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In this paper the results of the studies of reduced activation ferritic-martensitic steel EK-181 (Rusfer-EK-181, Fe–12 Cr–2 W–V–Ta–B) developed in Russia (Bochvar High-Technology Scientific Research Institute of Inorganic Materials—VNIINM) as a structural material for application as the core components of fast neutron, fusion, and hybrid reactors are summarized. Various aspects of hydrogen interaction with Rusfer steel, primarily retention, diffusion, and the effect of various defects on retention, are considered.

We consider a specific version of the authors’ approach to the synthesis of bases of discrete orthogonal transforms (DOTs). The approach takes into account the relation between the structure of basis functions of a transform and the existence of a certain numeral system on the (multidimensional) index set of an input signal. In contrast to Chernov’s prototype paper “Discrete orthogonal transforms with bases generated by self-similar sequences” (2018), which was concerned with DOTs associated with irredundant numeral systems (where each index of the input signal has a unique representation in a chosen numeral system), in the present paper we study the case of the so-called complete numeral systems. In this case, there is no bijection between the set of input indices of DOTs and the set of their digital representations. Potentially, such statements of applied problems naturally appear in image recognition, artificial intelligence, theory of formal languages, mathematical programming, and other areas where the analyzed objects are characterized by many heterogeneous attributes, which can be quantitative, qualitative, and mixed. There may be several copies of each object, and the copies may have inconsistent descriptions, which must be considered and analyzed as a whole. Such objects with many attributes can be represented as multisets (“sets with repetitions”). Since discrete spectral analysis is a basic tool for solving the described problems in the classical “multiple” interpretation of objects, we try to extend some ideas and methods of spectral analysis to the case of multiset objects.

Using the methods of scanning and transmission electron microscopy, a study is performed of the influence of high-temperature annealing on the parameters of structural-phase states of low-activation alloys of the V–Me(Cr, W)–Zr system after different modes of thermomechanical treatments. By the active tensile loading at different temperatures the effect of the treatment regimes and final annealing temperatures on the strength and plasticity characteristics is investigated. The main factors determining the thermal stability of plasticity of the structural-phase state and the mechanical properties of these alloys are discussed.

The elastic (Young’s) modulus and relaxation properties (amplitude-independent internal friction) of bcc metals and alloys (vanadium, V–4Cr–4Ti, V–W–Cr, and V–Ta–Cr—Zr alloys) have been studied in the temperature range of 25–400°С by means of dynamic mechanical spectroscopy within a low-frequency range (0.5–30.0 Hz). No carbon in vanadium and V–W–Cr alloy in solid-solution state is revealed. In the case of vanadium and V–W–Cr alloy, the solid-solution concentrations of oxygen and nitrogen and the diffusion characteristics thereof (diffusion activation energy, characteristic relaxation time, and the preexponential factor in the diffusion equation) have been determined. In the case of V–4Cr–4Ti alloy, carbon, oxygen, and nitrogen solid solutions have not been observed. In V–Ta–Cr–Zr alloy, the solid-solution concentrations of interstitial atoms (C, O, N) are substantially lower than those in vanadium and V–W–Cr alloy. The values of elastic modulus in vanadium alloys can be either higher or lower than the elastic modulus inherent in vanadium depending on type of alloy (alloying) and on temperature. The V–4Ti–4Cr alloy exhibits the smallest value of the elastic modulus among all the materials under study. The temperature curves of the elastic (Young’s) modulus for the studied materials exhibit no features, except for a slight local relaxation of the Young’s modulus in the case of vanadium and V–W–Cr alloy in the temperature range of the relaxation peaks.

The results of an investigation of the influence of microstructure on the oxidation rate of an alloy of the V–Cr–W–Zr system investigated under the conditions of its heat treatment in air are presented. It is shown that the formation of the defect state in the alloy favors an increase in the constant and rate of oxidation. The maximum microstructure effects on the oxidation processes are observed during short treatment durations.

