Microstructures and electrochemical characteristics of Mm0.3Ml0.7Ni3.55Co0.75Mn0.4Al0.3 hydrogen storage alloys prepared by mechanical alloying

The as-cast alloy with the composition of Mm0.3Ml0.7Ni3.55Co0.75Mn0.4Al0.3 prepared by induction melting was milled for 6, 15, 40 and 50 h in this work. The microstructures of alloys were analyzed by XRD and DSC. Two broadening effects of XRD peak caused by crystallite and microstrain were separated by approximate function method and least square method. Crystallite sizes and microstrains of the alloys were calculated. The results show that alloys milled for 6 h or 15 h consist of nanocrystalline and polycrystalline phase. Lattice parameters (a, c) and volumes of alloy increase with the increasing milling time, whereas the ratio of c/a keep constant. Moreover, the crystallite sizes decrease and the microstrains in the alloys increase first and then decrease with the increase of milling time. The alloys milled for 40 h or 50 h transform partly into amorphous structures. The maximum discharge capacities of alloys decrease with the increase of milling time. The cycle stabilities of the milled alloys are better than those of the as-cast. And they increase with the increasing milling time.