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High-entropy alloys (HEAs) and medium-entropy alloys (MEAs) have attracted a great deal of attention for developing nuclear materials because of their excellent irradiation tolerance. Herein, formation and evolution of radiation-induced defects in NiCoFe MEA and pure Ni are investigated and compared using molecular dynamics simulation. It is observed that the defect recombination rate of ternary NiCoFe MEA is higher than that of pure Ni, which is mainly because, in the process of cascade collision, the energy dissipated through atom displacement decreases with increasing the chemical disorder. Consequently, the heat peak phase lasts longer, and the recombination time of the radiation defects (interstitial atoms and vacancies) is likewise longer, with fewer deleterious defects. Moreover, by studying the formation and evolution of dislocation loops in Niâ€"Coâ€"Fe alloys and Ni, it is found that the stacking fault energy in Niâ€"Coâ€"Fe decreases as the elemental composition increases, facilitating the formation of ideal stacking fault tetrahedron structures. Hence, these findings shed new light on studying the formation and evolution of radiation-induced defects in MEAs. [ABSTRACT FROM AUTHOR]

Abstract The classical molecular dynamics simulation was conducted to investigate the effect of Mo atom addition upon the atomic structure and glass-forming ability of Ni 64 Zr 36-x Mo x (x = 0, 6, 12, 18, 21, 24, 27) metallic glasses (MGs), in terms of the system energy, pair distribution functions (PDFs), and the largest standard cluster analysis. It is found that Mo atoms do not simply replace Zr atoms, but remarkably change the atomic and chemical order; resulting in a more stable, more compact and more complex structures indicated by the split of the first major peak on PDF curves. The addition of Mo atoms does not favor the formation of icosahedrons but enhances the topologically close-packed (TCP) structures that are not only responsible for the split of the first major peak on the PDF curves, but also positively correlation with the GFA predicted by formation enthalpy. Thus, as a superset of icosahedrons, TCP structures are one of the essential characteristic of MGs and significantly enhances the GFA of Ni 64 Zr 36-x Mo x ternary glass metals. These findings shed a new light on the understanding of the structure and the structure-GFA relationship of MGs. Graphical abstract Image 1 Highlights • The Mo-addition in Ni 64 Zr 36-x Mo x changes the s- and d-electronic structures. • Separated with x = 21 PDF curves, atomic volume, T g , and bond-length are different. • Bond length deduces or unchanges with x; Mo-Zr is abnormally the smallest one. • TCP rather than ICO is responsible for the split first peaks on PDF curves. • Amount evolution of TCP rather than ICO is consistent with GFA of alloys. [ABSTRACT FROM AUTHOR]

The study of the corrosion behaviors of structural materials exposed to liquid lithium (Li) is very important for the application of liquid Li as a potential plasma-facing or blanket material in future fusion device. It was demonstrated that the temperature plays an important role in the corrosion process. The corrosion behaviors of 304 stainless steel (304SS) in static liquid Li at 600 K and 640 K for 1320 h under high vacuum have been compared in the present work. The results show that the weight loss and corrosion depth of the 304SS specimens in static liquid Li at 640 K are about 3 times more than those at 600 K. After exposure to liquid Li, all the surfaces produce non-uniform damage which includes pitting and grain boundary corrosion. The surface damage of 304SS specimens at 640 K is more serious than that at 600 K. The corrosion mechanisms include physical dissolution and chemical corrosion; the effect of the latter on the corrosion behavior at 640 K is much more than that at 600 K. [ABSTRACT FROM AUTHOR]

Titanium (Ti) decoration is considered as a promising strategy for preventing metallic uranium (U) surface from oxidization and corrosion. The O adsorption and diffusion behaviors on the clean and Ti-decorated γ-U(0 0 1) surfaces have been investigated by density functional theory (DFT) calculations in the present work. The preferred sites and stable configurations for O atoms on the surface and in the subsurface have been evaluated. It is found that O atoms tend to adsorb on the surface instead of absorbing in the subsurface. With nudged elastic band method, O atom on Ti-doped surfaces departs from the energetically favored site which there is a higher barrier than it on clean U surface. O and Ti can form a chemical bond of Ti-O, reducing the interaction of U and O, thereby enhancing the corrosion resistance of U surface. [ABSTRACT FROM AUTHOR]

An interatomic potential for the Cu–Al system based on the modified analytic embedded-atom method was proposed, which provides a reasonable description of the phase stability across the phase diagram. Combining with this potential, Monte Carlo simulations were performed to study strain-induced element segregation and intermixing in bulk and nanostructured Cu 95 Al 5 and Cu 90 Al 10 alloys. Al with a large atomic size is found to segregate to the tensile region while Cu to the compressive region. The elemental depletion or enrichment in dilute or nanostructured alloy is more notable than that in concentrated or bulk one, due to alloy effects or change of local stress. In particular, phase separation in nanostructured alloys leads to a single pure Cu inclusion in the matrix, which will induce strain hardening. The element segregation also affects the chemical ordering that will provide solid-solution strengthening. [ABSTRACT FROM AUTHOR]

The alloying processes of solid–solid (at 400 K) and liquid–solid (at 500 K) Li–Pb interfaces are investigated by molecular dynamics simulations with embedded-atom method (EAM) potentials. As a comparison, a critical Li–Pb interface at 450 K near the melting point of Li is also studied. Three-stage feature, including the interface disordering, nucleation and growth of an intermetallic phase (B2-LiPb), has been clearly observed in these three cases. It is found that the alloying products are the same, however, the nucleation of the intermetallic phase at the solid–solid Li–Pb interface is earlier than that in the other two cases. The block Li in the solid–solid interface sample keeps the body-centered cubic structure during the course of simulation, while in the critical Li–Pb interface sample, it collapses from the excessive lattice distortion. As simulation time increasing, the interface widths increase gradually with decreasing growth rates, and the growth rate is the largest for the liquid–solid interface and the smallest for the solid–solid interface. The interface width of the solid–solid Li–Pb interface saturates at about 0.3 ns for the diffusion barrier—B2-LiPb almost traversed across the entire interface plane at that time. [ABSTRACT FROM AUTHOR]

