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Improved mechanical properties of oxide dispersion strengthened (ODS) steels, the advanced materials for the reactor core, are due to the high density of uniformly distributed nanosized oxide inclusions. Transformation of the nanostructure of ODS steels under irradiation determines their stability during operation in the reactor conditions. In this work, three ODS steels are studied: Eurofer ODS, 10Cr ODS, and KP-3 ODS with different alloying systems. In these steels, the chromium content varies from 9 to 14 at %; such alloying elements as V, Ti, Al, W, and Mn are present in different proportions. The effect of irradiation with iron ions up to 3, 6, and 30 dpa at a temperature of 350°C was studied. The radiation-induced changes were analyzed by transmission electron microscopy and atom probe tomography. Although the sizes of oxide inclusions remained almost without change under irradiation, a decrease in their number density was observed in 10Cr ODS and KP-3 ODS steels, while the number density of oxides in Eurofer ODS steel did not change under the irradiation to 30 dpa. On the whole, the strengthening of the ODS steels due to inclusions during the irradiation to 30 dpa at 350°C changed insignificantly, which indicates their radiation resistance and their low propensity for low-temperature radiation strengthening and embrittlement.

The enhanced mechanical properties of oxide dispersion-strengthened (ODS) steels are mainly due to the high density of homogeneously distributed oxide inclusions. It is well known that some alloying elements, such as Ti, V, and Al, play an important role in the formation of oxides/nanoclusters and influence the density and size of these inclusions. In this paper, a wide range of ODS steels containing different alloying elements were studied. The microstructural analysis was performed using transmission electron microscopy and atom probe tomography. Different types of inclusions were found in the steels: oxides of the Y–Ti–O or Y–Al–O types with sizes of ~2–15 nm, and nanoclusters (2–5 nm) enriched in Y, O, and Cr, as well as Ti, V, and Al, when these elements were present in the material. It was shown that oxides made the main contribution to the steel strengthening, while the cluster contribution was comparable with that of oxides only in Austenitic ODS and 14Cr ODS steels.

In this paper, the results of study of the AlCoCrFeNi high-entropy alloy by means of atom probe tomography are presented. Two phases were found, one enriched in Fe and Cr and the other enriched in Ni and Al. Owing to the complex surface morphology and spatial configuration of the phases, they were analyzed by various statistical methods. The Fe–Cr phase has a honeycomb structure that contains Co particles with the characteristic size of ~10 nm. The enrichment of the cell boundaries in Fe and Cr atoms reaches 50 at %. In turn, the Al–Ni phase is enriched in each of these elements up to 30 at % and contains nanoscale precipitates of Fe and Cr atoms. The volume density of these clusters is ~5 × 1022 cm–3.

Segregation of chemical elements was studied in ferritic-martensitic steels RUSFER-EK-181 and ChS-139—promising structural materials for fast neutron reactor core. To simulate the radiation effects, Fe ions with an energy of 5.6 MeV at temperatures of 250–400°C to damage doses of ~6 dpa and at temperatures of 350–450°C to a damage dose of 30 dpa were used. RUSFER-EK-181 steel was also studied after thermal aging at 450°C for 5000 h. Z-contrast analysis of the irradiated steels revealed the segregation of alloying elements on dislocations at small-angle tilt and mixed grain boundaries. Atom probe tomography of the ion-irradiated ChS-139 steel showed that clusters enriched in Ni, Si, and Mn were formed on the dislocations, including dislocations of small-angle grain boundaries. Clusters enriched in Si were formed on dislocations in the RUSFER-EK-181 steel. In the aged state of RUSFER-EK-181 steel, segregation of Cr, V, Mn, Si, and N was shown at dislocations of the small-angle grain boundary. The calculated misorientation angles of the small-angle grain boundaries were ~1°–3°, and the twist angle of the mixed boundary was ~3°.

Monitoring the characteristics of nanoscale objects is a necessary step in the development of new materials and complex low-dimensional systems. Atom-probe tomography is among the few methods that allow one to study nanoscale objects with a complex chemical composition. However, preliminary optimization of the instrument parameters is necessary for each speciment to obtain the most accurate characteristics of the materials. In this study, the results of optimization of conditions for the analysis of silicon and the titanium–titanium-oxide transition layer on a APPLE-3D atom-probe tomograph with the purpose of refining the atom-probe-tomography technique for metal–semiconductor structures are presented. The optimal laser-pulse power for studying mixtures of these materials is determined. The atomic structure of the titanium–titanium-oxide interface layer is visualized, and the concentration profiles of evaporated Ti and TiOx ions in the transition layer are obtained.

