Local structure in Ti-Hf-Ni metallic glasses and its evolution with hydrogenation

The effect of hydrogenation on the local structure of a Ti ₂₅Hf₅₀Ni₂₅ amorphous alloy was studied by extended x-ray absorption fine structure (EXAFS) measurements. The samples were loaded to different hydrogen-to-metal ratios, H/M, 1.2 and 1.4. For the non-hydrogenated alloy, the local structure was found to be different from that in the crystalline Ti-Hf-Ni phase. A new icosahedral ordering, similar to that in the Ti₂Ni crystal, is identified around the nickel atoms. Upon hydrogenation, little change is observed in the environment of the nickel atoms. As in the 3/2 phase and in the Ti-Zr-Ni alloys, the perturbation of the local structure with hydrogenation concerns mainly the environments of hafnium (zirconium) and titanium atoms. This indicates that the hydrogen atoms sit preferentially near hafnium (zirconium) and titanium neighbours. Moreover, a drastic decrease of the disorder parameter for the Hf-Ti correlation could be explained by a stiffening of the structure of the glass, possibly due to the formation of a hydrogen network.