Formation of nanocrystalline aluminum in Al-Y-Fe amorphous alloys

A microstructure composed of nanocrystalline aluminum in a matrix of amorphous material has been produced via rapid solidification processing of Al-Y-Fe alloys. Melt-spun ribbon (MSR) of the nominal compositions Al-5 at.% Y-5 at.%Fe and Al-7 at.%Y-5 at.%Fe were characterized by differential scanning calorimetery (DSC), scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The Al-5 at.%Y-5 at.%Fe as-solidified MSR exhibits two phase microstructure of nanocrystalline aluminum and amorphous material. The A1-7 at.%Y-5 at.%Fe as-solidified MSR exhibits a microstructure that is predominately amorphous with a sparse distribution of large, micron size intermetallic crystals. Thermal cycling of the as-solidified MSR showed an exothermic signal on first heating at around 200 degrees C for the Al-5 at.% Y-5 at.%Fe alloy and around 280 degrees C for the Al-7 at.%Y-5 at.%Fe alloy. The first exothermic reaction has been determined to be from the formation and growth of nanocrystalline aluminum in the Al-7 at.%Y-5 at.%Fe alloy and growth of the nanocrystalline aluminum in the Al-5 at.% Y-5 at.%Fe alloy. Further heating of both alloys resulted in crystallization of the remaining amorphous material. The relationship between the formation of nanocrystalline aluminum and the reported observance of a glass transition in the Al-Y-Fe alloys is examined.