Molecular dynamics simulation of tensile deformation mechanisms in nanocrystalline TWIP steel

We perform tensile deformation studies on nanocrystalline twinning-induced plasticity (TWIP) steels using molecular dynamics (MD) simulations and observe significant volume changes during incremental deformation. The meta-atomic potential function is employed to define atomic interactions in TWIP steels. The nucleation and propagation of dislocations lead to a reduction in tensile stress, which is positively correlated with the average grain size. Tensile tests show that TWIP steels undergo a phase transformation during plastic deformation, primarily from the face-centred cubic (FCC) to the HCP phase. This transformation results in the formation of stacking faults (SFs) and twin boundaries (TBs). The slip of dislocations is intercepted by grain boundaries (GBs) and TBs, leading to stress concentration. When the stress reaches a critical threshold, cracks initiate and propagate at these weak points, causing volume expansion during plastic deformation. This volume change results from the interaction between the material’s complex microstructure and the generation and progression of cracks. In contrast, nanocrystalline Cu exhibits nearly constant volume during the plastic deformation stage, attributed to the insufficient dislocation slip and phase transformations in Cu. Overall, the observed volume increase is specific to TWIP steels and contributes to their high ductility.