CA2044171C - Corrosion-resistant rare earth metal-transition metal series magnets and method of producing the same - Google Patents
Corrosion-resistant rare earth metal-transition metal series magnets and method of producing the same Download PDFInfo
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- CA2044171C CA2044171C CA002044171A CA2044171A CA2044171C CA 2044171 C CA2044171 C CA 2044171C CA 002044171 A CA002044171 A CA 002044171A CA 2044171 A CA2044171 A CA 2044171A CA 2044171 C CA2044171 C CA 2044171C
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
- H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
- H01F1/047—Alloys characterised by their composition
- H01F1/053—Alloys characterised by their composition containing rare earth metals
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
- C22C1/04—Making non-ferrous alloys by powder metallurgy
- C22C1/0433—Nickel- or cobalt-based alloys
- C22C1/0441—Alloys based on intermetallic compounds of the type rare earth - Co, Ni
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C19/00—Alloys based on nickel or cobalt
- C22C19/07—Alloys based on nickel or cobalt based on cobalt
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
- H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
- H01F1/047—Alloys characterised by their composition
- H01F1/053—Alloys characterised by their composition containing rare earth metals
- H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
- H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
- H01F1/0571—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
- H01F1/0575—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together
- H01F1/0577—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together sintered
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Abstract
This invention provides permanent magnets being considerably excellent in not only magnetic properties but also corrosion resistance by using magnetically useful two phases, i.e. RE2TM14B phase having a high residual magnetic flux density and a low melting point RE-TM phase or RE-TM-B phase enhancing the sinterability and possessing a cleaning action against grain boundary of main phase and further forming an electrochemically noble composition as a starting material to prepare a two phase magnet.
Description
~044~~ ~
SPECIFICATION
CORROSION-RESISTANT RARE EARTH METAL-TRANSITION
METAL SERIES MAGNETS AND METHOD OF PRODUCING THE SAME
TECHNICAL FIELD
This invention relates to rare earth metal-transition metal series magnets having not only excellent magnetic properties but also improved corrosion resistance and temperature-dependent properties and a method of producing the same.
BACKGROUND ART
As a typical permanent magnet manufactured at the present, there are mentioned Alnico magnets, ferrite magnets, rare earth metal magnets and the like.
The Alnico magnets are manufactured from the old time, but their demand is lowering in accordance with the development of cheap ferrite magnets and rare earth metal magnets having higher magnetic properties. On the other hand, the ferrite magnets are chemically stable and low in the cost because oxides are used as a main starting material, so that they are the main current as a magnet material even at the present, but they have a drawback that maximum energy product is small.
Recently, Sm-Co series magnets having a combina-tion of magnetic isotropy inherent to rare earth metal ion and magnetic moment inherent to transition metal element have been developed, whereby the conventional value of maximum energy product is largely increased.
However, the Sm-Co series magnet is mainly composed of resourceless Sm and Co, so that it is obliged to become expensive.
Now, it has been attempted to develop cheap magnet alloys containing no expensive Sm and Co and having high magnetic properties, and consequently Egawa et al developed stable ternary alloys by sintering process (Japanese Patent Application Publication to No. 61-34242 and Japanese Patent laid open No. 59-132104) and J. J. Groat et al developed alloys having a high coercive force by liquid quenching process (Japanese Patent laid open No. 59-64739). These magnets are composed of Nd, Fe and B, and their maximum energy product exceeds that of Sm-Co series magnet.
However, Nd-Fe-B series magnets contain greater amounts of a light rare earth element such as Nd having very high activity or the like and corrosive Fe as a main component, so that the corrosion resistance is poor 2o and hence the magnetic properties are degraded to damage the reliability as an industrial material.
Therefore, in order to improve the corrosion resistance, there are taken countermeasures such as surface plating (Japanese Patent laid open No. 63-77103), coating treatment (Japanese Patent laid open No. 60-63901) and the like on the sintered magnets, ~''~ 64881-387 204 417' and surface treatment on resin bonded type magnets before kneading magnet powder with a resin and the like, but they can not be said to be an effective rustproof treatment over a long period of time, and the cost becomes higher due to such a treatment and further there are caused problems such as magnetic flux loss due to the presence of protective film and the like.
As a solution to the above problems, the inventors have previously proposed rare earth metal-1o transition metal-boron series magnet alloys in which Fe in the Nd-Fe-B series magnet is replaced with high concentrations of Co and Ni (Japanese Patent laid open No. 2-4939).
Such magnets are excellent in the corrosion resistance and high in the Curie point, so that the reliability as a magnet material is largely increased.
The invention is concerned with rare earth metal-transition metal series magnets of two phase structure further developed from the above magnet.
2o Moreover, magnets having excellent magnetic properties through two alloying process in which rare earth rich phase and rare earth poor phase are mixed and sintered in liquid phase state have previously been proposed as Nd aeries magnet of two phase structure (Japanese Patent laid open No. 63-93841 and No. 63-164403). In this case, the magnetic properties _4_ 2 04 4 1 7 ~
are improved, but there is still remaining a problem on the corrosion resistance.
DISCLOSURE OF INVENTION
The invention is to advantageously solve the aforementioned problems and to propose rare earth metal-transition metal series magnets of two phase structure being excellent in not only the magnetic properties but also the corrosion resistance and a method of advantageously producing the same.
1o At first, details of elucidating the invention will be described.
The inventors have made various metallographical studies on the above magnet using high resolution electron microscope or the like, and confirmed that this magnet contains Nd2(Fe, Co, Ni)14B phase having a large saturated magnetic flux density, and intergranular phases surrounding crystal grains of the above phase and developing a strong coercive force such as Nd2(Fe, Co, Ni)1~, Nd(Fe, Co, Ni)5, Nd2(Fe, Co, Ni)7, Nd(Fe, Co, 20 Ni)4H and Nd(Fe, Co, Ni)12B6 and further Ndl_~TM~ of CrB
structure (TM is mainly Ni) and the like.
