Atomistic Study of the Interface Energy in Nickelbase Superalloys

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High-temperature components as they are used in turbines are usually made of nickel-base superalloys. The high strength of these alloys is due to precipitated particles. Since large components are wrought, the strengthening particles must not be present during the forging process and may precipitate only at lower temperatures. Other precipitates (the niobium-containing delta and the titanium-containing eta-phase) have to be present during forging because they improve the microstructure of the alloy. To increase the service temperature of these alloys thus requires to adapt the properties of the delta- and eta-phase.The precipitation of particles of the delta- and eta-phase is determined by the interfacial energy between these phases and the nickel matrix. It is the aim of this proposal to calculate the interfacial energy of these and the so-called gamma"-phase and to investigate how alloying elements affect the interface. This will improve the understanding of the precipitation of these particles and how to keep them stable at higher temperatures.Atomistic simulations are used to achieve this goal. The density functional theory method allows to calculate the energy of arbitrary configurations of atoms. However, it is restricted to several hundred atoms. Additionally, the so-called classical molecular dynamics method is used that can simulate large numbers of atoms. This method, however, needs empirical parameters as input and thus cannot be used to investigate all alloying elements. Using both methods allows to study different aspects of the interfacial energy. The results will also be confirmed by a limited amount of experimental investigations.