The Magnetic Properties And Microstructure Of Hot-pressed And Hot-deformed Nd-Fe-B/PrCo₅ Hybrid Magnets

Iron based magnets (RE-Fe-B) and cobalt based magnets (RE-Co) are widely used. Cobalt based magnets (RE-Co) have high Cruie temperature and high thermal stability while their magnetic properties are low compared to the Iron based magnets (RE-Fe-B) which have high magnetization but quite low Cruie temperature and thermal stability. It will be of great significance to broaden the application fields of permanent materials if one can combine the advantages of the two kinds of magnets.In this paper Nd-Fe-B/PrCos and (Nd,Dy)-Fe-B/PrCos hybrid magnets were prepared by hot-pressing and hot-deformation method. The effects of hot-pressed temperature, hot-deformed temperature, strain rate and particle size on magnetic properties of Nd-Fe-B/PrCos and (Nd,Dy)-Fe-B/PrCos hybrid magnets as well as the effects of PrCos addition on microstructure and density were studied. The magnetization behaviors of the hybrid magnets were also studied. The main conclusions are as follows:(1) The Nd-Fe-B and PrCo5 melt-spun ribbons and (Nd,Dy)-Fe-B and PrCo5 melt-spun ribbons were mixed, and then by the hot-pressing and hot-deformation method, the Nd-Fe-B/PrCo5 and (Nd,Dy)-Fe-B/PrCo5 hybrid magnets were prepared susscessfully. The results of XRD, SEM and M-T curve indicate that the Pr-Co alloy in the two hot-pressed hybrid magnets and hot-deformed hybrid magnets still possesses the PrCos structure, which is attribute to the fast heating and cooling rate.(2) SEM images show that the PrCo5 agglomerate into large particles in both Nd-Fe-B/PrCos and (Nd,Dy)-Fe-B/PrCo5 hot-pressed hybrid magnets. The compactness of hybrid magnets decreases with the increase of PrCos addition. The temperature coefficient of coercivity is improved when the PrCos addition is less than 8%for Nd-Fe-B/PrCos hot-pressed hybrid magnets, while the coercivity of (Nd,Dy)-Fe-B/PrCo5 hot-pressed hybrid magnets is larger. The magnetic properties of the hot-pressed hybrid magnets decrease with the increase of PrCos addition. When the P1C05 addition is 8%, the magnetic properties of Nd-Fe-B/PrCo5 hot-pressed hybrid magnet are:Br=8.09 kGs, Hcj=14.21 kOe, (BH)m= 14.31 MGOe; the magnetic properties of (Nd,Dy)-Fe-B/PrCo5 hot-pressed hybrid magnet are:Br=8.11 kGs, Hcj=20.55 kOe, (BH)m=14.27 MGOe respectively.(3) It is found that the magnetic properties of the Nd-Fe-B/PrCos and (Nd,Dy)-Fe-B/PrCo5 hot-deformed hybrid magntes increase firstly and then decrease with the increase of hot-deformed temperature, strain rate and partcile size. The hysteresis loops along different directions of the hybrid magnets and the patterns of XRD show that the hybrid magnets are changing from isotropy to anisotropy after hot deformation. When the PrCos addition is less than 12%, the magnetic properties of hot-deformed hybrid magnets are superior to the Sm-Co based magnets. When the PrCo5 addition is 8%, the comprehensive magnetic properties of Nd-Fe-B/PrCo5 hybrid magnets are:Br=13.05 kGs, Hcj=9.91 kOe, (BH)m=39.6 MGOe; the comprehensive magnetic properties of (Nd,Dy)-Fe-B/PrCo5 hybrid magnets are:Br=12.74 kGs, Hcj=11.62 kOe, (BH)m=36.6 MGOe. We find that a complex transition layer appears in the interface of the two phases, which is result from the diffusion between Nd2Fei4B and PrCos.(4) There is exchange-coupling effect between the transition layer and the matrix in both hot-pressed and hot-deformed hybrid magnets.