Deformation-induced ω phase in nanocrystalline Mo

A deformation-induced hexagonal ω phase was first observed in pure nanocrystalline body-centered cubic (bcc) Mo using high-resolution transmission electron microscopy. As the grains were refined into nanometer sizes by deformation using high-pressure torsion under a pressure of ∼4 GPa at room temperature, the ω phase formed at the grain boundaries of bcc Mo with a crystallographic relationship close to the {1 1 2}〈1 1 1〉 twin orientation. Its formation was mainly attributed to the shear deformation on {1 1 2} planes in bcc Mo.