Energetics of small hydrogen–vacancy clusters in bcc iron

Abstract

Hydrogen may be trapped in voids in iron, leading to undesirable material properties. In this paper, the energetics of small hydrogen-vacancy clusters in body centered cubic iron are investigated. Results from two interatomic potentials are compared. We use molecular dynamics and Monte Carlo methods to find the minimum energy configurations of voids of up to ten vacancies containing up to 50 hydrogen atoms with ratios of hydrogen to vacancy of 10 or less. The formation energies and binding energies of defects to these clusters are calculated. Our results indicate that the hydrogen stabilizes bubbles by causing vacancies to be more tightly bound to clusters, while neighboring irons are less tightly bound. Hydrogen itself becomes less well bound to clusters as the inventory increases. The more physically relevant potential indicates a maximum supported ratio of hydrogen atoms to vacancies of about 4.

The interaction of dislocations and hydrogen-vacancy complexes and its importance for deformation-induced proto nano-voids formation in α-Fe

“…Many first-principle calculations have shown that multiple H atoms can bond to Va in perfect crystals as Va + nH → VaH n (Hayward and Deo, 2011;Lu and Kaxiras, 2005;Tateyama and Ohno, 2003). The product is a relatively stable complex.…”

“…More recently, several groups have utilized atomistic modeling to study the energetics of hydrogen-vacancy complexes in α-Fe (Hayward and Deo, 2011;Hayward and Fu, 2013;Tateyama and Ohno, 2003). The density functional theory (DFT) calculations show that vacancies can be stabilized by H as H lowers both the vacancy formation energy and also bind strongly with vacancies to form the VaH n complexes (Hayward and Fu, 2013;Tateyama and Ohno, 2003).…”

“…of Va by dislocations (Etienne et al, 2010; Fu et al, 2005; Hardouin Duparc et alof Va/H with Va m H n clusters(Hayward and Deo, 2011;Liu et al, 2009) …”

Helium bubbles in bcc Fe and their interactions with irradiation

“…This structure was determined by using a Monte Carlo algorithm [28]. It assumes that the He atoms are located in pre-existing vacancies in the bcc Fe system.…”

“…For all calculations periodic boundary conditions and constant volume are used. The Monte Carlo algorithm used to determine the lowest energy configuration of the cluster [28] is organised as follows. First, the energetics of voids without helium are investigated.…”