CN102737801B - Method for preparing Sm-Fe-N anisotropic magnetic powder - Google Patents

Abstract

The invention discloses a preparation method of Sm-Fe-N anisotropic magnetic powder, which belongs to the field of magnetic materials. The process flow is: preparation of alloy melt → control of rapid solidification process parameters, control of cast sheet thickness → rapid solidification of fine Sm ₂ Fe ₁₇ columnar crystals with nearly uniform orientation → crystallization treatment → coarse crushing → nitriding → fine Grinding → anisotropic Sm-Fe-N magnetic powder. Its main feature is to control the cooling speed and crystallization process of the melt through the control of the cooling copper roll speed, melt injection gas pressure, nozzle size, melt temperature, and melt composition, so as to obtain fine columnar crystals Sm ₂ Fe ₁₇ consistent The oriented quick-setting cast sheet lays the foundation for the preparation of anisotropic magnetic powder and bonded magnets with consistent magnetic crystal orientation. The preparation method of the Sm-Fe-N anisotropic magnetic powder avoids the long-term high-temperature homogenization annealing of the Sm-Fe alloy ingot that is usually required.

Description

A kind of preparation method of Sm-Fe-N anisotropic magnetic powder

technical field

The invention belongs to the field of magnetic materials and relates to a preparation method of Sm-Fe-N anisotropic magnetic powder.

Background technique

Sm2Fe ₁₇ N _x has excellent intrinsic magnetic properties, and is known as a new generation of permanent magnet materials after Nd-Fe-B. Compared with Nd ₂ Fe ₁₄ B, it has a higher Curie temperature (nearly 160°C higher), particularly high magnetocrystalline anisotropy, H _A =11.2MA/m (140KOe), second only to SmCo ₅ , which is twice that of Nd ₂ Fe ₁₄ B, and the theoretical magnetic energy product is 472KJ/m ³ (59.2MGOe), roughly equivalent to Nd ₂ Fe ₁₄ B (509KJ/m ³ ). Since Sm ₂ Fe ₁₇ N _x will decompose at high temperature, it cannot be sintered and can only be made into a bonded magnet. In terms of intrinsic magnetic properties, the saturation magnetic polarization of Sm ₂ Fe ₁₇ N _x is slightly lower than that of Nd ₂ Fe ₁₄ B, but its Curie temperature and magnetocrystalline anisotropy field are much higher than the latter. In addition, from a practical point of view, Sm ₂ Fe ₁₇ N _x is better than Nd ₂ Fe ₁₄ B in thermal stability, oxidation resistance and corrosion resistance. Another outstanding advantage of it is that it can be made into anisotropic bonded magnetic powder and bonded magnet.

At present, the methods for preparing Sm ₂ Fe ₁₇ N _x mainly include: mechanical alloying method (MA), hydrogen fragmentation method (HDDR), reduction diffusion method (R/D), rapid quenching method (RQ), powder metallurgy method (PM) . The technological process and characteristics of the preparation of Sm ₂ Fe ₁₇ powder and its Sm ₂ Fe ₁₇ N _x magnetic powder by various methods are as follows:

Mechanical alloying method (MA): pure component powder mixing → high energy ball milling → forming layered particles → diffusion annealing, forming nanocrystals → nitriding → Sm ₂ Fe ₁₇ N _x magnetic powder. The preparation of Sm ₂ Fe ₁₇ by mechanical alloying requires long-term high-energy ball milling, the powder has high activity and fine particles, and it is easy to increase the oxygen content in the process of nitriding and preparing bonded magnets; because the powder particles are too small, it is difficult to prepare High-density bonded magnets are produced; although the powder particles are small, they are not necessarily single-crystal single-domain particles, and are mainly suitable for the preparation of isotropic magnetic powder.

