Crystallization and fracture behavior of the Zr65−xAl7.5Cu17.5Ni10Six bulk amorphous alloys

The crystallization behavior of amorphous Zr65−xAl7.5Cu17.5Ni10Six alloys, x = 0-10, was studied by means of differential scanning calorimetry, X-ray diffractometry, and TEM. The calculated Trg (Tg/Tl) 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 Zr65−xAl7.5Cu17.5Ni10Six 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 Zr61Al7.5Cu17.5Ni10Si4 alloy. During isothermal annealing the Zr61Al7.5Cu17.5Ni10Si4 alloy at 698 K, the Zr2Cu 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 Zr3Al (∼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 Tg and Tx.