US2170047A - Permanent magnet of copper-cobalt-nickel alloy - Google Patents

Description

at... Augzz, 1939 UNITED STATES.

PERMANENT MAGNET or corms-oonAL'r-mcxEL ALLOY Walter Danniihl and Hans Neumann, Berlin-Siemensstadt, Germany, assignors to Siemens & Halske Aktiengesellschaft, Siemensstadt, near Berlin, Germany, a corporation of Germany No Drawing. Application November 17, 1936, Se-

rial No. I 111,252.

In Germany April 9, 1936 9 Claims. '(Cl- 175-21) Our invention relates to alloys and to methods for manufacturing permanent magnets having a great coercive force and a strong remanent magnetism. I

5 In recentyears it has been possible to manufacture with success high-grade permanent magnets of iron-nickel and iron-nickel-cobalt, alloys containing aluminum or titanium. The materials are, however, only valuable as regards the mag- 10 netic properties. They present certain drawbacks in cases in which other properties are also essential. That is-tosay, the magnets consisting of such alloys are very diflicult to machine; in

general, they can only be ground, but cannot 16 be machined by the use of drills and other cutting tools. It is, therefore, necessary that they be giventheir final form by casting. The alloys have a coarse-grained structure and tend to form flaws and pipes. That is the reason why the same 20 favorable properties are not frequently attained in finished magnets as is possible with magnets free of flaws and pipes obtained in laboratories.

The strength and the tenacity of the mentioned alloys are relatively small so that they can be 25 hardly employed for mechanically highly stressed magnets; for instance, for rotating magnet wheels of electric machines or for other magnets, which .are subjected when in operation to vigorous or continuous shocks. 7

Permanent magnets are known which may be machined by drills and cutting tools and which have also a greater strength and tenacity than the above-mentioned alloys containing aluminum and titanium. However, the magnetic properties,

' particularly the residual magnetism and the co- ;ercive force of the known machineable alloys are considerably inferior.

' The object of our invention is the provision of alloys and of methods for manufacturing permanent magnets which have excellent magnetic properties and which are as regards the abovementioned other properties superior to magnets consisting of nickel steels and cobalt-nickel steels containing aluminum and titanium.

According to our invention alloys containing ,5 to 70% cobalt, 10 to 50% nickel and 20 to 85% copper are employed in the manufacture of }permanent magnets. Magnets consisting of such alloys have a very 50 great coercive force and a strong'residual mag-'- netism. Depending upon the composition of the alloys 9. coercive force up to about 1,000 oersteds and a residual magnetism up to about8,000 gauss may be obtained. In some alloys both the coercive force and the residual magnetism present higher values than those hitherto obtained. In this case the properties of the magnets are highly stable as to thermal influences and shocks. Furthermore, they have great strength and tenacity and tend to a considerably smaller extent to form flaws or pipes than is the case with the hitherto known high-grade magnetic alloys. The alloys according to the invention may be easily machined; for instance, by turning, milling, filing, drilling and other cutting operations.

Particularly favorable magnetic properties may, be obtained with alloys containing 15 to 35% nickel, to 65% copper and 15 to 65% cobalt.

The alloys according to the invention composed essentially of copper-nickel-cobalt may also 20 contain other constituents, Particularly a portion of the nickel and cobalt content may be replaced by iron. By adding iron to the alloy the residual magnetism is in general increased,

, the coercive force lowered, and the machineability is improved. It is, therefore, possible with an iron content of about 5 to 10% to obtain also permanent magnets having superior magnetic properties. In exceeding a certain percentage of iron the magnetic power of the alloy, however, decreases. Consequently, the iron content should not exceed 30% of the total weight of the alloy. The alloys may contain other metals, such as manganese or chromium, and also traces of metalloids, such as silicon. The total percentage of a suitable. After annealing the'alloys are cooled down. The rapidity with which the cooling is effected in the most favorable manner depends upon the composition of the alloy and upon the fact as to whether a greater coercive force or a stronger residual magnetism is preferable. It is particularly advantageous to quench the alloys after annealing and to subject them to a further heat treatment at a temperature between 500' and 700 degrees centigrade.

In connection with the following table particulars as to the composition and heat treatment are hereinafter described.