Highlights: [•] The work predicts the γ/γ′ interface structure with Monte Carlo simulations. [•] Results indicate that Re atoms preferentially occupy the Al sites in γ′ precipitates. [•] The influence of Re content on the interface characteristics are determined. [•] The solubility limit of Re solute in γ′ precipitates is provided. [ABSTRACT FROM AUTHOR]

Highlights: [•] The work predicts Ni self-diffusion coefficients with first-principles calculations. [•] Positive binding energies imply solute–vacancy pair is not a favorable binding. [•] Correlation factor for solutes Co, Ru and Re are determined. [•] The clear trend in diffusivities of Co, Ru and Re is determined. [ABSTRACT FROM AUTHOR]

Abstract: Vanadium alloys are one of the candidates for first-wall materials. Due to the impact of high energy neutrons and transmutation helium during a fusion reaction, voids will be formed and the mechanical properties of the first-wall materials will be degraded. It is necessary to investigate the effect of voids on the mechanical behavior of the material. In the present paper, the tensile properties of vanadium nanowires with a void have been studied with molecular dynamics simulations. During a deformation process, the generation of 〈111〉/{112} stacking faults to form twinnings in vanadium nanowires. The void facilitates the nanowire’s rupture and alters the deformation behavior of nanowires. For the nanowire with a void, the twin initiates near the vicinity of the void rather than a random location as in a nanowire without void. Twinning boundaries propagate towards the ends of nanowire until the whole wire transforms from the initial orientation (z-〈001〉) to a new configuration (z-〈110〉) with a rotation of 90° under a tensile stress. The nucleation and growth of the twin is inhibited as void size increases, and the nanowires crack is mainly induced by the disordering of vanadium atoms near the void rather than twinning deformation for large size void. A critical effective cross sectional width is determined for different deformation mechanisms. © 2012 Elsevier Science. All rights reserved [Copyright &y& Elsevier]

Abstract: The interaction between an edge dislocation and the solid solution elements (Co, Ru and Re) of different concentration in Ni is investigated by means of molecular dynamics simulation. It is figured out that Ru atoms hinder dislocation movement more effectively than Co atoms under the same concentration. The solid solution strengthening of Re atoms being introduced to Ni crystal is obviously stronger than that of Co and Ru atoms addition. With first-principles density functional theory approach, it is found that one of the leading factors of solid solution strengthening can be attributed to the interaction between host atoms and solid solution elements located in the slip plane, which leads to the stacking-fault energy increasing. [Copyright &y& Elsevier]

Abstract: A new interatomic potential for Fe–He interactions has been developed by fitting to the results obtained from ab initio calculations. Based on the electronic hybridization between Fe d-electrons and He s-electrons, an s-band model, along with a repulsive pair potential, has been developed to describe the Fe–He interaction. The atomic configurations and formation energies of single He defects and small interstitial He clusters are utilized in the fitting process. The binding properties and relative stabilities of the He–vacancy and interstitial He clusters are studied. The present Fe–He potential is also applied to study the emission of self-interstitial atoms from small He clusters in α-Fe matrices. It is found that the di-He cluster dissociates when the temperature is higher than 400K, but the larger He clusters can create an interstitial Fe atom. The temperature for kicking out an interstitial Fe atom is found to decrease with increasing size of the He clusters. [Copyright &y& Elsevier]

Abstract: First-principles calculations based on density functional theory (DFT) have been performed to study the properties of interstitial helium atoms, the vacancy, substitutional, and small helium-vacancy clusters He m V n (m, n =0–4) in palladium. The result indicates that the vacancy has the strongest ability of capturing helium atoms and the octahedral interstitial configuration is more stable than the tetrahedral one, while the energy difference between them is very small. In the palladium crystal, helium atom will migrate from one octahedral interstitial site to another one through the O–T–O path. The formation energies and binding energies of an interstitial helium atom and an isolated vacancy to the helium-vacancy clusters are also determined in palladium. It is found that the formation energies increase with the increasing of helium atoms and the binding energies mainly depend on the helium to vacancy ratio of the clusters rather than the cluster size. [Copyright &y& Elsevier]

In the present paper, the modified analytic embedded-atom method (MAEAM) many-body potentials are provided for fcc and hcp elements. The segregation energies of Mg in Al host are calculated with the MAEAM potentials. The composition depth profiles of Al–Mg alloys are obtained with Monte Carlo simulation method based on grand canonical ensemble. It is found that Mg segregates strongly to the surface layers at 600 K and the composition near the surface is monotonic to the bulk one. The simulation results are reasonable agreement with other experimental and theoretical data. [Copyright &y& Elsevier]

Simple modified analytic embedded atom method (MAEAM) many-body potentials are constructed for bcc molybdenum and hcp rhenium metal in the present paper. Using the MAEAM and analytic alloy potentials, the segregation profiles for (1 0 0) surface in Mo–Re bcc-type random alloys were studied with Monte Carlo simulation technology. The simulation results show that the topmost surface is almost completely enriched with molybdenum, the subsurface is depleted of molybdenum, and the molybdenum concentration oscillates toward the bulk value. The simulation results are in good agreement with available low-energy electron diffraction and low-energy ion scattering experiment data, and the calculations from tight-binding Ising model. [Copyright &y& Elsevier]

Using the analytic modified EAM potentials, the surface concentrations and concentration depth profiles of (1 1 1) and (1 0 0) faces of Pt–Pd and Pt–Ir binary alloys are studied with Monte Carlo simulation based on the grand canonical ensemble statistical rule. In Pt–Pd alloy, the topmost surface is enriched with Pd, and the subsurface layer is depleted of Pd. The simulation results show a damped oscillation of Pd concentration in the whole composition range. A strong Pd segregation is observed for both the orientation faces, while the amount of Pd segregation in the (1 1 1) face is significantly less than that in the more open (1 0 0) face. However, Pt segregates to the surface strongly in the Pt–Ir alloy, and the amount of Pt segregation in the (1 0 0) and (1 1 1) face is almost the same. The simulation results are in good agreement with the available experiment data and other theoretical values. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

