WO2016086398A1 - Method for preparing high-coercivity sinterednd-fe-b and product obtained thereby - Google Patents

Abstract

Disclosed is a method for preparing a high-coercivity sintered Nd-Fe-B, comprising: preparing a main phase alloy powder and a grain boundary phase alloy powder; uniformly mixing the prepared grain boundary phase alloy powder and main phase alloy powder in a protective medium protected by nitrogen gas or argon gas, the grain boundary phase alloy powder added being 0.1-10% by weight; orientation-compressing and cold-isostatic-pressing the mixed alloy powder; in a vacuum sintering furnace, sintering a compressed magnet block at 1000-1100˚C for 2-4 hours, and performing a primary tempering at 800-950˚C for 2-4 hours and a secondary tempering at 450-650˚C for 2-4 hours to obtain the sintered Nd-Fe-B. Also disclosed is a high-coercivity sintered Nd-Fe-B. The present invention reduces a wetting temperature between the grain boundary phase and the main phase via a low melting point auxiliary alloy, and extends wetting time, thus improving the utilization of heavy rare earths, and reducing the usage amount of the rare earths; and the preparation method has a simple process and low cost, thus facilitating large-scale production.

Description

Preparation method and product of high coercivity sintered NdFeB Technical field

The invention belongs to the technical field of permanent magnet materials, and particularly relates to a preparation method and a product of high coercive sintering NdFeB.

Background technique

In 1983, Japan’s Sagawa Shinren et al. used a powder metallurgy process to prepare NdFeB sintered with a magnetic energy product of up to 290 kJ/m ³ on the basis of extensive research on RE-Fe-X ternary alloy. The magnet has created the third generation rare earth permanent magnet material. Sintered Nd-Fe-B is widely used in military equipment, electro-acoustic devices, motors, generators, computer hard disk drives (HDD), voice coil motors (VCM), human magnetic resonance imaging (MRI), microwave communication technology, controllers. , instruments, magnetic separation devices, magnetic chucks and other devices and equipment that require permanent magnetic fields.

The sintered NdFeB magnet is a structure in which a Nd ₂ Fe ₁₄ B compound is mainly composed of a rare earth-rich phase. The main technical indicators include remanence B _r , maximum magnetic energy product (BH) _max , coercivity H _cj , Curie temperature T _c . After more than 20 years of research and development, a reasonable alloy composition and mature preparation process have been designed, so that the remanence B _r of the magnet reaches more than 96% of the theoretical value, and the magnetic energy product can reach 474kJ/m ³ , which is close to the theoretical magnetic energy. The product has 93% of 512kJ/m ³ . Although the coercivity has been improved by a certain degree, compared with the theoretical value of 5600kA/m, there is still a big gap. The current level can be reached about 1/10 of the theoretical value of coercivity. 1/3. This greatly limits the application of NdFeB magnets in high operating temperature environments. In order to solve this problem, scientists have engaged in a large number of research, mainly including heavy rare earth alloying, which can easily and effectively increase the coercive force of the magnet, but due to the antiferromagnetic coupling of heavy rare earth atoms and iron atoms, the magnet The remanence and maximum magnetic energy product index will be greatly reduced. In addition, the traditional direct alloying requires more heavy rare earths. Generally, it is necessary to add 2 to 10% by weight of rare earths, which will also increase the production cost of the magnet. At present, some enterprises and scientific research units at home and abroad have adopted the method of surface diffusion of magnets, which can reduce the amount of heavy rare earths on the basis of effectively increasing the coercive force. However, this method has a complicated process and is not suitable for actual production. The diffusion distance of heavy rare earth is limited (<5 μm), which makes the size of the magnet for diffusion too small and is not suitable for the practical application market.

Summary of the invention

The invention provides a method for reducing the amount of heavy rare earth and improving the coercive force of the sintered NdFeB magnet.

The invention also provides a sintered NdFeB magnet prepared by the above method, which has high coercive force.

