US3892598A - Cobalt-rare earth magnets comprising sintered products bonded with solid cobalt-rare earth bonding agents - Google Patents

Abstract

Permanent cobalt alloy magnets of large size are prepared. At least two compacts of particulate permanent magnet cobalt alloy are provided and a layer of particles of a bonding magnetic cobalt alloy agent is deposited on the bonding surface of one compact. The bonding surface of the second compact is contacted with the deposited bonding agent substantially coextensively therewith and the resulting assembly is sintered to produce a sintered bonded composite. The bonding agent is a solid at sintering temperature.

Description

United States Patent Martin July 1, 1975 [54] COBALT-RARE EARTH MAGNETS 3,239,323 3/1966 Folweiler 65/43 COMPRISING SINTERED PRODUCTS 3,370,342 2/1968 Argyle et a1. 29/472.7 3,655,463 4/1972 Benz 148/101 BONDED WITH SOLID COBALT-RARE EARTH BONDING AGENTS Donald L. Martin, Elnora, N.Y.

General Electric Company, Schenectady, NY.

Filed: Jan. 7, 1974 Appl. No.: 431,126

Inventor:

Assignee:

Field of Search 148/3157, 101, 103, 105; 29/472], 473.1, 470, DIG. 1; 264/56, DIG.

References Cited UNITED STATES PATENTS 2/1966 Heimke et a1. 148/3157 Primary Examiner-Walter R. Satterfield Attorney, Agent, or Firm-Jane M. Binkowski; Joseph T. Cohen; Jerome C. Squillaro [5 7 1 ABSTRACT Permanent cobalt alloy magnets of large size are prepared. At least two compacts of particulate permanent magnet cobalt alloy are provided and a layer of particles of a bonding magnetic cobalt alloy agent is deposited on the bonding surface of one compact. The bonding surface of the second compact is contacted with the deposited bonding agent substantially coextensively therewith and the resulting assembly is sintered to produce a sintered bonded composite. The bonding agent is a solid at sintering temperature.

2 Claims, 1 Drawing Figure COBALT-RARE EARTH MAGNETS COMPRISING SINTERED PRODUCTS BONDED WITH SOLID COBALT-RARE EARTH BONDING AGENTS The present invention relates to the art of cobalt-rare earth alloy permanent magnets and more particularly it relates to the art of bonding these magnets to produce magnets of desired large size or geometry without deleterious effect on magnetic properties.

Permanent magnets, i.e., hard" magnetic materials, such as the cobalt-rare earth alloys, are of technological importance because they can maintain a high, constant magnetic flux in the absence of an exciting magnetic field or electrical current to bring about such a field.

Cobalt-rare earth intermetallic compounds or alloys exist in a variety of phases. Thus far, cobalt rare earth alloys containing a substantial amount of Co R phase (in each occurrence R designates a rare earth metal) have exhibited the best magnetic properties. However, to produce a permanent magnet with satisfactory properties, the bulk Co-R alloy must be reduced to a powder which is then usually compressed in an aligning magnetic field to form an aligned pressed-powder compact. Specifically, the powder particles are magnetically aligned along their easy axis of magnetization prior to or during compaction since the greater their magnetic alignment, the better are the resulting magnetic properties.

The aligned pressed powder or green compact is sintered to produce a sintered body of the desired density. A magnetizing field is applied to the sintered body parallel to its easy axis of magnetization, generally at room temperature, to produce a permanent magnet.

A disadvantage of this technique is that the sintered body or magnet is limited by the size of the pressedpowder or green compact. The green compact, itself, is limited in size because of the high pressure required to press the powder into a compact with sufficient strength so that it can be handled without excessive breakage before sintering. Experience indicates that a minimum pressure of about 100,000 psi is needed. Thus, large magnets with an area greater than 4 to 5 square inches are difficult to make because of the need for pressure greater than 200 tons.

One way of making a large magnet piece is to join smaller magnets together. Unfortunately, a suitable joining or bonding medium has not been found. Low temperature bonding with solder or epoxy cement has been used to join cracked sintered pieces. The solder or epoxy bonding method while attractive for many applications, limits the use of such bonded magnets at elevated temperatures, particularly at temperatures in the range of 100C to 200C which deteriorate these bonding agents and weaken the bond significantly. Also, materials such as solder or epoxy cement are nonmagnetic thereby introducing an air gap which dilutes the magnetic properties of the joined magnets some what.

