Hydride or martensite? Identification of a new phase in cold-rolled hexagonal close-packed Ti

Two types of lamellar γ-phases are observed in cold-rolled pure α-Ti: the P-type adopting [0001]_α//[001]_γ and (101¯0)_α//(110)_γ, and the B-type adopting [21¯1¯0]_α//[101]_γ and (0001)_α//(1¯1¯1)_γ. By using high-resolution transmission electron microscopy, selected area electron diffraction and stereographic projection, the γ-phase is identified to have a face-centered tetragonal (fct) structure. In situ heating experiment further confirms the γ-phase to be hydride (TiH) precipitate in α-Ti. This work provides convincing evidences that the so-called stress-induced face-centered cubic (fcc) martensite in deformed α-Ti reported previously could be mistakenly identified. Available approaches to distinguish the fcc-Ti martensite from the fct-hydride are also discussed.