A method for preparing high coercive sintered NdFeB, comprising:

(1) The main phase NdFeB alloy is made into ingot or quick-setting strip by casting process or rapid-coagulation stripping process, and then the main phase ingot or quick-setting strip is crushed by hydrogen explosion and jet milling. a primary alloy particle powder having an average particle diameter of 2 to 10 μm, the main alloy being in atomic percentage, and having a composition of (Nd _a Pr _1-a ) _b Fe _100-bcd B _c M _d ;

Among them: Nd is yttrium element, Pr is yttrium element, Fe is iron element, B is boron element, M is Dy (镝), Tb(铽), Ce(铈), Co(cobalt), Ni(nickel), V (vanadium), Ti (铊), Mo (molybdenum), Mn (manganese), Ga (gallium), Al (aluminum), Cu (copper), Zr (zirconium), Ta (钽), Ag (silver), Si One or more of (silicon) and Nb (铌) elements; a, b, c, d satisfy the following relationship: 0.7≦a≦1,10≦b≦20, 5.5≦c≦6.5,0≦d≦ 2.

Among them, M is further preferably a combination of Dy, Al, and Nb or a combination of Al, Co, Cu, Zr, and Ga. The main phase NdFeB alloy is further preferably: (Pr, Nd) _13.62 Fe _bal M _1.58 B _5.98 wherein M = Al, Co, Cu, Zr, Ga; or (Pr, Nd) _13.05 Dy _0.12 Fe _bal Al _0.25 Nb _0.07 B _5.7 ;

Wherein, a, b, c, and d satisfy the following relationship: a = 0.8, 13.05 ≦ b ≦ 13.62, 5.7 ≦ c ≦ 5.98, 0.44 ≦ d ≦ 1.58;

The average particle diameter of the main alloy particle powder is further preferably from 2 to 5 μm, still more preferably from 3 to 4 μm;

(2) The grain boundary phase rich rare earth alloy is prepared by smelting, rapid setting, mechanical crushing, protective medium ball milling or direct atomization to prepare grain boundary phase alloy powder with an average particle diameter of 0.1-2 μm. The alloy is in atomic percentage and its composition is (R _x R' _1-x ) _y M'_100-y;

Wherein: R is one or more of La (镧), Ce, Pr, Nd, R' is one or more of Tb, Dy, Ho (钬), and M' is Fe, Cr (chromium) , Co, Ni, V, Ti, Mo, One or more of Mn, Ga, Al, Cu, Zr, Ta, Ag, Si, Ca, B, Mg, Zn, In (indium), and Sn elements; wherein x and y satisfy the following relationship: 0≦x <1,0<y<100;

Wherein R is preferably Pr; R' is preferably Dy; and M' is preferably one or more of Fe, Cu, Co; and x, y further satisfy the following relationship: 0≦x<0.6 20<y<70; the grain boundary phase alloy is preferably Pr ₃₇ Dy ₃₀ Cu ₃₃ , Dy _32.5 Fe ₆₂ Cu _5.5 , Dy ₆ Co ₁₃ Cu ₅ ;

In the step (1) and the step (2), a further preferred combination of the main phase NdFeB alloy and the grain boundary phase alloy is:

(Pr _0.2 Nd _0.8 ) _13.62 Fe _78.82 M _1.58 B _{5.98 in} combination with Pr ₃₇ Dy ₃₀ Cu ₃₃ ;

Or (Pr _0.2 Nd _0.8 ) _13.05 Dy _0.12 Fe _80.81 Al _0.25 Nb _0.07 B _{5.7 in} combination with Dy _32.5 Fe ₆₂ Cu _5.5 ;

Or (Pr _0.2 Nd _0.8 ) _13.62 Fe _bal M _1.58 B _{5.98 in} combination with Dy ₆ Co ₁₃ Cu ₅ .

In particular, when (Pr _0.2 Nd _0.8 ) _13.62 Fe _bal M _1.58 B _{5.98 is} combined with Dy ₆ Co ₁₃ Cu ₅ , the obtained sintered NdFeB magnet has a coercive force of 1629.0 kA/m;

The grain boundary phase alloy preferably has an average particle diameter of 0.1 to 1.5 μm, and more preferably 0.8 to 1.5 μm;

(3) Prepare the grain boundary phase alloy powder and the main phase NdFeB alloy powder with a mass fraction of 0.1-10%, in a gasoline, petroleum ether or other organic protective medium, nitrogen or argon-protected mixing machine Fully mixed evenly;

In this step, the mass percentage of the grain boundary phase alloy powder is preferably from 1 to 5%, further preferably from 2 to 3%;

(4) The mixed alloy powder is subjected to orientation molding under a magnetic field of 1.2 to 3.0 T; and the magnetic block of the molding is subjected to cold isostatic pressing at 100 to 220 MPa to be pressed into a green body;

The outward pressing type is preferably carried out under conditions of 1.8 T; the cold isostatic pressing is performed at 200 MPa;

