Radiation-enhanced Diffusion Research Articles

On the SRIM prediction of ranges for Ni ions.

An experiment to determine the range of Ni ions in matter consisting in the implantation of nickel ions into samples followed by the determination of the depth profile of the implanted ions by nuclear reaction resonance profiling was performed. The experimentally obtained ranges for Ni ions in Fe and Mo were compared with SRIM-2013 (www.srim.org) and TRIM-98 predictions. It was found that the ranges predicted by SRIM-2013 are significantly overestimated whereas the calculation results obtained with TRIM-98 modified to take into account radiation-enhanced diffusion are consistent with the experimental data.

Demystify radiation-enhanced hydrogen isotope diffusion in Fe-Ni-Cr austenitic stainless steels

Understanding and containing hydrogen isotope diffusion is crucial for many nuclear applications. In situ experiments have consistently shown that radiation significantly enhances isotope diffusion in austenitic stainless steels. Despite extensive research, the mechanism behind this phenomenon remains elusive, as most radiation-induced defects (e.g., vacancies, dislocations, and grain boundaries) typically trap hydrogen, thereby slowing diffusion. While grain boundaries may increase in-plane diffusivity and interstitials may enhance diffusion due to material swelling, these effects are relatively minor. Utilizing an Fe-Ni-Cr-H interatomic potential for stainless steels, we conducted extensive molecular dynamics simulations to investigate the origins of radiation-enhanced diffusion. Our findings reveal that when a system is resolidified, mimicking defects created by radiation displacements, the resulting structure contains a mixture of phases, boundaries, and dislocation networks. This defective structure significantly increases hydrogen diffusivity, enhancing it by approximately 1.7 times at 900 K. These results suggest that the complex defect structures formed during radiation displacements are the primary drivers of the observed diffusion enhancement, providing valuable insights into the mechanisms underlying radiation-enhanced diffusion in nuclear materials.

Effects of energetic electron irradiation on electric, magnetic, and mechanical properties of Cu-1.2 at.%Fe alloy

Cu-1.2 at.% Fe samples were irradiated with 1.5 MeV electrons at 333 K and 448 K. Effects of the irradiation were observed as an increase in electrical conductivity and magnetization. In contrast, the Vickers hardness was little changed by the irradiation. The experimental results were explained as due to small Fe-rich clusters produced through radiation-enhanced diffusion. The present study shows that electron irradiation provides a fine control of the magnetic and electric properties of the Cu-Fe alloy.

Radiation-induced Fe segregation in the dual-phase FeCrNiMnAl high-entropy alloy under high-dose helium ion irradiation

This study investigates the radiation-induced Fe segregation in the dual-phase FeCrNiMnAl high-entropy alloy (HEA) under the helium (He) ion irradiation with a dose of 5 × 1017 ions/cm2. The superior bubble swelling resistance of the chemical-ordered NiAlMn phase with B2 structure is observed compared to the FCC FeCrMn matrix, which can be attributed to their differences in atomic packing factors. Fe segregation at phase boundaries (PBs) is detected after irradiation, as evidenced by a higher concentration of Fe at PBs than in the matrix by about 10 at.%. This phenomenon can be ascribed to the migration of Fe interstitials induced by irradiation cascades and the punching mechanism during bubble growth. In essence, the Fe segregation in this study is driven by the radiation-enhanced diffusion and metastable state of FCC-structured FeCrMn with supersaturated Fe atoms. These insights provide theoretical foundations and innovative perspectives for the radiation-induced segregation (RIS) in HEAs.

Features of thermal processes and the influence of pulsed heating of surface layers of titanium on the diffusion transfer of dopants during high-intensity ion implantation

Methods for modification of surface and near-surface layers of materials and coatings by ion beamshave prospects for application in many fields of science and technology. The method of high-intensityimplantation by high-power density ion beams with submillisecond duration involves significantpulsed heating of the irradiated target’s surface layer, followed by its rapid cooling due to heatremoval into the material due to thermal conductivity and the implementation of repetitively-pulsedradiation-enhanced diffusion of atoms to depths significantly exceeding the projective ion range. Thispaper considers features of thermal processes and the effect of pulsed heating of near-surface titaniumlayers on diffusion transfer under conditions of synergy of high-intensity titanium ion implantationand energy impact of a high-power density repetitively-pulsed beam on the surface to increase iondoping depth due to radiation-enhanced diffusion under conditions of limited heating of the entiresample. The paper presents the data of numerical simulation of dynamic changes in temperature fieldsin titanium and titanium self-diffusion under the action of ion beams with a submillisecond durationand a pulse power of tens of kW/cm2 and fluence of ions in a pulse 1.25×1015 ion/cm2.

