Deformation-induced ambient temperature α-to-β phase transition and nanocrystallization in (α + β) titanium alloy

Ambient temperature α-to-β phase transition and nanocrystallization in the aged Ti–25Nb–3Mo–3Zr–2Sn titanium alloy was achieved by surface mechanical attrition treatment (SMAT). The phase transition occurs at α/β interfaces and extends to α phase interiors with increasing strain. It is irreversible and diffusion controlled. The stress-induced increase of Gibbs energy and enrichment of Nb may cause a high order of lattice instability of the α phase adjacent to the α/β interfaces and compel the α phase to β phase. The presence of fine α needles in the aged alloy and the phase transition from α to β with increasing strain are viewed to play a crucial role in the subsequent nanostructuring.