A non-homogeneous single-crystal magnetic powder, a preparation method and application thereof

Abstract

The application discloses a kind of heterogeneous single crystal magnetic powder and its preparation method and application.A kind of preparation method of heterogeneous single crystal magnetic powder, including the following steps: the particle size of La / Ce / Y rich (Sm, R1) 2Fe 17 The alloy powder is used as a master alloy magnetic powder, the Sm diffusion source alloy powder is mixed with a volatile organic solvent to form a paste, the master alloy magnetic powder is uniformly mixed with the paste to obtain a mixture, the mass ratio of the master alloy magnetic powder to the diffusion source alloy powder is 88:12-97:3, then the mixture is sequentially subjected to diffusion heat treatment, hydrogen explosion treatment, dehydrogenation treatment, powdering and nitriding to obtain the heterogeneous single crystal magnetic powder.The application uses a low-melting-point alloy as the Sm element diffusion source, and through heat treatment, Sm is evaporated onto the surface of the La / Ce / Y-rich single crystal magnetic powder, and then through low-temperature diffusion reaction, a thin shell layer rich in Sm is formed on the surface of the La / Ce / Y-rich single crystal magnetic powder.

Description

Technical field:

[0001] The present invention relates to rare earth permanent magnetic materials, in particular to a heterogeneous single crystal magnetic powder and a preparation method and application thereof. Background technology:

[0002] In 1982, Masato Sagawa of Sumitomo Special Metals invented sintered Nd-Fe-B permanent magnets. These magnets have gained widespread application due to their previously unseen high magnetic energy product, high coercivity, relatively inexpensive raw materials, and simple preparation methods, making them the most widely used rare earth permanent magnets. Bonded magnets made from rapidly quenched Nd-Fe-B magnetic powder, invented by General Electric, have also gained widespread market recognition for their high dimensional accuracy and ease of fabrication for special-shaped magnets. Rare earth permanent magnets have become an essential building block in modern society, with applications in a wide range of industries, including computers, automobiles, instruments, home appliances, petrochemicals, healthcare, and aerospace.

[0003] In 1990, Professor Coey's research group at Trinity University in Ireland and Professor Yang Yingchang's research group at Peking University discovered Sm2Fe based on the interstitial atom effect of nitrogen in rare earth-transition metal compounds. 17 N x (referred to as SmFeN) and Nd(Fe,M) 12 N x (NdFeN for short) has excellent intrinsic magnetic properties, comparable to NdFeB, and has a higher Curie temperature than NdFeB. SmFeN and NdFeN are considered to be candidates for the next generation of rare earth permanent magnets.

[0004] Known Sm2Fe 17 N3 compounds have a huge magnetocrystalline anisotropy field. 17 N3 single crystal magnetic powder has a high coercivity when the particle size is 3μm. Sm element is a scarce resource with limited global production. If Sm2Fe 17 N3 permanent magnet materials will cause a shortage of Sm element supply. However, rare earth elements such as La, Ce, and Y are in large surplus and relatively cheap. 17 When less than 85% of the Sm in an N3 compound is replaced by other rare earth elements, the compound still maintains easy c-axis magnetization and high magnetization, but the magnetocrystalline anisotropy field decreases significantly with increasing substitution. The coercivity of magnetic powder is closely related to the compound's magnetocrystalline anisotropy field, and increasing the amount of substitution inevitably leads to a significant decrease in the powder's coercivity. Therefore, simply replacing it with high-abundance elements like La, Ce, and Y will not solve the Sm resource shortage problem. Summary of the invention:

[0005] In order to solve the problems existing in the prior art, the present invention proposes a heterogeneous single crystal magnetic powder and its preparation method and application. The present invention uses a low-melting-point alloy as the diffusion source of the Sm element, and evaporates Sm onto the surface of the La / Ce / Y-rich single crystal magnetic powder through heat treatment. Then, through a low-temperature diffusion reaction, a thin Sm-rich shell layer is formed on the surface of the La / Ce / Y-rich single crystal magnetic powder. This heterogeneous single crystal magnetic powder is nitrided to become a La / Ce / Y-rich anisotropic permanent magnet powder with high coercivity.

