THERMALLY ASSISTED SOLID-STATE AMORPHIZATION OF ROD MILLED AL50NB50 ALLOY

Differential thermal analysis, differential scanning calorimetry, optical metallography, scanning electron microscopy, and transmission electron microscopy were used to study the amorphization and crystallization processes of mechanically alloyed Al50Nb50 powder prepared by the rod-milling technique. The results have shown that the crystalline-to-amorphous transformation occurs in three stages. At the intermediate stage of milling, the transformation from crystalline into amorphous was conducted by heating the alloy to 800 K. This transformation has occurred due to a thermally assisted solid-state amorphization between the layers of the elemental starting material of the composite particles. At the final stage of milling, the mechanical driving force which was generated by the rods causes the formation of a homogeneous and uniform amorphous alloy. The amorphization temperature, T(a), and the crystallization temperature, T(x), are determined to be 650 and 1105 K, respectively. Moreover, the enthalpy change of amorphization, DELTA-H(a), and the enthalpy change of crystallization, DELTA-H(x), were evaluated to be - 1.80 kJ/mol and - 13 kJ/mol, respectively. Furthermore, the activation energy of amorphization, E(a), was calculated to be 170 kJ/mol.