Electron microscope observations of athermal omega-phase crystal formationand growth behaviors in a beta-Ti alloy cooled to 77 K

It is known that omega-phase crystals in beta-Ti alloys are formed by quenc hing, aging and stressing. It has also been predicted that athermal omega-p hase crystals are formed by cooling from the negative temperature dependenc e of electrical resistivity in the alloys at low temperature. In order to c larify the formation of athermal omega-phase crystals formed by cooling, in -situ dark field image observations of an as-quenched Ti-15 mass%Mo alloy w ere carried out from room temperature to 77 K. In a specimen cooled to 77 K without electron irradiation, the formation of athermal omega-phase crysta ls was clearly observed, but when irradiated with electron beam the crystal s were annihilated.