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5MODELING OF GRAIN BOUNDARY SEGREGATION AND PRECIPITATION
Gornostyrev Yu.N., Karkina L.E., Karkin I.N., Kuznetsov A.R.
Institute of Metal Physics UB RAS, Yekaterinburg, Russia [email protected]
Grain boundary (GB) segregation of alloying elements have a significant effect on many properties of polycrystals. They can significantly change the strength and ductility of the material, the phase equilibrium of the alloy and the thermal stability of the structure. The role of GB segregation become especially significant in ultrafine-grained alloys, where fractions of the GB atoms is comparable to the bulk one. Although the problem of GB segregations has long attracted considerable attention of researchers, the physical mechanisms underlying this phenomenon remain a subject of debate.
Here we present a brief overview of recent progress in atomistic modeling of GB segregation formation, their morphology and opposite impact of segregations on the GB structure. We employed different scale simulation approaches: from ab initio calculations to combine Molecular Dynamic (MD) / Monte - Carlo (MC) simulations. To clarify the factors that determine the segregation capacity of GBs and the morphology of segregations, special GBs, deviating from special ones and GBs of the common type were considered. As typical examples we consider Al-based and Fe-based alloys as well as high-entropy Kantor alloy and focus on the role of chemical and deformation contribution to solute-host atoms interactions in segregation formation.
Summarizing the obtained results, we concluded that the following main scenarios of segregation are possible: (1) the formation of narrow layers (less 1 nm) on the GBs close to special ones, (2) moderate segregations (width up to 3-5 nm) on asymmetric and general type GBs, and (3) wide segregations in the case of GB precipitation. The latter case should also include the formation of unusually wide segregations in a high-entropy alloy. It is shown that the formation of segregations is usually accompanied by reconstruction of the GB structure and these two processes are closely related. The effect of segregations on the cohesive properties of GBs and GBs dislocation sliding is also discussed.