Reduction diffusion method (R/D): a certain ratio of raw materials such as Sm ₂ O ₃ , Ca, Fe, etc. → mixing → briquetting → reduction diffusion reaction → product separation → nitriding → fine grinding → Sm ₂ Fe ₁₇ N _x magnetic powder . This method is mainly suitable for the preparation of isotropic magnetic powder. The difficulty of this method is mainly the separation of reaction products and the oxidation prevention of Sm-Fe alloy powder during the separation process. Powder metallurgy (PM): a certain proportion of alloy raw materials → smelting → Homogenization treatment → coarse crushing → ball milling → nitriding → fine grinding → Sm ₂ Fe ₁₇ N _x magnetic powder.

Powder metallurgy (PM): a certain ratio of alloy raw materials → smelting → homogenization treatment → coarse crushing → ball milling → nitriding → fine grinding → Sm ₂ Fe ₁₇ N _x magnetic powder. Powder metallurgy can produce high-performance anisotropic Sm ₂ Fe ₁₇ N _x magnetic powder, which has a better application prospect because the remanence and energy product of anisotropic magnetic powder are much higher than that of isotropic magnetic powder. Disadvantages of this method require long-term high-temperature homogenization annealing of the smelted alloy. Due to the slow cooling rate of the induction smelting water-cooled copper mold casting process, the solidified alloy structure is coarse and the composition of the ingot is unevenly distributed; due to L+Fe→Sm ₂ The characteristics of the Fe ₁₇ peritectic reaction, the reaction is not complete, and there are more α-Fe and Sm-rich phases in the alloy. In order to obtain more Sm ₂ Fe ₁₇ phase structure, transform the alloy structure with incomplete peritectic reaction into Sm ₂ Fe ₁₇ phase, it must be homogenized at high temperature (about 1020°C) for a long time, generally for about 20 hours. achieve better results. In addition, the alloy does not necessarily fracture along the grain boundaries during the powder making process, and some of the obtained Sm-Fe-N powder particles may be composed of polycrystals. Due to the different grain orientations, these powder particles do not have anisotropy.

Hydrogen disintegration method (HDDR): master alloy smelting→homogenizing annealing→coarse crushing→hydrogen treatment in HDDR process→nitriding→Sm ₂ Fe ₁₇ N _x magnetic powder. The HDDR method is to process the homogenized master alloy through hydrogenation, disproportionation decomposition, dehydrogenation and recombination to refine the Sm ₂ Fe ₁₇ grains, and obtain isotropic magnetic powder with high coercive force through nitriding.

Rapid quenching method (RQ): master alloy smelting → rapid quenching into thin strips (amorphous state) → crystallization treatment (nanocrystals) → crushing, ball milling into powder. Adding a small amount of Co, Zr, and B to the Sm-Fe alloy can increase the Curie temperature of Sm ₂ Fe ₁₇ N _x , refine the grains of Sm ₂ Fe ₁₇ and amorphize the rapidly quenched ribbon. The medium and fine α-Fe phase exchange coupling effect improves the remanence of Sm ₂ Fe ₁₇ N _x magnetic powder, and the isotropic magnetic powder with remanence and magnetic energy product better than other methods such as HDDR method has been obtained so far.

The powder metallurgy method can produce high-performance anisotropic magnetic powder, but because the ingot requires long-term homogenization annealing treatment, it hinders the popularization and application of the powder metallurgy method in industrial production. The key to restricting the development of this method is Sm ₂ Fe ₁₇ alloy fabrication parts. Compared with other methods, the rapid quenching method shows a good development prospect. At present, it is reported that the isotropic Sm-Fe-N magnetic powder is produced by the rapid quenching method. Magnetic and magnetic energy products create favorable conditions.

