KINETIC PHASE FIELD PARAMETERS FOR THE Cu-Ni SYSTEM DERIVED FROM ATOMISTIC COMPUTATIONS

摘要

In the phase field model of binary solidification the mobility terms which appear in the govern- ing rate equations can be estimated from the liquid diffusion coefficients of the pure elements and the vel- ocity of the solid-liquid interface as a function of undercooling. Molecular dynamics simulations utilizing embedded atom potentials have been employed to compute the liquid diffusivities for pure Cu and Ni in the vicinity of their melting points. In both cases the diffusion coefficient is found to vary linearly with tem- perature and the results are in good agreement with experimental values which are available for Cu. The simulations were also employed to obtain the boundary velocities in three different low index growth direc- tions. The results for Cu and Ni were found to be very similar, with the slope of the velocity-undercooling curve at small undercoolings varying in the range 45-18 cm/s/K. Anisotropy in the growth behavior was observed with V_1oo ＞ V_110 ＞ V_111. The solid-liquid interface velocities were found to be a factor of 4-5 less than the theoretical upper limit derived previously.