Accumulation Of Radiation Defects Research Articles

Effects of Structural Radiation Disorder in the Near-Surface Layer of Alloys Based on NbTiVZr Compounds Depending on the Variation of Alloy Components

This research investigated how changes in the composition of Nb–Ti–V–Zr-based alloys affect their resistance to radiation damage and the preservation of strength characteristics when exposed to the heavy ions Kr15+ and Xe23+. These heavy ions simulate the impact of nuclear fuel fission fragments on the material. The primary objective of this study was to explore how variations in alloy components influence radiation resistance and the retention of alloy strength properties. Accumulation of radiation defects can potentially lead to embrittlement and a decrease in resistance to external factors during operation. An analysis of the X-ray diffraction data obtained from the initial alloy samples, in relation to the variations in the number of components, revealed that an increase in the number of components leads to the formation of a denser crystal structure. Additionally, this resulted in the emergence of a dislocation strengthening factor associated with changes in crystallite size. Concurrently, when assessing changes in the strength characteristics of the irradiated alloys, it was observed that the NbTiV and NbTiVZr alloys demonstrated the highest resistance to strength property degradation, specifically a 2.5- to 5-fold increase in resistance against a significant decrease in hardness. It was confirmed that the significant factor contributing towards the enhancement and preservation of the structural and strength properties is the dislocation strengthening mechanism. An increase in dislocation strengthening effectively enhances resistance against destructive embrittlement, particularly when exposed to high-dose irradiation.

Radiation damage evolution in High Entropy Alloys (HEAs) caused by 3–5 MeV Au and 5 MeV Cu ions in a broad range of dpa in connection to mechanical properties and internal morphology

High Entropy Alloys (HEAs) are prospective materials for nuclear fusion reactors and were irradiated in this study at a broad range of energetic ion fluences. Different ion masses (Cu and Au ions) and energies (3 and 5 MeV) were selected to investigate dpa (displacement per atom) development, radiation defect accumulation based on prevailing collision processes (Au ions) and ionization processes (Cu ions) in various HEAs. The studied HEAs differ in terms of elemental composition, internal morphology (grain structure) and other modifiers. Dpa values of 1 to ∼66 were achieved at Cu and Au ion fluences from 4 × 1014 to 1.3 × 1016 ions.cm−2 at room temperature, which generated varying levels of lattice damage. Theoretical simulations were performed to estimate the energy stopping and dpa depth distribution using SRIM code and compared with Au-concentration depth profiles determined by Rutherford backscattering spectrometry for Au-ions with 3 MeV ion energy. The prevailing energy losses of ions via ionization processes for Cu-5 MeV ions were found to increase the damage through lattice strain and probable lattice distortion, although the main defect introduction is expected to occur via collisions during nuclear stopping. Structural modification and defect accumulation were investigated by positron annihilation spectroscopy (PAS), which revealed a broader damaged layer with defects, where HEA-Nb (NbCrFeMnNi) exhibited the least damage accumulation from chosen alloys with no strong relation to the Au-5 MeV ion implantation fluence, whereas strong defect accumulation was recorded in the Au-ion implanted Eurofer97 used for comparison and HEA-Co (CoCrFeMnNi). PAS analysis also allowed defect sizes to be determined as an additional structural characteristic. The observed trends were also confirmed by thermal property analysis, with a worsening of thermal effusivity recorded after the irradiation in HEA-Co and Eurofer97. The worsening of the thermal properties was confirmed by the layer thickness, where the layer identified by PAS was found to be broader than the SRIM theoretical predictions. Nanoindentation measurements confirmed less pronounced radiation hardening of HEA-Nb relative to that observed in HEA-Co and Eurofer97. Transmission Electron Microscopy (TEM) analysis revealed layer thicknesses in reasonable agreement with the dpa depth profiles. The thermal effusivity decreased in the surface-irradiated layer in all investigated samples, the least influenced material was HEA-Nb.

