Size-dependent deformation mechanisms in two-phase γ-TiAl/ α2-Ti3Al alloys

Polysynthetic twinned (PST) TiAl single crystals, consisting of alternating layers of gamma-TiAl and alpha 2-Ti3Al, exhibit excellent mechanical properties. However, size-dependent deformation mechanisms have not yet been fully elucidated. In this work, we investigated the deformation process of two-phase gamma-TiAl/alpha 2-Ti3Al alloys with different layered sizes via uniaxial tensile loading using molecular dynamics simulations. The results show that with the decreasing phase boundary (PB) spacing 7 or domain boundary (DB) spacing d, the excess free volume at the intersection of DB and PB decreases, leading to increased yield stress. We found that a higher interface density (smaller 7 or d) can accommodate more dislocations, and the size-dependent ultimate strength follows an approximate Hall-Petch relation. These findings offer an essential understanding for the size-dependent PST TiAl single crystals with high strength.