First-principles study of interface structure and energy of Fe/NbC

Precipitates play an important role in the strengthening of steel. Important factors for controlling the growth of precipitates in steel are the interface energy between the precipitate and the iron and the strain energy around the precipitate. The calculations of coherent and semi-coherent interfaces that include 21 and 1463 atoms, respectively, were achieved using the O(N) Krylov-subspace method of the first-principles electronic structure calculation. Successful reproduction of a dislocation core structure at the semi-coherent interface between the iron and NbC phases provided the interface energy. A classical molecular dynamics simulation was also performed to estimate the strain energy around the precipitate. The side lengths of the broad plane of the plate-like rectangular parallelepiped shaped precipitates at the transition from the coherent to the semi-coherent interface were estimated to be 18 angstrom and 16 angstrom for precipitate thicknesses of 5.36 angstrom and 8.94 angstrom, respectively, by comparing the interface and strain energies of the semi-coherent precipitates with those of the coherent precipitates.