Some long-period superstructures and the related motion of dislocations in Al-rich TiAl single crystals

Various long-period superstructures that appear in Al-rich TiAl are composed of three pairs of primitive cells, Ti₂Al, Ti₃Al, and Ti₄Al, having periodic atomic arrangements in unique shapes of lean rhombi, fat rhombi, and squares, respectively, on the (002) Ti layers. These primitive cells can produce long-period superstructures such as Al ₅Ti₃, Al₃Ti₂, and h-Al ₂Ti. The long-period superstructures play an important role in the operative deformation mode, configuration of dislocations, and related plastic deformation behavior in Al-rich TiAl, depending on the Al concentration. Fourfold ordinary dislocations, for example, often move as a group in the Al₅Ti₃ superstructure in the shapes of lean rhombi and squares embedded in the L1₀ matrix. In this study, the relationship between the periodic long-period superstructures and dislocation motion will be discussed from the viewpoint of anti-phase boundaries that form in each superstructure and their energies. The plastic deformation behavior in Al ₅Ti₃ and h-Al₂Ti single-phase single crystals is also discussed.