Authors: Lyudmila N. Paritskaya, Yuri S. Kaganovsky, V.V. Bogdanov
Abstract: The phenomenon of low-temperature homogenization (LTH) during interdiffusion is studied under condition a t Dv £ 2 / 1 ) ( (Dv is the bulk diffusion coefficient, a is the lattice parameter) using nano-objects of binary Cu-Ni and Cr-Ni systems compacted from nano-powders and produced by mechanical alloying. Two stages of LTH were detected: at the first stage (t £ 103 s) the volume fraction of solution rapidly grows; at the second stage (t > 103 s) the volume fraction of solutions grows slowly with practically constant average solution concentration. The first stage of LTH correlates with active grain growth caused by small size (l) of structural element and nonequilibrium structure of nano-objects. Obtained results are analyzed theoretically in terms of interdiffusion along migrating GBs due to grain growth at the first stage and DIGM mechanism at the second stage. It is shown that the GB concentration distribution during interdiffusion along migrating GBs and the kinetics of LTH depend on a parameter l/l where 2 / 1 ) / ( b b V sD d l= is the
characteristic diffusion length. The mechanisms and criteria of LTH are proposed.
Abstract: Coefficient of 65Zn heterodiffusion in Mg17Al12 intermetallic and in eutectic alloy Mg -
33.4 wt. % Al was measured in the temperature region 598 – 698 K using serial sectioning and
residual activity methods. Diffusion coefficient of 65Zn in the intermetallic can be written as DI =
1.7 × 10-2 m2 s-1 exp (-155.0 kJ mol-1 / RT). At temperatures T ≥ 648 K, where the mean diffusion
path was greater than the mean interlamellar distance in the eutectic, the effective diffusion
coefficient Def = 2.7 × 10-2 m2 s-1 exp (-155.1 kJ mol-1 / RT) was evaluated. At two lower
temperatures, the diffusion coefficients 65Zn in interphase boundaries were estimated: Db (623 K) =
1.6 × 10-12 m2 s-1 and Db (598 K) = 4.4 × 10-13 m2 s-1.
Abstract: In this paper, we show how lattice–based random walks of virtual particles directed by
Monte Carlo methods (Lattice Monte Carlo) can be used to address a variety of complex
phenomenologically mass diffusion problems. Emphasis is put on the practical details of doing the
calculations. It is shown how concentration depth profiles can be determined: this is exemplified
with diffusion in the presence of isolated dislocation pipes, grain boundary slabs, and oxygen
segregation at interfaces in metal-ceramic oxide composites. It is also shown how effective
diffusivities can be determined in materials. We also show how temperature profiles and the
effective thermal conductivity can be determined for the thermal diffusion analogue of mass
diffusion. A detailed comparison is made in one case with the results of the Finite Element method.
Authors: Yu Dong Fu, Gang Wang, Chen Liu, Qing Fen Li
Abstract: In the present paper, the non-equilibrium grain-boundary segregation of P atom was
studied in low alloy steels subjected to a low tensile stress at different temperatures. The AES
(Auger electron spectroscopy) experiments and dynamic analyses were conducted to study on the
non-equilibrium grain-boundary segregation of P atom. The research results show that
non-equilibrium segregation of phosphorus occurred at the grain boundaries of the steels
2.25Cr1Mo and 12Cr1MoV, while the critical time reached about 0-1 hour at constant temperatures
773 and 813K. The relationship between the diffusion rate and the diffusion time for the complex
and the phosphorus atom was investigated based on the experimental results. Eventually the
diffusion coefficients of complex and P were calculated with using a proposed dynamic model.
Abstract: Some unresolved problems of grain boundary diffusion – restrictions of Fisher-Gibbs model, refinement of the conditions for B- and C-regimes, relation between segregation (s) and enrichment (b) coefficients, grain boundary width, non-linear segregation effects on grain boundary diffusion – are discussed.