Abstract: Molecular dynamics method has been applied to investigate the effects of substitutional helium atoms on the displacement cascades in α-Fe. It is found that the defects production decreases at low temperature and increases at high temperature with the increase of substitutional helium concentration. The clusters sizes and spatial distribution of defects depend on the concentration of helium. Large He–Vacancy clusters can be observed and different defects distribute in different zones, which is different from pure iron under the same radiation conditions. [Copyright &y& Elsevier]

The influence of defects on the plastic properties of materials always captures much attention for ultrahigh strain-rate loading. By virtue of the planar shock compression in [0001], [ 10 1 ¯ 0 ] , and [ 1 ¯ 2 1 ¯ 0 ] directions, our large-scale molecular dynamics simulations reveal that the prismatic nanopores facilitate the inelastic deformation, such as basal and prismatic glides, reorientation, and amorphization. And that, the nanopores with different center axial directions contribute to activation of various slip systems, such as basal and prismatic dislocation slip. The inelastic deformation induced nanopore collapse is an important mechanism of nanopore collapse at weak shock intensity. Three modes of collapse are obtained: a transverse and a longitudinal collapse from the basal glide, and an inclined collapse from the amorphization at the tip of the prismatic nanopore. The shear stress is highly concentrated at the elastic region about to be plastic deformation, and then attenuates mainly during inelastic deformation and nanopore collapse. The shock energy dissipation is correlated to the conversion between kinetic energy and internal energy, which leads to a higher local temperature around the prismatic nanopore. [ABSTRACT FROM AUTHOR]

In the fusion environment, a complex stress field is generated in materials, which affects the evolution of radiation defects. In this study, the behaviors of radiation-induced defects under the effect of stress gradient field in tungsten are carefully simulated at the atomic scale with the molecular dynamics (MD) method. It was found that the stress gradient field affects the migration properties of interstitial defects, resulting in the energy barriers changing with the stress and stress gradient. In the axial stress gradient field, the movement of the 1/2 <111> interstitial dislocation loop is significantly accelerated, and it tends to move toward the region where the stress is concentrated. Within the time scale of the classical MD simulation, the stress gradient has little effect on the migration of vacancies. These results suggested that the stress gradient would cause interstitial defects to accumulate to the region where the stress is concentrated, thereby significantly changing the properties of the tungsten materials. [ABSTRACT FROM AUTHOR]

A characteristic region with vacancy concentration ranging from 0% to 2% was introduced into the single-crystal iron to investigate the effects of vacancies on plasticity and phase transformation of single-crystal iron under shock loading. The simulations were implemented by applying non-equilibrium molecular dynamics simulations with an excellent modified analytic embedded-atom method (MAEAM) potential. A fixed piston velocity of vp = 0.5 km/s was applied in our simulations, under which no plasticity or phase transformation occurred in the perfect single-crystal iron based on the description of the used MAEAM potential. The plasticity and phase transformation in iron were observably influenced by the vacancies as shown in this work. Significant anisotropy of shock response was distinctly exhibited. The nucleation and growth of dislocation loops emitting from the vacancy region were clearly observed in the sample that was shocked along the [110] direction, and the activated slip systems were determined as (11 2 ¯) [111] and (112) [ 11 1 ¯ ]. The vacancies and the vacancies-induced dislocation loops provided preferential nucleation positions for the subsequent phase transformation, which resulted in the phenomenon that the phase transformation product (HCP phase) always preferentially appeared in the vacancy region. The influences of different vacancy concentrations on plasticity and phase transformation were also discussed. [ABSTRACT FROM AUTHOR]

Tungsten (W) and W-based alloys are potential candidates for next-generation fusion reactors, which would withstand both irradiation damages and heavy heat load. In this work, we employed the molecular dynamic method to simulate the behaviors of different radiation defects under the effect of the temperature gradient field, which is induced by heat load. The rotation of the ⟨ 111 ⟩ dumbbell and habit plane of 1/2 ⟨ 111 ⟩ interstitial loops is analyzed in detail. The results show that these two behaviors are not significantly affected by the temperature gradient. Contrary to the thermal equilibrium state, temperature gradient results in the directional diffusion of ⟨ 111 ⟩ dumbbell and 1/2 ⟨ 111 ⟩ interstitial loops in tungsten from the cold to the hot region. The energy barrier is also reduced in the temperature gradient field, which accelerates the defect diffusion. These results indicate that the accumulation of radiation defects in the high-temperature region is expected in temperature gradient fields, which would lead to more severe radiation damages and degradation of materials. [ABSTRACT FROM AUTHOR]

Using a first-principles method in combination with thermodynamic models, we investigate the interaction between rhenium/osmium (Re/Os) and defects to explore the mechanism of radiation-induced Re/Os precipitation in tungsten (W). We demonstrate that radiation-induced defects play a key role in the solute precipitation in W, especially for self-interstitial atoms (SIAs). The presence of SIAs can significantly reduce the total nucleation free energy change of Re/Os, and thus facilitate the nucleation of Re/Os in W. Further, SIA is shown to be easily trapped by Re/Os once overcoming a low energy barrier, forming a W-Re/Os mixed dumbbell. Such W-Re/Os dumbbell forms a high stable Re/Os-Re/Os dumbbell structure with the substitutional Re/Os atoms, which can serve as a trapping centre for subsequent interstitial-Re/Os, leading to the growth of Re/Os-rich clusters. Consequently, an interstitial-mediated migration and aggregation mechanism for Re/Os precipitation in W has been proposed. Our results reveale that the alloying elements-defects interaction has significantly effect on their behaviors under irradiation, which should be considered in the design of W-based alloys for future fusion devices. [ABSTRACT FROM AUTHOR]

