Phase transformations during cooling in α+ β titanium alloys

Abstract

A simplified methodology for investigating the effects of cooling rate from elevated temperature on phase transformations observed in α+ β titanium alloys is described. It involves adaptation and refinement of a circumferentially insulated and instrumented Jominy end quench bar, time–temperature profiles obtained during cooling at locations along the bar length providing a complete thermal history. The ability of this procedure to examine the phase transformation for α+ β titanium alloys has been demonstrated in Ti–6Al–4V where varying cooling rates from 525 to 1.5°C s −1 are shown to result in a series of martensitic, massive and diffusional phase transformations. Cooling rates above 410°C s −1 result in a fully martensitic microstructure, a massive transformation being observed between 410 and 20°C s −1, this transformation being gradually replaced by diffusion controlled Widmanstätten α formation with decreasing cooling rate.