First-Principles Study of BCC/FCC Phase Transition Promoted by Interstitial Carbon in Iron

Abstract

We report the effect of carbon on the phase transition between body centered cubic (BCC) and face centered cubic (FCC) in iron along Bain pathway, taking into account magnetic configurations, using density functional theory in combination with the generalized solid-state nudged elastic band method. We found that, for pure iron system, the energy barrier of 13.22 kJ·mol⁻¹ is needed for the BCC-to-FCC process happens, while 2.41 kJ·mol⁻¹ is needed for the reverse process (FCC-to-BCC). In the presence of carbon at the octahedral interstitial site of iron BCC/FCC lattice, the energy barrier of 4.53 kJ·mol⁻¹ is needed for the transition from FCC to BCC while the 12.25 kJ·mol⁻¹ is needed for a transition from BCC to FCC along the Bain path. Thus, carbon promotes the transition from BCC to FCC while it prevents the phase transition in opposite direction, from FCC to BCC. This is due to the local stress field formed in the vicinity of carbon atom which pushes the iron atoms aligning with carbon along [001] direction away.