Furthermore, it has been found that better corrosion resistance is exhibited as the amount of Nd phase being a point of causing corrosion is less and the concentration of Ni or Co in the above intergranular phase becomes high.
Now, the inventors have made further studies with respect to this point and found that the above intergranular phase hardly appears in a range of Nd-Fe-B
ternary phase diagram other than Nd2(Fe, Co, Ni)1~ and is rather a phase appearing only in the range of Nd-Co-B
system.
For the reference, Nd-Fe-B ternary phase diagram is shown in Fig. 1 (N. F. Chaban, Yu. B. Kuzma, N. S.
Bilonizhko, O. O. Kachmar and N. U. Petrov, Akad Nauk, 1o SSSR, SetA, Fiz.-Mat. Tekh, Nauki No. 10 (1979) 873), and Nd-Co-B ternary phase diagram is shown in Fig. 2 (N.
S. Bilonizhko and Yu. H. Kuzma, Izv. Akad. Nauk SSSR
Neorg. Mater, 19 (1983) 487) (In the original report, Nd2Fel4H phase and Nd2Co14H phase are misinterpreted as Nd2Fe9B phase and Nd2Co9B phase, so that they are corrected in Figs. 1 and 2).
In Fig. 1, a phase of number 1 is Nd2Fe14B phase, and NdFe4B4 phase (phase of number 2), Nd phase, Nd2Fel~
phase and Fe phase appear as a composition near thereto.
2o In Fig. 2, however, Nd2Col~ phase, NdCoS phase, Nd2Co~
phase, NaCo4B phase (phase of number 2) and NdCol2BS Phase (phase of number 7) appear in a magnet prepared from a composition close to Nd2Co14B phase of number 1, and Nd phase does not naturally appear at an equilibrium state.
As previously mentioned, Nd phase is not only a point of causing rust but also a magnetically useless phase, so that it should be eliminated.
It is, therefore, an object of the invention to provide permanent magnets having excellent magnetic properties and corrosion resistance by using magnetically useful two phases, i.e. REZTM14B phase having a high residual magnetic flux density and a low melting point RE-TM phase or RE-TM-B phase enhancing the sinterability and possessing a cleaning action against grain boundary of main phase and further forming an electrochemically nobel composition as a starting material to prepare a two phase magnet.
That is, the invention provides a corrosion-resistant rare earth metal-transition metal series permanent magnet consisting essentially of RE: not less than 10 at% but not more than 25 at% (where RE: one or more Y, Sc and lanthanide), B:
not less than 2 at% but not more than 20 at% and the remainder being substantially TM (TM is one or more of Fe, Co and Ni), wherein the magnet has a texture comprised of (i) a phase of REZTM14B (TM is the same as mentioned above) having Nd2Fe14B
structure and (ii) a phase of at least one member selected from the group consisting of an RE-TM series intermetallic compound (TM is Ni or a mixture of Ni and Fe or Co), RE-TM series eutectic structure (TM is Ni or a mixture of Ni and Fe or Co) and RE-TM-B series intermetallic compound (TM is Ni or a mixture of Ni and Fe or Co) each having a melting point lower than that of the RE2TM14B phase.
Furthermore, the invention provides a method of producing such a corrosion-resistant rare earth metal-transition metal series magnet, which comprises subjecting a '~.
r _ 7 _ mixture of powder composed mainly of RE2TM14B series intermetallic compound phase (TM is one or more of Fe, Co and Ni) and powder having a melting point lower than that of the above powder and composed of mainly at least one member selected from the group consisting of an RE-TM series intermetallic compound phase (TM is Ni or a mixture of Ni and Fe or Co), RE-TM series eutectic structure (TM is Ni or a mixture of Ni and Fe or Co) and RE-TM-B series intermetallic compound (TM is the same as mentioned above) to a compression molding to form a molded body and then sintering the molded body.
In the invention, in order to further improve the corrosion resistance, it is effective to make the intergranular phase electrochemically more nobel than the main phase, so that it is preferable that the content of Ni and/or Co in TM of the low melting point RE-TM and RE-TM-B series phase is made higher than that in RE2TM14B phase.
Particularly, the increase of Ni content is effective to improve the corrosion resistance and to reduce the cost.
In the invention, it is favourable that a ratio of RE2TM14B intermetallic compound phase to RE-TM, RE-TM-B series intermetallic compound phase is about 95:5 to 40:60 as a formula unit. Because, when this ratio is 2~441~y outside the above range, there is caused a disadvantage of bringing about considerable degradation of coercive force and saturated magnetic flux density. The term "formula unit" used herein corresponds to a case that Nd2FelqB is considered as one molecule (this is called as formula in case of solid). The particle size of each of the above powders to be mixed is desirable to be about 0.5-5 ~m for handling easiness and homogeneous mixing.
A typical composition of RE-TM series intermetallic compound phase (inclusive of eutectic structure, same as above) and RE-TM-B series intermetallic compound phase having a melting point lower than that of RE2TMIqB intermetallic compound phase is as follows.
~RE-TM series RE2TM17, RETMS, RE2TM7, RETM3, RETM2, RE1TM1_x, RE7TM3, REgTM and RE-TM eutectic structure ~RE-TM-B series RETMqB, RE3TM11Bq, RE2TM5B2, RE2TM7B3, RE2TM5B3, RETM12B6r RETM2B2, RETMgBq, RE2TMB3 Moreover, powder composed mainly of the above RE2TMIqB, RE-TM series and RE-TM-B series intermetallic compound phases can be obtained as follows.
That is, constitutional elements are weighed so as to have a given composition and shaped into an ingot by arc melting or high frequency melting under vacuum or _ 9 _ 20441y fi in an inert gas atmosphere. Then, the ingot is held at a temperature of 600-1000°C under vacuum or in an inert gas atmosphere for 1-30 days to form a single phase of intermetallic compound. In general, the intermetallic compound phase has frequently a solid solution range to a certain extent (~20~), so that the starting composition is allowed to have a composition width in accordance therewith.
