PERMANENT MAGNETIC MATERIALS OF THE R-FE-B TYPE AND PROCESS OF MANUFACTURE

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to magnetic material compositions and a process for their manufacture, and more particularly performance magnetic material of the iron-boron-rare earth type (Fe-B-R).

[0002] Use of high performance permanent magnets of Fe-B-R type, where R is a rare earth element containing high concentrations of the element Neodymium (Nd) has become common in industry since the early 1980's. For example, computer hardware manufacturers who manufacture small footprint, large capacity computer data storage and retrieval hardware need permanent magnets in such devices. Due to severe size and weight restrictions inherent in such data storage devices, the permanent magnets contained therein must be relatively small yet have very strong magnetic properties to generate the required magnetic field. This has necessitated the use of very high performance Fe-B-R rare-earth permanent magnets within such devices.

[0003] In addition, medical diagnostic devices in the medical field, namely, magnetic resonance imaging (MRI) devices employ vast quantities (up to 133.4 MPa (1.5 tons)) of permanent magnetic material, typically Fe-B-R magnets which contain high percentages of the rare earth Nd as the rare earth component.

[0004] Accordingly, due to the sale of these devices since the early 1980's employing Fe-B-R permanent magnets wherein the rare earth component is principally comprised of Nd, the worldwide demand for Nd has increased. As a result, the cost of the raw material Nd used in manufacture of such permanent magnets has greatly increased.

[0005] A real need has arisen to develop Fe-B-R magnets of substantially equal performance, which utilize less Nd to thereby reduce the cost of the manufacture of such magnets and the devices which contain such magnets.

[0006] Permanent magnets of the Fe-B-R type, where R is one or more rare earth elements of which at least 50% of R is Nd and/or Praseodymium (Pr), are known. For example, U.S. Patents 4,684,406 and 4,597,938 both teach a high performance sintered permanent magnetic material of the Fe-B-R type. Such patents teach a high performance magnet consisting of, by atomic percent, (i) 12.5%-20% R wherein R is at least one rare earth element (selected from the group consisting of Nd, Pr, La, Ce, Tb, Dy, Ho, Er, Eu, Sm, Gd, Pm, Tm, Yb, Lu and Y) and at least 50% of R consists of Nd and/or Pr; (ii) 4-20%B; and (iii) the balance Fe with impurities. Likewise, as may be seen from U.S. 4,597,938, U.S. 4,975,130 and U.S. 4,684,606, such patents teach a process of preparing such a permanent magnet comprising forming powders. of alloys of the above composition; melting same to form an ingot; pulverizing the ingot to form an alloy powder having a mean particle size from 0.3 to 80 µm; compacting such powder at a pressure of 44.5 to 711.7 MPa (0.5 to 8 Ton/cm²); subjecting the compacted body to a magnetic field of about 557 to 1035 kA/m (7 to 13 kOe); and lastly sintering at a temperature between 900 to 1,200 °C (preferably 1,000 to 1,180 °C). A permanent magnet prepared in the above fashion specifically comprised of 77 Fe-9 B-9 Nd-5 Pr (wherein Nd and Pr together comprise the rare earth component), sintered at 1,120 °C for four hours in an inert atmosphere can acquire a high maximum energy product (BH)max of approximately 246.7 kJ/m³ (31.0 MGOe). Likewise, a permanent magnet comprised of 79 Fe-7 B-14 Nd, sintered at 1,120 °C for one hour at (atmosphere), can acquire a maximum energy product (BH)_max of approximately 26.9 kJ/m³ (33.8 MGOe) (ref. Table 1, U.S. 4,975,130). A sintered permanent magnet comprising 77Fe-7B-16Pr, sintered at 1,040 °C in a vacuum at 13.3 mPa (1x10^-4 torr) for two hours can be produced having a maximum energy product somewhat less, namely, 195 kJ/m³ (24.5 MGOe).

[0007] None of these prior art patents disclose or suggest what significance, if any, the amount of Ce present or the concentration of Ce as part of R may have on Fe-B-R magnet performance. Nor does the prior art teach or suggest ranges of concentrations of Ce which may form part of the rare earth component of an Fe-B-R magnet in substitution for Nd which will give equal or better magnetic performance of an Fe-B-(Nd and/or Pr) permanent magnet.

