Interatomic Fe-H potential for irradiation and embrittlement simulations

Abstract

The behavior of hydrogen in iron and iron alloys is of interest in many fields of physics and materials science. To enable large-scale molecular dynamics simulations of systems with Fe-H interactions, we develop, based on densityfunctional theory calculations, an interatomic Fe-H potential in the TersoffBrenner formalism. The obtained analytical potential is suitable for simulations of H in bulk Fe as well as for modeling small FeH molecules, and it can be directly combined with our previously constructed potential for the stainless steel Fe-Cr-C system. This will allow simulations of, e.g., hydrocarbon molecule chemistry on steel surfaces. In the current work, we apply the potential to simulating hydrogen-induced embrittlement in monocrystalline bulk Fe and in an Fe bicrystal with a grain boundary. In both cases, hydrogen is found to soften the material.

Review and construction of interatomic potentials for molecular dynamics studies of hydrogen embrittlement in Fe─C based steels

“…Hence, we do not consider Nguyen et al's BOPs in the interest of simulating iron carbides. We also notice that Kuopanportti et al increase the cutoff distance for the Fe─Fe interaction of their Fe─H BOP to improve Young's modulus during MD simulations . This change of cutoff distance will obviously change other properties of the potential.…”

“…BOP can capture properties of various iron and iron carbide phases. More importantly, BOP parameters for the three relevant binary systems Fe─H, Fe─C, and C─H are available. As a result, we will construct a Fe─C─H ternary potential using the binary BOP parameters.…”

“…The same C─H BOP (by Brenner) was used in literature studies of C─H systems . Likewise, the same Fe─H BOP (by Kuopanportti et al and Muller et al) was used to study Fe─H systems . Hence, these C─H and Fe─H BOPs are used to construct the ternary Fe─C─H BOP.…”

“…Our ternary BOP formalism is described in Appendix A and constructed parameters for BOP I and BOP II are listed in Tables A1 – A4. To make the potentials more general, we assume that all three‐body parameters depend on three species whereas in literature, some of the parameters depend only on two species. These three‐body parameters can be implemented using the polymorphic pair style in LAMMPS, which requires tabular forms of BOP I and BOP II whose electronic files (Supporting Information) can be founded here…”

“…Note that in Table , the Fe─H properties from BOP I and BOP II match exactly. This is because BOP I and BOP II use the same Fe─H potential …”