New aspects of globularization crystallography and dynamic phase evolution during thermomechanical processing of Ti–6Al–4V alloy

Microstructural and crystallographic aspects arising from thermomechanical processing of a Ti–6Al–4V alloy in βand α+β phase fields were studied by electron backscatter diffraction and both conventional and high energysynchrotron X-ray diffraction. The impact of deformation in the single β field on the final microstructure has beenacknowledged by an increase of the retained β phase content and decrease of martensitic c/a ratio with thereduction of strain rate, although no significant influence of strain rate on the well-defined fiber texture of α’ hasbeen observed. During deformation in the α+β field, texture weakening has been observed, and misorientationangle/axis distribution analysis has evidenced randomization and loss of the Burgers orientation relationshipbetween α and β upon globularization. The behavior of deformed α lamellae in the α+β field was also evaluatedin terms of internal misorientation spread and lattice rotation around the deformation axis, corroborating thatglobularization takes place through dynamic recrystallization, boundary splitting and shearing. Globularizedgrain size was shown to be exponentially proportional to strain rate decrease. Lower strain rates in the α+β fieldalso increase the β phase fraction and decrease the c/a ratio of the α phase, leading to values closer to the idealone for titanium. However, an excessive amount of β causes its instability during quenching, resulting in itsdecomposition into secondary α during cooling