US 3331712 A
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Description (OCR text may contain errors)
July 18,1967 A. J. GRIEST, JR., ET AL 3,331,712
METHOD OF MAKING MAGNETIC MATERIAL Filed March 25, 1964 FIG. I
INVENTORS Andrew J. Ggies'gdn Orville W.Reen
mwbg ATTORNEY United States Patent METHOD OF MAKING MAGNETIC MATERIAL Andrew J. Griest, Jr., Pittsburgh, and Orville W. Reen,
Natrona Heights, Pa., assignors to Allegheny Ludlum Steel Corporation, Brackenrid'ge, Pa., a corporation of Pennsylvania Filed Mar. 25, 1964, Ser. No. 354,742 5 Claims. (Cl. 148105) This invention relates to magnetic material, and more particularly to the production of material suitable for use as permanent magnets.
In even more particular aspects, this invention relates to a method of forming material suitable for use as permanent magnets which method involves the use of atomized prealloyed metal powder.
It is Well known in the art that optimum permanent magnet characteristics are obtained in materials which have elongated, single domain, magnetic particles disposed in a non-magnetic, or magnetically weaker matrix. Several prior art techniques of producing such materials have been proposed but all of them are relatively costly or result in relatively poor magnetic characteristics.
It is, therefore, a principal object of this invention to provide an improved material suitable for use as a permanent magnet.
It is a related object of this invention to provide an improved method of producing material suitable for forming into permanent magnets.
A more specific object of this invention is to provide a method for providing a material suitable for use in permanent magnets, which material has a dispersion of a finely divided elongated precipitate of a magnetic phase in a matrix of a non-magnetic phase.
Still a further, more particular object of this invention is to provide a method of forming a material suitable for use as permanent magnets, which method incorporates mechanically Working a piece formed from prealloyed powder having a finely divided precipitate of a magnetic phase in a non-magnetic phase.
These and other objects, together with a fuller understanding of the invention, will become apparent from the following description when taken in conjunction with the accompany drawings in which:
FIGURE 1 is a light micrograph at 1500X of a section through a powder particle formed according to this invention, and
FIG. 2 is an electron micrograph at 6000X of material formed from particles of powder of the type shown in FIG. 1 and mechanically cold worked to thin sheet or strip.
In order to form material for use as a permanent magnet according to this invention, an alloy is selected that has a single homogeneous phase when liquid and has two phases in the solid state at ambient temperatures, one of which is magnetic and the other non-magnetic, or at least substantially less strongly magnetic, this phase being referred to hereinafter as a non-magnetic phase. Alloy systems which fulfill these conditions include the binary systems of copper-iron, copper-cobalt, gold-nickel, goldiron and gold-cobalt and the ternary system of copperiron-cobalt. The alloy is melted and the composition adjusted so that upon solidification the non-magnetic phase will be in excess of the magnetic phase (on a volume basis) so that the non-magnetic phase will act as a matrix. The melted alloy of the proper composition is made into a powder by the so-called atomization technique. According to this technique, a stream of the molten alloy is drastically quenched by a high velocity gas or liquid stream to break up the molten metal stream into powder particles. Each of the particles so-formed will have substantially the same composition as the other particles and ice the melt, since a homogeneous mixture or a single phase mixture was used as the starting composition. Each of these powder particles will have a fine dispersion of the magnetic phase in a matrix of the non-magnetic phase. Atomizing conditions, such as temperature of the molten metal, velocity of the dispersing media and mechanical adjustments of the atomizing jets, control the size of the particles. In general, the smaller the particle size of the particles formed, the smaller will be the size of the dispersed precipitate of the magnetic phase. Since single domain behavior requires extremely small sizes, it is desirable that the magnetic phase precipitate be as fine as possible, and thus a Very drastic quenching is desired. A stream of nitrogen has been found to be very effective as a quenching medium to produce such fine particle sizes.
The powder formed from the atomization of the alloy is consolidated into solid form such as by rolling, or by pressing in dies, or extrusion, or any other suitable method of producing a relatively solid structure of the metal. The temperatures employed if sintering is done or in extrusion, should not exceed the temperature at which agglomeration of the magnetic phase takes place. The solid metal is then mechanically worked to provide strip or wire of material suitable for forming into a permanent magnet; as much of this mechanical working as possible and preferably all, should be done cold or at least below the temperatures at which magnetic precipitate begins to agglomerate to any appreciable extent or dissolve to any appreciable extent in the non-magnetic phase. The working also should be done unidirectionally so as to elongate the magnetic phase precipitate particles to make them as close as possible to the ideal shape for single domain particles, that shape being a prolate ellipsoid. Single domain characteristics of such a shaped particle can be obtained if the particle has a major axis of the order of magnitude of 5000 A. and a minor axis of the order of magnitude of 500 A. or less.
