Environmental properties of Zr-based metallic glasses and nanocrystalline alloys

Abstract

Zr-Cu-Ni-Al belongs to the best glass forming systems known; these glasses are suitable as precursor material for nanocrystalline alloys. For an application as hydrogen storage materials for example it is of great interest to know more about these metastable materials in regard to their environmental properties. Corrosion as studied by a salt spray test or anodic polarization in aqueous solutions exhibit a rather high sensitivity with no significant differences between the amorphous and nanocrystalline state. Hydrogen charging was performed electrochemically in a glycerine-phosphoric acid electrolyte. In Zr-Cu-Ni-Al alloys absorption kinetics and storage capacity were found to be very similar for the amorphous and the nanocrystalline phase. In the nanocrystalline alloy consisting mainly of a fcc (big cube) phase with a NiTi2 type structure a hydrogen induced amorphization was observed. Oxidation of metastable Zr-based materials in air was studied below the glass transition temperature at 360°C by thermogravimetry. Oxidation resistance was found to improve very significantly from the amorphous to the nanocrystalline microstructure. The scales formed on both materials consist mainly of columnar ZrO2 with diameter in the nanometer range; Probably including the other metals as a nanocrystalline solid solution.