Experimental studies of the phase separation mechanism in Ti-15at%A1

The phase decomposition mechanism operating in a binary Ti-A1 alloy in the two-phase α+α2 region has been investigated. A Ti-15at%A1 alloy was aged in the range 550–750°C for various times to produce material at different stages of phase separation. The resulting microstructures have been examined experimentally using three-dimensional atom probe field ion microscopy and neutron diffraction. Results indicate that significant ordering occurs in the system prior to the onset of chemical phase separation which occurs via a spinodal reaction. The mechanism is believed to lie in the class of ‘conditional spinodal’ mechanisms in which one stage of the phase separation process is thermodynamically contingent upon another.