A study on improving the cycling stability of (Ti_0.8Zr_0.2)(V_0.533Mn_0.107Cr_{0.1 6}Ni_0.2)₄ hydrogen storage electrode alloy by means of annealing treatment: I. Effects on the structures

The effects of annealing treatment on the alloy structures of the hydrogen storage electrode alloy (Ti_0.8Zr_0.2)(V_0.533Mn_0.107Cr_{0.1 6}Ni_0.2)₄ have been investigated in this part. In the as-cast alloy, there are three phases: the C14 Laves phase with hexagonal structure, the V-based solid solution phase with BCC structure and the TiNi-based third phase with BCC structure, as determined by XRD and EDS analysis. The C14 Laves phase forms a continuous matrix, the V-based solid solution phase is the main phase in dendritic structure, and the TiNi-based third phase is precipitated both in the C14 Laves phase and in the V-based solid solution phase and tends to disappear after annealing treatment. The annealing treatment makes the composition of the alloy more homogeneous by redistribution of elemental constituents. Additionally, the annealing treatment leads to an increase of the lattice parameters and unit cell volumes of both the C14 Laves phase and the V-based solid solution phase and also the growth of the dendrites.