High-performance NdFeB permanent magnet comprising nitride phase and production method thereof

Abstract

A high-performance NdFeB permanent magnet including a nitride phase and a production method thereof are provided. A main phase of the NdFeB permanent magnet has a structure of R.sub.2T.sub.14B; a grain boundary phase is distributed around the main phase and contains N, F, Zr, Ga and Cu; a composite phase containing R1, Tb and N exists between the main phase and the grain boundary phase and includes a phase having a structure of (R1, Tb).sub.2T.sub.14(B, N). R represents at least two rare earth elements, and includes Pr and Nd; T represents Fe, Mn, Al and Co; R1 represents at least one rare earth element, and includes at least one of Dy and Tb; the main phase contains Pr, Nd, Fe, Mn, Al, Co and B; and the grain boundary phase further contains at least one of Nb and Ti. Through placing partially B by N, a magnetic performance is increased.

Claims

1. A method for producing a NdFeB permanent magnet comprising a nitride phase, comprising steps of: (1) sending a portion of raw materials, comprising pure iron, ferro-boron, and rare earth fluorides, into a crucible of a vacuum melting chamber under a vacuum condition, heating the portion of raw materials to a temperature of 1400-1500 C., refining the portion of raw materials, and obtaining a first melting liquid; (2) sending a NdFeB slag cleaning device to a surface of the first melting liquid in the crucible of the vacuum melting chamber through a lifting device, absorbing slags to the slag cleaning device, and lifting the slag cleaning device up; (3) sending a rest of raw materials into the crucible of the vacuum melting chamber, filling argon into the vacuum melting chamber, refining the first melting liquid and the rest of raw materials in the crucible, and obtaining a second melting liquid; (4) pouring the second melting liquid after refining onto a surface of a water-cooled rotation roller through a tundish, forming alloy flakes, and controlling an average thickness of the alloy flakes in a range of 0.1-0.3 mm; (5) sending two kinds of alloy flakes, respectively containing R and R1, and TbF.sub.3 powders into a hydrogen decrepitation furnace, and processing with a hydrogen decrepitation process; wherein: at least one kind of alloy flakes is prepared through the steps (1)-(4); during the hydrogen decrepitation process, a heating temperature is controlled in a range of 560-900 C. for more than 2 hours; R represents at least two rare earth elements, and comprises Pr and Nd; R1 represents at least one rare earth element, and comprises at least one of Dy and Tb; (6) sending the alloy flakes after the hydrogen decrepitation process into a nitrogen jet mill, milling the alloy flakes into powders by the nitrogen jet mill, and controlling an average particle size of the powders in a range of 1.6-3.3 m; (7) under a protection of nitrogen, processing the powders with magnetic field pressing, and obtaining a pressed compact with a density controlled at 4.1-4.8 g/cm.sup.3; (8) under the protection of the nitrogen, through evacuating and heating, processing the pressed compact after magnetic field pressing with degassing, purifying and presintering; and forming a presintered block with a presintered density controlled at 5.1-7.2 g/cm.sup.3; (9) machining the presintered block into a part; (10) attaching powders or a film containing Tb on a surface of the part; and (11) sending the part, with the surface attached by the powders or the film containing Tb, into a vacuum sintering furnace; processing the part with vacuum sintering and aging, controlling a vacuum sintering temperature in a range of 960-1070 C. and an aging temperature in a range of 460-640 C.; and obtaining the NdFeB permanent magnet with a density of 7.4-7.7 g/cm.sup.3; wherein: an average grain size of the NdFeB permanent magnet is in a range of 3-6 m; a main phase of the NdFeB permanent magnet has a structure of R.sub.2T.sub.14B, and a grain boundary phase is distributed around the main phase and contains N, F, Zr, Ga and Cu; a composite phase containing R1, Tb and N exists between the main phase and the grain boundary phase and comprises a phase having a structure of (R1, Tb).sub.2T.sub.14(B, N); R represents at least two rare earth elements, and comprises Pr and Nd; T represents Fe, Mn, Al and Co; R1 represents at least one rare earth element, and comprises at least one of Dy and Tb; the main phase contains Pr, Nd, Fe, Mn, Al, Co and B; and the grain boundary phase further contains at least one of Nb and Ti; and contents of N, F, Mn, Al, Tb, Dy, Pr, Nd, Co, Ga, Zr and Cu in the NdFeB permanent magnet are respectively: 0.03 wt %N0.09 wt %; 0.005 wt %F0.5 wt %; 0.011 wt %Mn0.027 wt %; 0.1 wt %Al0.6 wt %; 0.1 wt %Tb2.9 wt %; 0.1 wt %Dy3.9 wt %; 3 wt %Pr14 wt %; 13 wt %Nd28 wt %; 0.6 wt %Co2.8 wt %; 0.09 wt %Ga0.19 wt %; 0.06 wt %Zr0.19 wt %; and 0.08 wt %Cu0.24 wt %.

