Molecular dynamics investigation on the regulatory role of stacking fault energy in Fe-Mn-C alloys at low temperatures

Abstract The stacking fault energy (SFE) exerts a decisive influence on dislocation dissociation, slip modes, and phase transformation behaviors in face-centered cubic (FCC) alloys. In this study, a gradient polycrystalline Fe–24Mn–0.2C model was employed as the research object. By using the mixed potential function combining MEAM, Tersoff/ZBL, and Lennard-Jones, the mechanism of dislocation dissociation, grain boundary (GB) crossing, and stress-induced martensitic transformation under low-temperature conditions is studied through a large-scale molecular dynamics simulation system. The results reveal that when the GB misorientation angle is less than 4.6°, Shockley partial dislocations can penetrate the GB and extend stacking faults. However, when the misorientation angle exceeds this threshold, the local SFE rises significantly due to the concentration of misfit stresses, leading to strong dislocation pile-up at the GB. As an interstitial solute element, C induces local distortion and stress concentration at the dislocation core, thereby increasing the local SFE, shortening the dislocation dissociation distance, and reducing its migration rate. During tensile deformation, stacking faults not only serve as preferential nucleation sites for α-martensite but may also hinder phase boundary migration due to dislocation pile-up, thus exhibiting a dual regulatory effect on phase transformation.