On the heredity and evolution of icosahedral clusters during the rapid solidification of liquid Cu50Zr50 alloys

A molecular dynamics simulation is performed to investigate the heredity characteristics of icosahedral clusters during the rapid solidification of liquid Cu50Zr50 alloy at a cooling rate of 5 K/ns. The analysis from a cluster-type index based on the H-A bond-type index shows that (12 0 12 0) icosahedra and their distorted configurations (12 8/1551 2/1541 2/1431) play a key role in the formation of glassy alloys. At Tg, the numbers of (12 0 12 0) and (12 8/1551 2/1541 2/1431) basic clusters significantly increase and most of which are Cu-centered Cu6Zr7, Cu7Zr6 and Cu5Zr8 clusters. An inverse tracking investigation on the configuration evolution during the rapid solidification further reveals that the configuration heredity of icosahedral clusters in the super-cooled liquid is an intrinsic feature of the rapidly solidified Cu50Zr50 alloys, but the onset of configuration heredity merely emerges in the super-cooled liquid region of Tm-Tg. Below Tg, the perfect heredity of icosahedra is dominant and a distinctly ascent in heredity fraction fi takes place at Tg. Relative to (12 8/1551 2/1541 2/1431) distorted icosahedra, the standard (12 0 12 0) icosahedra are of high structural stability and large genetic ability, and most of which are passed down by means of the configuration rather than the chemical order.