The single phase of the intermetallic compound is roughly ground by means of a hammer mill and then finely divided into a particle size of 0.5-5 ~m by using a jet mill or an attritor . Moreover, when the hardness is low and the pulverization is difficult in the low melting point RE-TM and RE-TM-B phases, hydrogen brittleness is previously carried out within a temperature range of room temperature to about 350°C for several hours before the grinding with a hammer mill, whereby the subsequent pulverization is made easy.
According to the invention, powder composed mainly of the previously prepared intermetallic compound having a composition of RE2TM14B is mixed with at least one powder composed mainly of the previously prepared RE-TM series intermetallic compound and RE-TM-B series intermetallic compound phases having a melting point lower than that of the above powder, pressed and sintered, whereby high magnetic properties and high corrosion resistance can simultaneously be provided.
This is considered to be due to the fact that the powder having a melting point lower than that of the powder composed mainly of RE2TM14B intermetallic compound phase promotes the sintering and forms an intergranular phase between crystal grains of REZTM14B
to improve coercive force.
In RE2TM14B phase, Nd and Pr are desirable as RE
from viewpoints of magnitude of magnetic moment and 1o magnetic coupling with TM atm as well as the cost, but it is needless to say that the other RE or a combination of Nd, Pr therewith may be used.
As to TM, one or more of Fe, Co and Ni is sufficient, and particularly it is preferable to increase the content of Ni from a viewpoint of high corrosion resistance of the magnet. Further, REZTMIaB
phase bears the saturated magnetic flux density of the magnet, so that the contents of Fe, Co and Ni in TM are desirable to be not less than 10 at% but less than 73 20 at% in Fe, not less than 7 at% but not more than 50 at%
in Co and not less than 5 at% but not more than 30 at%
in Ni. Even when the main phase is RE2TM14H phase in which Fe as TM is 100%, the corrosion resistance of the permanent magnet according to the invention is superior to that of the conventional RE-TM-H magnet, so that the above phase can naturally be used as a main phase in accordance with the use purpose of the magnet.
As RE in the low melting point phase of RE-TM
system and RE-TM-B system, light rare earth element such as La, Ce. Pr, Nd or the like is advantageously adaptable importantly considering the cost, and middle to heavy rare earth elements from Sm to Lu and Y, Sc and the like are adaptable for more enhancing the corrosion resistance.
As to TM, the presence of Ni and/or Co, particularly Ni is effective to improve the corrosion resistance, so that according to the invention Ni is necessarily contained as TM. In this case, the content in TM is preferable to be not less than about 8~.
The addition effect of Ni is as follows.
i) The melting point of RE-TM system and RE-TM-B system is lowered, and the wetting of liquid phase in the liquid phase sintering is promoted to increase the sintering density and enhance the residual magnetic flux density.
ii) The effect of cleaning grain boundary in liquid phase is enhanced in the liquid phase sintering to more increase the coercive force by the same reason as in the above item i).
iii) It is effective to the improvement of corrosion resistance and cheap as compared with Co.
Furthermore, when the ratio of Ni and/or Co in -12 - 20441' 4 the low melting point phase is made higher than that of REzTMI4B phase, the corrosion resistance can be more improved because the phases of these powders tend to preferentially corrode in the grain boundary as compared with RE2TM14B phase in the sintered body if the structure of TM is same and is advantageously acted by previously making electrochemically noble. Furthermore, the magnetically useless Nd phase can be eliminated, so that the residual magnetic flux density increases and hence the maximum energy product (BH)max also increases.
In this connection, even when an alloy having an average composition as a whole magnet is melted from the first as in the conventional technique, pulverized, pressed and sintered so as to approach to an equilibrium state, the Nd phase is not obtained. For this purpose, it is necessary to conduct the heating at a high temperature for long time, during which abnormal growth of crystal grain is undesirably caused to considerably degrade the coercive force.
Moreover, it is not necessary that the same element is used in RE of the main phase and RE of the low melting point phase. And also, in the magnet consisting of the above two phases, the effect of the invention is not lost even when a part of RE and TM is replaced with at least one of Mg, A1, Si, Ti, V, Cr, Mn, Cu, Ag, Au, Cd, Rh, Pd, Ir, Pt, Zn, Ga, Ge, Zr, Nb, Mo, - 20441' In, Sn, Hf, Ta and W in an amount up to 8 ate of a full magnet.
As to the production method, there may be carried out a method wherein a mixture of powder of RE2TM14B composition and powder composed mainly of low melting point RE-TM series and/or RE-TM-B series intermetallic compound phases is placed in an iron pipe under vacuum and then sintered while hot rolling as a method of producing large size magnets in addition to the method in which the above powder mixture is subjected to compression molding and then sintered.
BRIEF DISCLOSURE OF DRAWINGS
Fig. 1 is a Nd-Fe-B three component phase diagram; and Fig. 2 is a Nd-Co-B three component phase diagram.
BEST MODE FOR CARRYING OUT THE INVENTION
Example 1 An alloy button was prepared by arc melting neodymium, transition metal and boron at an atomic ratio of 2:14:1, which was subjected to a normalizing treatment in a vacuum furnace at 950°C for 7 days and further to rough grinding and fine pulverization, whereby fine powder having a particle size of few microns was obtained. In this case, the ratios of Fe, Co, Ni in the transition metal were varied to produce a 20 .441w' ~
plurality of alloy powders.
Similarly, powder having a ratio of neodymium or (neodymium + dysprosium) to nickel of 1:1 was prepared.
In this case, the normalizing treatment conditions were 680°C and 5 days.
Then, powders selected from the above two groups were mixed at a mixing ratio shown in Table 1, pressed while applying a magnetic field of 15 kOe, sintered at 1000°C under vacuum for 2 hours and then quenched to room temperature.
The magnetic properties and corrosion property of the thus obtained samples were measured to obtain results shown in Table 1. Moreover, the corrosion property was evaluated by exposing the sample to an environment at a temperature of 70°C and a humidity of 95~ for 48 hours and measuring a rusted area ratio on the surface of the sample.
