A generalized Peierls–Nabarro model fitted to generalized stacking-fault energies calculated from ab initio density functional theory was used to study the effect of interstitial N content on stacking faults in {111} plane of face-centered cubic Fe-N alloys. These simplified systems were reliable representatives of face-centered cubic Fe-Mn-N steels, for example, as Mn acted to stabilize face-centered cubic relative to the body-centered phase but hardly affected the generalized stacking-fault energies. Here a study was made of the dependence of the stable stacking-fault widths of Fe–N alloys upon generalized stacking-fault energies versus %N. In contrast to the classical Volterra solution, in which the stacking-fault width depended only upon the intrinsic stacking-fault energy value, the results revealed a strong dependence of stacking-fault width upon intrinsic, unstable and maximally unstable stacking-fault energy values. The model predicted finite stacking-fault widths for negative intrinsic stacking-fault energy values. This result could not be explained by the Volterra model, but arose due to the finite (and positive) unstable stacking-fault energy barrier that had to be surmounted even if the intrinsic stacking-fault energy was negative (stable). This result was of critical importance for the observed stacking-fault formation and maximum widths. That is, the stacking-fault width was found to depend non-monotonically upon the percentage of N, with a maximum critical shear stress at 1wt% (4at%)N, in agreement with experiment, and also suggested a non-monotonic critical shear stress dependence upon the N content.

Effect of Nitrogen on Generalized Stacking Fault Energy and Stacking Fault Widths in High Nitrogen Steels. S.Kibey, J.B.Liu, M.J.Curtis, D.D.Johnson, H.Sehitoglu: Acta Materialia, 2006, 54[11], 2991-3001

Table 3

Bulk Diffusion of 99Mo in Fe76Mo8Cu1B15