Composition Design And Properties Investigation Of Novel High B_s Iron Based Amorphous/Nanocrystalline Alloys

In the present thesis, based on FeSiB amorphous alloys, the effect of P on the glass forming ability (GFA), thermal stability and soft magnetic properties of the Fe-based amorphous have been investigated. In addition, based on FePC amorphous alloys, the influence of Cu, Mo, Nb, Co on the glass forming ability (GFA), thermal stability, soft magnetic properties, corrosion resistance and microstructure of crystalline phases and precipitation mechanism of Fe-based nanocrystalline alloys have been discussed as well.The influence of P on the GFA, thermal stability and soft magnetic properties of FeSiB alloys were investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), vibrating sample magnetometer (VSM), transmission electron microscopy (TEM) and Ab initio molecular dynamics simulations. The results show that the FeSiBP alloy contains no expensive glass-forming metal elements and can be prepared in air; The addition of a P atom in the FeSiB melt increases the clusters and has a strong solute-solute avoidance effect, resulting in the alloy system having a good melt stability and enhanced GFAs. The Fe79Si5B13P3 amorphous alloy exhibited a high saturation magnetic flux density of up to 1.66 T, a low coercivity of about 2.2 A/m, and a high effective permeability of more than 2×104 at 1 kHz under a field of 1 A/m.The influence of Cu, Mo and Nb on the GFA, soft magnetic properties and the structure and primary crystalline precipitation mechanism of FePC alloys have been investigated by XRD, DSC and VSM. The results show that the substitution of Mo or Nb for Fe in this alloy system improves annealing temperatures and contributes to the precipitation of the a-Fe phase. Nb has larger effect on inhibiting the grain growth and improving the stability of the amorphous phase than Mo. The Fe82.75P9C7Cu0.75Nb0.5 nanocrystalline alloy exhibits the best properties with a high saturation magnetisation (1.66 T), low coercivity (6.8 A/m).The effect of Co on the GFA, soft magnetic properties, high temperature thermal stability and precipitation mechanism of FeSiBPCu alloys were investigated by XRD, DSC and TEM. The results show that the substitution of Co for Fe in this alloy system improved the heat treatment temperature and contributed to the precipitation of the a’-FeCo phase. The addition of Co weakens the Cu clusters that act as nucleation sites for the formation of primary crystals during the melt-spinning process. The (Fe0.65Co0.35)84Si4B8P3Cu1 nanocrystalline alloy exhibited a high saturation magnetisation (1.68 T), low coercivity (5.4 A/m).