Characteristics of dislocation structure in creep deformed lamellar TiAl alloy within primary regime

In this investigation, dislocations of a lamellar TiAl alloy are analyzed after creeping in the primary range at 800 degrees C/200MPa in order to interpret their mobility. It was found that the dislocation density in gamma-laths decreased as the creep deformation proceeds within primary creep regime. Schmid factor analysis suggests that the creep deformation in the early stage of the primary creep regime is controlled by the gliding of some of the initial dislocations which have a high enough Schmid factor. As the creep deformation progressed, those dislocations with high Schmid factors slip preferentially to be annihilated at the alpha(2)-gamma interface. For further continuous deformation, dislocation generation is required, and for this, alpha(2)-phase is transformed to gamma-phase in order to generate new dislocations. A slow dislocation generation process by phase transformation of alpha(2)-phase compared with the absorbing rate to sinks is responsible for the decreasing dislocation density as the creep strain increases.