Dependence of the concentration of point defects in the ChS-68 austenitic steel on the rate of their generation and temperature upon neutron irradiation

A model of migration of point defects to sinks under neutron irradiation is represented. Expressions for the diffusion times of vacancies and interstitials upon migration to different types of sinks have been obtained. Equations for the stationary concentrations of point defects under neutron irradiation have been constructed. Dependences of the vacancy and interstitial concentrations in the ChS-68 steel on the irradiation temperature and defect-generation rate have been calculated within the framework of the model suggested. It is demonstrated how the results obtained can be used for an analysis of radiation-induced swelling.     

Radiation-induced defects and low-temperature hardening in the Fe–Cr alloy

Positron annihilation spectroscopy was used to study processes of accumulation and annealing of vacancy defects in the Fe-15.7 at % Cr alloy of commercial purity and the influence of these processes on the low-temperature hardening of the alloy upon electron irradiation to a damaging dose of 10⁻³ dpa in a temperature range of 270–370 K. Tensile tests were carried out both in the process of irradiation of the alloy and upon the subsequent annealing. It is shown that at the initial stages of irradiation the increase in the yield stress is caused by the accumulation of vacancy-carbon complexes. With an increase in the radiation dose, the growth of the yield stress is connected with an increase in the density of three-dimensional vacancy clusters. For the alloy irradiated at 370 K, the possibility of the contribution from a high-chromium phase, which is generated as a result of irradiation-accelerated α-α′ phase separation has also been considered.     

Effect of neutron and electron irradiation on radiation-induced separation of solid solutions in the Fe-Ni and Fe-Ni-P alloys

Processes of radiation-induced separation of solid solutions in Fe-34.7 at % Ni and Fe-34.7 at % Ni-0.1 at % P alloys have been investigated at T _irr ～ 320K. A comparative analysis of these processes upon electron (cascade-free) and neutron (cascade-inducing) irradiations has been performed. It has been shown that the efficiency of electron irradiation is higher than that of neutron irradiation. The minimum fraction of freely migrating vacancies upon neutron and electron irradiations is 0.5–0.6 and 6–9%, respectively. Upon annealing of the irradiated samples, several substages of the processes of dissociation of vacancy clusters have been observed. Their energies for activation have been determined. For both types of irradiation the presence of phosphorus increases the fraction of vacancies retained after irradiation. The efficiency of the irradiation in the realization of processes of separation is determined by the concentration of freely migrating point defects and the diffusion length of their migration to sinks.     

The Influence of Grain Boundaries on Radiation-Induced Point Defect Production in Materials: A Review of Atomistic Studies

Radiation-induced defects cause severe degradation of materials properties during irradiation that can ultimately cause the material to fail. Consequences of these defects include swelling, embrittlement, and undesirable phase transformations. Nanocrystalline materials, which contain a high density of grain boundaries, have demonstrated enhanced radiation tolerance compared to large grain counterparts under certain conditions. This is because, as has long been recognized, grain boundaries can serve as defect sinks for absorbing and annihilating radiation-induced defects. Increasingly, researchers have examined how grain boundaries influence the direct production of defects during collision cascade, the origin of the radiation-induced defects. In this review article, we analyze the computational studies in this area that have been performed during the past two decades. These studies examine defect production near grain boundaries in metallic, ionic, and covalent systems. It is found that, in most systems, grain boundaries absorb more interstitials than vacancies during the defect production stage. While this is generically true of most boundaries, the detailed interaction between defects and grain boundaries does depend on boundary atomic structure, the stress state near the boundary, cascade-boundary separation, and materials properties. Furthermore, the defect distribution near boundaries is qualitatively different from that in single crystals, with the former often exhibiting larger vacancy clusters and smaller interstitial clusters than the latter. Finally, grain boundaries that are damaged after cascades have occurred exhibit different interaction behavior with defects than their pristine counterparts. Together, these atomistic simulation results provide useful insight for both developing higher-level modeling of defect evolution at long timescales and how interfaces influence radiation damage evolution.     

Accumulation and annealing of radiation defects under low-temperature electron and neutron irradiation of ODS steel and Fe-Cr alloys

The processes of accumulation and annealing of radiation defects at low-temperature (77 K) electron and neutron irradiation and their effect on the physicomechanical properties of Fe-Cr alloys and oxide dispersion strengthened (ODS) steel have been studied. It has been shown that the behavior of radiation defects in ODS steel and Fe-Cr alloys is qualitatively similar. Above 250 K, radiation-induced processes of the solid solution decomposition become conspicuous. These processes are much less pronounced in ODS steel because of specific features of its microstructure. Processes related to the overlapping of displacement cascades under neutron irradiation have been considered. It has been shown that, in this case, it is the increase in the size of vacancy clusters, rather than the growth of their concentration, that is prevailing. Possible mechanisms of the radiation hardening of the ODS steel and the Fe-13Cr alloy upon irradiation and subsequent annealing have been discussed.     

