Interstitial Formation Energies Research Articles

Properties of radiation-induced point defects in austenitic steels: a molecular dynamics study

Austenitic steels are recognized as excellent structural materials for pressurized water reactors due to their outstanding mechanical properties and radiation resistance. However, compared to the widely studied FeCrNi series of steels, little is known about the radiation resistance of FeCrNiMn steel. In this study, the generation and evolution of radiation-induced defects in FeCrNiMn steel were investigated by molecular dynamics simulations. The results showed that more defect atoms were produced in the thermal spike stage, but fewer defects survived at the end of the cascades in FeCrNiMn compared to pure Fe. Point defect properties were analyzed by molecular statics, and the formation energies of defects in FeCrNiMn were lower than those of pure Fe, while the migration energies were higher. Compared to FeCrNi, FeCrNiMn had smaller migration energies and a larger overlap of vacancy and interstitial migration energies. The low vacancy formation energies and widely overlapping migration energies suggested that the number of point defects in the thermal spike stage was higher, but the possibility of recombination was greater. Additionally, Mn exhibited the smallest interstitial formation energies and migration energies. The difference in defect migration energies revealed that vacancy and interstitial defects migrate through different alloy constituent elements. This study revealed the underlying mechanism for the excellent irradiation resistance of FeCrNiMn.

Thermal expansion, lattice vibration, and isotope effect on hydrogen diffusion in BCC Fe, Cr, and W from first-principles calculations.

Fe, Cr, and W are important elements in the alloys of in-reactor materials and operate in high-temperature environments with thermal expansion. Their tritium-impeding abilities are crucial to the radiation safety of various nuclear reactors. In this study, first-principles density functional theory is combined with quasi-harmonic approximation to evaluate factors that can affect the interstitial formation energy and diffusion coefficient of hydrogen isotopes in body-centered cubic (BCC) Fe, Cr, and W, including thermal expansion, metal host lattice vibrations, phonon density-of-states (pDOS) coupling diffusing atoms, and isotope effects. Calculation results indicate that the interstitial formation energy decreases as lattice expansion increases, whereas the jump barriers remain almost constant. Thermal expansion, host lattice vibration, and pDOS coupling minimally affect the diffusion coefficients of hydrogen isotopes in Fe, Cr, and W. The diffusion coefficient ratios between hydrogen isotopes are higher than the inverse ratio of the square root of the isotope mass at low temperatures. However, they decrease to the inverse ratio of the square root of the isotope mass at temperatures exceeding 800K. This study comprehensively investigates factors that affect the diffusion coefficients of hydrogen isotopes in BCC Fe, Cr, and W, thus providing a firm theoretical foundation for predicting the diffusion coefficients of tritium at different temperatures using protium/deuterium diffusion coefficients.

First-principles study of behaviors of point defects in Mo-14 Re alloy

Molybdenum alloys with rhenium additions of 14 % (Mo-14 Re) are regarded as structural materials for advanced nuclear reactors. The performance of Mo-14 Re alloy under irradiation is crucial for its application. Irradiation performance is related to the behaviors of point defects produced by irradiation. The behaviors of point defects in Mo-14 Re alloy were investigated using first-principles methods in this work. Compared with the results in pure Mo alloy, the formation energy and the migration energy of vacancy in Mo-14 Re were both reduced, and the migration energy of interstitial dumbbell increased while the formation energy decreased in Mo-14 Re. In Mo-14 Re, vacancy preferred to form and diffuse faster in Re-enriched environment. Knowing the number of Re atoms in the 1NN (first nearest neighbor) shell of the vacancy and saddle point, the vacancy formation energy and migration energy can be estimated. Since the interstitial atom has a certain orientation, the distribution of the atoms around it is anisotropic. To estimate the interstitial formation energy, it was necessary to count the number of Re atoms at the tensile and compressive sites at the 1NN shell around the interstitial. The interstitial motion was three-dimensional (3D) in Mo-14 Re. At 1200 K, the diffusion coefficient of Re atom was a little higher than that of Mo atom, which could lead to the segregation of Re atoms at defect sinks and the formation of Re-enriched phase. It is possible to investigate the longer-term evolution of microstructure using cluster dynamics (CD) or kinetic monte carlo (KMC) techniques based on these results.