Per- Per- Per- Alloy No. cent cent cent B, 3., B,X:H.X 10" Cu Ni Co 60 20 20 1600 100 2. 6 20 20 2100 930 19. 40 40 4900 440 21. 9 21 20 69 7930 110 8. 5 30 20 50 6300 300 18. 0 34 23 43 6340 373 19. 9 37 38 4600 500 23. 0 31.5 25 31.5 4000 5m 7 20.8 45 25 3400 710 24. 1 50 25 25 3300 700 25. 4 50 30 20 3200 670 21. 5 32 33 4540 480 21. 8 35 25 3480 410 14. ii

In this table the second, third and fourth col- 'umns contain the percentage of copper, nickel and cobalt, while the fifth column, gives the value of the residuaLmagnetism Br, the sixth column that of the coercive force JHc and the seventh column contains the product of the value of the firth and sixth columns multiplied by l0- (.1H denotes the coercive force for a magnetization J =0 as compared to the value sH=coercive force for an induction 3:0).

The alloy 1 was investigated directly after chill casting without subsequent heat treatment and gave for Br 2. value of 1,600 and for He a value of 160. The same alloy was then heated at 1,050 degrees centigrade, then quenched in oil and finally annealed for two hours at 650 degrees centigrade. The values thus obtained are those shown for the alloy No. 2. As will be seen from the above table the coercive force attained the particular high value 01030.

The alloy 3 was heated at a temperature of 1,150 degrees centigrade for five hours, then quenched in oil and finally annealed for four hours at 650 degrees centigrade.

The alloys 4, 5 and 10 were heated at 1,050

degrees centigrade, quenched in oil and then annealed for six hours at 650 degrees centigrade. This treatment gave according to the composition of the alloy particularly favorable values for the coercive force (alloy No. 10) or for the residual magnetism (alloy No. 4). Also some alloys are indicated in the table in which both the coercive force and the remanent magnetism have high values, for instance in the alloys No. 7 and 8.

The alloy 6 was heated for five hours at 1,150 degrees centigrade, quenched in oil and annealed for five hours at 650 degrees centigrade. Alloy 8 was heated for ten hours at 1,100 degrees centigrade, quenched in oil and then annealed for sixteen hours at 650 degrees centigrade. Alloy 9 was heated for tenhours at 1,100 degrees centigrade, quenched in oil and then annealed for thirty-two hours at 600 degrees centigrade.

The alloys 11 and 12 were heated for 10 hours at 1,100 degrees centigrade, quenched in oil and then annealed for sixty hours at 600 degrees cen-* heating or annealing is. as a rule, the shorter,

the higher the temperature at which the heat treatment is effected. If the alloys are annealed after heating and cooling or quenching-which is the case with the majority of the above-mentioned examples-the magnetic hardness (coercive force) increases considerably, for instance, up to 100 times and over the value obtained without annealing the alloys, whereas the mechanical hardness varies substantially to a lesser extent, generally only about trom,\5 to 10%. In the alloys indicated in the above table a mechanical hardness of 160 'to 200 Brinell units was measured after casting, heating and quenching. After annealing, the hardness amounted to 180 to 200 Brlnell units. Thisslight increase in mechanical hardness with increasing coercive force results in a further advantage of the alloy as compared to the permanent magnets hitherto known of great coercive force and residual magnetism. That is to say, the alloys according to the invention may be machined and given their final form not only prior to the heat treatment but also the magnetic properties may be at first improved by a heat treatment and the alloys may be then finally machined. In the case of martensitic magnet steels such a method of manufacture is not possible. ,With such steels the hardening can only be effected after the machining. In this case the magnets, particularly in the case of complicated forms, are liable to shrink or change their sihape. Thisis avoided according to the invent on. a

