MORPHOLOGICAL AND CALORIMETRIC STUDIES ON THE AMORPHIZATION PROCESS OF ROD-MILLED AL50ZR50 ALLOY POWDERS

Amorphous Al50Zr50 alloy powders have been prepared by rod-milling technique using mechanical alloying (MA) method. The amorphization and crystallization processes of the alloyed powders were followed by optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), differential thermal analysis (DTA), and differential scanning calorimetry (DSC). The results have shown that the formation of amorphous Al50Zr50 alloy powders occurs through three stages, agglomeration, disintegration, and homogenization. At the disintegration stage, the alloyed powders contain many fine layers of Al and Zr. An amorphous phase has been formed at about 880 K as a result of heating these layered particles in a thermal analyzer. The crystalline-to-amorphous transformation at this stage of milling is attributed to a thermally assisted solid-state amorphizing reaction. The present study corroborates the similarity of the amorphization process through the MA with the solid-state interdiffusion reaction in multilayered thin films. The amorphization temperature, T(a), and the activation energy of amorphization, E(a), are 675 and 156 kJ/mol, respectively. In addition, the enthalpy change of amorphization, DELTA-H(a), was evaluated to be -3.5 kJ/mol. On the other hand, the crystallization temperature, T(x), and enthalpy change of crystallization, DELTA-H(x), were 1000 K and -68 kJ/mol, respectively.