Isothermal α Precipitation and Evolution in a Hot-Rolled near β Titanium Alloy

Evolution of secondary α precipitates in a near β titanium alloy Ti-7Mo-3Al-3Nb-3Cr hot-rolled bars (Φ14mm and Φ22mm) with different rolling processes was investigated. The results indicated that the morphological evolution of secondary α phase was almost the same, despite of different rolling processes. While the precipitation kinetics of secondary α phase in short-term aging process changed significantly. Secondary α phase precipitated along β grain boundaries (αGB) and inside β grains as dot shape initially, when aged at 500oC. With time increasing, dot-shaped α phase precipitates connected together as line. And nucleation of α-laths from the grain boundaries (αWGB) appeared as time reached to 10 minutes. Meanwhile, chevron-shaped secondary α phase precipitated from β matrix. Secondary α phase evolved into acicular shape, when aging time was extended to 20min or much more, and the angle between each other was about 90o or 60o. The volume fraction of secondary α phase in Φ22mm bar was larger and changed faster than that of Φ14mm bar with the changing of aging temperature (500oC-600oC) and time (≤60minutes). αWGB formed both along high angle GB and low angle GB after aged at 500oCfor tenminutes, with two sides of αGB.