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In this study, the influence of Fe doping on the microstructure and mechanical properties of Gd–Al–Co “metallic glass” fibers (MGF) was systematically investigated, and a fracture mechanics model was constructed based on the fracture morphology of MGF. Furthermore, the mechanism by which Fe doping improves the mechanical properties was revealed. The results indicate that the Gd–Al–Co–Fe series MGF has a typical amorphous structure, and with an appropriate amount of Fe increases the order degree of structure ψ, indicating that a small number of nanocluster micro-regions are formed on the amorphous matrix. With an increase in Fe doping, the tensile strength of MGF presents an initial increase and subsequent decrease. The tensile strength, Rm, of the GdAlCoFe2 MGF was the largest (up to 1199 MPa), and its fracture reliability was also superior (the threshold value of fracture was 581.93 MPa). The tensile fracture of the Gd–Al–Co–Fe series MGF is a flat fracture, showing the characteristics of brittle fracture, with vein-shaped patterns, splitting, and shear bands. A specific amount of nanocluster micro-regions formed by Fe doping effectively hindered the growth rate of crack tips during the stretching and deformation of the microfibers, and significantly improved the mechanical properties of the Gd–Al–Co–Fe series MGF. This study lays the foundation for its engineering applications in the fields of mechanics and machinery.

Herein, the effect of Ni-doping amount on microstructure, magnetic and mechanical properties of Fe-based metallic microwires was systematically investigated further to reveal the influence mechanism of Ni-doping on the microstructure and properties of metallic microwires. Experimental results indicate that the rotated-dipping Fe-based microwires structure is an amorphous and nanocrystalline biphasic structure, the wire surface is smooth, uniform and continuous, without obvious macro- and micro-defects that have favorable thermal stability, and moreover, the degree of wire structure order increases with an increase in Ni-doping amount. Meanwhile, FeSiBNi2 microwires possess the better softly magnetic properties than the other wires with different Ni-doping, and their main magnetic performance indexes of Ms, Mr, Hc and μm are 174.06 emu/g, 10.82 emu/g, 33.08 Oe and 0.43, respectively. Appropriate Ni-doping amount can effectively improve the tensile strength of Fe-based microwires, and the tensile strength of FeSiBNi3 microwires is the largest of all, reaching 2518 MPa. Weibull statistical analysis also indicates that the fracture reliability of FeSiBNi2 microwires is much better and its fracture threshold value σu is 1488 MPa. However, Fe-based microwires on macroscopic exhibit the brittle fracture feature, and the angle of sideview fracture θ decreases as Ni-doping amount increases, which also reveals the certain plasticity due to a certain amount of nanocrystalline in the microwires structure, also including a huge amount of shear bands in the sideview fracture and a few molten drops in the cross-section fracture. Therefore, Ni-doped Fe-based metallic microwires can be used as the functional integrated materials in practical engineering application as for their unique magnetic and mechanical performances.

This work comparatively investigates the influence of alcohol and liquid nitrogen medium-current annealing on GMI effect of rotated-dipping Co-based microwires. The temperature field distribution of Co-based microwires during current-annealing process is accordingly simulated, further to acquire experimental parameters of annealing current. Experimental results indicate that, GMI characteristics of current-annealed microwires in mentioned two mediums are both significantly improved, and GMI ratio [ΔZ/Z max]max and magnetic field response sensitivity ξ max of alcohol-medium current-annealed microwires increase more observable. When the excitation current frequency f = 3 MHz, [ΔZ/Z max]max and ξ max of microwires annealed by alcohol medium at 300 mA can reach 240.8% and 78.7%/Oe, respectively. During different type medium-current annealing, the higher-intensity annealing current can generate a larger circular magnetic field, which can effectively regulate the magnetic domain structure of Co-based microwires, so that, they tend to arrange densely and orderly, and the domain walls become much clearer. Meanwhile, the circular permeability μ φ of microwires is significantly improved, thereby enhancing their GMI characteristics. Accordingly, the medium-current annealed Co-based microwires can be used as a typically sensitive material to provide technical support for the potential application of micromagnetic measurement field.