Formation of icosahedral clusters in amorphous Ni-Zr alloy

Formation of icosahedral clusters in Ni_66.7Zr_33.3 alloy during rapid solidification is studied with molecular dynamics simulations. It is found that the growth rate of the smallest icosahedral cluster (Ih13) in Ni_66.7Zr_33.3 alloy reaches its maximum at glass transition temperature region. The Ih13 in Ni_66.7Zr _33.3 alloy contain the retained from the higher temperatures and the new grown, which reach its maximum at about 900K as well as the new grown vertex atoms of Ih13. The ratio of new grown center atoms to the new grown vertex atoms increases with decreasing temperatures, which implies that the new Ih13 form beside original Ih13 and the icosahedral clusters coalesce to the larger ones during solidification. The stabilities of center atoms and vertex atoms of Ih13 increase with decreasing temperatures, and the stability of the center atoms becomes larger than that of vertex atoms blow 900K because of its rapid increase at glass transition temperatures. The results show that the evolutions of atomic arrangement during cooling change abruptly at glass transition region.