CA1276486C - Method of making rare-earth element containing permanent magnets - Google Patents
Method of making rare-earth element containing permanent magnetsInfo
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- CA1276486C CA1276486C CA000489948A CA489948A CA1276486C CA 1276486 C CA1276486 C CA 1276486C CA 000489948 A CA000489948 A CA 000489948A CA 489948 A CA489948 A CA 489948A CA 1276486 C CA1276486 C CA 1276486C
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Abstract
ABSTRACT OF THE DISCLOSURE
A method for making rare earth-permanent magnets wherein a molten mass of a rare earth magnet alloy is produced such as by induction melting and while in a protective atmosphere is introduced in the form of a stream into a chamber having a protective atmosphere and a bottom portion containing a cooling medium, such as a cryogenic liquid which may be liquid argon. After cooling and solidification, the alloy is collected from the chamber and comminuted to produce particles. The particles are formed into a magnet body. Alternately, the stream may be atomized, as by striking the same with a jet of inert gas, to produce discrete droplets, which droplets are directed to the cooling medium at the chamber bottom for cooling, solidification and collection.
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A method for making rare earth-permanent magnets wherein a molten mass of a rare earth magnet alloy is produced such as by induction melting and while in a protective atmosphere is introduced in the form of a stream into a chamber having a protective atmosphere and a bottom portion containing a cooling medium, such as a cryogenic liquid which may be liquid argon. After cooling and solidification, the alloy is collected from the chamber and comminuted to produce particles. The particles are formed into a magnet body. Alternately, the stream may be atomized, as by striking the same with a jet of inert gas, to produce discrete droplets, which droplets are directed to the cooling medium at the chamber bottom for cooling, solidification and collection.
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Description
~L~7~48~;
It is known to produce permanent magnets containing at least one rare earth element as a significant alloying constituent, which elements may be for example samarium, praseodymium, neod~mium, lanthanum9 cerium, yttrium, or mischmeta~.
These magnets are conventionally produced by the vacllum induction mel~ing of a prealloyed charge to produce a molten mass of the desired magnet alloy composition. The molten mass is poured into an ingot mold for solidification. The solidified ingot is then comminuted to form fine particles on the order of 2 to 5 microns ~0 by an initial crushing operation followed by ball milling or jet milling to final particle size. The particles so produced are l formed into the desired magnet body either by cold pressing ¦followed by sintering or by the use of a plastic binder or other I low-melting point material suitable for use as a binder within 1l which the magnetic particles are embedded to form the magnet body.
Because of the relatively slow solidification rate of the ingot from which the particles are made, the ingot and thus the particles are not uniforr~ as a result of ingot segregation ' during cooling. Also, during the comminuting operation the small 'O , particles are subjected to surface oxidation. In addition, during the comminuting operation the mechanical working incident thereto introduces stresses and strain in the resulting particles, as well as defects in the particles introduced by the grinding medium, All of these factors in the conventional practice of ma~ing rare earth permanent magnets contribute to nonhomogeneity with respect to the composition of the resul~ing magnet body as well as non-uniformity thereof. This in turn adversely affects the magnetic properties.
It is accordingly a primary object of the present ,0 invention ~o provide a method for manufacturing rare earth ~k ~27~486 permanent magnets wherein a magnet body may be produced that is characterized by excellent compositional homogeneity and absence of defects and impurities.
A more specific object o~ the present invention is to provide a method for manufacturing particles from which a permanent magnet body may be manufactured, which particles are - s~bstantially compositionally uniform, homogeneo~s and lacking in impurities and defects~
These and other ob;ects of the invention, as well as a .0 ~more complete understanding thereof, may be obtained from the following description and drawings, in which~
FIGUR~ 1 is a schematic showing of one embodiment of apparatus suitable for use with the method of the invention;
,I FIGURE 2 is a graph relating to a preferred rare earth 1' permanent magnet alloy composition with which the method of the 0l, jinvention finds particular utility and showing the energy product attainable by the use thereof; and FIGURE 3 is a graph similar to FIGo 2 for the same ; composition showing the coercive force obtainable by the use ~O thereo in accordance with the practice of the invention.
Broadly, in accordance with the practice of the present invention, the method comprises producing a molten mass o the desired rare earth magnet alloy, such as by induction melting in the well known manner, and while maintaining the molten mass in a protective atmosphere a stream thereof is introduced into a chamber, also having a protective atmosphere, and with a bottom portion containing a cryogenic liquid, such as liquid argon.
The stream is permitted to strike the cryogenic liquid or a bottom plate cooled by the cryogenic liquid or other suitable cooling medium whereupon the stream is cooled to form a solidified massO
~ 7 64~6 The solidified mass is removed from the chamber, comminuted in the conventional manner to for~n fine particles which particles are sui~able for the production of magnet bodies. Because of the rapid solidification of the molten mass of rare earth magnet alloy it is of relatively uniform co~position throughout, which uniformity is maintained in the particles produced therefrom.
