The specific features of helium penetration into aluminum and its alloys, V95 and D16T, at a temperature of 4.2 K under uniaxial tension, compression, and reversal of the sign of the load are investigated. The role played by serrated strain in the intensity of the effect under consideration and the influence of impurities on the number of helium atoms penetrating into strained samples are elucidated. It is shown that the condition of additivity of the effect observed under successive reversal of the sign of the load depends on the specific features of the tensile and compressive strains.

The specific features of the mechanodynamic penetration of helium under plastic deformation into fcc (Cu) and bcc (Fe, Nb) metals with different initial defect structures (single-crystal, nanocrystalline, and porous samples) are investigated. The intensity of mechanodynamic penetration into these metals is shown to depend on the type of bonding (metallic or covalent), which determines the degree of localization of the plastic flow of these metals, as well as on the type of defect structure and on the character of plastic flow (dislocation deformation, twinning, grain-boundary sliding). Curves of helium extraction from samples at different strains are obtained. It is found that the helium release exhibits a wide variety of peaks depending on the degree and character of plastic deformation of the metals under investigation. This suggests that the metals contain different types of helium traps, which determine the content of helium and the specific features of its release in the temperature range studied.

A relation between the characteristics of plastic deformation and the specific features of mechanodynamic penetration of helium into nanocrystalline iron compressively strained at 4.2 K is investigated. Iron samples with a grain size of about 200 nm are prepared by the multiple equal-channel angular pressing technique. The samples deformed in giant (6–7%) sample-averaged serrations, which amounts to several thousand percent strain in a shear band. The amount of helium in samples strained to various degrees is measured, and curves of helium extraction from these samples are obtained in the temperature range 300–1400 K. At a strain of ∼50%, the amount of helium built up in a sample is found to be substantially higher (more than hundredfold) than that in samples subjected to lower strains. It is found that an increase in the strain rate gives rise to a strain within a serration (the strain localization is enhanced) and that the amount of accumulated helium decreases, most probably, because of the shorter deformation time. The helium extraction curves obtained with increasing temperature exhibit several peaks. The temperature positions of some of them are about the same for samples strained to different extents, while the other peaks are characteristic of samples subjected to a specific strain only. The results obtained suggest the existence of helium traps of different types, which depend on the original structure and the magnitude of the strain and differ both in the amount of helium they contain and in the temperatures at which helium is released from these traps.

Quantitative relations governing the penetration of helium atoms into various types of solids in the course of their plastic deformation in liquid 3 He ( T = 0.6–1.8 K) and 4 He ( T = 4.2 K) and dispersion in gaseous helium at 300 K were obtained and analyzed. Experiments were carried out on metals with different lattice types, ionic single crystals, amorphous alloys, and barite and titanium dioxide powders dispersed in helium. Curves illustrating helium extraction from deformed specimens under dynamic annealing were obtained. The temperature range of helium extraction was found to correlate with the melting temperature and the initial and deformed structures of a material, which determine the number and character of helium traps present in the material. The dependence of helium penetration intensity on the type of defects forming under plastic deformation for various materials, as well as the formation of chemical bonds of helium atoms to the defected structure of these materials, is discussed.

This paper reports on experimental data on the penetration of helium atoms into single-crystal and nanocrystalline copper samples subjected to tensile and compressive strains at T=4.2 K, respectively. The dependences of the helium concentration N in the samples on the strain ɛ and the curves of helium extraction in the temperature range 300–1000 K at different strains ɛ are determined. It is found that the dependences N(ɛ) and σ(ɛ) correlate qualitatively with each other for single-crystal copper and do not correlate for nanocrystalline copper. This is associated with the different mechanisms of deformation in these samples. The deformation proceeds through the dislocation mechanism in single-crystal copper and through the jumpwise (twinning, rotational) mechanisms in nanocrystalline copper during local heating in regions of plastic shears. These factors are also responsible for the considerable difference between the curves of helium extraction from samples of both types. The curves of helium extraction exhibit two maxima for single-crystal copper and five maxima for nanocrystalline copper samples. The results obtained are discussed in terms of both the dynamic dislocation pipe diffusion and grain-boundary mechanisms of particle penetration from the surrounding medium into copper through different-type moving defects under applied stresses and due to the gradient of the chemical potential at the metal-surrounding medium interface.