The present process provides a method of bonding cobaltrare earth alloy compacts without having any significant deleterious effect on the magnetic properties of the resulting bonded sintered magnet composite. Also, the bond in the composite is substantially as stable at elevated temperatures as the bonded sintered magnets. Specifically, the present bonding agent is a magnetic cobalt-rare earth alloy.

Those skilled in the art will gain a further and better understanding of the present invention from the detailed description set forth below, considered in conjunction with the figure accompanying and forming a part of the specification which is the cobalt-Samarium phase diagram. It is assumed herein, that the phase diagram at 300C, which is the lowest temperature shown in the figure, is substantially the same at room temperatures.

Briefly stated, the present process comprises providing at least two compacts to be bonded together and sintered at a sintering temperature ranging from 900C to 1250C. Each compact consists essentially of compacted particulate permanent magnet alloy selected from the group consisting of Co-R, (Co-Fe)R, (Co- Cu)R, and (Co-Fe-Cu)R, where R is a rare earth metal. A layer of particles of a bonding magnetic'alloy agent is deposited onthe bonding surface of one of the compacts, said agent being selected from the group consisting of Co-R, (Co-Fe)R, (Co-Cu)R, and (Co-Fe-Cu)R, where R is a rare earth metal. The bonding agent is a solid at sintering temperature and contains the rare earth metal component in a minimum amount of at least 0.1 atom higher than that contained in the compacts being bonded. The bonding surface of the second compact is contacted with the deposited bonding agent substantially coextensively therewith, and the resulting assembly is sintered at a sintering temperature ranging from 900C to 1250C in an atmosphere in which it is substantially inert to bond and sinter said assembly to produce a solid composite sintered product having a density of at least 87%.

The rare earth metals useful in forming the present bonding agents and the permanent magnet alloy or alloys of the present compacts are the 15 elements of the lanthanide series having atomic numbers 57 to 71 inclusive. The element yttrium (atomic number 39) is commonly included in this group of metals and, in this specification, is considered a rare earth metal. A plurality of rare earth metals can also be used to form the present cobalt-rare earth alloys which, for example may be ternary, quartenary or which may contain an even greater number of rare earth metals as desired.

Representative of the cobalt-rare earth alloys useful in the present invention are cobalt-cerium, cobaltpraseodymium, cobalt-neodymium, cobaltpromethium, cobalt-Samarium, cobalt-europium, cobalt-gadolinium, cobalt-terbium, cobalt-dysprosium, cobalt-holmium, cobalt-erbium, cobalt-thulium, cobalt-ytterbium, cobalt-lutecium, cobalt-yttrium, cobaltlanthanum and cobalt-mischmetal. Mischmetal is the most common alloy of the rare earth metals which contains the metals in the approximate ratio in which they occur in their most common naturally occurring ores. Examples of specific ternary alloys include cobalt-samarium-mischmetal, cobalt-ceriumpraseodymium, cobalt-yttrium-praseodymium, and cobalt-praseodymium-mischmetal.

[n the present process at least two compacts are provided which are to be bonded together and sintered at a sintering temperature ranging from 900C to 1250C. Each compact consists essentially of compacted particulate permanent magnet alloy selected from the group consisting of Co-R, (Co-Fe)R, (Co-Cu)R, and (Co-Fe- Cu)R, where R is a rare earth metal or metals. The permanent magnet alloy can be formed by a number of conventional methods and converted to particulate form in a conventional manner. Its particle size may vary and it can be in as finely divided a'form as desired. For most applications, average particle size will vary from about 1 micron or less to about 10 microns. Larger sized particles can be used but the maximum intrinsic coercive force obtainable is lower because it decreases with increasing particle size. The powder particles are magnetically aligned along their easy or preferred axis of magnetization prior to or during compression since the greater the magnetic alignment, the better are the resulting magnetic properties. The aligned powder is pressed to a compact of desired size and shape. Compression can be carried out by a number of conventional techniques such as hydrostatic pressing or methods employing steel dies. The density of the aligned compacts generally ranges from about 70 to 80% of theoretical.

