CN101265529A - Preparation method of bulk nanocrystalline SmCo permanent magnet material - Google Patents

Abstract

A method for preparing a bulk nanocrystalline SmCo permanent magnet material belongs to the technical field of magnetic materials. The existing methods can only prepare powder samples, but cannot prepare bulk nanocrystalline SmCo permanent magnets. The method provided by the present invention is to melt the alloy whose composition is SmCo ₅ , Sm ₂ Co ₁₇ and Sm(Co, Cu, Fe, Zr) _7.5 into a master alloy, and then rapidly quench it at a speed of 40-50 m/s. Nanocrystalline thin strips; the thin strips are high-energy ball milled for 5-10 hours to obtain amorphous powders, which are put into molds and pre-pressed at 10-30MPa, and then sintered by SPS technology to obtain permanent magnet materials. The sintering temperature is 650°C-750°C. The sintering pressure is 300-1000MPa, the heating rate is 50-200°C/min, and the holding time is 0-10min. The permanent magnet material prepared by the invention has good density, high coercive force, good high-temperature magnetic performance, and the grain size is less than 100 nanometers.

Description

Preparation method of bulk nanocrystalline SmCo permanent magnet material

technical field

The invention belongs to the technical field of magnetic materials, and in particular relates to a preparation method of a fully dense block SmCo series nanocrystalline permanent magnet material.

Background technique

SmCo series (1:5 and 2:17 series) rare earth permanent magnets have excellent high-temperature magnetic properties, and are mainly used in high-temperature permanent magnet fields such as aviation, aerospace and military industry. The preparation process of this type of material is relatively strict and complicated. For example, SmCo ₅ needs to be sintered at high temperature and then cooled slowly and then quickly to obtain high coercive force. The process conditions are relatively harsh, and the coercive force will not be high if the treatment is not good; The coercive force of Sm ₂ Co ₁₇ is very low (about 2KOe), and the cellular structure is obtained after adding Fe, Cu, Zr and other elements through complicated precipitation hardening treatment, so that the Sm(Co, Cu, Fe, Zr) _z alloy can obtain high Coercivity. However, the current study found that the material has the largest coercive force when the grain size is close to the monodomain particle. Therefore, as long as the microstructure of the material is nanosized, the material can easily obtain high coercive force without complicated processes. People have prepared nanocrystalline Nd ₂ Fe ₁₄ B permanent magnets by means of melt rapid quenching and mechanical alloying (Kneller EF, et al.IEEE.Trans.Magn., 1991, 27: 3588; International Electronics Magnetics Special Journal of the Institute of Electrical Engineering) and nanocrystalline SmCo ₅ with a coercive force up to 5T (J.Ding, et al.J.Alloys Compd., 1993, 191:197) and other nanocrystalline permanent magnet materials. However, most of these materials currently prepared are thin strips or powders. When the traditional sintering process is used to prepare dense blocks, the grains will grow and the coercive force will be severely reduced, thereby significantly reducing the magnetic properties. Therefore, it can only be made into bonded Magnets, this is a difficult problem in the practical application of such permanent magnet materials.

Contents of the invention

The purpose of the present invention is to solve the problems in the prior art, and to provide a block-like material with high density, fine grain structure (grains less than 100 nanometers), high coercive force and high service temperature prepared by spark plasma sintering technology. A method for SmCo nanocrystalline permanent magnet materials.

The preparation method of bulk SmCo series nanocrystalline permanent magnet material provided by the invention comprises the following steps:

1) Smelting the alloy with the composition of SmCo ₅ , Sm ₂ Co ₁₇ and Sm(Co, Cu, Fe, Zr) _7.5 into a master alloy in an electric arc furnace, and then making the master alloy into a nanocrystalline state by melt rapid quenching The rapid quenching thin strip, the line speed of melt quenching is 40-50 m/s;

2) under the protection of an inert gas, high-energy ball milling for 5-10 hours with the rapid-quenching strip prepared in step 1), and the ball-to-material ratio is 15:1 to obtain an amorphous powder;

3) The amorphous powder prepared in step 2) is loaded into a WC cemented carbide mold and pre-pressed, and the pressure range is 10-30MPa;

4) Using spark plasma sintering technology to sinter the pre-pressed amorphous powder in step 3) to obtain a massive nanocrystalline SmCo permanent magnet material; wherein, the sintering temperature is 650-750°C, and the sintering pressure is 300-1000MPa, The heating rate is 50-200°C/min, and the holding time is 0-10min.