[0006] Since the magnetocrystalline anisotropy field of the surface shell of the magnetic powder is an important factor determining the coercive force of the magnetic powder, the present invention forms a thin Sm-rich shell on the Sm-poor single crystal magnetic powder. This can not only replace a large amount of Sm, but also greatly improve the coercive force of the magnetic powder through the Sm-rich shell on the surface of the magnetic powder, thereby realizing the replacement of Sm with high-abundance elements such as La, Ce, and Y, thereby solving the problem of Sm resource shortage.

[0007] The first object of the present invention is to provide a Sm diffusion source alloy, the composition expressed in atomic percentage is Sm d M1 100-d , 50≤d≤95, M1 is Cu and / or Zn.

[0008] A second object of the present invention is to provide a method for preparing the above-mentioned Sm diffusion source alloy, comprising the following steps: induction melting Sm and M1 alloy under argon protection to obtain a melt, using a water-cooled copper roller at a speed of 10-50 m / s to form a rapid-quenching diffusion source alloy thin strip, and grinding the rapid-quenching diffusion source alloy thin strip into particles with a particle size of 10-500 μm to obtain Sm diffusion source alloy powder.

[0009] The melting point of the prepared diffusion source alloy ribbon is lower than 960° C. The rapidly quenched ribbon is ground into particles of 10-500 μm using a jet mill or a ball mill to form diffusion source alloy powder.

[0010] The third object of the present invention is to provide a method for preparing heterogeneous single crystal magnetic powder, comprising the following steps: preparing La / Ce / Y-rich (Sm, R1)2Fe 17 The alloy powder serves as a master alloy magnetic powder. The aforementioned Sm diffusion source alloy powder is mixed with a volatile organic solvent to form a paste. The master alloy magnetic powder and the paste are then uniformly mixed to obtain a mixture. The mass ratio of the master alloy magnetic powder to the diffusion source alloy powder is 88:12 to 97:3. The mixture is then sequentially subjected to diffusion heat treatment, hydrogen explosion treatment, dehydrogenation treatment, pulverization, and nitriding to obtain heterogeneous single crystal magnetic powder. The aforementioned organic solvent is preferably anhydrous ethanol. The mass ratio of the master alloy magnetic powder to the diffusion source alloy powder is preferably 95:5 to 91:9.

[0011] The present invention is rich in La / Ce / Y (Sm, R) 2Fe 17A Sm-rich shell is formed on the grain, and this shell has a 2:17 structure, that is, a (Sm, R)₂Fe 17 heterogeneous single crystal combined magnetic powder is formed.

[0012] Preferably, the composition of the (Sm, R₁)₂Fe alloy powder rich in La / Ce / Y is expressed in atomic percentage as: (Sm 17 R₁ 1-α ) α Fe b M₂ 100-b-c , where R₁ is at least one rare earth element other than Sm, 0.2 < α < 1; 9 < b < 13; M₂ is selected from at least one of Co, Si, Ga, Al, Ni, Ti, Cu, V, Cr, Zr, Hf, Nb, Ta, Mo, and W, and 0 ≤ c ≤ 30. c

[0013] More preferably, R₁ is selected from at least one of La, Ce, and Y.

[0014] Preferably, the preparation steps of the master alloy magnetic powder are as follows: proportion the materials according to (Sm 1-α R₁ ) α Fe b M₂ 100-b-c . Since Sm is easy to volatilize, add 10% more as compensation based on the theoretical value. Put the prepared metallic Sm, pure Fe, R₁, and M₂ into an induction melting furnace and melt them in high-purity Ar. Use induction heating to make the alloy completely molten and uniform to obtain a melt. Use a water-cooled copper roller to quickly prepare a rapidly solidified cast sheet. Place the master alloy cast sheet in a heat treatment container and perform heat treatment under argon protection. After air cooling, crush the master alloy cast sheet into master alloy magnetic powder with an average particle size of 1 - 20 μm. c

[0015] Preferably, the surface linear speed of the water-cooled copper roller is 10 - 30 m / s, the heat treatment temperature is 900 °C - 1000 °C, and the heat treatment time is 30 - 50 min.

