Fachgruppe Nanostrukturierte Materialien    

Melt-spun Al alloys containing 2.7-10 at.% La were studied by means of x-ray diffraction, transmission electron microscopy, electrical resistivity, thermal and microhardness measurements. Fully amorphous structures were only obtained for thin AlLa7.7 and AlLa10 ribbons and exhibit concentration fluctuations. Phase separation into two metastable bcc structures is observed; they appear successively and are finally replaced by the equilibrium phases (fcc)Al and (orthorhombic)Al11La3. The transformation kinetics is analysed in terms of a general Johnson-Mehl-Avrami-Kolmogorov model and of local kinetic parameters. The Avrami exponent monitors changes in the crystallization behaviour; nucleation of the stable phases occurs after partial dissolution of the metastable phases. The low values of the activation energy reflect the high instability of these glasses.