Preparation method for anisotropic nd 2fe 14b / α-fe bulk nanocrystalline composite permanent magnet material

Abstract

Disclosed in the present invention is a preparation method for an anisotropic Nd2Fe14B / α-Fe bulk nanocrystalline composite permanent magnet material. The preparation method comprises the following steps: preparing a master alloy; crushing the master alloy into bulks, and, by means of a melt rapid quenching method, preparing amorphous ribbons; grinding the amorphous ribbons to obtain amorphous powder; cold-pressing the powder into bulks; and placing the bulks into a stainless steel mold, and heating and then rolling same, the stainless steel mold being of a plate-shaped structure, and a chamber for accommodating the bulks being formed in the stainless steel mold along the thickness direction thereof. The present invention presses the NdFeB amorphous powder into bulks, embeds same in the stainless steel mold, and performs rolling at a temperature below a crystallization temperature, so as to achieve high-temperature amorphous material crystallization. During this process, great stresses and strains are introduced by means of rolling, so as to induce the Nd2Fe14B phase to grow in preferred orientations during the crystallization process, thereby obtaining the Nd2Fe14B / α-Fe bulk nanocrystalline composite permanent magnet material having anisotropy.

Description

Anisotropic Nd2Fe 14 Preparation method of B / α-Fe bulk nanocrystalline composite permanent magnetic material Technical Field The present invention relates to the technical field of permanent magnetic materials, and in particular to an anisotropic Nd2Fe 14 A method for preparing B / α-Fe bulk nanocrystalline composite permanent magnetic material. Background Art Bulk permanent magnet materials have very important applications in electric vehicles, wind power generation, aerospace, military and other fields. The most important indicator for measuring the performance of permanent magnet materials is the maximum magnetic energy product. At present, the permanent magnet with the best magnetic properties is the "permanent magnet king" neodymium iron boron, but the magnetic energy product of existing neodymium iron boron permanent magnet materials is close to the theoretical maximum value, but it cannot meet the high-tech demand for super-strong permanent magnets. To break through the theoretical maximum value, it is necessary to increase the saturation magnetization intensity of the material. At the nanoscale, fine-grained Fe with higher saturation magnetization intensity is added to the neodymium iron boron magnet to form Nd2Fe 14 B / α-Fe nanocrystalline composite magnets are the best way to improve the theoretical magnetic energy product. This type of material has a higher theoretical magnetic energy product and thus has greater room for development. Unfortunately, the bulk Nd2Fe 14 B / α-Fe nanocrystalline composite permanent magnet materials are all isotropic and have a relatively low magnetic energy product, because the theoretical magnetic energy product of an isotropic magnet is only one-fourth of that of an anisotropic magnet. 14 B / α-Fe nanocrystalline composite magnets require Nd2Fe in the magnet 14 The B phase must be preferentially oriented along the c-axis at the nanoscale to form an anisotropic bulk. However, in actual preparation, it is very difficult to form nanocrystalline anisotropic bulk materials. Summary of the invention In view of the above technical problems, the present invention provides a method for preparing anisotropic Nd2Fe14B / α-Fe bulk nanocrystalline composite permanent magnet material. To achieve the above object, the technical solution adopted by the present invention is: In one aspect, the present invention provides an anisotropic Nd2Fe 14 The preparation method of B / α-Fe bulk nanocrystalline composite permanent magnetic material comprises the following steps: Step 1: preparing master alloy; Step 2: crushing the master alloy in step 1 into