PHASE-TRANSFORMATIONS IN TI3AL AND TI3AL + MO ALUMINIDES

We have analyzed the phase relationships in two titanium aluminides containing 3.4 at. % Mo with different aluminum compositions. The alloys were first homogenized in the beta field, then cooled continuously at different cooling rates from 80-degrees-C/s to 0.1-degrees-C/s. The continuous cooling transformation diagrams (CCT) show that phase transformations and resulting microstructures are highly dependent on cooling rate. The microstructure consists of ordered alpha-2 (DO19), ordered beta-0 (B2), and athermal omega (hexagonal) phases. The "tweed microstructure" is observed. The evolution of microhardness was determined as well as the relative partitioning of Al and Mo in (alpha-2', alpha-2) and beta-0 phases as a function of cooling rate.