Phase Transformation Induced Plastic Deformation Mechanism in α2-Ti3Al

Abstract

TiAl plays a crucial role in the field of aero-engine as a new lightweight high-temperature alloy. The γ/α₂ lamellar TiAl single crystals exhibit the highest recorded plasticity, much higher than the soft phase γ-TiAl. This suggests that the hard phase α₂-Ti₃Al may have a unique plastic deformation mechanism, which is important for essentially understanding the origin of unusual plasticity and further improving the mechanical properties of TiAl. Here, we found the dynamic sequential phase transformation between HCP and FCC under shear loading in α₂-Ti₃Al, which is a novel plastic deformation mechanism comparable to twinning. We attribute this to the bond-breaking formation process called “catching bond”, which is the origin of atomic mechanism of phase transformation occurrence. This “catching bond” process is an effective way of energy dissipation that can release the internal stress while maintaining the integrity of structure. The higher cleavage energy than the generalized stacking fault energy (GSFE) guarantees the continuity of phase transformation during shearing. Moreover, the γ/α₂ coherent interface can reduce the GSFE, thus decreasing the critical resolved shear stress (CRSS) of the phase transformation by 35%, which suggests that the phase transformation induced plastic mechanism easily occurs in the lamellar structure. This study reveals the plastic deformation mechanism of α₂-Ti₃Al and explores the role of γ/α₂ coherent interface on the plasticity, which is expected to provide guidance for further improving the mechanical properties of TiAl alloys.