Accumulation and annealing of radiation defects and the hydrogen effect thereon in an austenitic steel 16Cr15Ni3Mo1Ti upon low-temperature neutron and electron irradiation

The effect of hydrogen, accumulation and annealing of radiation defects on the physicomechanical properties of an austenitic Kh16N15M3T1 steel (16Cr15Ni3Mo1Ti) has been investigated upon low-temperature (77 K) neutron and electron irradiations. It has been shown that, when its concentration is about 300 at ppm, hydrogen reduces plasticity by 25%. The presence of helium (2.0–2.5 at ppm) introduced by the tritium-trick method exerts an effect on the yield strength and hardly affects embrittlement. Upon both electron and neutron irradiation, there is a linear relation between the increment of the yield strength and the square root of the increment of the residual electrical resistivity (the concentration of radiation defects). The annealing of vacancies occurs in the neighborhood of 300 K (energy for vacancy migration is 1.0–1.0 eV). Vacancy clusters dissociate near 480 K (energy for dissociation is 1.4–1.5 eV).     

Phase separation of solid solution in Fe-Ni and Fe-Ni-P alloys during irradiation,deformation, and annealing

Measurements of residual resistivity and thermal expansion coefficient have been used to study processes of phase separation in the solid solution of the Fe-34.7 at % Ni and Fe-34.7 at % Ni-0.1 at % P alloys that occurred during deformation, electron irradiation, and subsequent annealings. It has been shown that during both deformation and irradiation, vacancy clusters appear with various multiplicities. In both the deformed alloys and alloys irradiated at room temperatures, the presence of phosphorus atoms in the solid solution facilitates the formation of the vacancy clusters and increases the fraction of vacancies that survive in the form of vacancy clusters. After deformation, irradiation, and subsequent annealings, the same changes are observed in the electrical resistance and thermal expansion coefficient. A nearly linear dependence of the increment in the electrical resistance on the thermal expansion coefficient has been obtained. The results agree well with the matrix model of the phase separation of the solid solution.     

Deuterium trapping in irradiated nickel

The effect of cold plastic deformation in nickel on the deuterium segregation induced by ion irradiation has been studied by the nuclear-reaction method. The irradiation and discrete measurements have been performed at room temperature and coordinated in time due to the use of a beam of accelerated deuterons with an energy of 700 keV in the reaction D (d,p) T. An analysis of the experimental dose dependences of the accumulation of implanted deuterium and of the results of calculation of the process of deuterium implantation using an SRIM program made it possible to reveal the basic laws of the deuterium segregation. It has been established that deuterium trapping in the irradiated volume occurs into initial traps (deformation-induced vacancies) and radiation-induced traps (vacancies and their clusters). The dislocations at room temperature are not efficient traps of deuterium. Dose ranges of deuterium trapping by different-type traps have been revealed, and a model of the formation and evolution of the deuterium segregates in nickel has been put forward.     

Structural and phase states and irradiation-induced defects in Ni-Cr alloys

The structural and phase states in alloys of the Ni-Cr-Mo system which were induced by both heat aging and electron irradiation at elevated temperatures have been studied by the methods of measurement of residual resistivity and positron annihilation. Migration of irradiation-induced defects during irradiation at 300°C is shown to initiate processes of ordering or phase separation depending on the initial alloy microstructure and chromium content. It has been established that in the alloy with 32 wt % Cr the concentration of accumulated vacancy defects in the state of short-range ordering after irradiation with 5-MeV electrons to a dose of ～1.5 × 10^?4 dpa at 200°C is half as high as that in the state of long-range ordering with a homogeneous distribution of domains (to 10 nm in size) of the ordered Ni₂Cr phase in the matrix.     

