Synthesis of Al-based metastable alloys by mechanical milling Al and amorphous Fe 78 Si 12 B 10 powders
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A. Q. He Laboratory of Atomic Imaging of Solids, Institute of Metal Research, Academia Sinica, Shenyang 110015, China
T. D. Shen, M. X. Quan, and J. T. Wang State Key Laboratory for Rapid Solidified-nonequilibrium Alloys, Institute of Metal Research, Academia Sinica, Shenyang 110015, China (Received 29 March 1993; accepted 23 November 1993)
Syntheses of Al-based metastable alloys from powder mixtures of elemental Al and amorphous Fe78Sii2B10 [x at. % Al + (100 — x) at. % (Fe78Sii2B10)] alloy by mechanical milling (MM) using a planetary ball mill are investigated. X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and transmission electron 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 milled product with a high content of Al (x = 90), nanocrystalline Al and 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 alloys are produced with the disappearance or shrinkage of diffraction peaks of Al in the XRD pattern. Further milling of the powder mixture with 75 at. % Al results in the crystallization of amorphous phase and the formation of nanocrystalline Al 3 Fe type phase. The crystallization products of all as-milled samples are very similar, composed of Ali 3 Fe 4 and AlFe 3 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 milling is diffusion process, but defects and strain also play an important role.
I. INTRODUCTION Within the last few years a lot of interest has been focused on the preparation of amorphous alloys by mechanical alloying. Starting from elemental crystalline powders, a large number of alloy systems, for example, Ni-Nb, 1 Ni-Ti, 2 Al-Fe, 3 and several transition metalZr systems,4 have been investigated. During the early stages, ball milling produces powder particles with a characteristically layered microstructure due to cold welding and repeated mechanical deformation.1-4 Further milling leads to the formation of an ultrafme composite, and finally a true alloying by solid-state reaction occurs, leading to formation of a homogeneous amorphous alloy.5 An example of amorphization of intermetallic compounds by mechanical milling was presented by
'^Present address: Department of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China. 866
J. Mater. Res., Vol. 9, No. 4, Apr 1994
Ermakov et al6 in the Y - C o systems such as YCo 3 , Y 2 Co 7 , YC05, and Y 2 Coi 7 . These intermetallic compounds were milled and found to exhibit the broadened diffraction peak and Mossbauer spectra of an amorphous alloy. During this process, the introduction of defects and bre
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