SYNTHESIS OF AL-BASED METASTABLE ALLOYS BY MECHANICAL MILLING AL AND AMORPHOUS FE78SI12B10 POWDERS

Syntheses of Al-based metastable alloys from powder mixtures of elemen tal Al and amorphous Fe78Si12B10 [x at. % Al + (100 - x) at. % (Fe78Si 12B10)] alloy by mechanical milling (MM) using a planetary ball mill a re investigated. X-ray diffraction (XRD), differential scanning calori metry (DSC), scanning electron microscopy (SEM), and transmission elec tron microscopy (TEM) are used to characterize their structure during the MM process. For the powder mixture with low content of Al (x = 75, 82), fully amorphous material can be obtained by MM, while for the mi lled product with a high content of Al (x = 90), nanocrystalline Al an d amorphous phases are obtained. During the initial milling stage, the Al atoms are dissolved into the amorphous Fe78Si12B10 matrix by heavy deformation. Consequently, the Al-enriched homogeneous amorphous allo ys are produced with the disappearance or shrinkage of diffraction pea ks of Al in the XRD pattern. Further milling of the powder mixture wit h 75 at. % Al results in the crystallization of amorphous phase and th e formation of nanocrystalline Al3Fe type phase. The crystallization p roducts of all as-milled samples are very similar, composed of Al13Fe4 and AlFe3 phases. It is suggested that the kinetics of nucleation and growth favor the formation of amorphous phase due to the existence of amorphous phase initially. The amorphization reaction by mechanical m illing is diffusion process, but defects and strain also play an impor tant role.