Development, validation and application of a magnetic bond order potential for the Fe-C system

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The iron-carbon system belongs to the technologically most important binary systems since it is the basis of steel, one of the main materials in today’s society. A great deal of progress has been made in theoretical understanding of the physical, thermodynamic and mechanical properties of this system. However, explicit modelling of atomic-scale processes in modern steels with complex chemistries and microstructures still presents a significant challenge. The reason is that most of these processes are governed by a subtle interplay between chemical and magnetic interactions.The primary objective of this research project is to develop a state-of-the-art magnetic bond-order potential (BOP) that will be capable of describing quantitatively the atomic-scale behavior of the Fe-C system. The developed BOP model shall be able to cover the whole composition range from individual elements over dilute C concentrations in the Fe matrix up to large C concentrations where diverse carbide phases are formed. Since BOPs are derived by a rigorous coarse-graining procedure from quantum mechanics they implicitly contain phenomena originating at the electronic structure level such as magnetism. At the same time, their real-space formulation in the form of many-body interatomic potentials makes them computationally efficient. This combination of physical accuracy and computational efficiency enables them to be employed in atomistic studies of complex configurations and conditions, for instance, properties of extended crystal defects or motion of phase interfaces, that govern not only the mechanisms of structural and magnetic phase transitions in the Fe-C system but also its macroscopic mechanical behavior.