TiAl中空位团的稳定构形及其对附近空位迁移行为的影响

用分子动力学方法,采用Finnis-Sinclair类型的多体势,对TiAl中小尺寸空位团（N0=2,3,4）的各种可能构形进行了模拟计算,计算了空位团的形成能、结合能,分析讨论了容位团最稳定的构形,在此基础上,研究了空位团对单空位迁移的影响。计算结果表明：在TiAl合金中,组成空位团的每个空位都尽可能地与其它空位保持最近邻关系,空位团附近有反位原子。当空位团较大时,空位团周围的原子会向空位中心埸陷,类似于空位团中包含有间隙原子。已有的空位团可作为空位的凝聚中心具有捕获或吸收附近空位的能力。     

冷轧纯锆在等时退火条件下的缺陷和组织演化

通过正电子湮没寿命(PAL)和透射电子显微镜(TEM)研究了不同程度冷轧纯锆在等时退火条件下的缺陷和显微组织演化行为。研究结果表明：纯锆经过冷轧变形产生高密度的位错和空位,随着冷轧变形量的增加到10%,正电子的平均湮没寿命逐渐增加,变形量进一步增大,正电子的平均寿命趋于饱和。在温度范围298~898 K的等时退火条件下,冷轧纯锆中的空位型缺陷并没有聚集形成空位簇。随着退火温度增加,冷轧纯锆中的空位和位错密度逐渐减小,在退火温度为873 K时回复基本完成。     

Investigation on the origin of vacancy formation in diamonds by electron-beam irradiation and heat-treatment

In this study, we have attempted to describe the phenomenon of vacancy formation in various types of diamonds (natural type IaAB, synthetic type Ib, synthetic type IIa, and type IaABC suspected of having been pretreated with an unknown method) using electron beam irradiation. After the electron beam irradiation, vacancies were formed in the natural type IaAB and synthetic type IIa diamonds, whereas vacancies were not formed in the synthetic type Ib and pre-treated type IaABC diamonds. From these results, we suggest a model of vacancy creation by electron beam irradiation in various types of diamonds. The irradiation was performed with electron dose densities of 1–6×10¹⁷/cm² at 10 MeV, and with a heat treatment of two hours at a temperature of 900 °C. Electron beam-irradiated and heat-treated samples were analyzed using UV-Vis-NIR, FT-IR, and PL spectroscopy.     

The Accumulation and Annealing of Radiation-Induced Defects and the Effect of Hydrogen on the Physicomechanical Properties of the V−4Ti−4Cr and V−10Ti−5Cr Vanadium-Based Alloys under Low-Temperature (at 77 K) Neutron Irradiation

The processes of the accumulation and annealing of radiation-induced defects that occur under low-temperature (at 77 K) irradiation (with an energy E > 0.1 MeV) of V?4Ti?4Cr and V?10Ti?5Cr bcc alloys both nonmodified and modified with hydrogen isotopes in a concentration of 200 ppm, as well as the effect of these processes on the physicomechanical properties of these alloys, have been studied. It has been found that the saturation of these alloys with hydrogen leads to slight changes in their strength and ductility characteristics. The irradiation of the alloys at the temperature of 77 K results in a substantial increase in their yield stress and ultimate strength, as well as a decrease in their ductility. In the course of the postradiation annealing of the alloys at a temperature of 130 K, the stage related to the migration of interstitial atoms is observed. At temperatures of 290–320 K, the recovery stage occurs due to the formation of vacancy clusters. The stage that occurs at a temperature of 470 K can be attributed to the formation of impurity-vacancy clusters. Possible mechanisms of the radiation-induced strengthening of the alloys during irradiation and subsequent annealing have been discussed.     

Migration of Point Defects in the Field of a Temperature Gradient

The influence of the temperature gradient over the thickness of the cladding of a fuel element of a fast-neutron reactor on the migration of point defects formed in the cladding material due to neutron irradiation has been studied. It has been shown that, under the action of the temperature gradient, the flux of vacancies onto the inner surface of the cladding is higher than the flux of interstitial atoms, which leads to the formation of a specific concentration profile in the cladding with a vacancy-depleted zone near the inner surface. The experimental results on the spatial distribution of pores over the cladding thickness have been presented with which the data on the concentration profiles and vacancy fluxes have been compared.     

氧化物弥散强化铁素体钢的电子辐照行为

本文利用超高压电子显微镜进行电子辐照实验，分析了我国试制的氧化物弥散强化（ＯＤＳ）铁素体钢的辐照行国．在６７０－７２０Ｋ下辐照时观察到了辐照空洞的形成．辐照条件为７２０Ｋ，９ｄｐａ时的辐照肿胀率小于０．１％．同时在电子衍射图样中发现了明显的衍射环，分析表明这些衍射环的出现是由于电子辐照促进了Ｙ２Ｏ３微细相形成的缘故．     

A positron investigation of electron-irradiation induced defects in γ-TiAl intermetallic compounds

The isochronal recovery of irradiation induced defects was investigated in γ-TiAl intermetallic compounds (with 50 and 54 at% Al) by positron lifetime measurements after 2.5 MeV electron irradiation at 21 K. In the as-irradiated condition, the analysis of the results and the comparison with published data led to a value τ_d=230±5 ps for the lifetime of vacancy-trapped positrons. The lifetime variations observed during isochronal anneals at increasing temperatures are consistent with vacancy migration around 450 K. The observation of a progressive decrease in the lifetime of trapped positron, during the migration and elimination of vacancies, suggests that they do not form unrelaxed three-dimensional clusters, and that another type of positron traps is simultaneously present.     