Effect of Al related chemical short-range order on the irradiation resistance of Al0.5CoCrFeNi multi-principal element alloy: A molecular dynamics simulation

Multi-principal element alloys (MPEAs) have received much attention for future nuclear materials due to their exceptional radiation resistance. This work investigated the effect of Al related chemical short-range ordered (CSRO) which caused by its large atomic size in face-centered cubic (FCC) Al0.5CoCrFeNi alloy on its irradiation damage behavior through mixed molecular dynamics and Monte Carlo simulations. The calculation results indicate that the CSRO structure effectively suppresses the generation of point defects during irradiation in Al0.5CoCrFeNi alloy, and this inhibitory effect increases with increasing irradiation energy. The enhanced radiation resistance of CSRO alloy is attributed to the high vacancy formation energy, interstitial atom formation energy, and vacancy migration energy barrier of Al. Moreover, the Al atoms in CSRO alloy can also act as defect barriers, preventing the migration of vacancy defects; The formation energy of interstitial atoms in the CSRO alloy exhibits a strong element dependence, and there is a significant difference in the formation energy of interstitial atoms between different points, which strengthens the hysteresis diffusion effect of MPEAs and further enhances the radiation resistance of MPEAs.

Development of an interatomic potential for the W–Ta system

A physics-inspired, data-driven interatomic potential framework for multi-element system is presented. This potential is based on the generalization of the embedded atom method potential and systematically incorporates two-, three- and many-body effects. Different atomic environments are described by atom-centered Gaussian basis sets which provides sufficient flexibility to capture diverse atomic environments and allows for easy optimization of the free parameters. An interatomic potential model for the tungsten–tantalum (W–Ta) system is developed using this framework by training on data from ab initio density functional theory (DFT) calculations. The potential is thoroughly tested at various compositions by comparing bulk and defect properties from experimental and DFT data. It is shown that the potential predicts the elastic constants, defect properties, such as vacancy and interstitial formation energies, core structures of dislocations, and melting points for both pure and tantalum and tungsten with an accuracy comparable to other single element machine learning based potentials. The potential model is used to investigate the formation energies of ordered alloys and vacancy formation energies for chemically random W–Ta alloys.

Dynamic heterogeneity of atomic transport in a body-centered cubic WTaVCr non-equiatomic high-entropy alloy

Compared to face-centered cubic (fcc) high-entropy alloys (HEAs), body-centered cubic (bcc) HEAs generally possess larger lattice distortion, resulting in distinct point defect properties. In this work, molecular dynamics (MD) simulations and molecular statics (MS) calculations were performed to study the dynamic heterogeneity in a bcc W40Ta35V10Cr15 non-equiatomic HEA with large lattice distortion. Defect energies in W40Ta35V10Cr15 HEA show a strong preference for a specific element and possess large energy spreads, resulting in dynamic heterogeneity of atomic transport in the process of defect diffusion and evolution. V and Cr interstitials exhibit higher occurrence probability and faster diffusion compared to W and Ta interstitials. Such diffusion heterogeneity brings about high recombination probabilities of W and Ta interstitials and large fractions of V and Cr in surviving interstitials during displacement cascades. The binding ability of interstitials correlates with the magnitude of interstitial formation energies. The smaller the interstitial formation energies, the weaker the binding abilities. A large number of surviving V and Cr interstitials with smaller interstitial formation energies exhibit weak binding abilities and discrete distribution. Our findings suggest that the dynamic heterogeneity in W40Ta35V10Cr15 HEA with large lattice distortion may be the underlying mechanism of outstanding irradiation resistance.

New Family of Interstitial Oxygen Ion Conductor Discovered By High-Throughput Computational Screening

