Growth of icosahedral medium-range order in liquid TiAl alloy during rapid solidification

• Icosahedral medium-range order improves glass forming ability and glass stability.
• Hexagonal connected icosahedral clusters have excellent structural stability.
• Dendritic icosahedral clusters based on hexagonal formation keep stable growth.
• Hexagonal junctions enhance compactness of icosahedral structures.
• Icosahedral medium-range order properly defines characteristics of TiAl alloy.

The formation and evolution of icosahedral medium-range order structures of TiAl alloy during the rapid solidification are investigated based on molecular dynamics simulations. The icosahedral medium-range order structural evolutions are described in detail by coordination number and icosahedral connectivity parameters. Simultaneously, the evolution of the medium-range order icosahedral clusters is analyzed by nano-clusters tracing method. The results reveal that the full growths of icosahedral medium-range order structures improve the glass forming ability and stability of metallic glass. Meanwhile, the hexagonal connected icosahedral clusters which link via volume-sharing have excellent structural stability, and the dendritic icosahedral clusters based on the hexagonal formation keep continuous growth below the Tg. The junctions which consist of the hexagonal formations enhance the compactness of icosahedral medium-range order structure. Moreover, the icosahedral medium-range order is an appropriate structural characterization which accurately defines the characteristics of amorphous TiAl alloy during the rapid solidification.