SUMMARY OF THE INVENTION

[0008] Applicants have discovered that relatively small percentages of Cerium, which in any event usually naturally occur in rare earth deposits containing Nd, may be included in certain defined percentages as part of the rare earth component "R" of an Fe-B-R magnet. R additionally comprises 70-76% Pr, 29.8-23.8% Nd and up to and including 5% Ce with no significant or only slight decrease in the magnetic performance of the resultant permanent magnet.

[0009] The applicants have further discovered that when certain low percentages of Cerium (0.5% wt. of R) are used in manufacture of an Fe-B-R permanent magnet in substitution of Nd, further substitution of Nd may further be made with Pr up to 76% which further substitution, particularly at Pr = 75%, will not reduce, and indeed appears to substantially equal or even enhance, the magnetic performance characteristics over a magnetic material made up of the same total percentage of rare earth elements but lacking Ce, or having Ce but having higher concentrations of Nd.

[0010] By substitution of portions of Nd with specific small percentages of Ce and greater amounts of Ce in accordance with the invention herein disclosed, significant cost savings can be achieved in the manufacture of high performance permanent magnets of the Fe-B-R type, while substantially maintaining the magnetic performance of the magnet. Even in respect of certain concentrations of added or entrained Ce which may cause a reduction in the magnetic performance of the Fe-B-R magnetic material as compared with Fe-B-R magnetic material which employs substantially pure Nd, additional magnetic material having Ce and Pr as described herein can be used so as to make up the deficit in strength of magnetic field required in an MRI device.

[0011] Accordingly, in one broad aspect the applicants' invention comprises a high performance permanent magnetic material of the Fe-B-R type, said material essentially consisting of:

(i) 13-19 atomic % R, where R comprises a mixture of rare earth elements Nd, Pr, and Ce wherein Ce is between 0.2% and no more than 5.0 wt. % of R and Pr is between 70-76 wt. % and 29.8-23.8 wt. % Nd;

(ii) 4-20 atomic % B;

(iii) the balance comprising Fe with impurities.

In preferred embodiments, the Fe-B-R magnet of the present invention essentially consisted of, by atomic %, 15-16% R, with Ce comprising 0.5-3 wt. %, and preferably 0.5%, with the remainder of R essentially consisting of Pr and/or Nd, preferably in the order of about 71.6 wt. % Pr and 24.9 wt. % Nd, i.e. a 3:1 ratio (by weight %).

[0012] The present invention further comprises a sintered permanent magnetic material of the Fe-B-R type when made in accordance with the following process, namely:

(a) preparing a metallic powder having a mean particle size of 0.3-80 µm said metallic powder formed from a composition essentially consisting of 15-16 atomic % R, wherein R essentially consists of the light rare earths Nd, Pr, and Ce, wherein Ce is between 0.2-5.0 wt. % of said R, the balance of R essentially consisting of 29.8-23.8 wt. % Nd and 70-76 wt. % Pr; 4-8 atomic % B, and at least 52 atomic % Fe;

(b) compacting said powder at a pressure of at least 133.4 MPa (1.5 ton/cm²);

(c) sintering the resulted body at a temperature of 900-1200 °C in a non-oxidizing or reducing atmosphere.

[0013] In addition, the applicants have found that while adding Cerium generally tends to decrease magnetic performance of Fe-B-R magnets having only Nd, by substituting Pr for Nd where Ce concentration is low will cause a substantial restoration of lost magnetic performance. Accordingly, the applicant has found that using low concentrations of Ce (0.5% wt.) of R with the balance of R essentially consisting of 74.6 wt. % Pr and 24.9 wt. % Nd, wherein the aforementioned process is carried out such will produce a permanent magnet having magnetic performance criteria, namely H_ci and (BH)_max values, substantially equal to or somewhat in excess of an Fe-B-R magnet wherein the R component is comprising of only Nd and/or Pr.

[0014] The invention further comprises a method for producing sintered permanent magnets. In particular, the invention also comprises a process for preparing a sintered permanent magnetic material of the Fe-B-R type, said process comprising:

(a) preparing a metallic powder having a mean particle size of 0.3-80 µm , preferably no more than 4.0 µm, wherein the metallic powder essentially consists of a composition consisting of 15-16 atomic % R, wherein R essentially consists of the light rare earths Nd, Pr, and Ce, wherein Ce is between 0.2-5.0 wt. % of said R and preferably 0.5% of R, the balance of R essentially consisting of Nd and Pr where Pr is between 70-76 wt. %, Nd is between 24.8-23.8 wt. % and preferably 74 wt. % Pr and 25 wt. % Nd; 4-24 atomic % B and preferably 6.5 atomic % B; and at least 52 atomic % Fe and preferably 78 atomic %;

