Crystallization kinetics of the Co₇₇Si₁₁B₁₂ amorphous alloy

Chem. Met. Alloys 14 (2021) 1-6

https://doi.org/10.30970/cma14.0410

M.M. LOPACHAK, L.M. BOICHYSHYN, V.K. NOSENKO, B.Ya. KOTUR

The amorphous metal alloy (AMA) Co₇₇Si₁₁B₁₂ obtained by melt-spinning was investigated by X-ray diffraction (XRD) and differential scanning calorimetry (DSC) at a speed of 5, 10, and 20 K/min. The DSC curves show three stages of crystallization for all heating rates in the range of 700-900 K, which are associated with the formation of clusters and crystalline phases. The first exothermic peak, which indicates the process of nanocrystallization, occurs in the temperature range from 761 to 814 K at different heating rates. Annealing the sample for 1 h at 765 K caused changes in the XRD profile: the pre-peak at 2θ ≈ 16.5° and the other three broad peaks at 2θ ≈ 43°, 55° and 82° became sharper, indicating the formation of different clusters in the amorphous matrix and nanocrystallization of fcc β-Co with the lattice parameter a ≈ 3.51 Å embedded in the amorphous matrix. The Kissinger method was applied for calculating the activation energies for the first, second and third DSC peaks. The activation energy E_a of nucleation and growth of nanocrystals in AMA Co₇₇Si₁₁B₁₂ are 347 and 374 kJ/mol, respectively. The S-like form of the dependences of the volume fraction of the crystalline phase for the first exothermic peak (α) upon temperature (T) indicates the predominance of diffusion-controlled processes at high heating rates. According to the Matusita model, the value of the growth parameter m showed that the growth of Co nanocrystals in AMA occurs by a three-dimensional mechanism, and the value of p = 0.5 indicates a diffusion-controlled crystallization.

XRD profiles of AMA Co₇₇Si₁₁B₁₂ for the as-quenched sample (green) and for the same sample annealed at 765 K (blue).

Keywords

Amorphous metallic alloys / Nanocrystallization / Cobalt / X-ray diffraction / Differential scanning calorimetry