(5) In the vacuum sintering furnace, the magnetic block completed by pressing is sintered at 1000-1100 °C for 2 to 4 hours, and then tempered at 800 to 950 °C for 2 to 4 hours and 450 to 650 °C for secondary tempering 2~ 4h, the final magnet is produced;

Further preferred sintering conditions in this step are: sintering at 1050 to 1090 ° C for 3 to 4 hours, followed by tempering at 890 to 900 ° C for 2 to 3 hours and 500 to 520 ° C for 2 to 4 hours. Further preferred sintering conditions are: sintering at 1050 to 1085 ° C for 3 to 4 hours, followed by tempering at 890 to 900 ° C for 2 hours and secondary tempering at 500 to 520 ° C for 3 to 4 hours, and the sintered ferroniobium obtained by the sintering condition is obtained. Boron magnet The coercive force is greater than 1400 kA/m; especially after sintering at 1050 ° C for 3 h, and then after tempering at 890 ° C for 2 h and 520 ° C for 2 h, the coercive force is greater than 1600 kA/m.

Coercivity is a structurally sensitive magnetic parameter. It is generally believed that the fine and uniform main phase particles are coated with a layer of 2 to 5 nm thick, uniform and continuous rare earth-rich phase, which is a high-coercivity sintered NdFeB magnet. The ideal microstructure. The invention adds a low melting point heavy rare earth alloy at the grain boundary, further optimizes the grain boundary structure and eliminates grain boundary defects, and in the sintering and tempering heat treatment process, the heavy rare earth diffuses to the main phase grain boundary layer to realize boundary magnetic hardening; Adding a low melting point rich rare earth grain boundary phase alloy to reduce the wetting temperature between the main phase and the grain boundary phase, prolong the wetting time, correspondingly reduce the sintering and heat treatment temperatures, inhibit the solid phase sintering and the abnormal length of the grains. Big. Therefore, under the condition that the main phase alloy is not added or a small amount of heavy rare earth is added, the amount of heavy rare earth is reduced, and a low-cost high-coercivity sintered NdFeB magnet is prepared.

The present invention also provides a high coercivity sintered NdFeB prepared by the method for preparing high coercivity sintered NdFeB according to any of the above aspects.

The invention utilizes a low melting point rich rare earth grain boundary phase alloy to reduce the wetting temperature between the grain boundary phase and the main phase through the low melting point auxiliary alloy during the sintering and heat treatment of the magnet, prolong the wetting time and improve the utilization rate of the heavy rare earth. Through low-melting grain boundary phase, improve grain boundary fluidity, reduce sintering and heat treatment temperature, optimize grain boundary structure, reduce grain boundary defects, and suppress magnetization nucleation; realize main phase crystal by heavy rare earth diffusion to main phase boundary layer Magnetic hardening of grain boundaries. In the main alloy which does not contain or contains a small amount of heavy rare earth, only a small amount of low-melting and heavy-rich rare earth alloy is added to the grain boundary, and the residual magnetism is maintained, the coercive force is greatly improved, and an efficient use of heavy rare earth is realized. The method provided by the invention has simple process, low cost and is suitable for large-scale production.

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

1) The invention designs a low melting point rich rare earth grain boundary phase, optimizes the wetting process in the liquid phase sintering process, prolongs the wetting time, improves the diffusion efficiency of the heavy rare earth to the main phase boundary layer, and realizes the grain boundary magnetic hardening and heavy rare earth Efficient use.

2) Improve the grain boundary structure, eliminate grain boundary defects, reduce the sintering and heat treatment temperatures, suppress the abnormal growth of crystal grains, and increase the coercive force.

3) The preparation process provided by the invention is simple, the dosage of the heavy rare earth is low, the coercive force is high, and the preparation of the low-cost high-coercivity sintered NdFeB is realized.

detailed description

A method for preparing high-coercivity low-cost sintered NdFeB, wherein the main phase NdFeB alloy is in atomic percentage, and its composition is (Nd _a Pr _1-a ) _b Fe _100-bcd B _c M _d , wherein Nd is yttrium element, Pr is yttrium element, Fe is iron element, B is boron element, M is Dy, Tb, Ce, Co, Ni, V, Ti, Mo, Mn, Ga, Al, Cu, Zr One, or one of Ta, Ag, Si, Nb elements; a, b, c, d satisfy the following relationship: 0.7≦a≦1, 10≦b≦20, 5.5≦c≦6.5, 0≦d≦ 2.

