Fabrication And Study Of Magnetic Properties Of Anisotropic Bulk Sm-Co-based Nanocrystalline Magnetic Materials

Permanent magnets,as the converters for electrical energy and mechanical energy,play a critical role in all aspects of social life and commercial production,while some important high-temperature fields such as aerospace,military industries,and environment-friendly technologies pose severe challenges to them.The fusion of Sm-Co based magnets with excellent high temperature magnetic properties and nanocrystalline materials is an important development direction for new type high-temperature magnets.In this dissertation,we focus on the SmCo₅ and SmCo₇ high-temperature permanent magnetic materials used above 250?and conducted the following research works.SmCo₅ amorphous precursors prepared by high energy ball milling were subjected to high pressure thermal deformation using spark plasma sintering technology.An anisotropic nanocrystalline bulk magnet with small grain size?¹3 nm?and strong texture was prepared.The magnet has a crystallographic texture(I_?002?/I_?111?=1.55)in the?00l?direction and exhibits a strong magnetic anisotropy.Under the condition of deformation temperature of 620°C and height reduction of 81%,we obtain a highest maximum energy product of 13.7 MGOe.The alloy ingot of SmCo_x?x=6.37-7.44?composition was obtained by vacuum arc melting,and then the coarsely crushed powders were subjected to high energy ball milling to obtain amorphous precursors.In combination with spark plasma sintering technology,anisotropic high performance SmCo₇ nanocrystalline bulk magnets were prepared.When the atomic ratio of the precursor is in the range of x=6.7-7.25,a single TbCu₇-type SmCo₇ phase can be formed in the deformation magnets and at x=7.25,we get the best magnetic properties whose the maximum energy product is 19 MGOe,I_?002?/I_?111?=0.45and the average grain size is about 23.6 nm.Using the same technique,anisotropic bulk(Sm_xPr_1-x)Co₇?0?x?1?nanocrystalline magnets were successfully prepared by partially replacing Sm with rare earth Pr element with the SmCo atomic ratio of 1:7.25.The thermal deformation magnets showed good magnetic properties at x=0 and 0.6.Their maximum energy product all reached 19.3MGOe,and the remanence ratio B_r^?/B_r^?of the easy and difficult magnetization direction was 1.73 and 1.55,respectively.The SmCo₅ magnet prepared in this paper has a small grain size and a strong texture,which fills in the blankness for the preparation of small grain size anisotropic SmCo₅nanocrystalline bulk magnets.Anisotropic bulk SmCo₇-based nanocrystalline magnets have been fabricated in this paper whose maximum energy product exceeds the maximum value recorded so far and exhibit good high-temperature properties.