Simultaneous Improvement of Glass-Forming Ability and Ductility in Co-Based BMGs Through Si/Fe Microalloying

Cobalt-based bulk metallic glasses (Co-based BMGs) offer a combination of high strength, corrosion resistance, and soft magnetic properties, yet their limited glass-forming ability (GFA) and poor room-temperature ductility restrict broader application. In this study, a microalloying strategy was applied to the Co61Nb8B31 base composition to develop Co-Nb-B-Si and Co-Fe-Nb-B-Si systems. The effects of Si addition and Fe substitution on GFA, thermal stability, and mechanical properties were systematically investigated. Si doping combined with Co/B ratio tuning broadened the supercooled liquid region and increased the critical glass-forming diameter from 1 mm to 3 mm. Further addition of 5 at.% Fe expanded the supercooled liquid region and enabled the fabrication of a fully amorphous plate with 1 mm thickness. The optimized Co63Nb8B27Si2 alloy exhibited a compressive strength of 5.18 GPa and a plastic strain of 3.81%. Fracture surface analysis revealed ductile fracture features in the Si-containing alloy and brittle characteristics in Fe-rich compositions. These results demonstrate that microalloying is effective in optimizing the balance between GFA and mechanical performance of Co-based BMGs, offering guidance for composition and processing design.