For the comparison, the measured results of a sample produced by the conventional method in which a full composition for the sintered magnet was melted at once and subjected to rough grinding - fine pulverization - pressing in magnetic field - sintering steps are also shown in Table 1.
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x 204~1'~1 As seen from the above table, the rare earth metal-transition metal series magnets of two phase structure according to the invention considerably improve not only the magnetic properties but also corrosion resistance as compared with those obtained by melting the full composition from the first as in the conventional technique.
Example 2 An alloy button was prepared by arc melting neodymium, transition metal and boron at an atomic ratio of 2:14:1, which was subjected to a normalizing treatment in a vacuum furnace at 950°C for 7 days and further to rough grinding and fine pulverization, whereby fine powder having a particle size of few microns was obtained. In this case, the ratios of Fe, Co, Ni in the transition metal were varied to produce a plurality of alloy powders.
Similarly, powder having a ratio of neodymium and/or dysprosium or praseodymium to nickel or (nickel + cobalt) of 3:1 was prepared. In this case, the normalizing treatment conditions were 485°C and 5 days.
The magnetic properties and corrosion property of the thus obtained samples were measured to obtain results shown in Table 2.
For the comparison, the measured results on the properties of a magnet produced by the technique 20441'1 disclosed in Japanese Patent laid open N0. 63-164403 are also shown in Table 2.
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i~:f~~~1'~1 As seen from the above table, the rare earth metal-transition metal series magnets of two phase structure according to the invention are excellent in the magnetic properties and corrosion resistance.
Furthermore, when Acceptable Example 8 is compared with Acceptable Example 13, it is apparent that the corrosion resistance is improved as the Ni ratio in RE3(Ni, Co)1 becomes particularly higher. Moreover, in the conventional example, the magnetic properties are good, but the corrosion resistance is poor because Ni is not contained.
Example 3 A fine alloy powder of REZTMIqB composition was prepared by the same manner as in Example 1, while a fine alloy powder in which ratios of Ni and Co in TM
were made higher than those of RE2TM14B powder was prepared as a starting powder. After these powders were mixed, a sintered magnet was produced by the same manner as in Example 1.
The properties of the thus obtained sintered magnet are shown in Table 3 together with those of the sintered magnet produced by the conventional method.
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- 2a~~~~1 As seen from the above table, when using the fine alloy powder in which the ratios of Ni and Co in TM
are higher than those of RE2TMIqB powder as a powder to be mixed, the more improvement of the corrosion resistance is attained.
INDUSTRIAL APPLICABILITY
According to the invention, the rare earth metal-transition metal series magnets having improved corrosion resistance and magnetic properties can be produced as compared with the conventional production method. Particularly, the corrosion resistance is improved, so that the considerable improvement of reliability as an industrial material is realized.
SPECIFICATION
CORROSION-RESISTANT RARE EARTH METAL-TRANSITION
METAL SERIES MAGNETS AND METHOD OF PRODUCING THE SAME
TECHNICAL FIELD
This invention relates to rare earth metal-transition metal series magnets having not only excellent magnetic properties but also improved corrosion resistance and temperature-dependent properties and a method of producing the same.
BACKGROUND ART
As a typical permanent magnet manufactured at the present, there are mentioned Alnico magnets, ferrite magnets, rare earth metal magnets and the like.
The Alnico magnets are manufactured from the old time, but their demand is lowering in accordance with the development of cheap ferrite magnets and rare earth metal magnets having higher magnetic properties. On the other hand, the ferrite magnets are chemically stable and low in the cost because oxides are used as a main starting material, so that they are the main current as a magnet material even at the present, but they have a drawback that maximum energy product is small.
Recently, Sm-Co series magnets having a combina-tion of magnetic isotropy inherent to rare earth metal ion and magnetic moment inherent to transition metal element have been developed, whereby the conventional value of maximum energy product is largely increased.
However, the Sm-Co series magnet is mainly composed of resourceless Sm and Co, so that it is obliged to become expensive.
Now, it has been attempted to develop cheap magnet alloys containing no expensive Sm and Co and having high magnetic properties, and consequently Egawa et al developed stable ternary alloys by sintering process (Japanese Patent Application Publication to No. 61-34242 and Japanese Patent laid open No. 59-132104) and J. J. Groat et al developed alloys having a high coercive force by liquid quenching process (Japanese Patent laid open No. 59-64739). These magnets are composed of Nd, Fe and B, and their maximum energy product exceeds that of Sm-Co series magnet.
However, Nd-Fe-B series magnets contain greater amounts of a light rare earth element such as Nd having very high activity or the like and corrosive Fe as a main component, so that the corrosion resistance is poor 2o and hence the magnetic properties are degraded to damage the reliability as an industrial material.
Therefore, in order to improve the corrosion resistance, there are taken countermeasures such as surface plating (Japanese Patent laid open No. 63-77103), coating treatment (Japanese Patent laid open No. 60-63901) and the like on the sintered magnets, ~''~ 64881-387 204 417' and surface treatment on resin bonded type magnets before kneading magnet powder with a resin and the like, but they can not be said to be an effective rustproof treatment over a long period of time, and the cost becomes higher due to such a treatment and further there are caused problems such as magnetic flux loss due to the presence of protective film and the like.
As a solution to the above problems, the inventors have previously proposed rare earth metal-1o transition metal-boron series magnet alloys in which Fe in the Nd-Fe-B series magnet is replaced with high concentrations of Co and Ni (Japanese Patent laid open No. 2-4939).
Such magnets are excellent in the corrosion resistance and high in the Curie point, so that the reliability as a magnet material is largely increased.
The invention is concerned with rare earth metal-transition metal series magnets of two phase structure further developed from the above magnet.
