Low-B bare earth magnet

Abstract

The present invention discloses a low-B rare earth magnet. The rare earth magnet contains a main phase of R.sub.2T.sub.14B and comprises the following raw material components: 13.5 at %4.5 at % of R, 5.2 at %5.8 at % of B, 0.3 at %0.8 at % of Cu, 0.3 at %3 at % of Co, and the balance being T and inevitable impurities, the R being at least one rare earth element comprising Nd, and the T being an element mainly comprising Fe. 0.30.8 at % of Cu and an appropriate amount of Co are co-added into the rare earth magnet, so that three Cu-rich phases formed in the grain boundary, and the magnetic effect of the three Cu-rich phases existing in the grain boundary and the solution of the problem of insufficient B in the grain boundary can obviously improve the squareness and heat-resistance of the magnet.

Claims

1. A low-B rare earth magnet containing a main phase of R.sub.2T.sub.14B and comprising the following raw material components: 13.5 at %14.5 at % of R, 5.2 at %5.8 at % of B, 0.3 at %0.8 at % of Cu, 0.3 at %3 at % of Co, and a balance being T and inevitable impurities, wherein: the R is at least one rare earth element comprising Nd, and the T is an element mainly comprising Fe the T further comprises X, the X is at least three elements selected from Al, Si, Ga, Sn, Ge, Ag, Au, Bi, Mn, Cr, P or S, and a total composition of the X is 0 at %-1.0 at %.

2. The low-B rare earth magnet according to claim 1, wherein: and in the inevitable impurities, an amount of O is below 1 at %, an amount of C is below 1 at % and an amount of N is below 0.5 at %.

3. The low-B rare earth magnet according to claim 1, wherein the low-B rare earth magnet is manufactured by the following processes: a process of preparing an alloy for rare earth magnet with molten rare earth magnet components; processes of producing a fine powder by coarsely crushing and finely crushing the alloy for rare earth magnet; and processes of obtaining a compact by a magnetic field compacting method, sintering the compact in a vacuum or inert gas at a temperature of 900 C.1100 C., and forming a first Cu crystal phase, a second Cu crystal phase and a third Cu crystal phase in a grain boundary of the low-B rare earth magnet, wherein: a molecular composition of the first Cu crystal phase is a phase of RT.sub.2 series, a molecular composition of the second Cu crystal phase is a phase of R.sub.6T.sub.13X series, a molecular composition of the third Cu crystal phase is a phase of RT.sub.5 series, and a total content of the first Cu crystal phase and the second Cu crystal phase is over 65 volume % of the grain boundary.

4. The low-B rare earth magnet according to claim 3, wherein the low-B rare earth magnet is a magnet of NdFeB series with a maximum magnetic energy product over 43 MGOe.

5. The low-B rare earth magnet according to claim 1, wherein: the total composition of the X is 0.3 at %1.0 at %.

6. The low-B rare earth magnet according to claim 5, wherein an amount of Dy, Ho, Gd or Tb is below 1 at % of the R.

7. The low-B rare earth magnet according to claim 5, wherein: the X comprises Ga, and an amount of Ga is 0.1 at %0.2 at %.

8. The low-B rare earth magnet according to claim 5, wherein oxygen content of the low-B rare earth magnet is below 0.6 at %.

9. A low-B rare earth magnet containing a main phase of R.sub.2T.sub.14B and comprising the following raw material components: 13.5 at %14.5 at % of R, 5.2 at %5.8 at % of B, 0.3 at %0.8 at % of Cu, 0.3 at %3 at % of Co, and a balance being T and inevitable impurities, wherein: the R is at least one rare earth element comprising Nd, the T is an element mainly comprising Fe the T further comprises X, the X is at least three elements selected from Al, Si, Ga, Sn, Ge, Ag, Au, Bi, Mn, Cr, P or S, and a total composition of the X is 0 at %-1.0 at %, and the low-B rare earth magnet is manufactured by the following processes: a process of preparing an alloy for rare earth magnet with molten rare earth magnet components; processes of producing a fine powder by coarsely crushing and finely crushing the alloy for rare earth magnet; and processes of obtaining a compact by a magnetic field compacting method, sintering the compact in a vacuum or inert gas at a temperature of 900 C.1100 C., forming a first Cu crystal phase, a second Cu crystal phase and a third Cu crystal phase in a grain boundary of the low-B rare earth magnet, and performing RH grain boundary diffusion at a temperature of 700 C.1050 C., wherein: a molecular composition of the first Cu crystal phase is a phase of RT.sub.2 series, a molecular composition of the second Cu crystal phase is a phase of R.sub.6T.sub.13X series, a molecular composition of the third Cu crystal phase is a phase of RT.sub.5 series, and a total content of the first Cu crystal phase and the second Cu crystal phase is over 65 volume % of the grain boundary.

10. The low-B rare earth magnet according to claim 9, wherein: the RH is selected from Dy, Ho or Tb, and in the inevitable impurities, an amount of O is controlled below 1 at %, an amount of C is controlled below 1 at % and an amount of N is controlled below 0.5 at %.

11. The low-B rare earth magnet according to claim 9, wherein the low-B rare earth magnet is further manufactured using an aging treatment comprising treating the magnet after the RH grain boundary diffusion at a temperature of 400 C.650 C.

12. The low-B rare earth magnet according to claim 10, wherein the low-B rare earth magnet is further manufactured using an aging treatment comprising treating the magnet after the RH grain boundary diffusion at a temperature of 400 C.650 C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates an EPMA detection result of a sintered magnet of embodiment 1 of embodiment 1.

(2) FIG. 2 illustrates an EPMA content detection result of a sintered magnet of embodiment 1 of embodiment I.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(3) The present invention will be further described with the embodiments.

(4) Embodiment I

(5) Raw material preparing process: preparing Nd with 99.5% purity, industrial FeB, industrial pure Fe, Co with 99.9% purity, and Cu, Al and Si respectively with 99.5% purity; being counted in atomic percent at %.

(6) The content of each element is shown in TABLE 1:

(7) TABLE-US-00001 TABLE 1 proportion of each element Composition Nd Co B Cu Al Si Fe Comparing sample 1 13.0 1.0 5.5 0.5 0.5 0.1 remainder Comparing sample 2 13.2 1.0 5.5 0.5 0.5 0.1 remainder Embodiment 1 13.5 1.0 5.5 0.5 0.5 0.1 remainder Embodiment 2 13.8 1.0 5.5 0.5 0.5 0.1 remainder Embodiment 3 14.0 1.0 5.5 0.5 0.5 0.1 remainder Embodiment 4 14.2 1.0 5.5 0.5 0.5 0.1 remainder Embodiment 5 14.5 1.0 5.5 0.5 0.5 0.1 remainder Comparing sample 3 15.0 1.0 5.5 0.5 0.5 0.1 remainder Comparing sample 4 15.2 1.0 5.5 0.5 0.5 0.1 remainder

(8) Preparing 100 Kg raw material of each sequence number group by weighing respectively, in accordance with TABLE 1.