The present bonding agent is a solid at room temperature and at elevated temperature ranging up to and including sintering temperature, and it is an alloy selected from the group consisting of Co-R, (Co-Fe)R, (Co-Cu)R, and (Co-Fe-Cu)R, where R is a rare earth metal or metals. The agent can vary in composition which can be determined from the phase diagram for the particular system or which can be determined empirically. For example, the accompanying figure shows that for the Co-Sm system, at a sintering temperature of 1100C, the solid bonding agent can obtain samarium in a maximum amount of about 42 atom The present bonding-agent is one which is at least 0.1 atom and preferably at least 5 atom richer in rare earth metal content than that of the compacts being bonded.

' This richenrare earth metal content is necessary to at- The bonding surfaces ofthe compacts are not even.

or level surface but have a roughness corresponding to the projections of the compacted particles. Although the particle size of the bonding agent can vary, it is preferably very fine in size so that when it is deposited on the uneven bonding surface of the compact, it will contact bonding surface between projections and thereby be in contact with a larger bonding surface area resulting in a stronger bond being formed during sintering. Specifically, since the particles in the compact generally range from about 1 micron to microns in size, the present bonding agent also preferably will range from about 1 micron to 10 microns in size. A bonding agent having a particle size significantly higher than 10 microns will not contact sufficient area of the bonding surface during sintering to produce a suitable bond. Specifically, the particles of bonding agent should be in contact with at least 50% of the surface area being bonded.

In carrying out the process of the present invention, a layer of the bonding alloy agent particles is deposited on a surface of one of the aligned compacts to be bonded. Since the aligned compact is somewhat magnetic, the deposited particles cling to its surface. The particular amount of the bonding agent deposited should be sufficient to result in a good bond in the sintered composite product and is determinable empirically. Preferably, the bonding agent is deposited to form a continuous layer or deposit on the bonding surface. The surface of the second compact to be bonded is then placed in contact with the deposited layer substantially coextensively therewith.

The resulting assembly is heated to sintering temperature in an atmosphere in which it is substantially inert. Frequently, the aligned compacts are sufficiently magnetic so that the assembly holds together, if maintained vertically, until the Curie temperature is reached and then just the weight of one compact on top of the other will hold it together during sintering. However, if desired, the assembly can be supported or held together by'conventional means such as a clamp.

The assembly is sintered in a substantially inert atmosphere to produce a solid sintered composite wherein the pores are substantially non-interconnecting, which generally is a sintered composite having a density of at least about 87% of theoretical. Such non-interconnectivity stabilizes the permanent magnet properties of the composite product because its interior is protected against exposure to the ambient atmosphere.

The present permanent magnet type cobalt alloy systems require a sintering temperature ranging from 900C to 1250C. The particular sintering temperature depends largely on the particular cobalt alloy system being sintered. For example, for Co,-,Sm type alloys a sintering temperature of 1 120C is particularly satisfactory. v

The sintered composite is cooled, preferably, in an atmosphere in which it is substantially inert, preferably to room temperature. A magnetizing field is applied to the sintered composite along its easy axis of magnetization, preferably at room temperature, to produce a permanent magnet.

The density of the sintered composite may vary. The particular density depends largely on the particular permanent magnet properties desired. In the present invention, the density of the sintered composite ranges from about 87 to lO0% of theoretical.

Specifically, magnet composition and sintering techniques particularly useful in the present invention are disclosed in US. Pat. Nos. 3,655,464; 3,655,463; and

3,695,945, all filed in the name of Mark G. Benz, and

assigned to the assignee hereof, and all of which by reference are made part of the disclosure of the present application. Each of the aforementioned patents discloses a process for preparing novel sintered cobaltrare earth intermetallic products which can be magnetized to form permanent magnets having stable improved magnetc properties.

The solid composite of the present invention has a bond' or joint which is visible to the naked eye. This bond is magnetic so that it does not diminish the prop- 5 upon the other, coextensively with each other and sintered, to form the desired bonded sintered composite structure.

