A new high-toughness Co-based nanocrystalline soft-magnetic alloy capable of large stress-induced anisotropy

Mechanical and magnetic properties for a new Co-base nanocrystalline soft magnetic alloy, Co₈₀Fe_1.5Mn_1.5Nb₈Si₂B₇ at.%, are compared to those of previously studied Co_(80–2x)-Fe_x−Mn_x-Nb₄-Si₂-B₁₄ at.% (where x = 2.3, 2.7, and 4) as cast and stress-annealed ribbons. The new alloy exhibits a fracture toughness,$K_C$, of 58 MPa$\sqrt{m}$ after stress-annealing at 500 °C and a stress-induced/stress-normalized magnetic anisotropy, $K_u/\sigma$, of 0.094 kJ/(MPa$·m^3$), i.e., a value nearly double that of other Co-base nanocrystalline alloys. The bulk magnetostriction, ${\lambda }_s^{bulk}$, of the new composition was also determined to be approximately zero after stress-annealing. XRD was used to identify the nanocrystalline phases in annealed ribbon, and the fracture morphologies were observed via SEM. The fracture surfaces of tough and brittle annealed ribbons contained morphologies indicative of local melting and traditional shear hackle/mist patterns, respectively, suggesting that the iron and manganese concentrations in Co-based nanocomposites influence the alloy’s mechanical properties and processability.