Abstract: Dynamic recrystallization (DRX) is of great significance for the thermomechanical processing and microstructural regulation of TiAl intermetallics. However, the underlying DRX mechanism remains poorly understood. In this study, an Avrami kinetics model for DRX was established, which was capable of predicting the DRX fraction accurately. In addition, the effect of Al₂O₃ short fiber on the DRX mechanisms of TiAl matrix composite during the isothermal compression was investigated for the first time. The results showed that other than inhibiting DRX by particles in the TiAl matrix composites, the addition of Al₂O₃ short fiber accelerated a novel DRX process, which was induced by twinning and twin intersections (TDRX). Thus, this composite exhibited a higher DRX rate than that of the as-cast TiAl monolithic alloy. The origin of the twin intersection and TDRX for the composite was revealed. The stress concentration near the Al₂O₃ fiber was above the critical shear stress for twinning and thus was favorable for the formation of twinning and twin intersections. The high stored strain energy at the regions of twins and twin intersections provided the driving force for TDRX. TDRX accelerated the grain refinement in the TiAl matrix near the Al₂O₃ fiber. The present findings would provide a new perspective on DRX mechanisms, and provide the scientific guidance for optimizing the microstructures of TiAl matrix composites.

Key words: TiAl matrix composite, Al₂O₃ fiber, Twin intersection, Dynamic recrystallization