Consequently, the particles are characteri~ed by a uniform and homogeneous microstructure, which serves to enhance the magnetic properties of magnets produced therefrom. This is in contras~ ~o the comminuting of a conventional ingot casting subjected to 1 relatively slow cooling rates and thus segregation throughout the il ~olidified ingot. The particles produced are typically within the i size range of 1 to 5 microns.
An alternate practice, in accordance with the invention, ~5 ¦¦ involves striking the stream from the molten alloy mass as it ¦ enters the chamber with an atomizing medium, such as argon gas, to form droplets, which droplets are cooled, solidified and Il collected in either said cryogenic liquid or alternately a !I bottom plate cooled by said cryogenic liquid or other suitable ?0 ' cooling medium. Thereafter, the resulting particles are removed from the chamber and used to form a magnet body either directly or after comminuting to further reduce the particle size, The stream may be atomized by the use of a jet of an inert fluid such as argon gas.
Although the method of the invention has utility generally with rare earth permanent magnet alloys7 as will be shown in detail hereinafter, it has particular utility with a rare earth magnet alloy within the composition limits, in weight percent, 35 to 38 neodymium, 60 to 64.8 iron and ~2 to 2 boron~
~le neodymium referred to in the specification and claims hereo ~2 7 ~86 with respect to this alloy has re~erence to "effective neodymium"O
Effective neodymium is the total neodymium minus that portion thereof that reacts with 'the oxyge~ present to form Ndz03. ~nis amount of neodymium is determined as follows:
% Nd (effective~ = /0 Nd ~total) - 6 x /oO2 For example, a 35% neodymium-containing alloy having 0.121% oxygen has an effective neodymium of 34.28%.
With the practice of the invention in producing rare earth magnets and powders ~or use in the manufacture thereof and 'lO specifically with regard to the specific aIloy compositions set forth above, drastically improved magnetic properties, l particularly induction and coercive force, are produced. Coercive force is improved with homogeneity of the grains of the particles' Il from which the magnet is made from the standpoint of both I metallurgical composition and absence of defects. The finer the particles the less will be the compositional variation within the grains thereof. Since the particles produced in accordance with the practice of the invention are of improved homogeneity over ij particles resulting from conventional practices this compositional homogeneity within the grains is maximized by the invention~
Improved induction results from fine particle sizes with correspondingly reduced crystals within each particleO This permits maximum orientation to in turn maximize induction. In accordance wîth the practice of the invention, as will be ~5 dem~nstrated hereinafter, it is possible to achieve these desired very fine particles for purposes of improving induction without the attendant disadvantages of increased stress and strain as a result of the great amaunt of mechanical work during comminution and without increasing defects as a result thereof.
~2~6486 In accordance with the method of the invention, FIG~RE
1 is a schem2tic showing of one embodiment of apparatus for use therewith~ As shown in FIG. 1 molten alloy is poured from a tiltable furnace 2 to a tundish 4. The tundish and furnace are in an enclosure 6 providing a protective atmosphere. The molten alloy, designated as 8, is of a prealloyed rare earth permanent magnet alloy. In the bottom of the tundish 4 there is a nozzle 10 through which the metal from the tundish in the form of a stream 12 enters a chamber 14 having a protective atmosphere therein.
LO The stream 12 may be atomized by jets 16 which direct streams of !, atomizing gas 18 onto the stream 12 to atomize the same into ¦ droplets 20. The droplets fall to the bottom of the chamber and are cooled in cryogenic liquid 22 for subsequent solidification lland removal. In accordance with the alternate embodim~nt of the 1¦ invention the stream 12 would not be atomized but instead would be jlintroduced directly to the cryogenic liquid for cooling, solidification and collection. Upon removal from the chamber 14, ~ithe solidified alloy would be comminuted to the desired particle jl slze.
'0 ' In accordance with the invention the solidification rate of the atomized particles would be on the order of 1000C per second to 1,0009000C per second depending upon the particle size distribution. This extremely rapid solidification rate prevents any variation in the structure of the particles resulting from ~S cooling.
The invention as described is beneficial for use with rare earth magnet alloys in general which alloys would contain for example 20 to 40% of at least one rare earth element which would include samarium, neodymium, praseodymium, lanthanum, cerium, ~0 yttrium and mischmetal. The remainder of tne alloy would be at ~2t~6~6 least one element from the group cobalt, iron or a transition metal such as nickel or copper. Boron up to about 2% by wei~ht as well as aluminum up to about 10% by weight could also be . included.
By way of a specific example to demonstrate the . homogeneity of the particles produced in accordance with the practice of the invention, as compared with conventional vacuum induction melted, ingot cast and ground particles, a vacuum induction melt of the following composition, in weight percent, was produced:
Neodymium 32~58 Iron 66.44 Boron 0.98 ll This alloy was conventionally ingot cast and ground to the l¦ particle sizes set forth in Table I and was also, in accordance j with the practice of the invention, atomized by the use of an ! argon gas jet and quenched in liquid argon.
