The structure of two high-chromium ( 14–15 at

Results of the study of the chemical composition of contacting γ- and γ'-phase particles in a granular heat-resistant nickel alloy (HNA) VV751P (Ni–15Co–12Cr–0.7V–0.3C–0.9W–2.7Mo–3.4Ti–2.0Nb–8.3Al–0.02Hf–0.008B, at %) by atom probe tomography are analyzed. Experimental and literature data on the preferential location of alloying elements in γ- and γ'-phase particles in different heat-resistant nickel alloys are considered. A criterion for the characterization of each of elements based on the ratio K = Еv/r2 (where Еv is the number of valence electrons and r is the atomic radius of an element) is suggested. It is shown that the higher the K value, the more probable the enrichment of γ-phase particles in this element and the higher the degree of such an enriching. The lower the K value, the more probable the enrichment of γ'‑phase particles in this element and the higher the degree of such an enriching. The effect of γ- and γ'-forming elements in heat-resistant nickel alloys and other factors on the stability of the γ- and γ' phases, mechanical characteristics of disc heat-resistant nickel alloys at room temperature, and long-term strength at operating temperatures is discussed.

The results of a comparative study of compacts obtained by spark plasma sintering from nano- and ultradisperse (UD) aluminum oxide powders with spherically shaped particles are reported. It is shown that the compacts obtained from UD-powder have higher density and greater strength, microhardness, and structural uniformity with smaller grains than compacts obtained from nanopowder. Preliminary magnetic-pulse compaction of powders prior to sintering improves the characteristics of both compacts but higher density and strength with smaller grains are achieved in compacts obtained from UD-powder. In both cases of preliminary preparation the UD-powder compacts have advantages over nanopowder compacts.

An aluminum-graphite composite was obtained by spark plasma sintering. The graphite particle size, compaction temperature, and soaking time were shown to influence the aluminum carbide formation process. It is demonstrated that the use of larger graphite plates decreases Al4C3 formation by almost a factor of two. The influence of the graphite content on the density, CLTE, and thermal conductivity of the composite was studied. It was found that for graphite weight content above 70% the thermophysical properties of compacts degrade significantly because large numbers of pores are formed.

We consider the conditions for reducing the threshold dose of radiation-gas splitting of a silicon single crystal by using a fixed-energy two-stage irradiation with hydrogen ions in a single production cycle. It has been experimentally established that a well-developed blister structure is formed in a sample in the mode of its two-stage irradiation with hydrogen ions with E = 12.5 keV and a dose of 0.5 × 1016 cm–2 at a normal angle of incidence at the first stage and, then, with a dose of 1.0 × 1016 cm−2 at an angle of 32° at the second stage (the total dose is 1.5 × 1016 cm–2). This structure is similar to the structure in a sample irradiated in the mode of single-stage irradiation to a dose of 5 × 1016 cm–2. This fact is the indication that the conditions for more than a threefold decrease in the threshold for the formation of hydrogen blisters in silicon upon twostage irradiation with monoenergetic hydrogen ions in a single production cycle.

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.

The effect of bombardment with iron ions on the evolution of gas porosity in silicon single crystals has been studied. Gas porosity has been produced by implantation hydrogen, deuterium, and helium ions with energies of 17, 12.5, and 20 keV, respectively, in identical doses of 1 × 1017 cm–2 at room temperature. For such energy of bombarding ions, the ion doping profiles have been formed at the same distance from the irradiated surface of the sample. Then, the samples have been bombarded with iron Fe10+ ions with energy of 150 keV in a dose of 5.9 × 1014 cm–2. Then 30-min isochoric annealing has been carried out with an interval of 50°C in the temperature range of 250–900°C. The samples have been analyzed using optical and electron microscopes. An extremely strong synergetic effect of sequential bombardment of silicon single crystals with gas ions and iron ions at room temperature on the nucleation and growth of gas porosity during postradiation annealing has been observed. For example, it has been shown that the amorphous layer formed in silicon by additional bombardment with iron ions stimulates the evolution of helium blisters, slightly retards the evolution of hydrogen blisters, and completely suppresses the evolution of deuterium blisters. The results of experiments do not provide an adequate explanation of the reason for this difference; additional targeted experiments are required.

