A ReaxFF force field was developed for Fe/Al/Ni binary alloys, based upon quantum mechanical calculations. In addition to the various bulk phases of the binary alloys, the (100), (110) and (111) surface energies and adatom binding energies were included in the force field parameterization of the Fe/Al/Ni binary alloys. A study was made of the elastic constants of the binary alloys at finite temperatures, of the diffusivity of alloy components in Al/Ni alloy and of segregation on the binary alloy surfaces. ReaxFF molecular dynamics simulations were also performed for Al or Ni diffusion in the system modelled as Al/Ni mixed layers with linear composition gradients. At 1000K, Al diffusivity at the pure Al end was 2 orders of magnitude larger than that in the Al trace layers. However, the diffusivity of Ni at the pure Ni end was only slightly larger than that in the Ni trace layers at the system temperature much lower than the melting temperature of Ni. Surface segregation of Al occurred most strongly in Fe3Al, whereas it occurred most weakly in Ni3Al. These results may support the segregation mechanism that surface segregation results from the interplay between the energetic stability of the ordered bulk phase and the surface reconstruction. In addition, the surface segregation induced the depletion layers of segregating metal species (Al in Fe3Al and Ni3Al, and Ni in Fe3Ni) next to the segregation layers. These simulation results qualitatively agreed with early experimental observations of segregation in Fe/Al/Ni binary alloys.

Development and Validation of a ReaxFF Reactive Force Field for Fe/Al/Ni Alloys: Molecular Dynamics Study of Elastic Constants, Diffusion, and Segregation. Shin, Y.K., Kwak, H., Zou, C., Vasenkov, A.V., Van Duin, A.C.T.: Journal of Physical Chemistry A, 2012, 116[49], 12163-74