Discovery and design of highly efficient oxygen-active materials which react with, absorb, and transport oxygen is essential for fuel cells and related applications. Currently, the predominant families of oxygen-active materials used in commercial devices are perovskites and fluorites, which diffuse oxygen via a vacancy mechanism and only have adequate oxygen diffusivity and surface exchange at high temperatures (e.g., ~800 ˚C), impeding their use at lower temperatures desirable for more cost-effective and long-lasting device operation. The development of alternative electrolyte/electrode materials with high oxygen ionic conductivity at low temperatures (e.g., room temperature to 400 °C) is of great interest. Interstitial oxygen ion conductors typically have significantly lower migration barriers than even state-of-the-art vacancy-mediated oxygen conductors, which can provide orders of magnitude kinetic enhancement at low temperatures. In addition, the interstitial oxygen defects typically become more thermodynamically favorable as the temperature is lowered, potentially providing an additional boost to the oxygen conductivity at low temperatures from a higher mediating defect concentration. The synergistic combination of low migration barriers and thermodynamically favorable interstitial oxygen content at low temperatures provides the tantalizing possibility that interstitial oxygen conductors may lead to transformative performance improvements in oxygen-active materials.In this work, we developed an approach to discover new interstitial-mediated oxygen conductors by performing high-throughput computational screening of the 34k oxide materials from the Materials Project database and discovered a new structural family of interstitial oxygen diffusers, perrierite-type oxide La4Mn5Si4O22+ 𝜹 (LMS). We used a hierarchy of screening criteria including the geometric free space, thermodynamic stability, synthesizability, redox-active elements, and presence of short diffusion pathways. This approach, based largely on simple, physically intuitive properties, quickly winnowed the field of 34k oxides down to just 345 oxides, an approximate 99% reduction in the search space considered, with essentially no significant computational cost. From this reduced set of promising materials, ab initio simulations were performed to calculate the interstitial oxygen formation energy and migration energy. Our screening has yielded several material families to date, among which the A4B5C4O22+ 𝜹, with La4Mn5Si4O22+ 𝜹 (LMS) as a representative material, was selected for investigation with higher-fidelity DFT hybrid functional calculations and experimental validations. The calculated formation energy of interstitial oxygen is -0.11 eV at a concentration of 2.3% under air condition, indicating that LMS is predicted to be oxygen hyperstoichiometric with an expected composition of La4Mn5Si4O22+0.5 in air. Two separate interstitial and interstitialcy (“kick-out”) diffusion mechanisms are revealed by ab initio molecular dynamics (AIMD) simulation. For the interstitial diffusion pathway, the moves through the channel in between the zigzag-arranged sorosilicate Si2O7 groups, with a barrier of 0.69 eV. For the interstitialcy diffusion pathway, the moves along the corner-sharing Si2O7-MnO2-Si2O7 framework by kicking out the lattice oxygen, with a barrier of 0.74 eV. These results align well with the experimental findings of stable interstitial oxygen content and high oxygen mobility in LMS (Please see a separate poster from Md Sariful Sheikhfor experimental results). This work provides a systematic approach to screening a large number of prospective materials and opens a new avenue of finding promising interstitial oxide ion conducting materials for potential applications in a range of fast oxygen ion conduction-based technologies.

Ab initio study of effects of Al on the defect behaviors of AlxCoCrFeNi high entropy alloys

The influence of Al on the defect behaviors of AlxCoCrFeNi high-entropy alloys (HEAs) is studied by ab initio calculations. The lattice distortion, defect formation energies, and defect migration energies were calculated for different Al concentrations ranging from 0 to 6.25 at. %. First, the increase in the lattice distortion of AlxCoCrFeNi by the addition of Al is demonstrated, but the increment is smaller than that predicted by the atomic size difference of constituent elements. Second, although formation energies of Al vacancies and dumbbells containing Al are higher, the addition of Al decreases the average formation energies of vacancies and interstitials, which is probably due to the Al-induced local strain field and lattice distortion. The migration energies of interstitials and vacancies exhibit opposite variations, the migration energies of interstitials are increased while that of vacancies are decreased with the Al content. Moreover, the distributions of formation and migration energies of both defects are significantly broadening with increasing Al content, which could further enhance the characteristic effects of HEAs and play a more important role in the irradiation resistances of HEAs. Based on the calculation results, the effects of Al on the irradiation responses of AlxCoCrFeNi are discussed.

Interactions between displacement cascades and grain boundaries in NiFe single-phase concentrated solid solution alloys

Single-phase concentrated solid solution alloys (SP-CSAs) are promising structural materials with excellent irradiation resistance. It is very important for their application in nuclear reactor structures to understand the interactions between their grain boundaries (GBs) and irradiation-induced defects. With molecular dynamics (MD) simulations, the displacement cascades in NiFe SP-CSAs with Σ5(210) symmetrical tilt GB were studied. Compared with pure Ni, NiFe has higher sink strength of GB for vacancies but has little effect on the interstitial absorption of GB. The formation energies of interstitials and vacancies near the GB are more dispersed, so that the point defects are more difficult to aggregate, which is beneficial for the recombination of interstitials and vacancies near the GB. Both the formation energies of point defects and the sink strengths of GB for point defects could be changed with the SP-CSA compositions. When the Fe atom concentration is higher than 30 at.%, the point defects are easier to annihilate. Both the effects of the PKA energy and the PKA-GB distance on the displacement cascades damage can be explained with the size of overlapping region between the cascade region and GB. In addition, the formation of SP-CSAs helps to annihilate the vacancies in NiFe with Σ37(750) symmetrical tilt GB and Σ5 twist GB.

