β Phase decomposition in Ti–5Al–5Mo–5V–3Cr

Abstract

The decomposition of the β phase during rapid cooling of the near β titanium alloy Ti–5Al–5Mo–5V–3Cr has been studied using in situ X-ray synchrotron diffraction combined with ex situ conventional laboratory X-ray diffraction and transmission electron microscopy (TEM). Evidence is found supporting the suggestion by De Fontaine et al. (Acta Mater. 1971;19) that embryonic ω structures form by the correlation of linear (1 1 1)β defects at high temperatures. Further cooling causes increased correlation of these defects and the formation of athermal ω structures within the β matrix at temperatures ∼500 °C. Post-quench aging at 570 °C resulted in the nucleation of α laths after ∼90 s at temperature, with the laths all initially belonging to a single variant type. Aging for 30 min produced an even distribution of α precipitates with a lath morphology ∼1.5 μm × 0.2 μm in size composed of both the expected Burgers variants. Mechanical property data suggests that the ω structures alone have no real effect; however, hardness increases were observed as the α phase developed. The utilization of thermal regimes similar to those presented in this paper could offer a method to engineer the α phase in near β titanium alloys and hence control mechanical properties.