Titanium has many limitations in coverage and frequency of application due to its expensive alloying elements and complex manufacturing process. The biocompatible Ti-Mo-Fe ternary beta titanium alloys were designed by replacing high-cost beta-stabilizer elements (V, Nb, Zr, etc.) with low-cost Mo and Fe elements. In addition, it was attempted to obtain a low-cost, high-strength beta-titanium alloy with 800 MPa or more by applying the powder metallurgy process technology to the Ti-Mo-Fe alloy system. The added Mo element has the effect of reducing the elastic modulus of the titanium alloy without reducing its strength. In this study, Ti-Mo-Fe alloys designed with different Mo contents were fabricated using a powder metallurgy process and analyzed in connection with microstructural properties, phase changes, and mechanical properties. As Mo contents are increased, the α-lath thickness of Widmanstätten decreases and the size of prior β grain decreases. It was confirmed that the hardness and tensile strength were excellent and were compared with the ingot material of the same alloy system.

Ti-xMo-2Fe alloys with high specific strength were designed by adding Mo and Fe as β-stabilizing elements. The influence of cold swaging on the martensitic transformations in Ti-xMo-2Fe (x = 3.4, 5, 9.2 wt.%) alloys was investigated. In these alloys, appropriate chemical compositions promote a stress-induced phase transformation from the β phase to orthorhombic α″ martensite, which improves elongation while maintaining high strength. As the Mo content increases from 3.4 to 5 wt.%, the amount of β-stabilizing elements increases and the β stability is enhanced, thereby altering the phase transformation mechanism. In the Ti-9.2Mo-2Fe alloy, both α″ martensite and a very hard ω phase were identified by X-ray diffraction and transmission electron microscopy. The hard and brittle ω phase causes premature brittle fracture prior to macroscopic yielding. Among the investigated alloys, the Ti-5Mo-2Fe alloy exhibits the best overall combination of high tensile strength, elongation to failure, and high fatigue strength.