T. E. Kurennykh

Effect of strengthening friction treatment on the chemical composition, structure, and tribological properties of a high-carbon steel

The structure and chemical composition of nanocrystalline layers formed on the surface of a steel U8 with 0.83 wt % C (quenched, as well as quenched and tempered at 200°C) under the conditions of frictional loading by a hard-alloy indenter in different media (gaseous and liquid nitrogen, air) have been investigated by the methods of transmission electron microscopy, X-ray diffraction analysis, nuclear reactions, Rutherford back scattering, and wave- and energy-dispersive microanalyses. Maximum levels of defectiveness (high density of dislocations and point defects) and microhardness of the nanocrystalline structure have been attained upon friction treatment of the low-temperature tempered steel in a liquid-nitrogen medium because of deformation localization in a thin surface layer, intensification of deformation-induced dissolution of the ɛ carbide phase, and saturation of the layer with nitrogen and oxygen atoms, the latter dissolved in the liquid nitrogen as an impurity. A comparative analysis of the in-depth distribution of microhardness in frictionally strengthened surface layers has been performed for the steel with initial structures of tetragonal (untempered) and low-tempered (tempered at 200°C) martensite. A markedly larger depth of strain hardening has been attained upon friction treatment in the quenched untempered steel due to effective development of deformation-induced dynamic aging of high-carbon martensite even at small deformations. It has been established that the strengthening upon deformation of the surface by a sliding indenter exerts a positive influence on the tribological properties (wear rate and friction coefficient) of the steel under the conditions of frictional heating of different intensity.

Structure evolution of pure iron upon low-temperature deformation under high pressure

Structure evolution of iron (99.97% purity) deformed by shear under pressure at 80 K in a medium of liquid nitrogen has been investigated. It has been found that, along with dislocation slip, twinning and development of deformation microbands become operative mechanisms of low-temperature deformation. This led to specific type of inhomogeneity of the structure in which, up to ultimately attained degrees of deformation, low-angle misorientations are retained and, unlike room-temperature deformation, no homogeneous submicrocrystalline (SMC) structure is formed. Twinning contributes to the refinement of structure elements that are more than 1 μm in size; the further refinement occurs by the dislocation-disclination mechanism and goes to the steady-state stage.

H/D isotope effect for solubility of hydrogen in doped perovskites

A novel method for studying the H/D isotope separation effect in the “nonstoichiometric oxide-gas” system is suggested. The theoretical scheme of this method is represented for doped perovskites of the ABO3 family, but this approach is also applicable to other compounds where the solubility of hydrogen is determined by the content of oxygen vacancies. The suggested approach is used to determine the H/D isotope effect in hydrogen solubility from the experimental data for proton-conducting oxides. The measurements have been taken using the nuclear microanalysis of fine-grain BaZr0.9Y0.1O3 − y powders. The method is based on the study of the products of the 2H(d, p)3H nuclear reaction. The observed pronounced isotope effect is in quantitative agreement with our theoretical predictions.

Oxygen Isotope Exchange between Gaseous Phase Enriched with 18O Isotope and Nanocrystal Oxides LaMnO3+δ Obtained by Severe Plastic Deformation

The kinetics of the isotope exchange between gaseous oxygen enriched with the 18O isotope and two LaMnO3+δ oxide samples – a nanopowder and a bulk nanocrystal – has been studied. The 18O isotope concentration has been measured by the acceleration nuclear microanalysis method. The coefficients of the volume and the nanograin boundary self-diffusion of oxygen have been evaluated at 500 °C. They are equal to 3.5·10 −20 and 1.5·10 −13 cm2/s, respectively.

Grain boundary self-diffusion of tracer 18O atoms in nanocrystalline oxide LaMnO3 + δ

Diffusion coefficients of tracer 18O atoms at boundaries of nanograins of LaMnO3 + δ oxide have been measured in the temperature range of 400–500°C. The samples of the nanocrystalline oxide are prepared with the use of the shockwave loading method. The concentration profile of the tracer atoms after diffusion annealing is measured with the use of the nuclear microanalysis method. The activation energies of the grain boundary diffusion amounts to about 2 eV and the boundary width is ∼0.05 nm. The measured coefficients of the grain boundary diffusion at 500°C exceed the corresponding coefficients of the volume diffusion by seven orders of magnitude.

