A. A. Nikitin

Effect of Irradiation by Heavy Ions on the Nanostructure of Perspective Materials for Nuclear Power Plants

An imitation experimental technique on the irradiation with heavy ions of structural materials of nuclear power plants using tomographic atom probe analysis has been elaborated. The scheme of irradiation of specimens for atom probe analysis has been realized on a MEVVA ion source of an TIPr accelerator (ITEP) with ion energy 75 keV per charge. Test experiments with irradiation and analysis of samples of the EK-181 steel by aluminum ions to a fluence of ∼2 × 1015 ion/cm2 have been performed. Experiments on the Fe-ion irradiation of the samples of ODS EUROFER perspective steel for fission and fusion reactors to different damaging doses have been carried out. The analysis of distribution of different chemical elements in the volumes tested has revealed that under ion irradiation a change in the composition of nanosized clusters, which are present in the initial material takes place. Comparison of the data obtained with the results of reactor irradiation of the ODS EUROFER steel has been carried out. These data testify a correspondence between nanoscale changes in the steels oxide dispersion strengthened in imitation experiments and under the conditions of reactor irradiation.

Nanostructure Evolution in ODS Eurofer Steel under Irradiation up to 32 dpa

The nanostructure of the ODS Eurofer steel (9% CrWVTa + 0.5% Y2O3) has been studied after irradiation by iron ions to a damaging dose of 32 dpa. This steel in the initial state is characterized by the presence of a significant amount (∼1024 m−3) of nanosized (2–4 nm) clusters containing atoms of V, Y, O, and N. An analysis of the distribution of various chemical elements in the tested volumes has revealed variations in the composition of the matrix and of the nanosized clusters during irradiation. The data obtained were compared with the results for the ODS Eurofer steel subjected to reactor irradiation to a dose of 32 dpa.

Atom probe study of radiation induced precipitates in Eurofer97 Ferritic-Martensitic steel irradiated in BOR-60 reactor

The nanostructure of Eurofer97 reduced activation 9% chromium ferritic-martensitic steel (9Cr1W0.2VTa0.1C) irradiated by neutrons in BOR-60 reactor at a temperature of 332°C up to 32 dpa is studied by atom probe tomography. A high number density (1024 m−3) of ∼3–5 nm clusters enriched in chromium, manganese, and silicon atoms is found in the material. An analysis of the redistribution of chemical elements in the material shows that the steel matrix becomes substantially depleted of chromium.

Atom probe tomography of nanoscaled features of oxide-dispersion-strengthened ODS Eurofer steel in the initial state and after neutron irradiation

Atom probe tomography has been used to investigate nanoscale features in the yttrium oxide dispersion strengthened steel ODS Eurofer, which is a perspective structural material for the reactor cores. In the initial material, a large number (∼2 × 1024 m−3) of ultrafine (∼2.5 nm in diameter) clusters enriched in yttrium, oxygen, nitrogen, and vanadium have been revealed. The investigation of the ODS Eurofer steel irradiated at 330°C to 32 dpa in the BOR-60 fast reactor has also revealed a large number of ultrafine (1–3 nm in diameter) nanoclusters significantly enriched in yttrium, oxygen, manganese, and chromium. In the irradiated material, an increase in the concentration of clusters and changes in the chemical composition of the clusters and matrix have been noted. The irradiation by fast neutrons leads to a partial transition of vanadium from the clusters into the surrounding matrix and to a general increase in the concentrations of yttrium and oxygen in the volumes under investigation.

Microstructure of Ti–5Al–4V–2Zr alloy in the initial condition and after irradiation with titanium ions

Chemical analysis of phases and inclusions in a specimen of Ti–5Al–4V–2Zr titanium alloy in the initial state and after irradiation with titanium ions up to the radiation damage dose of ~1 dpa at 260°C was carried out and the microstructure was studied. Microstructural analysis was performed by the methods of transmission electron microscopy, energy dispersion X-ray spectroscopy, and atom probe tomography. Results of the chemical analysis of the matrix α phase and inclusions of β phase grains are given. It is shown that the α phase is enriched in aluminum up to 10 at % and the β phase is enriched in vanadium up to 20 at % in the initial state in the Ti–5Al–4V–2Zr alloy. Heavy ion irradiation induces the formation of dislocation loops of 3 to 12 nm with the number density of ~1022 m–3. A high number density (up to ~1024 m–3) of nanoscale precipitations with the average size of ~2 nm is formed during alloy irradiation in the α phase.

Nanoscale characterization of 13.5% Cr oxide dispersion strengthened steels with various titanium concentrations

The influence of titanium alloying (Ti content of 0, 0.2, 0.3, and 0.4 wt %) on the nanostructure of yttrium oxide (Y2O3) dispersion strengthened steel with a composition Fe-13.5% Cr-2% W-0.3% Y2O3 is investigated. The spatial distribution of chemical elements is analyzed in the investigated volumes. The matrix composition and average size and concentration of nanoscale clusters are compared for different samples. It is shown that the average nanocluster size (∼3 nm) is almost unchanged with increasing Ti concentration, while the cluster concentration grows from ∼1 × 1023 m−3 (for Ti-free steel) to ∼1.5 × 1024 m−3 (for 0.4 wt % Ti alloy).

Atom Probe Tomography Analysis of Materials using Femtosecond-Laser Assisted Evaporation

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.

Study of Nanostructure of Ferritic-Martensitic Steel ChS-139 in Initial State and after Fe Ion Irradiation

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.

Study of nanostructure of experimental Ti–5Al–4V–2Zr alloy

The microstructure and chemical composition of phases and inclusions in Ti–5Al–4V–2Zr alloys are studied in the initial state, after irradiation by titanium ions to radiation damage dose of ~1 dpa at 260°C, and after thermal aging at 450°C for 1000 h. Microstructural studies are carried out using scanning electron microscopy and atom probe tomography. Phase analysis is performed using energy dispersive X-ray spectroscopy. Chemical analysis of grains of the matrix phase and β-phase is presented. Spatial distribution of chemical elements in α- and β-phase lamellae is analyzed by atom probe tomography. Formation of nanosized vanadium pre-precipitates in the α-phase is observed in irradiated material.