Orientation Relations During the α-ω Phase Transition of Zirconium: In Situ Texture Observations at High Pressure and Temperature

Transition metals Ti, Zr, and Hf have a hexagonal close-packed structure (alpha) at ambient conditions, but undergo phase transformations with increasing temperature and pressure. Of particular significance is the high-pressure hexagonal omega phase which is brittle compared to the alpha phase. There has been a long debate about transformation mechanisms and orientation relations between the two crystal structures. Here we present the first high pressure experiments with in situ synchrotron x-ray diffraction texture studies on polycrystalline aggregates. We follow crystal orientation changes in Zr, confirming the original suggestion by Silcock for an alpha -> omega martensitic transition for Ti, with (0001)(alpha)parallel to(11 (2) over bar0)(omega,) and a remarkable orientation memory when omega reverts back to alpha.