Amorphous-to-crystalline transformation induced by thermal annealing of a metastable Al₉₀Fe₁₀ composite

Abstract

Crystallization from the amorphous state to metastable crystalline Al₆Fe was induced by thermal annealing of mechanically alloyed Al₉₀Fe₁₀ composite powders (where the composition is given in atomic per cent), which consisted of fcc Al nanocrystals in an amorphous matrix. The microstructural evolution and the transformation kinetics were characterized in detail. A thermodynamic analysis of the transformation was given, showing the nature of the polymorphous crystallization in the amorphous composite. The influence of the pre-existing crystals on crystallization was not morphologically distinctive. The observed linear kinetics law behaviour in combination with an Avrami exponent value of 2.7 ± 0.1 suggest that the growth of a fixed nuclei population at a constant rate in three dimensions governs crystallization. The activation energy for crystallization was found to be close to the activation energy for the diffusion of Fe atoms in A1.