Interpretation of ω-hcp Phase in β-Ti Alloys by Double Diffraction of Overlapping Body-Centered Cubic Lattice

Abstract

The ω-phase in metastable β-Ti alloys is traditionally considered to be an hcp lattice. The diffraction spots of the ω-phase known so far consist of a major bcc spot originating from the parent β-bcc and additional spots of forbidden sites that do not appear in the bcc lattice. Therefore, the ω-phase has been interpreted as an hcp lattice due to the forbidden spots. However, we show that the forbidden spots are double diffraction spots of a moiré superlattice due to overlapping bcc lattices. That is, the diffraction pattern of the ω-phase is interpreted as double diffraction due to overlapping lattices. To demonstrate this double diffraction due to overlapping lattices, we printed lattice spots with spacing of 25 to 43 μm on a transparent film and visually simulated the diffraction pattern by transmitting green laser light through the film.

Keywords: metastable β-Ti alloy, ω-hcp phase, lattice overlap, moiré superlattice, double diffraction