blocks, and then preparing amorphous strips by melt rapid quenching method; Step 3: Grind the amorphous strip obtained in step 2 to obtain amorphous powder; Step 4: cold-press the powder obtained in step 3 into blocks; Step 5: placing the block obtained by cold pressing in step 4 in a stainless steel mold, heating it, and then rolling it; The stainless steel mold is a plate-shaped structure, and a cavity for accommodating the block is provided on the stainless steel mold along its thickness direction. As a preferred embodiment, in step 5, the heating is heating to 500-530°C. As a preferred embodiment, in step 5, the inner diameter of the chamber is adapted to the outer diameter of the block; Preferably, after placing the block in the cavity opened on the stainless steel mold, the process further includes sealing the cavity with a metal material; the metal material is preferably copper; and the sealing is performed in an inert atmosphere; In some specific embodiments, the seal is made by using a sheet metal material slightly larger than the inner diameter of the cavity opened on the stainless steel mold to be pressed into the cavity containing the block by a hydraulic press to ensure the flatness of the seal; In some specific embodiments, the stainless steel mold is a plate-shaped stainless steel mold with a thickness of 5 to 10 mm; the bottom thickness of the chamber is 0.3 to 0.5 mm, and the bottom thickness of the chamber refers to the thickness of the stainless steel at the bottom of the chamber. As a preferred embodiment, in step 5, the roller speed of the rolling roller is 0.9-1.5 m / s; Preferably, during the rolling process, the deformation of the block is ≥70%. In the technical solution of the present invention, the deformation refers to the percentage of reduction in the height of the block. As a preferred embodiment, in step (1), the chemical composition of the master alloy is as shown in the following formula (1): Nd x Fe y-m B z X m (1); In formula (1), X is an additive element selected from at least one of Nb, Zr, Ti, Cu, Ga and Al. m is the total atomic percentage of the added elements, among which the atomic percentage of a single element does not exceed 1 at%; x, y, and z are atomic percentages, x is 8 to 10 at%, y is 84 to 88 at%, and z is 4 to 6 at%. As a preferred embodiment, in step 1, the preparation of the master alloy is often carried out by vacuum melting. As a preferred embodiment, in step 2, the quenching speed of the melt is 27 to 32 m / s; Preferably, in step 2, the stripping temperature in the melt rapid quenching is 1250-1350°C. Preferably, the thickness of the amorphous strip is 10-15 μm, and the width is not limited. As a preferred embodiment, in step 3, the grinding method is not particularly limited and may be manual grinding or ball milling. In order not to destroy the strip structure obtained in step 2, manual grinding is preferred. In the technical solution of the present invention, the grinding is performed until the particle size of the amorphous powder is ≤300 mesh. As a preferred embodiment, in step 4, the density of the cold pressed blocks is ≥80%; In certain specific embodiments, when the powder is cold pressed into blocks using a cold pressing mold, the inner diameter of the mold can be selected from 5 to 30 mm, the thickness of the blocks obtained by cold pressing generally does not exceed 3 mm, and the pressing temperature can be selected at room temperature or at a certain temperature, and can be pressed in air or in an argon atmosphere. In another aspect, the present invention provides anisotropic Nd2Fe 14 B / α-Fe bulk nanocrystalline composite permanent magnet material. In the technical solution of the present invention, the anisotropic Nd2Fe 14 B / α-Fe bulk nanocrystalline composite permanent magnet material is composed of Nd2Fe 14 The B phase and the α-Fe phase are composited, wherein the content of the α-Fe phase is 20-40%, and the Nd2Fe 14 The B phase grains grow in an oriented manner and have

