First Principles Assessment of Carbon Absorption into FeAl and Fe₃Si: Toward Prevention of Cementite Formation and Metal Dusting of Steels

Abstract

We assess two alloys, FeAl and Fe3Si, in terms of their ability to inhibit ingress of carbon into steels using periodic density functional theory to model alloy thin films. Absorption of carbon into Fe3Si via its (100) and (110) surfaces is predicted to be considerably more endothermic compared to absorption into FeAl or pure Fe. Predicted energy barriers for surface to subsurface diffusion are ∼1 eV or larger for all four surfaces studied. A very endothermic dissolution enthalpy (1.65 eV) and large diffusion activation energies (e.g., 1.29 eV) suggest Fe3Si should inhibit carbon uptake into bulk steel and slow bulk diffusion. Combined with the results of other recent work [Johnson, D. F.; Carter, E. A. Acta Mater. 2010, 58, 638], we expect that a protective coating of Fe3Si should be effective at preventing steel degradation by hydrogen and carbon containing gases.

Insights on finite size effects in ab initio study of CO adsorption and dissociation on Fe 110 surface

“…At this point, Fe atoms diffuse into cementite and erupt as Fe metal dust [2,3]. As carburization is the initiating step in the metal dusting corrosion (MDC) and is also important for cutting the emission of greenhouse gases CO and CO 2 , it has been studied widely both experimentally and numerically, with the use of various computational approaches [1,[4][5][6]. The reaction between CO and Fe surface can be broken into two consecutive processes, adsorption and dissociation.…”

Influence of surface vacancy defects on the carburisation of Fe 110 surface by carbon monoxide

“…Vacancy defects in metals can be formed in a number of ways, but mostly appear during solidification, and are of vital importance in deciding key chemical and structural properties of the metal and its alloys. Single vacancy defects are known for affecting atomistic position, migration and segregation of other impurity atoms such as C, Cr, and Mn, that are common components in steels, [1][2][3] or H, He, N, O that are unwanted impurities. [3][4][5] Vacancy defects are also known for self-segregation, leading to voids that act as trap centres for alloying atoms and pinning centres for larger defects such as dislocations and affects the overall structural properties.…”

“…10,13,14 Over the past decade, extensive studies of the atomistic characteristics of the vacancy defect in α-iron using density functional theory have demonstrated the importance of ab initio calculations for understanding the kinetics of defects at the surface as well as in bulk systems. 2,[37][38][39][40] In this work we follow these approaches to characterize a single vacancy defect on the Fe-110 surface and study its role in the adsorption and dissociation of CO. The formation energy of such a vacancy defect is calculated and is found to be 0.87 eV, which is much lower than that in the bulk (1.9-2.2 eV 5,39 ).…”

Exploration of Properties from Both the Bulk and Surface of Iron Silicides: A Unified Theoretical Study

“…All calculations were performed at the density functional level of theory with the Vienna ab initio simulation package. , The generalized gradient approximation (GGA) formulated by Perdew, Burke, and Ernzerhof (PBE) was employed for the exchange and correlation energy terms because the spin-polarized GGA approximation describes spin-polarized 3d metals such as Fe and related compounds better than the local (spin-polarized) density approximation. , Our benchmark study (see the Supporting Information “The comparison of calculation methods” part) also showed that the GGA–PBE approximation describes iron silicides well. Spin polarization was included for an accurate description of the magnetic properties of these compounds. ,,,,− Iterative solutions of the Kohn–Sham equations were done using a plane-wave basis set defined by a kinetic energy cutoff of 400 eV, and the samplings of the Brillouin zone were obtained from the Monkhorst–Pack k -mesh scheme . A second-order Methfessel–Paxton electron smearing with σ = 0.2 eV was used to ensure accurate energies with errors less than 1 meV per unit cell.…”

“…The Carter group has reported elegant examples to tackle key problems in steel corrosion from their computational contribution. − The adsorption, diffusion, and dissociation of many key chemical species (such as H, C, CO, and H 2 S) on low-index facets of Fe 3 Si have been systematically explored. These studies significantly advance the understanding of energetics and kinetics of crucial elemental processes as a function of well-defined surface structural features. − Nonetheless, it is noteworthy that previously reported experimental investigations on iron silicides were carried out under a range of T and pressure, − rather than 0 K and 0 atm employed in Carter’s theoretical studies. ,, Therefore, it is reasonable to assume that the thermal stability of the exposed facets would be affected and thereby altered by the change of the T and pressure. As a consequence, the changed stability accompanied by different surface free energies of the exposed facets would trigger and drive the morphology evolution of Fe–Si crystals.…”