Icosahedral order in Amorphous and Nanostructured Al-Fe based Alloys

FERNANDO AUDEBERT; FABIANA SAPORITI; MARINA GALANO

Paris

Simposio; Ismanam 2005; 2005

Al-based alloys produced by rapid solidification can be obtained with different kinds of microstructures which combine amorphous, crystalline and quasicrystalline phases. Therefore it is possible to obtain alloys with excellent corrosion behaviour, high mechanical strength or with superplasticity behaviour among other properties with great potential for technological applications. Thus, it is very important to know which the effect of each alloy element is in order to obtain a determined microstructure. The microstructure of a rapid solidified alloy is mainly controlled by the nucleation process. Then, in order to achieve a good structural control on the amorphous and nanostructured alloys the study should be focused on the liquid structure and the nucleation process. An Al-Fe alloy was study by molecular dynamic simulation and was observed an increasing of icosahedral cluster as the undercooling increases. The melt-spun Al-Fe alloy was also characterised by X-ray diffraction and Mössbauer Spectroscopy. The effect of different alloy elements on the Al- Fe based alloy was studied. It was observed that elements as V, Cr and Nb stabilised the icosahedral order whereas Ni and Sb led to nucleate crystalline phases. Moreover, it was observed that the use of Nb in an Al-Fe-Cr based nanoquasicrystalline alloys, which are composed by nanoicosahedral particles embedded in an α-Al matrix, stabilised the icosahedral phase delaying its decomposition at higher temperature. The dissolving process of the icosahedral particles was followed by means of in-situ transmission electron microscopy. The results suggest that Al-Fe icosahedral clusters are formed in the undercooled liquid and this order can be modified or stabilised depending of the alloy elements.