Effect of silicon on the thermal properties of the zirconium-based bulk amorphous alloys

The thermal properties and microstructural development of Zr_65-xAl_7.5Cu_17.5Ni₁₀Si_x alloys during the annealing of amorphous alloys have been investigated by a combination of differential thermal analysis, differential scanning calorimetry, X-ray diffractometry and TEM. The glass transition temperature for the Zr_65-xAl_7.5Cu_17.5Ni₁₀Si_x alloys are measured around 665 K (392°C) with very lager deviation. However, the crystallization temperature increase with increasing the silicon content to 10 at. % and obtains a relative lager temperature interval Δ T_x a bout 67 K. In addition, the value of T_rg the alloys with the addition of silicon present an increasing trend with increasing Si content. The activation energy of crystallization for the alloy 4Si was measured about 350 - 370 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 based alloy (310kJ/mol.). This implies that the silicon additions exhibit the effect of improving the thermal stability for the Zr-based amorphous alloy. The average value of the Avrami exponent n were calculated around 1.94-2.45 for the alloys with silicon additions. This indicates that these six alloys present similar crystallization process, a diffusion controlled growth process with a decreasing nucleation rate.