Contents of the invention

The object of the present invention is to provide a method for preparing Sm-Fe-N anisotropic magnetic powder by rapid quenching of the melt, by controlling the rotation speed of the copper roll, the pressure of the melt injection gas, the size of the nozzle, the temperature of the melt, and the Bulk composition, to control the cooling rate of the melt and the thickness of the quick-solidified cast sheet, to achieve the goal of obtaining the main phase of the quick-solidified thin band Sm ₂ Fe ₁₇ arranged in fine columnar crystals, the columnar crystals are basically in the same orientation, perpendicular to the quick-solidified cast After further crystallization treatment, crushing, nitriding, and fine grinding, the anisotropic Sm-Fe-N magnetic powder and anisotropic bonded magnet with the same orientation of the easy magnetization direction of the magnetic crystal in the powder particle are obtained.

The process of preparing Sm-Fe-N magnetic powder in the present invention is as follows: raw material selection and proportioning→vacuum induction melting (alloy melt preparation)→quick quenching (control of rapid solidification process parameters, control of cast sheet thickness)→alloy structure analysis →Small Sm ₂ Fe ₁₇ columnar crystals with nearly uniform orientation of quick-setting cast sheet →Coarse crushing →Heat treatment (Sm ₂ Fe ₁₇ further crystallized) →Crushing→Nitriding→Fine grinding→Anisotropic Sm-Fe-N magnetic powder→ Test powder magnetic properties. The prepared Sm-Fe-N magnetic powder has obvious anisotropic characteristics. Compared with isotropic samples, the remanence after orientation increases by more than 20%.

Process of the present invention:

(1) With Sm and Fe ingredients, a small amount of Co, V, Zr, B can be added, according to the molecular formula of Sm ₂ (Fe _1-x M _x ) ₁₇ , M is one of Co, V, Zr, B or Several kinds, the atomic percentage of each substituting Fe is not more than 5%. Since Sm is easy to volatilize, there should be a certain excess, and generally add 18% to 35% of the calculated amount. Apply high-temperature induction melting alloy, the molten alloy flows to the rotating copper roller and quickly solidifies into a thin strip, by controlling the rotation speed of the copper roller (4~15m/s), the size of the nozzle (0.2~0.65mm in width), and the pressure of the melt injection gas Gas pressure (0.5~1.5atm) and melt temperature (1520-1570°C), a thin ribbon structure with Sm ₂ Fe ₁₇ phase in the form of fine columnar grains distributed nearly parallel, with a thickness of 0.1~0.4mm is obtained.

(2) Use electron microscope to observe and analyze the thin ribbon section to determine whether columnar crystal structure is formed; use X-ray diffraction analysis to determine whether the main phase structure of the quick-setting thin ribbon is Sm ₂ Fe ₁₇ phase.

(3) Coarsely crush the qualified quick-setting cast sheet to 1~5mm, and further crystallize and heat treat it under the protective atmosphere of high-purity argon at 700~800°C to promote atomic diffusion, so that the crystallinity of the Sm ₂ Fe ₁₇ phase is more whole.

(4) Breaking: Under the protection of petroleum ether medium or high-purity argon gas protection medium, the Sm-Fe alloy powder is broken to below 320 mesh, so as to facilitate the diffusion of N atoms into the interior during the nitriding process.

(5) Nitriding treatment: Sm-Fe alloy powder is nitrided in a mixed atmosphere of high-purity nitrogen or NH ₃ and H ₂ , the nitriding gas pressure is 0.1~1.0MPa, the nitriding temperature is 400~500°C, nitrogen The curing time is 3~5 hours.

(6) Fine grinding: use petroleum ether as the ball milling medium, the ball-to-material ratio is 4:1~30:1, and ball mill for 3~20 hours.

(7) Drying and sample preparation. After ball milling, the discharged material is vacuum-dried at room temperature to obtain anisotropic Sm-Fe-N magnetic powder. Sampling the powder, using AB glue as a binder, and preparing and measuring the size of the sample under a 2T magnetic field for orientation curing Powder magnetic properties were measured using a vibrating sample magnetometer (VSM).

