SEM and HRTEM study of zirconium-based glass forming alloys cast at various cooling rates

The microstructure of Zr–Ti–Ni–Cu–X (X=Ag,Al) ingots or melt-spun ribbons was investigated. The ingots were analyzed using a scanning electron microscope with an X-ray energy-dispersive spectroscopy system, and the alloy composition was modified to increase the amount of eutectic on expense of primary crystals. High-resolution electron microscopy observation of thin foils from ribbons of a composition near the eutectic show only extremely small ordered aggregates, while ribbons from alloys near the NiTiCu compound contain nanocrystallites. The addition of silver into Zr–Ti–Ni–Cu alloys results in precipitation of spherical silver crystallites in slowly cooled and melt-spun ribbons. However, their presence has no effect on the alloy’s glass forming ability, as they do not serve as nucleation sites for other phases.