FIG. 2 shows a longitudinal sectional view through a strand of material of a composition of approximately 35% iron, 65 copper, formed according to this invention. The light areas of the micrograph show an elongated magnetic phase precipitate, while the non-magnetic phase matrix shows gray. To form the material, a melt was prepared of an alloy having a composition of about 35% iron and 65% copper. This melt was atomized by high pressure gas in a conventional manner to produce a powder, each particle of which had a dispersion of the iron phase in the copper matrix as shown in FIG. 1. The powder was screened and the fraction which passed through the openings of a US. Standard 325 mesh sieve (44-micron opening) was selected. The powder was reduced in a hydrogen atmosphere at about 1000 F. to remove the surface oxides in a conventional well-known manner. The reduced powder was then pressed by dies into a block 2" x /8" x 8" and the block was sintered in a hydrogen atmosphere at about 1800 F. This temperature is about the maximum that can be used without encountering substantial agglomeration of the iron phase, and it is preferred to use lower sintering temperatures, preferably around 1300 F. to 1500 F., since magnetic properties are better when the material is sintered at these lower temperatures. The sintered block was then cold rolled to 0.120 thick, after which it was stress relieved at 1000 F. for 10 minutes and then cold rolled to 0.045". After another stress relief for 10 minutes at 1000 F. the piece was cold rolled to final gauge of 0.0032". The piece was tested for magnetic properties which were: Br 6600 gauss, Hc 70 oersteds, and BH max. 240,000 gaussoersteds. This is suitable for many low energy permanent magnet applications, but is cited only as an example of the microstructure as higher energy products can be obtained, as will appear hereinafter.
cold work into the material as is possible without damag- Although all of the alloy systems listed produce material suitable for use as paterial or unduly embritthng it.
h several embodiments of this invention have been shown and described, various adaptations and modi- 5 fications may be made without departing from the scope OD mu m mu 05 n i hs e it! vnapa ms 6 r Y m 0 mo n3 NW5 C the gold-nickel, gold-iron and goldvery expensive and are 0 Of the remainin f little commercial significance. three sy per-iron,
cobalt and copper-i on-cobalt the comer-iron system has and appended claims. resulted in material having excellent magnetic properties.
e entire? 1. A method of making permanent magnet material comprising, selecting an alloy composition characterized a single phase in the melted state and two substantially mutually insoluble phases in the solid state at ambient temperatures, one of said two solid phases being magnetic and the other non-magnetic, and the latter being present in a major proportion by volume, melting said ained 10 by with various materials cold Worked to various deg es. Of the various compositions tested, the 62% co 5% ults and,
TABLE I y sat- Table I below shows the magnetic properties obt pper, 3
although the other two systems do provid isfactory material.
iron composition appears to produce the best re hence, this approximate composition is preferred.
5 Powder pressed into 3" billet in a copper jacket, extruded at about 1.3a0 F. to bars 0.750 in diameter, swaged at about 1,300 I to 0.250, than (501d swagretl and drawn to size.
lowder pressed into 3 billet in a copper jacket, extruded between about 1. it)0 F. and 1,500 F. to bars 0.375" diameter. then cold swayed 1,300 F. to bar 0.7511 in diameter. hnr swnged at about 1.
l-cet, extruded at about i r Powder pressed into 7 LllrtlilClOl billet in copper jacket, preheated for 1 hour, cooled, then reheated and extruded at; 1,500 l. to bar 1. diameter, bar
3 Powder pressed into 3 billet in a copper j 1,300 F. to liars 0.750 in dimnetez, copper acket revoved and bar swa zed to 0.250 diameter at about 1,000" F., then cold swayed and drawn to size.
4 Powder pressed into 3 billet. in a copper jacket, extruded at about: and drawn to s 1,300 F. to bars 0.750 in diameter, bar s god at about 1,300 F. to 0.500 in diameter, then cold swegcd and d n to size.
each particle of which contains a finely divided precipitate of the magnetic phase in a matrix of the nonmagnetic phase, forming said powder, and mechanically working the same at a temperature below which the magthe material and thus it is desirable to introduce as much 75 netic phase dissolves in the non-magnetic phase or ag- An examination of Table 1 above shows that increas- 70 alloy, atomizing said melted alloy to form a powder, ing amounts of cold work (i.e. mechanical work at temperatures below the temperature at which the magnetic phase precipitate agglomcrates or dissolves in the nonmagnetic phase), increases the magnetic properties of glomeration of the magnetic phase occurs, w-hereby to produce a material suitable for permanent magnets.
2. A method of making permanent magnet material comprising, selecting an alloy from a group consisting of copper-iron, copper-cobalt and copper-iron-cobalt, said alloy being characterized by a single phase in the melted state and two phases in the solid state at ambient temperature, one of said two solid phases being magnetic and the other non-magnetic, the latter being present in a major amount by volume, melting said alloy, atomizing said melted alloy to form a powder, each particle of which contains a dispersion of the magnetic phase in a matrix of the non-magnetic phase, forming said powder and mechanically working the same at a temperature below that at which the magnetic phase dispersion dissolves in the nona-magnetic phase or agglomeration of the magnetic phase occurs, whereby to produce a material suitable for permanent magnets.
3. The method of claim 2 wherein the alloy is coppercobalt.
4. The met-hod of claim 2 wherein the alloy is copperiron-cobalt.
5. The method of claim 2 wherein the alloy contains about 62% copper and about 38% iron.
References Cited UNITED STATES PATENTS 1,999,850 4/1935 Smith et al 75153 2,112,971 4/1938 Neumann 148-31.55 2,118,285 5/1938 Zumbusch 148-31.55 2,147,844 2/1939 Kelly 75-153 2,384,892 9/1945 Comstock 75-0.5 2,754,193 7/1956 Graham et al. 75-0.5 2,870,485 1/1959 Jones 750.5 3,009,205 11/1961 Monson et al. 750.5 3,128,177 4/1964 Rennhack 75153 3,238,040 3/1966 Durer et al. 75165 OTHER REFERENCES Kaufmann: Alien Property Custodian, Ser. No. 268,- 381, July 1943.
HYLAND BIZOT, Primary Examiner.
DAVID L. RECK, Examiner.
N. F. MARKVA, Assistant Examiner.