The alloys according to the invention have great magnetic stability as manifested by low values of the reversible permeability r. The reversible permeability is the permeability which corresponds to the intersectionof the magnetization curve with the ordinate (11:0) 'after the material has been demagnetiz'ed from positive H values down to negative values and remagnetized up to the value H=0. This reversible permeability is a measure for the degree of stability of a permanent magnet against demagnetizing influences. As example the following'furth'er particulars are given as to the alloys 8 and 9. The composition and heat treatment of both alloys have been already mentioned above. In the alloy No. 8 BHmalx=591,000. With an induction B=2,400 the reversible permeability ar=3.8. With B=3,200 .1'=3.6. The values for ar are, therefore, very small. In the alloy No. 9 BHmax=690,000. With an induction B=2,000 #1'=2.9 and with B=2,600 uT=2.8. The particular low values of the reversible permeability which in part lie below the values hitherto attained with high-grade magnetic alloys show that the magnetic stability for comparatively high values of the residual magnetism is extremely great. The magnets are, therefore, highly insensitive to the influence of demagnetizing fields.

Magnets according to the invention have, further, great thermal stability. This is due to the fact that the alloys while not having a martensitic character have a high Curie-point (700 to 900 degrees centigrade). The magnetic propelnection the invention provides a method of man- 1| compositions: to 35% copper, 10 to 35% nickel and over 35% cobalt. By adding iron the residual magnetism may be increased. For other purposes in electrical engineering it is, however, more important to attain high values of the coercive force, in which case also a good machineabflity and strength are required. For such special cases alloys having the following compositions are particularly suitable: 40 to 65% copper, 15 to nickel and less than cobalt.

Magnets according to the invention may advantageously employed in electricity meters,

moving coil galvanometers, oscillographs, polar-- ized relays, motors, generators, tachomete'rs, magnetos and other inductors, electromagnetic and electrodynamic telephones, loudspeakers and microphones, magnetic couplings for measuring and controlling'purposes, rotary magnets for signal 1 transmitters employed in signalling systems,

blow-out coils and magnetic compasses.

An important sphere of application is magnet wheels fon' electric machines and apparatus, further magnets for signalling systems, for instance,

magnets for railways or other fields of application in which great resistance to shocks isimportant.

While the known aluminum-nickel-iron particularly nickel-iron-titanium-, iron-cobalt-molybdenum-, iron cobalt-tungstenand similar alloys for permanent magnets have a cubic cen- 'a coercive force above.100 oersted and a remanence above 1,000 gauss.

' 2. A permanent magnet formed of an alloy containing 5,- cobalt, l0-50% nickel, the remainder substantially copper, characterized by a coercive force above 100 oersted and a remanence above 1,000 gauss. 1

Y n 3. A permanent magnet comprising 540% cobalt, 10-50% nickel, at least-20% copper, the remainder consisting of from traces to 5% of a metal of the chromium group and a small amount of impurities, said magnet being magnetized to have a coercive force above 100 oersted.

4. A permanent magnet composed essentially.

of 20-65% copper and a remainder of cobalt and nickel, the percentages'of cobalt and nickel having a mutual proportion between ,5 and said magnet being magnetized so as to have a coercive force above 100 oersted.

'5. A permanent magnet containing at. most copper, and a remainder consisting substantially of at least 5% cobalt and at least, 10% nickel, the copper content forming a higher percentage than each of the metals cobalt and nickel, and the percentages of cobalt and nickel having a mutual proportion between $5 and 31, said magnet being magnetized so as to have a coercive force above oersted.

6. A permanent magnet formed of an alloy comprising as essential 'ingredients20-35% cobalt, 15-30% nickel, and 40-65%.copper, characterized by a coercive force of above 100 oersted and a remanence above 1,000 gauss.

7. A permanent magnet formed of a machineable alloy consisting substantially of 15-65%' cobalt, 15-35% nickel, l5-65% copper, minor additions and usual impurities, and having enhanced magnetic properties-produced by a heating and quenching treatment and being magnetized to a coercive force above 100 oersted.

8. A permanent magnet comprising 15-35% nickel, 20-65% copper, the balance consisting substantially of cobalt and comprising from traces to 2% manganese, said magnet beingmagnetized to have a coercive force above 100 oersted.

9. A permanent magnet formed of an alloy containing 20-85% copper, and a remainder consisting substantially all of ferromagnetic metals comprising 5-70% cobalt and 10-50% nickel, and being magnetized up to a coercive force above 100 oersted and a remanence above 1,000 gauss.

-WALTER DANNfiHL. HANS NEUMANN.