2. The method for producing the NdFeB permanent magnet comprising the nitride phase, as recited in claim 1, wherein: in the step (1), the rare earth fluorides comprise at least one member selected from the group consisting of praseodymium-neodymium fluorides, terbium fluorides, and dysprosium fluorides.

3. The method for producing the NdFeB permanent magnet comprising the nitride phase, as recited in claim 1, wherein: in the step (1), the portion of raw materials further comprises NdFeB scraps; a weight of the NdFeB scraps is 20-60% of a total weight of the raw materials; and a weight of the rare earth fluorides is 0.1-3% of the total weight of the raw materials.

4. The method for producing the NdFeB permanent magnet comprising the nitride phase, as recited in claim 1, wherein: in the step (1), the portion of raw materials further comprises NdFeB scraps; during refining, a vacuum degree is controlled in a range of 810.sup.1-810.sup.2 Pa; and the content of Mn in the NdFeB permanent magnet is controlled in a range of 0.01-0.016 wt %.

5. The method for producing the NdFeB permanent magnet comprising the nitride phase, as recited in claim 1, wherein: the hydrogen decrepitation process comprises steps of: firstly adding terbium fluoride powders into the alloy flakes; then heating the alloy flakes to a temperature of 400-800 C., and keeping the temperature for 10 minutes to 8 hours; cooling the alloy flakes to 100-390 C.; absorbing hydrogen; heating the alloy flakes to a temperature of 600-900 C. and keeping the temperature; and cooling the alloy flakes to below 200 C.; and the content of Tb in the NdFeB permanent magnet is in a range of 0.1-1.9 wt %.

6. The method for producing the NdFeB permanent magnet comprising the nitride phase, as recited in claim 1, wherein: in the step (4), after pouring the second melting liquid after refining onto the surface of the water-cooled rotation roller through the tundish, the alloy flakes are formed, the formed alloy flakes are crushed, then fall into a water-cooled rotation cylinder, and are processed with secondary cooling.

7. The method for producing the NdFeB permanent magnet comprising the nitride phase, as recited in claim 1, wherein: in the step (6), the nitrogen jet mill for milling the alloy flakes into the powders is a nitrogen jet mill without discharging ultrafine powders; the powders prepared through the nitrogen jet mill comprise ultrafine powders having a particle size smaller than 1 m and conventional powders having a particle size larger than 1 m, and the ultrafine powders have a higher nitrogen content and a higher heavy rare earth element content than the conventional powders; after uniformly mixing the ultrafine powders and the conventional powders, the ultrafine powders surround the conventional powders.

8. The method for producing the NdFeB permanent magnet comprising the nitride phase, as recited in claim 1, wherein: before milling the alloy flakes into powders by the nitrogen jet mill in the step (6), the step (6) further comprises a step of adding a lubricating agent into the alloy flakes after the hydrogen decrepitation process; and the lubricating agent contains F.

