Microstructural evolution of rapid solidified Al-Ni alloys

Abstract

In this study, Al-Ni alloy ribbons in hypoeutectic, euctectic and hypereutectic compositions were obtained by melt spinning. The microstructural changes of the samples, from the as-cast to rapid solid-ification processes at different Cu wheel tangential velocities were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The rapid solidification caused morphological transformation of the Al-Al3Ni microstructure from acicular in the as-cast condition to globular in the melt spun ribbons and the growth of the metastable Al9Ni2 intermetallic compound, which acted as reinforcing particles. Due to the increment of the Ni content and the presence of these intermetallic compounds, with size of ~5nm, distributed in the aluminum matrix, the hardness of the alloys significantly increased from the hypoeutectic (90 VHN) to the hypereutectic (205VHN) composition.