# Effect of Molybdenum on Microstructural Evolution and High Cycle Fatigue Properties of Ti-xMo-2Fe Alloys

## TL;DR

Adding molybdenum to titanium alloys improves their strength and flexibility, but too much can make them brittle and prone to breaking.

## Contribution

The study reveals how varying molybdenum content affects phase transformations and mechanical properties in Ti-xMo-2Fe alloys.

## Key findings

- Ti-5Mo-2Fe shows optimal balance of strength and elongation.
- High Mo content introduces brittle ω phase, leading to early fracture.
- Cold swaging influences martensitic transformation mechanisms.

## 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.