Structure, bonding, and adhesion at the TiC(100)/Fe(110) interface from first principles

Metal carbide ceramics offer potential as protective coatings for steels. Here we report a pseudopotential-based density functional (DFT) investigation of one such coating, wherein we predict the atomic structure, bonding, and the ideal work of adhesion (W(ad)(ideal)) of the interface between a TiC(100) coating and a bcc Fe(110) substrate. Calibration of the DFT approximations used yields TiC and Fe bulk properties in reasonable agreement with experiment. Subsequent characterization of the low-index TiC and Fe surfaces reveals that all surfaces retain near bulk termination, in agreement with experiment. Stabilities of both TiC and Fe surfaces increase with their packing densities, i.e., (110)<(111)<(100) for TiC and (111)<(100)<(110) for bcc Fe. We estimate that the minimum critical stress required for crack propagation in bcc Fe is 27% larger than that in TiC. The TiC(100)/Fe(110) interface exhibits a lattice mismatch of similar to2.1%, leading to a smooth interface with only a small structural relaxation, except for the ultrathin 1 monolayer (ML) coating. A mixture of metallic and covalent bonding dominates across the interface, due to significant C p-Fe d interaction and somewhat less pronounced Ti d-Fe d mixing; the latter is found to decrease with increasing coating thickness, but reaches a saturation value for 3-ML-thick coating. The asymptotic value of W(ad)(ideal) for the TiC(100)/Fe(110) interface is predicted to be similar to2.56 J/m(2) and is reached for a 3-ML-thick coating of TiC on Fe. This interface strength is considerably smaller than the energy required for cracking TiC or Fe, but may still be strong enough to survive as a coating for steel in extreme environments. (C) 2003 American Institute of Physics.