TWIN PROPAGATION IN TIAL

In situ deformation experiments have been performed on TiAl in order to study the twin propagation in two different cases. In the first case the deformation is due to only one twinning system, whereas in the second case both twinning and simple dislocations are activated. In the first case twin propagation has been found to be controlled by frictional forces acting on the Shockley dislocations. In the second case Frank dislocations are formed at the twin interface as the result of reactions between Shockley dislocations and simple dislocations. The twin propagation is hence controlled by the crossing of these Frank dislocations by the other Shockley dislocations. The effects of these mechanisms on the mechanical properties are discussed in relation to the specimen orientation.