Thermodynamic and kinetic analyses of formation of amorphous and nanocrystalline alloys with the aid of computer and database

Thermodynamic and kinetic simulations were performed to clarify the formations of amorphous and nanocrystalline alloys On the basis of the Miedema's model partially assisted by a database, the amorphous-forming composition region (AFCR) and crystallization temperature (T_x) of the multicomponent amorphous alloys were calculated from thermodynamic approaches. On the other hand, kinetic simulations were performed for Ni-Nb binary eutectic system by the phase field model. The AFCRs calculated for ternary alloy systems containing practically important elements such as Al, Cu, Fe, Ni, Ti agree with the experimental trends. The values of T_x for iron-group-based alloys are calculated with approximate errors of several tens of Kelvin to the experimental data. For Ni_62.4Nb_37.6 alloy, the critical cooling rate (R_c) for formation of amorphous phase and incubation time (τ) for crystallization are calculated to be R_c= 3 × 10² K/s and τ=1000 s. These values are closed to the value calculated from the time-transformation diagram for crystallization based on the homogeneous nucleation theory (R_c=1.4 × 10³ K/s ×=10⁵ s). The present study indicates the importance of the simultaneous analyses of transformations from thermodynamic and kinetic aspects for the development of amorphous alloys in near future.