Microstructure evolution in Cr0.6FeNiMn and CrFeNiCoPd under ion irradiation

It has been suggested that CrFeNi-based multi-principal element alloys (MPEAs) may be attractive materials for nuclear energy applications due to promising mechanical properties and possible increased resistance to irradiation damage compared to traditional alloys. However, phase stability during irradiation at intermediate temperatures remains a concern and expanding the range of irradiation conditions is of prime importance to understand the radiation damage mechanisms operating in these alloys. Here, the effects of dose and dose rate on the microstructures of two model alloys, Cr0.6FeNiMn and CrFeNiCoPd, during heavy ion irradiation were investigated. Both alloys exhibited phase decomposition under thermal aging and ion irradiation. Under ion irradiation, the decomposition process followed a thermodynamically driven radiation-enhanced diffusion process that is susceptible to cascade mixing effects at high ion irradiation dose rates.

A study on the competition and synergy between irradiation and temperature on the texture and recrystallization of nanocrystalline nickel

The application of nickel coatings on structural materials in molten salt reactors for corrosion resistance is being researched. For corrosion resistance, the coatings must have specific texture and grain boundary characteristics that withstand irradiation. While most reported results concern textural changes caused by room-temperature irradiation, research in the thermally-assisted regime, which is the operating temperature range of nuclear reactors, is limited. In this study, we investigate the effect of 1.4 MeV Ni+ ion irradiation on the texture, recrystallization, and grain boundary characteristics of nanocrystalline Ni at temperatures ranging from 250 °C to 550 °C. Thermal activation at 350 °C and 450 °C results in partially and fully recrystallized microstructures, respectively. A concurrent decrease of <100>//ED and evolution of <111>//ED, as well as minor orientations that reduces surface energy, are detected up to 450 °C; nevertheless, textural reversal is found at higher temperatures. Irradiation accelerated the recrystallization kinetics, resulting in a fully recrystallized microstructure at temperatures 100 °C lower. Irradiation at temperatures above 350 °C increased the thermally-induced texture; at 250 °C, this trend reversed. Calculated radiation-enhanced diffusion (RED) coefficients at 250 °C revealed that ion mixing drives the growth of <100> by consuming <111> orientations. Conversely, the increasing RED contribution at higher temperatures strengthens the thermally-induced textures.

Analysis of position-dependent cavity parameters in irradiated metals to obtain insight on fundamental defect migration phenomena☆

Motion of point defects is a fundamental process that governs microstructure and properties of materials. Here, we examine the near-surface and grain boundary cavity swelling depth profiles in neutron- and ion-irradiated simple metals (Cu, Ni, and Fe-Cr) and investigate diffusional broadening of implanted Ni ions in Fe-Cr alloys. Vacancy migration energies and radiation-enhanced diffusion were experimentally estimated. Cavity denuded zone widths near planar sinks are shown to be dependent on temperature, damage rate, balance of point defects and sinks, and vacancy migration energies. An enhanced cavity swelling zone adjacent to the void-denuded zone was observed in specimens with low to moderate sink strength and interpreted as evidence of 1D gliding interstitial clusters. Radiation-enhanced diffusional broadening of implanted Ni ions (at 400–550 °C) in Fe and Fe-Cr was up to 250 nm toward the surface, which leads to a much broader near-peak-damage region where cavity swelling is suppressed. Diffusional broadening of implanted ions is calculated to be similarly pronounced for self-ion irradiations, particularly near the peak and higher swelling temperature regimes. Adequately high ion energies (∼8–15 MeV) are recommended for ion-irradiation studies to provide a sufficiently broad midrange safe analysis region with minimized surface and injected ion effects.

Computational determination of a primary diffusion mode in [formula omitted]U-10Mo under irradiation

