Carbon–vacancy interactions in austenitic alloys

Several research results suggest the binding energy of carbon–vacancy (C–V) complexes is of the order 35–55 kJ/mole in face-centered cubic (fcc) iron-base alloys. In addition to point-defect anelasticity, we examine data on self-diffusion of Fe in fcc Fe, which are quantitatively consistent with our results on point-defect structure modeling. Quenching, cold work, and electron irradiation increase the height of damping peaks associated with C motion, consistent with a contribution of C–V complexes to the relaxation strength of these peaks. The effect of increasing C content on self-diffusion of Fe in fcc Fe is to decrease the activation energy for self-diffusion, hence increase the diffusivity, and implies a C–V binding energy of ∼40 kJ/mol. We have used first-principles gradient-corrected density functional calculations to determine directly the binding energy of nearest-neighbor C–V pairs in fcc iron. A value of ∼35 kJ/mol is obtained.