Dumbbell Interstitials Research Articles

First-principles study of Re in BCC-Mo: Diffusion behavior and interaction with point defects

Due to their some beneficial properties, molybdenum-based alloys, such as Mo-Re alloys, are recognized as potential structural materials for nuclear power reactors. Irradiation induced precipitation of rhenium (Re) atoms causes hardening and embrittlement of Mo-Re alloys, restricting their application. The interaction of rhenium (Re) atoms with point defects (PDs), as well as the diffusion behavior of Re atoms in BCC-Mo (Body Center Cubic-molybdenum), were investigated using first-principles methods. The results revealed that Re atoms exhibited high binding energies with both vacancy (Vac) and interstitial dumbbells. Furthermore, the binding energies increased with the number of Re atoms. The binding energies of Re with self-interstitial dumbbell (SIA, ie., Mo-Mo) and mixed interstitial dumbbell (Mo-Re) were quite close to. Due to the high exchange barrier between Vac and Re, the diffusion of rhenium through the vacancy-drag mechanism was difficult. Due to the low migration and rotation barrier of Mo-Re mixed interstitial dumbbell, the diffusion of Re atoms in Mo was dominated by the interstitial-mediated mechanism. From the perspective of diffusion dynamics, only interstitial dumbbells can promote the aggregation of Re atoms. By comparing the binding energy of interstitial dumbbell with interstitial dumbbell and interstitial dumbbell with Re atoms, pairs of Mo-Re interstitial dumbbell was suggested to be the nucleation sites to attract more interstitial dumbbells, thereby promoting the precipitation of Re clusters. It was because they had high binding energy and were difficult to decompose once combined.

Fast relaxation in metallic glasses studied by measurements of the internal friction at high frequencies

We performed high-frequency (0.4–1.7 MHz) measurements of the internal friction (IF) on 14 bulk metallic glasses (MGs). It is found that 12 of these MGs display relaxation IF peaks at temperatures ≈ 400–500 K, which are weakly affected by heat treatment within the amorphous state. The corresponding relaxation time is about 0.3 μs. This fast relaxation is reported for the first time in the literature. The apparent activation enthalpy for 4 MGs is determined. It is shown that if measured at a low frequency of 1 Hz, these IF peaks would appear near room temperature or by 30–50 K below it. Thus, the IF peaks found in the present investigation are direct analogues of low-temperature/low-frequency β′- and/or γ-relaxations described in the literature. It is argued that the origin of these IF peaks is related to the relaxation of structural defects similar to dumbbell interstitials, which are frozen in solid glass from the liquid state upon melt quenching. These defects can be considered as elastic dipoles and their re-orientation in the applied stress provides anelastic deformation and corresponding IF peak. After correction for temperature dependence of the shear modulus, the true activation enthalpy (0.62–1.08 eV) and activation entropy (4 ≤ΔS∕kB≤15) for defect re-orientation are determined.

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.

Tailoring the chemical environments and magnetic moments of the interstitials of high-entropy alloys

The interstitial defects play a crucial role in controlling the irradiation performance of high-entropy alloys (HEAs) particularly of CrMnFeCoNi. However, the site-to-site chemical and magnetic disorder of HEAs prohibits understanding the behavior of interstitials in HEAs. Herein we demonstrate that the chemical bonding dominates the formation of dumbbells at the weak magnetic effect, whereas the strong magnetic effect can perform over the chemical bonding in determining the formation of dumbbells. Accordingly, Ni-containing dumbbells are particularly unstable due to its weak chemical bonding and magnetic effect, while the spin-down Cr and the magnetic adaptive Mn are essential for stabilizing CrMnFeCoNi. Note that the chemical bonding and magnetic effects can be quantitatively characterized by the cohesive and band-filling descriptors. Our study elucidates a physical understanding of the dumbbell interstitials of HEAs and provides a rational guidance for designing advanced structural alloys with optimal irradiation resistance.