9. The method for producing the NdFeB permanent magnet comprising the nitride phase, as recited in claim 1, wherein: in the step (11), the vacuum sintering temperature is controlled in a range of 1010-1045 C., and the aging temperature is controlled in a range of 460-540 C.; the content of Tb in the NdFeB permanent magnet is controlled in a range of 0.1-2.8 wt %, and the density of the NdFeB permanent magnet is controlled at 7.5-7.7 g/cm.sup.3.

10. The method for producing the NdFeB permanent magnet comprising the nitride phase, as recited in claim 1, wherein: the step (10) comprises steps of: immersing the part in a solution containing TbAl alloy powders, and attaching the TbAl alloy powders on the surface of the part; and the step (11) comprises steps of: sending the part, with the surface attached by the TbAl alloy powders, into the vacuum sintering furnace; processing the part with vacuum sintering and aging, and controlling the vacuum sintering temperature in a range of 1010-1045 C. and the aging temperature in a range of 460-540 C.; and obtaining the NdFeB permanent magnet with a density of 7.5-7.7 g/cm.sup.3; the content of Tb in the NdFeB permanent magnet is in a range of 0.1-0.4 wt %; the content of Al is in a range of 0.1-0.3 wt %; F exists in the grain boundary phase; and, the composite phase containing Tb and N exists between the main phase and the grain boundary phase, and has a structure of (R1, Tb).sub.2T.sub.14(B, N).

11. The method for producing the NdFeB permanent magnet comprising the nitride phase, as recited in claim 1, wherein: in the step (8), the presintered density of the presintered block is controlled at 5.1-6.2 g/cm.sup.3; the step (10) comprises steps of: immersing the part in a solution containing terbium fluoride powders, and attaching the terbium fluoride powders on the surface of the part; and the step (11) comprises steps of: sending the part, with the surface attached by the terbium fluoride powders, into the vacuum sintering furnace; processing the part with vacuum sintering and aging, and controlling the vacuum sintering temperature in a range of 1020-1045 C. and the aging temperature in a range of 470-540 C.; and obtaining the NdFeB permanent magnet with a density of 7.5-7.7 g/cm.sup.3; the NdFeB permanent magnet prepared through the method has the average grain size in the range of 3-6 m; and, in the NdFeB permanent magnet, a composite phase, having a Tb content higher than an average Tb content of the NdFeB permanent magnet, exists between the main phase and the grain boundary phase.

12. The method for producing the NdFeB permanent magnet comprising the nitride phase, as recited in claim 1, wherein: the step (10) comprises a step of: through a pressure immersing method, attaching the powders containing Tb on the surface of the part.

13. The method for producing the NdFeB permanent magnet comprising the nitride phase, as recited in claim 1, wherein: the step (10) comprises a step of: through at least one method of sputtering, evaporating and spraying, forming the film containing Tb on the surface of the part.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows distribution trends of average concentrations of F and Tb in a magnet according to the prior art, wherein the average concentrations gradually increase from a center of the magnet to a surface of the magnet.

(2) FIG. 2 shows distribution trends of average concentrations of F and Tb in a NdFeB permanent magnet D1, relative to a depth from a surface of the NdFeB permanent magnet D1, according to a first example of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(3) Obvious effects of the present invention are further illustrated with following examples.

