Formation of Mg₂Ni nanofibres in a Mg-based metal matrix composite

Abstract

A Mg–Mg₂Ni nano-eutectic and MgO-reinforced Mg-based metal matrix composite (Mg-MMC) was synthesized by in-situ reactions. When a Mg-rich sample containing 20 wt% NiO is sintered at 420°C, MgO, Ni and Mg₂Ni are formed in the Mg matrix. When a sample molten at 550°C is furnace-cooled to room temperature, a lamellar two-phase Mg–Mg₂Ni eutectic is formed, with the Mg₂Ni lamella about 1.5 µm thick. Proeutectic Mg together with the MgO formed in situ act as heterogeneous nuclei for the growth of the Mg–Mg₂Ni eutectic. Quenching the molten sample to room temperature results in a lamellar two-phase eutectic containing Mg₂Ni nanofibres. In the eutectic grown at the Mg grain, the Mg₂Ni nanofibres with a diameter of about 25 nm are bent, whereas in the eutectic grown at the MgO grain, the Mg₂Ni nanofibres with a diameter of about 30 nm are long and straight, while the Mg phase of this eutectic is oxygen enriched. The differences in morphologies between the two Mg–Mg₂Ni eutectics are ascribed to the growth rates of Mg and Mg₂Ni, which differ in the eutectic grown at the Mg grain, but remain similar when growth takes place at the MgO grain.

Acknowledgement

This work was supported by a Hong Kong Special Administration Region Government RGC 2001 Earmarked Research Grant (project code 2150303).