Vacancy Formation and Trapping by Carbon in Ferritic Iron: A First‑Principles Study

Olga Kulitckaya; Vladislav Kulitckii

doi:10.4028/p-Vixj6S

Paper Titles

Fatigue Life Prediction of a CNC Machine Spindle Support Shaft under Realistic Loading Using RecurDyn Simulation
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Dynamic Analysis of CNC Machine Tool Structures Using FBGMT and R-Flex Flexible Multibody Dynamics Approaches
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Assessing Barely Visible Impact Damage in Thermoplastic Composites through the Logarithmic Slope Histogram Sequence
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Failure Analysis of Cast Iron Overlay Material in Grinding Rollers by SEM/EDS and XRD Characterization
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Vacancy Formation and Trapping by Carbon in Ferritic Iron: A First‑Principles Study
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Influence of Nickel on Microstructure and Property in Die-Cast Ductile Iron
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Vacancy Formation and Diffusion in FeCr Alloys
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Conjugate Heat Transfer Analysis of Teflon-Coated Steel Surfaces Exposed to Premixed Flame Jets
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Comparative Study of Rhodium Recovery from Plating Solutions via Cementation, Chemical Precipitation and Electrowinning
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HomeDefect and Diffusion ForumDefect and Diffusion Forum Vol. 453Vacancy Formation and Trapping by Carbon in...

Vacancy Formation and Trapping by Carbon in Ferritic Iron: A First‑Principles Study

Abstract:

The vacancy-carbon interactions control defect kinetics and the properties of ferritic iron. Here we use spin‑polarized density‑functional theory on 3×3×3 bcc‑Fe supercells with one to four carbon atoms in octahedral interstitial sites to quantify how carbon modifies vacancy energetics. Two limiting families are considered: dilute configurations with C far from the vacancy and compact VCₙ clusters (n=1-4) with C placed in the nearest octahedral shell. For the dilute case, the vacancy formation energy remains close to that of pure Fe. In contrast, for compact clusters the effective formation energy of a vacancy bound to carbon, E_{f_VC}, decreases markedly with increasing n, while the total binding energy increases and then saturates. The incremental stabilization E_add stays positive up to n = 3 and turns negative for n=4. E_trap is small and positive for n=1-2, but becomes negative for n ≥ 3, consistent with carbon‑rich microenvironments biasing vacancies into VCₙ states. Increasing n moderately reduces N(E_F), particularly in the minority-spin channel, which is consistent with strengthened Fe-C hybridization and the larger binding energies of the VC_n complexes. Finally, using a Seydel thermodynamic trapping model parameterized by our ab initio E_bind (VC_n) we predict effective vacancy diffusivities D_{v_eff}(T,C_tot) that exhibit trends in line with prior analyses, while reflecting the stronger trapping implied by our energetics. Consistent with our DOS analysis, increasing carbon content strengthens Fe-C hybridisation, shifts Fe d states to lower energies and reduces N(E_F), indicating a gradual transition from metallic Fe-Fe bonding to a more covalent Fe-C bond character. This work closes an important gap between electronic-structure data and mesoscale modelling by providing a consistent set of vacancy-carbon energetics and effective vacancy diffusivities for dilute C in α-Fe, which serves as a model system for ferritic Fe-based alloys.