TABLE I
Powder Size and Method Phases Present, %
of Preparation, Microns (~) NdlsFe~0 B5 Fe2B
. VIM, Argon Gas Atomized, and Liquid Argon euenched . VIM, Ingot Cast, and Gro~md :
-590 83 l7 -37 86 . 2 13 . 8 VIM = Vacuum Induction Melted ~2764~
The as-quenched particles were screened to the size fractions set forth in Table I ~nd tested by Curie temperature measurements ~o determine the metallurgical phases thereof. As may be seen from Table I, in the conventionally ingot cast alloy two phases were present in each instance, namely the tetragonal Nd~sFe~Q Bs and ~h~
Fe2B phases. For the particles produced in accordance with the invention only the former phase was present indicating complete homogeneity.
To de nstrate the alternate practice of the invention wherein the stream of the rare earth magnet alloy is introduced , directly to the cryogenic liquid or liquid cooled plate for cooling and solidification, without atomization, various rare ~learth magnet alloys of the compositions MnCos, SmCoS, Nd, Fe, l,and Sm2Col7 were vacuum induction melted, solidified at various 1I rates characteristic of the method used. Oxygen measurements were¦
made using standard chemical analysis. These are reported in iTable II.
In accordance with the practice of the invention a ~Istream of the alloy was introduced to a chamber having liquid 1 argon in the bottom thereof which served to rapidly cool the molten alloy stream. During subsequent comminution it was ; determined that this material was more amenable to the formation of desired fine particles than conventional cast material of the same alloy composition. This is demonstrated by the data set forth in Table II wherein the oxygen content of the conventional powder was significantly higher than comparable size powder produced both by liquid argon quenching of atomized lten alloy , and molten alloy introduced directly without atomization to the liquid argon for cooling and solidification, both of which practices are in accordance with the invention.
~7 ~8 TABLE I I
Oxygen Content Method of Pre~ rin~ Rare Earth/Metal Powder ppm Cast ingot, crushed and ground (conventional) 2000 - 2800 Argon gas atomized, liquid argon quench, ground ~invention) 130 - 180 Direct liquid argon quench, ground (invention) 110 - 150 l.0 Table III demonstrates the improvemen~ in magnetic properties, namely induction ratios (Br/BS) and coercive force, for vacuum induction melted rare earth magnet alloy of the following composition produced both by conventional ingot casting , and also in accordance with the invention by atomization and ~5 , quenching in liquid argon. The composition of the alloy, in ¦! percent by weight, is as follows: i Neodymium 32.58 ,¦ Iron 66.44 ~I Boron .98 , It may be seen from Table III that with the particl.e size of less t'nan 74 microns with the practice of the invention the coercive force is similar to the much finer 2.8 micron particle produced in accordance with conventional practice. Both the coercive force and induction ratio (Br/BS) values for rare earth magnet alloy particles show a drastic improvement at a particle size between 88 and 74 microns.
~27~4aG
TABLE III
Particle Sizes Hci Method of Production ~ __ Br/Bs Oe VIM, atomized, liq. quenched -74 0.38 1500 S VIM, atomized, liq. quenched -88 0.17 525 VIM, atomized, liq. quenched -1000~15 450 VIM, atomized, liq. quenched -250Orl2 400 VIM, ingot cast, ground, jet 2~80~61 1600 milled The data in Table IV demonstrates the improvement in coercive force achieved with the practice of the invention with a SmCo5 alloy, as compared to this same alloy conventionally ingot cast and ground to form particles for use in producing a permanent Imagnet. In this test, with both the powder produced in accordance~
L5 1I with the invention and the conventionally produced powder ~he ¦l powder was loaded into a die cavity and a magnetic field was applied to the powder to orient the same. The powder was then ~¦ compressed during application of the magnetic field. The cold-I' pressed compact was then sintered at a temperature of 2050F, followed by a heat treatment at 1750F for 3 hours.
TABLE IV
Mesh Size Hci Microns (~ e) I Vacuum Melted, Atomized, and Inert Liquid Gas Quenched Particles -300 to +150 22,000 -lSO to ~75 19,400 Vacuum Melted, Ingot Cast, and Ground Powder -300 to +150 S, -150 to +75 9,000 r ~7~ 86 As may be seen from Table LV the coercive ~orce values achieved in accordance with th~ practice of the invention ~or all size ranges of powder were drastically improved over the values achieved with the canventional practice. The atcmized particles produced in accordance with the invention wére divided into the reported size fractions by a screening operation and used to produce the magnet body without further grinding.
