The Study Of Structure And Magnetic Properties For Si-rich Nanocrystalline Alloys

We main study the effect of annealing temperature and Co and Al content on the structure and magnetic properties of(Fe1-x Cox)74.5Nb2Si17.5B5Cu1(x=0, 0.1, 0.5)、Fe73.5-x Alx Si17.5B5Cu1Nb3(x=0, 0.2, 0.4, 0.6, 0.8, 1.0) alloys. The main experiment we conducted was as follow: we used differential scanning calorimetry(DSC) to determine the crystallization temperature of amorphous ribbons; the microstructure of as-quenched and annealed samples were examined by x-ray diffraction(XRD); Coercivity Hc, saturation magnetic induction Bs, initial permeability μi, maximum permeability μmax were measured by the static magnetic measurement system. Use impedance analyzer to measure the variation of initial permeability μi with temperature T(μi-T curves) for the annealed alloys to study the high-temperature permeability.The Curie temperature of amorphous phase and crystalline phase were both higher, when partial substitution of Fe by Co in Fe74.5Nb2Si17.5B5Cu1 alloy. The as-quenched sample also exhibits a larger crystallized interval temperature. For(Fe0.9Co0.1)74.5Nb2Si17.5B5Cu1 alloy annealed at 500-650 °C, the optimum magnetic softness at elevated temperature is observed for the sample annealed at 600 °C. Although the room temperature permeability of 600 °C-annealed nanocrystalline(Fe0.9Co0.1)74.5Nb2Si17.5B5Cu1 alloy is not as high as that of nanocrystalline Fe74.5Nb2Si17.5B5Cu1 alloy, the high temperature μi from 520 °C to 670 °C is larger than that of Fe74.5Nb2Si17.5B5Cu1 alloy. The higher permeability at high temperature makes it to be of interest for high temperature applications. After annealing at different temperature, the common feature of μi-T curves for(Fe0.9Co0.1)74.5Nb2Si17.5B5Cu1 alloy is that the μi increases with T from room temperature and reaches a peak value, then μi decreases with T. This kind of μi-T curves is different from that of the common Co-contained Finemet-type alloys ever reported.The interval temperature of Fe73.5-x Alx Si17.5B5Cu1Nb3 alloys is higher and is enlarged from 208 to 234 °C which is higher than Fe73.5-x Alx Si13.5B9Cu1Nb3 alloys. This means that the increaseing of Si content is effect to the increase the interval temperature. When Al is added, the primary crystallization temperature decreases, and the secondary crystallization temperature increases, so the interval temperature shows a general increased tendency After annealing at various temperatures, the results show that the Fe72.7Al0.8Si17.5B5Cu1Nb3 alloy exhibited excellent room-temperature soft magnetic properties with a very low Hc of about 1A/m, a high Bs of 1.13 T, a high μi of 35,000 and a high μmax of 128,000 respectively. It also exhibited excellent high temperature soft magnetic properties, the μi above 2800 at 10 KHz can keep up to 500 °C.