The advantages of the present invention are: the obtained Sm-Fe alloy quick-setting cast slab has a uniform structure and does not need long-term high-temperature homogenization annealing treatment; since the fine Sm ₂ Fe ₁₇ columnar crystals are perpendicular to the surface of the quick-setting cast slab and are nearly uniformly oriented, the This is used as a raw material to prepare anisotropic Sm-Fe-N magnetic powder.

Description of drawings

Figure 1. Columnar grain structure (not corroded) perpendicular to the copper roller. In the figure, the light gray phase is mainly Sm ₂ Fe ₁₇ columnar grains, and the white phase distributed between grains is Sm-rich phase

Figure 2. XRD analysis of the quick-setting cast sheet. It can be seen from X-diffraction that the Sm ₂ Fe ₁₇ phase is mainly formed, and there is also a Sm-rich phase——SmFe ₃

Detailed ways

Example 1

Use pure iron with a purity of 99.9% and rare earth Sm as raw materials, clean the Fe rods, and mix according to Sm ₂ Fe _17. Since Sm is easy to volatilize, add 22% to the calculated amount. , Put the prepared Sm and Fe raw materials into the magnesia crucible of the vacuum induction melting furnace, close the furnace and evacuate, when the vacuum degree reaches 0.01Pa, start heating, heat to about 700°C, and fill with 0.05MPa high-purity argon Gas (purity is 99.999%), as the temperature rises, the Sm melts completely first, and the Fe melts completely after continuing to heat for 3 minutes. At a temperature of about 1540°C, it is poured into a water-cooled copper mold after heat preservation and refining for 3 minutes. Cool for more than 30 minutes and take out the ingot. Then, it is induction heated and remelted in the quartz tube of the quick-setting cast sheet preparation device under vacuum conditions, and is poured on a copper roller rotating at a high-speed rotation speed of 5m/s under the action of a spray pressure of 0.8 atmospheres to form a thickness of about 0.24mm. Ribbons were sampled at the ribbon interface and observed under an electron microscope to form columnar crystals. XRD analysis proved that the Sm ₂ Fe ₁₇ phase was mainly formed. Break this fast-setting thin strip into 1~5mm flakes, put it into a material box, put it into a quartz tube, first vacuumize it to 4×10 ^-3 Pa, and fill it with high-purity argon (purity is 99.9995 %), put the quartz tube into the furnace, heat it at 730°C for 1 hour, take out the furnace tube, and take out the alloy sheet after cooling to room temperature. Under the protective medium of high-purity argon, crush it with an alloy steel mortar and pass through a 500-mesh sieve; put the sieved powder into a material box, put it into a quartz tube, pump it to a high vacuum of 4×10 ^-3 Pa, and turn off the pumping Valve, filled with high-purity nitrogen, nitrogen pressure up to 0.5MPa, put into the furnace for nitriding, the nitriding temperature is 480 ° C, after 5 hours of heat preservation, take out the furnace tube, take out the powder after cooling to room temperature; 30:1. Petroleum ether is used as the ball milling medium, and the ball mill is loaded with material. After 9 hours of ball milling, the material is discharged and precipitated. The excess petroleum ether is recovered, and the slurry is vacuum-dried at room temperature; the dried powder is used as a binder with AB glue. Orientation solidification under 2T magnetic field to prepare samples for measurement by vibrating sample magnetometer (VSM), and obtain powder magnetic properties by VSM measurement. The orientation properties are: H _ci 2113Oe, Br0.89T; the properties without magnetic field orientation (same sex sample) are: H _ci 2230Oe, Br0.7T.