[0016] ​Preferably, the mixture is subjected to diffusion heat treatment, hydrogen explosion treatment, dehydrogenation treatment, powder making and nitriding in sequence to obtain heterogeneous single crystal magnetic powder. The specific steps are: placing the mixture in a vacuum furnace under high-purity Ar protection for diffusion heat treatment, the diffusion heat treatment temperature is 650°C-960°C, and the heat treatment time is 0.5-10h; placing the casting after diffusion heat treatment in H2 at 150°C-250°C for 1-3h, performing hydrogen explosion treatment, raising the furnace temperature to 550°C-600°C, and vacuum dehydrogenation treatment for 1.5-2.5h; grinding the casting after dehydrogenation treatment to obtain magnetic powder, and nitriding the magnetic powder at 400°C-450°C for 30-40h using high-purity nitrogen to obtain heterogeneous single crystal magnetic powder.

[0017] The specific steps of grinding the dehydrogenated cast sheet to obtain magnetic powder are as follows: grinding the dehydrogenated cast sheet using a low-energy ball mill, using 6mm stainless steel beads, a ball-to-material ratio of 5:1, setting the planetary ball mill speed to 150rpm, and grinding time for 2h.

[0018] The purpose of the diffusion heat treatment of the mixture is to volatilize the Sm in the low melting point diffusion source and combine it with the master alloy powder to form an Sm-rich phase. In the subsequent heat treatment, the Sm-rich phase and the La / Ce / Y-rich (Sm, R1)2Fe 17 Diffusion occurs between grains and forms a Sm-rich shell. (Sm,R1)2Fe with Sm-rich shell 17 After nitriding, the grains have a surface layer with high magnetocrystalline anisotropy field, which improves the coercive force of the magnetic powder.

[0019] Preferably, the heterogeneous single crystal magnetic powder is composed of a first phase, a second phase and a third phase, wherein the first phase is composed of rare earth elements Sm, R1, Fe and transition metal elements M2, and has Th2Zn 17 or Th2Ni 17 The main phase has a spherical or equiaxed shape and an Sm-rich shell, that is, the Sm / (Sm, R1) atomic content ratio within the thickness of 0.15 μm in the surface layer is more than 20% higher than that in the center of the grain, and the thickness of the Sm-rich shell is between 0.1-1.0 μm; the atoms constituting the main phase account for 80-99% of the atoms of the parent alloy; the second phase is a rare earth-rich auxiliary phase, the atoms constituting the rare earth-rich auxiliary phase account for 0.5-19% of the parent alloy, and the rare earth-rich auxiliary phase is composed of any three of (Sm, R1)(Fe, M2)2, (Sm, R1)(Fe, M2)T3, (Sm, R1)(Fe, M2)M1, and (Sm, R1)M12 phases; the third phase is oxides or nitrides of rare earths Sm and R1 and other unavoidable impurities.

[0020] The present invention also protects the use of the inhomogeneous single crystal magnetic powder in preparing anisotropic bonded permanent magnetic materials or sintered anisotropic permanent magnetic materials.

[0021] Compared to existing technologies, the present invention offers the following advantages: The diffusion source, composed of a low-melting-point Sm-M1 alloy, easily melts during heat treatment and promotes the volatilization of the Sm element, allowing the Sm element to react uniformly with the surface of the master alloy powder particles to form a rare-earth-rich auxiliary phase. This allows the beneficial Sm element to diffuse into the main phase grains at a relatively low temperature, forming an Sm-rich shell. Furthermore, after the rare-earth-rich auxiliary phase forms on the surface of the main phase grains, the low-melting-point rare-earth-rich auxiliary phase promotes the migration of atoms on the particle surface, promoting spheroidization of the powder particles and forming spherical or equiaxed grains. Under optimal conditions, the addition of the low-melting-point diffusion source to angular master alloy powder can lead to spheroidization at temperatures below 850°C. The spheroidized grains have a lower demagnetization factor, which facilitates higher coercivity. Furthermore, the spherical anisotropic magnetic powder particles are more easily oriented during injection molding. Specific implementation method:

[0022] The following is a further description of the present invention, but not a limitation of the present invention.