Revealing nanoscale strain mechanisms in ion-irradiated multilayers

Tailoring interfaces is a powerful way of reducing the accumulation of radiation defects. Understanding strain evolution induced by ion bombardment in nuclear materials with high interface density is crucial for next-generation reactors since induced defects are responsible for volumetric swelling and catastrophic failure. X-ray and selected-area diffraction patterns (SADPs) measurements reveal, after Cu implantation, that a relatively high out-of-plane strain is created in thin Zr/Nb6 multilayers, while thick Zr/Nb96 is barely distorted. The absence of layer deformation in Zr/Nb96 is explained by local TEM strain mapping showing the presence of two oppositely distorted regions (inner and interface-affected regions) within one layer producing only a small overall strain, whereas the whole individual layers of Zr/Nb6 are affected by the interface manifesting high strain. Using MD simulations, the types of defects responsible for layer distortion are identified. The opposite distortion within the layer is attributed to the inequality of the defect flux from the inner to interface-affected region due to the difference in migration energy barriers of the point defects. Moreover, the interface sink efficiency (defect annihilation) is determined for Zr/Nb as an illustration which provides a strategy for designing new derivate structures of multilayers with high radiation damage resistance.

Study of the Effect of Y2O3 Doping on the Resistance to Radiation Damage of CeO2 Microparticles under Irradiation with Heavy Xe22+ Ions

This paper presents the results of a study on the influence of Y2O3 doping on the resistance to radiation damage and an assessment of structural changes associated with the accumulation of radiation defects in CeO2 microparticles under irradiation with heavy Xe22+ ions. The relevance of this study consists of the prospects for the use of CeO2 microparticles as materials and candidates of inert matrices of nuclear fuel. A method of solid-phase synthesis was applied to obtain microparticles with different concentrations of dopant. It included grinding of CeO2 and Y2O3 microparticles followed by thermal sintering at 1100 °C in an oxygen-containing medium to produce highly ordered microparticles. During the study of the structural characteristics of the synthesized microparticles, it was found that increasing the dopant concentration from 0.05 mol.% to 0.15 mol.% leads to an increase in the crystallinity degree as well as a decrease in dislocation density. According to the results of the assessment of the resistance of microparticles to radiation damage, it was found that an increase in the dopant concentration leads to a decrease in swelling and structural distortion by more than 2.5–3 times, which indicates an increase in the radiation resistance.

Revealing Nanoscale Strain Mechanisms in Ion-Irradiated Multilayers

Tailoring of interfaces is a powerful way of reducing the accumulation of radiation defects. Understanding strain evolution induced by ions bombardment in nuclear materials with high interface density is crucial for next-generation reactors since induced defects are responsible for volumetric swelling and catastrophic failure. X-ray and SADPs measurements reveal that, after Cu implantation, a relatively high out-of-plane strain is created in thin Zr/Nb 6 multilayers, while the thick Zr/Nb 96 is barely distorted. The absence of the layer deformation in Zr/Nb 96 is explained by Astar strain mapping showing the presence of two oppositely distorted regions (inner and interface-affected regions) within one layer producing only a small overall strain, whereas the whole individual layers of Zr/Nb 6 are affected by the interface manifesting high strain. Using MD simulations, the type of defects responsible for layer distortion is identified. The opposite distortion within the layer is attributed to the inequality of the defect flux from the inner to interface-affected region due to the difference in migration energy barriers of the point defects. Moreover, the interface sink efficiency (defect annihilation) is determined for Zr/Nb as an illustration which provides a strategy for designing new derivate structures of multilayers with high radiation damage resistance.

Radiation damage behavior of amorphous SiOC polymer-derived ceramics: the role of in situ formed free carbon

Free carbon networks (FCN) in situ formed in the amorphous SiOC polymer-derived ceramics (PDCs) have been reported to have significant effects on the material microstructures as well as the related structural and functional properties. In this paper, detailed effects of the FCN on the radiation damage process and mechanisms of the amorphous SiOC PDC are investigated by using ab initio molecular dynamics simulations. The radiation simulations were conducted by introducing a random Si atom with kinetic energy of 80 eV as the primary knock-on atom. The FCN are proven to be beneficial to absorb the ion induced kinetic energy and convert it into thermal spike, which can be dissipated as thermal energy. The FCN interfaces with Si-O-C matrix can also capture the displaced atoms easily, thus reducing the cascade damage. The SiOC PDC is promising to be radiation tolerant materials for the prevention of radiation defect accumulation by the contained amorphous phase and FCN structure.

