Effect of annealing on microstructure and hydrogenation properties of TiFe + X wt% Zr (X = 4, 8)

The effect of annealing on the hydrogenation characteristics of the TiFe alloy was investigated. Pellets of TiFe + X wt% Zr (X = 4, 8) were synthesized by arc melting, using industrial grade Fe (ASTM 10005) and Ti (ASTM B265 grade 1) and annealed at 1173 K for 24 h under argon atmosphere. Crystal structure and lattice parameters were determined by X-ray diffraction (XRD) pattern. Scanning electron microscopy (SEM) image of these alloys showed important differences in the microstructure before and after annealing. The main effect of annealing was to reduce the scale of the secondary phase. Change of composition for the TiFe phase and the secondary phases was relatively limited. Despite the relatively minor changes in crystal structures, the first hydrogenation kinetics was much slower and hydrogen capacity smaller for annealed samples compared to their as-cast counterparts. The mechanism responsible for the degradation of hydrogenation kinetics is still unclear but it may be due to modification in the chemical composition of the interface between the TiFe phase and the secondary phase.