Deformation mechanisms in nanotwinned γ-TiAl by molecular dynamics simulation

In this work, the plastic deformation mechanisms and fracture toughness of nanotwinned gamma-TiAl with different twin boundary (TB) spacing are investigated by using molecular dynamics simulation. The simulation results reveal that there are pronounced shifts in the mechanical behaviour of nanotwinned gamma-TiAl when the TB spacing is 3.50, 4.20 and 4.90 nm. In addition, the variation of the dislocation density with strain at these three TB spacing illustrates that a smaller TB spacing induces a higher dislocation density. Different TB spacing has an influence on the dislocation behaviour. The dislocation pile-up, dislocation-dislocation, dislocation-twin and twin-twin reactions, hierarchical twins including their generation and density, step formation, dislocation emission from steps and TB migration are the main plastic deformation mechanisms. The results also show that TB migration, twinning formation and interaction of crack and TB dominate the deformation mechanism of nanotwinned gamma-TiAl with crack. The generation of hierarchical twins, lower distance between crack surface plane and twin plane, dislocation-twin, twin-twin interaction and crack deflection increase the fracture toughness of nanotwinned gamma-TiAl.