(9) Melting process: placing the prepared raw material of one group into an aluminum oxide made crucible at a time, performing a vacuum melting in an intermediate frequency vacuum induction melting furnace in 10.sup.2 Pa vacuum and below 1500 C.

(10) Casting process: after the process of vacuum melting, filling Ar gas into the melting furnace until the Ar pressure reaches 50000 Pa, then obtaining a quenching alloy by being casted by single roller quenching method at a quenching speed of 10.sup.2 C./s10.sup.4 C./s, thermal preservation treating the quenching alloy at 600 C. for 60 minutes, and then being cooled to room temperature.

(11) Hydrogen decrepitation process: at room temperature, vacuum pumping the hydrogen decrepitation furnace with the quenching alloy, then filling hydrogen with 99.5% purity into the furnace until the pressure reaches 0.1 MPa, after the alloy being placed for 120 minutes, vacuum pumping and heating at the same time, vacuum pumping at 500 C. for 2 hours, then being cooled, and the powder treated after hydrogen decrepitation process being taken out.

(12) Fine crushing process: performing jet milling to the powder after hydrogen decrepitation in the crushing room under a pressure of 0.4 MPa and in the atmosphere of oxidizing gas below 100 ppm, then obtaining fine powder with an average particle size of 4.5 m. The oxidizing gas means oxygen or water.

(13) Screening partial fine powder after the fine crushing process (occupies 30% of the total fine powder by weight), then mixing the screened fine powder and the unscreened fine powder. The amount of powder which has a particle size smaller than 1.0 m reduce to less than 10% of total powder by volume in the mixed fine powder.

(14) Methyl caprylate is added into the powder after jet milling, the additive amount is 0.2% of the mixed powder by weight, further the mixture is comprehensively mixed by a V-type mixer.

(15) Compacting process under a magnetic field: a vertical orientation magnetic field molder being used, compacting the powder added with methyl caprylate in once to form a cube with sides of 25 mm in an orientation field of 1.8 T and under a compacting pressure of 0.2 ton/cm.sup.2, then demagnetizing the once-forming cube in a 0.2 T magnetic field.

(16) The once-forming compact is sealed so as not to expose to air, the compact is secondly compacted by a secondary compact machine (isostatic pressing compacting machine) under a pressure of 1.4 ton/cm.sup.2.

(17) Sintering process: moving each of the compact into the sintering furnace, firstly sintering in a vacuum of 10.sup.3 Pa and then maintained at 200 C. and at 900 C. respectively, then sintering for 2 hours at 1030 C., after that filling Ar gas into the sintering furnace until the Ar pressure reaches 0.1 MPa, then being cooled to room temperature.

(18) Heat treatment process: annealing the sintered magnet for 1 hour at 620 C. in the atmosphere of high purity Ar gas, then being cooled to room temperature and taken out.

(19) Machining process: machining the sintered magnet after heat treatment as a magnet with 15 mm diameter and 5 mm thickness, the 5 mm direction being the orientation direction of the magnetic field.

(20) Magnetic property evaluation process: testing the sintered magnet by NIM-10000H type nondestructive testing system for BH large rare earth permanent magnet from National Institute of Metrology.

(21) Thermal demagnetization evaluation process: firstly testing the magnetic flux of the sintered magnet, heating the sintered magnet in the air at 100 C. for 1 hour, secondly testing the magnetic flux after being cooled; wherein the sintered magnet with a magnetic flux retention rate of above 95% is determined as a qualified product.

(22) The magnetic property of the magnets manufactured by the sintered body for comparing samples 14 and embodiments 15 are directly tested without grain boundary diffusion treatment. The evaluation results of the magnets of the embodiments and the comparing samples are shown in table 2.

(23) TABLE-US-00002 TABLE 2 magnetic property evaluation of the embodiments and the comparing samples Retention rate of the Br H.sub.cj (BH).sub.max magnetic NO. (KGs) (KOe) SQ (%) (MGOe) BHH flux (%) Comparing 14.92 10.4 85.6 52.1 62.5 88.0 sample 1 Comparing 14.51 11.32 88.3 51.2 62.52 90.5 sample 2 Embodi- 14.70 13.35 96.7 50.7 64.05 95.2 ment 1 Embodi- 14.58 14.20 98.4 49.8 64.00 96.2 ment 2 Embodi- 14.52 14.68 99.4 49.1 63.78 97.5 ment 3 Embodi- 14.39 14.43 99.6 48.7 63.13 97.2 ment 4 Embodi- 14.30 15.23 97.2 47.9 63.13 98.5 ment 5 Comparing 14.21 13.28 93.4 47.3 60.58 94.7 sample 3 Comparing 13.98 13.45 87.5 46.1 59.55 94.1 sample 4

(24) In the manufacturing process, special attention is paid to the control of the contents of O, C and N, and the contents of the three elements O, C, and N are controlled below 0.3 at %, 0.4 at % and 0.1 at %, respectively.

(25) In conclusion, in the present invention, when the content of R is less than 13.5 at %, SQ and H.sub.cj would decrease, this is because the reduction of R-rich phase leads to the existence of grain boundary phase without R-rich phase. Contrarily, when the content of R exceeds 14.5 at %, SQ would decrease, which is due to the existence of surplus R-rich phase in the grain boundary, and SQ would decrease similar to the conventional technique.

(26) Testing the Cu component of the sintered magnet according to embodiment 1 with FE-EPMA (Field emission-electron probe micro-analyzer), the results are shown in FIG. 1.

(27) Numeral 1 in FIG. 1 represents high-Cu crystal phase, the molecular formula of the high-Cu crystal phase is RT.sub.2 series, numeral 2 represents moderate Cu content crystal phase, the molecular formula of the moderate Cu content crystal phase is R.sub.6T.sub.13X series, numeral 3 represents low-Cu crystal phase.

(28) Calculated from FIG. 2, the content of the high-Cu crystal phase and the moderate Cu content crystal phase is over 65 volume % of the grain boundary composition.

(29) Similarly, testing embodiments 25 with FE-EPMA, the content of the high-Cu crystal phase and the moderate Cu content crystal phase is over 65 volume % of the grain boundary composition by calculation.

(30) What needs to be explained is that BHH stated by the present embodiment is the sum of (BH).sub.max and H.sub.cj, the concept of BHH stated by embodiments 27 is the same.

(31) Embodiment II

(32) Raw material preparing process: preparing Nd with 99.5% purity, Fe with 99.9% purity, Co with 99.9% purity, and Cu, Al, Ga and Si respectively with 99.5% purity; being counted in atomic percent at %.

