The effect of cooling rates on hereditary characteristics of icosahedral clusters in rapid solidification of liquid Cu56Zr44 alloys

A molecular dynamics simulation is performed to investigate the influence of cooling rates γ on the hereditary characteristics of icosahedral clusters during the rapid solidification of liquid Cu56Zr44 alloys. The analysis from an extended cluster-type index method based on the H-A bond-type index shows (12 0 12 0 0 0 0 0 0 0) standard icosahedra and (12 0 8 0 0 0 2 2 0 0) as well as (12 2 8 2 0 0 0 0 0 0) defective icosahedra play a key role in the formation of Cu56Zr44 glassy alloys. With the increase of cooling rates γ, the glass transformation temperature Tg rises, but the clustering degree towards icosahedra descends in the rapidly solidified solid. An inverse tracking of atom traces reveals the icosahedral clusters at 300 K mainly originate from the configuration heredity below Tg, and the perfect heredity is dominant among perfect, core and segmental heredity modes. Relative to (12 0 8 0 0 0 2 2 0 0) and (12 2 8 2 0 0 0 0 0 0) defective icosahedra, (12 0 12 0 0 0 0 0 0 0) standard icosahedra are of high structural stability and large heredity ability, and their descendible efficiencies and heredity behaviors vary with γ. In the case of high γ, not only the descendible fractions fi of icosahedral clusters above Tg are enlarged, but also their initial descendible temperatures Tonset in the super-cooled liquid region are elevated. As a result, icosahedral medium-range orders (IMROs) can be easily formed and grown in the super-cooled liquid. Therefore, a big Trg = Tg/Tm of Cu56Zr44 alloys at high γ can be attributed to the ascent of Tonset caused by increasing γ to some extent.