The effect of boron on the thermal properties of the zirconium-based bulk amorphous alloys

Ribbons of amorphous Zr65−xAl7.5Cu17.5Ni10Bx alloys with 0.1 mm thickness were prepared by melt-spinning. The thermal properties and microstructural development during the annealing of amorphous alloys have been investigated by the combination of differential thermal analysis (DTA), differential scanning calorimetry (DSC), high-temperature optical microscope, X-ray diffractometry (XRD), and transmission electron microscopy (TEM). The glass transition temperature for the Zr65−xAl7.5Cu17.5Ni10Bx alloys were measured around 645 K. The crystallization temperature increased with increasing boron content to 4 at.% and obtained a relative large temperature interval ΔTx of around 88 K. The calculated Trg for Zr65Al7.5Cu17.5Ni10 alloy, Zr63Al7.5Cu17.5Ni10B2 alloy, and Zr61Al7.5Cu17.5Ni10B4 alloy exhibit the same value of 0.57. The activation energy of crystallization for the Zr61Al7.5Cu17.5Ni10B2 alloy was about 360 or 380 kJ/mol, as determined by the Kissinger or Avrami plot, respectively. These values are about 20% higher than the activation energy of crystallization for the base alloy (314 kJ/mol as determined by the Kissinger plot). The average value of the Avrami exponent n were calculated to be 1.96±0.25 for Zr65Al7.5Cu17.5Ni10 alloy, 1.75±0.15 for Zr63Al7.5Cu17.5Ni10B2 alloy, and 1.9±90.45 for Zr61Al7.5Cu17.5Ni10B4 alloy. This indicates that these three alloys exhibit similar crystallization process, a diffusion controlled growth process with a decreasing nucleation rate.