Effect of irradiation with continuous 28 MeV He2+ ion beam and short-pulsed 200 keV C+ ion beam on optical properties of multilayer Al-Si-N coatings

The article reports on radiation defect formation parameters and radiation resistance of multilayer coatings from thin layers of aluminum and silicon nitrides deposited on sodium-calcium-silicate glass and monocrystalline silicon substrates by reactive magnetron sputtering. The samples were irradiated with helium ions of 28 MeV on a cyclotron and carbon ions 200 keV on an accelerator in the mode of short-pulse implantation. The characteristics of local absorption and luminescence centers before and after irradiation and their probable nature were determined. The optical centers had been identified as point intrinsic defects of a growth and radiation nature. The accumulation of radiation defects in layers of amorphous silicon nitride a-Si3N4 prevailed over the accumulation in crystalline c-AlN layers due to the diffusion of defects in amorphous layers and the formation of secondary defects in them. Changes in optical properties led to the conclusion about the high radiation resistance of the coatings. The main reasons for the resistance of coatings to ion irradiation were the high concentration of growth defects, their strong interaction and the wide band gap of the nitrides. Coatings deposited on silicon substrates had a higher radiation resistance compared to the same coatings deposited on glass substrates.

The peculiarities of the radiation damage accumulation kinetics in the case of defect complex formation

The kinetics of radiation defect accumulation under irradiation by heavy particles is theoretically analysed under the assumption of defect complex genesis, particularly, the ones of anion and cation vacancies. The obtained analytical mathematical model and revealed peculiarities of radiation dose dependencies can be used for analysis of the experimental results for different crystalline materials for solid-state electronics and photonics.

Peculiarities of the diffusion-controlled radiation defect accumulation kinetics under high fluencies

Theory is developed for kinetics of the diffusion-controlled radiation defect accumulation in crystalline solids under high fluencies taking into account recently observed correlation between the defect diffusion energy and pre-exponential (known as the Meyer-Neldel rule in chemical kinetics) and their dependence on the radiation fluence (Kotomin et al., J Phys Chem A 122 (2018) 28). The predicted accumulation kinetics could be applied to all kinds of solids. It considerably differs from the commonly used, in particular, suggesting that concentration growth at high fluencies could be nonmonotonous and the saturation defect concentrations independent on the temperature.

Molecular dynamics simulation of the diffusion of self-interstitial atoms and interstitial loops under temperature gradient field in tungsten

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.

Effect of confinement of SIA cluster diffusion by impurities on radiation defect accumulation due to 14 MeV neutrons in tungsten

Impurities acting as traps reduce the self-interstitial atom (SIA) cluster mobility, thereby increasing recombination and, in turn, enhancing radiation-resistance of polycrystalline materials. However, at elevated temperatures, depending on SIA-trap (impurity) binding energy, SIA clusters may trap and detrap (detach) numerous times. In tungsten, SIA clusters of all sizes glide one-dimensionally (1D) along their Burgers vector direction. This can result in detrapped SIA clusters to retrace their original 1D path, confining their 1D-glide between traps. However, SIA clusters can change the direction of their 1D-glide by overcoming a rotation barrier and impurities or solutes are known to reduce this barrier. A lower rotation barrier can result in detrapped SIA clusters to diffuse in a random 1D direction, effectively leading to 3D (net-3D) diffusion. Here we investigate the effect of two cases of SIA diffusion, namely the confined-1D diffusion and the net-3D diffusion, on the damage accumulation in polycrystalline tungsten under 14 MeV neutron irradiation using the object kinetic Monte Carlo method. Simulations were performed using cascade debris obtained from molecular dynamics simulations with primary knock-on atom (PKA) energies corresponding to 14 MeV neutrons. In the simulations with net-3D diffusion, SIA clusters of all sizes diffuse in a random 1D direction after the clusters detrap. While for the confined 1D diffusion case, clusters larger than size 5 retain their original direction of 1D glide. In both types of simulations, trapped vacancies are assumed to be permanently immobilized. Unexpectedly, the damage accumulation was lower with confined 1D diffusion than that with net-3D. We present a systematic comparison of the influence of the two cases of SIA diffusion on the radiation damage accumulation as a function of dose rate, detrapping barrier, and impurity concentration at 1025 K.

К моделям для оценки пострадиационного дефектного состояния -фазы

Processes that take place in the precipitates of -phase under irradiation with fast neutrons are topical and draw attention when one searches for ways of improving radiation resistance of structural reactor steels. A special feature of these processes is that the formation of vacancies and interstices proceeds at the background of a disordering of the initial crystal lattice, which mani-fests itself in the formation of antisite defects. X-ray and neutron diffraction techniques are efficient tools of studying changes that occur in the post-radiation structural state of such systems. However, interpretation of the experimental results calls for more complicated models for the description of structural effects exerted by accumulation of radiation defects in the material than those developed before for elementary metals. Several models are proposed in this paper.

