Effect of solidification rate and composition on microstructure and crystallization in Al-Ni-La metallic glasses

Al87La7Ni6-xAgx (x = 0,1) alloys, prepared by copper mould
casting and melt-spinning at different wheel speeds, were
studied by X-ray diffraction, scanning electron microscopy,
differential scanning calorimetry and microhardness
measurements. The Cu-mould cast ingot shows a hypereutectic
microstructure. At the highest cooling rate (wheel speed 40 m/
s) the ribbon is completely amorphous, while at lower wheel
speeds mixed structures comprising amorphous and crystalline
phases or only crystalline phases were observed. Both the
ribbons (with and without Ag containing alloys) show two stage crystallization process on annealing. Crystallization
kinetics was analysed by Kissinger and Johnson-Mehl-Avrami
approaches. The low values of activation energy reflect the
instability of these amorphous alloys. Microhardness of all the ribbons was examined at different temperatures and was
correlated with the corresponding evolution of phases.