The bulk nanocrystalline SmCo permanent magnet materials described in step 4) are SmCo ₅ , Sm ₂ Co ₁₇ and Sm(Co, Cu, Fe, Zr) _7.5 .

Spark plasma sintering technology (Spark Plasma Sintering, referred to as SPS technology) is a pressure sintering method that uses DC pulse current to conduct sintering (the schematic diagram of the device is shown in Figure 1). The basic principle is that by passing a DC pulse current to the electrode, the discharge plasma generated instantaneously causes each particle in the sintered body to uniformly generate Joule heat and activate the surface of the particle, and realizes sintering while pressurizing. This technology has the following characteristics: (1) The sintering temperature is low, generally 200-300°C lower than the ordinary sintering temperature; (2) The sintering holding time is short, only 3-10 minutes; (3) The pressure can be applied during sintering, the highest It can reach 1000MPa; (4) It can obtain high-density materials; (5) It can obtain fine and uniform grain structure. Therefore, the SPS sintering method can effectively suppress the grain growth inside the material while realizing the densification of the SmCo-based powder, thereby ensuring that the magnet obtains a nanocrystalline structure and ideal magnetic properties. This is of great significance for further expanding the application fields of such materials.

Compared with the prior art, the present invention has the following beneficial effects:

1) The density of the permanent magnet material prepared by the method of the present invention reaches more than 98% of the theoretical density of the alloy with the same composition, which solves the problem of low density of bonded magnets and greatly improves the magnetic properties of the magnets;

2) The permanent magnet material prepared by the inventive method has high coercive force (see Table 1) and good high-temperature magnetic properties;

3) The permanent magnet material prepared by the method of the present invention has uniform microstructure, fine grains, and the grain size is less than 100 nanometers (see Figures 2, 3, and 4).

Description of drawings

Figure 1. Schematic diagram of the structure of spark plasma sintering equipment.

Fig. 2, transmission electron microscope and selected area diffraction photos of the bulk nanocrystalline SmCo ₅ permanent magnet material prepared in Example 1.

Fig. 3. Transmission electron microscope and selected area diffraction photographs of the bulk nanocrystalline Sm ₂ Co ₁₇ permanent magnet material prepared in Example 3.

Fig. 4, transmission electron microscope and selected area diffraction photos of the bulk nanocrystalline Sm (Co, Cu, Fe, Zr) _7.5 permanent magnet material prepared in Example 5.

Fig. 5, the hysteresis loop (a) of the bulk nanocrystalline SmCo ₅ permanent magnet material prepared in Example 1 and the demagnetization curve (b) at different temperatures.

Fig. 6. The hysteresis loop diagram of the bulk nanocrystalline Sm ₂ Co ₁₇ permanent magnet material prepared in Example 3.

Fig. 7, the hysteresis loop diagram of the bulk nanocrystalline Sm(Co, Cu, Fe, Zr) _7.5 permanent magnet material prepared in Example 5.

Among them, in Figures 5 to 7: μ ₀ H(T): the size of the external magnetic field, the unit is Tesla (T); μ ₀ Hc(T): the size of the coercive force of the material, the unit is Tesla (T ); 4πM(T): the magnitude of the magnetization of the material, the unit is Tesla (T); 4πMs(T): the magnitude of the saturation magnetization of the material, the unit is Tesla (T); 4πMr(T): the remaining material The size of the magnetization, the unit is Tesla (T).

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

Detailed ways

Example 1

1) The alloy whose composition is SmCo ₅ is smelted in an electric arc furnace and subjected to rapid quenching of the melt, and the line speed of rapid quenching is 50 m/s;

2) High-energy ball milling the quenched alloy for 5 hours under the protection of an inert gas to obtain an amorphous powder with a ball-to-material ratio of 15:1;

3) Put the amorphous powder into the WC cemented carbide mold and pre-press molding, the pressure is 10MPa;

4) The pre-pressed amorphous powder is sintered into SmCo ₅ bulk material by discharge rapid sintering technology (see Table 1 for properties). The specific sintering process is: under the sintering pressure of 1000MPa, from room temperature at a heating rate of 50°C/min After heating up to 650°C, hold the temperature for 0 min.

