Synthesis of nanocrystalline and amorphous phases in complex metallic alloys during mechanical milling

Abstract

The synthesis of nanocrystalline, amorphous and their composite phases in complex metallic alloys (CMAs) appears to be beneficial in order to overcome the brittleness problem of these alloys. Mechanical milling among the various processing techniques, have been adopted for the purpose of synthesizing nano-phase/amorphous and their composites. The aim of the present work is to investigate the stability and phase evolution on some complex metallic alloys during mechanical milling. The milling is carried out in a planetary ball mill at various milling intensity with varying the ball to powder ratio in a suitable milling medium. The samples are characterized with the help of XRD, SEM and TEM. It is found that these alloys can give rise to the formation of nanocrystalline phases of grain sizes to a certain minimum value as well as amorphous phase. At present it is not clear why, given a milling energy, some alloy systems restrict to the formation of nanograin of a particular size and do not lead to the complete formation of amorphous phase. Attempts will be made to discuss the evolution and stability of these nano/amorphous phases based on the modified Miedema model of free energy by including the contribution from grain size effects generated during milling.