(33) The contents of each element are shown in TABLE 3:

(34) TABLE-US-00003 TABLE 3 proportioning of each element Composition Nd Co B Cu Al Ga Si Fe Comparing sample 1 14 2 4.8 0.4 0.4 0.1 0.1 remainder Comparing sample 2 14 2 5 0.4 0.4 0.1 0.1 remainder Embodiment 1 14 2 5.2 0.4 0.5 0.1 0.1 remainder Embodiment 2 14 2 5.4 0.4 0.4 0.1 0.1 remainder Embodiment 3 14 2 5.6 0.4 0.4 0.1 0.1 remainder Embodiment 4 14 2 5.8 0.4 0.4 0.1 0.1 remainder Comparing sample 3 14 2 6 0.4 0.4 0.1 0.1 remainder Comparing sample 4 14 2 6.2 0.4 0.4 0.1 0.1 remainder

(35) Preparing 100 Kg raw material of each sequence number group by weighing respectively, in accordance with TABLE 3.

(36) Melting process: placing the prepared raw material of one group into an aluminum oxide made crucible at a time, performing a vacuum melting in an intermediate frequency vacuum induction melting furnace in 10.sup.2 Pa vacuum and below 1500 C.

(37) Casting process: after the process of vacuum melting, filling Ar gas into the melting furnace until the Ar pressure reaches 50000 Pa, then obtaining a quenching alloy by being casted with single roller quenching method at a quenching speed of 10 C./s10.sup.4 C./s, thermal preservation treating the quenching alloy at 600 C. for 60 minutes, and then being cooled to room temperature.

(38) Hydrogen decrepitation process: at room temperature, vacuum pumping the hydrogen decrepitation furnace placed with the quenching alloy, then filling hydrogen with 99.5% purity into the furnace until the pressure reaches 0.1 MPa, after the alloy being placed for 125 minutes, vacuum pumping and heating at the same time, performing the vacuum pumping at 500 C. for 2 hours, then being cooled, and the powder treated after hydrogen decrepitation process being taken out.

(39) Fine crushing process: performing jet milling to the powder after hydrogen decrepitation in the crushing room under a pressure of 0.41 MPa and in the atmosphere of oxidizing gas below 100 ppm, then obtaining fine powder with an average particle size of 4.30 m of fine powder. The oxidizing gas means oxygen or water.

(40) Screening partial fine powder which is treated after the fine crushing process (occupies 30%/o of the total fine powder by weight), removing the powder with a particle size of smaller than 1.0 m, then mixing the screened fine powder and the remaining unscreened fine powder. The amount of the powder which has a particle size smaller than 1.0 m is reduced to less than 10% of total powder by volume in the mixed fine powder.

(41) Methyl caprylate is added into the powder treated after jet milling, the additive amount is 0.25% of the mixed powder by weight, further the mixture is comprehensively mixed by a V-type mixer.

(42) Compacting process under a magnetic field: a vertical orientation type magnetic field molder being used, compacting the powder added with methyl caprylate in once to form a cube with sides of 25 mm in an orientation field of 1.8 T and under a compacting pressure of 0.2 ton/cm.sup.2, then demagnetizing the once-forming cube in a 0.2 T magnetic field.

(43) The once-forming compact is sealed so as not to expose to air, the compact is secondly compacted by a secondary compact machine (isostatic pressing compacting machine) under a pressure of 1.4 ton/cm.sup.2.

(44) Sintering process: moving each of the compact to the sintering furnace, firstly sintering in a vacuum of 10.sup.3 Pa and respectively maintained for 2 hours at 200 C. and for 2 hours at 900 C., respectively, then sintering for 2 hours at 1000 C., after that filling Ar gas into the sintering furnace until the Ar pressure reaches 0.1 MPa, then being cooled to room temperature.

(45) Heat treatment process: annealing the sintered magnet for 1 hour at 620 C. in the atmosphere of high purity Ar gas, then being cooled to room temperature and taken out.

(46) Machining process: machining the sintered magnet after heat treatment as a magnet with 15 mm diameter and 5 mm thickness, the 5 mm direction being the orientation direction of the magnetic field.

(47) Magnetic property evaluation process: testing the sintered magnet by NIM-10000H type nondestructive testing system for BH large rare earth permanent magnet from National Institute of Metrology.

(48) Thermal demagnetization evaluation process: firstly testing the magnetic flux of the sintered magnet, heating the sintered magnet in the air at 100 C. for 1 hour, secondly testing the magnetic flux after being cooled; wherein the sintered magnet with a magnetic flux retention rate of above 95% is determined as a qualified product.

(49) The magnetic property of the magnets manufactured by the sintered body for comparing samples 14 and embodiments 15 are directly tested without grain boundary diffusion treatment. The evaluation results of the magnets of the embodiments and the comparing samples are shown in TABLE 4.

(50) TABLE-US-00004 TABLE 4 magnetic property evaluation of the embodiments and the comparing samples Retention rate of the Br H.sub.cj (BH).sub.max magnetic NO. (KGs) (KOe) SQ (%) (MGOe) BHH flux (%) Comparing 14.71 11.87 82.4 50.64 62.51 85.5 sample 1 Comparing 14.67 12.38 88.5 50.35 62.73 90.1 sample 2 Embodi- 14.63 13.34 97.4 50.06 63.40 95.2 ment 1 Embodi- 14.58 13.83 99.2 49.71 63.54 96.8 ment 2 Embodi- 14.53 14.17 99.5 49.39 63.56 97.5 ment 3 Embodi- 14.48 13.99 96.7 49.07 63.06 96.8 ment 4 Comparing 13.43 14.79 96.2 43.74 58.53 98.6 sample 3 Comparing 13.39 14.78 96.2 43.43 58.21 98.4 sample 4

(51) In the manufacturing process, special attention is paid to the control of the contents of O, C and N, and the contents of the three elements O, C, and N are controlled below 0.4 at %, 0.3 at % and 0.2 at %, respectively.

(52) In conclusion, when the content of B is less than 5.2 at %, SQ would decrease sharply, this is because the reducing of the content of B leads to SQ decrease as same as the conventional technique. Contrarily, when the content of B exceeds 5.8 at %, SQ would decrease, the sintering property would decrease sharply, and the sintered density may not be sufficient, therefore Br and (BH).sub.max would decrease and one may not obtain a magnet with high magnetic energy product.

(53) Similarly, testing embodiments 14 with FE-EPMA, the content of the high-Cu crystal phase and the moderate Cu content crystal phase is over 65 volume % of the grain boundary composition by calculation.

(54) Embodiment III

(55) Raw material preparing process: preparing Nd with 99.5% purity, industrial FeB, industrial pure Fe, Co with 99.9% purity, and Cu with 99.5% purity; being counted in atomic percent at %.

(56) The contents of each element are shown in TABLE 5:

(57) TABLE-US-00005 TABLE 5 proportioning of each element Composition Nd Co B Cu Fe Comparing sample 1 14.0 1.0 5.5 0.2 remainder Embodiment 1 14.0 1.0 5.5 0.3 remainder Embodiment 2 14.0 1.0 5.5 0.4 remainder Embodiment 3 14.0 1.0 5.5 0.6 remainder Embodiment 4 14.0 1.0 5.5 0.8 remainder Comparing sample 2 14.0 1.0 5.5 1 remainder Comparing sample 3 14.0 1.0 5.5 1.2 remainder

(58) Preparing 100 Kg raw material of each sequence number group by weighing respectively, in accordance with TABLE 5.