Low enriched uranium (< 20 %235U)-molybdenum (U-Mo) monolithic fuel is the primary candidate for high-performance research and test reactors and is in the process of being qualified to replace highly-enriched uranium (≥ 20 %235U) fuel. As part of the qualification process, it is critical to understand and predict the behavior of fission gas bubbles under irradiation, which affects fuel swelling and fuel failure. Mechanistic fuel models are being developed that can both reproduce the existing experimental data for fuel swelling, and be further applied to irradiation conditions beyond the experimental scope. Diffusion of species under irradiation conditions is an important parameter in the mechanistic fuel models; however, no temperature-relevant experimental diffusion data exists. In the present work, radiation-enhanced diffusion coefficients of U, Mo, and Xe in γU-10wt.%Mo were calculated in the temperature range between 300 K and 1400 K via rate-theory models and molecular dynamics simulations with an embedded-atom method interatomic potential for the U-Mo-Xe system. Accordingly, total diffusion coefficients under relevant irradiation conditions are determined using previously obtained intrinsic thermal diffusion and radiation-driven diffusion coefficients, as well as the newly calculated radiation-enhanced diffusion coefficients presented herein. Radiation-enhanced diffusion of U and Mo was dominant in the intermediate temperature range, whereas radiation-enhanced diffusion of Xe did not significantly contribute to total diffusion of Xe at the relevant fission rate densities. Radiation-enhanced diffusion of Xe became faster than both intrinsic thermal diffusion and radiation-driven diffusion at a fission rate density of 5×1022fiss/m3/s, which is higher than the typical fission rate density range in research reactors. The temperature regime where radiation-enhanced diffusion of each element dominated was dependent on the fission rate density. The total diffusion coefficients of U, Mo, and Xe, updated in this work, will be utilized as parameters in the mechanistic fuel models to help predict the behavior of fission gas bubbles under irradiation more accurately.

Investigation of radiation-enhanced diffusion using first-passage time

The approach the first-passage time (FPT) of a random process to a certain level is applied to the description of radiation-enhanced diffusion. This is an integral approach to describing the problem of radiation-enhanced diffusion, which does not specify the details of the process but takes into account the overall change in entropy during the process. Relationships are obtained to take into account the influence of radiation effects on the diffusion coefficient. The theoretical results obtained are compared with the experimental ones.

Dynamic substrate reactions during room temperature heavy ion irradiation of CoCrCuFeNi high entropy alloy thin films

High entropy alloys (HEAs) are promising materials for various applications including nuclear reactor environments. Thus, understanding their behavior under irradiation and exposure to different environments is important. Here, two sets of near-equiatomic CoCrCuFeNi thin films grown on either SiO2/Si or Si substrates were irradiated at room temperature with 11.5 MeV Au ions, providing similar behavior to exposure to inert versus corrosion environments. The film grown on SiO2 had relatively minimal change up to peak damage levels above 500 dpa, while the film grown on Si began intermixing at the substrate–film interface at peak doses of 0.1 dpa before transforming into a multi-silicide film at higher doses, all at room temperature with minimal thermal diffusion. The primary mechanism is radiation-enhanced diffusion via the inverse Kirkendall and solute drag effects. The results highlight how composition and environmental exposure affect the stability of HEAs under radiation and give insights into controlling these behaviors.

Formation of manganese-enriched austenite at abnormally low temperatures for diffusion type processes at “cascade radiation shaking” of Fe–6.35 at.% Mn alloy with accelerated Ar+ (E = 15 keV) ions

Using the methods of Mössbauer spectroscopy and transmission electron microscopy, it was found that short-term (for 4 s) irradiation of cold-rolled foils of the Fe–6.35 at.% Mn composition with a thickness of 25 μm with Ar+ ions (E = 15 keV) with heating to 300–450 °C causes an α → γ phase transformation with the formation of the repeatedly enriched with manganese austenite (from 23.8 to 38.0 at.%). The estimates made do not allow us to explain these processes by the phenomena of thermal and radiation-enhanced diffusion. As an explanation, the role of nanoscale dynamic effects associated with shaking the medium by powerful post-cascade solitary waves is considered. Such waves, becoming undamped in metastable media and playing, in a certain sense, the role of temperature, cause a short-term giant increase in the mobility of atoms and the transition of these media to a state with minimum free energy. The concentrations of Mn c1 and c2 in the α-and γ-phases, calculated on the basis of decoding the Mössbauer spectra for irradiation temperatures 311, 378 and 449 °C, correspond quite well to the results of extrapolation of the lines of the equilibrium phase diagram to the low temperature region.