Curves describing the liberation of helium from Sn single crystals deformed by stretching in liquid 3 He and 4 He and from Cd polycrystals in 4 He are analyzed. It is found that the stress-strain diagrams for Sn are in qualitative agreement with the concentration of helium in the samples. The peaks in the amount of He liberated from Cd and Sn at temperatures both below and above the melting point are found to be of different types. The reasons for this difference are investigated, and the assumption concerning the existence of a chemical bond between helium atoms and structural defects of the metals under investigation is formulated.

Evidence is obtained for the first time for penetration of helium atoms into amorphous films subjected to tensile strain in liquid helium at T = 0,5-4,2 K. The amounts of helium entering the amorphous films and plots of its extraction are obtained and the helium extraction rate peaks corresponding to the crystallisation and melting points of these materials are revealed. It is shown that helium penetrates into amorphous films in the region of plastic shears while being practically absent in the non-strained parts of the samples

The penetration of helium atoms into amorphous films extended to fracture in liquid helium has been investigated. It is found that helium atoms penetrate into the eutectic alloy films Pd84.5-Si15.5 in 3He (T=0.5 K) and Ni78-Si8-B14 in 4He (T=4.2 K). The spectra of helium liberation from these materials after deformation are obtained upon dynamic (4–5 K/min) annealing at T=293–1323 K. The maximum amount of helium is observed in the regions of local plastic microshears running across the whole width of films and also in the sample regions containing fracture macrocracks and isolated groups of slip bands. The spectra of helium liberation from different regions of destroyed samples show several peaks that correlate with the temperatures of crystallization and melting of the studied films. The data obtained are interpreted within the model of mechanochemical penetration of helium atoms through the dynamically excited dislocation-like defects, which are typical of the amorphous films under consideration.

Mass-spectra of the release of3He and 4He have been obtained for highand technical purity titanium deformed in tension in liquid 3He (T = 1K) and 4He from the titanium oxide, subjected to a dispersion in gaseous 4He at 293 K has also been investigated. A drastic increase of the amount of He has been found in deformed titanium samples and in the powder of titanium oxide after dispersion. Mass-spectra of the He evolution exhibit one or two peaks in a temperature domain T = 160-6200C. The phenomenon of Dislocation Dynamic Diffusion penetration of He atoms along moving dislocation into material being deformed is used to account for the experimental results.

Tritium (T) is incorporated in materials stored in the presence of a background tritium source, and the same is true for /sup 3/He, which is produced from tritium by ..beta.. decay. The processes responsible for sample contamination are elucidated. Measurements of /sup 3/He and /sup 4/He using a magnetic resonance mass spectrometer and a T-proportional counter revealed that dust particles carrying tritium (T) and /sup 3/He are the cause of the contamination. When tritium is presented in the laboratory as a component of gaseous molecules, almost all of the tritium adheres to the large, exposed surface of the dust particles and remains there for extended periods. The concentration of T and /sup 3/He in dust particles is measured, and it is established that the rate of helium-3 evolution during dynamic annealing is a maximum at 250 /sup 0/C, which is much less than the temperatures at which /sup 3/He is evolved for other typical naturally occurring samples. The /sup 3/He evolution curve thus gives information regarding the level of contamination by T/sup -/ and /sup 3/He-bearing dust particles. It is also established that /sup 3/He is retained longer in dust particles than T, so that tritium leakage into the laboratorymore » over extended periods of time can be detected by measuring the /sup 3/He concentration or the ratio /sup 3/He//sup 4/He.« less