Abstract
Based on the previously proposed model of paired covalent bond, the reasons for the brittleness for covalent crystals have been studied. It is shown that the brittleness of a covalent crystal is due to the “duplicity” of the paired interatomic interaction potential for elastic (reversible) and plastic (irreversible) deformation. This leads to the fact that the specific surface energy during plastic deformation of a covalent crystal is more than two times less than the specific surface energy during elastic deformation. Therefore, with a small deformation of a covalent crystal, it is energetically more advantageous to create a surface by breaking than by elastic stretching it. It is shown that the brittle-ductile transition temperature for single-component covalent crystals has an upper limit: TBDT/Tm < 0.45, where Tm is the melting temperature.
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