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

Abstract

The effect of hydrogenation on the local structure of aTi25Hf50Ni25 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 and1.4. For the non-hydrogenated alloy, the local structure was found to be different from thatin the crystalline Ti–Hf–Ni phase. A new icosahedral ordering, similar to that in theTi2Ni crystal, is identified around the nickel atoms. Upon hydrogenation, little change is observedin the environment of the nickel atoms. As in the 3/2 phase and in the Ti–Zr–Ni alloys, theperturbation of the local structure with hydrogenation concerns mainly the environments ofhafnium (zirconium) and titanium atoms. This indicates that the hydrogen atoms sitpreferentially near hafnium (zirconium) and titanium neighbours. Moreover, a drasticdecrease of the disorder parameter for the Hf–Ti correlation could be explained by astiffening of the structure of the glass, possibly due to the formation of a hydrogen network.