Abstract:The microstructural evolution of a Mg-10Ni-2Mm (molar fraction, %) (Mm=Ce, La-rich mischmetal) hydrogen storage alloys applied with various solidification rates was studied. The results show that the grain size of melt-spun ribbon is remarkably reduced by increasing the solidification rate. The microcrystalline, nanocrystalline and amorphous microstructures are obtained by applying the surface velocities of the graphite wheel of 3.1, 10.5 and 20.9 m/s, respectively. By applying the surface velocity of the graphite wheel of 3.1 m/s, the melt-spun specimen obtains full crystalline with a considerable amount of coarse microcrystalline Mg and Mg₂Ni except for some Mm-rich particles. The amount of nanocrystalline phases significantly increases with increasing the surface velocity of the wheel to 10.5 m/s, and the microstructure is composed of a large amount of nanocrystalline phases of Mg and Mg₂Ni particles. A mixed microstructure containing amorphous and nanocrystalline phases is obtained at a surface velocity of the wheel of 20.9 m/s. The optimal microstructure with a considerable amount of nanocrystalline Mg and Mg₂Ni in an amorphous matrix is expected to have the maximum hydrogen absorption capacity and excellent hydrogenation kinetics.

Key words: hydrogen storage materials; Mg-based alloys; rapid-solidification; microstructure; transmission electron microscopy