Computational Screening of La2NiO4+δ Cathodes with Ni Site Doping for Solid Oxide Fuel Cells.

Doping on the crystal structure is a common strategy to modify electronic conductivity, ion conductivity, and thermal stability. In this work, a series of transition metal elements (Fe, Co, Cu, Ru, Rh, Pd, Os, Ir, and Pt) doped at the Ni site of La2NiO4+δ compounds as cathode materials of solid oxide fuel cells (SOFCs) are explored based on first-principles calculations, through which the determinant factors for interstitial oxygen formations and migrations are discussed at an atomistic level. The interstitial oxygen formation and migration energies for doped La2NiO4 are largely reduced in contrast to the pristine La2NiO4+δ, which is explained by charge density distributions, charge density gradients, and Bader charge differences. In addition, based on a negative correlation between formation energy and migration barrier, the promising cathode materials for SOFCs were screened out between the doped systems. The Fe-doped structures of x = 0.25, Ru-doped structures of x = 0.25 and x = 0.375, Rh-doped structures of x = 0.50, and Pd-doped structures of x = 0.375 and x = 0.50 are screened out with interstitial oxygen formation energy less than -3 eV and migration barrier less than 1.1 eV. In addition, DOS analysis indicates that doping to La2NiO4+δ also facilitates the electron conductions. Our work provides a theoretical guideline for the optimization and design of La2NiO4+δ-based cathode materials by doping.

Effect of local chemical environment on the point defects in AlNbTiZr refractory high entropy alloys

The effect of local chemical environment (i.e., type and content of atom neighboring to defects) on the point defect properties has been thoroughly investigated in bcc AlNbTiZr refractory high-entropy alloys (HEAs). It has been shown that the randomness of local chemical environments in AlNbTiZr HEAs leads to a wide distribution of vacancy and interstitial formation energy rather than to definitive values. One interesting aside here is that the number of Al and Nb atoms locating at the first-nearest neighbor (1nn) of vacancy drives the evolution of vacancy formation energy (VFE) in AlNbTiZr system, as vacancies preferred Al-rich and Nb-poor environments. What another worth noticing is that the most stable interstitial defects are in the form of dumbbells. What's more, the Al-Al dumbbell is the easiest interstitial defect while the Zr-Zr dumbbell is the least according to the lowest formation energy and electronic characteristics. Along with the results of vacancies preferred Al-rich environments, Al in AlNbTiZr can stabilize the single vacancy and inhibit its migration and diffusion to form large-size vacancy clusters. Therefore, the initial irradiation resistance can be improved by adjusting the concentration and distribution of Al in AlNbTiZr. One can infer from the results obtained present that it is beneficial in improving the irradiation resistance by controlling different processing experimentally methods to increase the occurrence of Al-Al arrangement in AlNbTiZr high-entropy alloys.

Predicting formation of chemically graded metal/ceramic interfaces

A gradual variation in chemical composition at an atomic level in a metal/ceramic interface would result in a gradual variation in structural features that can give rise to unusual properties of the heterostructure. One of the ways such atomic-level chemical gradation can be achieved is by diffusion of anions from ceramic to metal. This process is perceived to be unfavorable because it requires the creation of anion vacancies in ceramic and anion interstitials in metal. We use the sum of C, N, or O vacancy formation energy in ceramics and their interstitial formation energy in metals to assess the possibility of migration of anions across the metal/ceramic interface, leading to an atomically chemically graded interface. We use the first-principles density functional theory to calculate the driving force for a few scientifically and technologically important metal/ceramic systems: a combination of 10 metals (M=Ti, Zr, Hf, V, Nb, Ta, Mg, Al, Cr, and Fe) and corresponding 30 ceramics MaXb (X=C, N, and O). The metal/ceramic systems that favor chemical gradation have metals from group IVB and VB mainly due to the large negative interstitial formation energies.

