The local structure of molten Ni1−xAlx: An ab initio molecular dynamics study

• Molten Ni1−xAlx is dominated by pentagonal bipyramids.
• Strong affinity between Ni and Al induces significant chemical order.
• Al atoms try to avoid bonding to Al so as to form Ni–Al bonds as many as possible.
• The chemical order is enhanced with increasing Al concentration.

The local structures of molten Ni1−xAlx (x = 0.102, 0.148, 0.204 and 0.25) at 1773 K have been studied by ab initio molecular dynamics simulations. Molten Ni1−xAlx is dominated by pentagonal bipyramids, while just small amounts of full icosahedral short-range orders (ISROs) are found. Most of the geometrical short-range orders (SROs) are more complex than a full ISRO. Generally, BCC-, FCC- and HCP-SROs do not exist in molten Ni1−xAlx. Strong affinity between Ni and Al induces significant chemical order. Al atoms try to avoid bonding to each other and prefer dispersing in the melt so as to form Ni–Al bonds as many as possible. Distorted zinc-blende-structure like network composed by Ni–Al bonds is formed gradually due to the strong affinity between Ni and Al and the growing Al concentration. With increasing Al concentration in molten Ni1−xAlx, the chemical order is enhanced and the geometrical order is weakened accordingly. The strong affinity between Ni and Al also induces the shell around Al being densely packed, which hinders the diffusion of Al.