A dramatic gain in the knowledge of precipitate formation, composition, and evolution in alloys has been achieved in the recent years with improvement of transmission electron microscopy techniques for direct structural imaging . A detailed understanding of the microstructure is often essential for control and manipulation of materials properties: an important example for metals is the significant hardening of Al alloys by particular precipitates from a sequence strongly dependent on alloying element concentration and the treatment of the material .
The wealth of experimental information provides a playground for theory in the context of elucidating precipitate growth mechanisms and influence on the host material. A head-on approach to atomistic modelling of these phenomena using an ab initio based scheme is conventionally deemed highly desired but impractical. The basic argument is that the system of any reasonably sized (i.e. realistic) and well isolated microstructure will simply contain too many atoms.
We will challenge this conventional view: it is argued that most of the atoms of the above mentioned system do not play an active role in the growth discussion, hence need not be included in the modelling. Subsequently, a model system is presented which offers a highly accurate description of the interface between the host lattice and a microstructure of an arbitrary size, for the case where this interface is coherent and compositionally abrupt. When used in conjunction with other approaches already available, this model system offers a direct approach to atomistic ab initio studies of microstructure growth.
A general introduction to the modelling scheme will be presented, with the particular application being the main hardening precipitate β'' in the Al-Mg-Si alloy.
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