Effect of Ni content on the structure and hydrogenation property of mechanically alloyed TiMgNix ternary alloys

In this study, TiMgNix samples (x = 0.2, 0.4, 0.6, 0.8, 1) have been prepared by mechanical alloying using a planetary high-energy ball mill. The structural transformations were characterized by XRD and indicated that all the as-milled TiMgNix alloys consist of mixtures of crystalline Mg and amorphous Ti-Ni-(Mg) phase. TEM analyses also show that nanocrystallites and amorphous phases coexist in the as-milled TiMgNi alloy. Electrochemical test shows that the TiMgNi composition yields the highest discharge capacity. The discharge capacities and activation properties of TiMgNix alloys linearly increase with increasing Ni content. The MgTiNi0.8 composition boasts the best cycling property which is consistent with its XRD pattern after the electrochemical test. No decomposition nor crystallization are found after 21 consecutive charge/discharge cycles which implies that the as-milled TiMgNix alloys possess a good corrosion resistance in alkaline electrolytes. PCI measurements were carried out at 598 K and 648 K on the TiMgNi composition. The pressure plateau during hydrogen absorption is raised by two steps and its level increases with increasing temperature. The hydrogen absorption capacity of TiMgNi is around 1.3 weight %. XRD analyses show that the dehydrogenated TiMgNi sample consists of TiH2, Mg, Mg2Ni and TiNi3, in which Mg and Mg2Ni are identified as the hydrogen absorption phases.