Atomic-scale structural evolution from disorder to order in an amorphous metal

In this paper, we performed molecular dynamics simulations to study the atomic-scale structural evolution from disorder to order during the isothermal annealing of an amorphous Ni. Three plateaus in the time dependent potential energy and mean square displacement (MSD) curves were observed, indicating that the atomic ordering process from amorphous to nanocrystalline Ni undergoes three distinct stages. The structural analyses reveal that the atomic structural evolution is associated with these three stages: Disordered atoms adjust their relative positions to form a one-dimensional (1D) periodic structure at the first stage, then form a 2D periodic structure at the second stage, and finally form a 3D periodic nanocrystal. Further analyses of potential energy and MSD difference and dynamics demonstrate that the structural change from the 2D to 3D structure is more difficult than that from the 1D to 2D structure, because both the 1D and 2D quasi-ordered structures belong to transition states and have similar structural features in nature. Our findings may provide new insights into the nanocrystallization of amorphous alloys and implications for producing nanostructured materials.