[0023] Example 1

[0024] A method for preparing heterogeneous single crystal magnetic powder comprises the following steps:

[0025] (1) Using 99.9% pure rare earth Sm, Ce, pure Fe, and pure Cu as raw materials, the ingredients are prepared according to the following chemical formula: (Sm 0.2 Ce 0.8 ) 11.58 Fe 87.42 Nb1Cu 1.00 (at%). Since Sm is easy to volatilize, 10% is added to the theoretical value as compensation. The prepared metal Sm, pure Fe, Ce, and pure Cu raw materials are placed in an induction melting furnace and smelted in high-purity Ar. Use induction heating to heat the alloy until the raw materials are completely melted and uniform. At this time, the temperature of the melt is about 1490°C, and a water-cooled copper roller is used to prepare a quick-setting casting sheet, and the copper roller surface linear speed is 10m / s. The casting is placed in a corundum crucible and heat treated at 950°C for 40 minutes under argon protection, and air-cooled. Use a ball mill to crush the master alloy casting into master alloy magnetic powder with an average particle size of 3μm.

[0026] (2) The diffusion source alloy composition is Sm 50 Cu 50 The thin ribbon was prepared by rapid quenching with a water-cooled copper roller at a surface speed of 30 m / s. The thin ribbon was ground into powder in a ball mill under Ar protection with an average particle size of 30 μm to obtain the diffusion source alloy powder.

[0027] (3) Diffusion source alloy powder is added to anhydrous alcohol in a volume ratio of 1:2 to form a paste. The paste and the master alloy magnetic powder are mixed evenly, and the diffusion source alloy powder accounts for 3-12 wt% of the total mass of the diffusion source alloy powder and the master alloy magnetic powder (as shown in Table 1). The evenly mixed mixture is placed in a vacuum furnace under high-purity Ar protection for diffusion heat treatment. The heat treatment temperature is 900°C and the heat treatment time is 1.2 h. The casting that has undergone diffusion heat treatment is placed in H2 at 200°C for 2 h for hydrogen explosion treatment. The furnace temperature is raised to 580°C and vacuum dehydrogenation treatment is carried out for 2 h. The casting that has undergone dehydrogenation treatment is ground using a low-energy ball mill, using 6 mm stainless steel balls, a ball-to-material ratio of 5:1, the planetary ball mill speed is set to 150 rpm, and the grinding time is 2 h. The magnetic powder is nitrided at 430°C for 35 h using high-purity nitrogen to nitride the magnetic powder through gas-solid reaction. Magnetic powder and hot paraffin were mixed in appropriate proportions and oriented in a magnetic field. The oriented samples were then tested using a vibrating magnetometer (VSM). The direction of the applied magnetic field was parallel to the easy magnetization axis of the sample. The magnetic properties of the magnetic powder samples are shown in Table 1 below:

[0028] Table 1 Diffusion source alloy composition Sm 50 Cu 50 Magnetic properties test table of nitrided magnetic powder when alloying

[0029] Diffusion source alloy content (wt%) Magnetic powder particle size (μm) Surface Ce / (Sm+Ce) ratio <![CDATA[B r (T)]]> <![CDATA[H cj (no)]]> <![CDATA[(BH) max (MGOe)]]> 0 3.0 0.80 0.71 1.1 2.3 3 3.0 0.41 1.26 3.8 14.6 5 3.0 0.38 1.24 4.6 21.5 7 3.0 0.32 1.22 5.7 25.4 9 3.0 0.27 1.20 6.6 28.6 12 3.0 0.22 1.17 7.2 22.4

[0030] It can be seen from Table 1 that with the increase of diffusion source alloy powder, the Sm content in the surface layer of the prepared nitrided magnetic powder increases and the Ce content decreases, so the coercive force and magnetic energy product of the magnetic powder are significantly improved, and the magnetic properties are significantly better than the original powder without diffusion heat treatment.