Example 1

(4) According to weight percent, preparing raw materials of praseodymium-neodymium alloys, metallic terbium, dysprosium fluorides, dysprosium-ferrum, pure iron, ferro-boron, metallic gallium, metallic zirconium, metallic cobalt, metallic aluminum and metallic copper into an alloy raw material having a composition of Pr.sub.6.3Nd.sub.23.1Dy.sub.2Tb.sub.0.6B.sub.0.95Co.sub.1.2Zr.sub.0.12Ga.sub.0.1Al.sub.0.2Cu.sub.0.2Fe.sub.rest; loading the pure iron, the ferro-boron, the dysprosium fluorides, and a small amount of the praseodymium-neodymium alloys into a first charging basket; loading a rest of praseodymium-neodymium alloys, the dysprosium-ferrum, the metallic terbium, and the metallic gallium into a second charging basket; loading the metallic zirconium, the metallic cobalt, the metallic aluminum and the metallic copper into a third charging basket; sending the three charging baskets into a vacuum loading chamber of a vacuum melting rapid-solidifying device; after evacuating, opening the vacuum loading chamber and a vacuum valve of a vacuum melting chamber; through a cooperation among a lifting device, a multistage rotation plate, and a trolley which moves back and forth, sending the raw materials in the first charging basket to a crucible of the vacuum melting chamber under a vacuum condition, heating to 1400-1500 C., refining the raw materials, and obtaining a first melting liquid; through the lifting device, sending a NdFeB slag cleaning device to a surface of the first melting liquid in the crucible of the vacuum melting chamber, absorbing slags to the slag cleaning device, and lifting the slag cleaning device up; adding the raw materials in the second charging basket and the third charging basket into the crucible of the vacuum melting chamber, filling argon into the vacuum melting chamber, refining the first melting liquid and the raw materials in the crucible, and obtaining a second melting liquid; after refining, tilting the crucible, pouring the second melting liquid onto a surface of a water-cooled rotation roller through a tundish, and forming an alloy flake material; leaving the water-cooled rotation roller and then falling into an alloy flake crushing device of an alloy flake cooling chamber by the alloy flake material, crushing the alloy flake material, then falling into a water-cooled rotation cylinder by the crushed alloy flake material, processing the crushed alloy flake material with secondary cooling, and forming first alloy flakes; sending the first alloy flakes and second alloy flakes having a composition of (Pr.sub.0.25Nd.sub.0.75).sub.30.1Fe.sub.restCo.sub.0.6Al.sub.0.1B.sub.0.95Cu.sub.0.1 Ga.sub.0.1Zr.sub.0.14 into a vacuum hydrogen decrepitation furnace, and processing the first alloy flakes and the second alloy flakes with a hydrogen decrepitation process, wherein the hydrogen decrepitation process comprises steps of: adding terbium fluoride powders into the first and second alloy flakes, then heating the first and second alloy flakes to a temperature of 650 C., keeping the temperature at 650 C. for 2 hours, cooling the first and second alloy flakes to 260 C., absorbing hydrogen, heating the first and second alloy flakes to the temperature of 650 C. again and keeping the temperature, and finally cooling the first and second alloy flakes to below 200 C.; sending the first and second alloy flakes after the hydrogen decrepitation process into a nitrogen jet mill without discharging ultrafine powders, milling the first and second alloy flakes into powders by the nitrogen jet mill, and controlling an average particle size of the powders at about 2.0-2.2 m; processing the powders with magnetic field pressing, obtaining a pressed compact, and presintering the pressed compact into a presintered block with a presintered density of about 5.8 g/cm.sup.3; machining the presintered block into a part; removing oil from the part, and then immersing the part into a solution containing the terbium fluoride powders; sending the part containing the terbium fluoride powders into a vacuum sintering furnace, processing the part with vacuum sintering and aging, and controlling a vacuum sintering temperature at about 1040 C. and an aging temperature at about 505 C.; and, after subsequent processes, obtaining a NdFeB permanent magnet D1 with a density of 7.5 g/cm.sup.3.

(5) Through detecting, it is found that the NdFeB permanent magnet D1 has a magnetic energy product of 50 MGOe and a coercive force of 25 kOe. FIG. 2 shows distribution trends of average concentrations of F and Tb in the NdFeB permanent magnet D1, relative to a depth from a surface of the NdFeB permanent magnet D1. From FIG. 2, it is seen that F and Tb are relatively uniformly distributed in the NdFeB permanent magnet D1; and the average concentrations of F and Tb are not in a trend showed in FIG. 1 that gradually increases from a center of the magnet to a surface of the magnet. NdFeB permanent magnet products, in the same batch of the NdFeB permanent magnet D1, have few broken edges and corners, and a low rejection rate.

