Microstructure and electrochemical properties of melt-spun Nd0.8Mg0.2(Ni0.8Co0.2)3.8 hydrogen storage alloy

The effects of rapid solidification on the microstructure and electrochemical properties of Nd0.8Mg0.2(Ni0.8Co0.2)3.8 alloy were systematically investigated. The microstructure of alloys was characterized by scanning electron microscopy (SEM), X-ray diffractometer (XRD) and transmission electron microscopy (TEM). It was found that the melt-spun Nd0.8Mg0.2(Ni0.8Co0.2)3.8 ribbons became thinner and the average grain size of the ribbons became smaller with increasing wheel speed. A fraction of amorphous phase was observed for the ribbons melt-spun at high wheel speed (≥20 m/s). Microstructural characterization revealed that two phases: (Nd,Mg)2(Ni,Co)7 main phase (Ce2Ni7 type structure) and NdNi5 second phase (CaCu5 type structure), existed in the samples in cast state and melt-spun. The cycle stability of the melt-spun alloys was significantly enhanced as compared with cast alloy, and the sample prepared at wheel speed of 20 m/s exhibited good comprehensive electrochemical properties.