The comprehensive study of radiation hardening of the ferritic-martensitic steels RUSFER-EK-181 (Fe–12 Cr–2 W–V–Ta–B–0.16 С) and ChS-139 (Fe–12 Cr–Ni–Mo–W–Nb–V–N–B–0.20 C) using Fe ion irradiation at temperatures of 250–400°С to damage doses of ~6 dpa is conducted. The quantitative analysis of radiation-induced changes in the RUSFER-EK-181 and ChS-139 steel microstructure is performed by transmission electron microscopy and atom probe tomography. The study of hardening of steel samples irradiated with ions by nanoindentation and the evaluation within the framework of the dispersed barrier model show that the detected radiation-induced clusters and dislocation loops play an important role in the low-temperature radiation hardening of the RUSFER-EK-181 and ChS-139 steels.

A comprehensive experimental–theoretical study of the processes of local ordering of multicomponent alloys has been carried out. Atom probe tomography and measurement of electrical resistance during isochronal annealing are used as experimental techniques. Atomistic modeling methods and the multiscale paradigm based on quantum mechanical calculations were used in the theoretical study. The experimental and theoretical approach used made it possible for the first time to detect the initial stage of decomposition of a CoCrFeNi alloy solid solution with the formation of Ni4Cr and Ni2Cr precipitates.

This work presents the results of the study of three different blanks used for the production of disks for gas-turbine engines made of a granular Ni-based superalloy. The blanks differed in the heat treatments performed and in the complexes of mechanical characteristics. The scanning electron microscopy of the studied materials showed that the size of the γ-matrix grains was 30–50 micrometers. In addition, particles of the γ and γ' phases with a size from 10 to 70 nm were revealed in the volumes of all blanks. The morphology of these particles has been studied. Within the particles of the γ' phase, homogeneously distributed equiaxed clusters of atoms of γ-forming elements were revealed with a size of 1–4 nm and flattened clusters of the same size and the same chemical composition aligned into chains. In the particles of both phases and in the transition layers between them, concentrations of the alloying components and impurities have been determined. In the studied volumes of the three different blanks of the disks, the volume fractions of the γ' phase were found to be 68 ± 1, 61 ± 2, and 62 ± 4%.

Atom probe tomography (ATP) is a technique that has actively been developed in recent years. This method allows one to investigate three-dimensional distributions of chemical elements in various materials with atomic spatial resolution. The raw APT data reconstruction algorithm uses the geometry of evaporated ion trajectories. However, the basic algorithm uses the approximation of rectilinear trajectories of ions moving from the specimen to the detector. In this study, we present the main approaches to adapting and optimizing the basic APT data reconstruction algorithm concerning the mass reconstruction procedure. Methods for taking into account the nonlinear distortions of ion trajectories due to the wide-angle detection system and other features of ion detection in atom probe tomography are demonstrated. Using a titanium alloy (Ti—5Al—2.7Mo—2Zr), we demonstrate that the consideration of the above effects in the reconstruction of ATP data makes it possible to increase the mass resolution, m/Δm50%, of the main peaks of the mass spectrum to 600 and above. In general, the set of performed procedures allows one to achieve a high accuracy of the positioning of the peaks up to 0.01 amu and ensures a significant (more than tenfold) increase in the mass resolution for mass spectrum peaks that are distant from the main peaks.

Specimens of ChS-139 steel (0.2 С–12 Cr–Ni–Mo–W–Nb–V–N–B) were irradiated up to 6 displacements per atom (dpa) with Fe ions at 250, 300, and 400°C. The radiation-induced clusters and Cottrell atmospheres enriched in Ni, Si, and Mn were revealed in irradiated samples by atom probe tomography. The typical sizes of the radiation-induced clusters were about 2–7 nm, and their number density was about (2–20) × 1023 m–3. It was shown that the highest irradiation temperature (400°C) is compliant with the lowest enrichment of clusters in Ni, Si, and Mn as well as with the largest average size of clusters (~5 nm) and the least number density (~2 × 1023 m–3). A noticeable decrease in the number density of radiation-induced clusters with an increase in the damage dose to 4 dpa at 300°C was found. At the same time, it was shown that the Cr–V–Nb–N clusters found in the initial state dissolve with the increase in the irradiation dose at all considered temperatures. The value of detected radiation-induced effects is indicative of their significant role in the low temperature radiation embrittlement of ChS-139 steel.