(b) compacting said powder at a pressure of at least 133.4 MPa (1.5 ton/cm²);

(c) sintering the resulted body at a temperature of 900-1200 °C in a non-oxidizing or reducing atmosphere.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The following drawings show particular embodimentes of the present invention in which;

Fig 1 is a graph of selected results from Table I, showing intrinsic coercive force H_ci of a permanent magnet material of the Fe-B-R type as a function of Praseodymium composition of R, at Cerium concentrations of 0.5% of R;

Fig. 2 is a graph of selected results from Table I, showing intrinsic coercive force H_ci of a permanent magnet material of the Fe-B-R type as a function of Praseodymium composition of R, at Cerium concentrations between 5.0-5.3 wt. % of R;

Fig. 3 is a graph similar to Fig. 4, showing selected result from Table I, plotting intrinsic coercive force H_ci of a permanent magnet material of the Fe-B-R type as a function of Cerium composition of R, at Praseodymium concentrations between 22.5 and 25 wt. % of R;

Fig. 4 is a graph similar to Fig. 3 showing selected result from Table I, plotting intrinsic coercive force H_ci of a permanent magnet material of the Fe-B-R type as a function of Cerium composition of R, at Praseodymium concentrations between 50-60 wt. % of R, and

Fig. 5 is a graph similar to Fig. 4, showing selected result from Table I, plotting intrinsic coercive force Hci of a permanent magnet material of the Fe-B-R type as a function of Cerium composition of R, at Praseodymium concentrations between 74.6-100 wt. % of R.

DETAILED DESCRIPTION OF THE INVENTION

[0016] Because the rare earth Ce typically occurs naturally in combination with Nd and Pr and because of the cost advantages in reducing the concentration of Nd in rare earth permanent magnets, the applicant has experimented with permanent magnets of the Fe-B-R type having various concentrations of Cerium as part of the rare earth component. The applicant has further varied the relative ratios and concentration of Nd and/or Pr of the rare earth component in relation to the amount of Ce, and measured the resultant magnetic properties of the Fe-B-R permanent magnets so created. Table I sets out the results for 35 samples of Fe-B-R type permanent magnets, where the composition of R was varied by utilizing various ratios of Ce, Pr, and Nd.

Table I

Test Sample	Pr (wt % of R)	Ce (wt. % of R)	Nd (wt. % of R)	Hci (kOe)*
B1-1	24.9	0.5	74.7	11.1
B1-2	24.9	0.5	74.7	11.3
B1-3	24.9	0.5	74.7	9.7
B2-1	24.0	4.0	72.0	9.5
B2-2	24.0	4.0	72.0	9.3
B2-3	24.0	4.0	72.0	9.8
B3-1	22.5	10.0	67.5	5.8
B3-2	22.5	10.0	67.5	6.2
B3-3	22.5	10.0	67.5	6.1
B4-1	4.5	0.5	95.0	10.0
B4-2	4.5	0.5	95.0	10.3
B4-3	4.5	0.5	95.0	10.3
B5-1	74.6	0.5	24.9	13.3
B5-2	74.6	0.5	24.9	10.5
B5-3	74.6	0.5	24.9	10.5
E0	0.0	0.0	100.0	11.1
E1	25.0	0.0	75.0	11.2
E2	24.0	4.0	72.0	10.0
E3	22.5	10.0	67.5	5.8
E4	4.5	0.5	95.0	11.5
E5	74.6	0.5	24.9	15.7
E6	48.6	5.3	46.2	9.5
E7	53.8	4.3	41.9	11.7
E-A	50.0	10.0	40.0	6.6
E-B1	60.0	0.0	40.0	11.7
E-B2	60.0	0.0	40.0	12.1
E-C1	90.0	10.0	0.0	7.7
E-C2	90.0	10.0	0.0	7.2
E-D1	100.0	0.0	0.0	9.8
E-D2	100.0	0.0	0.0	10.7
E-AB1	55.0	5.0	40.0	7.9
E-AB2	55.0	5.0	40.0	9.0
E-CD1	95.0	5.0	0.0	9.0
E-CD2	95.0	5.0	0.0	9.3
E-ABCD	75.0	5.0	20.0	7.7

* 1 kOe = 79.58 kA/m

[0017] Figs. 1-5 appended hereto are graphical plots of selected data from Table I, compiled for the purposes of assisting in interpreting the data in Table I and showing trends in magnetic performance arising from the various compositions of the R component of the 78 Fe-B 6.5-R 15.5 permanent magnet alloy compositions tested.

