A.I. Ryazanov

Kinetics and physical mechanisms of the growth of helium bubbles at dislocations

Abstract The kinetics of annealing of gas bubbles in nickel containing 0.15 at% of helium implanted by irradiation of the material with alpha particles have been investigated. It is shown that a major portion of the bubbles formed by annealing is associated with dislocations. A theoretical calculation is made of the diffusion growth of gas bubbles at dislocations and in the grain volume. The data obtained make it possible to explain the more rapid growth of bubbles at dislocations in comparison with volume bubbles. Comparison of the theoretical and experimental results suggests that a more rapid growth of gas bubbles at dislocations is due to the pipe diffusion of gas atoms along the dislocation line to these bubbles. Dislocation voids are shown to have a significant effect on the change of the macroscopic characteristics of materials containing high concentrations of helium.

The contribution of grain boundary cavities and cracks to the high temperature irradiation embrittlement of structural materials

Abstract This paper deals with the effect of an infinite row of equal elliptic cavities (which include voids or cracks on a grain boundary as limiting cases) on the stress distribution near them. It is shown that the contemporary widespread theoretical models overestimate the role of grain boundary cavities (helium bubbles) in the high temperature irradiation embrittlement (HTIE). It is also shown that the most effective interaction is realized for the row of cracks and the collective effects in the ensemble of cracks located in some plane can lead, in contrast to the ensemble of cavities, to the new qualitative effects (for example to the loss of stability of growing cracks due to the inner loading only). The growth kinetics of grain boundary cracks due to gaseous impurity accumulation in them is investigated in more detail.

Void bias factor in materials with weak cubic anisotropy

Abstract Computational results concerning the effect of void-point defect elastic interaction on void (gas bubble) capture efficiency for vacancies and self-interstitial atoms, as well as on point defect spatial distributions, are reported for the case of weakly anisotropic cubic crystals. Although the anisotropy is weak in the materials considered, it can substantially contribute to the void bias factor alteration and lead to a strong angular dependence of the point defect concentration near the void.

Kinetics of the growth of helium bubbles at the grain boundaries. formation of the spatially inhomogeneous distribution of helium bubbles near the grain boundaries

Abstract In the present paper the kinetics of nucleation and development of gas bubbles near and at the grain boundaries have been investigated. A self-consistent theoretical calculation of the diffusion growth of three ensembles of gas bubbles has been made: bubbles at the grain boundaries, bubbles on dislocations and bubbles in the grain interior. Emphasis is placed on investigating the influence of the spatially inhomogeneous distribution of the dislocation density on the kinetics of growth of ensembles of gas bubbles. The theory formulated makes it possible to explain the more rapid growth of bubbles at the grain boundaries in comparison with the growth of bubbles on dislocations and in the grain interior. We have obtained a spatially inhomogeneous distribution of gas bubbles near the grain boundaries. The basic results of the theory are compared with the results of an experiment on the kinetics of nucleation of helium bubbles under the conditions of annealing near and at the grain boundaries in polycrystal nickel irradiated with alpha particles.

The mechanism responsible for suppression of swelling of materials by cold work

Abstract The damage pattern of irradiated materials in the initial stages of irradiation has been investigated within the framework of a model which takes account of microscopic processes in the dislocation cores. A mechanism responsible for suppression of swelling in materials by cold work is proposed.

The influence of dissociation of small helium-vacancy clusters on the growth of helium bubbles, the accumulation of helium at the grain boundaries and the kinetics of helium desorption from irradiated materials

Abstract This paper deals with the effect of thermal dissociation of small helium-vacancy clusters on the currents of helium atoms to gas filled bubbles and to grain boundaries. The theory proposed demonstrates the possibility of accelerated accumulation of helium in the bubbles and at the grain boundaries. Also the desorption of helium from metal foils being irradiated with alpha-particles is considered and the effective coefficient of helium diffusion in the material is determined.

Grain boundary cavities and cracks during high temperature irradiation embrittlement

Abstract This paper discusses a possible role of grain boundary cavities in the high temperature irradiation embrittlement (HTIE) of reactor structural materials. It is demonstrated that grain boundary voids alone can hardly provide the dominance of intergranular fracture mode during HTIE. An alternative mechanism based on the growth of helium accumulating cracks is discussed and the resulting predictions for material failure parameters are presented.

Temperature dependence of irradiation creep due to dislocation climb

Abstract The creep of materials under irradiation due to dislocation climb is investigated theoretically. In calculating the irradiation creep rate, point defect recombination and the effect of dislocation pipe diffusion are taken into account. The mechanism of irradiation creep based on a stress enhanced jog nucleation on dislocations with favourable orientations with respect to the tension direction is proposed. This mechanism enables one to give a good qualitative description of the experimental temperature dependence of irradiation creep rate.

Amorphization of NiNb based alloys irradiated with alpha-particles

Abstract The structure of the NiNbAl alloys irradiated by alpha-particles in a charge-particle accelerator was investigated by an X-ray diffraction technique. It has been found that the irradiation by alpha-particles with an energy of 2 to 3.25 MeV and a fluense of 10 17 cm −2 leads to neither crystallization of the initial amorphous alloy nor any change in their amorphous structure. The feasibility of radiation amorphization of some alloys has been studied.

Investigation of the radiation damage of the amorphous Ni60Nb40 alloy and microcrystalline Ni during irradiation of 2.5MeV alfa-particles

Abstract The paper treats the critical doses for different types of surface radiation damage for the amorphous Ni 60 Nb 40 alloy, microcrystalline Ni and polycrystalline Ni and Cu.