Low-temperature radiation hardening of prospective structural steel Eurofer 97 as the material for the first wall of the DEMO fusion reactor is studied in this work. Specimens of Eurofer 97 steel were irradiated with Fe ions up to 10 dpa at temperatures of 250, 300 and 400°C. Irradiated samples were studied by transmission electron microscopy and atom probe tomography. TEM study of irradiated samples showed preferential formation of dislocation loops at all temperatures of irradiation. Pair-correlation function analysis detected the initial stage of matrix solid solution decomposition of Eurofer 97 steel only at the temperature of 400°C. Detected microscopic changes and calculated hardening in the framework of the DBH (dispersed barrier hardening) model have shown that formation of dislocation loops is the main origin of low temperature radiation hardening of Eurofer 97 under irradiation with Fe ions with fluence up to 10 dpa.

We study the possibilities of the chemical analysis of materials with determination of the positions of individual atoms of various chemical elements in a sample using an APPLE-3D atom probe tomograph with femtosecond-laser assisted evaporation, developed at the Institute of Theoretical and Experimental Physics of the National Research Center “Kurchatov Institute.” The results of investigations of ferritic-martensitic steels and an aluminum alloy are presented; the characterization and visualization of features with a size on the order of 10 nm are demonstrated.

The chemical element distributions and the fine structure were studied using atom probe tomography in ChS-139 steel (Fe–12Cr–Nb–Mo–W–V–N–B) after conventional heat treatment (normalizing at 1190°C for 25 s and subsequent tempering at 720°C for 2 h) and after subsequent Fe ion irradiation at room temperature up to the damage doses of 8 and 16 displacements per atom (dpa). A large number of nanosized clusters (~1023 m−3) enriched in chromium, vanadium, nitrogen, and niobium were found throughout the Ch-139 steel after conventional heat treatment. The chemical element distribution in the M23C6 carbide, Nb2(C, N) and M6(C, N) carbonitride phases, pre-precipitates of M6X carbide phases, and the Cottrell atmosphere were studied. The changes in the cluster composition and sizes resulting from irradiation at room temperature were found. An increase in the cluster sizes upon irradiation was accompanied by a reduction in the concentrations of chromium, vanadium, nitrogen, and niobium.

Atom probe tomography (APT) analysis with a femtosecond laser is one of the most promising techniques to characterize local variations of chemical distribution in materials with subnanometer spatial resolution. In this study, the effect of APT analysis conditions on the accuracy of data recovery for chromium steels and Fe-Cr alloys is investigated. Dependences of mass resolving power and the detected composition of chromium as a function of laser power, specimen geometry, and evaporation rate are presented.

The results of development, creation, and tests of an atom-probe prototype with femtosecond laser evaporation and a position-sensitive microchannel detector with delay lines for the tomographic (3D) analysis of chemical composition of materials are presented. The atom-probe tomography is based on the principle of atom-by-atom “disassembling” of materials and projection magnification, which was previously used in field-ion microscopy, as well as the time-of-flight mass spectrometry that is applied to each evaporated ion. The prototype characteristics (mass resolution, spatial resolution, and data-collection efficiency) were demonstrated in study of tungsten.

Reduced activation ferritic/martensitic steels for in-vessel components of a fusion reactor have shown a decrease in plasticity and radiation hardening at low irradiation temperatures. The formation of dislocation loops and embryos of α' phase is considered the main reason for these effects. In this work, Eurofer 97 steel was irradiated with 5.6 MeV Fe2+ ions up to 1020 m−2 at 250, 300 and 400 °C. Transmission electron microscopy study of ion irradiated samples revealed nucleation of dislocation loops. The pair-correlation analysis of atom probe tomography data detected an initial stage of solid solution decomposition. The hardening of ion-irradiated Eurofer 97 was calculated with the dispersed barrier hardening model, taking into account radiation-induced dislocation loops to compare it with the change of yield stress in neutron-irradiated Eurofer 97. According to the obtained results, it can be supposed that the formation of dislocation loops plays the main role in the low-temperature radiation hardening of Eurofer 97 at a dose level up to ~10 dpa.

The statistical frequency method is used to analyze the experimental data obtained on the Stend-B reactor–laser complex. It is shown that high-order harmonics strongly influence the damping decrement of the neutron flux. The results of a numerical experiment confirm this conclusion.

Experiments measuring the absolute power of the MATR-2 reactor by a modified frequency method are described. A theoretical substantiation of the method employed is given. Experimental results are presented. 3 figures, 1 table, 4 references.

Experiments measuring the lifetime of prompt neutrons in the system BARS-6 reactor—laser unit by the statistical frequency method are described. A theoretical substantiation of the method employed is given on the basis of a point model of the kinetics. Experimental results are presented. 4 figures, 1 table, 13 references.