Strain controlled fatigue testing of the metastable β-titanium alloy Ti-6.8Mo-4.5Fe-1.5Al (Timetal LCB)

Highlights: → Strain controlled fatigue tests on the β-alloy Ti-6.8Mo-4.5Fe-1.5Al. → Characterization of deformed microstructure by TEM. → Deformation induced precipitation takes place in solution treated condition. → Deformation of aged state is characterized by subgrain formation in secondary α-phase. - Abstract: The present work covers the mechanical behaviour of Timetal LCB under fatigue loading and utilizes transmission electron microscopy (TEM) to study the associated microstructural evolution. Fatigue specimens were taken out of LCB wire made for automotive suspension spring manufacturing in a solution treated as well as an additionally aged state. Uniaxial fatigue tests were carried out in total strain control with R = 0.1. Solution treated specimens tested at 3% and 4% maximum total strain showed a saturating force response, which differed from all other total strain controlled tests, and a distinct fracture behaviour. In addition, an increase of the dynamic Young's modulus is observed under these test conditions and in this material state. These findings are interpreted as a deformation induced precipitation of nanosize α- or ω-phase. In the aged state, the α-phase carries the major part of deformation work, noticeable by distinct α-substructures in fatigued specimen states.