Study Of Preparation, Structure And Magnetic Properties For Nd₂Fe₁₄B/α-Fe Two-Phase Composite Nanocrystalline Rare-Earth Permanent Magnet

Nd2Fe14B/a -Fe two-phase composite nanocrystalline rare-earth permanent magnet is a new kind of magnetic material being developed internationally since the end of 1980s. This magnet consists of two phases whose grain sizes are in nano-scales, magnetically hard Nd2Fe14B and soft a -Fe. The rotation of magnetic moments in the a -Fe phase is controlled by Nd2Fe14B phase through exchange coupling interactions, which gives this magnet high remanence with Jr/Js>0. 5. However, experimental studies have shown that the magnetic properties of nanocomposite magnet are far below the theoretical value. In view of this deficiency, we focus on the effects of preparation technique and alloy composition on the magnetic properties and structure of Nd2Fe14B/ a -Fe nanocomposite magnet and have prepared the magnet with better magnetic properties by directly rapid quenching(DRQ).At first, magnetic properties of Nd~Fe-B ternary primal alloy and the alloy ribbons are analyzed and compared .The results show that the coercivity and remanence of ribbons are much higher than those of primalalloy, Whereas the saturate magnetization of alloy ribbons is far lower than that of primal alloy.Secondly, the influences of wheel speed, spraying pressure and amorphous crystallization on structure and magnetic properties of the magnet are investigated. The experimental results suggest that the optimal wheel speed of alloy is different and the thickness of ribbons decreases with increasing wheel speed. For NdRFe86B6 alloy, the best magnetic properties are achieved by DRQ at v=18m/s and P=0. 09Mpa. In addition, when annealing temperature remains invariable, the larger volume fraction of amorphous phase must be annealed a relatively longer time in order to achieve ideal nano-grains.Thirdly, the effects of basic elements Nd, B and addition elements Dy, Nb content on structure and magnetic properties of nanocomposite alloys are studied. It is found that the coercivity increases remarkably and simultaneously the remanence decreases with the increasing Nd content. For NdxFt94-xB6 alloy with Nd content x=8 and Nd7.5Fe92.5-YBY alloy with B content y=6.5, the best magnetic properties are achieved by the DRQ at the optimal wheel speed. It can also be seen that the coercivity is enhanced remarkably by small addition of Dy, while Dy makes nearly no contribution to the remanence. The decrease in the grain size caused by the Nb'-additive can be regarded as a direct reason for the significant improvement of the hard magnetic properties.Finally, High coercivity, high remanence, and high magnetic energy product have been obtained in Nd8Dy1Fe84Nb1B6 alloy ribbons by the DRQ. The best magnetic properties of Mr, Mr/Ms, Hc and(BH)max are 76. 48em /g, 0. 68, 4600. 40e and 102. 24em /g kOe, respectively.