[0018] Individual plots of the data are made for magnetic performance H_ci versus Ce concentration, at constant or substantially constant values of Pr and Nd %, the percentage Nd being simply (100-[Ce]-[Pr])%. Fig.3 shows a plot of magnetic performance H_ci as a function of Cerium addition, at relatively constant values of Pr (from 22.5 to 25% wt. of R).

[0019] Fig. 4 shows a plot of magnetic performance H_ci as a function of Cerium addition, at relatively constant values of Pr (from 50-60 wt. %). Fig.5 likewise shows a plot of magnetic performance H_ci as a function of Cerium addition, at relatively constant values of Pr (from 74.6 to 100%).

[0020] In each of the aforementioned cases, as seen from Figs. 3-5, it can broadly be said addition of Cerium, at least in the ranges between 5-10%, will cause a reduction in H_ci, from a value of 795.8-955 kA/m (10-12 kOe) at Ce-0% to a range of 485.4-620.7 kA/m (6.1-7.8 kOe) when Ce=10% of R.

[0021] Importantly, however, from a perusal Table I and Figs. 3-5, the applicant has observed that for ranges of Cerium addition over 0% and up to about 5%, the reduction in magnetic performance (H_ci) is not that significant, and in some cases, the lower ranges of H_ci at Ce-0% are exceeded by some of the upper ranges of H_ci at Ce concentrations between 4-5%.

[0022] Analysis in the trends reflected in the data set out in Table I produce another surprising result. In particular, plots of H_ci as a function of Pr (wt. %) where Ce amount is kept approximately constant generally tended to show an increase in magnetic performance H_ci as the percentage of Pr was increased, at least for ranges of Ce concentrations at 0.5% and 10%.

[0023] Figs. 1 and 2 show a plot of the magnetic performance of the sample, as measured by H_ci, as a function of Pr addition, for ranges of Ce=0.5% (Fig. 1) and Ce=5.0-5.3% (Fig. 2). For Ce=5.0-5.3% (Fig. 2), as may be seen from Fig. 2, substituting Pr for Nd and generally increasing the concentration of Pr from 48% to 95% (i.e. reducing Nd from 47% to 0%) had an average, as seen from a "best fit" line plotted in Fig. 2, no effect on H_ci.

[0024] In the case of Ce=5% (Fig. 1) increasing Pr from 4.5% to 74.6% created an increase in H_ci from an average of 835.6 kA/m (10.5 kOe [i.e. (10.0+10.3+10.3+11.5)/4]) to an average of 994.8 kA/m (12.5 kOe [i.e. (13.3+10.5+10.5+15.7)/4]). Because the decrease in H_ci caused by adding Ce was not significant at Ce=0.5%, such addition of Pr up to in substitution of Nd, wherein Pr/Nd=3:1 appears to surprisingly have caused H_ci to exceed the H_ci for permanent magnets with no Ce added. In particular, the average H_ci for Ce=5%, with Pr=74.6 and Nd=24.9%, was found to be 994.8 kA/m (12.5 kOe), whereas, as stated earlier, average H_ci for ranges of Pr and Nd with no Cerium added was only found to be 883.3 kA/m (11.1 kOe). Indeed, the maximum H_ci value of 1249.4 kA/m (15.7 kOe) (at Pr=74.6% and Ce=0.5%) far exceeded the maximum value of H_ci of 12.1 kOe where Ce=0.0%.

[0025] The manner of preparing the test specimens and obtaining the data of Table I will now be described.

(1) The raw material for each respective magnet sample containing the predetermined respective composition was measured out and melted by high frequency induction. The obtained melt was cast in a cooled mold to obtain an ingot specimen.

(2) The resulting ingot specimen was crushed, and subsequently finely pulverized in a ball mill, until powders having a particle size of 0.3 to 80 µm were obtained.

(3) A magnetic field of 557.1 to 1591.6 kA/m (7 to 20 kOe) was thereafter applied to the milled powders to co-align each powder particle;

(4) The powders were subsequently compacted at a pressure of 133.4 MPa (1.5 Ton/cm²) to produce a compacted body with a resultant density of approximately 6g/cm²;

(5) The compacted body was sintered in an inert gas atmosphere at a temperature of 1120 °C for 2 hours.

[0026] Values of H_ci were then measured for each of the individual samples, and recorded in Table I.

