Papers by Author: Boris S. Bokstein

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Authors: Boris S. Bokstein, I.L. Balandin
Authors: I.L. Balandin, Boris S. Bokstein, V.K. Egorov, P.V. Kurkin
Authors: Mikhail Mendelev, Alexey Rodin, Boris S. Bokstein
Abstract: We present results of the molecular dynamics study of Al selfdiffusion, Al and Fe diffusion in Al-Fe dilute alloys. We found that addition of Fe does not change the vacancy formation energy but considerably slows down Al diffusion. We also found that Al and Fe migration energies, i.e. energies of vacancy exchange with Al and Fe atoms, differ very strongly. Both activation energies for Al and Fe diffusion are in satisfactory agreement with available experimental data.
Authors: Mikhail Mendelev, A.O. Rodin, Boris S. Bokstein
Abstract: We performed molecular dynamics simulation of diffusion along symmetric <100> 5 and <111> 7 and one non-symmetric <100> 5 tilt grain boundaries in Al in the presence of Fe impurities. The simulation results are in reasonable agreement with available experimental data. The addition of Fe considerably decreases both Al and Fe diffusivities and increases the activation energy for diffusion. The simulation data indicate that the mechanism of diffusion is different in different grain boundaries. The diffusion along <100> 5 grain boundaries reminds that in liquid alloys.
Authors: Vladimir Esin, Boris S. Bokstein, Alexey Rodin
Abstract: Thermodynamics of the atomic complexes formation in a grain boundary (GB) is discussed applying to AB complex. It is shown that the AB complex formation leads to the nonlinearity of segregation isothermes. Consequently, the concentration profiles for GB diffusion are nonlinear. The total (free and bound into complexes) concentration of diffusant B decreases at the given depth as the molar fraction of the complexes increases.
Authors: N. Balandina, Boris S. Bokstein, A. Ostrovsky
Authors: Boris S. Bokstein, Alexander Epishin, Vladimir Esin, Mikhail Mendelev, Alexey Rodin, Sergei Zhevnenko
Abstract: Three cross diffusion-stresses effects are considered: mobility-stress effect, flux-stress effect and vacancy-stress effect. The value of the migration volume for vacancies in Al is found from atomistic computer simulation. A cross vacancy-stress effect is applied to the process of the pores growth and dissolution in Ni-based superalloys.
Authors: Boris S. Bokstein, O.N. Petrova
Abstract: The data are presented for Ni selfdiffusion and Au heterodiffusion in nanocrystalline Ni. Volume diffusion coefficients are much greater than those for a coarse – grained polycrystals extrapolated from high temperatures. Interface diffusion parameters were calculated based on the assumption that B – kinetic regime is realized at temperature range more than 448 K, while C – kinetic regime is realised at temperatures less than 423 K. The consistency of obtained results with the proposed cluster diffusion model is discussed. Diffusion in Au – Cu thin films (from several tens to several hundreds nanometers) was studied with the use of the Rutherford Back Scattering, RBS, under the kinetic regime B (448 – 523 K). The RBS spectra were transformed in the concentration depth profiles for both volume and grain boundary (GB) diffusion. The triple products Pn = snδDn (sn is the enrichment coefficient, while δ is the nanograin boundary width) were calculated using Whipple model. As a result of this analysis the s – value for Cu – Au system was determined to be of the order of unity. The paper is focused on a difference between GB diffusion parameters in nano – and coarse grained materials.
Authors: Boris S. Bokstein
Abstract: Evidence for solid-state diffusion (the second half of the 19th century). The first measurements of solid state diffusion (W. Roberts-Austen, 1896–1922). The first tracer experiments to determine the solid-state diffusion (G. von Hevesy, 1913–1923). The first evidence of accelerated diffusion in polycrystalline materials (1924–1935). Autoradiographic studies of grain boundary diffusion (50s of 20th century). The first quantitative experimental and theoretical studies of the “short circuiting” diffusion (beginning from 1949, D. Turnbull and R. Hoffman – General Electric Research Lab.): radiotracer serial sectioning method, the Fisher model (1951) for grain boundary diffusion, exact solutions and developments of the Fisher model (1954–1963). The progress in the experimental methods for determination of grain boundary diffusion data and results of measurements for different metallic systems (up to date). The measurements of grain boundary diffusion parameters in the B and C regimes. Grain boundary diffusion and grain boundary segregation. Nonlinear segregation effects. Structural effects of grain boundary diffusion. Diffusion in bicrystals. Diffusion in nanocrystals. Computer simulation of grain boundary diffusion. Mechanisms of grain boundary diffusion.
Authors: Boris S. Bokstein, S.A. Gulevsky, A.L. Petelin, A.O. Rodin
Abstract: The interaction between liquid and solid metals where the liquid-solid interface contains three grain boundary lines which meet in triple junction point is considered. The assumption that the liquid grooves may be formed not only along grain boundaries but along triple junctions is presented. The variation of Gibbs energy during the formation of triangle pyramidal groove along triple junction is determined. The dependence of Gibbs energy variation from groove dimensions shows that the wetting of triple junctions occurs by lower temperatures than the wetting of grain boundaries. This result allows to take into account the existence of grain size effect on the liquid phase penetration depth into the polycrystalline sample. The proposed mechanism of wetting in polycrystalline metal contains two stages: the outstrip melt penetration along triple junctions and the liquid grooving on grain boundaries forming the triple junctions. One of the processes – triple junction diffusion or liquid diffusion – may control the wetting in the polycrystalline sample.
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