Role of Fe substitution for Co on thermal stability and glass-forming ability of soft magnetic Co-based Co-Fe-B-P-C metallic glasses

Soft magnetic Co-based bulk metallic glasses (BMGs) with large supercooled liquid region (delta T-x) of 47 K and high saturation magnetic flux density (Bs) up to 1.21 T have been developed in a new Co-Fe-B-P-C alloy system without early transition metal and rare earth elements. Substitution of Co by 10-35 at.% Fe in a Co75B10P7.5C7.5 alloy promotes the occurrence of glass transition and enhances the stability of supercooled liquid and glass-forming ability (GFA). The delta T-x of 37-47 K and a critical sample diameter up to 1.2 mm can be achieved for Co40-55Fe20-35B10P7.5C7.5 BMGs. The improved thermal stability and GFA are attributed to complicated primary crystallization phases and stabilized alloy melts, respectively. The addition of Fe enhances the Bs of the Co-based BMGs from 0.79 to 1.21 T, and increases coercivity from 1.1 to 7.2 A/m. The Co-based BMGs also exhibit high yield strength of 3243-3665 MPa with plastic strain up to 2.3% and low viscosity of around 3.0 x 109 Pa.s in the supercooled liquid state.