TABLE V
Hci, e Vacuum melted, gas atomized, inert Illiquid gas quenched, and jet milled ' to 3 microns 23,000 !I Vacuum melted, ingot cast, ground `land jet milled to 3 microns 18,000 Ij Table V reports magnets produced from this same powder ¦¦as used in the test reported in Table IV with the powder being further comminuted to a 3-micron powder size by a conventional jet milling operation. This powder was compared to conventional lingot cast, ground and jet milled powder of the same 3-micron ;Isize. As may be seen from Table V there is a significant improve-ment in coercive force as demonstrated by the magnets produced by the powder manufactured in accordance with the invention.
TABLE VI
r Hc~ M ~
SmCoS Vacuum melted, liquid 8,650 >25,000 18.5 .~ . J argon quenched, crushed to 3 microns, pressed and sintered magnet SmCo5 Vacuum melted, ingot 8,700 16,000 18.0 . cast, crushed to 3 ~ microns, pressed and sintered MMCo5 Vacuum melted, liquid 7,950 19,000 15.0 argon quenched, crushed to 3 microns, pressed and sintered magnet MMCo5 Vacuum melted, ingot 7,200 13,300 13.0 ~, ., cast, crushed to 3 microns, pressed and sintered ~27~8~
Table VI reports a series of magnetic property ~ests c~nducted on magnets of the following compositions, in weight percen~:
Alloy 1 A~loy_~
Mischmetal 35 Samarium 35 Cobalt 65 Cobalt 65 In these tests magnets were produced from both compositions where-in the particles of the alloy used to make the magnets were both liquid argon quenched in the absence of atomizing and then comm;nuted to a 3-micron particle size, and ingot cast and comminuted to a 3-micron particle size in accordance with conventional practice. In both instances the magnets produced ! from the particles were manufactured by the conventional practice of sintering at temperatures of 1900 to 2080F and heat treating ¦at 160~ to 1800F.
~5 il As may be seen from Table VI, there is a significant increase in coercive force and maximum energy product for magnets llproduced in accordance with the invention, as compared with ~.he !lconventionally produced magnets. It is believed that this , improvement in magnetic properties is related to ~he beneficial , effect of the i~proved homogeneit~ and lower oxygen content of the powder produced in accordance with the invention, as compared to the conventionally produced powder.
It has been determined that if the practice of the invention is used with a rare earth magnet alloy composition in ~25 weight percent 35 to 38 neodymium, 60 to 64.8 iron and 0.2 to 2 boron, it is possible to achieve drastic improvement with regard to energy product (BHmaX) on the order of 30,000,000 gauss oersteds minimum. To demonstrate this rare earth magnet alloys of the following compositions, in weight percent, were produced for testing:
~2~76486 Total Nd Oxygen Effective Hci BHmax % ! - _Nd,_%_ Oe COe x 106 35 . O O . 121 34 . 28 3, 700 23 37 . O O . 15 36 . l 12 ~ 000 31 . 5 34 . 9 0 . 126 34 . 22 3 J 350 24 36 . ~ O . 12~ 36 . 08 ll, 650 30 . 3 34 . 2 0, 120 33 . 4 3, 250 17 . O
These rare earth magnet alloy compositions were used to produce particles for the manufacture of permanent magnet bodies in accordance with the inventlon by argon gas atomization and liquid argon quenching.
i~ As may be seen from FIG, 2 maximu~ energy product values are achieved within the neodymium range of approximately 35 to 1~ 38% by weight. Likewise, as may be seen in FIG, 3 optimum coercive Il force of 10,000 oersteds or greater is achieved within this same L5 i¦ neodymium range. Consequently, the method of the invention finds il particular utility with an alloy having neodymium within the 'i range of 35 to 38%, iron within the range of 60 to 64.8% and boron within the range of 0,2 to 2%.
!
It is known to produce permanent magnets containing at least one rare earth element as a significant alloying constituent, which elements may be for example samarium, praseodymium, neod~mium, lanthanum9 cerium, yttrium, or mischmeta~.
These magnets are conventionally produced by the vacllum induction mel~ing of a prealloyed charge to produce a molten mass of the desired magnet alloy composition. The molten mass is poured into an ingot mold for solidification. The solidified ingot is then comminuted to form fine particles on the order of 2 to 5 microns ~0 by an initial crushing operation followed by ball milling or jet milling to final particle size. The particles so produced are l formed into the desired magnet body either by cold pressing ¦followed by sintering or by the use of a plastic binder or other I low-melting point material suitable for use as a binder within 1l which the magnetic particles are embedded to form the magnet body.
Because of the relatively slow solidification rate of the ingot from which the particles are made, the ingot and thus the particles are not uniforr~ as a result of ingot segregation ' during cooling. Also, during the comminuting operation the small 'O , particles are subjected to surface oxidation. In addition, during the comminuting operation the mechanical working incident thereto introduces stresses and strain in the resulting particles, as well as defects in the particles introduced by the grinding medium, All of these factors in the conventional practice of ma~ing rare earth permanent magnets contribute to nonhomogeneity with respect to the composition of the resul~ing magnet body as well as non-uniformity thereof. This in turn adversely affects the magnetic properties.
