Nanocomposite Nd2fe14b/a-fe, Magnetic Materials Structure And Magnetic Properties

The nanocomposite Nd₂ Fe₁₄B/α-Fe magnet is a new kind of magnetic materialdeveloped since the end of l980s.This magnet consists of two phases, magnetically hardNd₂Fe₁₄B and soft α-Fe. The rotation of magnetic moments in the α-Fe phase iscontrolled by Nd₂Fe₁₄B phase through exchange coupling effect, which gives this magnethigh remanence with J_I/J_S>0.5. However, the existence of α-Fe is detrimental to theintrinsic coercivity _iH_c. In view of this deflciency, the influence of alloy composition onthe _iH_c and other magnetic properties are investigated in current study which has beenespecially focused on the different roles played by additional elements under two kindsof manufacture process, directly rapid quenching (DRQ) and rapid quenching+crystallization (RQC). The above-mentioned work has led to the preparation ofisotropic melt-spun powdef, boned magnets and hot-pressed magnets with usefulmagnetic properties. The crystallization of amorphous Nd-Fe-B alloy has high academicresearch value. In order to optmize the crystallization treatment, the precipitation ofamorphous Nd-Fe-B alloy under different conditions has been explored thoroughlyFinally, the initial magnetization curve and the magnetically hardening mechanism ofNd₂Fe₁₄B/α-Fe magnet were also studied.The influence of Nd contellt on the microstructure and magnetic properties ofnanocomposite Nd_xFe_94-xB₆ (x=7,8,9,l0) alloys was first examined. The results show thathigher Nd content is advalltageous to the formation of amorphous phase. Thecrystallization process of amorphous Nd-Fe-B alloys and the Nd content are also closelyrelated. In DTA experiments, amorphous alloys with x>7 crystallize into Nd₂Fe₁₄B andα-Fe directly. In the amorphous Nd₇Fe₈₇B₆ alloy, howevef, the intermediate metastableNd₂Fe₂₃B₃ phase first appears at lower temperature and decomposes at highertemperature. After the final formation of Nd₂Fe₁₄B and α-Fe, the magnetic properties offour melt-spun ribbons were measured. Nd₉Fe₈₅B₆ exhibits best performance and themagnetic propefties of Nd₇Fe₈₇B₆ alloy are the lowest. This difference may beenattributed to the existence of large α-Fe grains found by HRTEM observation inNd,Fe,,B, ribbons.Based pn the above-introduced research, N4Fe,,B, was selected as the basic alloycomposition for the next study of additional elements Dy, Co and Nb. This inspectionbegins with the change of glass formation ability of Nd-Fe-B alloy upon the addition ofDy, Co and Nb. The experiment results suggest that the volume difference betWCencomponent atoms is the crucial factor in dettrmining the glass formation ability of Nd-Fe-M-B (M= Dy, Co, Nb) alloys. Due to the fact of AVNb-F.>AVDy-Nd>AVc.&, Nb is moreeffective in improving the glass formation ability than Dy, and Co makes nearly nocontribution tO the formation of amorphous phase.The existence fOrms of additiona1 elements and their influence on microstructureand magnetic properties are the emphasis of current study Since almost all the pastreference were limited in only one preparation method, either RQC or DRQ, theoriginality of the present study is to compare the different roles played by one elemeniunder two kinds of production aPproaches. It was fOund that the existence form of Dyatoms varies with different preparation processes. Under RQC, nearly all Dy atoms areused to substitute Nd in the Nd,Fe,#B phase and improve the,H,' Under DRQ, howevef,Dy atoms uniformly distributed in bOth Nd,Fe,.B and a-Fe grains. The actual amount ofDy atoms used to modify the intrinsic magnetic properties of 2fl4:l phase is reduced.The existence forms of Co under DRQ and RQC are the same. The Co atoms scatter inboth Nd,Fe,.B and a-Fe phases, which improves the Curie temperature Tc significantlyAs to Nb, the evidence of its existing in the form of NbFe phase was reported for the firstin current study NbFe grains cluster in the corners of Nd,F...