EFFECT OF COHERENCY STRESSES ON ALPHA-EQUILIBRIA IN TI-AL ALLOYS(ALPHA(2) PHASE)

Experiments were performed on two Ti-Al alloys to examine recent theor etical predictions concerning the characteristics of coherent two-phas e equilibria in binary alloys. Equilibrium phase compositions in both the coherent and incoherent alpha + alpha2 states at 725 and 800-degre es-C were determined by analytical electron microscopy. The results pr ovide experimental evidence for the following predictions: (1) tie-lin e ends (equilibrium phase compositions) need not coincide with phase b oundaries in the temperature-composition phase diagram and (2) the tie -line ends change with alloy composition at constant temperature. The experimental results have been compared with theoretical calculations of alpha + alpha2 phase equilibria incorporating both elastic and orde ring effects.