Synthesis and characterization of nanocrystalline Mg2Ni prepared by mechanical alloying: Effects of substitution of Mn for Ni

The Mg2Ni(1−x)Mnx (x = 0, 0.125, 0.25, 0.375) hydrogen storage alloys have been synthesized by mechanical alloying (MA). The effects of substitution of Mn for Ni on the phase composition and microstructures of Mg2Ni-type alloys have been investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD results of milled samples indicate that substitution of Mn for Ni could inhibit the formation of MgNi2 phase and the solid solubility of Mn in Mg2Ni phase is low. The calculation of average crystallite size and microstrain of Mg2Ni(1−x)Mnx alloys milled for 8 h shows that with the increase of substitution amount of Mn for Ni from x = 0 to x = 0.375, the average crystallite size decreases first from 12.5 nm to 9.6 nm and then increases from 9.6 nm to 11.8 nm with the minimum 9.6 nm obtained at x = 0.25, while the microstrain monotonously decreases from 1.39% to 0.82%. SEM has revealed that the sizes of subparticles that constitute the powder particles in the composition Mg2Ni0.75Mn0.25 are much smaller than those in other compositions.