower UTS of 540 MPa was observed in Alloy 2. The elastic modulus decreased from 85 GPa in Alloy 1 to 74 GPa in Alloy 2, while micro-Vickers hardness increased significantly from 353 Hv0.5 in Alloy 1 to 428 Hv0.5 in Alloy 2. The high strength and modulus in Alloy 1 illustrated that the alloy could be considered as a potential alloy for biomedical applications such as those in vascular stents.