Synergistic Effect of Alloying Atoms on Intrinsic Stacking-Fault Energy in Austenitic Steels

Intrinsic stacking-fault energy is a critical parameter influencing the various mechanical performances of austenitic steels with high Mn concentrations. However, quantitative calculations of the stacking-fault energy (SFE) of the face-centered cubic (fcc) Fe, including the changes in concentrations and geometrical distribution of alloying atoms, cannot be obtained by using previous computation models. On the basis of the interaction energy model, we evaluated the effects of a single alloying atom (i.e., Mn, Al, Si, C and N), as well as its aggregates, including the Mn–X dimer and Mn2–X trimer (X = Al, Si, C and N) on the SFE of the fcc Fe via first-principle calculations. Given low concentrations (<10 wt%) of alloying atoms, dimers and trimers, theoretical calculations reveal the following: (1) Alloying atom Mn causes a decrease in the SFE, whereas Al, Si, C and N significantly increase the SFE; (2) combination with other alloying atoms to form the Mn–X dimer (X = Al, Si, C and N) exerts an effect on SFE that, to a certain extent, is close to that of the corresponding single X atom; (3) the interaction between Mn2–X and the stacking fault is stronger than that of the corresponding single X atom, inducing a significant increase in the SFE of fcc Fe. The theoretical results we obtained demonstrate that the increase in SFE in high-Mn steel originates from the synergistic effect of Mn and other trace alloy atoms.