It is accordingly a primary object of the present ,0 invention ~o provide a method for manufacturing rare earth ~k ~27~486 permanent magnets wherein a magnet body may be produced that is characterized by excellent compositional homogeneity and absence of defects and impurities.
A more specific object o~ the present invention is to provide a method for manufacturing particles from which a permanent magnet body may be manufactured, which particles are - s~bstantially compositionally uniform, homogeneo~s and lacking in impurities and defects~
These and other ob;ects of the invention, as well as a .0 ~more complete understanding thereof, may be obtained from the following description and drawings, in which~
FIGUR~ 1 is a schematic showing of one embodiment of apparatus suitable for use with the method of the invention;
,I FIGURE 2 is a graph relating to a preferred rare earth 1' permanent magnet alloy composition with which the method of the 0l, jinvention finds particular utility and showing the energy product attainable by the use thereof; and FIGURE 3 is a graph similar to FIGo 2 for the same ; composition showing the coercive force obtainable by the use ~O thereo in accordance with the practice of the invention.
Broadly, in accordance with the practice of the present invention, the method comprises producing a molten mass o the desired rare earth magnet alloy, such as by induction melting in the well known manner, and while maintaining the molten mass in a protective atmosphere a stream thereof is introduced into a chamber, also having a protective atmosphere, and with a bottom portion containing a cryogenic liquid, such as liquid argon.
The stream is permitted to strike the cryogenic liquid or a bottom plate cooled by the cryogenic liquid or other suitable cooling medium whereupon the stream is cooled to form a solidified massO
~ 7 64~6 The solidified mass is removed from the chamber, comminuted in the conventional manner to for~n fine particles which particles are sui~able for the production of magnet bodies. Because of the rapid solidification of the molten mass of rare earth magnet alloy it is of relatively uniform co~position throughout, which uniformity is maintained in the particles produced therefrom.
Consequently, the particles are characteri~ed by a uniform and homogeneous microstructure, which serves to enhance the magnetic properties of magnets produced therefrom. This is in contras~ ~o the comminuting of a conventional ingot casting subjected to 1 relatively slow cooling rates and thus segregation throughout the il ~olidified ingot. The particles produced are typically within the i size range of 1 to 5 microns.
An alternate practice, in accordance with the invention, ~5 ¦¦ involves striking the stream from the molten alloy mass as it ¦ enters the chamber with an atomizing medium, such as argon gas, to form droplets, which droplets are cooled, solidified and Il collected in either said cryogenic liquid or alternately a !I bottom plate cooled by said cryogenic liquid or other suitable ?0 ' cooling medium. Thereafter, the resulting particles are removed from the chamber and used to form a magnet body either directly or after comminuting to further reduce the particle size, The stream may be atomized by the use of a jet of an inert fluid such as argon gas.
Although the method of the invention has utility generally with rare earth permanent magnet alloys7 as will be shown in detail hereinafter, it has particular utility with a rare earth magnet alloy within the composition limits, in weight percent, 35 to 38 neodymium, 60 to 64.8 iron and ~2 to 2 boron~
~le neodymium referred to in the specification and claims hereo ~2 7 ~86 with respect to this alloy has re~erence to "effective neodymium"O
Effective neodymium is the total neodymium minus that portion thereof that reacts with 'the oxyge~ present to form Ndz03. ~nis amount of neodymium is determined as follows:
% Nd (effective~ = /0 Nd ~total) - 6 x /oO2 For example, a 35% neodymium-containing alloy having 0.121% oxygen has an effective neodymium of 34.28%.
With the practice of the invention in producing rare earth magnets and powders ~or use in the manufacture thereof and 'lO specifically with regard to the specific aIloy compositions set forth above, drastically improved magnetic properties, l particularly induction and coercive force, are produced. Coercive force is improved with homogeneity of the grains of the particles' Il from which the magnet is made from the standpoint of both I metallurgical composition and absence of defects. The finer the particles the less will be the compositional variation within the grains thereof. Since the particles produced in accordance with the practice of the invention are of improved homogeneity over ij particles resulting from conventional practices this compositional homogeneity within the grains is maximized by the invention~
Improved induction results from fine particle sizes with correspondingly reduced crystals within each particleO This permits maximum orientation to in turn maximize induction. In accordance wîth the practice of the invention, as will be ~5 dem~nstrated hereinafter, it is possible to achieve these desired very fine particles for purposes of improving induction without the attendant disadvantages of increased stress and strain as a result of the great amaunt of mechanical work during comminution and without increasing defects as a result thereof.
~2~6486 In accordance with the method of the invention, FIG~RE
1 is a schem2tic showing of one embodiment of apparatus for use therewith~ As shown in FIG. 1 molten alloy is poured from a tiltable furnace 2 to a tundish 4. The tundish and furnace are in an enclosure 6 providing a protective atmosphere. The molten alloy, designated as 8, is of a prealloyed rare earth permanent magnet alloy. In the bottom of the tundish 4 there is a nozzle 10 through which the metal from the tundish in the form of a stream 12 enters a chamber 14 having a protective atmosphere therein.