The atom probe tomography of the nanostructure evolution in ODS 1 Eurofer, ODS 13.5Cr, and ODS 13.5Cr–0.3Ti steels under heavy ion irradiation at 300 and 573 K is performed. The samples were irradiated by 5.6 MeV Fe 2+ ions and 4.8 MeV Ti 2+ ions to a fluence of ~10 15 cm –2 . It is shown that the number of nanoclusters increases by a factor of 2–3 after irradiation. The chemical composition of the clusters in the steels changes after irradiation at 300 K, whereas the chemical composition of the clusters in the 13.5Cr–0.3Ti ODS steel remains the same after irradiation at 573 K.

Особенности влияния облучения ионами железа на развитие гелиевых, водородных и дейтериевых блистеров в кремнии© В.Ф.Реутов, 1 С

The influence of deformation on the retention of helium in samples of the chromium–nickel austenitic steel uniformly saturated with helium using bombardment with α particles in a cyclotron has been studied. It has been shown that, under certain conditions, helium atoms can be carried away by moving dislocations, which can have a significant impact on the removal of helium from material, exit to the grain boundaries and redistribution it over the sample volume.

Transmission electron microscopy was used to study the effect of heavy-ion irradiation on the structure and the phase state of three oxide dispersion strengthened (ODS) steels: ODS Eurofer, ODS 13.5Cr, and ODS 13.5Cr–0.3Ti (wt %). Samples were irradiated with iron and titanium ions to fluences of 10 15 and ~3 × 10 15 cm –2 at 300, 573, and 773 K. The study of the region of maximum radiation damage shows that irradiation increases the number density of oxide particles in all samples. The fraction of fine inclusions increases in the particle size distribution. This effect is most pronounced in the ODS 13.5Cr steel irradiated with titanium ions at 300 K to a fluence of 3 × 10 15 cm –2 . It is demonstrated that oxide inclusions in ODS 13.5Cr–0.3Ti and ODS 13.5Cr steels are more stable upon irradiation at 573 and 773 K than upon irradiation at 300 K.

We analyze the effect of irradiation by heavy ions on the formation of blisters on the silicon surface preliminarily ion-doped with hydrogen. An attempt is made at differentiating inelastic and elastic processes of interaction between ions and Si atoms using bombardment of the sample with high-energy charged particles through a bent absorbing filter by varying the radiation doses and the energy of bombarding Xe ions. It is found that irrespective of specific ionization energy losses of heavy ions, the blister formation is completely suppressed in the zone of the inelastic interaction during postradiation annealing. Conversely, stimulated development of hydrogen porosity takes place at the same time in the zone of elastic interaction, which is manifested in the form of blisters and flaking.

Excellent mechanical properties of ODS steels are directly related to the high density of homogeneously distributed, well-formed oxide particles (such as Y2O3, or Y-Ti-O). However, atom probe tomography study of ODS steels revealed that in addition they contain almost a hundred times more nanoclusters enriched in Y, O and V/Ti (if present in the alloy composition) than larger oxide particles. In this work, we carried out atom probe tomography (APT) and transmission electron microscopy (TEM) studies of three different ODS steels produced by mechanical alloying: ODS Eurofer, 13.5Cr ODS and 13.5Cr-0.3Ti ODS. These materials were investigated after irradiation with Fe (5.6 MeV) or Ti (4.8 MeV) ions up to 1015 ion/cm2 and part of them up to 3 × 1015 ion/cm2. In all cases, areas for TEM investigation were cut at a depth of ∼ 1.3 µm from the irradiated surface corresponding to the peak of the radiation damage dose. It was shown that after irradiation at RT and at 300 °С the number density of oxide particles in all the samples grew up. Meanwhile, the fraction of small particles in the size distribution has increased. APT revealed an essential increase in nanoclusters number and a change of their chemical composition at the same depth. The nanostructure was the most stable in 13.5Cr-0.3Ti ODS irradiated at 300 °С: the increase of the fraction of small oxides was minimal and no change of nanocluster chemical composition was detected.