The grain boundary phase alloy is in atomic percentage, and its composition is (R _x R' _1-x ) _y M' _100-y , R is one or more of La, Ce, Pr, Nd, and R' is Tb, One or more of Dy and Ho, M' is Fe, Cr, Co, Ni, V, Ti, Mo, Mn, Ga, Al, Cu, Zr, Ta, Ag, Si, Ca, B, Mg, One or more of Zn, In, Sn elements; wherein x, y satisfy the following relationship: 0 ≦ x < 1, 0 < y < 100.

The invention relates to a method for preparing high-coercivity low-cost sintered NdFeB, wherein the grain boundary rich rare earth alloy has a melting point of between 300 and 900 ° C, and after being made into powder particles, the size is between 0.1 and 1 μm. .

High-coercivity low-cost sintered NdFeB magnet preparation method, low melting point rich rare earth grain boundary phase alloy, in the sintering and tempering heat treatment process, heavy rare earth diffuses to the main phase grain boundary layer to realize boundary magnetic Hardening; using low-melting grain boundary phase alloy, prolonging wetting time, improving grain boundary phase fluidity, optimizing grain boundary structure, reducing grain boundary defects; adding low melting point rich rare earth grain boundary phase alloy through grain boundary, reducing sintering and heat treatment The temperature suppresses solid phase sintering and abnormal growth of crystal grains. In the main phase alloy without adding or adding a small amount of heavy rare earth, the grain boundary is added to reduce the amount of heavy rare earth, and a low-cost high-coercivity sintered NdFeB magnet is prepared.

A method for preparing high-coercivity low-cost sintered NdFeB, the steps of which are:

1) The main phase NdFeB alloy is made into ingot or quick-setting strip by casting process or quick-setting stripping process, and then the main phase ingot or quick-setting strip is broken into average by hydrogen explosion and jet milling. a particle powder having a particle diameter of 2 to 10 μm, the main alloy being in atomic percentage, and having a composition of (Nd _a Pr _1-a ) _b Fe _100-bcd B _c M _d ;

2) The grain boundary phase rich heavy rare earth alloy is prepared by smelting, rapid setting, mechanical crushing, protective medium ball milling or direct atomization to prepare a powder having an average particle diameter of 0.1 to 1 μm, and the grain boundary phase alloy is in atomic percentage. , the composition is (R _x R' _1-x ) _y M'_100-y;

3) The grain boundary phase alloy powder and the main alloy powder are prepared to have a mass fraction of 0.1 to 10%, and are uniformly mixed in a gasoline, petroleum ether or other organic protective medium by a nitrogen or argon-protected mixer;

4) performing the orientation molding on the mixed alloy powder in a magnetic field of 1.2 to 3.0 T; and performing the cold isostatic pressing of the pressed magnetic block at 100 to 220 MPa to form a green compact;

5) In the vacuum sintering furnace, the magnetic block completed by pressing is sintered at 1000~1100 °C for 2~4h, then tempered at 800~950°C for 2~4h and 450~650°C for 2~4h. , the final magnet was made. Compared with the prior art, the invention has the beneficial effects: 1) The invention designs a low melting point rich rare earth grain boundary phase, optimizes the wetting process of the liquid phase sintering process, prolongs the wetting time, and improves the heavy rare earth to the main phase boundary. The diffusion efficiency of the layer enables magnetic hardening of grain boundaries and efficient use of heavy rare earths. 2) Improve the grain boundary structure, eliminate grain boundary defects, reduce the sintering and heat treatment temperatures, suppress the abnormal growth of crystal grains, and increase the coercive force. 3) The preparation process provided by the invention is simple, the dosage of the heavy rare earth is low, the coercive force is called high, and the preparation of the low-cost high-coercivity sintered NdFeB is realized.

The invention will be further illustrated by the following specific examples, but the invention is not limited to the following examples.

