I.M. Neklyudov

Features of structure-phase transformations and segregation processes under irradiation of austenitic and ferritic-martensitic steels

Abstract The difference between crystal lattices of austenitic and ferritic steels leads to distinctive features in mechanisms of physical-mechanical change. This paper presents the results of investigations of dislocation structure and phase evolution, and segregation phenomena in austenitic and ferritic-martensitic steels and alloys during irradiation with heavy ions in the ESUVI and UTI accelerators and by neutrons in fast reactors BOR-60 and BN-600. The influence of different factors (including different alloying elements) on processes of structure-phase transformation was studied.

Effect of electron irradiation on properties of high-Tc superconductors

The effect produced by high energy electron irradiation at temperatures of 5, 185 and 375K on the critical parameters of high-T c superconducting Y-Ba-Cu-O and La-Ba-Cu-O compounds has been studied. It is ound that irradiation at 5K with a subsequent annealing at 105K results in the increase of the To value. Irradiation at 185 and 375K leads to T c decrease.

Microstructural evolution and radiation stability of steels and alloys

Abstract Results of a systematic investigation of structure–phase transformations in the main FSU (Former Soviet Union) construction steels and alloys of ferritic and austenitic classes irradiated in reactors and in heavy ion accelerators are presented. Features in the dislocation structure evolution for these steels related to differences in stacking fault energy are considered and the role of cold deformation in swelling behaviour is investigated. The mechanisms of infiltration and compulsory alloying of second phase precipitates during irradiation as a result of mutual recombination at structural defects in interphase boundaries are discussed. The role of second phase formation and evolution on swelling behavior processes is investigated. The influence of undersized and oversized alloying elements (B, Si, Ti, Nb, Mo, Sc) on different aspects of structure–phase transformations, which are generally defined as radiation stability over a wide interval of irradiation temperature and dose, is considered.

On the effect of radiation-induced segregation on void shape and growth rate

Abstract Microstructural changes have been studied in Cr18Ni10Ti steel irradiated in BOR-60 up to 40 dpa at 580–600 °C. It was found that in the vicinity of the voids associated with G-phase particles the composition of steel is practically the same as the average matrix one, whereas the isolated voids are surrounded by Ni and Si-enriched zones. The shape and size of a void depend on local composition near it — the mean size of octahedral voids (associated with G-phase particles) is greater than that of isolated cubic voids. A theoretical model is developed to explain the observed difference between growth rates of free and precipitate-attached voids.

Microstructure investigation of Cr and Cr alloys irradiated with heavy ions

Abstract The results of microstructure investigation of pure Cr and low- and high-doped Cr alloys (Cr with low additions of La, Ta, Re; Cr doped with low additions of La, Ta, V; Cr alloyed with low additions of Fe, La; and 66Fe33CrAl, 33Fe66CrAl) irradiated by Cr ions in the temperature range 550 to 800°C up to dose of 180 dpa are presented. Dislocation structure evolution in low-doped Cr alloys differs from that in α-Fe alloys: loop faulting disappears in the beginning of irradiation; perfect loops have mainly Burgers vector ( a /3)〈112〉 on {111} planes and appreciably less have Burgers vector ( a /2)〈111〉 on {110} planes. High stability for dislocation loops in Cr alloys irradiated to high dose levels was discovered. The temperature and dose dependences obtained allowed evaluation of swelling resistance in Cr alloys. It was established that the swelling behavior is similar to that for other refractory metals having a bcc lattice. The maximum value of swelling is 9% at an irradiation dose level of 180 dpa in the temperature range from 730 to 750°C. Voids in Cr alloys are formed at dose levels of 1–2 dpa, similar to other refractory metals having a bcc lattice. The voidage is characterized by a homogeneous distributions of fine voids. It was established that a preliminary heat treatment, CW or alloying with low additions do not have significant effects on either the void nucleation process or swelling response. Void lattice formation was observed in Cr alloyed with low additions of La, Ta and V. The homogeneous distribution of fine voids through the matrix may be the cause of loss in ductility of the material. Highly-alloyed Cr alloys undergo intensive solid solution decomposition leading to heterogeneous swelling.

Utilization of electron accelerators for simulation and studies of radiation effects on mechanical properties of fusion reactor materials

Abstract Based on fundamental research in the field of radiation damage of materials, a method is developed to simulate and investigate principal mechanical properties of materials with the help of high-energy electron and gamma-ray beams. This method allows a simultaneous simulation of radiation damage arising during use of materials in nuclear fission and fusion reactors with different helium impregnation-to-damage generation rate ratios. The method is used to simulate and study radiation hardening, low-temperature and high-temperature radiation embrittlement and radiation creep phenomena. A correlation is established between the reactor and simulation experiments. This allows one to forecast the changes of mechanical properties of materials under operating conditions.

Changes of structure and properties of yttrium doped copper at deformation, annealing and irradiation

Abstract Results on the study of structural changes in pure and yttrium microalloyed copper (0.01–0.03 wt%) after rolling deformation to 40–90% and after isothermal and high velocity nonisothermal annealing in the wide temperature range (150–1050°C) are presented. The addition of yttrium in copper raises the recrystallization temperature, forms a fine grained homogeneous structure, changes the dislocation structure and raises the radiation resistance of copper.

Microstructural evolution of austenitic stainless steels irradiated in a fast reactor

Austenitic stainless steels (16Cr15Ni3MoNb, 18Cr10NiTi, etc.) used as basic core structural materials undergo irreversible structural-phase changes leading to radiation-induced swelling especially at neutron fluence of (3--5) {times} 10{sup 27} m{sup {minus}2} typical for operation of existing and designed fast-neutron reactors and fusion facilities. Here, analysis of the microstructure of the stainless steels 16Cr15Ni3MoNb and 18Cr10NiTi, irradiated at temperatures where changes in phase stability occur due to radiation-induced segregation, shows that the stability of second-phase particles depends on the structure of particle-matrix interface.

The influence of pulsed plasma jet irradiation on the mechanical properties of KH16N15M3B and KH18N10T austenitic stainless steels

Abstract The influence of pulsed jets of hydrogen, helium and mixed hydrogen-helium plasmas with a specific power of 2–3 MW/cm2 on the mechanical properties of austenitic stainless steels of types KH16N15M3B and KH18N10T has been investigated. It was found that the irradiation results in a 1.8 fold increase in the yield point of the above steels and, more importantly, that the elongation values decreased 2.3–2.7 times. It is suggested that such modifications of mechanical properties are caused by the formation of a cellular structure in the subsurface layers of the materials.

Features of structure-phase changes in high-manganese type EP-838 austenitic stainless steel irradiated with heavy ions and neutrons

Abstract Production of ecologically acceptable fusion energy is closely connected with development of low-activated materials. Microstructure and irradiation behaviour for Fe-Cr-Mn alloys, a lower activation class of alloys relative to commercial Fe-Cr-Ni-Mo steels, have not been sufficiently investigated, especially phase stability and void swelling characteristics. This paper presents results of an investigation on the microstructural development in austenitic high-manganese alloy type EP-838 (solution-annealed (SA) and 30% cold-worked (CW) during ion (Cr2+, E = 3 MeV ) and fast-neutron irradiation, as a function of dose and temperature. It was found that the swelling rate of alloy type EP-838 was lower than that of steel type Cr16Ni15Mo3Nb, but was still high after a dose of 100 dpa in the temperature region 550–650°C. The influence of cold work on swelling is weak. Differences in defect structure in these steels are connected with the difference in behaviour of point defects in nickel and manganese austenite.