[0027] It is recommended that the magnetic field applied to the powders to co-align the powder particles be at least 557.1 kA/m (7 kOe). Further, the magnetic field that is applied to the powder may have a range of about 557.1 to 2387.4 kA/m about (about 7 to about 30 kOe). In another embodiment, the magnetic field may range from about 557.1 to about 1591.6 kA/m (about 7 to about 20 kOe).

[0028] The Fe-B-R magnet of the present invention containing Cerium in certain defined percentages may be prepared by the powder metallurgical sintering procedure used in preparation of the aforementioned samples. A description of the applicant's process, insofar as it relates to a process for the manufacture of the applicant's new composition, is set out below.

[0029] A metallic powder having a mean particle size of 0.3-80 µm, preferably less than 10 µm is formed from a composition consisting of

i) 13-19 atomic % R, preferably 15.16 atomic % R, wherein R essentially consists of the light rare earths Nd and/or Pr, and Ce, wherein Ce is between 0.2 to 5.0 wt. %, and preferably 0.5%, the balance of R essentially consists of Nd and Pr where Pr is between 70-76 wt. % and Nd is between 29.8-28.8 wt. %, and preferably 74.6 wt. % Pr and 24.9 wt. % Nd.

ii) 4-8 atomic % B; preferably 6.5 atomic % B; and

iii) the balance, preferably 78 atomic % Fe.

[0030] Such powder may be produced by known ball milling procedures, or Alpine jet milling. Since the distribution of particle size of the powder made by ball milling is wider than with powders made from Alpine jet mill, which definitely affects magnet alignment, Br, and thus (BH)_max, the latter set milling procedure is preferred.

[0031] The resultant powder may optionally be exposed to a magnetic field, of a strength equal to 557.1 to 1591.6 kA/m (7.0 to 20 kOe) as in the case of the sample specimens. The metallic powder is then compacted at a pressure of at least 133.4 MPa (1.5 ton/cm²) to produce a resultant compacted body having a density of at least 5g/cm².

[0032] The resulting compacted body is then sintered in a reducing as or inert gas atmosphere, or as in a vacuum, at a temperature between 900-1200 °C, and preferably between 1000-1180 °C, for a period of 15 minutes to 8 hours and preferably for at least 1 hour.

[0033] While there have been described herein what are considered to be preferred and exemplary embodiments of the present invention, other modifications of the invention will now be apparent to those skilled in the art from the teachings herein. For a complete definition of the scope of the invention, reference is to be made to the appended claims.

Claims

1. A high performance permanent magnetic material of the Fe-B-R type, said material essentially consisting of:

(i) 13-19 atomic % R, where R essentially consists of a mixture of rare earth elements Nd, Pr, and Ce wherein Ce is between 0.2 wt. % and no more than 5.0 wt. % of R, Pr is between about 70-76 wt. % and Nd is 29.8-23.8 wt. %;

(ii) 4-20 atomic % B; and

(iii) the balance comprising Fe with impurities.

2. The permanent magnetic material of the Fe-B-R type as claimed in claim 1, wherein Ce is 0.5-5.0 wt. % of R.

3. The permanent magnetic material of the Fe-B-R type as claimed in claim 1, wherein R is 14.0-16.0 atomic %.

4. The permanent magnetic material of the Fe-B-R type as claimed in claim 1, wherein B is 5.0-7.0 atomic %.

5. The permanent magnetic material of the Fe-B-R type as claimed in claim 1, R essentially consisting of Pd and Nd in a 3:1 ratio respectively (by weight %).

6. Use of the permanent magnetic material according to claim 1 in a magnetic resonance imaging (MRI) apparatus.

7. The permanent magnetic material of the Fe-B-R type as claimed in claim 1, wherein Ce is 0.5-3.0% wt. % of R.

8. The permanent magnetic material of the Fe-B-R type as claimed in claim 7, wherein Pr is 74.6% of R, Ce is 0.5% of R, and the remaining percentage of R consists essentially of Nd.

9. The permanent magnetic material of the Fe-B-R type as claimed in claim 4, wherein B is 6.5 atomic %.

10. The permanent magnetic material of the Fe-B-R type as claimed in claim 9, wherein R is 15.5 atomic %.

11. A process for preparing a sintered permanent magnetic material of the Fe-B-R type, said process comprising the steps of:

(a) preparing a metallic powder having a mean particle size of 0.3-80 microns said metallic powder formed from a composition consisting of 15-16 atomic % R, wherein R essentially consists of the light rare earths Nd, Pr, and Ce, wherein Ce is between 0.2-5.0 wt. % of said R, the balance of R essentially consisting of Nd and Pr where Pr is between about 70-76 wt. %, Nd is between 29.8-23.8 wt. %; 4-8 atomic % B; and at least 52 atomic % Fe;

(b) compacting said powder at a pressure of at least 133.4 MPa (1.5 ton/cm²);

(c) sintering the resulted body at a temperature of 900-1200°C in a non-oxidizing or reducing atmosphere.

