NdFeCo magnetic powder was prepared by the process of smelting,high-energy ball milling and oxidation heat treating.The effects of oxidation heat treatment and Co content on phase composition and microwave absorbing properties of NdFeCo magnetic powder were investigated by an X-ray diffractometer(XRD)and vector network analyzer.The minimum reflectivity of Nd23.25Fe36.75Co40 powder before oxidation heat treatment was-6.2 dB,and that of oxidized powder decreased to-14.0 dB.The microwave absorbing properties of NdFeCo magnetic powder could be improved effectively by oxidation heat treatment.With the increase of Co content,the Fe2O3 reduced and the Nd2O3 increased;Fe3Co7 phase appeared when the content of Co increased to 40%(mass ratio);the absorption peak was found to move towards lower frequency region first,and then it moved towards a higher frequency region.Nd23.25Fe66.75Co10 powder had better comprehensive properties in absorbing microwave in the frequency band of 3-13 GHz.The value of minimum reflectivity and absorption peak frequency,when the coating thickness(d)was 1.8 mm,were-19.7 dB and 4.8 GHz,respectively.
The Tb-Fe-Cr alloy powders were prepared by the arc melting method and high energy ball milling.The phase structure and themicrostructure of the alloys powders were analyzed by X-ray diffraction(XRD) and scanning electron microscopy(SEM),and then their microwave absorbing properties were analyzed by Vector network analyzer.The results showed that the absorption peak values of Tb9Fe88Cr3alloy with a material thickness of 2.0 mm were lower than-16.5 dB when ball milling time was from 50 to 60 h,and the wide frequency ofreflectivity under-10 dB were all more than 4 GHz.When the ball milling time was 50 h,the alloy powders had better electromagnetic properties.The absorption peak value of alloy reached-25.8 dB,and the wide frequency of reflectivity under-10 dB reached 4.8 GHz.When theball milling time was more than 70 h,the alloy powders would become thinner,leading to worse electromagnetic properties of the alloy,theabsorption peak shifted towards low frequency under the same material thickness.The TbxFe97-xCr3(x=7,9,11,13,15 mol.%) alloy dealtwith 60 h ball milling time had better wide-frequency characteristic under 1.8 mm of material thickness.The absorption peak shifted towardshigher frequency region from lower frequency region with increased atom percent of Tb in the alloy,and the inflexion point appeared whenx=13.At low frequency,the microwave absorbing properties of Tb11Fe86Cr3 alloy was better than those of the others.The absorption peakvalue of Tb15Fe82Cr3 alloy was-24 dB,and the wide frequency of reflectivity under-10 dB was 4.5 GHz.
