Cu–Zr–Al (Ti) bulk metallic glasses: Cluster selection rules and glass formation

The present paper investigates the bulk metallic glass formation in Cu–Zr–Al and Cu–Zr–Ti ternary systems by using the cluster line criterion. The binary basic clusters are first selected for constructing cluster lines. Three cluster selection rules are proposed: topologically dense packing, chemical short-range order and composition distance to deep eutectics. Three Cu–Zr clusters Cu8Zr5, Cu6Zr5 and Cu5Zr6 are selected according to the three rules. The bulk metallic glass-forming ranges in these two systems are determined. The thermal characteristic parameters of the Cu–Zr–Al BMGs on every composition line increase with increasing Al content and decrease with increasing Ti content in the Cu–Zr–Ti glass-forming range. The optimum bulk amorphous compositions in the Cu–Zr–Al system are Cu58.1Zr35.9Al6 and Cu39.7Zr47.1Al13.2, respectively, located in Cu8Zr5–Al and Cu5Zr6–Al cluster lines. In the Cu–Zr–Ti system, the Cu64Zr28.5Ti7.5 composition with the largest Tg/Tl is located in Cu9Zr4–Ti cluster line and the Cu57.6Zr32.4Ti10 composition with the largest glass-forming ability is located in Cu64Zr36–Ti line.