Studying distribution of gaseous impurities and carbon in titanium alloys using nuclear microanalysis

The mechanism of the formation and modification of macrodefects containing atoms of light elements upon melting and thermal and mechanical treatment of titanium alloys has been studied. To this end, an approach based on the investigation of the concentration distribution of oxygen, nitrogen, and carbon in the zone of a macrodefect using nuclear microanalysis with a locality of measurements over the sample surface to about 90 μm has been used. It has been established that a decrease in the concentration of carbon in tungstencarbide-based macrodefects upon alloy melting occurs according to the diffusion mechanism. The same mechanism is characteristic of the process of dissolution of defects of deformation origin, such as titanium oxynitrides, upon solid-state heat treatment.

Effect of mechanical activation on the morphology and structure of hydroxyapatite

We have studied the effect of grinding in planetary mills on the phase composition, morphology, and water content of hydroxyapatite powder. The results indicate that milling for even relatively short times, which reduces the average particle size by a factor of 2, causes the monetite present in the unmilled powder to disappear and reduces the crystallite size of the hydroxyapatite. The fraction of nanoparticles in the powder is then 98% and remains constant during further milling. Milling for longer times leads to hydroxyapatite amorphization. For an average size of large particles R ≥ 1 μm, the surface area of the particles per unit volume, E (cm−1), is determined only by R (E ∼ 1/R).

Diffusion of Insoluble Carbon in Zirconium Oxides

The diffusion coefficient of insoluble carbon in zirconium oxides has been obtained for the temperature range of 900–1000°C. There are no published data on the diffusion of insoluble impurities; these data are of current interest for the diffusion theory and nuclear technologies. Tracer atoms 13C have been introduced into oxides by means of ion implantation and the kinetics of their emission from the samples in the process of annealing in air has been analyzed. The measurements have been performed using the methods of nuclear microanalysis and X-ray photoelectron spectroscopy. The diffusion activation energy is 2.7 eV and the carbon diffusion coefficient is about six orders of magnitude smaller than that for oxygen self-diffusion in the same systems. This result indicates the strong anomaly of the diffusion properties of carbon in oxides. As a result, zirconium oxides cannot be used in some nuclear technologies, in particular, as a material of sources for accelerators of short-lived carbon isotopes.

Diffusion in Concentrated Jahn–Teller Systems

Abstract The effect of strontium on the diffusion coefficients D of oxygen tracers in the La 1− y Sr y MnO 3− δ , temperature dependence of the oxygen tracer diffusion coefficient in La 1−y Sr y MnO 3−δ (y=0.025) were determined. The D values were measured using 18 O tracers and the nuclear microanalysis method. Analysis of the concentration dependences of the diffusion coefficients D was made using the approach, which takes into account variation of the number of orbitally degenerate (JT) states of 3d-ions during non-isovalent alloying.

THE DIFFUSION OF TRACER OXYGEN ATOMS IN NI FERRITES

Oxygen tracer diffusion in polycrystalline nickel ferrites Ni(1−x)Fe(2+x)O(4) (x=0.1; 0.2; 0.4) at temperatures of 450–700 °C was studied. The number of 18O atoms diffusing to the sample was determined using the 18O(p,α)15N nuclear reaction at the energy of the primary beam particles equal to 762 keV. The nuclear physical experiments were performed on a 2 MV Van de Graaff accelerator. It has been established the oxygen diffusion is characterized by relatively small activation energy (0.89 eV for x=0.2) and low pre-exponential factors (∼10−13 cm2/s for x=0.2). These results suggest that oxygen diffusion in the ferrites under consideration occurs by means of structural vacancies with their concentration about 10−9–10−11.