Fe-H

Abstract: A multi-scale study was carried out to quantify the effect of interstitial hydrogen concentration on plasticity in α-Fe. In this work, the influence of hydrogen on the screw dislocation glide behavior was examined across several length-scales. The insights obtained were integrated to provide an accurate continuum description for the effect of hydrogen on the dislocation based plasticity in polycrystalline α-Fe. At the outset of this work, a new Fe-H interatomic potential was formulated that enhanced the atomistic estimation of the variation in dislocation glide behavior in presence of hydrogen. Next, the dislocation core reconstruction observed due to the addition of hydrogen using atomistic simulations was validated with the help of large-scale DFT calculations based on the DFT-FE framework. Several atomistic simulations were carried out to comprehensively quantify the effect of hydrogen on the non-Schmid behavior exhibited during the dislocation glide in α-Fe. Finally, crystal plasticity simulations were carried out to understand the effect of hydrogen on the meso-scale deformation behavior of polycrystalline α-Fe.

Abstract: To understand the physics of hydrogen embrittlement at the atomic scale, a general-purpose neural network interatomic potential (NNIP) for the 𝛼-iron and hydrogen binary system is presented. It is trained using an extensive reference database produced by density functional theory (DFT) calculations. The NNIP can properly describe the interactions of hydrogen with various defects in 𝛼-iron, such as vacancies, surfaces, grain boundaries, and dislocations; in addition to the basic properties of 𝛼-iron itself, the NNIP also handles the defect properties in 𝛼-iron, hydrogen behavior in 𝛼-iron, and hydrogen-hydrogen interactions in 𝛼-iron and in vacuum, including the hydrogen molecule formation and dissociation at the 𝛼-iron surface. These are superb challenges for the existing empirical interatomic potentials, like the embedded-atom method based potentials, for the 𝛼-iron and hydrogen binary system. In this study, the NNIP was applied to several key phenomena necessary for understanding hydrogen embrittlement, such as hydrogen charging and discharging to 𝛼-iron, hydrogen transportation in defective 𝛼-iron, hydrogen trapping and desorption at the defects, and hydrogen-assisted cracking at the grain boundary. Unlike the existing interatomic potentials, the NNIP simulations quantitatively described the atomistic details of hydrogen behavior in the defective 𝛼-iron system with DFT accuracy.

Abstract: We present a new many-body interatomic potential for H in body-centered cubic (bcc) Fe. The potential is developed based on extensive energetics and atomic configurations of an H atom and H-H interactions in Fe from density functional theory calculations. In detail, the potential is parameterized by fitting not only to a single H atom in the perfect bcc Fe lattice and to the properties of H trap binding to a vacancy and surfaces as being done by previous studies, but also to multiple H trapping to a vacancy and H-H interaction in Fe lattice. With such a fitting strategy, the developed potential outperforms existing potentials in its ability not only describing the behaviors of a single H atom in Fe, but also capturing the features of H-H interaction reliably, which is of key importance in revealing H behaviors in local H accumulation around dislocation cores, grain boundaries and crack tips.

Abstract: A modified embedded-atom method (MEAM) interatomic potential for the Fe-H binary system has been developed using previously developed MEAM potentials of Fe and H. The potential parameters were determined by fitting to experimental data on the dilute heat of solution of hydrogen in body-centered cubic (bcc) and face-centered cubic (fcc) Fe, the vacancy-hydrogen binding energy in bcc Fe, and to a first-principles calculation for the lattice parameter and bulk modulus of a hypothetical NaCl-type FeH. The potential accurately reproduces the known physical properties of hydrogen as an interstitial solute element in bcc and fcc Fe. The applicability of the potential to atomistic approaches for investigating interactions between hydrogen atoms and other defects such as vacancies, dislocations and grain boundaries, and also for investigating the effects of hydrogen on various deformation and mechanical behaviors of iron is demonstrated.