First-principles study of Mn, Al and C distribution and their effect on stacking fault energies in fcc Fe

Using ab initio simulation of manganese, aluminum and carbon impurities in fcc Fe, we demonstrated the features in their distribution, which involves repulsion of interstitial carbon atoms, formation of Mn-C pairs as well as short range Al-ordering of the D0(3)-type. We modeled the formation of stacking faults (SF) and analyzed the impurity effect on the intrinsic stacking fault energy (SFE), which controls the plasticity mechanism in austenitic alloys. First, we found that impurities have an influence on the SFE only when they are located within a few atomic layers near a stacking fault. As a result, the SFE is highly sensitive to the concentration of impurities in the vicinity of stacking fault defect. Aluminum and carbon as well as manganese for concentrations higher than 15 at.% increase the SFE, while the formation of Mn-C pairs and Al-ordering restrain the SFE growth. Short range Al-ordering strongly decreases the unstable stacking fault energy (USFE) making the formation of the stacking fault much easier, but does not affect the SFE that can explain the observed planar glide deformation before the occurrence of mechanical twinning regardless of the SFE. (c) 2013 Elsevier B.V. All rights reserved.