2o Moreover, magnets having excellent magnetic properties through two alloying process in which rare earth rich phase and rare earth poor phase are mixed and sintered in liquid phase state have previously been proposed as Nd aeries magnet of two phase structure (Japanese Patent laid open No. 63-93841 and No. 63-164403). In this case, the magnetic properties _4_ 2 04 4 1 7 ~
are improved, but there is still remaining a problem on the corrosion resistance.
DISCLOSURE OF INVENTION
The invention is to advantageously solve the aforementioned problems and to propose rare earth metal-transition metal series magnets of two phase structure being excellent in not only the magnetic properties but also the corrosion resistance and a method of advantageously producing the same.
1o At first, details of elucidating the invention will be described.
The inventors have made various metallographical studies on the above magnet using high resolution electron microscope or the like, and confirmed that this magnet contains Nd2(Fe, Co, Ni)14B phase having a large saturated magnetic flux density, and intergranular phases surrounding crystal grains of the above phase and developing a strong coercive force such as Nd2(Fe, Co, Ni)1~, Nd(Fe, Co, Ni)5, Nd2(Fe, Co, Ni)7, Nd(Fe, Co, 20 Ni)4H and Nd(Fe, Co, Ni)12B6 and further Ndl_~TM~ of CrB
structure (TM is mainly Ni) and the like.
Furthermore, it has been found that better corrosion resistance is exhibited as the amount of Nd phase being a point of causing corrosion is less and the concentration of Ni or Co in the above intergranular phase becomes high.
Now, the inventors have made further studies with respect to this point and found that the above intergranular phase hardly appears in a range of Nd-Fe-B
ternary phase diagram other than Nd2(Fe, Co, Ni)1~ and is rather a phase appearing only in the range of Nd-Co-B
system.
For the reference, Nd-Fe-B ternary phase diagram is shown in Fig. 1 (N. F. Chaban, Yu. B. Kuzma, N. S.
Bilonizhko, O. O. Kachmar and N. U. Petrov, Akad Nauk, 1o SSSR, SetA, Fiz.-Mat. Tekh, Nauki No. 10 (1979) 873), and Nd-Co-B ternary phase diagram is shown in Fig. 2 (N.
S. Bilonizhko and Yu. H. Kuzma, Izv. Akad. Nauk SSSR
Neorg. Mater, 19 (1983) 487) (In the original report, Nd2Fel4H phase and Nd2Co14H phase are misinterpreted as Nd2Fe9B phase and Nd2Co9B phase, so that they are corrected in Figs. 1 and 2).
In Fig. 1, a phase of number 1 is Nd2Fe14B phase, and NdFe4B4 phase (phase of number 2), Nd phase, Nd2Fel~
phase and Fe phase appear as a composition near thereto.
2o In Fig. 2, however, Nd2Col~ phase, NdCoS phase, Nd2Co~
phase, NaCo4B phase (phase of number 2) and NdCol2BS Phase (phase of number 7) appear in a magnet prepared from a composition close to Nd2Co14B phase of number 1, and Nd phase does not naturally appear at an equilibrium state.
As previously mentioned, Nd phase is not only a point of causing rust but also a magnetically useless phase, so that it should be eliminated.
It is, therefore, an object of the invention to provide permanent magnets having excellent magnetic properties and corrosion resistance by using magnetically useful two phases, i.e. REZTM14B phase having a high residual magnetic flux density and a low melting point RE-TM phase or RE-TM-B phase enhancing the sinterability and possessing a cleaning action against grain boundary of main phase and further forming an electrochemically nobel composition as a starting material to prepare a two phase magnet.
That is, the invention provides a corrosion-resistant rare earth metal-transition metal series permanent magnet consisting essentially of RE: not less than 10 at% but not more than 25 at% (where RE: one or more Y, Sc and lanthanide), B:
not less than 2 at% but not more than 20 at% and the remainder being substantially TM (TM is one or more of Fe, Co and Ni), wherein the magnet has a texture comprised of (i) a phase of REZTM14B (TM is the same as mentioned above) having Nd2Fe14B
structure and (ii) a phase of at least one member selected from the group consisting of an RE-TM series intermetallic compound (TM is Ni or a mixture of Ni and Fe or Co), RE-TM series eutectic structure (TM is Ni or a mixture of Ni and Fe or Co) and RE-TM-B series intermetallic compound (TM is Ni or a mixture of Ni and Fe or Co) each having a melting point lower than that of the RE2TM14B phase.
Furthermore, the invention provides a method of producing such a corrosion-resistant rare earth metal-transition metal series magnet, which comprises subjecting a '~.
r _ 7 _ mixture of powder composed mainly of RE2TM14B series intermetallic compound phase (TM is one or more of Fe, Co and Ni) and powder having a melting point lower than that of the above powder and composed of mainly at least one member selected from the group consisting of an RE-TM series intermetallic compound phase (TM is Ni or a mixture of Ni and Fe or Co), RE-TM series eutectic structure (TM is Ni or a mixture of Ni and Fe or Co) and RE-TM-B series intermetallic compound (TM is the same as mentioned above) to a compression molding to form a molded body and then sintering the molded body.
In the invention, in order to further improve the corrosion resistance, it is effective to make the intergranular phase electrochemically more nobel than the main phase, so that it is preferable that the content of Ni and/or Co in TM of the low melting point RE-TM and RE-TM-B series phase is made higher than that in RE2TM14B phase.
Particularly, the increase of Ni content is effective to improve the corrosion resistance and to reduce the cost.
In the invention, it is favourable that a ratio of RE2TM14B intermetallic compound phase to RE-TM, RE-TM-B series intermetallic compound phase is about 95:5 to 40:60 as a formula unit. Because, when this ratio is 2~441~y outside the above range, there is caused a disadvantage of bringing about considerable degradation of coercive force and saturated magnetic flux density. The term "formula unit" used herein corresponds to a case that Nd2FelqB is considered as one molecule (this is called as formula in case of solid). The particle size of each of the above powders to be mixed is desirable to be about 0.5-5 ~m for handling easiness and homogeneous mixing.