The. present invention is useful for preparing large A magnetizing field of 60 kiloersteds was applied at room temperature along the easy axis of magnetization to the control sample as well as the bonded composite and their magnetic properties were determined as and/or complex permanent magnet structures for such 5 shown in the following table where: diverse applications as meters and instruments, mag- B is the saturation induction. netic spafatofs, p and microwave devices- B, is the residual or remanent induction, i.e., the flux The mvention ls further illustrated by the following h th li d ti fi ld is reduced to zero, example. i Normal coercive force H is the field strength at 10 which the induction B becomes zero.

EXAMPLE Particles of a 66 7 wt 7 cobalt 33 3 wt 7 samarium 4 gi HR helps characterslze i Squareness of the g, 1r emagnetization curve. peci ically, 1-1,, is the de- 23 5 7 l'j l t fig t W1th P li t Q f i fi magnetizing field required to drop the magnetization W 0 Co a W 0 Samaflum a y 0 0m 3 10 percent below the remanence B That is, 41rM, Ough {mixture PQ of 63 Cobalt 37 .9 B and H is the corresponding field strength. H, is samarlum' The part1cles had an average 512? Of about a useful parameter for evaluating demagnetization re- 6 microns. sistance.

A Portion of the miXture was magnetically aligned The intrinsic coercive force H is the field strength along the easy axis by an aligning magnetizing field of at hi h h ti ti n (3-1-1) 01' 4 i-M i Zero, 60 kllO61'StClS. After magnetic alignment, it was The maximum energy product (Bf-D represents pressed to form a compact which was in h h p of the maximum product of the magnetic field H and the a bar about one inch long and about Vs inch in diameter induction B determined on the demagnetization curve.

TABLE 13, B, H Hi- HV. -Hm", Sample gauss gauss oers. ocrs. ocrs. l0gauss ocrs.) Density Alignment Control Sample 9,740 8,970 8,900 23.300 29,500 l9.8 94.2 .977

Sample Sintercd Piece Bonded Sintcred 9,790 9,160 9,000 21,500 28,100 20.7 95.1 .984

Composite and had a ackin of about 80 ercent. This sample, As shown b the table, the resent bonded com osite P g P y P P which was the control sample, was sintered in an atmohas magnetic properties which are substantially the 5 here of ar on at a tem erature of ll20C for one same as those of the control sam le.,This illustrates P g P P hour, furnacecooled to 875C where it was heat-a ed that the resent bondln a ent has no si nlficant effect g P g g for 5 hours and then cooled to room temperature 1n the on the magnetic properties of the bonded magnets. Same atmosphem The control sam le and the bonded com osite were Two additional portions of the mixture were aligned then placed in anpair oven maintained and compacted m a substantially the same manner as about 24 hours and the coolgd to room temperature Control l to form two conzpzictsi each in air. Force applied manually to the bonded portion of l h F z 233 $12351?sgggiifgg atgft o the composite 1nd1cdatied that hiatmgl lnbairdat this ele- 31116 In l e 6f vated temperature i not wea en t e on percent. The bonding surface of one of these compacts, l i.e., the surface across the width thereof, was plunged i z i g g 'i l i g ga i E 4 into particles of a bonding alloy agent, and when it was 1 z i a g removed therefrom, it had a substantially continuous agne S an omposl e on even a 6 1n the name of Donald L. Martin and asslgned to the aslayer of bondmg agent particles clinging thereto. h f d h b f d t f The bonding alloy agent was composed of 59 Wt.% 3 lereo 1C fi 6 j cobalt-41 wt.% samarium and had a particle size of 1 :1 Osure O f presedn E Q ere IS about 10 microns. All of this bonding agent was a solid C 056 t g f a t h Sm ere permanfa'n at room temperature as well as at elevated temperav O arge Slze' e procfess compnses providmg at least two compacts of particulate permatures including smtermg temperature, and it was about nent magnet alloy, depos1t1ng a layer of part1cles of a 4 atomic rlcher 1n samarium than the samarlum conbonding magnet1c cobalt alloy agent on the bondlng tent of the compacts being bonded. The bonding sursurface of one compact, contacting the bonding surface face of the second compact was contacted with the def the S c d C m act with the d sit d be di posited bonding alloy agent substantially coextensively 0 e on 0 p e ng agent substantially coextensively therewith, and slntertherewith to form an assembly 1n the form of a bar mg the resultlng assembly to produce a smtered bonded about one inch long. The assembly was sintered at a o composite. At least 1% by volume of the bonding agent temperature of 1120 C for one hour then furnaceasses throu h a li uid hase at an elevated tem eracooled to a temperature of 875C where it was heat- F e g q P P aged for five hours and then cooled to room temperature in the same atmosphere. The bonded portion of what 15 Claimed the resulting comPosite pp as an uneven thln l. A cobalt-rare earth alloy permanent magnet havline. The bonded portion of the composite appeared to be strong and did not break when force was applied manually.

