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

摘要

Ribbons of amorphous Zr_(65-x).Al_(7.5)Cu_(17.5)Ni_(10)B_x 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 Zr_(65-x)Al_(7.5)Cu_(17.5)Ni_(10)B_x alloys were measured around 645 K. The crystallization temperature increased with increasing boron content to 4 at.% and obtained a relative large temperature interval ΔT_x of around 88 K. The calculated T_(rg) for Zr_(65)Al_(7.5)Cu_(17.5)Ni_(10) alloy, Zr_(63)Al_(7.5)CU_(17.5)Ni_(10)B_2 alloy, and Zr_(61) Al_(7.5)Cu_(17.5)Ni_(10)B_4 alloy exhibit the same value of 0.57. The activation energy of crystallization for the Zr_(61) Al_(7.5)CU_(17.5)Ni_(10)B_2 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 Zr_(65) Al_(7.5)Cu_(17.5)Ni_(10) alloy, 1.75 ± 0.15 for Zr_(63)Al_(7.5)Cu_(17.5)Ni_(10)B_2 alloy, and 1.9 ± 90.45 for Zr_(61) Al_(17.5)Cu_(17.5)Ni_(10)B_4 alloy. This indicates that these three alloys exhibit similar crystallization process, a diffusion controlled growth process with a decreasing nucleation rate.