(6) Alternatively, it is feasible to machine the presintered block into the part, and then immerse the part into any other solution containing powders of Tb, or attach powders containing Tb on a surface of the part though a pressure immersing method, or form a film containing Tb on the surface of the part though at least one method of sputtering, evaporating and spraying; next, the part, with the surface attached by the powders or the film containing Tb, is sent into the vacuum sintering furnace and processed with vacuum sintering, aging, and subsequent processes. The obtained permanent magnet has a similar magnetic performance as the NdFeB permanent magnet D1. Permanent magnet products, in the same batch of the permanent magnet, have few broken edges and corners, and a low rejection rate. F and Tb are relatively uniformly distributed in the permanent magnet; and average concentrations of F and Tb are not in the trend showed in FIG. 1 that gradually increases from the center of the magnet to the surface of the magnet.

Contrast Example 1

(7) According to weight percent, preparing raw materials of praseodymium-neodymium alloys, metallic terbium, dysprosium-ferrum, pure iron, ferro-boron, metallic gallium, metallic zirconium, metallic cobalt, metallic aluminum and metallic copper into an alloy raw material having a composition of Pr.sub.6.3Nd.sub.23.1Dy.sub.2Tb.sub.0.6B.sub.0.05Co.sub.1.2Zr.sub.0.12Ga.sub.0.1Al.sub.0.2Cu.sub.0.2Fe.sub.rest; loading the pure iron, the ferro-boron, and a small amount of the praseodymium-neodymium alloys into a first charging basket; loading a rest of praseodymium-neodymium alloys, the dysprosium-ferrum, the metallic terbium, and the metallic gallium into a second charging basket; loading the metallic zirconium, the metallic cobalt, the metallic aluminum and the metallic copper into a third charging basket; melting the raw materials in the three charging baskets with the same steps in the example 1, and forming third alloy flakes having a same composition as the first alloy flakes in the example 1; sending the third alloy flakes and second alloy flakes having a composition of (Pr.sub.0.25Nd.sub.0.75).sub.30.1Fe.sub.restCo.sub.0.6Al.sub.0.1B.sub.0.95Cu.sub.0.1Ga.sub.0.1Zr.sub.0.14 into a vacuum hydrogen decrepitation furnace, and processing the third alloy flakes and the second alloy flakes with a hydrogen decrepitation process, wherein the hydrogen decrepitation process comprises steps of: heating the third and second alloy flakes to a temperature of 260 C., absorbing hydrogen, heating the third and second alloy flakes to a temperature of 650 C. and keeping the temperature, and finally cooling the third and second alloy flakes to below 200 C.; sending the third and second alloy flakes after the hydrogen decrepitation process into a conventional nitrogen jet mill, milling the third and second alloy flakes into powders by the conventional nitrogen jet mill, and controlling an average particle size of the powders at about 3.3-3.6 m; with the same steps in the example 1, processing the powders with magnetic field pressing, obtaining a pressed compact, presintering the pressed compact into a presintered block, machining the presintered block into a part, removing oil from the part, and immersing the part into a solution containing terbium fluoride powders; sending the part containing the terbium fluoride powders into a vacuum sintering furnace, processing the part with vacuum sintering and aging; and, after subsequent processes, obtaining a NdFeB permanent magnet C1.

(8) Through detecting, it is found that the NdFeB permanent magnet C1 has a magnetic energy product of 45 MGOe and a coercive force of 21 kOe. NdFeB permanent magnet products, in the same batch of the NdFeB permanent magnet C1, have few broken edges and corners, and a low rejection rate.