An investigation of the features of structural-phase transformations during heating and cooling of the lowactivation 12%-chromium ferritic-martensitic steel EK-181 (Fe–12Cr–2W–V–Ta–B) is performed in the range of temperatures from 30 to 1100°C by the methods of high-temperature X-ray diffraction analysis (XRD) in situ. The critical points of an (α →γ) - transformation (Ас1 ≈ 850°С, Ас3 ≈ 950°С) in the course of steel heating and the temperature interval (910–890°C) of the diffusion-induced transformation of the austenite →α-ferrite type under cooling are determined. It is shown that the position of these points changes depending on the method (XRD or differential scanning calorimetry) of their identification, which is attributed to the differences in their heating-cooling rates. During heating in the range of temperatures of 830–875°C, a significant increase in the volume fraction of М23С6 carbides is observed. Further temperature increase up to 1000–1100°C leads to their complete dissolution. In the course of cooling of the steel specimens from 1100 to 30°C, there is no carbide particle precipitation.

Vanadium alloys are considered as candidate structural materials for thermonuclear fusion reactors (FR) and fast neutron reactors. Some properties of vanadium alloys are especially attractive for FR: fast decay of induced activity, durability in liquid lithium, high temperature strength. At the same time vanadium alloys absorb and dissolve hydrogen isotopes, and hydrogen fluxes through them are quite high. Hydrogen affects on plasticity of vanadium alloys and significantly decreases it at high concentrations. This should be taken into account considering the possibility of vanadium alloys usage as the material of fusion and fission reactors, especially if these materials are assumed to be in contact with radioactive tritium. In this work deuterium permeation through V-4Cr-4Ti alloy with deposited AlN coatings on an adhesion sublayer of Al on it was investigated. Deposition of insulating coatings on blanket structural materials allows to reduce the influence of strong magnetic fields of the tokamak on liquid metal coolant (e.g., lithium flow). It has been demonstrated that the coatings also reduce deuterium permeating fluxes by several times in comparison with V-4Cr-4Ti covered with natural oxide film and about 3–4 orders of magnitude in comparison with literature data for vanadium and its alloys with oxide-free surfaces. Taking into account thermomechanical and insulating properties, moderate swelling under neutron irradiation, thermal conductivity an order of magnitude higher than that of oxide coatings AlN coatings seem to be attractive for application in FR both as insulating and as a coating for hydrogen permeability suppression.

The data on the influence of thermomechanical treatment modes on characteristics of the short-term strength and plasticity of vanadium alloys of different systems (V–Ti–Cr, V–Zr–C, V–Cr–Zr, V–Cr–W–Zr, V–Cr–Ta–Zr) are generalized. It is shown that an application of a modified mode ensures an appreciable increase in the short-term strength at room temperature and elevated temperatures, while maintaining an acceptable plasticity. The principal mechanisms of metastable carbide transformations into oxicarbonitride phase particles with phase-forming elements participation and the conditions of their realization are discussed.

Molecular dynamics simulations have been performed to investigate the defect structure evolution at different development stages of atomic displacement cascades with energies up to 50 keV in iron crystallites in the temperature range from 300 to 900 K. The number of surviving radiation defects in iron crystallites increases according to a power law with increasing energy of the primary knocked-on atom. An increase in the crystallite temperature slightly increases the number of surviving defects. It is found that atomic displacement cascades can lead to radiation-induced grain boundary migration due to the melting and crystallization of the radiation-damaged region. The crystallographic orientation of the irradiated free surface strongly affects the radiation damage behavior. Craters with adatom islands are formed on the (111) free surface, and vacancy loops are nucleated in the (110) near-surface region. Point defects aggregate into clusters of various types during the evolution of atomic displacement cascades. It is shown that the number of surviving point defect clusters can significantly decrease under uniaxial elastic compression.

The effect of electron and neutron irradiation and post-radiation annealing on the properties of 12% chromium ferritic-martensitic low-activated EK-181 steel treated under various heat conditions has been studied using transmission electron microscopy and resistometry. Both electron and neutron irradiation of EK-181 steel in the 300–340 K temperature range result in radiation-induced solid solution separation during all subsequent heat treatments. Isochronous annealing in the 300–500 K temperature range causes additional solid solution separation. Nanoclusters of point defects with a size from 1.5 to 5 nm and a concentration of 5 × 1016 cm–3 have been observed after neutron irradiation at a fluence of (1–5) × 1019 cm–2. Thermal homogenization of the solid solution occurs above 650 K.

