Micro-mechanism of the effect of grain size and temperature on the mechanical properties of polycrystalline TiAl

A molecular dynamic method was utilized to analyze the microscopic deformation mechanism of polycrystalline TiAl alloy under the influence of grain size and temperature. The results showed that, for a grain size of < 8 nm, the yield stress of the nano-polycrystalline TiAl alloy increased with increasing grain size (inverse Hall-Petch relation). Such a plastic deformation was mainly the result of the migration of grain boundaries (GB) and grain rotation. When the grain size exceeded 8 nm, the sensitivity of yield stress on the grain size decreased. The dislocation slip and the deformation twin in the interior of the grain gradually dominated the plastic deformation. With increasing grain size, the Young's modulus also increased. The temperature also influenced the Young's modulus. Increasing the temperature resulted in an increase of the distance between atoms, which decreased the bonding force between atoms, and thus decreased the Young's modulus. With increasing temperature, the dislocation density decreased and the dislocation emission on the GB delayed.