The role of Cr atom in the early steam oxidation of Fe‐based alloys: An atomistic simulation

Abstract

This study employed the density functional theory to capture the atomic‐level dissociation processes of steam and investigate the ions migration on Fe(001) and FeCr(001) surfaces, revealing the role of Cr atom in the early oxidation. Various coadsorption structures with different steam‐derived species have been systematically examined to find the most energetically favored surface site. The results showed that the steam dissociation on the alloy surface underwent two steps. First, H2O molecule on the top site was dissociated into OH group and H atom, which further combined with metal atoms on the bridge site and hollow site. Second, the OH group was decomposed into O and H atoms, which moved to two adjacent hollow sites and generated an oxide. On further oxidation, the Fe atom migrated outward and formed an outer Fe oxide, whereas the Cr oxide could only grow inward as O atom passed through oxide. It was found that the presence of Cr atom on the surface was thermodynamically beneficial, which could promote steam oxidation. The Cr atom could effectively block ion diffusion across the oxide scale and protect the underlying substrate from further oxidation. These results were in good agreement with experimental observation.

Reactive molecular dynamics study of the oxidation behavior of iron‐based alloy in supercritical water

“…Our previous work revealed that water molecules are dissociated on the surface and gain electrons from metal atoms, resulting in the oxidation of alloy. [10] Figure 3 shows the loss of electrons on the surface layer and subsurface layer of Fe and FeCr alloy during the initial oxidation (0-1000 ps). Figure 3a reveals that the charge of Fe atoms on the surface increases at a varying rate, which could be roughly divided into three stages.…”

“…[6][7][8][9] Considerable effort has been devoted to analyze the formation of oxide scale on FeCr alloys. [1,[10][11][12] Zhu et al [1] investigated the oxidation behavior of a ferritic-martensitic steel exposed to deaerated SCW at 560-650°C and 25 MPa by oxidation experiment, and the oxidation kinetics at different temperature was analyzed. Shen et al [13] conducted a detailed characterization of material microstructure formed on stainless steels.…”

“…First-principles calculations can provide accurate descriptions of the steam oxidation on FeCr alloy. [10] However, their substantial computational costs restrict the total atoms number and running time. Re-axFF reactive MD simulations bridge the gap between first-principles empirical force-field methods, which could conduct large simulations and maintain a high accuracy.…”

“…We have recently studied the dissociation processes of steam on the Fe(001) and FeCr (001) surfaces by density functional theory (DFT). [10] Reactive dynamics simulations are applied to analyze the initial chemisorption reactions and atoms diffusion behavior across the oxide scale. In this paper, atoms diffusion at metal-inner oxide interface, inner oxide-outer oxide interface, as well as outer oxide-steam interface is considered.…”

Data analytics approach to predict high-temperature cyclic oxidation kinetics of NiCr-based Alloys

“…Hence, developing the capability to predict the high-temperature oxidation kinetics of multi-component alloys is highly desirable and of great interest in many applications involving extreme environments. Although computational approaches using conventional analytical and physics-based simulations have made significant advancements in investigating high-temperature oxidation, they are usually only applicable for a given length/time scale [3][4][5][6] or specific oxidation-related phenomena [7][8][9][10][11] .…”