A typical composition of RE-TM series intermetallic compound phase (inclusive of eutectic structure, same as above) and RE-TM-B series intermetallic compound phase having a melting point lower than that of RE2TMIqB intermetallic compound phase is as follows.
~RE-TM series RE2TM17, RETMS, RE2TM7, RETM3, RETM2, RE1TM1_x, RE7TM3, REgTM and RE-TM eutectic structure ~RE-TM-B series RETMqB, RE3TM11Bq, RE2TM5B2, RE2TM7B3, RE2TM5B3, RETM12B6r RETM2B2, RETMgBq, RE2TMB3 Moreover, powder composed mainly of the above RE2TMIqB, RE-TM series and RE-TM-B series intermetallic compound phases can be obtained as follows.
That is, constitutional elements are weighed so as to have a given composition and shaped into an ingot by arc melting or high frequency melting under vacuum or _ 9 _ 20441y fi in an inert gas atmosphere. Then, the ingot is held at a temperature of 600-1000°C under vacuum or in an inert gas atmosphere for 1-30 days to form a single phase of intermetallic compound. In general, the intermetallic compound phase has frequently a solid solution range to a certain extent (~20~), so that the starting composition is allowed to have a composition width in accordance therewith.
The single phase of the intermetallic compound is roughly ground by means of a hammer mill and then finely divided into a particle size of 0.5-5 ~m by using a jet mill or an attritor . Moreover, when the hardness is low and the pulverization is difficult in the low melting point RE-TM and RE-TM-B phases, hydrogen brittleness is previously carried out within a temperature range of room temperature to about 350°C for several hours before the grinding with a hammer mill, whereby the subsequent pulverization is made easy.
According to the invention, powder composed mainly of the previously prepared intermetallic compound having a composition of RE2TM14B is mixed with at least one powder composed mainly of the previously prepared RE-TM series intermetallic compound and RE-TM-B series intermetallic compound phases having a melting point lower than that of the above powder, pressed and sintered, whereby high magnetic properties and high corrosion resistance can simultaneously be provided.
This is considered to be due to the fact that the powder having a melting point lower than that of the powder composed mainly of RE2TM14B intermetallic compound phase promotes the sintering and forms an intergranular phase between crystal grains of REZTM14B
to improve coercive force.
In RE2TM14B phase, Nd and Pr are desirable as RE
from viewpoints of magnitude of magnetic moment and 1o magnetic coupling with TM atm as well as the cost, but it is needless to say that the other RE or a combination of Nd, Pr therewith may be used.
As to TM, one or more of Fe, Co and Ni is sufficient, and particularly it is preferable to increase the content of Ni from a viewpoint of high corrosion resistance of the magnet. Further, REZTMIaB
phase bears the saturated magnetic flux density of the magnet, so that the contents of Fe, Co and Ni in TM are desirable to be not less than 10 at% but less than 73 20 at% in Fe, not less than 7 at% but not more than 50 at%
in Co and not less than 5 at% but not more than 30 at%
in Ni. Even when the main phase is RE2TM14H phase in which Fe as TM is 100%, the corrosion resistance of the permanent magnet according to the invention is superior to that of the conventional RE-TM-H magnet, so that the above phase can naturally be used as a main phase in accordance with the use purpose of the magnet.
As RE in the low melting point phase of RE-TM
system and RE-TM-B system, light rare earth element such as La, Ce. Pr, Nd or the like is advantageously adaptable importantly considering the cost, and middle to heavy rare earth elements from Sm to Lu and Y, Sc and the like are adaptable for more enhancing the corrosion resistance.
As to TM, the presence of Ni and/or Co, particularly Ni is effective to improve the corrosion resistance, so that according to the invention Ni is necessarily contained as TM. In this case, the content in TM is preferable to be not less than about 8~.
The addition effect of Ni is as follows.
i) The melting point of RE-TM system and RE-TM-B system is lowered, and the wetting of liquid phase in the liquid phase sintering is promoted to increase the sintering density and enhance the residual magnetic flux density.
ii) The effect of cleaning grain boundary in liquid phase is enhanced in the liquid phase sintering to more increase the coercive force by the same reason as in the above item i).
iii) It is effective to the improvement of corrosion resistance and cheap as compared with Co.
Furthermore, when the ratio of Ni and/or Co in -12 - 20441' 4 the low melting point phase is made higher than that of REzTMI4B phase, the corrosion resistance can be more improved because the phases of these powders tend to preferentially corrode in the grain boundary as compared with RE2TM14B phase in the sintered body if the structure of TM is same and is advantageously acted by previously making electrochemically noble. Furthermore, the magnetically useless Nd phase can be eliminated, so that the residual magnetic flux density increases and hence the maximum energy product (BH)max also increases.
In this connection, even when an alloy having an average composition as a whole magnet is melted from the first as in the conventional technique, pulverized, pressed and sintered so as to approach to an equilibrium state, the Nd phase is not obtained. For this purpose, it is necessary to conduct the heating at a high temperature for long time, during which abnormal growth of crystal grain is undesirably caused to considerably degrade the coercive force.
Moreover, it is not necessary that the same element is used in RE of the main phase and RE of the low melting point phase. And also, in the magnet consisting of the above two phases, the effect of the invention is not lost even when a part of RE and TM is replaced with at least one of Mg, A1, Si, Ti, V, Cr, Mn, Cu, Ag, Au, Cd, Rh, Pd, Ir, Pt, Zn, Ga, Ge, Zr, Nb, Mo, - 20441' In, Sn, Hf, Ta and W in an amount up to 8 ate of a full magnet.
As to the production method, there may be carried out a method wherein a mixture of powder of RE2TM14B composition and powder composed mainly of low melting point RE-TM series and/or RE-TM-B series intermetallic compound phases is placed in an iron pipe under vacuum and then sintered while hot rolling as a method of producing large size magnets in addition to the method in which the above powder mixture is subjected to compression molding and then sintered.