Compact A15 Frank-Kasper nano-phases at the origin of dislocation loops in face-centred cubic metals

It is generally considered that the elementary building blocks of defects in face-centred cubic (fcc) metals, e.g., interstitial dumbbells, coalesce directly into ever larger 2D dislocation loops, implying a continuous coarsening process. Here, we reveal that, prior to the formation of dislocation loops, interstitial atoms in fcc metals cluster into compact 3D inclusions of A15 Frank-Kasper phase. After reaching the critical size, A15 nano-phase inclusions act as a source of prismatic or faulted dislocation loops, dependent on the energy landscape of the host material. Using cutting-edge atomistic simulations we demonstrate this scenario in Al, Cu, and Ni. Our results explain the enigmatic 3D cluster structures observed in experiments combining diffuse X-ray scattering and resistivity recovery. Formation of compact nano-phase inclusions in fcc structure, along with previous observations in bcc structure, suggests that the fundamental mechanisms of interstitial defect formation are more complex than historically assumed and require a general revision. Interstitial-mediated formation of compact 3D precipitates can be a generic phenomenon, which should be further explored in systems with different crystallographic lattices.

Atomic-scale study of He ion irradiation-induced clustering in α-Zirconium

Zircaloy-4 alloy specimens consisting of α-Zr grains were irradiated on a tandem accelerator with 5 MeV He ions to a fluence of 5 × 1021 ions m − 2 at different temperatures. Defect clusters and He bubbles were observed in the TEM micrographs of the irradiated microstructure. The small defect clusters and He bubbles were found to exhibit spherical shapes whereas the large defect clusters showed plate-like shapes. Molecular dynamics simulations and crystallography analyses revealed that the defect clusters are mainly composed of Zr interstitials. During He-ion irradiation, the clustering of Zr dumbbell interstitials results in the formation of small and spherical defect clusters. With further irradiation, the Zr interstitials prefer to occupy the octahedral sites that align along the {12¯14} planes with other site interstitials, forming cluster sections. These initial planar clusters then grow by extending along the <101¯0> directions and by forming more cluster sections along the <12¯16> directions, leading to large plate-like defect clusters on the {1¯21¯1}planes. He bubbles nucleate by the clustering of He atoms and vacancies that are formed by kicking out the lattice atoms, and then grow by the migration and coalescence of helium-vacancy clusters. Small He atoms have many interstitial sites to occupy in the α-Zr HCP crystal, allowing He bubbles to grow to spherical shapes. In addition, grain boundaries induce the accumulation of primary point defects and He atoms and high irradiation temperature accelerates diffusion, and hence larger defect clusters and He bubbles form in the grain boundary regions and at higher irradiation temperature.

Formation and stability of the early stage solute and defect clusters in Cu-free ferritic steels during irradiation

• The mechanism of the role of specific element species in the local stability of the Mn-Ni-Si quartet clusters are investigated by DFT. • The interaction of Mn with the dumbbell interstitials is stronger than other solutes. and this is favorable for formation of the cluster. • Si can stabilize solute clusters because it forms stable covalent bonds with other solutes at 1nn. Irradiation induced significant volume fractions of Mn-Ni-Si clusters have been characterized as severe cause for the matrix embrittlement in low-Cu reactor pressure vessel steels (RPV) at high flux. The formation mechanism of these clusters is still unclear, especially when the RPV does not contain Cu. In this work, we perform density functional theory (DFT) calculations to examine the mechanism of the role of specific element species in the local stability of clusters in Fe-Mn-Ni-Si system. The binding energy of different species or configurations for quartets including Mn, Ni, Si, vacancies, and interstitial atoms is presented. Based on the DFT data, we found that point defects are more likely to promote cluster formation, and when Mn is present near the dumbbell interstitials, is favorable for formation of the cluster. Si also plays an important role by forming stable covalent bonds at 1nn to other solutes, but Si atoms cannot be close to each other because this would interfere with the magnetic properties of the surrounding Fe atoms to the extent of reducing the stability of the clusters. These results are helpful for a better understanding of the cluster formation mechanism and can provide fundamental parameters for the solute-cluster evolution with larger scale simulations.

