Point defect interactions in iron lattice: a first-principles study

Abstract

The interaction of point defects (interstitial atoms and vacancy) in both BCC Fe and FCC Fe lattices were investigated by first-principles calculations. The goals were to find the equilibrium separation of two interstitial atoms in the iron lattice and to establish the maximum trapping capacity of a mono-vacancy in the iron lattice. Based on our study, the equilibrium separation values of C–C, B–B and C–B were about 5.31 Å in the BCC Fe lattice. In the FCC Fe lattice, the equilibrium separation of C–C, B–B and C–B was about 6.42 Å. A mono-vacancy is shown to be capable of steady trapping as many as 3 atoms to form VX_n (X = C/B, n = 0, 1, 2, and 3) and VCB, VC₂B and VCB₂ complexes in the BCC Fe lattice. For the FCC Fe lattice, it is energetically favorable for a mono-vacancy to accommodate 2 C atoms, 3 B atoms, 2 C atoms and 1 B atoms, 1 C atoms and 2 B atoms, and 1 C atoms and 3 B atoms to form VC₂, VB₃, VC₂B, VCB₂ and VCB₃ clusters, respectively. However, when four interstitial atoms are in the same plane and occupy the nearest interstitial sites around the vacancy, they can also form VC₄, VB₄, VC₂B₂ and VCB₃ in the BCC Fe lattice and VB₄ and VC₂B₂ in the FCC Fe lattice. Moreover, we also found that the trapping ability of a vacancy is stronger in BCC Fe than in FCC Fe. These results are in good agreement with the available calculations and experiments results.