The mechanical behavior of bulk metallic glasses (BMGs) was investigated by nanoindentation with a spherical indenter. The transition from perfectly elastic behavior to plastic deformation was clearly observed as a pop-in event (sudden displacement excursion) on the load-displacement curves. Hertzian stress analysis was used to describe fully the load-displacement behavior during elastic deformation and to determine the theoretical shear strengths of the BMGs.

Recent advancement in bulk metallic glasses, whose properties are usually superior to their crystalline counterparts, has stimulated great interest in fabricating bulk amorphous steels. While a great deal of effort has been devoted to this field, the fabrication of structural amorphous steels with large cross sections has remained an alchemist’s dream because of the limited glass-forming ability (GFA) of these materials. Here we report the discovery of structural amorphous steels that can be cast into glasses with large cross-section sizes using conventional drop-casting methods. These new steels showed interesting physical, magnetic, and mechanical properties, along with high thermal stability.

In this study, we discovered that a small addition of Y is very effective in improving glass-forming ability of Fe-based alloys. As-cast bulk amorphous alloys containing 2 at.% Y showed large thermal stability, with glass transition temperatures above 900 K and supercooled liquid regions above 55 K, and high strength, with Vickers hardnesses larger than HV 1200. The beneficial effect of Y on glass formation is twofold: (1)Y adjusted the compositions closer to the eutectic and thus lowered their liquidus temperatures, and (2) Y improved the manufacturability of these alloys by scavenging the oxygen impurity from it via the formation of innocuous yttrium oxides.