Example 2

Use pure iron with a purity of 99.9%, rare earth Sm, Co, and V as raw materials, clean the Fe rods, and mix according to Sm ₂ (Fe _0.94 Co _0.02 V _0.04 ) _17. Since Sm is easy to volatilize, add more on the basis of the calculated amount. 25%. The preparation process is similar to that of Example 1, and the alloy ingot is obtained by vacuum induction melting and cooling in a water-cooled copper mold. Then, it is induction heated and remelted in the quartz tube of the quick-setting cast sheet preparation device under vacuum conditions, and is poured on a copper roller rotating at a high-speed rotation speed of 7m/s under the action of a spray pressure of 0.8 atmospheres to form a thickness of about 0.16mm. Ribbons were sampled at the ribbon interface and observed under an electron microscope to form columnar crystals. XRD analysis proved that the Sm ₂ Fe ₁₇ phase was mainly formed. The quick-setting thin strips were broken into 1-5mm flakes, and then kept at 780°C for 0.5 hours under a high-purity argon atmosphere to further crystallize the Sm ₂ Fe ₁₇ phase. Under the protective medium of high-purity argon gas, the alloy flakes are crushed with an alloy steel mortar to below 500 mesh for nitriding treatment; the nitriding treatment uses high-purity nitrogen gas pressure of 0.2MPa, the nitriding temperature is 490°C, and the temperature is kept for 5 hours; ball milling , Drying, and sample preparation are the same as in Example 1 to obtain powder magnetic properties, orientation properties: H _ci 4980Oe, Br0.83T; non-magnetic field orientation properties: H _ci 5260Oe, Br0.66T.

Example 3

Use pure iron with a purity of 99.9%, rare earth Sm, and V as raw materials, clean the Fe rods, and mix according to Sm ₂ (Fe _0.95 V _0.05 ) _17. Since Sm is easy to volatilize, add 23% to the calculated amount. The preparation process is similar to that of Example 1, and the alloy ingot is obtained by vacuum induction melting and cooling in a water-cooled copper mold. Then it is induction heated and remelted in the quartz tube of the quick-setting cast sheet preparation device under vacuum conditions, and poured on the copper roller rotating at a high-speed rotation speed of 6m/s under the action of 0.8 atmospheric pressure injection pressure to form a thickness of about 0.19mm. Ribbons were sampled at the ribbon interface and observed under an electron microscope to form columnar crystals. XRD analysis proved that the Sm ₂ Fe ₁₇ phase was mainly formed. The quick-setting thin strips were broken into 1-5mm flakes, and then kept at 780°C for 0.5 hours under a high-purity argon atmosphere to further crystallize the Sm ₂ Fe ₁₇ phase. Under the protective medium of high-purity argon, the alloy flakes are broken into 320 meshes or less with an alloy steel mortar for nitriding treatment; the mixed gas of NH ₃ and H ₂ (volume ratio 3:7) is used for nitriding, and the gas pressure is 0.12 MPa, nitriding temperature is 450 ° C, heat preservation 3.5 hours; ball milling, drying, sample preparation are the same as in Example 1, obtain powder magnetic properties, orientation properties are: H _ci 3920Oe, Br0.85T; non-magnetic field orientation properties are: H _ci 4130Oe, Br0.68T.

Example 4

Use pure iron with a purity of 99.9%, rare earth Sm, Co, and V as raw materials, clean the Fe rods, and mix according to Sm ₂ (Fe _0.94 Co _0.02 V _0.03 ) _17. Since Sm is easy to volatilize, add more on the basis of the calculated amount. 25%. Vacuum induction furnace melting is omitted, and the alloy is directly melted by induction heating in the quick-setting cast sheet preparation device and sprayed onto the copper roll rotating at a high speed of 15m/s on the roll surface. The width of the pouring nozzle is 0.65mm, and high-purity argon is sprayed. The gas pressure is 1 atm to form a thin strip with a thickness of about 0.3mm, and the microstructure and phase composition of the quick-setting cast sheet are detected to obtain the microstructure of the arrangement of fine Sm ₂ Fe ₁₇ columnar crystals. The quick-setting thin strips were broken into 1-5mm flakes, and then kept at 750°C for 1 hour under a high-purity argon atmosphere to further crystallize the Sm ₂ Fe ₁₇ phase. The alloy flakes were ball-milled for 1 hour with petroleum ether as the medium and the ball-to-material ratio was 8:1, then the material was discharged and precipitated, and the slurry was vacuum-dried at room temperature to obtain alloy powder; in NH ₃ and H ₂ (volume ratio 3 :7) Nitriding treatment is carried out in the mixed gas, the gas pressure is 0.12MPa, the nitriding temperature is 450°C, and the heat preservation is 3.5 hours; the powder ball milling process after nitriding is that the ball material ratio is 8:1, and the ball milling time is 12 hours. Then the material is discharged and precipitated, and the slurry is dried in vacuum at room temperature, and the magnetic properties of the powder are measured with the sample preparation in Example 1. The results are: the orientation properties are: _Hci 4580Oe, Br0.84T; the non-magnetic field orientation properties are: _Hci 4720Oe, Br0 .67T.