Example 2

1) The alloy whose composition is SmCo ₅ is smelted in an electric arc furnace and subjected to rapid quenching of the melt, and the line speed of rapid quenching is 50 m/s;

2) High-energy ball milling the quenched alloy for 5 hours under the protection of an inert gas to obtain an amorphous powder with a ball-to-material ratio of 15:1;

3) Put the amorphous powder into the WC cemented carbide mold and pre-press molding, the pressure is 10MPa;

4) The pre-pressed amorphous powder is sintered into SmCo ₅ bulk material by using discharge rapid sintering technology (see Table 1 for properties). The specific sintering process is: under the sintering pressure of 500MPa, from room temperature at a heating rate of 50°C/min After heating up to 700°C, keep it warm for 3 minutes.

Example 3

1) The alloy whose composition is Sm ₂ Co ₁₇ is smelted in an electric arc furnace and then subjected to rapid quenching of the melt, and the line speed of rapid quenching is 40 m/s;

2) High-energy ball milling the quenched alloy for 8 hours under the protection of an inert gas to obtain an amorphous powder with a ball-to-material ratio of 15:1;

3) Put the amorphous powder into the WC cemented carbide mold and pre-press molding, the pressure is 20MPa;

4) The pre-pressed amorphous powder is sintered into Sm ₂ Co ₁₇ bulk material by using discharge rapid sintering technology (see Table 1 for properties). After the heating rate was raised to 700°C, the temperature was kept for 10 minutes.

Example 4

1) The alloy whose composition is Sm ₂ Co ₁₇ is smelted in an electric arc furnace and then subjected to rapid quenching of the melt, and the line speed of rapid quenching is 40 m/s;

2) High-energy ball milling the quenched alloy for 8 hours under the protection of an inert gas to obtain an amorphous powder with a ball-to-material ratio of 15:1;

3) Put the amorphous powder into the WC cemented carbide mold and pre-press molding, the pressure is 20MPa;

4) The pre-pressed amorphous powder is sintered into Sm ₂ Co ₁₇ bulk material by using discharge rapid sintering technology (see Table 1 for properties). The specific sintering process is: under the sintering pressure of 500MPa, from room temperature to After the heating rate was raised to 750°C, the temperature was kept for 5 minutes.

Example 5

1) The alloy whose composition is Sm(Co, Cu, Fe, Zr) _7.5 is smelted in an electric arc furnace and then subjected to rapid quenching of the melt, and the line speed of rapid quenching is 45 m/s;

2) High-energy ball milling of the quenched alloy for 10 hours under the protection of an inert gas to obtain an amorphous powder with a ball-to-material ratio of 15:1;

3) Put the amorphous powder into the WC cemented carbide mold and pre-press molding, the pressure is 30MPa;

4) The pre-pressed amorphous powder is sintered into a Sm(Co, Cu, Fe, Zr) _7.5 bulk material (see Table 1 for properties) by using discharge rapid sintering technology. The specific sintering process is: under the sintering pressure of 300MPa, from After the room temperature was raised to 750°C at a heating rate of 200°C/min, the temperature was kept for 5 minutes.

The performance of the bulk nanocrystal SmCo system permanent magnet material prepared by the present invention of table 1

Claims (2)

1, a kind of preparation method of block-shaped nano-crystal SmCo series permanent magnetic material is characterized in that, may further comprise the steps:

1) be SmCo with composition ₅, Sm ₂Co ₁₇And Sm (Co, Cu, Fe, Zr) _7.5Alloy in electric arc furnace, be smelted into mother alloy, with melt-quenching method mother alloy is made the fast quenching thin strap of crystalline state nanometer again, the linear velocity of melt-spun is the 40-50 meter per second;

2) with the fast quenching thin strap for preparing in the step 1), under protection of inert gas, high-energy ball milling 5-10h, ratio of grinding media to material is 15: 1, obtains amorphous powder;

3) with step 2) amorphous powder pack into the WC sintered-carbide die and the pre-molding of preparation, pressure range 10-30MPa;

4) utilize discharge plasma sintering technique to obtain block-shaped nano-crystal SmCo series permanent magnetic material with carrying out sintering through the amorphous powder of pre-molding in the step 3); Wherein, sintering temperature is 650-750 ℃, and sintering pressure is 300-1000MPa, and temperature rise rate is 50-200 ℃/min, and soaking time is 0-10min.

2, method according to claim 1 is characterized in that, the block-shaped nano-crystal SmCo series permanent magnetic material described in the step 4) is SmCo ₅, Sm ₂Co ₁₇Or Sm (Co, Cu, Fe, Zr) _7.5

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