Hydrogenation of Ti–Zr–Ni quasicrystals synthesized by mechanical alloying

Abstract

Mechanical alloying of a Ti 45Zr 38Ni 17 powder mixture formed an amorphous phase, but subsequent annealing caused the formation of an icosahedral (i) quasicrystal phase with a small amount of the Ti 2Ni-type crystal phase. After high-pressure hydrogenation at 573 K at a hydrogen pressure of 3.8 MPa, the amorphous phase transformed to a TiH 2-type hydride, while the i-phase was structurally stable even after the hydrogenation. The maximum hydrogen concentration for the high-pressure hydrogenation was the same (hydrogen-to-metal atom ratio ≈1.5) for the i-phase and amorphous powders, suggesting structural similarities between the i-phase and the amorphous phase. Pressure–composition isotherms (PCTs), measured under low-pressure hydrogenation at a temperature of 423 K, showed sloping plateau-like features at equilibrium hydrogen pressures lower than 1 kPa for both the i-phase and amorphous powders. The plateau-like region for the i-phase powder was steeper and narrower than that for the amorphous powder, indicating a slight difference in site energy distribution of hydrogen in the i-phase and the amorphous phase.