Soft magnetic Co-based Co–Fe–B–Si–P bulk metallic glasses with high saturation magnetic flux density of over 1.2 T

Co-based (Co, Fe)75B15Si7P3 bulk metallic glasses (BMGs) without any early transition metal or rare-earth elements have been successfully developed, which possess outstanding soft magnetic properties with high saturation magnetic flux density (Bs) and good mechanical properties. Addition of an appropriate amount of P into a Co75B15Si10 alloy promotes the occurrence of glass transition and increases the stability of the supercooled liquid, and a Co75B15Si7P3 metallic glass exhibits a large supercooled liquid region of 33 K. Subsequent replacement of Co by 15–35 at.% Fe enhances the glass-forming ability (GFA) of the Co75B15Si7P3 alloy, and the BMG rods with diameters up to 2.0 mm are obtained. The improved GFA might be originated from the high thermal stability of the alloy melts as indicated from the large undercoolings. The Co-based (Co, Fe)75B15Si7P3 BMGs possess low coercivity of 0.8–4.6 A/m, high Bs of 1.02–1.24 T, effective permeability of 12700–18500 at 1 kHz, and Curie temperature of 739–789 K, indicating superior soft magnetic properties compared to other reported Co-based BMGs. The BMGs also exhibit high compressive yield strength of 3343–3590 MPa with distinct plastic strain up to 2.7% and high Vickers hardness of 1150–1175. The combination of high GFA and excellent soft magnetic and mechanical properties makes the Co-based BMGs a good prospect of functional materials.