Claims (4)

1. a preparation method for Sm-Fe-N anisotropic magnet powder, is characterized in that: technological process is: the control of alloy melt preparation → rapid solidification parameter, the control of slab thickness → tiny Sm ₂fe ₁₇rapid hardening slab → crystallization processing → coarse crushing → nitrogenize → fine grinding → anisotropy Sm-Fe-N magnetic of the nearly consistent orientation of column crystal, concrete preparation process is as follows:

(1) by Sm, Fe batching, application high temperature induction melting alloy, melted alloy flows on the copper roller of rotation and is rapidly solidificated into strip, by controlling the wide 0.2 ~ 0.65mm of rotating speed 4 ~ 15m/s, jet size, melt jet gas pressure 0.5 ~ 1.5atm, the melt temperature 1520-1570 ° C of copper roller, obtain Sm ₂fe ₁₇be mutually the strip tissue of the brilliant nearly parallel distribution of fine columnar, strip thickness 0.1 ~ 0.4mm;

(2) applying electronic microscope carries out observation analysis to strip cross section and determines whether to have formed columanar structure; Applying X-ray diffraction analysis determines whether rapid hardening strip main phase is organized is Sm ₂fe ₁₇phase;

(3) qualified rapid hardening slab carry out coarse crushing to 1 ~ 5mm, further crystallization and thermal treatment under 700 ~ 800 ° of C high-purity argon gas protective atmospheres, promotes atom diffusion, to make Sm ₂fe ₁₇phase degree of crystallinity is more complete;

(4) fragmentation: under application benzinum media protection or high-purity argon gas protective medium, Sm-Fe alloy powder is crushed to below 320 orders so that in nitridation process N atom to diffusion inside;

(5) nitrogen treatment: Sm-Fe alloyed powder is at High Purity Nitrogen or NH ₃and H ₂mixed atmosphere in carry out nitriding, nitriding gas pressure is at 0.1 ~ 1.0Mpa, 400 ~ 500 ° of C of nitriding temperature, nitridation time 3 ~ 5 hours;

(6) fine grinding: taking benzinum as ball-milling medium, ratio of grinding media to material is 4:1 ~ 30:1, ball milling 3 ~ 20 hours;

(7) dry and sample preparation: after ball milling is good, discharging normal-temperature vacuum is dry, obtains anisotropy Sm-Fe-N magnetic.

2. the preparation method of a kind of Sm-Fe-N anisotropic magnet powder according to claim 1, is characterized in that: when batching, Sm is total excessive in 18% ~ 35%.

3. the preparation method of a kind of Sm-Fe-N anisotropic magnet powder according to claim 1, is characterized in that: in the time of preparation rapid hardening strip, cooling copper roll surface speed is at 4 ~ 15m/s.

4. the preparation method of a kind of Sm-Fe-N anisotropic magnet powder according to claim 1, is characterized in that: add a small amount of Co, V, Zr, B, by Sm ₂(Fe _1-xm _x) ₁₇molecular formula batching, M is one or more in Co, V, Zr, B, every kind of atomic percent that replaces Fe is not more than 5%.