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Comparative study for the formation of the NiAl, TiAl, FeAl intermetallic compounds by mechanical alloying

Abstract:

Mechanical Alloying is an interesting method to obtain intermetallic compounds of nanometric dimensions at room temperature. In this process the alloying behavior varies considerable from one element to another. Different elements take different reaction paths depending on the particular structural characteristics of the starting powders resulting in different phase transformations. In order to study the effect of the structure on the alloying behavior of M-Al compounds (M=Fe, Ni, Ti) elemental powders of Fe (bcc), Ni (fcc), Ti(hcp) were mechanically alloyed to Al in equiatomic ratio, for different periods up to 50h. The characterization of the products was carried by x-ray diffraction, scanning and transmission electron microscopy, for each milling interval. The three systems showed a completely different alloying behavior, for the same milling periods. The formation of the intermetallic AlNi was observed after only one hour of milling which transforms into a fcc-Ni solid solution after prolonged milling. For the Fe-Al the formation of a solid solution of aluminum in iron was observed from 5h onwards. For the Ti-Al system the formation of a hep Ti(Al) solid solution is observed up to 5h of milling followed by an amorphization stage and a transformation to a fee Ti (Al) phase after prolonged milling.