Preparation and properties of Fe-Co-B-Si-Nb-Cr soft-magnetic bulk amorphous alloys

Fe-Co-B-Si-Nb-Cr bulk amorphous alloys with critical diameters up to 4 mm were prepared by copper mold casting method using micro-alloying technology. The glass-forming ability (GFA) and soft magnetic properties of the obtained bulk amorphous alloys were characterized by means of XRD, TEM, DSC, DTA and VSM. Corrosion and mechanical properties of bulk amorphous alloys were measured using potentiodynamic polarization, macro compressive experiment and nanoindentation testing techniques. The results show that the addition of Cr element slightly decreases GFA of Fe-Co-B-Si-Nb alloys, but is very effective in increasing corrosion resistance and improving mechanical properties and soft magnetic properties for the glassy alloys. The copper-mold-cast alloys exhibit high GFA with diameters up to 4 mm. These Fe-based bulk amorphous alloys exhibit high saturation magnetization of 0.81-1.04 T, extremely low coercive force of 0.6~1.6 A/m, Yong's modulus of 200-215 GPa, elastic strain of about 2% and plastic strain of 0.7%, and they also possess ultrahigh fracture strength of 3840-4043 MPa. The plastic deformation of the {[(Fe_0.6Co_0.4)_0.75B_0.2 Si_0.05]_0.96Nb_0.04}₉₆ Cr₄ bulk amorphous alloy at room temperature was studied by depth-sensing nanoindentation technique. It is shown that the deformation behavior of the bulk amorphous alloys depends on the applied loading rate during nanoindentation. Distinct serrated flow was observed in the loading rate range from 0.75 to 3 mN/s. However, it disappeared at a loading rate of 6 mN/s. Furthermore, corrosion measurements show that corrosion rate and corrosion current density of the bulk amorphous alloys in 0.5 mol/L NaCl solution decrease from 7.0×10^-1 to 1.6×10^-3 mm/y and from 3.9×10^-6 to 8.7×10^-7 A/cm², respectively, with increasing Cr content from x=0 to x=4(at%).