Precipitation induced recrystallisation in a Ti-Fe-Mo bcc-superalloy driven by lattice misfit

Abstract Grain refinement is key to improving the mechanical performance of titanium alloys, however, this traditionally requires extensive thermo-mechanical treatment to drive recrystallisation. Here we show an unusual recrystallisation behaviour within body-centred-cubic (bcc) β -Ti bcc-superalloys, comprising an A2 β -Ti matrix reinforced by ordered-bcc intermetallic B2 $${\\beta }^{{\\prime} }$$ β ′ -TiFe precipitates, which occurs without externally applied strain ( i.e . no thermomechanical processing). Ageing at 750 °C for 72 hours greatly reduces the mean grain size from 364 ± 12 to 30 ± 2 μ m and increases the hardness by 60 HV. Electron microscopy revealed a two-phase nanolamellae structure, nucleating at grain and phase boundaries, and advancing through discontinuous precipitation. The high lattice misfit of −5.4% between the Ti-rich matrix and TiFe precipitates produces high strains at the interfaces and advancing fronts that drive recrystallisation and new grain formation. These findings establish precipitation induced recrystallisation (PIX) as an innovative heat-treatment-only route to refine the grain structure and strengthen titanium superalloys.