The aging behavior of a Ti-6Al-4V alloy with different starting microstructures was evaluated by means of synchrotron X-ray diffraction, scanning-transmission electron microscopy and micro-hardness measurements. Initial microstructures were produced by thermal and thermomechanical treatments and comprised different morphologies of α phase (martensitic, lamellar, bimodal and globular), as well as the presence or absence of the β phase. Results show that one or more of the following phenomena can take place during aging and contribute to the hardening of the alloy: β decomposition into fine secondary α laths; transformation of the metastable martensitic α′ into the equilibrium α phase; and precipitation of the intermetallic Ti3Al. The composition and distribution of the β phase was shown to affect the precipitation of secondary α during aging, while the composition of the α phase plays a key role on the formation of Ti3Al. In situ X-ray diffraction studies of the early stages of aging show the kinetics of the α′ → α conversion by the reduction in FWHM of XRD reflections, indicate the contribution to hardening by the increase of the c/a ratio and the consequent limitation of active slip systems and depict the chemical homogenization and decomposition of the β phase.
- Phase transformation
- Secondary precipitation
- Synchrotron X-ray diffraction
- Titanium alloys