The effects of Mo content on the mechanical and microstructural properties of as-cast Ti-10Mo wt.% and Ti-15Mo wt.% alloys were measured in order to evaluate their possible use in biomedical applications. The microstructure and phase analysis of as-cast specimens were studied using an optical microscopy and X-ray diffraction (XRD). The micro-Vickers hardness properties of the alloys were examined using Vickers equipment and the elastic modulus was determined using the tensile test. Results indicated that the Mo content influenced the structure-property relationship. The relative density increased significantly with the addition of Mo, the optical microscopy results showed that CP Ti was characterised with an α’-phase lamellar structure and with the addition of Mo, the microstructure composed of β phase with equiaxed grains of different sizes with sub-grain boundaries were observed. The measured XRD patterns showed that the CP Ti consisted of α’-phase and with the addition of Mo, the resultant alloys consisted of the β-phase. The micro-Vickers hardness and elastic modulus increased significantly after the addition of 10 wt.% Mo and then decreased significantly when the Mo content was raised to15 wt.%.

This study presents the phase analysis, microstructural characteristics, and mechanical property evaluation of the as-cast and quenched Ti–15Mo–xFe alloys with high iron content ranging from 4 to 12 weight percent. All the four alloys were produced in a vacuum-arc melting furnace. Heat treatment in the form of solution treatment was performed in a muffle furnace at a temperature of 1100 °C, with 1-h holding time and the samples were rapidly quenched in ice-brine. X-ray diffractometer (XRD) was used to analyses the phases present in each alloy whereas the optical microscope (OM) was employed to track the microstructural evolution and percentage porosity. The mechanical properties of the alloys were evaluated using a tensile test and compression test method while the micro-Vickers hardness measurements were conducted to evaluate hardness of the alloys. The XRD patterns of as-cast showed peaks belonging to the β and α″ phases and intermetallic B2 TiFe phases. The as quenched XRD peaks illustrated β phase only and Fe·Ti·O₂ phases. The as-cast OM micrographs revealed equiaxed β grains, substructures, dendritic structure, and pores forming around the grain boundaries. The quenched OM showed only β equiaxed grains with pores throughout the grain boundaries. The tensile properties such as ultimate tensile strength (UTS) and elastic modulus (E) of as-cast TMF0 were 264 MPa and 79 GPa respectively and these properties changed upon quenching to 411 MPa and 66 GPa respectively. The elastic modulus of TMF1 in as-cast condition was 74 GPa. The UTS and E of TMF1, TMF2, and TMF3 in as-cast and quenched conditions were not recorded due to the fragility of the samples that failed prior to yielding any useful data. The compressive strength in as-cast and in quenched condition decreased with an increase in Fe content. The micro-Vickers hardness in as-cast and quenched conditions showed a similar trend with hardness increasing slightly upon quenching for TMF0, TMF1, and TMF3 alloys but slightly decreased in the case of TMF2. The fracture surfaces of all the as-cast and quenched alloys were comprised of ductile and brittle fracture.

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 Hv_0.5 in Alloy 1 to 428 Hv_0.5 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.