DEFORMATION TWINNING IN METALS AND ORDERED INTERMETALLICS-TI AND TI-ALUMINIDES

The role of deformation twinning in the strength and ductility of metals and ordered intermetallic alloys is examined on the basis of crystallography, energetics and kinetics of deformation twinning. A systematic analysis is made by taking Ti, Ti3Al, TiAl, and Al3Ti as four model systems. In comparison with profuse twinning in Ti, the intrinsic difficulty of twinning in Ti3Al is rationalized in terms of the interchange shuffling mechanism. A fault (SISF) dragging mechanism based on the interaction torque explains the physical source for the low mobility of screw superdislocations in TiAl, which may lead to (111) [112BAR] twin nucleation. In TiAl and Al3Ti alloys, the twin-slip (ordinary) conjugate relationship makes an important contribution to the strain compatibility for high-temperature plasticity. Potentially beneficial alloying additions to promote twinning are discussed.