Influence of Gd and Fe on crystallization of Al87Y5Ni8 amorphous alloy

Crystallization of amorphous Al-based alloys (Al-Y-Gd-Ni-Fe) was investigated by applying differential scanning calorimetry (DSC), X-ray diffraction (XRD) and high resolution electron microscopy (HREM). It was shown that the crystallization in the examined alloys proceeds in three stages (DSC maxima). The two first stages are attributed to formation of solid solution of fcc Al(RE) nanograins in amorphous matrix. In the third stage the precipitation of ternary compound Al₁₉Ni₅RE₃ of the orthorhombic Al₁₉Ni₅Gd₃-type structure was observed. A partial substitution of Ni by Fe causes a change of stoichiometry and crystal structure of the ternary compounds: Al₈TM₄RE (TM = Fe, Ni; RE = Y, Gd) of the tetragonal ThMn₁₂ (Al₈Mn₄Ce)-type structure. A partial replacing of Y atoms by Gd in the Al₈₇Y₅Ni₈ based alloy shifts the Al(RE) nanocrystallization to lower temperatures. In contrast to this a partial replacing of Ni by Fe shifts the nanocrystallization to higher temperatures.