Composition dependence of structural evolution of Ni-Zr alloys during cooling

The solidification of binary alloys NixZr100-x (x = 5.0, 10.0, 16.7, 33.3, 0.50, 66.7, 83.3, 90.0, 95.0 at.%) at a cooling rate of 2.0 x 10(11) K s(-1) is studied with molecular dynamics simulation methods. The simulation results show that the number of icosahedral clusters with 13 atoms (Ih13) in these solidified NixZr100-x alloys at 300 K increases first and then decreases with increasing Ni concentrations, and reach a maximum at x = 66.7. Both the increasing rates of icosahedral pairs 1551 and 2331 and the decreasing rate of atomic diffusions during cooling in liquid Ni66.7Zr33.3 alloy are the largest among all those in the liquid Ni-Zr alloys simulated. It is the highest changing rates of icosahedral pairs that result in the highest glass-forming ability of the alloy Ni66.7Zr33.3. This illustrates that the structural evolutions of liquid alloys play a paramount role in determining the final structures of these solidified alloys, and further determine the glass-forming ability of alloys.