The study of the diffusion bonding of Mo-Ti interface is of very importance to joint the composite structures. In the present work, new analytical interatomic potentials for Mo, Ti and Mo-Ti alloy have been developed. Based on those potentials, the diffusion bonding of Mo-Ti interface has been investigated, in which the temperature effect and orientation dependence are studied detailedly by using molecular dynamics (MD) simulations. The results indicated that the asymmetrical diffusion phenomenon exists in Mo-Ti interface, and temperature plays a crucial role during the diffusion. Three interfacial orientations of the Mo substrates have been discussed, and the interfaces are characterized by the fine-scale profiles and concentration distribution along the Z axis. It is found that the interface diffusion is obviously anisotropic, and (1 1 1) plane is more beneficial to atomic diffusion than the (1 0 0) and (1 1 0) planes. [ABSTRACT FROM AUTHOR]

The LiF-BeF 2 -ThF 4 molten salt is designed as the fuel salt mixture in the Thorium Molten Salt Reactor. In the present work, a polarizable force field was used to describe the interionic interactions and the transport properties (such as self-diffusion, electrical conductivity, and viscosity coefficients) of the molten salt have been studied by molecular dynamics simulations within the temperature ranging from 873 K to 1273 K. It is found that the local structure of ThF 4 dissociated significantly, the electrical conductivity of the fuel salt melts increased linearly and the viscosity decreased exponentially with the temperature increasing. It is also found viscosity increased slightly and electrical conductivity decreased significantly with mole fractions of ThF 4 increasing. [ABSTRACT FROM AUTHOR]

A modified analytic embedded atom potential has been developed for the Li-W system. The potential has been fitted to physical quantities derived from density functional theory calculations. It is shown that the new potential is capable of reproducing the solubility of solid solution for Li-W systems. The wetting behaviors between solid tungsten and liquid Li are examined by using molecular dynamics simulations. The MD simulation results for the Li droplet wetting on the W surface illustrated that our MAEAM potential model has a good forecasting ability for the contact angle of liquid Li on W the cleaning surface above the wetting temperature. And the results of Li film dewetting from the W surfaces are consistent with relative experimental results. It is believed that the potential can be used to investigate the surfaces wettability of liquid Li on W substrate. We also simulated the lithium droplet on grooved surface. It is shown that the grooving W surfaces can obviously improve the wetting of liquid Li on W surfaces. [ABSTRACT FROM AUTHOR]

The Fe(110)-Li and Fe(111)-Li solid-liquid interfaces are investigated using molecular dynamics simulations (MD), and the results are detailedly compared with each other as well as with our previous findings obtained from the Fe(001)-Li solid-liquid interface. Due to the different intrinsic surface properties of the Fe substrates, the interface properties show remarkable orientation dependences. As for the Fe substrates, the three Fe surfaces suffer different impacts from the liquid Li on their relaxation behavior. The fine-scale density profiles suggest that the liquid Li atoms near the Fe(110)-Li solid-liquid interface are dramatically layered along the interface normal and the layers’ two-dimensional density maps indicate the layers present high degree of lateral order, which are very similar to the results acquired from the Fe(001)-Li solid-liquid interface. Interestingly, these phenomena observed in the Fe(110)-Li solid-liquid interface do not reproduce in the Fe(111)-Li solid-liquid interface, but some distinct Li layers are detected along the [110] direction at 500 K. In addition, the Li atoms near the Fe(111)-Li solid-liquid interface diffuse faster and invade into the Fe substrate easier than those near the other two interfaces. These orientation-dependent characteristics are well explained in terms of the different surface properties of the Fe substrates. [ABSTRACT FROM AUTHOR]

The interaction of plasticity and martensitic transformation in iron bicrystals under shock has been investigated via nonequilibrium molecular-dynamic simulations with our modified analytic embedded-atom model potential. Our results show that grain boundaries (GBs) can change the kinetics of α → ɛ martensitic transformations. The condition that GBs trigger strain induced transformation (SIT) is revealed, that is, the local structure of GBs can be converted to a hexagonal close packing (HCP) lattice with a lower potential barrier than the BCC → HCP transformation (stress assist transformation, SAT) because the driving energy of transition can be partly provided by the energy of GBs. It can explain why the threshold of the phase transition can be greatly reduced in samples containing some types of GBs. The threshold of SIT is lower than that of SAT, which agrees well with experimental results. Then, the nucleation kinetics of phase transition induced by dislocations are described. The propagation of dislocation provides the driving force for the nucleation of the phase transition. The dislocations can be directly emitted from the GBs under shock, which provides a new view that the phase transition is not always preceded by dislocations near GBs. In addition, dislocations can be induced by pre-existing dislocations under shock, which makes it understandable that GBs can emit dislocations. Our findings have an important significance for experimental studies and macroscopic and mesoscopic scale simulations regarding iron martensitic transformation. [ABSTRACT FROM AUTHOR]

The mechanical properties and fatigue crack propagation of irradiated Ni were investigated using molecular dynamic simulations. The irradiation specimens were obtained by cascade collision, and the primary knocked-on atom (PKA) energy was 10 keV. Tensile results showed that the irradiation led to the decrease in yield stress and yield strain, and also induced the variation of elastic modulus. Analysis of the microstructure in irradiated Ni showed that the irradiation defects inhibited the dislocation motion so that the extension of slip bands was limited, and caused the density of slip bands decreasing. Beside, the influence of irradiation defects on fatigue crack propagation was investigated. It was found that the irradiation defects could slow down the formation of blunting and slip bands and hindered effectively the fatigue crack propagation at 100 K. At 300 K, the crack attracted irradiation defects together, which accelerated the crack propagation with the formation of many slip bands. [ABSTRACT FROM AUTHOR]

