Hydrogenation and Crystallization of Zr-Cu-Ni-Al Glasses

Abstract

Zr-Cu-Ni-Al belongs to the best glass forming systems known. Hydrogen charging was performed electrochemically in a 2:1 glycerin-phosphoric acid electrolyte. In comparison to binary Zr-Ni glasses the absorption kinetics in amorphous Zr-Cu-Ni-Al were found to be slower, but the storage capacity is similar. Desorption is hindered by the formation of thin ZrO₂ layers. Partial replacement of Ni by Pd in an amorphous Zr_{68 5}Cu₁₃Ni₁₁Al_7.5 alloy was found to change the absorption behavior to a faster kinetic and to improve the desorption.

The influence of hydrogen on the thermal stability was studied by DSC as well as by xray diffraction and TEM. Hydrogen was observed to play an important role. With increasing H/M ratio amorphous Zr_69.5Cu₁₂Ni₁₁Al_7.5 was found to transform during annealing above the glass transition temperature into a quasicrystalline structure with decreasing grain size until a nanocrystalline microstructure is achieved. Above a hydrogen content of H/M = 0.05 instead of quasicrystals a tetragonal phase with lattice parameters close to those of Zr²Ni is formed. At very high hydrogen contents phase separation is assumed to take place followed by the formation of nanocrystalline ZrH² and other phases with reduced Zr content.