(59) Melting process: placing the prepared raw material of one group into an aluminum oxide made crucible at a time, performing a vacuum melting in an intermediate frequency vacuum induction melting furnace in 10.sup.2 Pa vacuum and below 1500 C.

(60) Casting process: after the process of vacuum melting, filling Ar gas into the melting furnace until the Ar pressure reaches 50000 Pa, then obtaining a quenching alloy by being casted with single roller quenching method at a quenching speed of 10.sup.2 C./s10.sup.4 C./s, thermal preservation treating the quenching alloy at 600 C. for 60 minutes, and then being cooled to room temperature.

(61) Hydrogen decrepitation process: at room temperature, vacuum pumping the hydrogen decrepitation furnace placed with the quenching alloy, then filling hydrogen with 99.5% purity into the furnace until the pressure reaches 0.1 MPa, after the alloy being placed for 97 minutes, vacuum pumping and heating at the same time, performing the vacuum pumping at 500 C. for 2 hours, then being cooled, and the powder treated after hydrogen decrepitation process being taken out.

(62) Fine crushing process: performing jet milling to the powder after hydrogen decrepitation in the crushing room under a pressure of 0.42 MPa and in the atmosphere of below 100 ppm of oxidizing gas, then obtaining fine powder with an average particle size of 4.51 m of fine powder. The oxidizing gas means oxygen or water.

(63) Methyl caprylate is added into the powder treated after jet milling, the additive amount is 0.25% of the mixed powder by weight, further the mixture is comprehensively mixed by a V-type mixer.

(64) Compacting process under a magnetic field: a vertical orientation magnetic field molder being used, compacting the powder added with methyl caprylate in once to form a cube with sides of 25 mm in an orientation field of 1.8 T and under a compacting pressure of 0.2 ton/cm.sup.2, then demagnetizing the once-forming cube in a 0.2 T magnetic field.

(65) The once-forming compact is sealed so as not to expose to air, the compact is secondly compacted by a secondary compact machine (isostatic pressing compacting machine) under a pressure of 1.4 ton/cm.sup.2.

(66) Sintering process: moving each of the compact into the sintering furnace, firstly sintering in a vacuum of 10.sup.3 Pa and maintained for 2 hours at 200 C. and for 2 hours at 900 C., respectively; then sintering for 2 hours at 1020 C., after that filling Ar gas into the sintering furnace so that the Ar pressure reaches 0.1 MPa, then being cooled to room temperature.

(67) Heat treatment process: annealing the sintered magnet for 1 hour at 620 C. in the atmosphere of high purity Ar gas, then being cooled to room temperature and taken out.

(68) Machining process: machining the sintered magnet after heat treatment as a magnet with 15 mm diameter and 5 mm thickness, the 5 mm direction being the orientation direction of the magnetic field.

(69) Magnetic property evaluation process: testing the sintered magnet by NIM-10000H type nondestructive testing system for BH large rare earth permanent magnet from National Institute of Metrology.

(70) Thermal demagnetization evaluation process: firstly testing the magnetic flux of the sintered magnet, heating the sintered magnet in the air at 100 C. for 1 hour, secondly testing the magnetic flux after being cooled; wherein the sintered magnet with a magnetic flux retention rate of above 95% is determined as a qualified product.

(71) The magnetic property of the magnets manufactured by the sintered body for comparing samples 13 and embodiments 14 are directly tested without grain boundary diffusion treatment. The evaluation results of the magnets of the embodiments and the comparing samples are shown in TABLE 6.

(72) TABLE-US-00006 TABLE 6 magnetic property evaluation of the embodiments and the comparing samples Retention rate of the Br H.sub.cj (BH).sub.max magnetic NO. (KGs) (KOe) SQ (%) (MGOe) BHH flux (%) Comparing 14.58 13.01 86.3 49.74 62.75 92.5 sample 1 Embodi- 14.56 13.68 98.1 49.60 63.28 95.3 ment 1 Embodi- 14.54 14.24 99.2 49.64 63.88 97.1 ment 2 Embodi- 14.50 14.67 99.7 49.18 63.85 97.6 ment 3 Embodi- 14.46 14.99 99.2 48.90 63.89 97.8 ment 4 Comparing 14.42 13.32 96.8 48.62 61.94 94.3 sample 2 ComparingX 14.37 13.34 91.2 48.35 61.69 94.5 sample 2

(73) In the manufacturing process, special attention is paid to the control of the contents of O, C and N, and the contents of the three elements O, C, and N are controlled below 0.4 at %, 0.3 at % and 0.2 at %, respectively.

(74) In conclusion, when the content of Cu is less than 0.3 at %, SQ would decrease sharply, this is because Cu has the effect of improving SQ essentially. Contrarily, when the content of Cu exceeds 0.8 at %, H.sub.cj and SQ would decrease, this is because the improving effect for H.sub.cj is saturated as the excessive addition of Cu, furthermore, other negative factors begins to affect the magnetic property, which worsen the phenomenon.

(75) Similarly, testing embodiments 14 with FE-EPMA, the content of the high-Cu crystal phase and the moderate Cu content crystal phase is over 65 volume % of the grain boundary composition by calculation.

(76) Embodiment IV

(77) Raw material preparing process: preparing Nd with 99.5% purity, industrial FeB, industrial pure Fe, Co with 99.9% purity, and Cu, Al, Si and Cr respectively with 99.5% purity; being counted in atomic percent at %.

(78) The contents of each element are shown in TABLE 7:

(79) TABLE-US-00007 TABLE 7 proportioning of each element Composition Nd Co B Cu Al Si Cr Fe Comparing sample 1 14.0 0.1 5.6 0.6 0.3 0.1 0.1 remainder Comparing sample 2 14.0 0.2 5.6 0.6 0.3 0.1 0.1 remainder Embodiment 1 14.0 0.3 5.6 0.6 0.3 0.1 0.1 remainder Embodiment 2 14.0 0.5 5.6 0.6 0.3 0.1 0.1 remainder Embodiment 3 14.0 1.0 5.6 0.6 0.3 0.1 0.1 remainder Embodiment 4 14.0 2.0 5.6 0.6 0.3 0.1 0.1 remainder Embodiment 5 14.0 3.0 5.6 0.6 0.3 0.1 0.1 remainder Comparing sample 3 14.0 4.0 5.6 0.6 0.3 0.1 0.1 remainder Comparing sample 4 14.0 6.0 5.6 0.6 0.3 0.1 0.1 remainder

(80) Preparing 100 Kg raw material of each group by weighing respectively, in accordance with TABLE 7.

(81) Melting process: placing the prepared raw material of one group into an aluminum oxide made crucible at a time, performing a vacuum melting in an intermediate frequency vacuum induction melting furnace in 10.sup.2 Pa vacuum and below 1500 C.

