High glass forming ability correlated with microstructure and hydrogen storage properties of a Mg―Cu―Ag―Y glass

Thermal characterization of an as-cast Mg sub(54)Cu sub(28)Ag sub(7)Y sub(11) bulk metallic glass revealed that this alloy exhibits excellent glass forming ability. High-resolution X-ray diffraction study and transmission electron microscopy show that heating and isothermal annealing treatment results in the nucleation of nanocrystals of several phases. The average size of these nanocrystals ( similar to 15-20 nm) only slightly varies with prolonged annealing, only their volume fraction increases. High-pressure calorimetry experiments indicate that the as-cast fully amorphous alloy exhibits the largest enthalpy of hydrogen desorption, compared to partially and fully crystallized states. Since the fully crystallized alloy does not desorb hydrogen, it is assumed that hydrogen storage capacity correlates only with the crystalline volume fraction of the partially crystallized Mg sub(54)Cu sub(28)Ag sub(7)Y sub(11) BMG and additional parameters (crystalline phase selection, crystallite size, average matrix concentration) do not play a significant role.