Abstract
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.