Special Physics Seminar
Speaker: Rafal Kozubski (Jagiellonian University in Krakow)
Title: Kinetics of structural transformations in nano-structured intermetallics: atomistic simulations
Date/Time: Nov 22st, Thursday @ 11:00-12:00
Place: Sabanci University, SUNUM building, room G111
Kinetics of vacancy-mediated atomic ordering processes in nano-layered L10 and triple-defect B2 ordered intermetallics was the subject of extensive atomistic simulations. The two groups of systems differ substantially in their vacancy thermodynamics: very low and very high vacancy concentration is observed in L10 and triple-defect B2 intermetallics, respectively. Special attention was focused on the analysis of an effect of free surfaces on superstructure stability and defect concentration in the examined materials.
Kinetic Monte Carlo (KMC) simulation of “order-order” kinetics in -oriented FePt nanolayers initially perfectly ordered in the c-variant L10 and modelled with two- and many-body interactions revealed a tendency for superstructure transformation from c-variant (monoatomic planes parallel to the (001) free surface) to a- and b-variants (monoatomic planes perpendicular to the (001) free surface).
The B2-ordering NiAl was modelled with the temperature-dependent equilibrium concentration of vacancies determined by means of Semi Grand Canonical Monte Carlo (SGCMC) simulations. The system was simulated by KMC for “order-order” kinetics which showed two stages: (i) extremely fast generation of triple defects, (ii) extremely slow continuation of the process towards thermodynamic equilibrium. It was shown that the slow rate of the stage (ii) was due to extremely low efficiency of disordering jumps of A-atoms. It is claimed that only the stage (ii) of “order-order” kinetics is observed experimentally. In nano-layers, an additional effect of vacancy segregation on free surfaces and its influence on ordering kinetics was modelled.
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