| Nanocomposite Nd2Fe14B/-Fe permanent magnets comprising of hard and softmagnetic phases have been attracted great attention due to their excellent magneticproperties resulting from exchange coupling between hard and soft magnetic phases.However, the maximum energy products obtained experimentally up to now issignificantly lower than theoretical maximum energy product. It is mainly due todifficulties to obtain optimum microstructure.In this work, the effects of quenching process including wheel speed, theambient pressure and the melt-spinning temperature parameters on the magneticproperties and microstructure of Nd9.5Fe76Co5Zr3B6.5nanocomposite permanentalloys have been investigated. The ribbion samples with good reproducibility andmagnetic properties are expected. X-ray diffraction (XRD), differential scanningcalorimeter (DSC), vibrating sample magnetometer (VSM), optical microscope(OM), scanning electron microscope (SEM) and transmission electron microscope(TEM) have been employed. The main results are as follows.When the melt-spinning melt temperature is about1200C and the ambientpressure is0.05MPa, the effects of wheel speed (8m/s,15m/s,18m/s and22m/s)on the magnetic properties and microstructure of Nd9.5Fe76Co5Zr3B6.5alloy have beeninvestigated. The results show that the optimum wheel speed is15m/s. On the basisof it, the effects of different gas pressure (0.02MPa,0.05MPa and0.07MPa) on themagnetic properties and microstructure of Nd9.5Fe76Co5Zr3B6.5alloy have been furtherstudied. The results indicate that good reproducibility and magnetic properties areobtained at the gas pressure of0.02MPa. Moreover, the number of gas pockets on thewheel surface is effectively decreased under0.02MPa resulting in obtaining finemicrostructure. Hence, one quenching process is obtained with melt-spinningtemperature of1203C, the wheel speed of15m/s and the gas pressure of0.02MPa.The ribbon samples of Nd9.5Fe76Co5Zr3B6.5alloy with good magnetic properties andreproducibility can be obtained by using this quenching process. The best magneticproperties are, Hci=643.76kA/m, Mr=80.84Am2/kg and (BH)max=80.40kJ/m3.When the melt-spinning temperature is increased approximately to1280C and the chamber pressure is0.05MPa, the effects of wheel speed (8m/s,15m/s,18m/sand22m/s) on the magnetic properties and microstructure of Nd9.5Fe76Co5Zr3B6.5alloy have been investigated. The results show that the optimum wheel speed is15m/s. On the basis of it, the effects of different gas pressure (0.02MPa,0.05MPa and0.07MPa) on the magnetic properties and microstructure of Nd9.5Fe76Co5Zr3B6.5alloyhave been further studied. The results show that, with an increase of chamber pressure,the volume percentage of hard magnetic phase decreases, while the amorphous phaseincreases. It deteriorates the magnetic properties. OM and SEM results show that thenumber of gas pockets on the wheel surface increases with increasing gas pressure,which is not helpful to optimize the microstructure. Therefore, another quenchingprocess is obtained with melt-spinning temperature of1276C, the wheel speed of15m/s and the gas pressure of0.02MPa. The ribbon samples of Nd9.5Fe76Co5Zr3B6.5alloy with good magnetic properties and reproducibility can be obtained by using thisquenching process. In comparison to the former quenching process, the magneticproperties can be further improved. That is, Hci=712.52kA/m，Mr=88.97Am2/kg，(BH)max=115.12kJ/m3。On the basis of comparing the two quenching processes, the effects of twodifferent melt-spinning temperatures (1203C and1276C) on the magneticproperties and microstructure of Nd9.5Fe76Co5Zr3B6.5have been investigated. TheXRD results show that the alloy is mainly consisted of soft magnetic-Fe，hardmagnetic Nd2Fe14B phase and a small amount of amorphous phase with themelt-spinning temperature of1203C, while hard magnetic Nd2Fe14B phase and asmall amount of amorphous phase at higher melt-spinning temperature of1276C.TEM results illustrate that the-Fe phase and Nd2Fe14B phase are observed in theribbon sample of Nd9.5Fe76Co5Zr3B6.5obtained by the first quenching process (T=1203C，p=0.02MPa，v=15m/s). However, the distribution and grain size of softmagnetic phase and hard magnetic phase is not uniform. It weakens the exchangecouple interaction between soft magnetic and hard magnetic phases resulting in adecrease of magnetic properties. Under the second quenching process (T=1276C, p=0.02MPa, v=15m/s), the alloy is mainly composed of hard magnetic Nd2Fe14Bphase. Although the grain size is not uniform, its distribution is uniform, whichimproves the squareness of hysteresis loop and magnetic properties of the Nd9.5Fe76Co5Zr3B6.5alloy. |
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