Atomic structure and molecular dynamics simulation of a symmetrical tilt [01¯1](511) Σ27 grain boundary in polysynthetically twinned TiAl crystals

Clarifying the structural evolution of grain boundaries (GBs) during deformation is important to deeply understand the mechanical properties of intermetallic compounds. In this study, the atomic structure, formation mechanism, and deformation behavior of a symmetrical tilt [0$\overline{1}$1] (511) $\Sigma$27 GB in γ-TiAl with the L1₀ structure have been investigated by aberration-corrected transmission electron microscopy and molecular dynamics simulations. The $\Sigma$27 GBs were formed to connect three 〈011〉 {111} $\Sigma$3 GBs in polysynthetically twinned TiAl crystals due to the twin-twin interactions during tensile deformation. The $\Sigma$27 GB was composed of periodically arranged GB structural units. There was a crystal displacement of (1/4) [0$\overline{1}$1] between two neighboring GB structural units due to the ordered atomic structure of γ-TiAl. The deformation behaviors of the Σ27 GBs at 300 K and 1000 K have been investigated by molecular dynamics simulations. The uniaxial tension loading was applied along the directions parallel and perpendicular to the GBs, respectively. It was found that the formation of stacking faults was the dominant deformation mechanism of the Σ27 GBs under both parallel and perpendicular tension loading. The stacking faults were easy to slide under parallel tension loading, while they were more stable under perpendicular tension loading due to the formation of stacking fault networks. The temperature significantly affected the density of stacking faults, while its role depended on the direction of tension loading.