Kinetics of radiation-stimulated processes on the surface of oxide materials

The analysis of the experimental data shows that the processes of gas adsorption and radiation defects accumulation in metal oxides correlate with each other and most likely can be described in terms of equivalent kinetic equations. Given this circumstance, the kinetics of accumulation of radiation defects in oxides of di erent metals was analyzed. The obtained equations were used to analyze: a) the kinetics of accumulation of radiation defects in di erent oxide compounds; b) the data on the destruction of radiationinduced defects in the atmosphere of di erent gases, and on the kinetics of absorption by oxides of oxygen, hydrogen, and carbon dioxide molecules. The results of such analysis are systematized and are given in the form of a table. The following conclusions were made: 1. The quantum yield of radiation defects increases monotonically with growth of the temperature of processing, tending to a certain limit value. 2. The constant of destruction of radicals from ionizing radiation increases as well. 3. The ratio of the number of surface and bulk defects in di erent oxides can be arranged in the following series: silicon oxide> beryllium oxide> aluminum oxide. Thus, the most optimal (convenient) material for creating absorbing systems by energy intensity is silicon dioxide, and by adsorption e ciency is beryllium oxide.

Effect of short-pulsed 200 keV C+ ion beam and continuous 350 keV He2+ ion beam irradiation on optical properties of Al-Si-N coatings with a various Si content

The article reports on the irradiation effects of 350 keV helium ions in the continuous mode and 200 keV carbon ions in the mode of short-pulsed implantation with doses of 20 MGy, 200 MGy and 600 MGy on the optical properties of crystalline aluminum nitride films and nanocomposite coatings based on Al-Si-N triple compound deposited by reactive magnetron sputtering onto a steel substrate. The energy and kinetic characteristics of the absorption spectra due to radiation defects and their simplest complexes are determined. Short-pulsed ion implantation is accompanied by intense radiation and thermal annealing of unstable radiation defects, along with their complexes and the formation of thermostable defect complexes. The influence of the interaction between the states of defects with the growth and/or radiation nature localized in the forbidden zone with the depth on the properties is established. Dose dependences of the optical characteristics indicate a high radiation resistance of the coatings. The radiation resistance of the coatings is due to the limiting effect of high concentration of growth defects on the accumulation of radiation defects, the wide band gap of nitrides, and the interaction of defects through the exchange of charge carriers between their levels.

Accumulation of radiation defects and modification of micromechanical properties under MgO crystal irradiation with swift 132Xe ions

Accumulation of F-type defects under irradiation of MgO crystals by 0.23-GeV 132Xe ions with fluence varying by three orders of magnitude has been investigated via the spectra of optical absorption and low-temperature cathodoluminescence. The number of single centers continuously increases with fluence without any marks of saturation. At the highest fluence, a mean volume concentration of 3.1 × 1019 and 3.35 × 1019 cm−3 is reached for F and F+ centers, respectively. The F+ emission strongly dominates in the cathodoluminescence of irradiated MgO and its enhancement with fluence is detected. However, the creation efficiency of the F2 aggregate centers is very low and fluence dependence has a complicated shape. Radiation-induced changes of micro-mechanical properties of the same samples have been analysed; the depth profiles of hardening correlate with the ion energy loss. A joint contribution of ionization and impact mechanisms in the formation of structural defects under MgO irradiation with Xe ions is considered.

Characterization and quantification of numerical errors in threshold displacement energy calculated by molecular dynamics in bcc-Fe

The accumulation of radiation defects in nuclear fusion/fission materials often causes adverse changes in material properties. The threshold displacement energy (TDE) is one of the fundamental quantities used to evaluate the number of formed radiation defects. In the present study, to understand the error sources in TDE calculation using the molecular dynamics method and to find an optimal strategy for accurate and precise calculation, we analyze how the calculated TDE is affected by the calculation settings, including the system shape and size, the recoil energy increment in searching the threshold value, the sampling numbers of recoil directions and recoil event time samples, and the potential model. Bcc-Fe is used as a test material, and three potential models are employed for comparison. As a result, the calculation errors caused by these settings are successfully classified into accuracy error and precision error and then quantified. The type and trend of the error caused by each setting are not qualitatively different between the tested potential models, although they are quantitatively different. This potential model dependence can often be reasonably explained from the recoil direction dependence of the TDE and the defect formation mechanisms. Finally, using the equations derived to quantify the accuracy and precision of the calculated TDE and the calculation cost, we suggest some strategies to minimize the error with a given limited computational resource.

