Structural characterisation and stability of new nanoquasicrystalline Al-based alloys

M GALANO; F AUDEBERT; I STONE; B CANTOR

Congreso; Rapidly Quenched & Metastable Materials; 2002

Nanoquasicrystalline Al-based alloys have been studied intensively in the last decade because of their promising mechanical properties. Recently a quaternary nanoquasicrystalline alloys with improved thermal stability and higher mechanical properties at elevated temperature were reported. This work describe a study of the influence of the fourth component (Ti, V, Nb, Ta) on an Al-Fe-Cr nanoquasicrystalline alloy. Melt-spun samples were produced and their structure was characterised by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM). The instability and the decomposition were studied by means of differential scanning calorimetry, and annealed samples were analysed by XRD and TEM. All the alloys showed a microstructure consisting of a spherical icosahedral phase embedded in an fcc-Al matrix. The fourth component produced a significant refinement of particle size and also improved the stability of the Al-Fe-Cr nanoquasicrystalline alloy. The quaternary quasicrystalline decomposition was observed at higher temperature than for the ternary alloy with an exothermic weak peak. The alloy containing Ta showed a multimodal transformation with a peak between two to three times weaker than the other alloys. The influence of different fourth elements on the microstructure formation and its stability is discussed. In order to correlate the structure with the mechanical properties, microhardness measurements were taken on the as-spun and annealed samples. The results of the microstructure characterisation and the microhardness values on samples heat treated at different temperatures are also discussed.