High-Energy Ball Milling of All-Based Alloys

摘要

Nanocomposites with an amorphous matrix containing metallic nanocrystals can be obtained through the controlled crystallisation of amorphous alloys. The microstructural control and knowledge of phase transformations associated with the amorphous precursors are important stages for development of such nanocomposites and in the present work we performed high-energy milling to produced the following Al-based amorphous alloys: Al_(90)Fe_5Nb_5, Al_(90)Fe_7Nb_3, Al_(90)Fe_5Cr_5, Al_(90)Fe_7Zr_3. Characterisation of the different mixtures as a function of milling time was accomplished by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Crystallite size variations after milling at different times were measured by X-ray peak broadening analysis and the crystallisation process or recrystallisation of the milled powders were followed by differential scanning calorimetry. Milling of all alloys, resulted in partial amorphisation and also in intermetallic compounds formation. The crystallisation temperatures of the primary phase and intermetallic compounds were found to be very closed for most alloys, what makes the production nanocomposite unfeasible. However for Al_(90)Fe_7Zr_3 milled alloy, crystallisation occurred in two distinct stages with significant differences in the crystallisation temperatures of the different phases presenting good perspectives for metallic nanocomposites development.