LO The stream 12 may be atomized by jets 16 which direct streams of !, atomizing gas 18 onto the stream 12 to atomize the same into ¦ droplets 20. The droplets fall to the bottom of the chamber and are cooled in cryogenic liquid 22 for subsequent solidification lland removal. In accordance with the alternate embodim~nt of the 1¦ invention the stream 12 would not be atomized but instead would be jlintroduced directly to the cryogenic liquid for cooling, solidification and collection. Upon removal from the chamber 14, ~ithe solidified alloy would be comminuted to the desired particle jl slze.
'0 ' In accordance with the invention the solidification rate of the atomized particles would be on the order of 1000C per second to 1,0009000C per second depending upon the particle size distribution. This extremely rapid solidification rate prevents any variation in the structure of the particles resulting from ~S cooling.
The invention as described is beneficial for use with rare earth magnet alloys in general which alloys would contain for example 20 to 40% of at least one rare earth element which would include samarium, neodymium, praseodymium, lanthanum, cerium, ~0 yttrium and mischmetal. The remainder of tne alloy would be at ~2t~6~6 least one element from the group cobalt, iron or a transition metal such as nickel or copper. Boron up to about 2% by wei~ht as well as aluminum up to about 10% by weight could also be . included.
By way of a specific example to demonstrate the . homogeneity of the particles produced in accordance with the practice of the invention, as compared with conventional vacuum induction melted, ingot cast and ground particles, a vacuum induction melt of the following composition, in weight percent, was produced:
Neodymium 32~58 Iron 66.44 Boron 0.98 ll This alloy was conventionally ingot cast and ground to the l¦ particle sizes set forth in Table I and was also, in accordance j with the practice of the invention, atomized by the use of an ! argon gas jet and quenched in liquid argon.
TABLE I
Powder Size and Method Phases Present, %
of Preparation, Microns (~) NdlsFe~0 B5 Fe2B
. VIM, Argon Gas Atomized, and Liquid Argon euenched . VIM, Ingot Cast, and Gro~md :
-590 83 l7 -37 86 . 2 13 . 8 VIM = Vacuum Induction Melted ~2764~
The as-quenched particles were screened to the size fractions set forth in Table I ~nd tested by Curie temperature measurements ~o determine the metallurgical phases thereof. As may be seen from Table I, in the conventionally ingot cast alloy two phases were present in each instance, namely the tetragonal Nd~sFe~Q Bs and ~h~
Fe2B phases. For the particles produced in accordance with the invention only the former phase was present indicating complete homogeneity.
To de nstrate the alternate practice of the invention wherein the stream of the rare earth magnet alloy is introduced , directly to the cryogenic liquid or liquid cooled plate for cooling and solidification, without atomization, various rare ~learth magnet alloys of the compositions MnCos, SmCoS, Nd, Fe, l,and Sm2Col7 were vacuum induction melted, solidified at various 1I rates characteristic of the method used. Oxygen measurements were¦
made using standard chemical analysis. These are reported in iTable II.
In accordance with the practice of the invention a ~Istream of the alloy was introduced to a chamber having liquid 1 argon in the bottom thereof which served to rapidly cool the molten alloy stream. During subsequent comminution it was ; determined that this material was more amenable to the formation of desired fine particles than conventional cast material of the same alloy composition. This is demonstrated by the data set forth in Table II wherein the oxygen content of the conventional powder was significantly higher than comparable size powder produced both by liquid argon quenching of atomized lten alloy , and molten alloy introduced directly without atomization to the liquid argon for cooling and solidification, both of which practices are in accordance with the invention.
~7 ~8 TABLE I I
Oxygen Content Method of Pre~ rin~ Rare Earth/Metal Powder ppm Cast ingot, crushed and ground (conventional) 2000 - 2800 Argon gas atomized, liquid argon quench, ground ~invention) 130 - 180 Direct liquid argon quench, ground (invention) 110 - 150 l.0 Table III demonstrates the improvemen~ in magnetic properties, namely induction ratios (Br/BS) and coercive force, for vacuum induction melted rare earth magnet alloy of the following composition produced both by conventional ingot casting , and also in accordance with the invention by atomization and ~5 , quenching in liquid argon. The composition of the alloy, in ¦! percent by weight, is as follows: i Neodymium 32.58 ,¦ Iron 66.44 ~I Boron .98 , It may be seen from Table III that with the particl.e size of less t'nan 74 microns with the practice of the invention the coercive force is similar to the much finer 2.8 micron particle produced in accordance with conventional practice. Both the coercive force and induction ratio (Br/BS) values for rare earth magnet alloy particles show a drastic improvement at a particle size between 88 and 74 microns.