Mechanism of interaction between interface and radiation defects in metal

High-energy particles’ radiation produces a large number of radiation defects in material, such as interstitial atoms, vacancies, dislocation loops, voids and helium bubbles. The formation and evolution of massive radiation defects cause the instability of microstructure in metal, which further degrades its mechanical performance. Interface engineering is an effective method to tune the radiation resistance of metal and alloy. By introducing a large number of grain boundaries, phase interfaces, free surfaces, etc., the recombination probability of radiation-induced vacancies and interstitial atoms increases, thereby reducing the accumulation of radiation defects, improving the structural stability of the metal and eliminating the harmful effects of radiation. In this paper, we briefly review the recent progress of the mechanisms of interactions between several typical interfaces and various types of irradiation defects. The influence of interface structure, irradiation condition and defect character on their interaction behavior are reviewed and discussed. We also propose some critical questions about the radiation damage to material which remain to be understood. It is necessary to combine multidisciplinary techniques, knowledge and theories in order to fully understand the mechanism of radiation damage and design the advanced radiation-tolerant materials.

Thermal conductivity degradation and recovery in ion beam damaged tungsten at different temperature

Studying the effects of radiation damage on tungsten (W), a primary candidate material for plasma facing components (PFCs), is of great significance in the thermal management of future fusion reactors. Investigation of accumulation and annihilation of radiation defects under ion irradiation in tungsten offers insights in selecting operational conditions in future fusion reactor designs. Here we investigate the dosage and irradiation temperature dependence on thermal conductivity (κ) of W under fusion-relevant radiation conditions by using an improved 3ω technique. Our results show a significant reduction in κ for W irradiated at room temperature with energetic (MeV) heavy ions. The damage, quantified by displacement per atom (dpa), spanned from 10−3 to 0.6 dpa for Cu ions and 0.2 dpa for W ions. With increasing Cu ion damage level, κ decreased and reached a minimum of 52 ± 13.6 W/m·K at 0.6 dpa, ∼30% of κ for pristine W. When the ion irradiation was performed at 1000 K, which is a temperature that is sufficiently high to induce significant dynamic annealing in W, κ was largely recovered to around 80% of the pristine value. We attribute this κ recovery to the thermal annealing and annihilation of the irradiation induced defects, i.e. through vacancy/self-interstitial atom (SIA) recombination. This finding is consistent with our prior observation of defect recovery probed by deuterium retention.

On the Implantation of Protons into Silicon Plates in the Case of a Mechanically Stressed Surface Layer

The effect of mechanical stresses of different signs on the formation of radiation defects in crystalline silicon is studied alongside the effect of strain on the accumulation of radiation defects in KEF-4.5 silicon after the implantation of protons with an energy of 140 and 500 keV and a dose of 2.5 × 1015 cm–2. The stress-strain state of a thin circular plate with a strained surface layer is calculated. It is shown that the applied mechanical stresses generally have an effect on the thickness of the damaged layer, whose thickness decreases with an increase in compressive stresses near the surface in comparison with its thickness in the undamaged sample and grows in the opposite case.

Simulations of irradiated-enhanced segregation and phase separation in Fe–Cu–Mn alloys

For reactor pressure vessel steels, the addition of Cu, Mn, and Ni has a positive effect on their mechanical, corrosion and radiation resistance properties. However, experiments show that radiation-enhanced segregation and/or phase separation is one of the important material property degradation processes. In this work, we develop a model integrating rate theory and phase-field approaches to investigate the effect of irradiation on solute segregation and phase separation. The rate theory is used to describe the accumulation and clustering of radiation defects, while the phase-field approach describes the effect of radiation defects on phase stability and microstructure evolution. The Fe–Cu–Mn ternary alloy is taken as a model system. The free energies used in the phase-field model are from CALPHAD. Spatial dependent radiation damage from atomistic simulations is introduced into the simulation cell for a given radiation dose rate. The radiation effect on segregation and phase separation is taken into account through the defect concentration dependence of solute mobility. Using the model, the effect of temperature and radiation rates on Cu and Mn segregation and Cu-rich phase nucleation were systematically investigated. The segregation and nucleation mechanisms were analyzed. The simulations demonstrate that the nucleus of Cu precipitates has a core–shell composition profile, i.e. Cu-rich at the center and Mn-rich at the interface, in good agreement with theoretical calculations as well as experimental observations.