The wettability of liquid lithium (Li) droplet on different copper (Cu) surfaces has been studied with molecular dynamics (MD) simulations. The contact angles, solid–liquid interface structures and the time-dependent radius of Li droplet on Cu surfaces are analyzed. A precursor film with single atomic thickness is observed on the Cu surfaces. The precursor film on Cu (1 0 0) and (1 1 1) surfaces presents a perfect circle, but an oval shape on Cu (1 1 0) surface. The spreading kinetics of the precursor film on Cu (1 1 1) surface is much faster than that on Cu (1 0 0) surface, which is attributed to the lower diffusion barriers of Li atom on the Cu (1 1 1) surface. The smallest contact angle is for Li droplet on Cu (1 1 1) surface and the biggest one is along the [0 0 1] orientation of Cu (1 1 0) surface where no precursor film exists. Besides, the temperature effect on the wettability is also studied, and Li droplet spreads more sufficiently with increasing temperature. [ABSTRACT FROM AUTHOR]

The mechanical properties of Ni/Ni3Al monocrystal of nanophases with varying temperatures, strain rates, and phase sizes have been studied using molecular dynamics simulation. The simulation results show that the primary deformation mechanisms in Ni/Ni3Al monocrystal of nanophases were slip bands and antiphase boundaries at room temperature. The studies on the effects of temperature showed that the yield strain, yield strength, and elastic module decreased as temperature increased. However, the influences of strain rate and phase size on the mechanical properties of Ni/Ni3Al monocrystal of nanophases showed that the high strain rate led to the increase of yield stress, and the phase sizes had no significant influence on the maximum yield stress. In addition, the behavior of crack propagation in the model of Ni/Ni3Al interface was investigated under cyclic loading, and it was found that the interface of Ni/Ni3Al was resistance to the fatigue crack propagation. [ABSTRACT FROM AUTHOR]

To study the behavior of noble gas atoms (He, Ne and Ar) in bulk tungsten, new DFT-based potentials for W–He, W–Ne and W–Ar interactions were developed by fitting the results obtained from density functional theory calculations. The new potentials adopt the embedded atom method (EAM) formalism, and the “s-band model” is used to describe the many-body interactions between each of the noble gas atoms and its neighboring W atoms. These potentials reproduce the formation energies of point defects and the migration barriers of single noble gas atoms. The simulations using these potentials successfully predict that the tetrahedral interstitial site is more stable than the octahedral interstitial site for X (= He, Ne or Ar) interstitials. Based on these new potentials, the binding interactions of a single X atom with the X n and X n –Vacancy clusters and the diffusion properties of X n clusters in bulk W were studied using molecular dynamics (MD) simulations. The present results indicate that the binding energies obtained using the new potentials are good in agreement with the results of DFT calculations. The migration energies of the clusters increase with both the increase in the atomic radius of noble gases and the increase in the size of the clusters. [ABSTRACT FROM AUTHOR]

The mobility of atoms at a Pb solid–melt interface has been studied using molecular dynamics simulation. Three cooperative diffusive mechanisms were directly observed: immobilization, vacancy diffusion and desorption-mediated jumps. We hold that the in-plane structural ordering and desorption-mediated diffusion mechanism result in the formation and movement of vacancies at the solid–melt interfaces. A one-dimensional random walk model was proposed to describe the atomic movement at the solid–melt interfaces. In addition, we suggested that in-plane structural ordering plays an important role in the diffusion process. [ABSTRACT FROM AUTHOR]

W-Ni-Fe tungsten heavy alloys (WHAs) are a kind of ductile phase toughened composites that are becoming increasingly interesting as promising alternatives to monolithic tungsten for fusion reactor plasma-facing materials, because of their outstanding combination of strength, ductility and toughness. Understanding the radiation-induced microstructural features of WHAs associated with their mechanical property changes is therefore a topic of active research. The theoretical study of radiation-induced collision cascades by means of atomistic simulations such as classical molecular dynamics (MD) is highly desirable to provide a detailed analysis for the atom-level primary damage production. Here, we develop a Finnis–Sinclair type interatomic potential for W-Ni-Fe ternary systems based on previously proposed unary W and Fe potentials, and use it to study the point defects and mechanical properties of WHAs. The developed potential yields the bulk and defect properties of pure Ni that are in good agreement with experimental data and density functional theory calculations. In addition, it is also capable of reproducing alloy properties with a satisfactory accuracy, especially regarding the solute migration energies, as well as the ground-state interstitial defect configurations. The constructed potential further shows reasonable transferability to other mechanically relevant properties that are not contained in the fitting database. The present potential here will enable large-scale MD simulations of cascade, deformation and fracture of WHAs. [ABSTRACT FROM AUTHOR]

[Display omitted] The corrosion of Zircaloy fuel cladding is one of the crucial issues during the operation of pressurized water reactors (PWR). In this work, a Zr-Nb-H-O reactive force field (ReaxFF) is constructed to study the corrosion mechanisms and irradiation effect of Zr-Nb alloys at the atomic landscape. This ReaxFF can describe the interactions between water dissociation products and Zr-Nb alloys, and the stability as well as diffusion properties of irradiation defects in Zr bulk. The molecular dynamics (MD) simulations based on the present ReaxFF show that Nb can thicken the suboxide layer during the corrosion process, as well as the promotion effect of irradiation on corrosion varies under different PKA (Primary Knock-on Atom) energies. The ReaxFF described here has the potential to be a new tool for understanding the in-reactor corrosion mechanism under the irradiation environment. [ABSTRACT FROM AUTHOR]

