{1 1 2}〈1 1 1〉 Twinning during ω to body-centered cubic transition

We propose an ω-lattice mechanism that is irrelevant to dislocation behaviors for a popular twinning ({1 1 2}〈1 1 1〉-type) system in body-centered-cubic (bcc) metals and alloys. The twinning process is dependent on the reverse transformation of ω (hexagonal) → bcc. The driving force of the twinning is attributed to the instability of a high density of nanoscale metastable ω precursors, and the mechanism has been experimentally and theoretically confirmed in bcc-Ti alloys with the {1 1 2}〈1 1 1〉-type twin formed under conditions free of external stress and internal strain. The ω-lattice mechanism involves bcc lattice shuffling only, thus can be applied to all bcc metals and alloys.