The causation of hydrogen embrittlement of duplex stainless steel: Phase instability of the austenite phase and ductile-to-brittle transition of the ferrite phase – Synergy between experiments and modelling

Various mechanisms have been proposed for hydrogen embrittlement of duplex stainless steel, but the causation of hydrogen-induced material degradation has remained unclear. This work shows that phase instability (decomposition) of the austenite phase and ductile-to-brittle transition of the ferrite phase precedes hydrogen embrittlement. In-situ diffraction measurements revealed that Ni-rich sites of the austenite phase decompose into metastable hydrides. Hydride formation is possible by increasing the hydrogen chemical potential during electrochemical charging and low defect formation energy of hydrogen interstitials. Our findings demonstrate that hydrogen embrittlement can only be understood if measured in situ and in real-time during the embrittlement process.

Spatial inhomogeneity of point defect properties in refractory multi-principal element alloy with short-range order: A first-principles study

Short-range order can be developed in multi-principal element alloys and influences the point defect behavior due to the large variation of the local chemical environment. The effect of short-range order on vacancy and interstitial formation energy and migration behavior was studied in body-centered cubic multi-principal element alloy NbZrTi by first-principles calculations. Two short-range order structures created by density functional theory and Monte Carlo method at 500 and 800 K were compared with the structure of random solid solution. Both vacancy and interstitial formation energies increase with the degree of short-range order. Point defect formation energies tend to be higher in regions enriched in Nb and lower in regions enriched in Zr and Ti. Both vacancies and interstitials prefer to migrate toward Zr,Ti-rich regions and away from Nb-rich regions, suggesting that Zr,Ti-rich regions can potentially act as recombination centers for point defect annihilation. Compared to an ideal random solid solution, the short-range order increases the spatial inhomogeneity of point defect energy landscape. Tuning the degree of short-range order by different processing techniques can be a viable strategy to optimize the point defect behavior to achieve enhanced radiation resistance in multi-principal element alloys.

An atomistic study of fundamental bulk and defect properties in [formula omitted]-uranium

Alpha-uranium plays an important role in the performance and structure evolution of metallic fuels under irradiation. It is a highly anisotropic material that demonstrates a complex microstructural response to irradiation dependent on the irradiation temperature, and the mechanisms that control this behavior are not well understood. In this work, fundamental bulk properties and energetic and thermodynamic properties of single point defects and di-defects in α-uranium are determined using molecular dynamics over the range of 400 K - 750 K. The constant pressure heat capacity, total volumetric thermal expansion, anisotropy of the thermal expansion, and single vacancy and single interstitial formation energies all agree well with previous experimental and ab initio results, lending support to the di-defect formation and binding energies and the diffusivity results. We find that the diffusion of vacancies and di-vacancies is strongly anisotropic, while interstitial and di-interstitial diffusion is slightly anisotropic, and the most rapidly migrating species changes depending on the temperature. The formation energy of vacancies and di-vacancies increases slightly with temperature, while the formation energy of interstitials and di-interstitials increases strongly with temperature. In addition, di-vacancies are very loosely bound over the entire temperature range, with an average binding energy of 0.017 eV. Conversely, di-interstitials are strongly bound (0.64 eV) until approximately 600 K, above which the binding energy decreases significantly, with an average binding energy of 0.31 eV. These results provide valuable new insights into the possible mechanisms of the complex irradiation damage behavior of α-uranium.

Development of a semi-empirical interatomic potential appropriate for the radiation defects in V-Ti-Ta-Nb high-entropy alloy

High-entropy alloys (HEAs) hold promise as candidate structural materials in future nuclear energy systems. Body-centred cubic V-Ti-Ta-Nb HEAs have received extensive attention due to their excellent mechanical properties. In this work, the Finnis-Sinclair interatomic potential for quaternary V-Ti-Ta-Nb HEAs has been fitted based on the defect properties obtained with the density functional theory (DFT) calculations. The new potential for Nb accurately reproduces the vacancy formation energy, vacancy migration energy and interstitial formation energy. The typical radiation defect properties predicted by the alloy potential were consistent with the DFT results, including the binding energies between substitutional solute atoms, the binding energy between substitutional atoms and vacancies, and the formation energy of interstitial solute atoms. In addition, the mixing enthalpies of the alloys were also consistent with the DFT results. The present potential can also describe reasonably the collision cascade process of quaternary V-Ti-Ta-Nb HEAs.

