PHASE TRANSFORMATION PROCESS IN NANOQUASICRYSTALLINE AL-BASED ALLOYS

M GALANO; F AUDEBERT; I STONE; B CANTOR

Simposio; Ismanam 2003; 2003

Nanoquasicrystalline Al-based alloys are alloys composed of sub-micrometre sized icosahedral particles embedded in an aluminium matrix that have shown higher strength at elevated temperature compared with commercial Al alloys. Improvement of the microstructural stability of these alloys is required for enhancing the possibility of technological application. In the present work, an investigation into Al93(Fe3Cr2)7 and Al93Fe3Cr2ETM2 (at%) (with ETM= Ti, V, Nb, Ta) produced by melt spinning, has been carried out with the aim of obtaining new nanoquasicrystalline alloys with improved thermal stability and better mechanical properties at elevated temperatures. Structural characterisation of the as quenched samples was carried out by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM). The thermal stability and decomposition of the icosahedral phase were studied by means of differential scanning calorimetry (DSC) and structural characterisation on heat treated samples at different temperatures using XRD, TEM and chemical analysis by means of energy dispersive X-ray analysis (EDX) in a scanning transmission electron microscope (STEM). In this paper the phase transformation processes of intermetallics precipitating from the super-saturated Al matrix and of the decomposition of the icosahedral phase are discussed. It is observed that the decomposition of the quasicrystalline phase occurs at higher temperature with the increasing melting point of the ETM (Ti, V, Nb and Ta) and those alloys containing Nb and Ta showed the highest stability retaining icosahedral particles even after heat treatment at 5500C.