Example 1:

1) The main alloy powder is prepared by using three alloy processes of rapid solidification casting, hydrogen explosion and jet milling, and the powder particles have a diameter of about 3.5 μm. The main alloy is atomic percentage and its composition is (Pr). _0.2 Nd _0.8 ) _13.62 Fe _78.82 M _1.58 B _5.98 , where Pr:Nd=1:4, M is Al=0.72, Co=0.49, Cu=0.14, Zr=0.14, Ga=0.09;

2) The grain boundary phase alloy is subjected to arc melting, mechanically crushed, and the protective medium is ball-milled to an average grain size of about 0.85 μm, and the auxiliary alloy is atomic percentage, and its composition is Pr ₃₇ Dy ₃₀ Cu ₃₃ ;

3) Prepare the grain boundary phase alloy powder and the main alloy powder in gasoline, petroleum ether or other organic protective medium, and mix thoroughly with nitrogen or argon-protected mixer. The auxiliary alloy powder accounts for 2.0 mass fraction. %;

4) The mixed alloy powder is subjected to orientation molding under a magnetic field of 1.8 T; the magnetic block completed by pressing is subjected to cold isostatic pressing at 200 MPa to be pressed into a green body;

5) In the vacuum sintering furnace, the pressed magnetic block was sintered at 1085 ° C for 4 h, and then subjected to a first-stage tempering at 900 ° C for 2 h and a second tempering at 500 ° C for 4 h to obtain a final magnet.

The prepared sintered NdFeB magnet was placed in a VSM to measure its magnetic properties. The results were as follows: B _r = 1.35 T, H _cj = 1450.2 kA/m, and (BH) _max = 351.75 kJ/m ³ .

Example 2:

1) The main alloy powder is prepared by using three alloy processes of rapid solidification casting, hydrogen explosion and jet milling, and the powder particles have a diameter of about 3.5 μm. The main alloy is atomic percentage and its composition is (Pr). _0.2 Nd _0.8 ) _13.05 Dy _0.12 Fe _80.81 Al _0.25 Nb _0.07 B _5.7

2) The grain boundary phase alloy is subjected to arc melting, mechanically crushed, and the protective medium is ball-milled to an average grain size of about 1.5 μm, and the auxiliary alloy is in mass percentage, and its composition is Dy _32.5 Fe ₆₂ Cu _5.5 .

3) Prepare the grain boundary phase alloy powder and the main alloy powder in gasoline, petroleum ether or other organic protective medium, and mix well with nitrogen or argon-protected mixer, wherein the auxiliary alloy powder accounts for 3.0 mass fraction. %:

4) The mixed alloy powder is subjected to orientation molding under a magnetic field of 1.8 T; the magnetic block completed by pressing is subjected to cold isostatic pressing at 200 MPa to be pressed into a green body;

5) In the vacuum sintering furnace, the pressed magnetic block was sintered at 1090 ° C for 4 h, and then subjected to tempering at 890 ° C for 2 h and 520 ° C for two tempering for 3.5 h to obtain a final magnet.

The prepared sintered NdFeB magnet was placed in a VSM to measure its magnetic properties. The results were as follows: B _r = 1.35 T, H _cj = 1329.0 kA/m, and (BH) _max = 369.71 kJ/m ³ .

Example 3:

1) The main alloy powder is prepared by using three alloy processes of rapid solidification casting, hydrogen explosion and jet milling, and the powder particles have a diameter of about 3.5 μm. The main alloy is atomic percentage and its composition is (Pr). _0.2 Nd _0.8 ) _13.62 Fe _bal M _1.58 B _5.98 , wherein M is Al=0.72, Co=0.49, Cu=0.14, Zr=0.14, Ga=0.09;

2) The grain boundary phase alloy is subjected to arc melting, mechanically crushed, and the protective medium is ball-milled to an average grain size of about 1.3 μm. The auxiliary alloy is atomic percentage and its composition is Dy ₆ Co ₁₃ Cu ₅ .

3) Prepare the grain boundary phase alloy powder and the main alloy powder in gasoline, petroleum ether or other organic protective medium, and mix well with nitrogen or argon-protected mixer, wherein the auxiliary alloy powder accounts for 3.0 mass fraction. %:

4) The mixed alloy powder is subjected to orientation molding under a magnetic field of 1.8 T; the magnetic block completed by pressing is subjected to cold isostatic pressing at 200 MPa to be pressed into a green body;

5) In the vacuum sintering furnace, the pressed magnetic block is sintered at 1050 ° C for 3 h, and then subjected to tempering at 890 ° C for 2 h and 520 ° C for 2 h to obtain a final magnet.

The prepared sintered NdFeB magnet was placed in a VSM to measure its magnetic properties. The results were as follows: B _r = 1.38 T, H _cj = 1629.0 kA/m, and (BH) _max = 398.63 kJ/m ³ .