For the first time it is shown that the development of resistance to melittin in Acholeplasma laidlawii, a mycoplasma that is widely spread in nature and that is the main contaminant of cell cultures and vaccines, is associated with significant changes in the genomic profile, in cellular and vesicular proteomes, as well as in virulence.

The features of the microstructure, structural-phase transformations, and regularities of the change in the short-term mechanical properties of low-activation 12% chromium ferritic-martensitic steel EK-181 together with the features of its plastic deformation and fracture by the active stretching method in a temperature range from–196 to 720°C are investigated. The high efficiency of dispersive hardening by nanoscale particles V(C, N) provides a weak temperature dependence of the steel strength properties with increasing temperature from 20 to 450°C. A significant increase in the temperature dependence of the steel yield strength is observed in the ductile-to-brittle transition interval (below T ~ 20°C). In a temperature range from–196 to 720°С, the change in the plasticity regularities and the mode of steel fracture are closely related to the features of the temperature dependence of the yield stress and ultimate tensile strength. In the region of temperatures above 0°С (up to ~450°С), these features are determined by the weak temperature dependence of the value of dispersion hardening by nanoscale vanadium carbonitride particles; in the temperature range below 0°С, they are determined by a strong temperature dependence of the thermally activated mobility of dislocations in the crystalline relief (the Peierls barrier, solid solution of impurities).

Thermal stability of the microstructure and high-temperature mechanical properties of the low-activate 12% Cr ferritic-martensitic steel EK-181 are studied at temperatures from 700 to 800°C. It is shown that after traditional heat treatment and annealing at temperatures from 700 to 800°C, the ferritic-martensitic structure of the steel is retained and the density of coarse-dispersed M23C6 particles is increased. After annealing at T = 800°C, the initial recrystallization stages with the formation of new submicrocrystalline ferritic grains are detected. An increase in the annealing temperature from 700 to 800°C leads to a decrease in the strength properties of the steel. Wherein, the character of the temperature dependence of the strength at temperatures from 700 to 800°C is similar to that observed at lower temperatures (from 500 to 700°C).

Static and fatigue strength at room temperature under conditions of repeated stretching of lowactivated ferrite-martensite 12% chromium steels EK-181 (Fe–12Cr–2W–V–Ta heat treatment + aging in lead at 600°C, 3000 h), EP-823 (Fe–12Cr–W–V–Ni–Mo–Nb, annealed condition), and alloy V–4Ti–4Cr (heat treatment + aging in lead at 600°C, 3000 h) were studied. It was shown that for materials there is straight-line dependence between the level of rupture resistance values and fatigue strength. The maximum fatigue limit of 600 MPa appears in steel EK-181 after a standard heat treatment and aging in lead at 600°C, 3000 h, and the minimal one of 300 MPa is observed in vanadium and V–4Ti–4Cr alloys. The fatigue failure mechanism is predominately of ductile character for all materials studied. The fatigue cracking originates near the surface and in some cases clustering of nonmetallic inclusions is the place of origin. The fatigue crack propagation is related to formation of a typical striation relief. Significant distinctions in the fracture surface relief of specimens after standard heat treatment and aging in liquid lead are not observed.

Nuclear and physical properties (activation and transmutation of elements) of BN and Al2O3 dielectric materials subjected to neutron irradiation for up to 5 years in Russian fast (BN-600) and fusion (DEMO-S) reactors were calculated using the ACDAM-2.0 software complex for different post-irradiation cooling times (up to 10 years). Analytical relations were derived for the calculated quantities. The results may be used in the analysis of properties of irradiated dielectric materials and may help establish the rules for safe handling of these materials.

The effect of high-temperature thermomechanical treatment with deformation in the austenite region on the microstructure and mechanical properties in low-activated 12% chromium ferritic-martensitic steel EK-181 (Fe–12Cr–2W–V–Ta–B) has been investigated. This treatment leads to a significant increase (compared to traditional regime of treatment) in the density of dislocations, dispersity, and volume fraction of nanosized particles V(C,N) and, as a consequence, to an increase in the yield strength while maintaining a sufficient reserve of ductility.

