Preferred precipitation of ordered α2 phase at dislocations and boundaries in near-α titanium alloys

The precipitation of α2 ordered phase in different aging conditions after solution treatment in β, high α+β, or α phase field in Ti–Al–Sn–Zr–Mo–Si–Nd (1#) and Ti–Al–Sn–Zr–Mo–Si–Nd–Nb (2#) near-α titanium alloys was investigated. The solution-treated microstructures consisted of either a single transformed β phase (βt), a duplex mixture of the primary α phase (αp) and transformed β phase (βt), or a single primary α phase (αp). The precipitation characteristics of α2 phase was determined as a function of aging temperature. When the aging temperature was high enough, the precipitation of α2 phase occurred predominately at the boundaries and the dislocations, instead of being uniform throughout the βt matrix. The precipitation of α2 phase in αp, however, was relatively uniform. No apparent difference in the size of α2 particles was observed. When the aging temperature decreased, the precipitation of α2 phase became relatively uniform in βt, but the preferred precipitation and growth of α2 phase at boundaries and dislocations was still obvious. When the temperature was sufficiently low, the precipitation of α2 phase was homogeneous at the boundaries and dislocations as well as throughout the primary α phase and transformed β phase matrix.