Claims (10)

1. A method for preparing high-coercivity sintered NdFeB, characterized in that it comprises:

   (1) A main phase alloy powder having an average particle diameter of 2 to 10 μm is prepared by using a main phase alloy having a composition of (Nd _a Pr _1-a ) _b Fe _100-bcd B _c M _d ;

   Wherein: M is one or more of Dy, Tb, Ce, Co, Ni, V, Ti, Mo, Mn, Ga, Al, Cu, Zr, Ta, Ag, Si, Nb elements; a, b, c, d satisfy the following relationship: 0.7≦a≦1, 10≦b≦20, 5.5≦c≦6.5, 0≦d≦2;

   (2) Using a grain boundary phase alloy to prepare a grain boundary phase alloy powder having an average particle diameter of 0.1 to 2 μm, the grain boundary phase alloy being in atomic percentage and having a composition of (R _x R' _1-x ) _y M' _{100- y} ;

   Wherein: R is one or more of La, Ce, Pr, and Nd elements, and R' is one or more of Tb, Dy, and Ho elements, and M' is Fe, Cr, Co, Ni, V, One or more of Ti, Mo, Mn, Ga, Al, Cu, Zr, Ta, Ag, Si, Ca, B, Mg, Zn, In, Sn elements; wherein x, y satisfy the following relationship: 0≦ x<1,0<y<100;

   (3) The grain boundary phase alloy powder and the main phase alloy powder are prepared in a protective medium, and the mixture is uniformly mixed with nitrogen or argon; the mass percentage of the grain boundary phase alloy powder is 0.1 to 10%;

   (4) The mixed alloy powder is subjected to orientation molding under a magnetic field of 1.2 to 3.0 T; and the magnetic block of the molding is subjected to cold isostatic pressing at 100 to 220 MPa to be pressed into a green body;

   (5) In the vacuum sintering furnace, the magnetic block completed by pressing is sintered at 1000-1100 °C for 2 to 4 hours, and then tempered at 800 to 950 °C for 2 to 4 hours and 450 to 650 °C for secondary tempering 2~ 4h, the final sintered NdFeB magnet was prepared.
2. The method for producing high-coercive sintered NdFeB according to claim 1, wherein the M is a combination of Dy, Al, and Nb or a combination of Al, Co, Cu, Zr, and Ga.
3. The method for producing high-coercivity sintered NdFeB according to claim 1, wherein the main alloy particle powder has an average particle diameter of 2 to 5 μm.
4. The method for preparing high-coercive sintered NdFeB according to claim 1, wherein R is Pr; R' is Dy; and M' is one of Fe, Cu, Co Or a plurality of; the x, y further satisfy the following relationship: 0 ≦ x < 0.6, 20 < y < 70.
5. The method for preparing high-coercive sintered NdFeB according to claim 1, characterized in that In the step (1) and the step (2), the main phase alloy and the grain boundary phase alloy are combined as follows:

   (Pr _0.2 Nd _0.8 ) _13.62 Fe _78.82 M _1.58 B _{5.98 in} combination with Pr ₃₇ Dy ₃₀ Cu ₃₃ ;

   Or (Pr _0.2 Nd _0.8 ) _13.05 Dy _0.12 Fe _80.81 Al _0.25 Nb _0.07 B _{5.7 in} combination with Dy _32.5 Fe ₆₂ Cu _5.5 ;

   Or (Pr _0.2 Nd _0.8 ) _13.62 Fe _bal M _1.58 B _{5.98 in} combination with Dy ₆ Co ₁₃ Cu ₅ .
6. The method for producing high-coercivity sintered NdFeB according to claim 1, wherein the grain boundary phase alloy powder has an average particle diameter of 0.1 to 1.5 μm.
7. The method for producing high-coercive sintered NdFeB according to claim 1, wherein the grain boundary phase alloy powder is added in a mass percentage of 1 to 5%.
8. The method for producing high-coercive sintered NdFeB according to claim 1, wherein the outward pressing type is preferably carried out under conditions of 1.8 T; and the cold isostatic pressing is performed at 200 MPa.
9. The method for preparing high-coercive sintered NdFeB according to claim 1, wherein the sintering condition in the step (5) is: sintering at 1050 to 1090 ° C for 3 to 4 hours, and then passing through 890 to 900 ° C for one level. Tempering 2 ~ 3h and 500 ~ 520 ° C secondary tempering 2 ~ 4h.
10. A high coercive sintered NdFeB characterized in that the sintered NdFeB is prepared by the preparation method according to any one of claims 1-9.