(82) Casting process: after the process of vacuum melting, filling Ar gas into the melting furnace until the Ar pressure reaches 50000 Pa, then obtaining a quenching alloy by being casted with single roller quenching method at a quenching speed of 10.sup.2 C./s10.sup.4 C./s, thermal preservation treating the quenching alloy at 600 C. for 60 minutes, and then being cooled to room temperature.

(83) Hydrogen decrepitation process: at room temperature, vacuum pumping the hydrogen decrepitation furnace placed with the quenching alloy, then filling hydrogen with 99.5% purity into the furnace until the pressure reach 0.1 MPa, after the alloy being placed for 122 minutes, vacuum pumping and heating at the same time, performing the vacuum pumping at 500 C. for 2 hours, then being cooled, and the powder treated after hydrogen decrepitation process being taken out.

(84) Fine crushing process: performing jet milling to the powder after hydrogen decrepitation in the crushing room under a pressure of 0.45 MPa and in the atmosphere of oxidizing gas below 100 ppm, then obtaining an average particle size of 4.29 m of fine powder. The oxidizing gas means oxygen or water.

(85) Screening partial fine powder which is treated after the fine crushing process (occupies 30% of the total fine powder by weight), removing the powder with a particle size of smaller than 1.0 m, then mixing the screened fine powder and the remaining unscreened fine powder. The amount of powder which has a particle size smaller than 1.0 m is reduced to less than 10% of total powder by volume in the mixed fine powder.

(86) Methyl caprylate is added into the powder treated after jet milling, the additive amount is 0.22% of the mixed powder by weight, further the mixture is comprehensively mixed by a V-type mixer.

(87) Compacting process under a magnetic field: a vertical orientation type magnetic field molder being used, compacting the powder added with methyl caprylate in once to form a cube with sides of 25 mm in an orientation field of 1.8 T and under a compacting pressure of 0.2 ton/cm.sup.2, then demagnetizing the once-forming cube in a 0.2 T magnetic field.

(88) The once-forming compact is sealed so as not to expose to air, the compact is secondly compacted by a secondary compact machine (isostatic pressing compacting machine) under a pressure of 1.4 ton/cm.sup.2.

(89) Sintering process: moving each of the compact to the sintering furnace, firstly sintering in a vacuum of 10.sup.3 Pa and maintained for 2 hours at 200 C. and for 2 hours at 900 C., then sintering for 2 hours at 1010 C., respectively after that filling Ar gas into the sintering furnace until the Ar pressure reaches 0.1 MPa, then being cooled to room temperature.

(90) Heat treatment process: annealing the sintered magnet for 1 hour at 620 C. in the atmosphere of high purity Ar gas, then being cooled to room temperature and taken out.

(91) Machining process: machining the sintered magnet after heat treatment as a magnet with 15 mm diameter and 5 mm thickness, the 5 mm direction being the orientation direction of the magnetic field.

(92) Magnetic property evaluation process: testing the sintered magnet by NIM-10000H type nondestructive testing system for BH large rare earth permanent magnet from National Institute of Metrology.

(93) Thermal demagnetization evaluation process: firstly testing the magnetic flux of the sintered magnet, heating the sintered magnet in the air at 100 C. for 1 hour, secondly testing the magnetic flux after being cooled; wherein the sintered magnet with a magnetic flux retention rate of above 95% is determined as a qualified product.

(94) The magnetic property of the magnets manufactured by the sintered body in accordance with comparing samples 14 and embodiments 15 are directly tested without grain boundary diffusion treatment. The evaluation results of the magnets of the embodiments and the comparing samples are shown in TABLE 8.

(95) TABLE-US-00008 TABLE 8 magnetic property evaluation of the embodiments and the comparing samples Retention rate of the Br H.sub.cj (BH).sub.max magnetic NO. (KGs) (KOe) SQ (%) (MGOe) BHH flux (%) Comparing 14.21 13.82 82.1 42.24 61.06 94.0 sample 1 Comparing 14.23 13.93 88.8 47.31 61.24 94.1 sample 2 Embodi- 14.25 15.65 96.5 47.42 63.07 96.5 ment 1 Embodi- 14.28 15.43 99.6 47.67 63.1 96.3 ment 2 Embodi- 14.3 15.53 99.5 47.84 63.37 96.5 ment 3 Embodi- 14.29 15.47 99.4 47.64 63.11 96.5 ment 4 Embodi- 14.26 15.64 97.3 47.45 63.09 96.8 ment 5 Comparing 14.24 13.83 88.3 47.32 61.15 94.0 sample 3 Comparing 14.21 12.81 84.5 47.24 60.05 93.7 sample 4

(96) In the manufacturing process, special attention is paid to the control of the contents of O, C and N, and the contents of the three elements O, C, and N are controlled below 0.6 at %, 0.3 at % and 0.3 at %, respectively.

(97) In conclusion, when the content of Co is less than 0.3 at %, H.sub.cj and SQ would decrease sharply, this is because the effect of improving H.sub.cj and SQ may be realized only if the RCo intermetallic composition which existed in the grain boundary phase reaches a certain minimum amount. Contrarily, when the content of Co exceeds 3 at %, H.sub.cj and SQ would decrease sharply, this is because the other phases with the effect of reducing coercivity may be formed if the RCo intermetallic composition existed in the grain boundary phase exceeds a fixed amount.

(98) Similarly, testing embodiments 15 with FE-EPMA, the content of the high-Cu crystal phase and the moderate Cu content crystal phase is over 65 volume % of the grain boundary composition by calculation.

(99) Embodiment V

(100) Raw material preparing process: preparing Nd with 99.5% purity, industrial FeB, industrial pure Fe, Co with 99.9% purity, and Cu, Al, Ga, Si, Mn, Sn, Ge, Ag, Au and Bi respectively with 99.5% purity; being counted in atomic percent at %.

(101) The contents of each element are shown in TABLE 9:

(102) TABLE-US-00009 TABLE 9 proportioning of each element Composition Nd Co B Cu Al Ga Si Mn Sn Ge Ag Au Bi Fe Comparing 13.6 3.0 5.7 0.6 0.3 0 0.1 remainder sample 1 Comparing 13.6 3.0 5.7 0.6 0.2 0 0.1 remainder sample 2 Embodiment 1 13.6 3.0 5.7 0.6 0.2 0.1 0.1 remainder Embodiment 2 13.6 3.0 5.7 0.6 0.2 0 0.1 0.1 0.3 remainder Embodiment 3 13.6 3.0 5.7 0.6 0.1 0.1 0.1 0.1 0.4 remainder Embodiment 4 13.6 3.0 5.7 0.6 0.1 0 0.1 0.5 remainder Embodiment 5 13.6 3.0 5.7 0.6 0.1 0 0.1 0.5 remainder Embodiment 6 13.6 3.0 5.7 0.6 0.1 0 0.1 0.5 remainder Embodiment 7 13.6 3.0 5.7 0.6 0.1 0 0.1 0.1 remainder Embodiment 8 13.6 3.0 5.7 0.6 0.2 0.1 0.2 remainder Comparing 13.6 3.0 5.7 0.6 0.1 0.2 0.1 0.8 remainder sample 3 Comparing 13.6 3.0 5.7 0.6 0.1 0.2 0.1 0.2 0.5 remainder sample 4

(103) Preparing 100 Kg raw material of each group by weighing respectively in accordance with TABLE 9.