~27~4aG
TABLE III
Particle Sizes Hci Method of Production ~ __ Br/Bs Oe VIM, atomized, liq. quenched -74 0.38 1500 S VIM, atomized, liq. quenched -88 0.17 525 VIM, atomized, liq. quenched -1000~15 450 VIM, atomized, liq. quenched -250Orl2 400 VIM, ingot cast, ground, jet 2~80~61 1600 milled The data in Table IV demonstrates the improvement in coercive force achieved with the practice of the invention with a SmCo5 alloy, as compared to this same alloy conventionally ingot cast and ground to form particles for use in producing a permanent Imagnet. In this test, with both the powder produced in accordance~
L5 1I with the invention and the conventionally produced powder ~he ¦l powder was loaded into a die cavity and a magnetic field was applied to the powder to orient the same. The powder was then ~¦ compressed during application of the magnetic field. The cold-I' pressed compact was then sintered at a temperature of 2050F, followed by a heat treatment at 1750F for 3 hours.
TABLE IV
Mesh Size Hci Microns (~ e) I Vacuum Melted, Atomized, and Inert Liquid Gas Quenched Particles -300 to +150 22,000 -lSO to ~75 19,400 Vacuum Melted, Ingot Cast, and Ground Powder -300 to +150 S, -150 to +75 9,000 r ~7~ 86 As may be seen from Table LV the coercive ~orce values achieved in accordance with th~ practice of the invention ~or all size ranges of powder were drastically improved over the values achieved with the canventional practice. The atcmized particles produced in accordance with the invention wére divided into the reported size fractions by a screening operation and used to produce the magnet body without further grinding.
TABLE V
Hci, e Vacuum melted, gas atomized, inert Illiquid gas quenched, and jet milled ' to 3 microns 23,000 !I Vacuum melted, ingot cast, ground `land jet milled to 3 microns 18,000 Ij Table V reports magnets produced from this same powder ¦¦as used in the test reported in Table IV with the powder being further comminuted to a 3-micron powder size by a conventional jet milling operation. This powder was compared to conventional lingot cast, ground and jet milled powder of the same 3-micron ;Isize. As may be seen from Table V there is a significant improve-ment in coercive force as demonstrated by the magnets produced by the powder manufactured in accordance with the invention.
TABLE VI
r Hc~ M ~
SmCoS Vacuum melted, liquid 8,650 >25,000 18.5 .~ . J argon quenched, crushed to 3 microns, pressed and sintered magnet SmCo5 Vacuum melted, ingot 8,700 16,000 18.0 . cast, crushed to 3 ~ microns, pressed and sintered MMCo5 Vacuum melted, liquid 7,950 19,000 15.0 argon quenched, crushed to 3 microns, pressed and sintered magnet MMCo5 Vacuum melted, ingot 7,200 13,300 13.0 ~, ., cast, crushed to 3 microns, pressed and sintered ~27~8~
Table VI reports a series of magnetic property ~ests c~nducted on magnets of the following compositions, in weight percen~:
Alloy 1 A~loy_~
Mischmetal 35 Samarium 35 Cobalt 65 Cobalt 65 In these tests magnets were produced from both compositions where-in the particles of the alloy used to make the magnets were both liquid argon quenched in the absence of atomizing and then comm;nuted to a 3-micron particle size, and ingot cast and comminuted to a 3-micron particle size in accordance with conventional practice. In both instances the magnets produced ! from the particles were manufactured by the conventional practice of sintering at temperatures of 1900 to 2080F and heat treating ¦at 160~ to 1800F.
~5 il As may be seen from Table VI, there is a significant increase in coercive force and maximum energy product for magnets llproduced in accordance with the invention, as compared with ~.he !lconventionally produced magnets. It is believed that this , improvement in magnetic properties is related to ~he beneficial , effect of the i~proved homogeneit~ and lower oxygen content of the powder produced in accordance with the invention, as compared to the conventionally produced powder.
It has been determined that if the practice of the invention is used with a rare earth magnet alloy composition in ~25 weight percent 35 to 38 neodymium, 60 to 64.8 iron and 0.2 to 2 boron, it is possible to achieve drastic improvement with regard to energy product (BHmaX) on the order of 30,000,000 gauss oersteds minimum. To demonstrate this rare earth magnet alloys of the following compositions, in weight percent, were produced for testing:
~2~76486 Total Nd Oxygen Effective Hci BHmax % ! - _Nd,_%_ Oe COe x 106 35 . O O . 121 34 . 28 3, 700 23 37 . O O . 15 36 . l 12 ~ 000 31 . 5 34 . 9 0 . 126 34 . 22 3 J 350 24 36 . ~ O . 12~ 36 . 08 ll, 650 30 . 3 34 . 2 0, 120 33 . 4 3, 250 17 . O
These rare earth magnet alloy compositions were used to produce particles for the manufacture of permanent magnet bodies in accordance with the inventlon by argon gas atomization and liquid argon quenching.
i~ As may be seen from FIG, 2 maximu~ energy product values are achieved within the neodymium range of approximately 35 to 1~ 38% by weight. Likewise, as may be seen in FIG, 3 optimum coercive Il force of 10,000 oersteds or greater is achieved within this same L5 i¦ neodymium range. Consequently, the method of the invention finds il particular utility with an alloy having neodymium within the 'i range of 35 to 38%, iron within the range of 60 to 64.8% and boron within the range of 0,2 to 2%.
