Crystallization and fracture behavior of the Zr 65− xAl 7.5Cu 17.5Ni 10Si x bulk amorphous alloys

Abstract

The crystallization behavior of amorphous Zr 65− x Al 7.5Cu 17.5Ni 10Si x alloys, x = 0–10, was studied by means of differential scanning calorimetry, X-ray diffractometry, and TEM. The calculated T rg ( T g/ T l) for these amorphous alloys increases with increasing silicon content from 0.55 to 0.60, which indicates that the silicon addition, could improve the GFA for the Zr 65− x Al 7.5Cu 17.5Ni 10Si x alloys. The activation energy of crystallization of the alloy 4Si was about 365 ± 5 kJ mol −1, both determined by the Kissinger and Avrami plot. This value is about 20% higher than the base alloy (314 kJ mol −), which implies that the silicon addition can increase the thermal stability for the Zr-based alloy. The average value of the Avrami exponent n were calculated to be 1.7–2.5 for the alloys in this study. In addition, the cube of crystal size as a function of isothermal annealing time presents a linear relationship for the Zr 61Al 7.5Cu 17.5Ni 10Si 4 alloy. During isothermal annealing the Zr 61Al 7.5Cu 17.5Ni 10Si 4 alloy at 698 K, the Zr 2Cu crystal with average size of 105 nm was first observed at the early stage (30% crystallization ratio) of crystallization. In addition, both nano-crystals of the ZrCu (∼100 nm) and the Zr 3Al (∼30 nm) were also observed to precipitate from the amorphous matrix upon the middle stage (50% crystallization ratio) of crystallization. The fracture surface presents typical ductile vein pattern for 4Si amorphous alloy ribbon after bended to 180°. However, a ductile–brittle transition phenomenon occurs at the amorphous ribbon after 50% crystallization ratio of isothermal annealing at the temperature between T g and T x.