BRIEF DISCLOSURE OF DRAWINGS
Fig. 1 is a Nd-Fe-B three component phase diagram; and Fig. 2 is a Nd-Co-B three component phase diagram.
BEST MODE FOR CARRYING OUT THE INVENTION
Example 1 An alloy button was prepared by arc melting neodymium, transition metal and boron at an atomic ratio of 2:14:1, which was subjected to a normalizing treatment in a vacuum furnace at 950°C for 7 days and further to rough grinding and fine pulverization, whereby fine powder having a particle size of few microns was obtained. In this case, the ratios of Fe, Co, Ni in the transition metal were varied to produce a 20 .441w' ~
plurality of alloy powders.
Similarly, powder having a ratio of neodymium or (neodymium + dysprosium) to nickel of 1:1 was prepared.
In this case, the normalizing treatment conditions were 680°C and 5 days.
Then, powders selected from the above two groups were mixed at a mixing ratio shown in Table 1, pressed while applying a magnetic field of 15 kOe, sintered at 1000°C under vacuum for 2 hours and then quenched to room temperature.
The magnetic properties and corrosion property of the thus obtained samples were measured to obtain results shown in Table 1. Moreover, the corrosion property was evaluated by exposing the sample to an environment at a temperature of 70°C and a humidity of 95~ for 48 hours and measuring a rusted area ratio on the surface of the sample.
For the comparison, the measured results of a sample produced by the conventional method in which a full composition for the sintered magnet was melted at once and subjected to rough grinding - fine pulverization - pressing in magnetic field - sintering steps are also shown in Table 1.
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d ri N ri m -1 N i O -I O ' O
~ ri a .-IW r-t ~ -I t7 ~ v N ~
. r - r '-id Tj ~ ~ ~ ~ ~ E r ~ ~ E ~ .Lt ~ -.1 1d -.ictf -.i c0 ~ cd ~ 10 ~ ~
-.a of y, x x x x p O N U N U N U N U N U N U
O rl N ~--IN r-1 ~ r-i d ' Ol 'o d w 2s >a o N u w o w 2s ~ b a w o .a b .c ro .o ~o .c .~ -c xx ~y xx a~ xx ~~ xx aw xx ~x.~xx a~
p ~ N M a m 1o r ao o~ '"1N
x 204~1'~1 As seen from the above table, the rare earth metal-transition metal series magnets of two phase structure according to the invention considerably improve not only the magnetic properties but also corrosion resistance as compared with those obtained by melting the full composition from the first as in the conventional technique.
Example 2 An alloy button was prepared by arc melting neodymium, transition metal and boron at an atomic ratio of 2:14:1, which was subjected to a normalizing treatment in a vacuum furnace at 950°C for 7 days and further to rough grinding and fine pulverization, whereby fine powder having a particle size of few microns was obtained. In this case, the ratios of Fe, Co, Ni in the transition metal were varied to produce a plurality of alloy powders.
Similarly, powder having a ratio of neodymium and/or dysprosium or praseodymium to nickel or (nickel + cobalt) of 3:1 was prepared. In this case, the normalizing treatment conditions were 485°C and 5 days.
The magnetic properties and corrosion property of the thus obtained samples were measured to obtain results shown in Table 2.
For the comparison, the measured results on the properties of a magnet produced by the technique 20441'1 disclosed in Japanese Patent laid open N0. 63-164403 are also shown in Table 2.
- ~U~41'~1 dr >r oao >COU01>01 00 >O dr-ISriNN 'N NM 'M dC' jct'1r10 ra r~ r~ ra ri r-i ri ra ri ri ri .i ri i'., ri ri ri r~ ri .~G ~ r.l1'7 ~ ~ +1 'n t~ .D y l.7y,r ~ t~ ~ .u O
d y d N G7 d d f .-I
a ~ t0 b c0 at 0 t0 ~ I ~ 10 ~ Id ~ tc ~ -.~
.-I.-1~ .-I.-m.-1 G7 G7 G7 C7 G7 G7 d G7 d c~ ~
1 ~ ~ u a u -I r~ -1 1 -1 +r a a --1 -a a -1 ~s ,. ~ w ~ ,. .. . >a . . . r + r r . E
o. a a n, a. . a , >a w >~ . >a c~ >~ a a a a a a c> a a a ~ c a E ~ ro ~ is ~ 1~ ~ . ,~ , ,~ , ,~ . ,~ ,~
E E E E E E d E d , a~ E . E . , a~
G! a~ d E E E E d GI E
E E
a~ ro a id a ~ a a, w a a o. x U ro U is U io U id U td U ft) U id U ~ >
id itt ed t~ id GL x E x E x E E E E E E w U x U x U x U x U X U x U x U x C
x x x x x w O w O w O '~ O ~ O '~ O ~ O EC O
d w '~ w ~ w w w w w w w w w w w ' U U U U U U U U U
b d td IffO O O O If7 M O N ~ M ~ M O M 00 N lf1 n-I N N N N n-1 s.y.
O
x~
O N N CO O N O tD O M rI lO 00 0 N t11117 ' ~ 1D Ifl ~ N N ~C'N M N if W O 00 r ~O tf1 f .'T. M M M M M M M M M M M M M M ri ri M
~.
