Novel deformation mechanism of nanolamellar microstructure and its effect on mechanical properties of TiAl intermetallics

Generally, dislocation slipping and mechanical twinning govern the plastic deformation of lamellar microstructure (LM) in TiAl intermetallics. However, when the interlamellar spacing is reduced to the nanometer scale, the deformation mechanism switches to another mode, triggering different mechanical responses. This work reveals that the development of long-period stacking-ordered (LPSO) structure along the lamellar interface, such as the 9R and 6H structures, dominates the tensile plastic deformation of nano-LM. The formation of two LPSO structures is due to the gliding of the 1/6 <11 2‾ > Shockley partial dislocations on the (111) close-packed plane. In particular, the periodic alternating gliding of Shockley partial dislocations on every third layer of atoms and continuous gliding of Shockley partial dislocations on three neighboring planes result in 9R and 6H structures, respectively. LPSO formation during deformation can induce greater high-temperature yield strength compared to LMs deformed via dislocation gliding or mechanical twinning. These findings advance the understanding of the deformation mechanism of nano-LM and pave a new route for designing TiAl alloys with better high-temperature mechanical performance.