Strong interface adhesion in Fe/TiC

Abstract

As an aid to understanding the superior toughness of Ti-modified steels provided by fine Ti(C, N) particles, first-principles full-potential linearized augmented plane wave (FLAPW) density functional calculations were performed on the Fe matrix/TiC particle interface. It was found that at equilibrium a strong covalent bonding between Fe–C is formed at the interface, and the magnetic moment of the interface Fe (1.98 μ _B ) is reduced from that of the tetragonally strained structure (2.51 μ_B). We then calculated with a rigid separation model the separation energy curve and the force separation law for the Fe–C debonding process at the interface, which predicts 2.45 J m₋₂ for the work of separation and 30.66 [GPa] for the force maximum. We also found that the strong Fe–C bond provides an interfacial fracture strength equal to that of the pure bcc Fe matrix. A clear picture is given for the microscopic origin of this strong metal/ceramic adhesion based on density of states (DOS) considerations. For a more realistic understanding of the Fe–C bonding, structural optimization calculations were performed at each separation distance. The effect of relaxation was found to be larger at short separation distances than in the large separation region, which leads to a crossover behavior in the separation energy curve from the elastically deformed to the clearly separated regime at a critical distance (∼1.75 Å), and to a discontinuity in the force separation law. Despite this large relaxation effect, the work of separation, 2.52 J m₋₂, is not changed much from that of rigid separation.

Acknowledgements

The authors are grateful to Y.N. Gornostyrev, O.Y. Kontsevoi, and C.F. Woodward for their fruitful discussions. This work was supported by the ONR (grant No. N00014-01-1-0953) under the Naval Materials by Design Grand Challenge and by grants of computer time at the NAVO and ERDC Supercomputing Centers.