[Display omitted] • The orientation-dependent growth mechanism of Cr-rich oxide precipitate is revealed. • The directed growth is thermodynamically preferred than the isotropic growth. • The outward diffusion of Fe atom leaving vacancies which enhancing the Cr diffusion. • O promotes the aggregation of Cr atoms along the [1 0 0] direction. Advanced characterization techniques and atomic simulations, including density functional theory calculation and molecular dynamics simulation, are performed to reveal the orientation-dependent growth mechanism of Cr-rich oxide precipitates in the internal oxide layer of Fe-9Cr steel under supercritical water environment. A new Fe/Cr/O/H reactive force field is constructed to address the limitations of existing empirical potentials in accurately describing the corrosion mechanism of FeCr alloy. The high-resolution characterization reveals the growth mechanism of needle-like FeCr 2 O 4 precipitates in the <1 0 0> direction of the matrix. Atomic simulation demonstrate that the directed growth is thermodynamically preferred than the isotropic growth. The vacancies generated by the outward diffusion of metal atoms enhancing the diffusion of Cr atoms, and O promote the aggregation of Cr atoms along the <1 0 0> direction. [ABSTRACT FROM AUTHOR]

• In all components, the nearest-neighbor coordination of Al3+ exhibits a tetrahedral [AlCl 4 ]– unit. • The tetrahedral [AlCl 4 ]– units remain isolated in a dilute AlCl 3 solution. • The tetrahedral [AlCl 4 ]– units polymerize into a dimer or trimer in a AlCl 3 enriched solution. • The aggregation of [AlCl 4 ]– units accelerates the breaking rate of Al–Cl and Li–Cl bonds. • Both the ionic conductivity and the diffusion coefficient of Li+ exhibit a peak at 50 % AlCl 3 concentration. The short–range and mid–range structural features, as well as thermodynamic properties of a LiCl–AlCl 3 mixed molten salt at 873 K, were investigated as a function of AlCl 3 concentration using ab initio molecular dynamics methods. In all solutions, the short-range structure of Al3+ reveals a regular tetrahedral [AlCl 4 ]– unit. These tetrahedral units exist in isolation within dilute AlCl 3 solution and polymerize into dimers or trimers through Al–Cl–Al bridge bonds in concentrated solutions. The dynamic dissociation analysis of Al3+ and Li+ structures indicates that the Al–Cl bond considerably stronger than Li–Cl bond. The polymerization of the [AlCl 4 ]– units leads to the dissociation of the Li+ coordination shells into freely isolated cations. Furthermore, we examined changes in density, self-diffusion coefficient, and ionic conductivity with varying AlCl 3 concentration in terms of thermodynamic properties. The conductivity and self-diffusion coefficient of Li+ showed a noticeable peak at 50 % concentration. This peak may be associated with the aggregation of [AlCl 4 ]– units and the dissociation of Li+ coordination shells. [ABSTRACT FROM AUTHOR]

The microscopic mechanism of the effect of alloying element on the shock behavior for alloy materials is still limited. In this work, based on our developed Finnis–Sinclair (F–S) interatomic potential of Mg-Y alloy, using nonequilibrium molecular dynamics (NEMD) simulations, we gave new insights into the role of alloying element Y in dynamic deformation of Mg-xat.%Y (x = 1, 3, 6, 8 and 10) alloys, and further revealed the deformation mechanisms of these solid solution alloys, which is dependent on the compositions of Y and the crystallographic orientations. The results confirm that the lattice instability caused by Y atoms results in the reduced yield stress. Under shock along the [0001] direction, the improved plasticity is mainly attributed to the increasing amorphous activity and decreasing amorphous annihilation rate with Y additions, but the other mechanisms, e.g., the dislocation nucleation and phase transition, are suppressed. Furthermore, for the [10 1 ¯ 0] direction, the energy barriers of stacking faults and disordering can be overcome at high Y content, so these two deformation modes are activated accompanying with the lattice reorientation to release the large internal stress, and the enhanced plastic activity is mainly related to the inhibited phase transition. This work can broaden the knowledge of the dynamic response of Mg-Y alloys at atomic-scale, which is significant for the shock experiments and material design. [Display omitted] • Lattice instability around Y atoms results in the reduced yield stress. • Increasing amorphous activity with Y additions improves plasticity in Mg-Y alloys. • Energy barriers of diverse deformation modes can be overcome at high Y content. • Inhabited phase transition enhances the plastic activities of Mg-Y alloys. [ABSTRACT FROM AUTHOR]

The fatigue crack propagation behavior of NiAl was studied using molecular dynamics simulation at room temperature. The simulation results showed that the deformation mechanisms and the crack propagation path were significantly influenced by the orientation of initial crack. The formation process of slip bands around the crack tip was investigated in various cracks and indicated that the slip bands were able to hinder the initiation and propagation of cracks. Besides, the crack growth rate was also calculated by the Paris equation, and the results revealed that the crack growth rate increased with the increasing stress intensity factor range. [ABSTRACT FROM AUTHOR]

Using EAM potentials and molecular dynamic simulations, the Fe(001)–Li solid–liquid interface is characterized in details with density, potential energy, stress, diffusion coefficient profiles, interface width and two-dimensional density map. In addition, the temperature effect on these quantities is also studied. The diffusion coefficient profile indicates Li atoms near the interface diffuse more difficultly. The interface width, calculated from coarse-grained density profile or potential energy profile, increases exponentially with increasing temperature. A “prefreezing” Li layer is observed. Moreover, the two-dimensional density maps for Li and Fe atoms in the first interfacial layer show clearly that Fe and Li formed immiscible two-dimensional domains, rather than an intermixed interfacial alloy. [ABSTRACT FROM AUTHOR]

In this work, new EAM potentials for Li, Pb and Li–Pb alloy have been constructed. Based on these potentials, the structural, thermodynamic and diffusion properties of Li, Pb and Li 17 Pb 83 have been studied with molecular dynamics simulations. The calculated radial distribution functions and static structure factors agree well with previous reported data. The partial radial distribution functions indicate that liquid Li 17 Pb 83 shows a hetero-coordination tendency and the partial Bhatia–Thornton structure factor S C C ( q ) suggests the concentration fluctuation in Li 17 Pb 83 is not large. As comparing to the self-diffusion coefficients, the component diffusion coefficients are much smaller for Li atoms, and almost the same for Pb atoms. Density, enthalpy, capacity, melting point, latent heat of fusion and surface tension are also in reasonable agreement with the literature data within the experimental error. [ABSTRACT FROM AUTHOR]

