Experiments were performed on two TiAl alloys to examine recent theoretical predictions concerning the characteristics of coherent two-phase equilibria in binary alloys. Equilibrium phase compositions in both the coherent and incoherent α + α2 states at 725 and 800°C were determined by analytical electron microscopy. The results provide experimental evidence for the following predictions: (1) tie-line ends (equilibrium phase compositions) need not coincide with phase boundaries 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 α + α2 phase equilibria incorporating both elastic and ordering effects.
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Acknowledgements--We gratefully acknowledge the financial support of the National Science Foundation throughG rantNos. DMR-8620026(J YH and WCJ) and DMR-8915770(J MH).
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