Interactions of solute atoms with self-interstitial atoms/clusters in vanadium: A first-principles study

The interactions of solute atoms with self-interstitial atoms (SIA)/clusters and their effect on stability of single SIAs and small SIA clusters in vanadium (V) were investigated using first-principles calculations. We calculated the binding energies of 16 substitutional solute elements (Cr, Ti, Al, Fe, Mo, Y, Nb, Cu, Mn, Ni, Ta, Zr, W, Si, S and P) with SIAs and found that the solute Cr/Fe/Mn/P/S prefers to form solute-V<111> mixed interstitial dumbbell. The interaction between solute Ti/Si/Y/Nb/Ta and <111> SIA dumbbell is attractive, while most of other solutes repel with the <111> SIA. The stable Cr- < 111> mixed interstitials and the Ti- < 111> SIA can attract five metal solutes (Ti, Y, Zr, Nb, and Ta), further stabilizing the SIA. The stability of small SIA clusters are determined and the parallel <111> SIA dumbbell clusters are the most stable configurations, followed by the parallel <110> SIA configurations. The small SIA clusters can attract three metallic solutes (Ti, Y and Zr) and two impurities (P and S), but will repel most solute atoms. The presence of solute atoms does not change the relative stability order among SIA clusters. The present calculations provide the basic data for understanding the influence solutes on the stability of SIAs/SIA clusters in V alloys under irradiation.

Molecular dynamics study of the point defects in bcc uranium

Thermodynamic properties of bcc uranium with point defects are studied using ab initio molecular dynamics (MD) simulations at 1100 K. The simulations were performed with canonical ensembles of ${\mathrm{U}}_{127}{\mathrm{M}}_{1}$, ${\mathrm{U}}_{128}{\mathrm{M}}_{1}$, and ${\mathrm{U}}_{126}{\mathrm{M}}_{1}{\ensuremath{\square}}_{1}$ for M = $\ensuremath{\square}$, He, Ne, Ar, Kr, Xe, Sr, Zr, I, Cs, and Pu disposed on a bcc lattice lying within a $4\ifmmode\times\else\texttimes\fi{}4\ifmmode\times\else\texttimes\fi{}4$ cubic supercell. This work provides formation energies of substitutional, self, and solute interstitial atom defects as well as binding energies of M-$\ensuremath{\square}$ pair defects. This work demonstrates that our computational scheme based on MD simulations gives reliable formation and binding energies of atomic defects in bcc uranium compared to conventional density functional theory calculations. The equilibrium volume, bulk modulus, and thermal expansion coefficient of pure bcc uranium obtained from our MD simulations compare very well with corresponding experimental results. The vacancy formation energy is predicted to be 0.88 eV. The experimental vacancy formation energy remains uncertain. Experimental study of the formation and binding energies of other point defects as well as the bulk modulus and thermal expansion coefficients of uranium with these defects is also not found in the literature. This work shows that point defects tend to decrease the bulk modulus and increase the thermal expansion coefficient of bcc uranium. The solute formation energies of noble gas atoms show a bearing on their size. A large solute (Xe) has a high formation energy, and vice versa. This size effect is not quite evident for the chemically reactive solutes, namely, Sr, Zr, I, Cs, and Pu. Our MD simulations further show that vacancies are the favorable point defects in bcc uranium rather than both vacancies and self interstitials as predicted by earlier calculations. The formation energies of self interstitial atoms are found to be lower than those of solute interstitial atoms, each calculated in six different basic interstitial dumbbell configurations. That is, bcc U accommodates self interstitials more easily than decay or fission gas interstitials (He, Kr, and Xe). Further, He atoms are found to have comparable formation energies in the substitutional and interstitial locations. The fission product atoms Kr and Xe prefer to occupy vacant substitutional lattice sites rather than interstitial sites. Binding energies of divacancy and solute-vacancy pairs (0.31 vs $\ensuremath{-}0.69$ eV for the Xe-$\ensuremath{\square}$ pair, for instance) from our MD simulation show that nucleation and growth of fission gas bubbles are supported by a thermodynamic driving force, whereas vacancies tend to stay apart. This is in agreement with literature reporting that bcc uranium softens and swells mainly by agglomeration of noble gas bubbles.