[0004] Crystallographic texture characteristics. The above technical solution has the following advantages or beneficial effects: In the preparation method provided by the present invention, NdFeB amorphous powder is pressed into a block, embedded in a stainless steel mold, sealed, heated to a temperature below the crystallization temperature, and then rolled. The heat generated by the rolling itself is used to raise the sample to a suitable temperature, and the sample is rolled with a large deformation at a suitable temperature to achieve high-temperature amorphous crystallization. In the high-temperature amorphous crystallization process, the large stress and strain introduced by rolling induces Nd2Fe 14 Phase B grows in a preferred orientation during the crystallization process. At the same time, during this process, a faster roll speed will Suppressing the growth of α-Fe phase, thus obtaining anisotropic Nd2Fe 14 B / α-Fe bulk nanocrystalline composite permanent magnetic material. The preparation method provided by the present invention can obtain nanocrystalline permanent magnetic materials with crystal texture, thereby realizing the preparation of high-performance anisotropic permanent magnetic materials, the method is simple, easy to implement, and suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS FIG1 is a schematic diagram of the process of rapid quenching of the melt in step 2 of Example 1 of the present invention. FIG. 2 is a schematic diagram of the grinding process in step 3 of Example 1 of the present invention. FIG3 is a schematic diagram of the cold pressing process in step 4 of Example 1 of the present invention. FIG. 4 is a schematic diagram of the process of placing the block obtained by cold pressing into a stainless steel mold in step 5 of Example 1 of the present invention. FIG. 5 is a schematic diagram of the rolling process in step 6 of Example 1 of the present invention. FIG. 6 is an XRD spectrum of the permanent magnet material parallel to the rolling surface prepared in Example 1 of the present invention. FIG. 7 is a hysteresis loop diagram of the easy magnetization and hard magnetization directions of the permanent magnetic material prepared in Example 1 of the present invention. DETAILED DESCRIPTION The following embodiments are only some embodiments of the present invention, rather than all embodiments. Therefore, the detailed description in the embodiments of the present invention provided below is not intended to limit the scope of the present invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work belong to the protection scope of the present invention. In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments are all conventional methods in the art unless otherwise specified. Embodiment 1: The anisotropic Nd2Fe 14 The preparation method of B / α-Fe bulk nanocrystalline composite permanent magnet material is as follows: Step 1: Use vacuum melting to obtain the master alloy, the alloy composition is Nd9Fe 84 CuB6; Step 2: crush the master alloy into blocks, and then use the melt rapid quenching method to make the alloy into strips, as shown in Figure 1, the specific operation is: put the alloy block 1 after the master alloy is crushed into a quartz tube 4 with a small hole at the lower end, and melt the alloy block 1 into alloy liquid 5 under the heating of the high-frequency copper coil 2, and blow the alloy liquid onto the rapidly rotating copper roller 3 under the action of argon gas with a pressure difference, and then the alloy strip 7 can be thrown out; wherein, the rotation speed of the copper roller 3 is 32m / s, the diameter of the quartz tube 4 is 0.6mm, the distance from the lower tube mouth of the quartz tube 4 to the copper roller 3 is 2mm, and the strip throwing temperature is 1300℃; the thickness of the prepared alloy strip 7 is about 13μm, the width is about 1.5mm, and the structure is an amorphous structure; Step 3: As shown in FIG. 2 , the alloy strip 7 obtained in step 2 is placed in an agate mortar 8 for manual grinding. After being ground to slightly fine size, the alloy strip is placed in a ball mill 9 , a ball milling medium 10 is added, and the alloy strip is ground on a ball mill for 2 minutes to obtain an amorphous powder 11 with a size of less than 300 meshes. Step 4: As shown in FIG3 , the amorphous powder 11 is placed in a cold pressing mold 13, the inner hole diameter of the cold pressing mold is 8 mm, a pressure rod column 15 is placed at the bottom of the inner hole of the mold, and then the mold 13 filled with the amorphous powder is placed on the cemented carbide lower pressure head 16, the upper pressure rod 17 is installed, and the cemented carbide upper pressure head 12 is placed. The upper / lower cemented carbide pressure heads 12 / 16 are pressurized together to perform block pressing. The thickness of the pressed block 18 is 3 mm and the density is 80%; Step 5: As shown in FIG4 , a semi-through hole 20 with an inner diameter of 8 mm is pre-processed on a 10 mm thick stainless steel plate 19, and the remaining steel plate thickness at the bottom of the semi-through hole 20 is 0.5 mm; the block 18 is stacked in the semi-through hole 20, and a total of 3 blocks are stacked, and then a copper sheet 21 is pressed into the semi-through hole by a hydraulic press in an argon protection environment to seal the opening of the semi-through hole; Step 6: Heat the stainless steel plate sealed in step 5 to 500°C, and then as shown in FIG5, place the heated stainless steel plate 22 on a rolling mill that has been started for rolling, with a roll gap 23 between two rolls of 2 mm and a roll speed of 0.9 m / s. In this embodiment, the deformation after rolling exceeds 75%; take out the embedded sample to obtain anisotropic Nd2Fe 14 B / α-Fe bulk nanocrystalline composite permanent magnet material. The anisotropic magnet of the permanent magnetic material prepared in this embodiment can be tested by its microstructure and magnetic properties: FIG6 shows the XRD spectrum of the permanent magnetic material parallel to the hot-rolled surface, in which “Rd” is “rod direction”, indicating that the direction indicated by the arrow is the rolling direction. From the spectrum, it can be seen that the (004) diffraction peak is consistent with the Nd2Fe 14 The ratio of the strongest peak (220) of phase B is 365%, which is significantly higher than the ratio of 67.5% of the PDF card, indicating that the prepared magnet has a preferred orientation of (004). Figure 7 shows the hysteresis loops of the magnet parallel and perpendicular to the rolling direction. It can be clearly seen that the magnet prepared by this method has obvious magnetic anisotropy. The magnetic energy product of the sample is 22.1MGOe, and the volume fraction of the α-Fe phase is 32.8%. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. Anisotropic Nd2Fe 14 The preparation method of B / α-Fe bulk nanocrystalline composite permanent magnetic material is characterized by: The following steps are involved: Step 1: preparing master alloy; Step 2: crushing the master alloy in step 1 into blocks, and then preparing amorphous strips by melt rapid quenching method; Step 3: Grind the amorphous strip obtained in step 2 to obtain amorphous powder; Step 4: cold-press the powder obtained in step 3 into blocks; Step 5: placing the block obtained by cold pressing in step 4 in a stainless steel mold, heating it, and then rolling it; The stainless steel mold is a plate-shaped structure, and a cavity for accommodating the block is provided on the stainless steel mold along its thickness direction.

