Plastic deformation mechanisms of tension-compression asymmetry of nano-polycrystalline tial: Twin boundary spacing and temperature effect

This study investigated the effects of twin boundary and temperature on both the mechanical properties and micro-deformation mechanism of nano-polycrystalline TiAl alloy under tension and compression loads, by molecular dynamics. An obvious tension-compression asymmetry in flow stress was found at a temperature of 300 K. Increasing the Twin Boundary Spacing (TBS) resulted in an increase of 14.9% in the average flow stress of nano-polycrystalline TiAl alloy under compression compared to that under tension. This value increased to 29.9% when the temperature increased to 600 K. When TBS was gradually decreased, the flow stress first increased and then decreased. This was mainly because the change of TBS resulted in the transformation of the plastic deformation mechanism of nano-polycrystalline TiAl alloy. For a TBS of less than or equal to 2.16 nm, partial dislocations nucleated and emitted at the grain boundary and moved parallel to the twin boundary. For a TBS exceeding 2.16 nm, dislocations nucleated and emitted at the intersection of twin boundary and grain boundary, and eventually intersected with the twin boundary. The critical TBS value for this transition was also affected by temperature. The critical TBS value was 3.59 nm at 600 K, which exceeds the critical TBS of 2.16 nm at 300 K.