The mechanism of crack propagation under cyclic loading in iron single crystal was investigated using molecular dynamics simulation. The cyclic loading was strain controlled and three typical specimens of pre-existing center crack of [0 0 1](0 1 0), [0 0 1 ¯] (1 1 0) and [1 1 2 ¯] (1 1 1) models were chosen to study the effect of orientation on fatigue crack propagation. The slip bands, vacancies and voids nucleation were observed during the process of crack growth under cyclic loading, the rate of crack growth and slip direction were different for the three models. No significant slip band was observed in [1 1 2 ¯] (1 1 1) model, and the crack propagation was brittleness. In addition, the influences of grain boundary on crack growth were analyzed on ∑ 3 〈1 1 2〉{1 1 1} and ∑ 5 〈3 1 0〉{0 0 1} models. No significant effect was observed for ∑ 3 on crack propagation, while ∑ 5 resisted crack growth remarkably and resulted in a decreasing rate of crack growth, during which a little hexagonal close-packed (hcp) slip bands appeared in the plastic deformation zone. [ABSTRACT FROM AUTHOR]

Highlights: [•] We develop a new EAM potential of iron appropriate to the high pressure condition. [•] Both plasticity and phase transition happen in our results. [•] The slip system associated with plastic processes is determined to be {112} 〈111〉. [•] The differences of shock response associated with the three orientations are explained. [•] The roles of plasticity are examined for iron single crystal. [Copyright &y& Elsevier]

Highlights: [•] The preferred sites for C, O and N atoms are the hollow ones on the (100) surface and the OIS sites in the bulk of vanadium. [•] O atom is easiest to diffuse on vanadium (100) surface along hollow–bridge–hollow path. [•] In vanadium bulk the diffusion barrier of N atom is the highest and the diffusion coefficient of C atom is the largest. [•] Foreign impurity atoms gain more negative charges from vanadium when they occupy the preferred sites. [Copyright &y& Elsevier]

We present a computational study employing Object Kinetic Monte Carlo simulations to investigate the behavior of D in self-irradiated Mo samples. Our simulations reveal that vacancy clusters contributing significantly to D diffusion, trapping, and desorption behavior. It is found that vacancy clusters play an important role in slowing the diffusion of D within the irradiated materials, which can be represented by an effective trapping energy that associated with mobile D atom interacting with the multiple types of vacancy clusters. Furthermore, we analyze the thermal desorption spectrum of D from irradiated Mo samples, demonstrating a saturation effect in D retention at higher damage levels. Notably, the presence of vacancy clusters significantly influences the thermal desorption spectrum, dominating D desorption at temperature higher than 500 K. We also investigate the D desorption behavior under constant temperature storage conditions, revealing a non-exponential desorption rate with a 1/t decrease over time. Our study sheds light on the complex interplay between D and vacancies/vacancy clusters in irradiated materials, highlighting the importance of considering vacancy clusters in modeling D retention and desorption processes. [Display omitted] [ABSTRACT FROM AUTHOR]

Zirconium alloys, being crucial materials in the nuclear industry, frequently encounter issues related to oxidative corrosion. Understanding the interaction between O atom and alloying atoms at the atomistic scale is helpful for optimizing Zr alloys with improved corrosion resistance. In the present study, a first-principles approach is used to understand the stability and diffusion properties of an O atom in α -Zr with different alloy atoms (Sn, Nb, Fe and Cr). Our findings reveal that the most stable position for oxygen is always the octahedral (Oct) site whether it coordinates with an alloy atom or not. Comparing to other alloy atoms, Fe tends to exclude interstitial O even at the long range and the interaction is stronger than others, while the long-range interaction of Nb is the weakest. All alloy atoms considered in this work can enhance interstitial O diffusion rate, and promote the anisotropy of O diffusion. This work also confirms that the kinetically resolved activation method is a reliable method to predict the O diffusion barrier in α -Zr. [ABSTRACT FROM AUTHOR]

Hydrogen embrittlement (HE) can lead to the unintentional fracture of large engineering materials, resulting in severe economic losses and safety hazards. It is critical to explore economical and scalable solutions to overcome the challenges of HE. In this work, the HE resistances of four face-centered cubic (FCC) concentrated solid solution alloys (CSAs), including NiFe 20 , NiCoCr, NiCoCrFe, NiCoCrFeMn, and pure Ni were comprehensively investigated and compared by using TDS, EBSD and TEM. It was found that Fe and Cr element can effectively inhibit the solubility of deuterium in the CSAs and alleviate the HE behaviors. In contrast, Mn element significantly increases the solubility of deuterium and caused brittle fractures. Tensile experiments were performed to compare the HE sensitivity of CSAs. The tensile strength of pure Ni and NiFe 20 alloys decreased after deuterium charged, whereas the tensile strength of NiCoCr, NiCoCrFe and NiCoCrFeMn alloys increased. Based on the experimental results, it is deduced that deuterium atoms promote dislocation accumulation and twin growth by reducing the stacking fault energy, which eventually leads to an increase in yield strength and a decrease in plasticity. In addition, the accumulation of deuterium atoms near grain boundaries and cracks during deformation leads to dislocation pinning and stress concentration, which ultimately promotes crack nucleation and propagation. The HE resistances of CSAs are strongly influenced by the deuterium concentration, which depends on the effects of constituent elements and deuterium charging time on the deuterium concentration. Collectively, the specific alloying elements play more important role for the HE resistances of CSAs than the number of elements in the current study. These results provide valuable insights for further understanding and design higher HE resistance CSAs in the future. [Display omitted] ● The addition of Fe and Cr elements to CSAs effectively inhibits deuterium dissolution and enhances the resistance to HE. ● The addition of the Mn element to CSAs significantly promoted deuterium dissolution and caused HE fractures. ● Deuterium atoms reduce the SFE and promote dislocation propagation and twin growth. ● The accumulation of localized stresses induced by deuterium promote the initiation and propagation of cracks. ● Higher deuterium concentrations and deuterium charging times are more likely to trigger HE. [ABSTRACT FROM AUTHOR]

