Local Order in Amorphous and Nano-Quasicrystalline Alloys

FERNANDO AUDEBERT; FABIANA SAPORITI; MARINA GALANO; PAUL QUINN; M. BOUDARD

Simposio; ismanam 2010; 2010

Rapid Solidified (RS) Al-based alloys can be obtained with several types of microstructures which combine amorphous, crystalline and quasicrystalline phases. Therefore, it is possible to obtain alloys with an excellent combination of properties, like high strength and toughness with good corrosion behaviour. Alloys with these characteristics have great potential for technological applications. The microstructure of these alloys is mainly controlled by nucleation process during the rapid solidification. Therefore, the chemical composition is a key factor for the microstructure and properties obtained in the RS Al-based alloys. Several alloys have been studied with a combination of experimental and modeling techniques, for instance using Mössbauer Spectroscopy (MS), XRD, EXAF, TEM and Molecular Dynamic Simulation (MDS). The total structure factors and the reduced atomic distribution functions were used in the comparative analysis. Moreover, cluster analyses at liquid and undercooled liquid states were performed using the Honeycutt-Andersen method. The results have been discussed against the structure of several known intermetallic compounds of the related systems. It was observed that alloys containing Ni do not show icosahedral phase, however this phase can be obtained in several Al-based alloys containing Fe, Cr or V as the main alloying elements. Moreover, it was observed that amorphous Al-based alloys containing Fe have higher fractions of icosahedral clusters than the ones containing Ni, even at the liquid state near the melting point. Third alloys elements have important effects on the phases and microstructure of the RS Al-based alloys. Some elements were found to stabilize an amorphous phase with a strong icosahedral local order; others lead to form metastable icosahedral particles with high stability at elevated temperature. Other elements showed a great GFA forming amorphous phases with lower fraction of icosahedral clusters. A guidedance of the alloying elements effect on the cluster formation during the rapid solidification is given.