Energetic driving force for preferential binding of self-interstitial atoms to Fe grain boundaries over vacancies

Abstract

Molecular dynamics simulations of 50 Fe grain boundaries were used to understand their interaction with vacancies and self-interstitial atoms at all atomic positions within 20Å of the boundary, which is important for designing radiation-resistant polycrystalline materials. Site-to-site variation within the boundary of both vacancy and self-interstitial formation energies is substantial, with the majority of sites having lower formation energies than in the bulk. Comparing the vacancy and self-interstitial atom binding energies for each site shows that there is an energetic driving force for interstitials to preferentially bind to grain boundary sites over vacancies. Furthermore, these results provide a valuable dataset for quantifying uncertainty bounds for various grain boundary types at the nanoscale, which can be propagated to higher scale simulations of microstructure evolution.

Binding of HenV clusters to α-Fe grain boundaries

“…While the experimental observation of h100i symmetric tilt grain boundaries (R5, R13 GBs) is below 1 MRD, these grain boundaries are commonly used in DFT studies due to the low periodic distances required in the grain boundary plane. The present set of boundaries is smaller than those previously explored 62,63 for two reasons. First, since we explored multiple starting configurations for the He n V clusters in this study, a larger number of simulations were required for each grain boundary than for the point defect studies, which only considered a single vacancy or self-interstitial atom.…”

“…These grain boundaries represent the ten low coincident site lattice (CSL) boundaries (R 13) within the h100i and h110i STGB systems. This is a subset of those boundaries used in prior studies of point defect absorption (vacancies and self-interstitial atoms) by a large range of grain boundary structures in pure a-Fe 62,63 and is identical to those used in our previous study of 1-2 atom He defect interactions with grain boundaries. 58 The current set of boundaries includes four h100i STGBs (R5, R13) and six h110i STGBs (R3, R9, R11).…”

“…Hence, there are more undercoordinated sites than overcoordinated sites, as would be expected at the grain boundary (i.e., positive free volume). Furthermore, the per-atom vacancy binding energies E v b from Tschopp et al 62,63 will be compared as part of this analysis, which may be relevant since the He n V clusters involve a monovacancy.…”

“…Recently, Tschopp and colleagues utilized an iterative approach to systematically quantify the interactions between point defects, carbon, hydrogen, and helium with Fe grain boundaries. 46,47,58,62,63 Herein, this approach is applied along with using multiple different starting positions, or instantiations, about each site to more precisely probe the formation and binding energy landscape about ten grain boundaries. In this paper, we present this approach for eight He n V clusters and we explore how the grain boundary structure interacts with He n V clusters using molecular static calculations.…”

“Bulk” Nanocrystalline Metals: Review of the Current State of the Art and Future Opportunities for Copper and Copper Alloys

“…173,174 Moreover, the atomic structure of the grain boundary has been shown to have an effect on the interaction with point defects. 171,175,176 This fact suggests that increasing the concentration of certain types of boundaries may also be beneficial in radiation resistance of nanocrystalline materials. For instance, molecular dynamics simulations in Cu have shown that the R3 coherent twin boundary, abundant in electrodeposited nanotwinned copper, has a much smaller interaction with radiation defects than most other general boundaries.…”