12. The process as claimed in claim 11, wherein said metallic powder is prepared by melting metallic material, cooling the resultant alloy, and pulverizing the alloy to form said metallic powder.

13. The process as claimed in claim 12, wherein said step of pulverizing the alloy comprises ball milling the alloy to form said powder.

14. The process as claimed in claim 12, wherein said step of pulverizing the alloy comprises jet milling the alloy to form said powder.

15. The process as claimed in claim 11, further comprising the step, while compacting said powder, applying a magnetic field of 557.1 to 1034.6 kA/m (7 to 13 kOe).

16. The process as claimed in claim 15 wherein said metallic powder is prepared by milling to produce a mean particle size no more than 10.0 µm.

17. A sintered permanent magnetic material of the Fe-B-R type when made in accordance with the following process, namely;

(a) preparing a metallic powder having a mean particle size of 0.3-80 µm , said metallic powder is formed from a composition consisting of 15-16 atomic % R, wherein R essentially consists of the light rare earths Nd, Pr, and Ce, wherein Ce is between 0.2-5.0 wt. % of said R, Pr is between about 70-76 wt. % and Nd is 29.8-23.8 wt. %; 4-8 atomic % B, and at least 52 atomic % Fe;

(b) compacting said powder at a pressure of at least 133.4 MPa (1.5 ton/cm²),

(c) sintering the resulted body at a temperature of 900-1200°C in a non-oxidizing or reducing atmosphere.

18. The permanent magnetic material as claimed in claim 17, wherein B is 5-7 atomic %.

19. The permanent magnetic material as claimed in claim 18, wherein the resulting body is sintered at a temperature of 1000-1180°C.

20. The permanent magnetic material as claimed in claim 18, wherein said metallic powder is prepared by milling to produce a mean particle size no more than 7.0 µm.

Ansprüche

1. Hochleistungs-Permanentmagnetmaterial des Fe-B-R Typs,
wobei das Material im wesentlichen besteht aus:

(i) 13-19 Atom% R, wobei R im wesentlichen aus einer Mischung von Seltenen-Erdelementen Nd, Pr und Ce besteht, wobei Ce zwischen 0,2 Gew.% und nicht mehr als 5,0 Gew.% von R beträgt und Pr zwischen etwa 70-76 Gew.% und Nd 29.8-23,8 Gew.% betragen,

(ii) 4-20 Atom% B und

(iii) der Rest Fe mit Verunreinigungen aufweist.

2. Permanentmagnetmaterial des Fe-B-R Typs nach Anspruch 1, wobei Ce 0,5-5,0 von R ist.

3. Permanentmagnetmaterial des Fe-B-R Typs nach Anspruch 1, wobei R 14.0 -16,0 Atom% ist.

4. Permanentmagnetmaterial des Fe-B-R Typs nach Anspruch 1, wobei B 5,0-7,0 Atom% ist.

5. Permanentmagnetmaterial des Fe-B-R Typs nach Anspruch 1, wobei R im wesentlichen aus Pd und Nd im Verhältnis 3:1 (nach Gew.%) besteht.

6. Verwendung des Permanentmagnetmaterials nach Anspruch 1 in einer Magnetresonanz-Bildgebungs(MRI)-Einrichtung.

7. Permanentmagnetmaterial des Fe-B-R Typs nach Anspruch 1, wobei Ce 0,5-3,0 Gew.% von R ist.

8. Permanentmagnetmaterial des Fe-B-R Typs nach Anspruch 7, wobei Pr 74,6 % von R ist, Ce 0,5 % von R ist und der restliche Prozentsatz von R im wesentlichen aus Nd besteht.

