Effects of hot working on the microstructure of Ti-base alloys

The titanium community has diverged in its approach to thermomechanical processing depending on the subclass of alloys being studied; conventional disorder alloys as opposed to intermetallic aluminides. For conventional α/β and near-β alloys, research has centered on schemes to enhance secondary processing such as superplastic forming or net shape forging. The ability to enhance the envelope of engineering properties through controlled working operations to gain precise control of the microstructure continues to drive research. Ordered aluminide alloys remain difficult to process due to their limited ductility and high strain rate/temperature sensitivity. Isothermal and ‘near-isothermal’ processes remain crucial to successful breakdown and microstructural refinement in the Ti2AlNb ‘orthorhombic’ and the TiAl ‘γ’ systems. This overview attempts to highlight these issues using examples from recent studies on Ti–4.4Al–5Mo–2Cr–1Ni (wt.%) a high β volume fraction α/β alloy, Ti–22Al–27Nb (at.%) an orthorhombic alloy and Ti–47Al–2Nb–2Cr–1Mo (at.%) a near-γ alloy.