(104) Melting process: placing the prepared raw material of one group into an aluminum oxide made crucible at a time, performing a vacuum melting in an intermediate frequency vacuum induction melting furnace in 10.sup.2 Pa vacuum and below 1500 C.

(105) After the process of vacuum melting, filling Ar gas into the melting furnace until the Ar pressure would reach 50000 Pa, then obtaining a quenching alloy by being casted by single roller quenching method at a quenching speed of 10.sup.2 C./s10.sup.4 C./s, thermal preservation treating the quenching alloy at 600 C. for 60 minutes, and then being cooled to room temperature.

(106) Hydrogen decrepitation process: at room temperature, vacuum pumping the hydrogen decrepitation furnace placed with the quenching alloy, then filling hydrogen with 99.5% purity into the furnace until the pressure reach 0.1 MPa, after the alloy being placed for 109 minutes, vacuum pumping and heating at the same time, performing the vacuum pumping at 500 C. for 2 hours, then being cooled, and the powder treated after hydrogen decrepitation process being taken out.

(107) Fine crushing process: performing jet milling to the powder after hydrogen decrepitation in the crushing room under a pressure of 0.41 MPa and in the atmosphere of below 100 ppm of oxidizing gas, then obtaining fine powder with an average particle size of 4.58 m. The oxidizing gas means oxygen or water.

(108) Screening partial fine powder which is treated after the fine crushing process (occupies 30% of the total fine powder by weight), removing the powder with a particle size of smaller than 1.0 m, then mixing the screened fine powder and the unscreened fine powder. The amount of powder which has a particle size smaller than 1.0 m is reduced to less than 10% of total powder by volume in the mixed fine powder.

(109) Methyl caprylate is added into the powder treated after jet milling, the additive amount is 0.22% of the mixed powder by weight, further the mixture is comprehensively mixed by a V-type mixer.

(110) Compacting process under a magnetic field: a vertical orientation magnetic field molder being used, compacting the powder added with methyl caprylate in once to form a cube with sides of 25 mm in an orientation field of 1.8 T and under a compacting pressure of 0.2 ton/cm.sup.2, then demagnetizing the once-forming cube in a 0.2 T magnetic field.

(111) The once-forming compact is sealed so as not to expose to air, the compact is secondly compacted by a secondary compact machine (isostatic pressing compacting machine) under a pressure of 1.4 ton/cm.sup.2.

(112) Sintering process: moving each of the compact to the sintering furnace, firstly sintering in a vacuum of 10.sup.3 Pa and maintained for 2 hours at 200 C. and for 2 hours at 900 C., respectively; then sintering for 2 hours at 1010 C., after that filling Ar gas into the sintering furnace until the Ar pressure would reach 0.1 MPa, then being cooled to room temperature.

(113) Heat treatment process: annealing the sintered magnet for 1 hour at 620 C. in the atmosphere of high purity Ar gas, then being cooled to room temperature and taken out.

(114) Machining process: machining the sintered magnet after heat treatment as a magnet with 15 mm diameter and 5 mm thickness, the 5 mm direction being the orientation direction of the magnetic field.

(115) Magnetic property evaluation process: testing the sintered magnet by NIM-10000H type nondestructive testing system for BH large rare earth permanent magnet from National Institute of Metrology.

(116) Thermal demagnetization evaluation process: firstly testing the magnetic flux of the sintered magnet, heating the sintered magnet in the air at 100 C. for 1 hour, secondly testing the magnetic flux after being cooled; wherein the sintered magnet with a magnetic flux retention rate of above 95% is determined as a qualified product.

(117) The magnetic property of the magnets manufactured by the sintered body in accordance with comparing samples 14 and embodiments 18 are directly tested without grain boundary diffusion treatment. The evaluation results of the magnets of the embodiments and the comparing samples are shown in TABLE 10.

(118) TABLE-US-00010 TABLE 10 magnetic property evaluation of the embodiments and the comparing samples Retention rate of the Br H.sub.cj (BH).sub.max magnetic NO. (KGs) (KOe) SQ (%) (MGOe) BHH flux (%) Comparing 14.58 12.98 83.4 49.73 62.71 94.2 sample 1 Comparing 14.56 12.78 86.7 49.26 62.04 94.3 sample 2 Embodi- 14.58 13.56 99.3 49.86 63.42 97.3 ment 1 Embodi- 14.65 13.45 99.4 50.42 63.87 97.0 ment 2 Embodi- 14.66 14.39 99.5 50.73 65.12 97.6 ment 3 Embodi- 14.63 14.54 99.3 50.53 65.07 97.8 ment 4 Embodi- 14.65 14.51 99.5 50.84 65.35 97.8 ment 5 Embodi- 14.62 14.52 99.5 50.73 65.25 98.0 ment 6 Embodi- 14.63 14.43 99.6 50.61 65.04 97.7 ment 7 Embodi- 14.54 14.36 99.4 49.56 63.92 97.6 ment 8 Comparing 14.36 14.40 93.9 48.20 62.60 95.5 sample 3 Comparing 14.27 14.23 94.2 47.60 61.83 95.6 sample 4

(119) In the manufacturing process, special attention is paid to the control of the contents of O, C and N, and the contents of the three elements O, C, and N are respectively controlled below 0.2 at %, 0.2 at % and 0.1 at %.

(120) In conclusion, the using of more than 3 types of X is the most preferably, this is because the existence of minor amounts of impurity phase has an improving effect when the coercivity-improving phase is formed in the crystal grain boundary, meanwhile, when the content of X is less than 0.3 at %, coercivity and squareness may not be improved, however, when the content of X exceeds 1.0 at %, the improving effect for coercivity and squareness is saturated, furthermore, other phases having a negative effect for squareness is formed, consequently, SQ decrease occurred similarly.

(121) Similarly, testing embodiments 18 with FE-EPMA, the content of the high-Cu crystal phase and the moderate Cu content crystal phase is over 65 volume % of the grain boundary composition by calculation.

(122) Embodiment VI

(123) Raw material preparing process: preparing Nd, Pr, Dy, Gd, Ho and Tb with 99.5% purity, industrial FeB, industrial pure Fe, Co with 99.9% purity, and Cu, Al, Ga, Si, Cr, Mn, Sn, Ge and Ag respectively with 99.5% purity; being counted in atomic percent at %.

