Local atomic structure near an Nb atom in aged β-Ti alloys

The local atomic structure near an Nb atom in a Ti-Nb binary β-Ti alloy single crystal was examined by means of X-ray fluorescence holography. In the single crystal, high density of the fine ω-Ti phase was homogeneously formed and was distributed in the β-Ti matrix phase by heat treatment. In the ω phase, the atomic displacement accompanying the ω phase formation is suppressed near Nb atoms. Thus, the atoms near an Nb atom tend to maintain the body centered cubic structure even in the ω phase, as Nb is a typical β-stabilizing element. The structural model near an Nb atom in the ω phase is similar to that of a collapsed ω structure. However, the degree of collapse is higher near an Nb atom than that far from it. This inhomogeneous displacement produces diffuse diffraction spots in selected area electron diffraction patterns of the ω phase.