Strain controlled fatigue testing of the metastable beta -titanium alloy Ti-6.8Mo-4.5Fe-1 .5Al (Timetal LCB)

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 alpha - or omega -phase. In the aged state, the alpha -phase carries the major part of deformation work, noticeable by distinct alpha -substructures in fatigued specimen states.