Diffusion in Solids and Liquids IV

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Authors: Ivan Campos-Silva, M. Ortíz-Domínguez, N. López-Perrusquia, R. Escobar Galindo, O.A. Gómez-Vargas, E. Hernández-Sánchez
Abstract: The boron diffusion in the Fe2B and FeB borided phases formed at the surface of AISI H13 tool steels during the paste boriding process was estimated. The treatment was carried out at temperatures of 1173, 1223 and 1273 K with 2, 4, 6 and 8 h exposure times for each temperature using a 4 mm layer thickness of boron carbide paste over the material surface. The boride layers were characterized by the GDOES technique to determine in quantitative form the presence of the alloying elements on the borided phases. The boron diffusion coefficients and were determined by the mass balance equation and the boride incubation time assuming that the boride layers obey the parabolic growth law. Also, the mass gain produced by both boride layers at the surface of the tool steels was determined. Finally, the boron diffusion coefficients were interpreted as a function of the treatment temperature, obtaining the activation energy values for the diffusion controlled growth of Fe2B and FeB hard coatings.
Authors: Vladimir V. Popov
Abstract: The results of interdiffusion studies in Fe-Ti-C, Fe-V-C, Fe-Cr-C, Fe-Mo-C and Fe-W-C ternary systems are summarized. Interdiffusion coefficients of substitution elements in austenite and ferrite are determined and their concentration and temperature dependencies are analyzed. Using the available literature data and the results of our own studies the analytical expressions for interdiffusion coefficients have been obtained.
Authors: Irina V. Belova, Graeme E. Murch
Abstract: Recently, the transition point between the Harrison Type-A to Type-B kinetics regimes as well as the emerging intermediate AB transition regime have been analysed in detail by making use of Lattice Monte Carlo simulations of tracer depth concentration profiles as a function of diffusion time and distance between grain boundaries e.g. [7-9]. The principal model in this area has been the grain boundary slab model. However, depending on the diffusion time and grain size a given tracer atom can be expected to cross a number of grain boundaries in its diffusion time. This has recently been taken into account in square and cubic grain models for determining the limit of the Harrison Type-A regime [1]. In the present study, we determine the limits of the intermediate AB transition regime where we have used the Lattice Monte Carlo method to analyse the tails of tracer concentration depth profiles. The applicability of different solutions for the grain boundary diffusion analysis is numerically investigated for the 3D model. The solutions are those by Whipple-Le Claire [12,13] and Suzuoka [11], Bokstein, Magidson and Svetlov [15], Levine and MacCallum [14] for the type B kinetic regime and that by Divinski and Larikov [2] for the intermediate Type-AB regime. We also review the progress that has been made concerning the limits of the various Harrison regimes supplemented with the results of the present simulations. An empirical factor of 1.5 should be applied when Suzuoka or Whipple-Le Clair solutions are applied to the analysis of the tracer diffusion profile, tail section, in the polycrystalline material and an empirical factor of 2.0 should be applied when Bokshtein-Magidson-Svetlov solution is applied to the analysis of the tracer diffusion problem in the polycrystalline material.
Authors: Paul Heitjans, Martin Wilkening
Abstract: Materials with an average particle size of less than about 50 nm often show new or at least enhanced physical properties. In many cases nanocrystalline ionic conductors exhibit a high increase of cation, e. g. Li+, or anion, e. g. F−, diffusivity. In the present contribution we review recent studies on ion dynamics in nanocrystalline ion conductors, both single-phase systems and composites, being prepared by high-energy ball milling. These include, e.g., LiTaO3, Li2O:Al2O3, LiF:Al2O3, BaF2, CaF2, BaF2:CaF2 and (BaF2:CaF2):Al2O3. Dynamic properties were probed by 7Li and/or 19F NMR line shape and relaxation as well as ion conductivity measurements.

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