Simulation of local cluster structure of binary system alni in liquid and supercooled states

We investigate short-range icosahedral order in liquid and supercooled Ni, Ni$_{95}$Al$_{5}$, Al, Al$_{95}$Ni$_5$ and Al$_{86}$Ni$_{14}$ by using molecular-dynamics simulation. The potentials of interatomic interaction within the framework of the embedded-atom method are used to generate realistic atomic configurations. The structural analysis using bonding orientational order technique have been performed in detail and the effect of undercooling on the cluster microstructure has been analyzed. We showed a monotonic increase in icosahedral order when the melts and alloys are supercooled and when the concentration of the second component is increased. At high temperatures all of our measured structural properties of Al, Al$_{95}$Ni$_5$, Al$_{86}$Ni$_{14}$, Ni and Ni$_{95}$Al$_{5}$ resembled each other. This suggests that a nearly universal structure exists for systems whose energetics are dominated by repulsive central forces. In a Ni$_{95}$Al$_{5}$ alloy replacing a few medium sized Ni atoms with larger Al atoms leading to increase of icosahedral order and inhibit crystallization. However, in Al$_{95}$Ni$_5$ and Al$_{86}$Ni$_{14}$ alloys inclusion of medium sized Ni atoms in larger Al also leading to increase of icosahedral order. The structure of supercooled Al$_{86}$Ni$_{14}$ alloy is inhomogeneous in terms of the chemical composition and is composed of two types of areas: the relative high-concentrated Ni-areas are embedded in a atomic structure of pure Al. Clustering of stable icosahedral regions may lead to a growth of icosahedral seeds at rapid cooling which will systematically increase their size from tens to a few hundreds atoms. Such icosahedron-like clusters may be the centers of "quasicrystallization" and form a quasicrystalline phase with local symmetry, which is not compatible with the long-range translation order.