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 mechanicalalloying (MA). The effects of substitution of Mn for Ni on the phase composition and microstructuresofMg2Ni-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 formationof MgNi2 phase and the solid solubility of Mn in Mg2Ni phase is low. The calculation of average crystallitesize and microstrain of Mg2Ni(1−x)Mnx alloys milled for 8 h shows that with the increase of substitutionamount of Mn for Ni from x=0 to x = 0.375, the average crystallite size decreases first from 12.5nm to9.6nm and then increases from 9.6nm to 11.8nm with the minimum 9.6nm obtained at x = 0.25, whilethe microstrain monotonously decreases from 1.39% to 0.82%. SEM has revealed that the sizes of subparticlesthat constitute the powder particles in the composition Mg2Ni0.75Mn0.25 are much smaller thanthose in other compositions.