Contrast Example 2

(9) According to weight percent, preparing raw materials of praseodymium-neodymium alloys, metallic terbium, dysprosium-ferrum, pure iron, ferro-boron, metallic gallium, metallic zirconium, metallic cobalt, metallic aluminum and metallic copper into an alloy raw material having a composition of Pr.sub.6.3Nd.sub.23.1Dy.sub.2Tb.sub.0.6B.sub.0.95Co.sub.1.2Zr.sub.0.12Ga.sub.0.1Al.sub.0.2Cu.sub.0.2Fe.sub.rest; loading the pure iron, the ferro-boron, and a small amount of the praseodymium-neodymium alloys into a first charging basket; loading a rest of praseodymium-neodymium alloys, the dysprosium-ferrum, the metallic terbium, and the metallic gallium into a second charging basket; loading the metallic zirconium, the metallic cobalt, the metallic aluminum and the metallic copper into a third charging basket; melting the raw materials in the three charging baskets with the same steps in the example 1, and forming third alloy flakes having a same composition as the first alloy flakes in the example 1; sending the third alloy flakes and second alloy flakes having a composition of (Pr.sub.0.25Nd.sub.0.75).sub.30.1Fe.sub.restCo.sub.0.6Al.sub.0.1B.sub.0.95Cu.sub.0.1Ga.sub.0.1Zr.sub.0.14 into a vacuum hydrogen decrepitation furnace, and processing the third alloy flakes and the second alloy flakes with a hydrogen decrepitation process, wherein the hydrogen decrepitation process comprises steps of: heating the third and second alloy flakes to a temperature of 260 C., absorbing hydrogen, heating the third and second alloy flakes to a temperature of 650 C. and keeping the temperature, and finally cooling the third and second alloy flakes to below 200 C.; sending the third and second alloy flakes after the hydrogen decrepitation process into a conventional nitrogen jet mill, milling the third and second alloy flakes into powders by the conventional nitrogen jet mill, and controlling an average particle size of the powders at about 3.3-3.6 m; processing the powders with magnetic field pressing, obtaining a pressed compact, processing the pressed compact with sintering and aging, and obtaining a sintered block, wherein a vacuum sintering temperature is controlled at about 1040 C., an aging temperature is controlled at about 505 C., and a density of the sintered block is controlled at 7.5 g/cm.sup.3; machining the sintered block into a part; removing oil from the part, and immersing the part into a solution containing terbium fluoride powders; processing the part containing the terbium fluoride powders with a diffusing heat treatment at a temperature below the sintering temperature; and, after subsequent processes, obtaining a NdFeB permanent magnet C2.

(10) Through detecting, it is found that the NdFeB permanent magnet C2 has a magnetic energy product of 45 MGOe and a coercive force of 21 kOe. NdFeB permanent magnet products, in the same batch of the NdFeB permanent magnet C2, have obviously more broken edges and corners than the products in the same batch of the NdFeB permanent magnet D1 and the NdFeB permanent magnet C1, and a relatively high rejection rate.