(124) The contents of each element are shown in TABLE 11:

(125) TABLE-US-00011 TABLE 11 proportioning of each element Composition Nd Pr Dy Gd Ho Tb Co B Cu Al Ga Si Cr Mn Sn Ge Ag Fe Embodiment 1 14.4 1.5 5.4 0.7 0.1 0.2 0.1 0.1 0.1 0.1 0.1 0.1 remainder Embodiment 2 11.4 3.0 1.5 5.4 0.7 0.1 0.2 0.1 0.1 0.1 0.1 0.1 0.1 remainder Embodiment 3 13.4 1.0 1.5 5.4 0.7 0.1 0.2 0.1 0.1 0.1 0.1 0.1 0.1 remainder Embodiment 4 13.4 0.5 1.5 5.4 0.7 0.1 0.2 0.1 0.1 0.1 0.1 0.1 0.1 remainder Embodiment 5 13.4 0.8 1.5 5.4 0.7 0.1 0.2 0.1 0.1 0.1 0.1 0.1 0.1 remainder Embodiment 6 13.4 0.6 1.5 5.4 0.7 0.1 0.2 0.1 0.1 0.1 0.1 0.1 0.1 remainder

(126) Preparing 100 Kg raw material of each sequence number group by weighing respectively, in accordance with TABLE 11.

(127) Melting process: placing the prepared raw material of one group into an aluminum oxide made crucible at a time, performing a vacuum melting in an intermediate frequency vacuum induction melting furnace in 10.sup.2 Pa vacuum and below 1500 C.

(128) Casting process: after the process of vacuum melting, filling Ar gas into the melting furnace until the Ar pressure would reach 50000 Pa, then obtaining a quenching alloy by being casted with single roller quenching method at a quenching speed of 10.sup.2 C./s10.sup.4 C./s, thermal preservation treating the quenching alloy at 600 C. for 60 minutes, and then being cooled to room temperature.

(129) Hydrogen decrepitation process: at room temperature, vacuum pumping the hydrogen decrepitation furnace placed with the quenching alloy, then filling hydrogen with 99.5% purity into the furnace until the pressure reach 0.1 MPa, after the alloy being placed for 151 minutes, vacuum pumping and heating at the same time, performing the vacuum pumping at 500 C. for 2 hours, then being cooled, and the powder treated after hydrogen decrepitation process being taken out.

(130) Fine crushing process: performing jet milling to the powder after hydrogen decrepitation in the crushing room under a pressure of 0.43 MPa and in the atmosphere of below 100 ppm of oxidizing gas, then obtaining fine powder with an average particle size of 4.26 m. The oxidizing gas means oxygen or water.

(131) Screening partial fine powder which is treated after the fine crushing process (occupies 30% of the total fine powder by weight), removing the powder with a particle size of smaller than 1.0 m, then mixing the screened fine powder and the remaining unscreened fine powder. The powder which has a particle size smaller than 1.0 m is reduced to less than 10% of total powder by volume in the mixed fine powder.

(132) Methyl caprylate is added into the powder treated after jet milling, the additive amount is 0.23% of the mixed powder by weight, further the mixture is comprehensively mixed by a V-type mixer.

(133) Compacting process under a magnetic field: a vertical orientation magnetic field molder being used, compacting the powder added with methyl caprylate in once to form a cube with sides of 25 mm in an orientation field of 1.8 T and under a compacting pressure of 0.2 ton/cm.sup.2, then demagnetizing the once-forming cube in a 0.2 T magnetic field.

(134) The once-forming compact is sealed so as not to expose to air, the compact is secondly compacted by a secondary compact machine (isostatic pressing compacting machine) under a pressure of 1.4 ton/cm.sup.2.

(135) Sintering process: moving each of the compact to the sintering furnace, firstly sintering in a vacuum of 10.sup.3 Pa and maintained for 2 hours at 200 C. and for 2 hours at 900 C., respectively then sintering for 2 hours at 1020 C., after that filling Ar gas into the sintering furnace so that the Ar pressure would reach 0.1 MPa, then being cooled to room temperature.

(136) Heat treatment process: annealing the sintered magnet for 1 hour at 620 C. in the atmosphere of high purity Ar gas, then being cooled to room temperature and taken out.

(137) Machining process: machining the sintered magnet after heat treatment as a magnet with 15 mm diameter and 5 mm thickness, the 5 mm direction being the orientation direction of the magnetic field.

(138) Magnetic property evaluation process: testing the sintered magnet by NIM-10000H type nondestructive testing system for BH large rare earth permanent magnet from National Institute of Metrology.

(139) Thermal demagnetization evaluation process: firstly testing the magnetic flux of the sintered magnet, heating the sintered magnet in the air at 100 C. for 1 hour, secondly testing the magnetic flux after being cooled; wherein the sintered magnet with a magnetic flux retention rate of above 95% is determined as a qualified product.

(140) The magnetic property of the magnets manufactured by the sintered body in accordance with embodiments 16 are directly tested without grain boundary diffusion treatment. The evaluation results of the magnets of the embodiments and the comparing samples are shown in TABLE 12.

(141) TABLE-US-00012 TABLE 12 magnetic property evaluation of the embodiments and the comparing samples Retention rate of the Br H.sub.cj (BH).sub.max magnetic NO. (KGs) (KOe) SQ (%) (MGOe) BHH flux (%) Embodi- 14.43 14.87 99.3 48.69 63.56 95.4 ment 1 Embodi- 14.41 16.15 99.5 48.58 64.73 97.4 ment 2 Embodi- 13.58 19.98 99.5 43.15 63.13 99.2 ment 3 Embodi- 13.68 18.99 99.3 44.26 63.25 98.3 ment 4 Embodi- 13.72 18.58 99.5 44.42 63.00 98.0 ment 5 Embodi- 13.71 22.56 99.2 44.01 66.57 99.5 ment 6

(142) In the manufacturing process, special attention is paid to the control of the contents of O, C and N, and the contents of the three elements O, C, and N are controlled below 0.5 at %, 0.3 at % and 0.2 at %, respectively.

(143) In conclusion, when the content of Dy, Ho, Gd or Tb of the raw material is less than 1 at %, a high-property magnet with maximum energy product over 43 MGOe may be obtained.

(144) Similarly, testing embodiments 16 with FE-EPMA, the content of the high-Cu crystal phase and the moderate Cu content crystal phase is over 65 volume % of the grain boundary composition by calculation.

(145) Embodiment VII

(146) Raw material preparing process: preparing Nd with 99.5% purity, industrial FeB, industrial pure Fe, Co with 99.9% purity, and Cu, Al and Si respectively with 99.5% purity; being counted in atomic percent at %.

(147) The contents of each element are shown in TABLE 13:

(148) TABLE-US-00013 TABLE 13 proportioning of each element Composition Nd Co B Cu Al Si Fe Comparing 13.8 0.5 5.5 0.2 0.3 0.5 remainder sample 1 Embodiment 1 13.8 0.5 5.5 0.3 0.3 0.5 remainder Embodiment 2 13.8 0.5 5.5 0.4 0.3 0.5 remainder Embodiment 3 13.8 0.5 5.5 0.6 0.3 0.5 remainder Embodiment 4 13.8 0.5 5.5 0.8 0.3 0.5 remainder Comparing 13.8 0.5 5.5 1 0.3 0.5 remainder sample 2 Comparing 13.8 0.5 5.5 1.2 0.3 0.5 remainder sample 3

(149) Preparing 100 Kg raw material of each sequence number group by weighing, respectively in accordance with TABLE 13.