• The TiC/V interface can be used as an effective sink for interstitial H and He atoms. • The TiC/V interface can be considered as a rapid diffusion channel for H and He in the interstices. • H clusters are more likely to aggregate between the first and second slab, whereas He clusters tend to aggregate at the V matrix of the first slab. • Doping Ti solute can promote the dissolution of H and He at TiC/V interface. To gain insights into the nucleation of H and He bubbles at the precipitate/matrix interface, first-principles calculations have been performed to investigate the trapping and diffusion behaviors of H and He at the TiC/V interface. As for the site preference, the calculation shows that H and He prefer to occupy the V-side tetrahedral site at the interface rather than the center of the interface. Considering the H and He clusters formation, H clusters are more likely to aggregate between the first and second slab, whereas He clusters tend to aggregate at the V matrix of the first slab. The diffusion of H and He across the TiC(110)/V(100) interface demonstrates that H and He atoms can reach the favorable segregation sites at the interface from the V bulk by overcoming energy barriers of 0.23 eV and 0.59 eV, respectively. Meanwhile, trapped H and He atoms are difficult to escape from the interface. H and He atoms are, however, highly susceptible to diffusion along the interface, which means that the diffusion path can act as a fast diffusion channel. Additionally, doping Ti can facilitate the trapping of H and He at the TiC/V interface, with no significant change in the diffusion barrier for H, while reducing the diffusion barrier for He to 0.45 eV. [ABSTRACT FROM AUTHOR]

The oxidation behavior of zirconium alloy in high-temperature steam plays a dominant role in the operation of nuclear reactors under accident conditions. The present work investigated the effect of Sn on the oxidation behavior of zirconium alloys in high-temperature steam at 1000 °C. The results of scanning electron microscopy (SEM), metallographic microscopy and synchrotron X-ray diffraction (S-XRD) analyses show that there are three layers in the oxidized sample, including prior β-Zr, α-Zr(O) and ZrO 2. High resolution analyses conducted in these layers by transmission electron microscopy (TEM) show that Sn atoms segregate around the oxide-metal (O-M interface and Zr-Sn intermetallic precipitates only present in the oxide film. Clear atomic arrangements of Zr 5 Sn 3 were obtained by TEM, resulting in accurate identification of the Zr-Sn intermetallic phase. Also, TEM energy dispersive spectroscopy (EDS) maps show that Zr-Sn particles invariably accompany the segregation or precipitation of Nb. However, no clear precipitation sequence was observed, which suggests that a co-precipitation mechanism of Sn and Nb is in operation. As oxidation proceeds, nanovoids next to the Zr-Sn intermetallic particles were observed accompanied by local areas deficient in oxygen, identified as ZrO. Combining the interdiffusion trend obtained by Density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations, a mechanism for the transformation from the Zr-Sn intermetallic precipitates to nanovoids was proposed. This proposed mechanism may shed new light into the role of Sn in the oxidation resistance of zirconium alloy under LOCA conditions. [Display omitted] [ABSTRACT FROM AUTHOR]

• Quantitatively evaluated equilibrium and diffusion behavior of mixed hydrogen-methane gas in gravity fields. • Effects of height, temperature, and mixing ratio on stratification and diffusion behavior of the mixture are revealed. • The gravitational stratification of hydrogen-methane mixture requires either an extremely strong gravity field or very large drops in altitude, being negligible for realistic pipes. • Temporary interruptions in pipeline gas transportation will not cause visible stratification due to slow diffusion of gases. Repurposing existing natural gas pipelines is a promising solution for large-scale transportation of mixed hydrogen-methane gas. However, it remains debatable whether gravitational stratification can notably affect hydrogen partial pressure in the gas mixture. To address this issue, we combined molecular dynamics simulation with thermodynamic and diffusion theories. Our study systematically examined the equilibrium distribution of hydrogen-methane mixtures in gravity fields. We demonstrated that partial pressures of both gases decrease with altitude, with hydrogen showing a slower decrease due to its smaller molar mass. As a result, the volume fraction of hydrogen is maximized at the top end of pipes. The stratification is more favorable at low temperatures and large altitude drops, with notable gas stratification only occurring at extremely large drops in altitude, being generally negligible even at a drop of 1500 m. Furthermore, we showed that the diffusion time required to achieve the equilibrium distribution is proportional to gas pressure and the square of pipeline height. This requires approximately 300 years for a 1500 m pipeline at 1 bar. Therefore, temporary interruptions in pipeline gas transportation will not cause visible stratification. Our work clarifies the effect of gravity on hydrogen-methane gas mixtures and provides quantitative insights into assessing the stratification of gas mixtures in pipelines. [ABSTRACT FROM AUTHOR]

Abstract: Molecular dynamic method has been used to investigate the diffusion behavior of helium atom in the LaNiAl alloy system. The results have shown that diffusion coefficient of helium atom increases as the temperature increases from 300 to 1500K, which indicates that helium atom gets more active via thermal desorption. The diffusion coefficient in LaNi5 and LaNi4Al are about 1.5×10−5 and 1.1×10−6 cm2/s at 1300K, respectively, and the diffusion barrier of He are 1.45 and 0.52eV, respectively. The helium diffusion is shown to be enhanced with temperature increasing. Compared with metallic La, Ni, Al and Pd, the simulation result implies that helium atom is more stable and difficult to diffuse in LaNi5 and LaNi4Al alloys, which are the most promising materials for helium retention in experiments. Our results indicate the correlation between diffusion behavior of helium atom and capacity of materials for helium retention. Therefore, it can be considered as a feasible method to evaluate the helium retention capacity of materials via determining the diffusion properties of interstitial helium atom. [Copyright &y& Elsevier]