Hardness of diamond-сBN nanocomposite

Abstract

The spatial densities of valence electrons and their cross sections, the total energies, and the force response on the deformation for modeling objects of the cC-cBN composite were evaluated by methods of the electron density functional and ab initio pseudopotential.The spatial distributions of the electron density of the chemical bonds CB and CN were obtained and discussed. The first principles calculation confirms that the chemical CN bond stronger than the CB bond; it affects the chemical inertness of different composite models.In this computer experiment, the imaginary indenter penetration process is simulated as the gradual relocation of atoms deep into the cluster. When the model cubical crystal of the cC-cBN composite with as sequence of layers as C, N, and B was deformed at the top like on figure, the record high hardness and the low reactivity combined. Model crystals of the cC-cBN composite with other order of layers C, N, and B have the high value of hardness too, but electron density, squeezed to the surface of the cluster, casts doubt on the chemical stability.In addition, it was identified physical mechanisms of the hardness of the materials, which have tetrahedral chemical bonds. The maps of the spatial distribution of the electron density of the deformed CN bond illustrated the increasing concentration of electron density along this bond.The changes of the total energy are interpreted as changes of the ionicity degree of deformed bonds in the model clusters.