Electron microscopy study on a new phase in β-titanium alloys aged at a high temperature

In a Ti–20mass%Mo alloys aged by two steps aging at 623 and 823 K, a new phase has been observed. In the first step aging, ω-phase crystals appear and at the second step aging, these crystals disappear and are replaced with the newly discovered phase crystals. Observations in the dark field image and analysis of composition of the new phase crystals have shown that the formation is closely related to the ω-phase structure. The new phase crystals have been also observed in four kinds of β-type Ti alloys and a (β+α) type Ti alloy aged at high elevated temperatures. Based on high-resolution electron microscope observations, the atomic structure of the new phase is assumed.