Papers by Keyword: Atomic Mobility

Abstract: Abstract: The atomic mobilities for impurity diffusion of Al, Au, Co, Cu, Mn, Mo, Nb, Ni, Pt, Sn and Zn in fcc Fe have been critically assessed based on the experimental diffusion coefficient data available in the literature. The impurity diffusion coefficients calculated from the atomic mobilities agree reasonably well with the reliable experimental data. This work provides a helpful guidance for the establishment of a general Fe-based mobility database to design new Fe-based alloys for practical purposes.

Abstract: The diffusion-couple experiments have been performed at 1273 K and 1423 K in order to verify and bias the controversial interdiffusion data in the literature. In the meantime, the literature data on the lattice parameter have been assessed to obtain the molar volume of fcc Fe-Co phase, which was in turn fed into the Sauer-Freise equation to retrieve the interdiffusion coefficients from the EPMA (Electron Probe Micro-Analysis) measured diffusion profiles. The reliable experimental data on the diffusion coefficients for fcc Fe-Co phase have finally been used to assess the atomic mobility. A general agreement has been reached between the calculated and experimentally measured data.

Abstract: A new atomic mobility database for Fcc_A1, L1₂, Bcc_A2, Bcc_B2, and liquid phases in the Al-Cu-Fe-Mg-Mn-Ni-Si-Zn system has been established via a hybrid approach of experiment, first-principles calculations and DICTRA (DIffusion Controlled TRAnsformation) software, focusing on the atomic mobility parameters in ternary systems. Various diffusivities can be computed as a function of temperature and composition. The reliability of this diffusivity database is further validated by comparing the calculated and measured diffusion properties in a series of ternary and quaternary diffusion couples, including concentration profiles, diffusion paths, interdiffusion fluxes, and so on. The effect of the diffusivity database on microstructure evolution during solidification is demonstrated by the phase field simulation of primary (Al) grains in Al356.1 alloy. The simulation results indicate that such accurate diffusivity database is highly needed for the quantitative simulation of microstructural evolution during solidification.

Abstract: This work is dedicated to simulate the spinodal decomposition of Fe-Cr bcc (body centered cubic) alloys using the phase field method coupled with CALPHAD modeling. Thermodynamic descriptions have been revised after a comprehensive review of information on the Fe-Cr system. The present work demonstrates that it is impossible to reconcile the ab initio enthalpy of mixing at the ground state with the experimental one at 1529 K using the state-of-the-art CALPHAD models. While the phase field simulation results show typical microstructure of spinodal decomposition, large differences have been found on kinetics among experimental results and simulations using different thermodynamic inputs. It was found that magnetism plays a key role on the description of Gibbs energy and mobility which are the inputs to phase field simulation. This work calls for an accurate determination of the atomic mobility data at low temperatures.

Abstract: This paper highlights the role played by diffusion processes to achieve a better characterization of structure and dynamics in atomic-scale studies of materials. Two classes of examples are presented. In the first, we take advantage of diffusion coefficients to assess the performances of different exchange-correlation functionals employed within the framework of density functional theory. By calculating the diffusion coefficients one is able to make a choice on the functional best suited to describe a prototypical disordered system, liquid GeSe2. In the second class of examples, we rely on classical molecular dynamics to describe diffusion mechanism on nanostructured substrates. The migration of a Co adatom on a stepped Pt(111) surface is analyzed in detail and correlated to the value of the different diffusion barriers. The diffusion behavior of Au adatoms on the reconstructed Au(111) substrate is described in terms of diffusion isotropy and anisotropy, by comparison with the case of Co/Au(111). Taken altogether, these studies exemplify the close link between diffusion properties, a realistic description of materials and the current level of performances of atomic-scale simulations methods.