Interphase boundaries in quasibinary eutectic systems


I. M. Frantsevich Institute for Problems of Materials Science of the NAS of Ukraine, Krzhizhanovsky str., 3, Kyiv, 03142, Ukraine
Mathematical Models and Computing Experiment in Material Science - Kiev: Frantsevich Institute for Problems of Materials Science NASU, 2019, #21


The volume of the averaged cell along the line of joining the boundaries of the two components using the eutectic concentration is calculated. The dependence of the energy of the electron-ion system on the arrangement of atoms along the docking line is estimated and the most favorable arrangement of atoms is chosen energetically based on the minimum total energy, which leads to the formation of quasicoherent boundaries. Based on the results obtained from a computational experiment:
1. In the process of formation of a two-component alloy, the crystal lattices of the components are joined so as to ensure the minimum of distortions arising due to the difference in the sizes of unit cells.
2. At the junction of two crystal lattices, all nodes must be populated by atoms, otherwise a vacancy will form, which will increase the total energy of the system.
3. At the interface, common atoms are responsible for the bond between the components. In the absence of common atoms, the bond is carried out with common atomic nodes belonging to the two components. The rupture of this connection leads to the formation of incomplete components, which are easily amenable to decay, which accounts for the relatively low melting temperature, compared with the melting temperature of the components.
4. The number of variants of arrangement of atoms of a component at the interface of the dock is determined by the concentration ratio necessary for the formation of a eutectic.
5. During the formation of a eutectic in this B4C―SiC system, boron carbide changes its stoichiometric composition, releasing excess carbon to ensure the appearance of quasicoherent component boundaries.
If the composition of the two-component system does not correspond to the concentration ratio of the eutectic for the entire material, then in those areas where the components are in contact, the formation of local eutectic systems will be observed according to the principle presented in paragraphs 1―4.