9. Hochleistungs-Permanentmagnetmaterial des Fe-B-R Typs nach Anspruch 4, wobei B 6,5 Atom% beträgt.

10. Hochleistungs-Permanentmagnetmaterial des Fe-B-R Typs nach Anspruch 9, wobei R 15,5 Atom% beträgt.

11. Verfahren zum Herstellen eines gesinterten Permanentmagnetmaterials des Fe-B-R Typs , wobei das Verfahren die Schritte enthält:

(a) Herstellen eines metallischen Pulvers mit einer mittleren Teilchengrösse von 0,3-80 Mikron, wobei das metallische Pulver aus einer Zusammensetzung gebildet ist, die aus 15-16 Atom% R besteht, wobei R im wesentlichen aus den leichten Seltenen-Erden Nd, Pr und Ce besteht, wobei Ce zwischen 0,2-5,0 Gew.% von R ist, der Rest von R im wesentlichen aus Nd und Pr besteht, wobei Pr zwischen etwa 70-76 Gew.% ist, Nd 29.8-23,8 Gew.% ist; 4-8 Atom% B und wenigstens 52 Atom% Fe,

(b) Kompaktieren des Pulvers bei einem Druck von wenigstens 133,4 MPa (1,5 t/cm²),

(c) Sintern des entstandenen Körpers bei einer Temperatur von 900-1200°C in einer nicht-oxidierenden oder reduzierenden Atmosphäre.

12. Verfahren nach Anspruch 11, wobei das metallische Pulver hergestellt wird durch Schmelzen des metallischen Pulvers, Kühlen der entstandenen Legierung und Pulverisieren der Legierung, um das metallische Pulver zu bilden.

13. Verfahren nach Anspruch 12, wobei der Schritt des Pulverisierens der Legierung enthält, daß die Legierung durch die Kugelmühle geschickt wird, um das Pulver zu bilden.

14. Verfahren nach Anspruch 12, wobei der Schritt des Pulverisierens der Legierung enthält, daß die Legierung durch die Strahlmühle geschickt wird, um das Pulver zu bilden.

15. Verfahren nach Anspruch 11, wobei ferner der Schritt vorgesehen ist, daß während des Kompaktierens ein Magnetfeld von 557,1 bis 1034,6 kA/m (7 bis 13 kOe) aufgebracht wird.

16. Verfahren nach Anspruch 15, wobei das metallische Pulver durch Mahlen hergestellt wird, um eine mittlere Teilchengrösse von nicht mehr als 10,0 µm zu erzeugen.

17. Gesintertes Permanentmagnetmaterial des Fe-B-R Typs, wenn es gemäss dem folgenden Verfahren hergestellt ist, nämlich:

(a) Herstellen eines metallischen Pulvers mit einer mittleren Teilchengrösse von 0,3-80 m, wobei das metallische Pulver aus einer Zusammensetzung gebildet wird, die aus 15-16 Atom% R, wobei R im wesentlichen aus den leichten Seltenen-Erden Nd, Pr und Ce besteht, wobei Ce zwischen 0,2-5,0 Gew.% von R ist, Pr zwischen etwa 70-76 Gew.% und Nd 29.8-23,8 Gew.% sind; 4-8 Atom% B und wenigstens 52 Atom% Fe,

(b) Kompaktieren des Pulvers bei einem Druck von wenigstens 133,4 MPa (1,5 t/cm²),

(c) Sintern des entstandenen Körpers bei einer Temperatur von 900-1200°C in einer nicht-oxidierenden oder reduzierenden Atmosphäre.

18. Permanentmagnetmaterial nach Anspruch 17, wobei B 5-7 Atom% ist.

19. Permanentmagnetmaterial nach Anspruch 18, wobei der entstehende Körper bei einer Temperatur von 1000-1180°C gesintert wird.

20. Permanentmagnetmaterial nach Anspruch 18, das metallische Pulver durch Mahlen hergestellt wird, um eine mittlere Teilchengrösse von nicht mehr als 7,0 µm zu erzeugen.

Revendications

1. Matière magnétique permanente à haute performance, du type Fe-B-R, qui est constituée essentiellement de :

(i) 13 à 19 % en atomes de R, R étant constitué essentiellement d'un mélange des éléments des terres rares Nd, Pr et Ce, où Ce figure en une proportion comprise entre 0,2 % en poids et pas plus de 5,0 % en poids, Pr figure en une proportion comprise entre environ 70 % en poids et environ 76 % en poids, et Nd figure en une proportion de 29,8 à 23,8 % en poids,

(ii) 4 à 20 % en atomes de B, et

(iii) le complément qui comprend Fe et des impuretés.

2. Matière magnétique permanente du type Fe-B-R selon la revendication 1, pour laquelle Ce représente 0,5 à 5,0 % en poids de R.

3. Matière magnétique permanente du type Fe-B-R selon la revendication 1, dans laquelle R représente 14,0 à 16, 0 % en atomes.

