Effect of La content on the room temperature ageing behavior of Al90-xNi6La4+x (x = 0 to 3) metallic glasses

The ageing behavior of Al90-xNi6La4+x (x = 0 to 3) amorphous alloys under ambient temperature (20 - 50 °C) has been studied. Partial crystallization has been observed in all alloys after several years of ageing under ambient conditions especially in Al90Ni6La4 and Al89Ni6La5 alloys, where the onset of crystallization temperatures are comparatively lower. The transformations have been studied by differential scanning calorimetry, x-ray diffraction and transmission electron microscopy. These alloys showed two-stages of crystallization upon heating. A significant decrease of first stage of crystallization enthalpy was observed after 5.5 years of room temperature ageing and showed a mixed structure containing fcc-Al nanocrystals (20-40 nm) in an amorphous matrix. The results are explained in terms of transformation kinetics at the ageing temperatures.