Texture Growth And Magnetism Of Anisotropic Bulk RCo₅（R=Sm,Pr） Nanocrystalline Magnetic Materials

Bulk permanent magnets have wide and important applications in energy conversion,information technology,national defense,etc.High energy product and high coercivity are required in high temperature applications.The Sm Co₅magnet is an ideal high temperature magnet operating above 400℃.The Sm Co₅magnets obtain high coercivity（>30 k Oe）presently,but the theoretical limit value of their energy product is only 30.3 MGOe.Replacing Sm with Pr element can improve the theoretical energy product,but it results a significant decrease in coercivity.An important approach to solve the inversion relationship between energy product and coercivity is to prepare nanocrystalline magnets with strong crystallographic texture.However,the grain size of the magnets prepared by traditional sinter or thermal deformation at high temperature is large（>100 nm）,while at low temperature the texture is usually poor.This paper designs strong bound high pressure thermal deformation technology with short time and low temperature,which is completely different from the traditional process,preparing bulk nanocrystalline（<100 nm）RCo₅（R=Sm,Pr）magnet with strong texture from amorphous precursor.The RCo₅magnets have the highest energy products among reported values.We also studied the texture formation mechanism and the relationship between processing technique and microstructure and magnetism in detail.The amorphous with an atomic ratio of Sm:Co=1:5 is prepared with high energy ball milling,and the hot deformation with short time（<1 min）and low temperature（<860℃）was carried out.Influence of Continuous Deformation and Two-step Deformation technology on microstructure and magnetic performance of the anisotropic bulk Sm Co₅nanocrystalline magnets is studied.Continuous Deformation rises to the highest temperature directly;Two-step Deformation firstly deformes at 630℃for about 10seconds,and then rises to the highest temperature.The texture strength I_（002）/I_（111）of the Sm Co₅magnet prepared by Continuous Deformation along[00l]direction is 790%,and the grain size is about 260 nm along the easy axis direction.The I_（002）/I_（111）of the Sm Co₅prepared by the Two-step Deformation carried out at the same maximum temperature（860℃）is 350%,and the grain size about 75 nm.The crystallographic texture of the Continuous Deformation Sm Co₅magnet is much stronger,which is attributed to the rapid heating process in the high pressure thermal deformation inhibiting the precipitation of the1:7 phase that is unfavorable to the orientation.The Two-step Deformation achieves better grain size control,which is attributed to the first period deformation that forms many nanostructures in the magnet and improves the nucleation rate.To obtain higher energy product,the effect of Pr element substitution on amorphous formation,phase composition and magnetic properties of the Two-step Deformation(Sm_xPr_1-x)Co₅（0≤x≤1）magnets is studied.The Sm-Pr-Co ternary alloy shows stronger amorphous formation ability than the binary Sm-Co binary alloy,and forms layer misstructure more easily.The grain size of the(Sm_0.2Pr_0.8)Co₅magnet along the stress direction is about 70 nm;the texture strength I_（002）/I_（111）=7500%,which is much higher than the Sm Co₅magnet（790%）.The coercivity is 8.6 k Oe,the remanence ratio is 0.965,the remanence is 11.0 k G,and the energy product reaches 28.8 MGOe.Realizing strong texture in nanocrystalline ensures both high coercivity and high remanence.The formation of strong texture in the nanocrystals is attributed to the superior amorphous formation ability with Pr substitution,which helps the（00l）planes of the grains orientedlly growth at an early nucleation period.On the other hand,the layer misstructure formed in the first period deformation is parallel to the（00l）planes,then under large stress and large strain,the layer misstructure slides for plastic deformation,thus driving the orientation arrangement of the（00l）planes.Based on above nanocrystalline preparation technology and texture formation mechanism,systematic study on the microstructure and the magnetism of the Pr Co₅magnets made from amorphous precursor was carried out.At a maximum deformation temperature of 790℃,the grain size of the Pr Co₅magnet is about 100 nm;I_（002）/I_（111）=3000%,101 times the isotropic magnet ratio of 29.6%.The energy product is 30 MGOe,which is the highest level of the RCo₅magnets;the coercivity is 7.8 k Oe,and the remanence is 11.2 k G.In addition,the coercivity temperature coefficient of the magnet relative to room temperature at 300℃is-0.19%/℃,which is better than the reported Pr Co₅magnet（-0.209%/℃）;the magnetic performance can still keep it basically the same at 350℃,showing fine temperature stability.