4. Matière magnétique permanente du type Fe-B-R selon la revendication 1, dans laquelle B représente 5,0 à 7,0 % en atomes.

5. Matière magnétique permanente du type Fe-B-R selon la revendication 1, pour laquelle R est constitué essentiellement de Pr et Nd selon un rapport du premier au second de 3 :1 (rapport des pourcentages en poids).

6. Utilisation de la matière magnétique permanente selon la revendication 1, dans un appareil de prise d'images par résonance magnétique.

7. Matière magnétique permanente du type Fe-B-R selon la revendication 1, pour laquelle Ce représente 0,5 à 3,0 % en poids de R.

8. Matière magnétique permanente du type Fe-B-R selon la revendication 7, pour laquelle Pr représente 74,6 % de R, Ce représente 0,5 % de R, le pourcentage restant étant constitué essentiellement de Nd.

9. Matière magnétique permanente du type Fe-B-R selon la revendication 4, dans laquelle B représente 6,5 % en atomes.

10. Matière magnétique permanente du type Fe-B-R selon la revendication 9, dans laquelle R représente 15,5 % en atomes.

11. Procédé de préparation d'une matière magnétique permanente frittée du type Fe-B-R, qui comprend les étapes consistant à :

(a) préparer une poudre métallique ayant une taille moyenne de particule de 0,3 à 80 µm, ladite poudre métallique étant constituée d'une composition contenant 15 à 16 % en atomes de R, 4 à 8 % en atomes de B et au moins 52 % en atomes de Fe, R étant constitué essentiellement des éléments légers des terres rares Nd, Pr et Ce, Ce représentant 0,2 à 5,0 % en poids de R et le complément de R étant constitué essentiellement de Nd et Pr, Pr étant présent en une proportion comprise entre environ 70 % en poids et environ 76 % en poids et Nd étant présent en une proportion comprise entre 29,8 et 23, 8 % en poids,

(b) agglomérer ladite poudre sous une pression d'au moins 133,4 MPa (1,5 tonne/cm²),

(c) fritter le corps résultant à une température de 900 à 1200 °C, dans une atmosphère non-oxydante ou réductrice.

12. Procédé selon la revendication 11, dans lequel on prépare ladite poudre métallique en faisant fondre les matières métalliques, en refroidissant l'alliage résultant et en pulvérisant l'alliage pour former ladite poudre métallique.

13. Procédé selon la revendication 12, dans lequel ladite étape de pulvérisation de l'alliage comprend le broyage de l'alliage par des boulets pour former ladite poudre.

14. Procédé selon la revendication 12, dans lequel ladite étape de pulvérisation de l'alliage comprend le broyage de l'alliage par projection pour former ladite poudre.

15. Procédé selon la revendication 11, qui comprend en outre l'étape d'application d'un champ magnétique de 557,1 à 1034,6 kA/m (7 à 13 kOe) lors de l'agglomération de ladite poudre.

16. Procédé selon la revendication 15, dans lequel on prépare ladite poudre métallique en effectuant un broyage de manière à obtenir une taille moyenne de particule ne dépassant pas 10,0 µm.

17. Matière magnétique permanente frittée du type Fe-B-R, qui est préparée conformément au procédé suivant :

(a) on prépare une poudre métallique ayant une taille moyenne de particule de 0,3 à 80 µm, ladite poudre métallique étant constituée d'une composition contenant 15 à 16 % en atomes de R, 4 à 8 % en atomes de B et au moins 52 % en atomes de Fe, R étant constitué essentiellement des éléments légers des terres rares Nd, Pr et Ce, Ce représentant 0,2 à 5,0 % en poids de R, Pr étant présent en une proportion comprise entre environ 70 % en poids et 76 % en poids et Nd étant présent en une proportion de 29,8 à 23,8 % en poids,

(b) on agglomère ladite poudre sous une pression d'au moins 133,4 MPa (1,5 tonne/cm²),

(c) on fritte le corps résultant à une température de 900 à 1200 °C, dans une atmosphère non-oxydante ou réductrice.

18. Matière magnétique permanente selon la revendication 17, qui contient 5 à 7 % en atomes de B.

19. Matière magnétique permanente selon la revendication 18, pour laquelle on effectue le frittage du corps résultant à une température de 1000 à 1180 °C.

20. Matière magnétique permanente selon la revendication 18, pour laquelle on prépare ladite poudre métallique en effectuant un broyage de manière à obtenir une taille moyenne de particule ne dépassant pas 7,0 µm.

Drawing