Defect dynamics in [formula omitted]-U, Mo, and their alloys

Defect dynamics constitutes the foundation for describing microstructural evolution in any material systems for nuclear applications, including body-centered cubic γ-U, Mo, and their alloys. However, defect properties and evolution, and the impact of a large atomic size mismatch between U and Mo atoms on defect dynamics have not been elucidated. In this work, we use molecular dynamics to extensively examine composition-dependent defect behavior in U-Mo alloys and the pure metals. It has been found that point defect migration is strongly correlated and mediated by minor atoms via preferential paths in alloys. Interstitial dumbbells migrate three-dimensionally through the major atoms with a preferred 〈110〉 configuration. Vacancies are less mobile than interstitials, but become comparable (one order of magnitude difference in diffusivity) in U-rich systems. Overall, compared with the pure metals, defect diffusivity can be tuned up or down based on the alloy composition. Finally, interstitial clustering is found to be unfavorable in U-rich systems, as opposed to Mo which exhibits an efficient formation of interstitial-type dislocation loop with 1D diffusion mode. These findings not only provide necessary input to high-fidelity meso-scale simulations of microstructural evolution in these systems, but also have important implications towards explaining radiation effects influenced by the dimensionality and rates of defect diffusion.

First-principles study of intrinsic point defects and Xe impurities in uranium monocarbide

Based on density functional theory (DFT) calculations, we perform an extensive investigation of intrinsic point defects and Xe impurities in uranium monocarbide (UC). The DFT calculations involve both the conventional generalized gradient approximation (GGA) and the GGA+U approach with the Hubbard parametric term (U), using up to 5×5×5 supercells. GGA calculations for the formation energy of intrinsic defects demonstrate the significant effect of using larger supercells than in previous studies. Results confirm that the ⟨111⟩ and ⟨100⟩ dumbbell interstitials are the most stable interstitial configurations for U and C, respectively. The interstitial mechanisms are favored for self-diffusion of both uranium and carbon and diffusion of Xe under equilibrium conditions. Calculations also reveal that the Xe substitutional defect at the C lattice site tends to adopt an off-site configuration, which can be interpreted as a Xe interstitial–C vacancy complex. We also utilize GGA+U to assess the impact of effective U parameter (Ueff) on the results. Moreover, we introduce a method to estimate the carbon chemical potential by fitting the phase diagram composition data and propose a selection Ueff=1.25 eV based on the experimental Xe diffusion activation energy. With this approach, GGA+U calculations reproduce the available experimental data for the formation energy of the carbon Frenkel pair and can explain the stepwise recovery of intrinsic properties and burst Xe release behavior in UC observed in annealing experiments.

A simple kinetic parameter indicating the origin of the relaxations induced by point(-like) defects in metallic crystals and glasses

Computer simulation shows that an increase of the volume V due to point defects in a simple metallic crystal (Al) and high entropy alloy (Fe20Ni20Cr20Co20Cu20) leads to a linear decrease of the shear modulus G. This diaelastic effect can be characterized by a single dimensionless parameter K = dln G/dln V. For dumbbell interstitials in single crystals K ≈ −30 while for vacancies the absolute K-value is smaller by an order of magnitude. In the polycrystalline state, K ≈ −20 but its the absolute value remains anyway 5–6 times larger than that for vacancies. The physical origin of this difference comes from the fact that dumbbell interstitials constitute elastic dipoles with highly mobile atoms in their nuclei and that is why produce much larger shear softening compared to vacancies. For simulated Al and high entropy alloy in the glassy state, K equals to −18 and −12, respectively. By the absolute magnitude, these values are by several times larger compared to the case of vacancies in the polycrystalline state of these materials. An analysis of the experimental data on isothermal relaxations of G as a function of V for six Zr-based metallic glasses tested at different temperatures shows that K is time independent and equals to ≈−43, similar to interstitials in single-crystals. It is concluded that K constitutes a important simple kinetic parameter indicating the origin of relaxations induced by point(-like) defects in the crystalline and glassy states.

Accelerated kinetic Monte Carlo: A case study; vacancy and dumbbell interstitial diffusion traps in concentrated solid solution alloys.

