Correlations Between Structural Characteristics And High Temperature Magnetic Properties Of Sm₂Co₁₇-based Permanent Magnets

Sm2Co17-based permanent magnets have received considerable attention since its inception due to its high Curie temperature(Tc),high magnetic properties,excellent thermal stability and corrosion resistance.At present,Sm2Co17-based permanent magnets are still one of the best permanent magnets used at high temperatures,which are widely used in microwave tubes,gyroscopes,accelerators,magnetic bearings,sensors and so on.In order to further improve the magnetic properties and the maximum operating temperatures of Sm2Co17-based permanent magnets,the effects of Sm content on the magnetic properties and microstructure of the Sm(CobalFe0.1Cu0.09Zr0.03)z(z=7-7.3)ingots,magnetic powders and magnets were firstly studied in this thesis.Then the solid solution process of Sm(CobalFe0.1Cu0.09Zr0.03)7.2 magnet was optimized from the perspective of high temperature magnetic properties.The effects of the quenching temperature(Tq)on the magnetic properties and microstructure of the Sm(CobalFe0.1Cu0.09Zr0.03)7.2 magnet were also studied.Finally,depending on the comparative study on the magnetic properties and microstructure of the Sm2Co17-based permanent magnets with different magnetic characteristics,the correlation of the structural characteristics and the magnetic properties of Sm2Co17-based permanent magnets were discussed in combination with the theoretical calculations.The following conclusions were drawn:(1)Sm(CobalFe0.1Cu0.09Zr0.03)7.2 magnet with a high Hcj of 8.2 kOe and a(BH)max of 11.9 MGOe at 500? was successfully prepared that has reached the international leading level.In combination with the experimental analysis and the Kronmullar coercivity theory,the influence mechanism of the microstructure on the Hcj temperature dependence was studied.it was found that increasing the Tc of the cell boundary phase and decreasing the ?? between cell and cell boundary phases are beneficial for the ? and the Hcj at high temperature of the Sm2Co17-based permanent magnets.However,a low ?? will result in a low Hcj at RT of the Sm2Co17-based permanent magnets.For the first time,It was experimentally and theoretically proved that the magnets with a high Hcj at room temperature do not always show a high Hcj at high temperature,the ? of the magnet was optimized to improve the Hcj at high temperature.(2)High temperature Sm2Co17-based magnet with a(BH)max of 12.4 MGOe at 500? was obtained via the comparative study on the magnetic properties and microstructure characteristics of the high temperature and high(BH)max Sm2Co17-based magnets.In combination with the elemental and the Kronmullar coercivity theory analysis,it was found that the suitable Fe content of the cell phases and the higher Tc of the cell boundary phases of the high temperature magnet are the main reasons for the higher Hcj at high temperature comparing with the high(BH)max magnet.(3)The influences of the Sm content on the microstructure and magnetic properties of the Sm(CobalFe0.1Cu0.09Zr0.03)z(z=7-7.3)ingots,magnetic powders and magnets were systematicly investigated.Sm content has no change on the phase structure of Sm(CobalFe0.1Cu0.09Zr0.03)z ingots,magnetic powders and magnets.The Sm(CobalFe0.1Cu0.09Zr0.03)z ingots and magnetic powders consist of 1:5 and 1:7 phases while the magnets consist of 2:17 and 1:5 phases.Sm content has seldom influence on the cell size of the Sm(CobalFe0.1Cu0.09Zr0.03)z magnets,but higher Sm content will lead to a wider cell boundary phase of the magnet.The wider Cu distribution of the cell boundary originated from the wider cell boundary was considered as the main reason for the low Hcj of the z=7.0 magnets.Sm content has no influence on the magnetic properties of the Sm(CobalFe0.1Cu0.09Zr0.03)z ingots and magnetic powders,while it has more influence on the magnetic properties of the magnets.With the z varying from 7.0 to 7.3,all of the Br,Hcj and(BH)max of the Sm(CobalFe0.1Cu0.09Zr0.03)z magnets increase at the beginning and then decrease.The Sm(CobalFe0.1Cu0.09Zr0.03)7.2 magnet shows the optimal magnetic properties as:Br=9.65kG,Hcj=28.3 kOe,(BH)max=22.5MGOe at RT.(4)In order to optimize of the solid solution process of the Sm(CobalFe0.1Cu0.09Zr0.03)7.2 magnet,the solid solution process of Sm(CobalFe0.1Cu0.09Zr0.03)7.2 magnet was investigated from the perspective of high temperature magnetic properties.The Sm(CobalFe0.1 Cu0.09Zr0.03)7.2 magnet solid soluted at 1195? for 4h shows the best magnetic properties as Br=7.22 kG,Hcj=7.6 kOe,(BH)max=11.6 MGOe at 500?.(5)The effects of Tq on the microstructure and magnetic properties of the Sm(CobalFe0.1Cu0.09Zr0.03)7.2 magnet were systematicly studied.Tq has no influence on the Br of the magnets.while the Tq has a great influence on the Hcj and its temperature dependence of the magnets.With Tq decreasing from 830? to 420?,the Hcj of the magnets increase from 1.406 kOe to 21.7 kOe,while the ?(RT-500?)deteriorates from+0.1113%/? of the Tq=830? magnet to-0.134%/? of the Tq=420? magnet.Analysis of the microstructure of the magnets with Tq=830? and 420? indicate that Tq has no effect on the cell size and the density of the lamella phase of the magnet,while has a great influence on the Cu distribution of the cell boundary phase.A higher Cu content with a sharp distribution was found in the cell boundary of the Tq=420?magnet,while the Cu content of the cell boundary of the Tq=830? magnet was low and implied a wider Cu distribution.The difference of the Cu content and its distribution was ascribed to be the main reason for the different Hcj and its temperature dependence behavior of the Tq=830? and 420? magnets.