Phase instabilities in austenitic steels during particle bombardment at high and low dose rates

Disruption of phase stability by energetic particle bombardment is a major challenge in designing advanced radiation-tolerant alloys and ion beam processing of nanocomposites. Particularly, ballistic dissolution susceptibility of different solute nanocluster species in alloys is poorly understood. Here, low dose rate neutron irradiations were conducted on a Fe-Cr-Ni based austenitic steel in the BOR-60 reactor (9.4 × 10−7 dpa/s, 318 °C) followed by accelerated dose rate ion irradiations at multiple temperatures (~ 10−3 dpa/s, 380 – 420 °C). Using atom probe tomography, the stability of radiation-enhanced Cu-rich and radiation-induced Ni-Si-Mn-rich nanoclusters was evaluated. During neutron irradiation, Cu-rich clusters nucleated with their core concentrations progressively increasing with dose, while Ni-Si-Mn-rich clusters formed and evolved into G-phase precipitates. Ion irradiations dramatically altered the nanoclusters. Cu-rich clusters were ballistically dissolved, but Ni-Si-Mn-rich clusters remained stable and coarsened with dose at 400 and 420 °C, highlighting that different nanocluster species in a single microstructure can have innately distinct ballistic dissolution susceptibilities. Solute-specific recoil rates were incorporated into the Heinig precipitate stability model, which shows that in addition to radiation-enhanced diffusion, recovery from ballistic dissolution depends on solute concentration gradient near cluster interfaces. The combined experimental-modeling study quantified the critical temperatures and damage rates where ballistic dissolution dominates for each cluster species.

Radiation-assisted chemical short-range order formation in high-entropy alloys

The chemical short-range order (CSRO) in a face-centered cubic equiatomic NiCoFeCrMn high-entropy alloy was revealed directly from advanced transmission electron microscopy in this work. Further, instead of controlling CSRO by conventional heat treatment, we show a new possibility of tailoring CSRO by radiation. The multiple types of atoms in such high-entropy system are more prone to form CSRO under radiation compared to that only under thermodynamic equilibrium conditions, due to the rearrangement of the chemical ordering during the non-equilibrium thermal spike period and the radiation-enhanced diffusion mechanism. Our results show an increase in the fraction of CSRO area by ∼45% after high-temperature irradiation with a dose of 50 DPA. Accordingly, we demonstrated that enhanced CSRO can be achieved by controlling the irradiation dose and temperature, which provides a new route to explore the kinetic evolution and effect of CSRO in complex alloy systems.

Understanding radiation effects in friction stir welded MA956 using ion irradiation and a rate theory model

An outstanding challenge in the manufacturing and joining of oxide dispersion strengthened steels is retaining the nanofeatures in the alloy throughout the fabrication and welding process. MA956 was friction stir welded with two different sets of welding parameters, resulting in a medium and high heat input. After welding, 5 MeV Fe++ ion irradiations were performed at doses ranging from 50 to 200 dpa in the temperature range of 400 to 500 °C. Post-irradiation characterization was performed with scanning transmission electron microscopy and energy-dispersive x-ray spectroscopy to investigate the Y-Al-O dispersoids, voids, and dislocations. After welding, the dispersoid microstructure coarsened, resulting in fewer and larger dispersoids regardless of heat input. After irradiation, the dispersoid behavior in the welded material was sensitive to temperature, exhibiting growth behavior attributed to Ostwald coarsening at 500 °C but a mixture of nucleation and more muted growth at 400 and 450 °C, attributed to competing mechanisms of radiation-enhanced diffusion and Ostwald coarsening. Void swelling correlated to heat input; being more prevalent in the welded conditions occurring at lower doses and in higher values relative to the base material. The low values of swelling despite microstructure coarsening caused by welding demonstrate the excellent swelling resistance of MA956, even after welding with the highest swelling values of 0.5% noted in the stir zone high heat input condition at 450 °C, 200 dpa. The dislocation behavior was inconsistent: the strongest trend was that network density was higher for welded versus base material, and an increase in loop diameter with temperature was observed. A rate theory model based on the observed microstructure suggests at high temperature interstitial loss to sinks was more likely to be dominant compared to mutual annihilation via point defect recombination, because of an increase of the radiation diffusion coefficient with temperature regardless of initial welded microstructure.

Features of silicon carbide synthesis by cold implantation of carbon recoil atoms

The Auger electron spectroscopy method confirmed a high concentration of carbon atoms (~ 85 at.%) introduced into silicon by cold implantation of recoil atoms. Carbon atoms are concentrated in a thin (~ 5 nm) near-surface region of silicon. Annealing of such a structure did not reveal a noticeable diffusion of carbon, which prevents obtaining a layer of SiC with a thickness of more than a few nm. This problem was solved by using radiation-enhanced diffusion. This made it possible to control the distribution profiles of carbon atoms in a wide range. Annealing at 1150oC allowed obtaining layers of amorphous-crystalline SiC with a thickness of 50-150 nm. Higher annealing temperatures are required to obtain a single-crystal SiC film. Keywords: cold implantation, radiation-enhanced diffusion, silicon carbide, recoil atom, thin films.