!
Claims (21)
1. A method for making rare-earth permanent magnets, said method comprising producing a molten mass of a rare-earth magnet alloy, maintaining said molten mass in a protective atmosphere while introducing said molten mass into a chamber having a protective atmosphere and a bottom portion containing a cryogenic liquid cooling medium, cooling and collecting said molten mass in said bottom portion to form a solidified mass, removing said solidified mass from said chamber, comminuting said solidified mass to produce particles and forming said particles into a magnet body.
2. The method of claim 1 wherein said molten mass of said rare-earth magnet alloy is produced by vacuum induction melting.
3. The method of claim 2 wherein said cryogenic liquid is liquid argon and said chamber has an argon atmosphere.
4. The method of claim 1 wherein said particles are within the size range of 1 to 5 microns.
5. A method for making rare-earth permanent magnets, said method comprising producing a molten mass of a rare-earth magnet alloy, maintaining said molten mass in a protective atmosphere while introducing a stream of said molten mass into a chamber having a protective atmosphere and a bottom portion containing a cryogenic liquid cooling medium, atomizing said stream to form droplets, cooling and collecting said droplets in said bottom portion to produce particles, removing said particles from said chamber and forming said particles into a magnet body.
6. The method of claim 5 wherein said stream is atomized by the use of an inert fluid.
7. The method of claim 6 wherein said inert fluid is argon gas.
8. The method of claim 7 wherein said molten mass of said rare-earth magnet alloy is produced by vacuum induction melting.
9. The method of claim 5 wherein said cryogenic liquid is liquid argon and said chamber has an argon atmosphere.
10. The method of claim 9 wherein said particles are comminuted to produce finer particles within the size range of 1 to 5 microns.
11. A method for making rare-earth permanent magnets, said method comprising producing a molten mass of a rare-earth magnet alloy of the composition in weight percent 35 to 38 neodymium, 60 to 64.8 iron and 0.2 to 2 boron, maintaining said molten mass in a protective atmosphere while introducing said molten mass into a chamber having a protective atmosphere and a bottom portion containing a cooling medium, cooling and collecting said molten mass in said cooling medium to form a solidified mass, removing said solidified mass from said chamber, comminuting said solidified mass to produce particles and forming said particles into a magnet body.
12. The method of claim 11 wherein said molten mass of said rare-earth magnet alloy is produced by vacuum induction melting.
13. The method of claim 11 wherein said cooling medium is a cryogenic liquid.
14. The method of claim 13 wherein said cryogenic liquid is liquid argon and said chamber has an argon atmosphere.
15. The method of claim 11 wherein said particles are within the size range of 1 to 5 microns.
16. A method for making rare-earth permanent magnets, said method comprising producing a molten mass of a rare-earth magnet alloy of the composition in weight percent 35 to 38 neodymium, 60 to 64.8 iron and 0.2 to 2 boron, maintaining said molten mass in a protective atmosphere while introducing a stream of said molten mass into a chamber having a protective atmosphere and a bottom portion containing a cryogenic liquid cooling medium, atomizing said stream to form droplets, cooling and collecting said droplets in said cooling medium to produce particles, removing said particles from said chamber and forming said particles into a magnet body.
17. The method of claim 16 wherein said stream is atomized by the use of an inert fluid.
18. The method of claim 17 wherein said inert fluid is argon gas.
19. The method of claim 18 wherein said molten mass of said rare-earth magnet alloy is produced by vacuum induction melting.
20. The method of claim 19 wherein said cryogenic liquid is liquid argon and said chamber has an argon atmosphere.
21. The method of claim 20 wherein said particles are comminuted to produce finer particles within the size range of 1 to 5 microns.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000489948A CA1276486C (en) | 1985-09-04 | 1985-09-04 | Method of making rare-earth element containing permanent magnets |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000489948A CA1276486C (en) | 1985-09-04 | 1985-09-04 | Method of making rare-earth element containing permanent magnets |
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| CA1276486C true CA1276486C (en) | 1990-11-20 |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109967748A (en) * | 2017-12-27 | 2019-07-05 | 宁波科宁达工业有限公司 | A method of manufacture rare earth permanent magnet alloy powder end |
-
1985
- 1985-09-04 CA CA000489948A patent/CA1276486C/en not_active Expired - Fee Related
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109967748A (en) * | 2017-12-27 | 2019-07-05 | 宁波科宁达工业有限公司 | A method of manufacture rare earth permanent magnet alloy powder end |
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