ATOMISTIC MODELLING OF SUPERSTRUCTURE REFINEMENT IN CRYSTALLINE MATERIALS

Rafal Kozubski 3Ewa Partyka 3Mirosław Kozłowski 3Véronique Pierron-Bohnes 1Wolfgang Pfeiler 2

1. Institut de Physique et Chimie des Materiaux de Strasbourg, UMR7504, CNRS - ULP, 23, rue du Loess, BP 43, Strasbourg CEDEX 2 67034, France
2. University of Vienna, Institute of Materials Physics, Wien, Austria
3. Jagiellonian University, Institute of Physics (IF UJ), Reymonta 4, Kraków 30-059, Poland

Abstract

Chemical ordering in multicomponent crystalline systems is of fundamental technological importance and knowledge of its dynamics (kinetics) is crucial in materials engineering. The process, however, always competes with the general tendency for entropy maximization and hence, at any non-zero temperature T finite concentration of antisite defects is observed and increases with increasing T. Consequently, a change of system temperature is followed by generation/annihilation of antisite defects, so-called "order-order" relaxation, whose mechanism (atomic migration) is the same as that of diffusion. The kinetics of both phenomena are different due to non steady-state conditions during relaxation. "Order-order" relaxation may be successfully modeled by computer simulations, which involves the following tasks: (i) approximation of system energetics (Hamiltonian), (ii) energetics and thermodynamics of structural defects (vacancies, interphases, surfaces), (iii) implementation of particular atomic-jump mechanism, (iv) adaptation/elaboration of computer codes.
"Order-order" relaxations have been modeled and simulated in binary systems showing different types of superstructures by combining Monte Carlo and Molecular Dynamics methods. Particular attention has been paid to the statistics (correlations) of atomic jumps, which appeared to control specific features of the relaxations experimentally observed in particular intermetallics and being important for designing technological processes. This concerns: different time scales active in the processes, differences between the activation energies for chemical ordering and for self-diffusion, differences between statically and dynamically modeled activation energies for atomic jumps, effective role of the high concentration of vacancies in increasing the rate of chemical ordering etc.
Current studies concern the effect of size limitation on "order-order" phenomena modelled in nanostructured intermetallics.

 

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Presentation: oral at E-MRS Fall Meeting 2004, Symposium H, by Rafal Kozubski
See On-line Journal of E-MRS Fall Meeting 2004

Submitted: 2004-02-19 17:51
Revised:   2009-06-08 12:55