Phase transformations during cooling in α+β titanium alloys

A simplified methodology for investigating the effects of cooling rate from elevated temperature on phase transformations observed in alpha+beta 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 alpha + beta titanium alloys has been demonstrated in Ti-6Al-4V where varying cooling rates from 525 to 1.5 degrees C s(-1) are shown to result in a series of martensitic, massive and diffusional phase transformations. Cooling rates above 410 degrees C s(-1) result in a fully martensitic microstructure, a massive transformation being observed between 410 and 20 degrees C s(-1), this transformation being gradually replaced by diffusion controlled Widmanstatten alpha formation with decreasing cooling rate. (C) 1998 Elsevier Science S.A. All rights reserved.