ReaxFF MD Investigation on the Effect of Microstructure on Polycrystalline Iron Oxidation

Y Chen and B Gu and B Wang, HIGH TEMPERATURE CORROSION OF MATERIALS, 103, 8 (2025).

DOI: 10.1007/s11085-025-10368-w

The oxidation reactions of monocrystalline iron (mono-1), bicrystal iron (poly-14), and four-grain iron (poly-1234) were assessed by ReaxFF MD simulations to systematically investigate grain boundary effects on iron oxidation. For both monocrystalline and polycrystalline irons, the surface of the oxide film was characterized by a rough and island-like texture. A transformation in the crystal structure of iron was observed after oxidation, and the disordered structure of grain boundaries would expand into the grains in polycrystalline irons. The oxidation process consists of a linear and rapid stage controlled by the chemical reaction and a parabolic and slow stage governed by the inward diffusion of oxygen and outward movement of iron. Atomic stress analysis showed that surface iron atoms and inner oxygen atoms exhibited a tensile stress state while inner iron atoms and surface oxygen atoms demonstrated a compressive stress state. Such a stress state could facilitate the atom diffusion and thus promote the oxidation process. The grain boundary is found to enhance the oxidation process, as evidenced by the greater oxide film thickness and phase transformation, accelerated oxidation rate and atom diffusion, higher O/Fe ratio and atomic stress in polycrystallines.

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