Crystallization kinetics and thermal stability of the Zr 60Al 7.5Cu 17.5Ni 10Si 4B 1 amorphous alloy studied by isothermal differential scanning calorimetry and transmission electron microscopy

Abstract

The Zr 60Al 7.5Cu 17.5Ni 10Si 4B 1 (numbers indicate at.%) amorphous alloy was selected for an investigation of its crystallization kinetics and thermal stability because of its high activation energy of 370 kJ/mol for crystallization and its extended incubation time during isothermal annealing in the supercooled temperature region. The crystallization behavior and microstructure development during isothermal annealing were examined by isothermal differential scanning calorimetry, X-ray diffractometry and transmission electron microscopy (TEM). When annealing the Zr 60Al 7.5Cu 17.5Ni 10Si 4B 1 alloy isothermally at 714 K, Zr 2Cu crystals with average size about 5 nm were first observed at the early stage of 1% crystallization by TEM. The Zr 2Cu crystal size increases with annealing time, then reaches an average size of about 25 nm at the stage of 72% crystallization. In addition, the grain growth time as a function of the cube of particle size of the Zr 2Cu type crystalline phases presented a good linear relationship. This indicates that the crystal growth of the Zr 60Al 7.5Cu 17.5Ni 10Si 4B 1 alloy is a thermally activated process. The activation energy for growth of Zr 2Cu particles in the Zr 60Al 7.5 Cu 17.5Ni 10Si 4B 1 amorphous alloy is found to be 210 ± 25 kJ/mol. The lower activation energy of crystal growth during crystallization in comparison with 440 kJ/mol for crystallization in Zr 65Cu 35 corresponds to the rearrangement of other smaller atoms in the glass, such as Al or Si (compare to Zr).