Enhancement of glass-forming ability and thermal stability of a soft magnetic Co75B25metallic glass by micro-alloying Y and Nb

Soft magnetic Co-based Co-Y-Nb-B bulk metallic glasses (BMGs) without Fe have been developed by micro-alloying Y and Nb into a Co(75)B(25)alloy. First, addition of 3-4 at.% Y promotes the occurrence of glass transition and increases the supercooled liquid stability and magnetic softness. Co(71.5)Y(3.5)B(25)metallic glass possesses a large supercooled liquid region (Delta T-x) of 33 K and low coercivity (H-c) of 1.5 A/m. Subsequent alloying 2-4 at.% Nb into Co(71.5)Y(3.5)B(25)alloy further enlarges Delta T(x)to 50 K, lowersH(c)to 0.9 A/m, and enables the formation of BMGs with a critical sample diameter up to 2.0 mm. The alloying Nb causes the formation of complex (Co, Nb, Y)(23)B(6)competing phase during crystallization and widens the melt undercooling during solidification, which improves the supercooled liquid stability and glass-forming ability, respectively. Co-Y-Nb-B BMGs also exhibit good soft magnetic and mechanical properties, i.e., lowH(c)of 0.9-1.2 A/m, relatively high saturation magnetic flux density of 0.36-0.57 T, high yielding strength of 3877-3930 MPa with plastic strain of 0.2%-0.3%, and high Vickers hardness of 1156-1201. The developed soft magnetic Co-based BMGs are promising for applications as structural and functional materials.