Abstract
The energetics and the electronic structure of fcc Co(001)/TiC(001) and Co(001)/TiN(001) interfaces, which are of much practical importance in the sintering of hardmetals, are investigated by means of first-principles density-functional calculations, using the plane-wave pseudopotential method. The effects of the large Co/Ti(C,N) lattice mismatch are incorporated within an approach based on a comparative analysis of a representative set of high-symmetry model interface structures. It is shown that the dominating mechanism of the Co/Ti(C,N) interface adhesion is strong covalent bonding between and orbitals. An extensive analysis of the electronic structure elucidates the interface-induced features of the Co-C(N) bonding and antibonding electronic states that are responsible for the enhanced strength of the interface Co-C(N) compared to bonds in bulk carbonitrides, the effect describable as metal-modified covalent bond. A detailed comparison of the energetics and relaxation effects at the Co/TiC and Co/TiN interfaces shows a weaker bonding and less pronounced relaxation effects in the Co/TiN case, which can be connected to the experimentally observed difference in the stability of those interfaces. The weaker Co/TiN adhesion is explained in terms of the relative position of the energy region of the states with respect to the states. The calculated adhesion strength is consistent with the available data from wetting experiments with liquid Co on a TiC surface.
- Received 17 January 2001
DOI:https://doi.org/10.1103/PhysRevB.64.045403
©2001 American Physical Society