Impact of sub-grain structure on radiation resistance in additively manufactured 316L stainless steels: An atomic insight into the mechanism

Laser-based additive manufacturing (AM) provides a new pathway for rapid manufacturing of radiation-resistant materials used in the nuclear engineering system. Ultrafine sub-grain boundary (SGB) structure in AM materials plays an important role in enhancing radiation resistance of materials. Here, we combined experimental and molecular dynamics simulation methods to investigate the interaction between cellular SGBs in AM 316L stainless steel (SS) and irradiation-induced defects. Experimental results prove that the laser powder-bed-fusion (L-PBF) 316L SS presents a more uniform distribution of the defect sizes and the mean defect size is smaller after irradiation compared with cold-rolled (CR) 316L SS. The energetics and dynamics simulation results show that the SGB structure is an efficient sinking site for interstitial atoms. Density of dislocation network on SGBs exerted a significant effect on the reduction of interstitial atom formation energy near SGBs. After irradiation, the evident increase of SGB volume ratio fails to improve the defect self-healing performance but reduces the dislocation density on the SGB, thereby impairing the radiation resistance of the material. This work provides an insight into better understanding of the AM radiation enhanced materials from the combination of atomic simulation and irradiation experiments.

An embedded-atom method potential for studying the properties of Fe-Pb solid-liquid interface

A new interatomic potential for Fe-Pb binary system is developed in the framework of an embedded atom model using the force-matching method. Compared with the ab initio calculations and experiment values, the developed Fe-Pb EAM potential can accurately describe the ground state, defects and liquid properties of crystal and Fe-Pb solid-liquid interface, such as equation of state, vacancy and interstitial formation energies, adsorption and escape energies, melting point, radial distribution function and density at high temperature. High accuracy and feasibility of the developed Fe-Pb EAM potential can provide the further reliable studies on the corrosion behavior of liquid Pb on steels used in complicate environment of the irradiation, high temperature, pressure in nuclear reactors.

First-principles calculations to study the metal-insulator transition of Al and Be doped RNiO3 (R = Pr, Nd, Sm, Gd, Tb, Dy, Ho and Er)

Rare earth nickelates (RNO) have been extensively studied in the past decades because of the metal-insulator phase transition. It was reported that the phase transition of RNO could be regulated with the electrons introduced by Li and H doping, but little is known about the multi-electrons (such as Be, Al) doping of RNO. In this paper, we applied the first-principles calculations to investigate the electronic structures, interstitial formation energies, migration behaviors and optical properties of Be and Al doped RNO. Results show that RNO would undergo a metal-insulator phase transition when the Be and Al doping concentrations respectively reach 50% and 25%. In addition, the migration of Be and Al along the [001] direction of RNO shows that as the radius of rare earth atoms decreases, the migration barrier generally shows a decreasing trend. As for optical properties, the absorption coefficient and reflectivity decrease in Be and Al doped RNO over the entire range of visible and infrared light. Generally, the transmissivity of RNO can be greatly improved by doping 50% of Be and Al.

Energetics of intrinsic point defects and hydrogen in tungsten borides: a first-principles study

To understand the irradiation resistance and hydrogen (H) behavior in tungsten borides (W x B y ) in a burning plasma fusion environment, the energetics of intrinsic point defects and H in six stable ground state W borides, including W2B, WB, WB2, W2B5, WB3 and WB4, have been investigated using first-principles density functional theory calculations. The results show that the formation energies of interstitials and vacancies do not directly depend on the W and B content in W borides. However, the interaction between vacancies of a stoichiometric vacancy (SV) cluster in W x B y is related to the atomic ratio of B to W (y/x). The vacancies of a minimum-size SV cluster in W x B y are energetically repulsive for y/x ⩽ 1, while the vacancies energetically bind together for y/x larger than 1. The formation energy of B Frenkel pairs in each W boride is lower than that of W Frenkel pairs. Among the six evaluated W x B y compositions, WB has the highest and the lowest formation energy of H interstitials and H-vacancy complexes, respectively; however, these two energies in WB2 are in reverse order. The average H binding energies to single vacancies in WB and WB4 are comparable with that in W, while this binding energy in WB3 and WB2 is obviously higher or lower than in W, respectively. The diffusion activation energy of H in W borides is anisotropic. One dimensional (1D) diffusion of H in W2B, as well as 1D/2D diffusion in WB, W2B5, WB3 and WB4 are preferred at relatively low temperatures; however, three-dimensional diffusion of H is predicted in WB2. The diffusion activation energy of H generally increases with B content in W borides due to the increasing local charge deficit caused by strong B–B covalent bonds. This study is useful for evaluating the performance of W borides in a fusion environment.