Example 2

(11) According to weight percent, preparing raw materials of praseodymium-neodymium alloys, metallic terbium, dysprosium fluorides, dysprosium-ferrum, pure iron, ferro-boron, metallic gallium, metallic zirconium, metallic cobalt, metallic aluminum and metallic copper, and NdFeB scraps into an alloy raw material having a composition of Pr.sub.6.3Nd.sub.23.1Dy.sub.1.5Tb.sub.1.0B.sub.0.95Co.sub.1.2Zr.sub.0.12Ga.sub.0.1Al.sub.0.2Cu.sub.0.2Fe.sub.rest; loading the pure iron, the ferro-boron, the dysprosium fluorides, and a small amount of the praseodymium-neodymium alloys into a first charging basket; loading the NdFeB scraps into a second charging basket; loading a rest of praseodymium-neodymium alloys, the dysprosium-ferrum, the metallic terbium, and the metallic gallium into a third charging basket; loading the metallic zirconium, the metallic cobalt, the metallic aluminum and the metallic copper into a fourth charging basket; sending the four charging baskets into a vacuum loading chamber of a vacuum melting rapid-solidifying device; after evacuating, opening the vacuum loading chamber and a vacuum valve of a vacuum melting chamber; through a cooperation among a lifting device, a multistage rotation plate, and a trolley which moves back and forth, sending the raw materials in the first charging basket and the second charging basket into a crucible of the vacuum melting chamber under a vacuum condition, heating to 1400-1500 C., refining the raw materials, and obtaining a first melting liquid; through the lifting device, sending a NdFeB slag cleaning device to a surface of the first melting liquid in the crucible of the vacuum melting chamber, absorbing slags to the slag cleaning device, and lifting the slag cleaning device up; sending the raw materials in the third charging basket and the fourth charging basket into the crucible of the vacuum melting chamber, filling argon into the vacuum melting chamber, refining the first melting liquid and the raw materials in the crucible, and obtaining a second melting liquid; after refining, tilting the crucible, pouring the second melting liquid onto a surface of a water-cooled rotation roller through a tundish, and forming an alloy flake material; leaving the water-cooled rotation roller and then falling into an alloy flake crushing device of an alloy flake cooling chamber by the alloy flake material, crushing the alloy flake material, then falling into a water-cooled rotation cylinder by the crushed alloy flake material, processing the crushed alloy flake material with secondary cooling, and forming third alloy flakes; sending the third alloy flakes and fourth alloy flakes having a composition of (Pr.sub.0.25Nd.sub.0.75).sub.30.5Fe.sub.restCo.sub.0.6Al.sub.0.1B.sub.0.95Cu.sub.0.1Ga.sub.0.1Zr.sub.0.14 into a vacuum hydrogen decrepitation furnace, and processing the third alloy flakes and the fourth alloy flakes with a hydrogen decrepitation process, wherein the hydrogen decrepitation process comprises steps of: adding terbium fluoride powders into the third and fourth alloy flakes, then heating the third and fourth alloy flakes to a temperature of 700 C., keeping the temperature at 700 C. for 2 hours, cooling to 260 C., absorbing hydrogen, heating the third and fourth alloy flakes to a temperature of 650 C. and keeping the temperature, and finally cooling the third and fourth alloy flakes to below 200 C.; sending the third and fourth alloy flakes after the hydrogen decrepitation process into a nitrogen jet mill without discharging ultrafine powders, milling the third and fourth alloy flakes into powders by the nitrogen jet mill, and controlling an average particle size of the powders at about 2.0-2.2 m; processing the powders with magnetic field pressing, obtaining a pressed compact, and presintering the pressed compact into a presintered block with a presintered density of 6.0 g/cm.sup.3; machining the presintered block into a part, removing oil from the part, and immersing the part into a solution containing TbAl alloy powders; sending the part containing the TbAl alloy powders into a vacuum sintering furnace, processing the part with vacuum sintering and aging, and controlling a vacuum sintering temperature at about 1040 C. and an aging temperature at about 505 C.; and, after subsequent processes, obtaining a NdFeB permanent magnet D2 with a density of 7.4 g/cm.sup.3.

(12) Through detecting, it is found that the NdFeB permanent magnet D2 has a magnetic energy product of 50 MGOe and a coercive force of 26 kOe. NdFeB permanent magnet products, in the same batch of the NdFeB permanent magnet D2, have few broken edges and corners, and a low rejection rate.

(13) Alternatively, it is feasible to machine the presintered block into the part, and then immerse the part into any other solution containing powders of Tb, or attach the powders containing Tb on a surface of the part though a pressure immersing method, or form a film containing Tb on the surface of the part though at least one method of sputtering, evaporating and spraying; next, the part, with the surface attached by the powders or the film containing Tb, is sent into the vacuum sintering furnace and processed with vacuum sintering, aging, and subsequent processes. The formed permanent magnet has a similar magnetic performance as the NdFeB permanent magnet D2. Permanent magnet products, in the same batch of the permanent magnet, have few broken edges and corners, and a low rejection rate.

(14) One skilled in the art will understand that the embodiment of the present invention as shown in the drawings and described above is exemplary only and not intended to be limiting.

(15) It will thus be seen that the objects of the present invention have been fully and effectively accomplished. Its embodiments have been shown and described for the purposes of illustrating the functional and structural principles of the present invention and is subject to change without departure from such principles. Therefore, this invention includes all modifications encompassed within the spirit and scope of the following claims.