[0031] Example 2

[0032] Same as Example 1, except that the diffusion source alloy composition is Sm 70 Cu 30 The magnetic properties of alloy and magnetic powder samples are shown in Table 2:

[0033] Table 2 Diffusion source alloy composition Sm 70 Cu 30 Magnetic properties test table of nitrided magnetic powder when alloying

[0034] Diffusion source alloy content (wt%) Magnetic powder particle size (μm) Surface Ce / (Sm+Ce) ratio <![CDATA[B r (T)]]> <![CDATA[H cj (no)]]> <![CDATA[(BH) max (MGOe)]]> 0 3.0 0.80 0.7 1.1 2.3 3 3.0 0.35 1.26 4.9 16.6 5 3.0 0.27 1.22 6.7 23.4 7 3.0 0.25 1.19 6.9 28.6 9 3.0 0.23 1.16 7.2 26.7 12 3.0 0.19 1.11 7.8 25.4

[0035] It can be seen from Table 2 that with the increase of diffusion source alloy powder, the Sm content in the surface layer of the prepared nitrided magnetic powder increases and the Ce content decreases, so the coercive force and magnetic energy product of the magnetic powder are significantly improved, and the magnetic properties are significantly better than the original powder without diffusion heat treatment.

[0036] Example 3

[0037] Same as Example 1, except that the diffusion source alloy composition is Sm 95 The magnetic properties of Cu5 alloy magnetic powder samples are shown in Table 3:

[0038] Table 3 Diffusion source is Sm 95 Magnetic properties test table of nitrided magnetic powder when Cu5 alloy is used

[0039] Diffusion source alloy content (wt%) Magnetic powder particle size (μm) Surface Ce / (Sm+Ce) ratio <![CDATA[B r (T)]]> <![CDATA[H cj (no)]]> <![CDATA[(BH) max (MGOe)]]> 0 3.0 0.80 0.7 1.1 2.3 3 3.0 0.36 1.17 4.9 16.8 5 3.0 0.29 1.08 6.9 23.5 7 3.0 0.24 0.98 7.2 18.8 9 3.0 0.20 0.91 7.6 15.4 12 3.0 0.16 0.77 8.4 10.3

[0040] It can be seen from Table 3 that with the increase of diffusion source alloy powder, the Sm content in the surface layer of the prepared nitrided magnetic powder increases and the Ce content decreases, so the coercive force and magnetic energy product of the magnetic powder are significantly improved, and the magnetic properties are significantly better than the original powder without diffusion heat treatment.

[0041] Sm2Fe 17 When less than 85% of the Sm element in the N3 compound is replaced by other rare earth elements such as La, Ce, and Y, the compound still maintains easy c-axis magnetization and high magnetization intensity, but the magnetocrystalline anisotropy field will drop significantly as the amount of substitution increases. The coercive force of the magnetic powder is closely related to the magnetocrystalline anisotropy field of the compound. As the amount of substitution increases, the coercive force of the magnetic powder will inevitably drop significantly. The present invention effectively increases the Sm content in the shell of the single crystal magnetic powder and reduces the Ce content by adding an Sm diffusion source and heat treatment, thereby effectively increasing the magnetocrystalline anisotropy field on the surface of the magnetic powder. Therefore, the coercive force of the magnetic powder is effectively improved, and the magnetic energy product is effectively improved as the magnetic powder's resistance to demagnetization increases. This method is suitable for alloys with different ratios of La, Ce, Y, and other rare earth elements replacing Sm.

[0042] The description of the above embodiments is only used to help understand the technical solution and core ideas of the present invention. It should be pointed out that for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the present invention. These improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing heterogeneous single crystal magnetic powder, characterized in that: The process includes the following steps: (Sm, R1)2Fe2O3O3O3O3O3O3O3O3O3O3O3O3O3O3O3O3O3O3O3O3O3O3O3O3O4 ...4 17 The alloy powder is used as the master alloy magnetic powder. The Sm diffusion source alloy powder is mixed with a volatile organic solvent to form a paste. The composition of the Sm diffusion source alloy expressed in atomic percentage is Sm d M1 100-d , 50≤d≤95, M1 is Cu and / or Zn, the master alloy magnetic powder and the paste are evenly mixed to obtain a mixture, the mass ratio of the master alloy magnetic powder to the diffusion source alloy powder is 88:12-97:3, and then the mixture is sequentially subjected to diffusion heat treatment, hydrogen explosion treatment, dehydrogenation treatment, pulverization and nitriding to obtain heterogeneous single crystal magnetic powder.