Using the method of transmission electron microscopy, the features of structural-phase state of an internally oxidized V–Cr–Zr–W alloy following severe plastic deformation by the method of torsion on Bridgeman’s anvils are investigated. A quantitative evaluation of the parameters of grain and defect structure is performed and the characteristic dimensions and phase composition of fine disperse particles are determined. The main factors controlling the special conditions of formation of nanostructured states are analyzed.

The investigation of plastic deformation nucleation in metals and alloys under irradiation and mechanical loading is one of the topical issues of materials science. Specific features of nucleation and evolution of the defect system in stressed and irradiated iron, vanadium, and copper crystallites were studied by molecular dynamics simulation. Mechanical loading was performed in such a way that the modeled crystallite volume remained unchanged. The energy of the primary knock-on atom initiating a cascade of atomic displacements in a stressed crystallite was varied from 0.05 to 50 keV. It was found that atomic displacement cascades might cause global structural transformations in a region far larger than the radiation-damaged area. These changes are similar to the ones occurring in the process of mechanical loading of samples. They are implemented by twinning (in iron and vanadium) or through the formation of partial dislocation loops (in copper).

A review on simulation of the primary radiation damage (PRD) and formation of radiation defects by atomic displacement cascades is conducted. Results of the simulation by the molecular dynamics method of the atomic displacement cascades and peculiarities of their interaction with the defects of the internal crystal structure (point defect, pores, dislocations, grain boundaries (GBs), and free surfaces) are given. It is shown that the defects exert a significant impact on the evolution of the atomic displacement cascades and formation of the PRD in metals.

The dislocation mechanisms of formation of the ductile–brittle transition temperature and the low-temperature brittle fracture of metals (single crystals, polycrystals) with various crystal lattices (bcc, fcc, hcp) are considered. The conditions of appearance of cold shortness and intracrystalline crack propagation (brittle fracture) are determined. These conditions can be met in bcc and some hcp metals and cannot be met in fcc and many hcp metals. The nondestructive internal friction (at 100 kHz) method is used to determine the temperature ranges of cold shortness (ductile–brittle transition temperatures) in bcc metals (ferritic–martensitic EK-181 steel, V–4Ti–4Cr alloy), which depend on their structure–phase state and strength (yield strength).

The static and cyclic mechanical properties of low-activation ferritic–martensitic EK-181 (Fe‒12Cr–2W–V–Ta–B–C) steel are studied in the temperature range 20–920°C (static tests) and at 20°C (cyclic tests). The fracture mechanisms of the steel under static tension and fatigue fracture conditions are analyzed by scanning electron microscopy.

Theoretical scheme is proposed for obtaining layered compounds consisting of carbon atoms in the sp-and sp2-hybridized states. This scheme is used to find the possibility of existing the seven basic structural modifications of graphyne: α-, β1-, β2-, β3-, γ1-, γ2-, and γ3-graphyne. The basic structural modifications of graphyne contain diatomic polyyne chains and consist only of carbon atoms in two different crystallographically equivalent states. Other nonbasic structural modifications of graphyne can be formed via the elongation of the carbyne chains and via the formation of graphyne layers with a mixed structure consisting of basic layer fragments. The geometrical optimization of the structure and the calculation of energy characteristics and electronic properties of graphyne layers were performed using ab initio calculations based on the density functional theory in the generalized gradient approximation. The energy of sublimation is found to be maximal for γ graphynes, which should be the most stable structural modifications of graphyne.

The strategy for the growth of nuclear power in our country in the first half of the 21st century provides for building and commissioning new-generation fast reactors with different coolants: sodium (BN-800, BN-1200, MBIR) and lead (BREST-OD-300). Structural materials with the required level of radiation and heat resistance as well as corrosion resistance upon exposure to the fission products of nuclear fuel, in the coolant, and the spent-fuel pool must be developed for the reactor cores in order to ensure the performance of the reactors under construction and to reach economically expedient burnup of nuclear fuel. The basic results of the performance validation of structural materials in application to their use in the cores of operating (BOR-60, BN-600) and advanced fast reactors with different types of coolants as well as the prospects for further advancement of the research are presented.

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.