Radiation effects on the microstructure of a 9Cr-ODS alloy

Oxide dispersion strengthened (ODS) steels are prime candidates for high-temperature, high-dose cladding in advanced nuclear reactors. When a 9Cr-ODS alloy was irradiated with 5 MeV nickel ions at temperatures of 500–700°C to doses up to 150 dpa, there was no significant change in the dislocation arrangement. For oxide particles, there is a small shrinkage in size and increase in density with increasing irradiation dose. This work confirms that oxide particles and the microstructure of the 9Cr-ODS show minimal changes under irradiation at temperatures up to 700°C and doses up to 150 dpa.     

Positron Annihilation Investigation of Embrittlement Behavior in Chinese RPV Steels after Fe-Ion IrradiationEI北大核心CSCD

The reactor pressure vessel (RPV) is the key component in the nuclear power plant, which is considered irreplaceable and can be the life-limiting feature of the operation of nuclear power plant if its mechanical properties degrade sufficiently. High temperature gas-cooled reactor (HTGR) has perfect inherent safety, which is intended to be one of the fourth generation advanced nuclear reactors. However, HTGR has different service temperature with pressurized water reactor (PWR), that the service temperature of HTGR is 250 degrees C and that of PWR is 290 degrees C. So the irradiation behaviour of RPV in HTGR is expected to be investigated. In this wok, 3 MeV Fe-ion irradiation was performed on Chinese A508-3 reactor pressure vessel steel which is employed by high-temperature gas-cooled reactors and pure Fe under room temperature (about 25 degrees C) and high temperature (250 degrees C). The ion doses were 0.1, 0.5 and 1.0 dpa for both room temperature irradiation and high temperature irradiation. SRIM modeling was performed before irradiation experiments to guide the experimental details. Positron annihilation Doppler broadening (PADB) spectroscopy experiments and nano-indentation tests (to study embrittlement behavior) were conducted for characterization. It is found that after both room temperature irradiation and high temperature irradiation, the densities of defects in the reactor pressure vessel steel and pure Fe increase, and the type of defects could be vacancy-type and solute cluster type from PADB results. The vacancy-type defect density under high temperature irradiation is lower than that under room temperature irradiation. That is because high temperature can recover the defects formed during irradiation. The hardness test results show that for both the reactor pressure vessel steel and pure Fe, the irradiation hardening increases with increasing dose. Compared to room temperature irradiation, high temperature irradiation can produce more solute clusters and fewer vacancy-type defects in the reactor pressure vessel steel. So the irradiation hardening of the reactor pressure vessel steel might be caused mainly by the formation of solute clusters.     

A finite difference calculation of vacancy migration under non-steady state conditions

The hydrogenation of metals, often a rapid process, may lead to the production of high vacancy concentrations in the solid when equilibrium is reached. The achievement of equilibrium in this “upquenching” process depends, at least in part, upon the migration of vacancies from the surface into the interior of the solid. Because individual vacancy jump frequencies may depend on position within the vacancy density gradient, particularly when the solid is under an applied stress, analytical solutions of Fick's second law are not appropriate. A finite difference method has been developed to treat such vacancy diffusion problems and applied to vacancy migration in nickel.     

Effects of MeV Fe Ions Irradiation on the Microstructure and Property of Nuclear Grade 304 Stainless Steel:Characterized by Positron Annihilation Spectroscopy,Transmission Electron Microscope and Nanoindentation

Nuclear grade 304 stainless steel was irradiated by 3.5 MeV Fe ions,with fluxes of 3.05E+ 15 ions/cm2 and 1.55E+ 16 ions/cm2.Irradiation effects were studied by positron annihilation spectroscopy (PAS),transmission electron microscope (TEM)and nanoindentation techniques.PAS results showed that different types of defects were produced after irradiation and that there was significant variance in defects formed when the samples were subjected to different irradiation doses.TEM char-acterization showed that the irradiation-induced dislocation loops enlarged in average size,but decreased in number density at higher irradiation doses.Nanoindentation test showed obvious irradiation hardening phenomenon,which was in good agreement with the PAS and TEM results.Irradiation hardening effect increased with an increase in irradiation dose and saturation occurred with an increase in irradiation dose from 3.2 to 16 dpa.Further statistical analysis showed that barrier strength of the Frank loop depends on the loop size and density produced by the ion irradiation.