In order to obtain a Ti-Al alloy with a nano-scale antiphase-domain/lamella mixed microstructure, and to achieve a strength higher than that obtainable by lamella refining alone, a study was made of antiphase domain growth and lamellar structure formation in Ti-39at%Al single crystals during isothermal annealing at α2 + γ dual-phase temperatures after quenching from an α disordered single-phase state. The effect of plastic deformation before annealing was also examined with respect to an acceleration of γ lamellae-formation via the preferential nucleation of γ-plates on dislocations. The lower the annealing temperature, the smaller were the antiphase domain size and the lamellar spacing at the moment of homogeneous lamellar structure formation. However, the antiphase domain size in the homogeneous lamellar structure was no smaller than 400nm. A structure with finer antiphase domains and finer lamellar structure was obtained by deforming the crystal before annealing, since lamellar structure formation was thereby accelerated and the time for antiphase domain growth before lamellar structure formation was shortened. A structure with an average lamellar spacing of 88nm, and an average antiphase domain size of 214nm, was obtained by deforming the crystals up to 10% plastic strain and then annealing at 1073K for 104s. No γ-plate formation was obtained by identical annealing without deformation. Such a microstructure imparted a hardness which was higher than that obtained only by refining the lamellar structure.

Evolution of Antiphase Domain/Lamella Mixed Microstructure in Ti-39at%Al Single Crystals. Y.Koizumi, K.Iwamoto, T.Tanaka, N.Tsuji, Y.Minamino: Materials Science and Engineering A, 2008, 478[1-2], 147-53