Mechanism Of High-Temperature Magnetic Properties For Nanocrystalline Alloys And The High-temperature Magnetic Properties For Si-rich Nanocrystalline Alloys

Structure and high-temperature magnetic properties of as-quenched and annealed(FexCo1-x)73.5Cu1Mo3Si13.5B9(x=0.5,1),(Fe0.75Co0.25)73.5Nb3Si13.5+xB9-xCu1(x=0,4),Ni5(Fe0.5Co0.5)68.5Nb3Si13.5+xB9-xCu1(x=0,4) alloys were investigated by differentialscanning calorimetry (DSC), x-ray diffraction (XRD), transmission electronmicroscopy (TEM), and the temperature dependence of initial permeability (-Tcurves) from room temperature up to730°C. The mechanism of high-temperaturemagnetic properties for nanocrystalline Fe-Co-Cu-Mo-Si-B alloy and the effect ofincreasing Si content on structure and magnetic properties for(Fe0.75Co0.25)73.5Nb3Si13.5B9Cu1,Ni5(Fe0.5Co0.5)68.5Nb3Si13.5B9Cu1alloys were mainlystudied.Substituting Co for Fe partially in Fe73.5Cu1Mo3Si13.5B9alloy decreases the onsettemperature of the primary crystallization，1，and increases the Curie temperatureof amorphous phase，. XRD patterns showed that a single α-FeCo crystallinephase was precipitated from amorphous matrix. By substituting Co for Fe partially inFe73.5Cu1Mo3Si13.5B9alloy, the saturation magnetostriction，λ，increases (>40ppm),room temperature decreases and high temperature increases. The490°Cannealed (Fe0.5Co0.5)73.5Cu1Mo3Si13.5B9alloys show good magnetic properties atelevated temperature, in which about1000at10KHz can hold up to600°C. Thegood magnetic softness at elevated temperature was attributed to the strongexchange-coupling interaction between α-FeCo grains.Increasing Si content in (Fe0.75Co0.25)73.5Nb3Si13.5B9Cu1alloy has no significanteffects on primary crystallization temperature,1, secondary crystallizationtemperatures,2, and the crystallized interval temperature,. The temperaturedependence of initial permeability (-T curves) from room temperature up to730°Cfor the two alloys showed that by increasing Si content the room-temperature decrease without obvious changes on high temperature. The660°C annealed(Fe0.75Co0.25)73.5Nb3Si13.5B9Cu1and640°C annealed (Fe0.75Co0.25)73.5Nb3Si17.5B5Cu1alloys both show good magnetic softness at elevated temperature. is roughlylinear correlation with T and can maintain a considerable value up to600°C. Increasing Si content in Ni5(Fe0.5Co0.5)68.5Nb3Si13.5B9Cu1alloy is in favor ofincreasing the onset secondary crystallization temperatures,2, the crystallizedinterval temperature,, and the maximum operation temperature,. Forsamples heating-cooling cycled at510–680°C, with increasing, theroom-temperature decreases but high-temperature one increases, leading to animprovement of its thermal stability extended from room temperature up to680°C.The optimum magnetic softness at elevated temperature is observed for the sampleheating-cooling cycled at640°C. The initial permeability above1000at10KHz cankeep up to600°C.