Characterization and first principle study of ball milled Ti-Ni with Mg doping as hydrogen storage alloy

Microstructures, electrochemical properties of Ti-Ni and ternary Ti-Ni-Mg alloy were studied after they had been submitted to high-energy ball milling. Influence of milling time and Mg addition on the microstructures of the mechanically milled Ti-Ni alloys was investigated by XRD, SEM. Cycling performances of the electrodes prepared by the milled powders were measured under galvanostatic conditions. It is found that the binary Ti-Ni alloy undergoes a refinement, dynamical recrystallization and amorphization process. With doping of Mg to the starting Ti-Ni powders, an FCC Ti-Mg structure was detected along with the main TiNi BCC phase. First principle calculation was applied to compare the thermodynamic stabilities of several binary alloys involving Ti, Ni and Mg. It was decided that the final product of milling Mg doped Ti-Ni contains an FCC structured TiMg3 phase, which damages electrochemical performance in general as a result of coating effect on the TiNi phase.