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Abstract

Segregation and precipitation of second phases in metals and metallic alloys are complex phenomena that are strongly influenced by the mechanical properties of the material. Models exist that describe the growth of coherent, semi- and incoherent precipitates. One of the parameters of these models, namely the energy of the interface between matrix and precipitate is investigated in more detail in this project. For reference, various structures of the molybdenum-carbon system have been investigated by ab-initio calculations based on the density functional theory. The energy of formation of these structures has been calculated and compared with experimental results where available. A metastable phase with a body-centered tetragonal structure, which is not present in the phase diagram, has been observed experimentally by high-resolution electron microscopy as a semi-coherent precipitate [1]. We assume that it is stabilized by the precipitate interface energy. The contribution of the interface energy of the body-centered tetragonal phase was modeled with the help of ab-initio calculations. The change in the lattice parameters and the energy of the system with varying carbon concentration have been calculated. The elastic strain energy stored in the precipitate was calculated and used to examine the coherency of the system depending on the size of the precipitate.