Численное моделирование динамики температурных полей в монокристаллическом кремнии при импульсно-периодической высокоинтенсивной ионной имплантации и энергетическом воздействии пучка на поверхность

Methods to modify surface and near-surface layers of materials and coatings by ion beams are used in many fields of science and technology. The method of high-intensity implantation by high-power density ion beams with submillisecond duration involves significant pulsed heating of the irradiated target’s near-surface layer, followed by its rapid cooling due to heat transfer into the material due to thermal conductivity and the implementation of repetitively-pulsed radiation-enhanced diffusion of atoms to depths exceeding the projective ion range. Using the numerical simulation, this work studies the dynamics of changes in temperature fields into silicon wafer under single-pulse and repetitively-pulsed exposure to submillisecond titanium ion beam with a pulsed power density in the range up to 109 W/m2. The conditions are determined under which the temperature in the ion-doped layer will correspond to the conditions of radiation-stimulated diffusion of the implanted element, and the temperature in the matrix material will not deteriorate its microstructure and properties.

Radiation-enhanced diffusion of copper in iron studied by three-dimensional atom probe

Radiation-enhanced diffusion (RED) of copper (Cu) in iron (Fe) is essential for understanding solute/impurity diffusion in nuclear materials, especially reactor pressure vessel steel, but has been rarely reported experimentally. In this study, we performed a high-precision investigation of RED using well-controlled electron irradiation and three-dimensional atom probe (3D-AP). Cu-Fe diffusion pairs were created using high-purity Fe and Cu as base materials, and irradiated by 2 MeV electron at a temperature of 773 – 893 K controlled to within ±3 K. Cu diffusion into the Fe matrix was observed at the atomic level using 3D-AP, and the diffusion coefficient was obtained directly using Fick's law. RED was clearly observed, and the ratio of diffusion under irradiation to thermal diffusion was increased as the irradiation temperature decreased. RED was quantitatively evaluated using the reaction kinetics model, and the model which consider only vacancies gave a good agreement. This gave experimental clarification that RED was dominated by irradiation-induced vacancies. In addition, the direct experimental results on the effect of irradiation on the solubility limits of Cu in Fe was obtained; solubility limits under irradiation were found to be lower than those under thermal aging.

Phase-field simulation of Cu enriched nanoparticles with variation of defects migration energy under neutron irradiation

Neutron radiation induces point defects and affects the diffusivity of atoms and the kinetics of precipitation. The phase-field simulation reveals the influence of migration energy of vacancy on the radiation-enhanced precipitation in Fe–Cu alloy. The study shows that radiation-enhanced diffusion (RED) also depends on the diffusivity of vacancy-associated migration energy and not only on the dose rate; the low migration energy of vacancy results in accelerated precipitation and a higher volume fraction of Cu precipitates. Interestingly, decreasing migration energy from 1.0 eV to 0.9 eV results in a 30% increase in the precipitates’ volume fraction. Also, the combination of the lowest dose rate 5.0 × 10−3 dpa s−1 and highest migration energy 1.0 eV delays the precipitation. The study also examines the influence of migration energy of vacancy on the radius of Cu precipitates. The lowest migration energy, 0.9 eV, increases the radius up to one-third. Finally, the work presents the drawbacks of the analytical digital image processing technique in the quantitative comparison with the script.

Carbon and Neon Ion Bombardment Induced Smoothing and Surface Relaxation of Titania Nanotubes.

Titania nanotube arrays with their enormous surface area are the subject of much attention in diverse fields of research. In the present work, we show that not only 60 keV and 150 keV ion bombardment of amorphous titania nanotube arrays yields defect creation within the tube walls, but it also changes the surface morphology: the surface relaxes and smoothens in accordance with a curvature-driven surface material’s transport mechanism, which is mediated by radiation-induced viscous flow or radiation-enhanced surface diffusion, while the nanotubes act as additional sinks for the particle surface currents. These effects occur independently of the ion species: both carbon and neon ion bombardments result in comparable surface relaxation responses initiated by an ion energy of 60 keV at a fluence of 1 × 10 ions/cm. Using atomic force microscopy and contact angle measurements, we thoroughly study the relaxation effects on the surface topography and surface free energy, respectively. Moreover, surface relaxation is accompanied by further amorphization in surface-near regions and a reduction in the mass density, as demonstrated by Raman spectroscopy and X-ray reflectivity. Since ion bombardment can be performed on global and local scales, it constitutes a versatile tool to achieve well-defined and tunable topographies and distinct surface characteristics. Hence, different types of nanotube arrays can be modified for various applications.