Effects of Cu additions on mechanical and soft-magnetic properties of CoFeBSiNb bulk metallic glasses

Abstract A novel ductile [(Co 0.7 Fe 0.3 ) 0.68 B 0.219 Si 0.051 Nb 0.05 ] 99.5 Cu 0.5 bulk metallic glass (BMG) with the strength of 4.4 GPa and the compressive plastic strain of 2.5% was successfully synthesized in this work. We found, by adding tiny Cu (0–0.9 at. %) element, both the plasticity and the saturation magnetization of CoFeBSiNb BMGs can be improved, which is attributed to the existence of ferromagnetic and ductile α-(Fe, Co) nanoparticles in the glass matrix. The abundant of vein patterns and high-density multiple shear bands were observed on the fracture surface of Cu-added Co-based bulk glassy rods. The reason for these results is that the nanoscale particles hinder the propagation of the shear band, promote the generation of multiple shear bands and enhance the plasticity. Our investigations shade a light on understanding the nano-scale precipitation phase enhanced ductility mechanism in high strength BMGs such as Fe- and Co-based BMGs and lead a map for finding new high strength BMGs with high plasticity.