Atomistic structural evolution with cooling rates during the solidification of liquid nickel

In this paper, molecular dynamics simulations based on the second-moment approximation of tight-binding scheme have been performed to investigate the effect of cooling rate on solidification microstructures of liquid Ni. Two transitional structures characterized by one-dimensional (1D) and 2D periodicities respectively between the crystal and amorphous states have been found as the cooling rates range from 6 × 10¹² K/s to 1 × 10¹³ K/s. As the cooling rates Q ≥ 1.5 × 10¹³ K/s, an amorphous structure can be obtained, whilst crystal structures are formed when Q ≤ 4 × 10¹² K/s. Moreover, our results reveal that the intensity ratio (g₂₁/g₂₂) of the two subpeaks, which split from the second peak on the pair distribution function for the amorphous state, can act as a structural indicator to differentiate amorphous, translational structure and crystalline states. As such, one may determine the structure state of a material by estimating the value of g₂₁/g ₂₂ from its pair distribution function.