Rapid solidification of cobalt melt by molecular dynamics simulation

Molecular dynamics simulation was applied to investigating the evolvement rule of cobalt melt microstructure during solidification at different cooling rates. The cooling rate for the formation of amorphous phase is determined by analyzing the radial distribution function, the H–A bond-type index and the mean square displacement. The simulation results showed that the nucleation undercooling increases with the initial temperature, and in the undercooling versus temperature curve, there are two inflection points. Besides, when the initial temperature reaches 2450 K, the undercooling will be stabilized at 1061 K. As the cooling rate is less than 1.0 × 10^11.0 K s⁻¹, the FCC and HCP crystal structures will be obtained. Amorphous structure will be obtained if the cooling rate is more than 1.0 × 10^13.0 K s⁻¹. If the cooling rate of the Co melt is between 1.0 × 10^11.0 and 1.0 × 10^13.0 K s⁻¹, the crystal and amorphous structures will be coexistent, which indicates that the critical cooling rate of crystal–amorphous transition is 1.0 × 10^11.0 K s⁻¹.