Crystallization kinetics of the Zr61Al7.5Cu17.5Ni10Si4 alloy using isothermal DSC and TEM observation

The crystallization behavior and microstructure development of the Zr61Al7.5Cu17.5Ni10Si4 alloy during annealing were investigated by isothermal differential scanning calorimetry, X-ray diffractometry and transmission electron microscopy. During isothermal annealing of the Zr61Al7.5Cu17.5Ni10Si4 alloy at 703 K, Zr2Cu crystals with an average size of about 5 nm were first observed during the early stages (30% crystallization) of crystallization by TEM. The Zr2Cu crystal size increased with annealing time and attained an average size of 20 nm corresponding to the stage of 80% crystallization. In addition, the change in particle size with increasing annealing time exhibited a linear relationship between grain growth time and the cube of the particle size for the Zr2Cu type crystalline phase. This indicates that the crystal growth of the Zr61Al7.5Cu17.5Ni10Si4 alloy belongs to a thermal activated process of the Arrhenius type. The activation energy for the grain growth of Zr2Cu is 155 ± 20 kJ/mol in the Zr61Al7.5Cu17.5Ni10Si4 amorphous alloy. The lower activation energy for grain growth in compared to that for crystallization in Zr65Cu35 440 kJ/mol crystal corresponds to the rearrangement of smaller atoms in the metallic glass, Al or Si (compare to Zr).