Crystallization characteristics of the Ti₅₃Cu₄₇ amorphous alloy

A thin Ti₅₃Cu₄₇ amorphous ribbon was prepared by rapid quenching from the melt. The crystallization behavior was investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The DSC results indicated that the activation energy for crystallization was 170 or 150 kJ/mole (1.76 or 1.55 eV/atom) based on the Kissinger or Arrhenius plot, respectively, which is close to that of chemical diffusion in the TiCu alloy: 166 kJ/mol (1.72 eV/atom). The Johnson-Mehl-Avrami (JMA) plot exhibited a linearity, with an exponent of n=2.0 ±0.2. The XRD patterns revealed the transformation to the equilibrium γ-TiCu phase. However, broad peaks due to nanocrystalline grains were not observed. From the TEM analysis, there was a metastable phase with an fcc structure based on the Cu structure pre-existing in the as-quenched ribbon. Only a few TiCu particles in the nanoscale dimension were observed to precipitate from the amorphous matrix upon both continuous and isothermal heatings. A theoretical calculation demonstrates that amorphous Ti₅₃Cu₄₇ has a very low nucleation frequency and thus, a low tendency to form nanocrystals.