Vacancy and self-interstitial atomic diffusion coefficients in concentrated solid solution alloys can have a non-monotonic concentration dependence. Here, the kinetics of monovacancies and ⟨100⟩ dumbbell interstitials in Ni-Fe alloys are assessed using lattice kinetic Monte Carlo (kMC). The non-monotonicity is associated with superbasins, which impels using accelerated kMC methods. Detailed implementation prescriptions for first passage time analysis kMC (FPTA-kMC), mean rate method kMC (MRM-kMC), and accelerated superbasin kMC (AS-kMC) are given. The accelerated methods are benchmarked in the context of diffusion coefficient calculations. The benchmarks indicate that MRM-kMC underestimates diffusion coefficients, while AS-kMC overestimates them. In this application, MRM-kMC and AS-kMC are computationally more efficient than the more accurate FPTA-kMC. Our calculations indicate that composition dependence of migration energies is at the origin of the vacancy's non-monotonic behavior. In contrast, the difference between formation energies of Ni-Ni, Ni-Fe, and Fe-Fe dumbbell interstitials is at the origin of their non-monotonic diffusion behavior. Additionally, the migration barrier crossover composition-based on the situation where Ni or Fe atom jumps have lower energy barrier than the other one-is introduced. KMC simulations indicate that the interplay between composition dependent crossover of migration energy and geometrical site percolation explains the non-monotonic concentration-dependence of atomic diffusion coefficients.

An AIMD+U simulation of low-energy displacement events in UO2

In UO2, due to the existence of U 5f electrons, the strong-correlation effects are significant, and correction of on-site Coulomb interaction is necessary. For strongly-correlated electronic system like UO2, however, it is a challenge to consider such correction during simulation of their dynamic processes under radiation. In this study, a new method, i.e., AIMD + U, in which ab initio molecular dynamics method and correction of on-site Coulomb interaction between U 5f electrons are combined, is employed to investigate the response of UO2 to low energy radiation. The threshold displacement energies for O and U atoms have been determined, and defect creation and distribution have been provided. New mechanism for defect generation, and novel defect types, including uranium (oxygen) dumbbell interstitials and uranium antisite defects, are revealed from this study.

Point Defects and Their Properties in the Fe20Ni20Cr20Co20Cu20 High-Entropy Alloy

The characteristics of interstitial atoms and vacancies in the Fe20Ni20Cr20Co20Cu20 high-entropy alloy have been determined by the molecular dynamics and statics methods. The effect of these defects on elastic moduli has been analyzed. It has been found that interstitial atoms are stable only in the form of dumbbells responsible for a significant diaelastic effect (decrease in the shear modulus). As compared to vacancies, an increase in the concentration of interstitial dumbbells much more rapidly reduces the shear modulus with an increase in the volume. Furthermore, interstitial dumbbells are responsible for the appearance of specific high- and low-frequency modes in the spectrum of the vibrational density of states. The latter modes are related to the observed diaelastic effect. The evolution of the diaelastic effect and vibrational spectrum during the transition of the system to a noncrystalline state has been studied.

Link between shear modulus and enthalpy changes of Ti16.7Zr16.7Hf16.7Cu16.7Ni16.7Be16.7 high entropy bulk metallic glass

Mechanical and thermal properties of materials are intricately linked. Particularly, this fully applies to metallic glasses. In this work, we study shear modulus behavior and heat effects occurring upon heating up of Ti16.7Zr16.7Hf16.7Cu16.7Ni16.7Be16.7 high entropy bulk metallic glass up to the full crystallization. In the framework of the Interstitialcy theory, we show that shear modulus relaxation data can be applied to quantitatively predict exo- and endothermal effects related to structural relaxation, glass transition and crystallization of this high entropy metallic glass. This fact suggests that the underlying physical mechanism responsible for this link can be conditioned by the relaxation of the system of structural defects, which by their properties are similar to dumbbell interstitials in metals.

Defect properties in a VTaCrW equiatomic high entropy alloy (HEA) with the body centered cubic (bcc) structure

We report first-principles results of the point defect properties in a V-Ta-Cr-W high-entropy alloy (HEA) with the body-centered cubic (bcc) structure. Different from the widely-investigated face-centered cubic (fcc) HEAs, the local lattice distortion is more pronounced in bcc ones, which has a strong influence on the defect properties and defect evolution under irradiation. Due to the large size of Ta, the exchange between vacancies and Ta exhibits lower energy barriers. On the other hand, interstitial dumbbells containing V and Cr possess lower formation energies. These defect energetics predicts an enrichment of V and Cr and a depletion of Ta and W in the vicinity of defect sinks. Besides, we find that interstitial dumbbells favor the [110] orientation in the HEA, instead of [111] direction in most nonmagnetic bcc metals, which helps to slow down interstitial diffusion significantly. Consequently, the distribution of migration energies for vacancies and interstitials exhibit much larger overlap regions in the bcc HEA compared to fcc HEAs, leading to the good irradiation resistance by enhancing defect recombination. Our results suggest that HEAs with the bcc structure may bear excellent irradiation tolerance due to the particular defect properties.