ing an area greater than 4 square inches and substantially uniform permanent magnet properties throughout, said magnet consisting essentially of a sintered product consisting essentially of at least two compacts bonded together by a magnetic bonding agent, each said compact being produced by providing a permanent magnet type alloy of cobalt and rare earth metal in particulate form having an average particle size up to about 10 microns, subjecting said particulate alloy to a magnetic field to align the particles along their easy axis of magnetization, and compressing said particulate alloy into a compact having a density of at least 70%, said sintered product being produced by depositing a layer of particles ranging in size up to 10 microns of a magnetic bonding agent on the bonding surface of one of said compacts substantially covering said surface with said agent, said agent being a solid at sintering temperature and consisting essentially of cobalt-rare earth alloy containing the rare earth component in an amount at least 5 atom greater than that of the alloy of each said compact with the maximum amount of rare earth component being 55 atom contacting the bonding surface of the second compact with said deposited bonding agent substantially coextensively therewith, and sintering and bonding the resulting assembly at a temperature ranging from 900C to 1250C in an atmosphere in which it is substantially inert producing a solid sintered composite product having a density of at least 87%.

2. -A permanent magnet according to claim 1 where R is samarium.

Claims (2)

1. A COBALT-RARE EARTH ALLOY PERMANENT MAGNET HAVING AN AREA GREATER THAN 4 SQUARE INCHES AND SUBSTANTIALLY UNIFORM PERMANENT MAGNET PROPERTIES THROUGHOUT, SAID MAGNET CONSISTING ESSENTIALLY OF A SINTERED PRODUCT CONSISTING ESSENTIALLY OF AT LAST TWO COMPACTS BONDED TOGETHER BY A MAGNETIC BONDING AGENT, EACH SAID COMPACT BEING PRODUCED BY PROVIDING A PERMANENT MAGNET TYPE ALLOY OF COBALT AND RARE EARTH METAL IN PARTICULATE FORM HAVING AN AVERAGE PARTICLE SIZE UP TO ABOUT 10 MICRONS, SUBJECTING SAID PARTICULATE ALLOY TO A MAGNETIC FIELD TO ALIGN THE PARTICLES ALONG THEIR EASY AXIS OF MAGNETIZATION, AND COMPRESSING SAID PARTICULATE ALLOY INTO A COMPACT HAVING A DENSITY OF AT LEAST 70%, SAID SINTERED PRODUCT BEING PRODUCED BY DEPOSITING A LAYER OF PARTICLES RANGING IN SIZE UP TO 10 MICRONS OF A MAGNETIC BONDING AGENT ON THE BONDING SURFACE OF ONE OF SAID COMPACTS SUBSTANTIALLY COVERING SAID SURFACE WITH SAID AGENT, SAID AGENT BEING A SOLID AT SINTERING TEMPERATURE AND CONSISTING ESSENTIALLY OF COBALT-RARE EARTH ALLOY CONTAINING THE RARE EARTH COMPONENT IN AN AMOUNT AT LEAST 5 ATOM % GREATER THAN THAT OF THE ALLOY OF EACH SAID COMPACT WITH THE MAXIMUM AMOUNT OF RARE EARTH COMPONENT BEING 55 ATOM %, CONTACTING THE BONDING SURFACE OF THE SECOND COMPACT WITH SAID DEPOSITED BONDING AGENT SUBSTANTIALLY COEXTENSIVELY THEREWITH, AND SINTERING AND BONDING THE RESULTING ASSEMBLY AT A TEMPERATURE RANGING FROM 900*C TO 1250*C IN AN ATMOSHERE IN WHICH IT IS SUBSTANTIALLY INERT PRODUCING A SOLID SINTERED COMPOSITE PRODUCT HAVING A DENSITY OF AT LEAST 87%.

2. A permanent magnet according to claim 1 where R is samarium.

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