2. The preparation method according to claim 1, characterized in that: In step 5, the heating is heating to 500-530°C.

3. The preparation method according to claim 1, characterized in that: In step 5, the inner diameter of the chamber is adapted to the outer diameter of the block; Preferably, after placing the block in the cavity opened on the stainless steel mold, the process further includes sealing the cavity with a metal material; the metal material is preferably copper; and the sealing is performed in an inert atmosphere; Preferably, the stainless steel mold is a plate-shaped stainless steel mold with a thickness of 5 to 10 mm; the bottom thickness of the chamber is 0.3 to 0.5 mm, and the bottom thickness of the chamber refers to the thickness of the stainless steel at the bottom of the chamber.

4. The preparation method according to claim 1, characterized in that: In step 5, the roller speed of the roller in the rolling is 0.9 to 1.5 m / s; Preferably, during the rolling process, the deformation of the block is ≥ 70%.

5. The preparation method according to claim 1, characterized in that: In step (1), the chemical composition of the master alloy is as shown in the following formula (1): x Fe y-m B z X m (1); In formula (1), X is an additive element selected from at least one of Nb, Zr, Ti, Cu, Ga and Al; m is the total atomic percentage of the additive elements, and the atomic percentage of a single element in the additive elements does not exceed Over 1at%; x, y, z are atomic percentages, x is 8-10at%, y is 84-88at%, and z is 4-6at%.

6. The preparation method according to claim 1, characterized in that: In step 1, the preparation of the master alloy is usually carried out by vacuum melting.

7. The preparation method according to claim 1, characterized in that: In step 2, the quenching speed in the melt quenching is 27 to 32 m / s; Preferably, in step 2, the stripping temperature in the melt rapid quenching is 1250-1350°C; Preferably, the thickness of the amorphous strip is 10-15 μm.

8. The preparation method according to claim 1, characterized in that: In step 3, the grinding is performed until the particle size of the amorphous powder is ≤300 mesh.

9. The preparation method according to claim 1, characterized in that: In step 4, the density of the cold-pressed blocks is ≥80%.

10. Anisotropic Nd2Fe obtained by the preparation method according to any one of claims 1 to 9 14 B / α-Fe bulk nanocrystalline composite permanent magnet material.

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