(150) Melting process: placing the prepared raw material into an aluminum oxide made crucible at a time, performing a vacuum melting in an intermediate frequency vacuum induction melting furnace in 10.sup.2 Pa vacuum and below 1500 C.

(151) Casting process: after the process of vacuum melting, filling Ar gas into the melting furnace so that the Ar pressure would reach 50000 Pa, then obtaining a quenching alloy by being casted with single roller quenching method at a quenching speed of 10.sup.2 C./s10.sup.4 C./s, thermal preservation treating the quenching alloy at 600 C. for 60 minutes, and then being cooled to room temperature.

(152) Hydrogen decrepitation process: at room temperature, vacuum pumping the hydrogen decrepitation furnace placed with the quenching alloy, then filling hydrogen with 99.5% purity into the furnace until the pressure reach 0.1 MPa, after the alloy being placed for 139 minutes, vacuum pumping and heating at the same time, performing the vacuum pumping at 500 C. for 2 hours, then being cooled, and the powder treated after hydrogen decrepitation process being taken out.

(153) Fine crushing process: performing jet milling to the powder after hydrogen decrepitation in the crushing room under a pressure of 0.42 MPa and in the atmosphere of oxidizing gas below 100 ppm, then obtaining fine powder with an average particle size of 4.32 m of fine powder. The oxidizing gas means oxygen or water.

(154) Screening partial fine powder which is treated after the fine crushing process (occupies 30% of the total fine powder by weight), removing the powder with a particle size of smaller than 1.0 m, then mixing the screened fine powder and the remaining unscreened fine powder. The powder which has a particle size smaller than 1.0 m is reduced to less than 10% of total powder by volume in the mixed fine powder.

(155) Methyl caprylate is added into the powder treated after jet milling, the additive amount is 0.22% of the mixed powder by weight, further the mixture is comprehensively mixed by a V-type mixer.

(156) Compacting process under a magnetic field: a vertical orientation magnetic field molder being used, compacting the powder added with methyl caprylate in once to form a cube with sides of 25 mm in an orientation field of 1.8 T and under a compacting pressure of 0.2 ton/cm.sup.2, then demagnetizing the once-forming cube in a 0.2 T magnetic field.

(157) The once-forming compact is sealed so as not to expose to air, the compact is secondly compacted by a secondary compact machine (isostatic pressing compacting machine) under a pressure of 1.4 ton/cm.sup.2.

(158) Sintering process: moving each of the compact to the sintering furnace, firstly sintering in a vacuum of 10.sup.3 Pa and maintained for 2 hours at 200 C. and for 2 hours at 900 C., respectively then sintering for 2 hours at 1020 C., after that filling Ar gas into the sintering furnace until the Ar pressure would reach 0.1 MPa, then being cooled to room temperature.

(159) Heat treatment process: annealing the sintered magnet for 1 hour at 620 C. in the atmosphere of high purity Ar gas, then being cooled to room temperature and taken out.

(160) Machining process: machining the sintered magnet after heat treatment as a magnet with 15 mm diameter and 5 mm thickness, the 5 mm direction being the orientation direction of the magnetic field.

(161) Cleaning the magnet manufactured by the sintered body of the comparing samples 13 and embodiments 13, coating DyF.sub.3 powder with a thickness of 5 m on the surface of the magnet in a vacuum heat treatment furnace after the surface cleaning, treating the coated magnet after vacuum drying in Ar atmosphere at 850 C. for 24 hours, finally performing Dy grain boundary diffusion treatment. Adjusting the amount of evaporated Dy metal atom supplied to the surface of the sintered magnet, so that the attached metal atom is diffused into the grain boundary of the sintered magnet before formed as a thin film with the metal evaporation material on the surface of the sintered magnet.

(162) Aging treatment: Aging treating the magnet with Dy diffusion treatment in vacuum at 500 C. for 2 hours, testing the magnetic property of the magnet after surface grinding.

(163) Magnetic property evaluation process: testing the sintered magnet with Dy diffusion treatment by NIM-10000H type nondestructive testing system for BH large rare earth permanent magnet from National Institute of Metrology.

(164) Thermal demagnetization evaluation process: firstly testing the magnetic flux of the sintered magnet with Dy diffusion treatment, heating the sintered magnet in the air at 100 C. for 1 hour, secondly testing the magnetic flux after being cooled; wherein the sintered magnet with a magnetic flux retention rate of above 95% is determined as a qualified product.

(165) The evaluation results of the magnets of the embodiments and the comparing samples are shown in TABLE 14.

(166) TABLE-US-00014 TABLE 14 magnetic property evaluation of the embodiments and the comparing samples Addition of Retention coercivity rate of the (BH).sub.max after diffusion magnetic NO. Br (KGs) H.sub.cj (KOe) SQ (%) (MGOe) BHH (KOe) flux (%) Comparing sample 1 14.53 18.96 78.5 49.43 68.39 5.95 96.4 Embodiment 1 14.50 23.94 99.1 49.3 73.24 10.26 99.4 Embodiment 2 14.51 24.31 99.4 49.37 73.68 10.07 99.0 Embodiment 3 14.47 24.95 99.5 48.92 73.87 10.28 99.3 Embodiment 4 14.41 24.99 99.3 48.69 73.68 10.00 99.5 Comparing sample 2 14.39 19.86 94.9 48.32 68.18 6.54 97.8 Comparing sample 3 14.31 19.54 87.3 47.93 67.47 6.20 97.5

(167) In the manufacturing process, special attention is paid to the control of the contents of O, C and N, and the contents of the three elements O, C, and N are controlled below 0.4 at %, 0.3 at % and 0.2 at %, respectively.

(168) In conclusion, comparing the magnet with grain boundary diffusion with the magnet without grain boundary diffusion, the coercivity is increased with more than 10 (KOe), and the magnet with grain boundary diffusion has a very high coercivity and a favorable squareness.

(169) In the composition of the present invention, reducing the melting point of intermetallic compound phase comprising high melting point (950 C.) RCo.sub.2 phase by adding minor amounts of Cu, Co and other impurities, as a result, all of the crystal grain boundary are melted at the grain boundary diffusion temperature, the efficiency of the grain boundary diffusion is extraordinarily excellent, and the coercivity is improved to an unparalleled extent, moreover, as the squareness reaches over 99%, a high-property magnet with a favorable heat-resistance property may be obtained.

(170) Similarly, testing embodiments 14 with FE-EPMA, the content of the high-Cu crystal phase and the moderate Cu content crystal phase is over 65 volume % of the grain boundary composition by calculation.

(171) While the foregoing written description of the invention enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, method, and examples herein. The invention should therefore not be limited by the above described embodiment, method, and examples, but by all embodiments and methods within the scope and spirit of the invention.