2. The method for preparing heterogeneous single crystal magnetic powder according to claim 1, wherein: The preparation method of the Sm diffusion source alloy comprises the following steps: induction melting Sm and M1 alloy under argon protection to obtain a melt, using a water-cooled copper roller at a speed of 10-50 m / s to form a rapid-quenching diffusion source alloy thin strip, and grinding the rapid-quenching diffusion source alloy thin strip into particles with a particle size of 10-500 μm to obtain Sm diffusion source alloy powder.

3. The method for preparing heterogeneous single crystal magnetic powder according to claim 1, characterized in that: The (Sm, R1)2Fe alloy powder rich in La / Ce / Y 17 has a composition expressed in atomic percentages as: (Sm 1-α R1 α ) b Fe 100-b-c M2 c , where R1 is at least one rare earth element other than Sm, 0.2 < α < 1; 9 < b < 13; M2 is selected from at least one of Co, Si, Ga, Al, Ni, Ti, Cu, V, Cr, Zr, Hf, Nb, Ta, Mo, and W, and 0 ≤ c ≤ 30.

4. The method for preparing heterogeneous single crystal magnetic powder according to claim 3, characterized in that: R1 is at least one selected from La, Ce and Y.

5. The method for preparing heterogeneous single crystal magnetic powder according to claim 3, characterized in that: The preparation steps of the master alloy magnetic powder are as follows: 1-α R1 α ) b Fe 100-b-c M2 c The prepared metals Sm, pure Fe, R1 and M2 are placed in an induction melting furnace and smelted in high-purity Ar. The alloy is heated by induction until the raw materials are completely melted and uniformly obtained. The melt is quickly prepared into a quick-solidification casting sheet using a water-cooled copper roller. The master alloy casting sheet is placed in a heat treatment container and heat treated under argon protection. After air cooling, the master alloy casting sheet is crushed into master alloy magnetic powder with an average particle size of 1-20 μm.

6. The method for preparing heterogeneous single crystal magnetic powder according to claim 5, characterized in that: The surface linear speed of the water-cooled copper roller is 10-30 m / s, the heat treatment temperature is 900° C.-1000° C., and the heat treatment time is 30-50 min.

7. The method for preparing heterogeneous single crystal magnetic powder according to claim 1, characterized in that: The specific steps of sequentially subjecting the mixture to diffusion heat treatment, hydrogen explosion treatment, dehydrogenation treatment, powder making and nitriding to obtain heterogeneous single crystal magnetic powder are as follows: placing the mixture in a vacuum furnace under high-purity Ar protection for diffusion heat treatment, the diffusion heat treatment temperature is 650°C-960°C, and the heat treatment time is 0.5-10h; placing the casting after the diffusion heat treatment in H2 at 150-250°C for 1-3h, performing hydrogen explosion treatment, raising the furnace temperature to 550°C-600°C, and vacuum dehydrogenation treatment for 1.5-2.5h; grinding the casting after the dehydrogenation treatment to obtain magnetic powder, and nitriding the magnetic powder using high-purity nitrogen at 400°C-450°C for 30-40h to obtain heterogeneous single crystal magnetic powder.

8. The heterogeneous single crystal magnetic powder prepared by the method for preparing heterogeneous single crystal magnetic powder according to claim 1 is characterized in that: The heterogeneous single crystal magnetic powder is composed of the first phase, the second phase and the third phase. The first phase is composed of rare earth elements Sm, R1, Fe and transition metal elements M2, and has Th2Zn 17 or Th2Ni 17 The main phase has a spherical or equiaxed shape and an Sm-rich shell, and the thickness of the Sm-rich shell is between 0.1 and 1.0 μm; the main phase constituent atoms account for 80% to 99% of the mother alloy atoms; the second phase is a rare earth-rich auxiliary phase, the constituent atoms of the rare earth-rich auxiliary phase account for 0.5% to 19% of the mother alloy, and the rare earth-rich auxiliary phase is composed of any three of (Sm, R1)(Fe, M2)2, (Sm, R1)(Fe, M2)3, (Sm, R1)(Fe, M2)M1, and (Sm, R1)M12 phases; the third phase is oxides or nitrides of rare earths Sm and R1 and other unavoidable impurities.

9. Use of the heterogeneous single crystal magnetic powder according to claim 8 in preparing anisotropic bonded permanent magnetic materials or sintered anisotropic permanent magnetic materials.