In a fusion reactor, plasma-facing materials simultaneously suffer high-flux low-energy helium/hydrogen irradiation and high-energy neutron bombardment. Numerous modeling studies have focused on ...radiation damage caused by individual particles, but ignored their synergistic effects. In this study, molecular dynamics simulations were performed to investigate the cascade damage near a pre-existing helium bubble in tungsten. The existence of helium bubbles generally inhibits defect generation but enhances interstitial-type dislocation loop formation. Furthermore, the distance between the primary knock-on atom and the bubble plays an important role in defect evolution. This corresponds to the defect distribution characteristics of the cascade damage in the perfect crystal. In addition, the change in morphology of helium bubbles during cascade damage was considered. Cascade-induced ballistic dissolution of helium from bubbles dominates helium ejection, but damage-assisted thermal dissolution is also observed. This work can contribute to understanding complex damage mechanisms in multiple irradiation fields, such as the fusion environment.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•The plastic deformation mechanisms of EHEAs are interfacial structure-dependent.•Coherent interfaces facilitate continuous slipping of dislocations and co-deformation.•Semicoherent ...interfaces activate amorphization by dislocation pileup during deformation.•Engineering semicoherent interfaces are desirable for designing high strength-ductile nanostructured EHEAs.
Eutectic high entropy alloys (EHEAs) are widely advocated materials for overcoming the strength-ductility trade-off due to their abundant heterogeneous interfaces. However, the lack of a full understanding of the plastic carrier-interface interaction mechanism obscures the essential role of the interface in the simultaneous enhancement of strength and ductility. To elucidate the underlying mechanisms from an interface perspective, FCC/BCC multilayers with semicoherent and coherent interfaces were prepared by a magnetron sputtering system. The mechanical properties and microstructure evolution of multilayers were investigated by using nanoindentation, X-ray diffractometer and transmission electron microscopy, respectively. Moreover, the dislocation motion behavior and stress distribution during plastic deformation were analyzed by MD simulation. It is found that the plastic deformation behavior and mechanical properties of EHEAs are sensitive to the heterogeneous interfacial structure. During plastic deformation, the coherent interface facilitates the continuous slip of dislocations, whereas the semicoherent interface promotes amorphization by dislocations pileup. The results are important for understanding the plastic carrier-interface interaction mechanism, and the findings provide new insights for the development of high strength-ductility HEA materials.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Silicon carbide (SiC) is a promising structural and cladding material for accident tolerant fuel cladding of nuclear reactor due to its excellent properties. However, when exposed to severe ...environments (e.g., during neutron irradiation), lattice defects are created in amounts significantly greater than normal concentrations. Then, a series of radiation damage behaviors (e.g., radiation swelling) appear. Accurate understanding of radiation damage of nuclear materials is the key to the design of new fuel cladding materials. Multi-scale computational simulations are often required to understand the physical mechanism of radiation damage. In this work, the effect of neutron irradiation on the volume swelling of cubic-SiC film with 0.3 mm was studied by using the combination of molecular dynamics (MD) and rate theory (RT). It was found that for C-vacancy (C
), C-interstitial (C
), Si-vacancy (Si
), Si-interstitial (Si
), and Si-antisite (Si
), the volume of supercell increases linearly with the increase of concentration of these defects, while the volume of supercell decreases linearly with the increase of defect concentration for C-antisite (C
). Furthermore, according to the neutron spectrum of a certain reactor, one RT model was constructed to simulate the evolution of point defect under neutron irradiation. Then, the relationship between the volume swelling and the dose of neutrons can be obtained through the results of MD and RT. It was found that swelling typically increases logarithmically with radiation dose and saturates at relatively low doses, and that the critical dose for abrupt transition of volume is consistent with the available experimental data, which indicates that the rate theory model can effectively describe the radiation damage evolution process of SiC. This work not only presents a systematic study on the relationship between various point defect and excess volume, but also gives a good example of multi-scale modelling through coupling the results of binary collision, MD and RT methods, etc., regardless of the multi-scale modelling only focus on the evolution of primary point defects.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The empirical electron surface model (EESM) based on the empirical electron theory and the dangling bond analysis method has been used to establish a database of surface energy for low-index surfaces ...of fcc-metals such as Al, Mn, Co, Ni, Cu, Pd, Ag, Pt, Au, and Pb. A brief introduction of EESM will be presented in this paper. The calculated results are in agreement with experimental and other theoretical values. Comparison of the experimental results and calculation values shows that the average relative error is less than 10% and these values show a strong anisotropy. As we predicted, the surface energy of the close-packed plane (1
1
1) is the lowest one of all index surfaces. For low-index planes, the order of the surface energies is
γ
(1
1
1)
<
γ
(1
0
0)
<
γ
(1
1
0)
<
γ
(2
1
0)
. It is also found that the dangling bond electron density and the spatial distribution of covalent bonds have a great influence on surface energy of various index surfaces.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Tungsten (W) has been used for plasma facing materials (PFMs) of tokamak. Under severe work condition, the irradiation damage of W is closely related to its thermal conduction, which has been ...researched systematically in this paper with molecular dynamics (MD). The thermal conductivities (TCs) by phonons with many different conditions, such as different temperatures, different heat flows, different crystallographic orientation and the presence of grain boundary (GB) have been calculated and discussed in detail. The finite size effect has been taken into account in the calculation of TCs, the relationship between the inverse of TC and the inverse of lateral dimension is linear. Research shows that the TCs are not depended strongly on heat flux, but they decrease gradually with the increase of temperature. We also find the thermal conduction of W is to some extent anisotropic, but the variations are smaller than that caused by temperature. A sharp discontinuity in temperature appears across the GB in the temperature-x profile. And the TC in the grain boundary phase region is less than one-tenth of the TC of bulk at 300K. However, the GB effect on TC of W polycrystalline sample is relatively small. These research results can help to account for the damage mechanisms of plasma facing material tungsten.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Molecular dynamics simulations were conducted to study the melting and dissociation of free tungsten nanoparticles. For the various interatomic potentials applied, the melting points of the tungsten ...nanoparticles increased with increasing nanoparticle diameter. Combining these results with the melting point of bulk tungsten in the experiment, the melting point of nanoparticles with diameters ranging from 4 to 12 nm could be determined. As the temperature increases, free nanoparticles are subject to dissociation phenomena. The dissociation rate was observed to follow Arrhenius behavior, and the Meyer–Neldel rule was obeyed. These results are useful in understanding the behavior of tungsten dust generated in nuclear fusion devices as well as for the preparation, formation, and application of tungsten powders.
