Gaseous hydrogen charging of Zr–Cu–Ni–Al glasses and quasicrystals

Abstract

Metallic glasses as well as quasicrystalline alloys are new materials with very promising properties. Zr-based metallic glasses for example are used in a number of applications due to their superior mechanical properties, e.g. for golf clubs or penetrators. Zr-based glasses as well as quasicrystals, however, have been observed only recently to store hydrogen up to a content close to that of best crystalline materials, thus opening a promising new field for application. The objective point of our present research is to investigate in detail hydrogen absorption in amorphous and quasicrystalline Zr69.5Cu12Ni11Al7.5 from the gas phase and to study the influence of the microstructure on hydrogenation. However, as during hydrogenation concentration changes are expected to move the metastable materials out of their stability range, these processes might be accompanied by phase transformations. Therefore, special emphasis was also being given on the influence of hydrogenation on the microstructure and thermal stability, also in comparison with alloys hydrogenated electrochemically. Our results show that hydrogen in the amorphous alloy does change the phase evolution. Instead of forming first the quasicrystalline phase followed by the stable crystalline intermetallics at higher temperatures, these hydrogenated samples crystallize to Zr-hydrides. We were, however, not able to prove whether the amorphous samples were truly amorphous or nanocrystalline after hydrogenation. In (partially) quasicrystalline alloys the hydrogenation from the gas phase does not result in transformations into the approximants or amorphization prior to the formation of crystalline hydrides as known from electrochemical charging.