The structure of EK-181 (RUSFER-EK-181, low-activation) and ChS-139 12% Cr ferritic–martensitic steels is investigated and their mechanical properties are tested after long-term (13500 h) aging at 450 and 620°C. The microstructure of the steels exhibits a high thermal stability, which provides the retention of their initial short-term mechanical properties at test temperatures.

The thermophysical properties (specific heat, thermal diffusivity, thermal conductivity, linear thermal expansion coefficient, density) of 12% chromium ferritic–martensitic steels EK-181 (RUSFER-EK-181) and ChS-139 and the structure–phase transformations that occur in them upon heating and cooling in the temperature range 20–1100°C are studied. The temperatures of the start and finish of the α → γ and γ → α transformations in these steels and the Curie temperature are determined by differential scanning calorimetry. Peaks in the temperature dependence of the specific heat and jumplike changes in the linear thermal expansion coefficient and the density and the minimum of thermal diffusivity are detected in the α → γ transformation range. Specific heat peaks, thermal conductivity minima, and inflection points in thermal diffusivity curves are also observed near the Curie temperature.

The influence of alloying of vanadium by Ti and Fe on helium bubble formation, gaseous swelling and helium release peculiarities is investigated by means of transmission electron microscopy and helium thermal desorption spectrometry (HTDS). The samples were irradiated by 40 keV He + ions up to a fluence of 5 ⋅ 10 20 m −2 at 293 and 923 K. It is found that large faceted pores/bubbles are formed in pure vanadium and it has the highest gaseous swelling. Alloying by any used quantity of Ti (from 0.1 up to 10 wt.%) or Fe (from 1 up to 10 wt.%) essentially decreases the helium swelling. The effect of alloying of vanadium by Ti on the bubble sizes and the helium swelling is nonmonotonic. The density of bubbles increases significantly and their sizes and swelling grow monotonically with increasing the Fe content in vanadium. With low-temperature helium implantation, alloying of V by Ti shifts the HTDS peaks to higher temperatures and the temperatures of peaks are decreased with increasing the Fe concentration. A significant portion of the helium releases in a high-temperature area beyond the main peak temperatures in the HTDS spectra. It is assumed that this is caused by formation of helium bubbles on the surfaces of incoherent particles of secondary phases (oxides, nitrides), having high binding energies with these particles.

Using the methods of transmission and scanning electron microscopy, the defect substructure of a V–4Ti–4Cr–(C, N, O) alloy dispersion strengthened with nanosized oxicarbonitride particles and the features of its fracture after deformation via active tensile loading at the temperatures 20 and 800°C are investigated. It is shown that the most representative features of deformation at the elevated temperature is primarily activation of grain-boundary mechanisms of deformation and fracture and secondly strain localization accompanied by crystal-lattice re-orientation. The reasons for these phenomena are discussed.

Molecular dynamics simulation is employed to study peculiarities of the formation and propagation of shock waves generated by atomic displacement cascades in iron crystallites under irradiation. The interaction of shock waves with point defects and their clusters is investigated. Atomic interactions are described with the use of the pair central-symmetric potential. Parameters of shock waves generated by atomic displacement cascades are evaluated and their dependence of the crystallographic direction, energy of a primary knock-on atom, and crystallite temperature is determined. These waves are shown to cause point defect clusters to rearrange.

The response of elastically stressed iron and vanadium crystallites to atomic displacement cascades was investigated by molecular dynamics simulation. Interatomic interaction in vanadium was described by a many-body potential calculated in the Finnis–Sinclair approximation of the embedded atom method. Interatomic interaction in iron was described by a many-body potential constructed in the approximation of valence-electron gas. The crystallite temperature in the calculations was varied from 100 to 600 K. The elastically stressed state in the crystallites was formed through uniaxial tension by 4–8% such that their volume remained unchanged. The energy of a primary knock-on atom was varied from 0.5 to 50 keV. It is shown that the lower the temperature and the higher the strain degree of an initial crystallite, the lower the threshold primary knock-on atom energy for plastic deformation generation in the crystallite. The structural rearrangements induced in the crystallites by an atomic displacement cascade are similar to those induced by mechanical loading. It is found that the rearrangements are realized through twinning.