•Displacement cascades generated by PKAs with energies 1~10 keV for 3C-SiC with temperatures 300~1800 K were studied with one modified Tersoff potential.•The number of various point defects and their ...clusters were analyzed. C defects dominate most of these defects and their clusters formed in cascades, while the dominance becomes less significant with the increase of temperature.•The number of point defects and their distribution are affected by PKA energy, but the PKA type and the temperature show little influence.
We use molecular dynamics (MD) methods to study collision cascades in cubic silicon carbide (3C-SiC), which is a candidate for various applications in nuclear industries. One Tersoff potential, which can reproduce the thermal and elastic properties of 3C-SiC, was firstly connected with ZBL potential. Collison cascades were generated by primary knock-on atoms (PKAs) with damage energies ranging between 1 keV and 10 keV at 300–1800 K. It was found that the temperature weakly influences the production of defects in the temperature range (300–1800 K). However, the number of point defects increases significantly as the PKA-energy increases. Carbon defects dominate most of the defects formed in collision cascades, and the dominance becomes less significant with the increase of temperature. Some high-density interstitial point defects were observed in the evolution of the collision cascade. As the PKA-energy increases, more and more defect clusters with larger sizes can be observed. For the current PKA energy range (≤10 keV), clusters with 1–5 vacancies and with 1–4 interstitials can be found, and clusters with a larger size are rare at the end of the quenching stage. The number of these defect clusters with various sizes is temperature independent. In these defect clusters, the carbon content exceeds 50% in most conditions. In addition, the carbon ratio in interstitial clusters is usually higher than the carbon site ratio in vacancy clusters. This work not only enriches the knowledge of the the number, size distribution and compositions of point defects and their clusters induced by neutron irradiation, but also can be input for the long-term simulation methods to understand the evolution of irradiated defects in 3C-SiC. Furthermore, the defect information can be used to study the thermal and elastic properties of 3C-SiC in future work.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Tungsten has been used for divertor materials in fusion reactor, which requires them to withstand high-energy neutron radiation. The produced displacement cascade has usually been studied with ...molecular dynamics simulation. In these simulations, most of the discrepancies come from the low reliability of the potential. To overcome this drawback, the extended Finnis–Sinclair potential has been modified by connecting ZBL universal potential. The potential performs very well in the case of the interaction between tungsten and point defects, fits well with experimental and other theoretical results. In this paper, displacement cascades have been simulated in the scenario of detection of Frenkel pairs and point defect clusters, using our new modified potential. The time evolution of the Frenkel pair has been analyzed, through comparing with the NRT predicted results. The effects of primary knock-on energy and temperature on point defect production have also been analyzed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Tungsten (W) and tungsten-based materials are being considered to be used in the divertor and the first wall as plasma facing materials (PFMs) in the fusion reactor, which requires them to withstand ...the heat loads. The influence of grain boundaries on the heat flux has been studied by the molecular dynamics (MD) simulations in this paper. Various grain boundaries have been constructed in simulation cells and their lattice thermal conductivities (LTCs) and thermal resistances have been calculated. It turns out that there exist sharp temperature drops across these grain boundaries, indicating that the LTCs near grain boundaries are much smaller than those inside the bulk tungsten. The grain boundary effect on the LTCs of polycrystalline W samples has been analyzed by the combination of MD and finite element results. The results may be potentially helpful for the design of the international thermonuclear experimental reactor (ITER) and the choice of PFMs.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Stacking faults (SFs) are often present in silicon carbide (SiC) and affect its thermal and heat-transport properties. However, it is unclear how SFs influence thermal transport. Using ...non-equilibrium molecular dynamics and lattice dynamics simulations, we studied phonon transport in SiC materials with an SF. Compared to perfect SiC materials, the SF can reduce thermal conductivity. This is caused by the additional interface thermal resistance (ITR) of SF, which is difficult to capture by the previous phenomenological models. By analyzing the spectral heat flux, we find that SF reduces the contribution of low-frequency (7.5 THz–12 THz) phonons to the heat flux, which can be attributed to SF reducing the phonon lifetime and group velocity, especially in the low-frequency range. The SF hinders phonon transport and results in an effective interface thermal resistance around the SF. Our results provide insight into the microscopic mechanism of the effect of defects on heat transport and have guiding significance for the regulation of the thermal conductivity of materials.
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