Nitrogen interstitial defects in silicon. A quantum mechanical investigation of the structural, electronic and vibrational properties

The vibrational features of eight interstitial nitrogen related defects in silicon have been investigated at the first principles quantum mechanical level by using a periodic supercell approach, a hybrid functionals, an all electron Gaussian type basis set and the Crystal code. The list includes defects that will be indicated as Ni (one N atom forming a bridge between two Si atoms), Ni-Ns (one interstitial and one substitutional N atom linked to the same Si atom), Ni-Ni (two Ni defects linked to the same couple of silicon atoms) and Ni-Sii-Ni (two Ni defects linked to the same interstitial silicon atom). Four 〈0 0 1〉 split interstitial (dumbbell) defects have also been considered, in which one lattice atom splits in two, and as a result the two interstitial atoms are three fold coordinated: they are two N (indicated as IN-N), one N and one Si (IN-Si), one N and one C (IC-N). For comparison, also the case with two Si atoms (ISi-Si) has been included. Four of these eight defects have unpaired electrons, and have been described through the UHF (Unrestricted Hartree-Fock like) computational scheme. The local defect geometry and the charge and spin density distributions have been analyzed. For the first time, intensities of IR and Raman spectra were calculated along with the frequencies, and this is crucial for the comparison of theoretical simulations with experiments. All these defects present very characteristic features in their IR spectrum, dominated by one or two very intense peaks. It has been possible to find a simulated counterpart to each one of the five peaks reported by Stein in 1985 (Applied Physics Letters, 47, 1339), and then to establish a correspondence between the microscopic structure of the defects and the IR intense peaks. The Raman spectra are in all cases dominated by the perfect silicon peak at about 530 cm−1, and are then not very useful for the characterization of the defects.

Interstitial clustering in metallic systems as a source for the formation of the icosahedral matrix and defects in the glassy state

The paper presents molecular dynamics and -statics simulations of a prototypical mono-atomic metallic system (aluminum) and its defects in the crystalline and glassy states. It is shown that there is a thermodynamic driving force for the association of dumbbell interstitials in the crystalline lattice into clusters consisting of different amounts of defects. Clusters containing seven interstitials constitute perfect icosahedra. Within the general framework of the interstitialcy theory, melting of simple metallic crystals is intrinsically related to a rapid increase of the concentration of dumbbell interstitials, which remain identifiable structural units in the liquid state. Then, the glass produced by rapid melt quenching contains interstitial-type defects. The idea of the present work is to argue that the major structural feature of many metallic glasses—icosahedral ordering—originates from the clustering of interstitial-type defects frozen-in upon melt quenching. Separate defects and their small clusters represent the defect part of the glassy structure.

Frenkel defect recombination in Ni and Ni‒containing concentrated solid‒solution alloys

Recombination of Frenkel defects is an important process that contributes to the performance of materials under irradiation. In this work, the recombination mechanisms of Frenkel defects in face-centered cubic Ni and Ni‒containing solid‒solution alloys are investigated based on interatomic potentials and ab initio calculations. It is found that, in pure Ni, the spontaneous recombination volume for a [100] dumbbell interstitial is 18Ω and 34Ω (Ω is the atomic volume) with the empirical potential and ab initio method respectively. Addition of Fe atoms increases the spontaneous recombination volume of Frenkel defects significantly. For those stable Frenkel defects that cannot recombine, a stronger attractive force between the interstitial and the vacancy is found in concentrated Ni‒Fe alloys compared to in pure Ni, which provides the driving force for enhanced recombination. The distribution of life-time for Frenkel defects at finite temperature suggests that recombination in Ni‒Fe alloys is delayed due to the sluggish diffusion of interstitials. Finally, recombination in Ni‒Fe‒Cr alloys is studied by substituting a portion of Fe in Ni‒Fe with Cr. A remarkable increase in recombination probability is observed in this case because of the presence of less stable Cr‒containing than Fe‒containing dumbbell interstitials and lower migration barriers of vacancies. This work reveals that higher defect recombination probability in concentrated alloys is responsible for the experimentally observed enhanced irradiation resistance.