Nonequilibrium Phase Transformations in Titanium Aluminides with Ternary Additions

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9616748 Wittig This research examines the massive phase transformations in binary and ternary Ti-Al alloys to determine the parent to product crystallographic relationships and the effects of ternary elements on the nucleation and growth of the massive transformation product. The base alloy has a composition of Ti-48at%Al. To this stoichiometry, additions of the ternary elements V, Nb, Cr, Mo, Mn, and Fe are added. Initially the work concentrates on the V, Cr, and Mn series from row four of the periodic table. By utilizing the University of Vanderbilt's undercooling, rapid quench technology, unique nonequilibrium microstructures are formed that should help clarify present confusion regarding the site preferences of ternary additions to gamma TiAl. The rapidly cooled, splat- quenched samples are analyzed using optical microscopy, X- ray diffraction, scanning electron microscopy and analytical electron microscopy. By employing ALCHEMI to compare the non-equilibrium microstructures of undercooled and rapidly quenched TiAl ternary alloys with equilibrium conditions, the site occupation of the ternary elements can be characterized as a function of Ti/Al stoichiometry. %%% Knowledge of the influence of ternary atom additions on the unit cell structure is critical to the understanding of the atomic mechanisms responsible for improved mechanical properties observed in the Ti-Al 48at% ternary alloys. The high cooling rate, solid-state transformations explored in this research give some insights onto other nonequilibrium processes such as those found in the heat-affected zones of welded alloys. ***