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Abstract

Segregation and precipitation of second phases in metals and metallic alloys are complex phenomena with a high influence on 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. Our example is a metastable Mo-C phase, the body-centered tetragonal structure, which has been observed experimentally by high-resolution electron microscopy as a semi-coherent precipitate [1]. It is assumed that it is stabilized by the precipitate interface energy. Furthermore, this interface is supposed to change from coherent to semi-coherent during the growth of the precipitate. We predict the critical thickness of the precipitate by calculating the different contributions to a semi coherent interface energy by means of ab-initio density functional theory calculations. The parameters in our model include the elastic strain energy stored in the precipitate as well as a misfit-dislocation energy that depends on the dislocation core width and the dislocation spacing. Our predicted critical thickness agrees well with experimental observations.