V. L. Arbuzov

Effects of phosphorus on defects accumulation and annealing in electron-irradiated Fe–Ni austenitic alloys

Abstract Pure austenitic alloy Fe–36% Ni and the same alloy doped with phosphorus (0.1% P) were irradiated with 5 MeV electrons at different temperatures (270–573 K). Using the methods of positron annihilation and residual resistivity it was shown that at the irradiation temperature of 270 K vacancies are mobile in both alloys and form vacancy clusters. In Fe–36Ni–0.1P alloy vacancy clusters are decorated with phosphorus atoms. After the irradiation at 423 K the decoration effect is not observed. At the irradiation temperature of 573 K the addition of phosphorus results in the suppression of vacancy supersaturation. A conclusion is made that, at the elevated irradiation temperatures, suppression of vacancy supersaturation occurs due to the interstitial–phosphorus interaction.

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.

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 Tirr ∼ 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.

Radiation-induced strengthening of Al- and Ti-modified Fe-Ni alloys during electron irradiation

A complex study of Fe-Ni, Fe-Ni-Ti, and Fe-Ni-Al alloys irradiated by electrons with an energy of 5 MeV at a temperature of 423 K has been carried out. The relationship between radiation-induced strengthening, radiation-induced defects, and radiation-induced structural and phase transformations has been considered. In the Fe-Ni alloy, vacancy clusters play a leading role in radiation-induced strengthening; in the Fe-Ni-Ti and Fe-Ni-Al alloys, in addition to the vacancy clusters, the evolution of secondary-phase precipitates and the relief of solid-solution hardening are of great significance.

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.

Radiation-induced segregation of deuterium in two-phase steel Kh16N9M3

Deuterium segregation produced in two-phase martensitic-austenitic steel Kh16N9M3 with a lath-type structure during irradiation with deuterons with an energy of 700 keV has been studied by the method of nuclear reactions. It has been shown that the intensity of the segregation and its evolution depend on the quantity and dispersion of structural constituents of the steel. It has been found that irradiation-induced austenite and deuterium-induced martensite are being formed during irradiation. The main deuterium traps in segregates are vacancy clusters and interphase boundaries.

The interaction of deuterium and tritium with radiation and other defects in austenitic steel and nickel

The methods of residual resistivity, annihilation of positrons, and nuclear reactions in nickel and austenitic steels were used to examine the interaction of deuterium and tritium with defects produced by electron- neutron- or ion-irradiation and plastic deformation. It was found that vacancies, dislocations and three-dimensional vacancy clusters captured hydrogen in nickel. Vacancy clusters were formed in the presence of deuterium and tritium at room temperature, when single vacancies were immobile. The type of the hydrogen isotope determined configurations of those clusters. Hydrogen atoms interacted with interstitial atoms at 150 K in nickel and at 220 K in steel. Deuterium segregation occurred both in nickel and austenitic steel under irradiation with deuterium ions, but the segregation exhibited a different behavior. A possible scheme of formation and evolution of deuterium segregation in the studied materials was proposed.

Radiation defects and hydrogen in austenitic and austenitic-martensitic steels under low-temperature neutron irradiation

The experimental data concerning the effect of hydrogen (300 appm), radiogenic helium, and low-temperature neutron irradiation (77 K) on the properties of the promising austenitic 16Cr15Ni3Mo1Ti and austenitic-martensitic 16Cr9Ni3Mo steels have been reported. It has been found that hydrogen saturation causes an increase in the yield stress, with this increase being larger in the martensitic than in the austenitic phase. The yield stress of both steels increases substantially after exposure to fast neutrons. The variation of the yield stress of the two-phase steel and its phase components under low-temperature neutron irradiation has been estimated. The displacement cascades begin overlapping under irradiation at a fluence larger than 1.5 × 1018 cm−2.

Separation of radiation defects in deformed nickel

Measurements of electrical resistivity and the electron-microscopy method have been used to study processes of the separation of radiation defects that arise upon the electron irradiation in pure nickel deformed by rolling. It has been shown that the effect of the separation of radiation defects is determined by the microstructure. In deformed Ni annealed at 450 K, there are two systems of sinks for point defects, i.e., the boundaries of subgrains and the dislocation structure in the bulk of subgrains. With an increase in dose, the increments of the electrical resistivity in deformed nickel (concentration of vacancies) approach a quasi-stationary level and depend on the degree of deformation nonmonotonically. The maximum of the increment is observed at a degree of deformation of about 40%. The kinetics of the postradiation annealing of vacancies accumulated upon irradiation is determined by the strength of sinks, just as for interstitial atoms in the process of irradiation.

The dissolution of intermetallic inclusions in atomic displacement cascades during neutron irradiation of dispersion-hardening alloys

The data of Mössbauer spectroscopy show evidence of a low-temperature (340 K) dissolution of dispersed intermetallic Ni3Ti particles in the fcc lattice of a Fe-Ni-Ti Invar-type alloy under the conditions of cascade-inducing neutron irradiation. The dissolution rate markedly increases with a decrease in the initial size of the intermetallic particles.