U O N O ~ if1p u1 ,...Itft N ~ M M r~ It1 M O
O
N ri If1 O ill O N O CO ttft0 r ~ p 01 t0 O
r~ rl rl rl ,-~ ~ ,..~rl N ri rl l0 r-IO 00 lt1M 10 M 00 lf7N OD ri M O p M
N M N N rl N r-IN r~ N N N N M ~ ~ N
yr ri ri ri r-1r~ r~ r~ ri r~ ri r~ ra ri ri ri N N N N ~ V' N M N
N _ N _ N _ N _ ~ _ M _ N _ 01 _ N
N ~ d' ..a .-1 r '"1- N M oo c .U -.1pp _ 00 _ a! _ ~ _ M _ O _ N _ O _ 1 x b N N ~D N N rl O d' N N ri tf1 N tD O M
C~ 01 ~O M ~ C~ W M
I 1 ~ - ~ - ~ - ~ - ~ - ~
O N N rl ri ri N rl N
t0 01 iD ri 00 N in 10 Lff r E d O r-I U1 d' M 00 ri N lt1 fV4"IW M ri r 00 d' 01 r-I in N
o r in a~ u i m w n O
C
O ~ 1 1 1 I I 1 I I ~ _ I 1 1 I 1 1 I
ra E-I.r., O A I I I I I I N - I I i I 1 1 1 ~ p E ri V ao 0 o c m c o r o .d 00 O O 10 1 1 If1 O p O
x ao ' oo ' ao ' ao - r ' a~ ' ' 00 .r., da ~' -~ -.~ -wn -.~ -~ -.10 .~ .~ -~
In o o o o o o o o x x x x x x x x x .. .. .. .. .. .. .. .. ..
. . . . . . . . .
dw w o0 00 00 00 oin o0 00 00 00 E
O U UM UM UN U'-I UN UM UN UM
v O C >~ G >~ >~ G C C
-'~
O
p .. O .. ~ .. O .. O .. O .. O .. O .. O ..
E . . . . . . . . .
-'"i -.-i O
.~ .,.., .,., .r., .,., .,a .,.., .,.., ~ JJ .LJ ~1 .IJ iJ JJ J
G7 .,1N .,iN - .,i!y .,id -O O to tn O - O - - O
i w H W ~ GfIN w Gy w N W u G ' W
r-1 r lO p CO 00 00 a a o , ct, a a, c~ n. o.
-~ in E in E in E in E o E o E in E in E in in in in ,n o o in in in 10 O 1D O 1D O 10 O r O r O ~D O it) O 1D
M M M M M M M er M
U U U U U U U U
ri 4.~ N N N ~~ N d GJ ty o w w w x w w ~-iu..l~-Iw w .-a ~. rl .-i ,-1 M r-, .-I .-a rl .-, ~
O
P
d O O O _ O O O O O
O O O O O O O O
-'i 3 M o 3 ~
o d~ tT tri b~ C~ O tT tr~ tr~O
x-~-~ 3 3 3 3 3 3 c a a a a o a o a a d -''i U
~
.-i,-rr-1 -.,,.-1-.1 .-~-..i,~ .i .-~1U.i r.~U.r .-1 -.ar-Ifs E ~ to to o d O d d G7 E m ~
~
pq > a7 r t~ ~ 00 .u W y C7 ~ to ~ t0 ~..>pct w ' > > >v > '~ > 00 > .I > > ~
N
C .-Ic .-ac r-I aTGI.-I~r r-1c~ r-1 er .-1~r ~ er o o o O o O ' 0 o d ~ ai .~ d .-ral ~--ia~ ~-axa~ ~,~d ~~,a~ ~ am ~-10 w ,--i.o ~-i ~ .-1~ r .o It ~ ~ ~-I
,o - E ~ E ~ E ~ E E E ~ E ~ E ~ E ~
V ~ id -~ e0 -~ 10 o~ id o irix 10 x aS -~ is1U
Hx Hx Hx H E
H.~ H'. Hx H...
p NM U NM U NM U N U NN U NM U NM U NM U NM
d d N d N Gf d d 'O l.,'O H 21 a 'o s.aH 1-~'O >a 'd a 'O N 'Cf 'O x 'O .r~Tf .C ~ .C S-~ .>~'O .>~ 'b .C >, .r~'O
xx ~~ xx ~x~xx ay x~.a~ ww a~ xx a~ xx ~~ xa ~~ xx o M a w ~a r ao c~ o ~ N M v i wo r o~ o~
x rl ri ri rl rl rl e1 N N N N N N N N N N
i~:f~~~1'~1 As seen from the above table, the rare earth metal-transition metal series magnets of two phase structure according to the invention are excellent in the magnetic properties and corrosion resistance.
Furthermore, when Acceptable Example 8 is compared with Acceptable Example 13, it is apparent that the corrosion resistance is improved as the Ni ratio in RE3(Ni, Co)1 becomes particularly higher. Moreover, in the conventional example, the magnetic properties are good, but the corrosion resistance is poor because Ni is not contained.
Example 3 A fine alloy powder of REZTMIqB composition was prepared by the same manner as in Example 1, while a fine alloy powder in which ratios of Ni and Co in TM
were made higher than those of RE2TM14B powder was prepared as a starting powder. After these powders were mixed, a sintered magnet was produced by the same manner as in Example 1.
The properties of the thus obtained sintered magnet are shown in Table 3 together with those of the sintered magnet produced by the conventional method.
~(~~41'~1 N v a~ ~ d p u~ ~n ~o ~c r r r-I ~ r-i ~ r-I ~
ri .~ .~ r-1 rl r-1 .n ~ ' a ~-I ~ -i ~ ~O
~ b ~ -I ~
' . r o. , r , a ~ o. ~' n, ~' c~. a a a, a n ~
v ~ v ~ v ~
e ro ro w ro ro d oW ~W oW ~W oW
U U U
.d N O M O M O M
~
CP
O
~, x~
is u~ ao m ~-~Ir ~ rl ri 01 O N ri Vr M M N M M M
O~
U N rl 1!1 00 O N
d xo ~; r vrf M oo vo a N
t9 f~ ~ N rl N ri .x' '. r-I .1 ri r-I .1 .1 a o 0 C1 _ M _ M
r ao ao a~ o~ o~
w o, o0 0 x ~ _ ~ _ ~ _ a~ p r E U r I ri _ ri N N N
O d t0 M M
p w ri _ r _ r _ p c a' a' .,., O o1 ~ d' ~ yD OD N
o x N _ N _ ~ _ U r1 ~~ rl O
O N 00 t0 .i .i O O
~ u'1 t0 O N O CO O
-ri M ri lff r-1 M ri O
N
i . .. .. .. .. .. ..
.. .. ..
..
l-i tf1 O
r-I
~
~J O O
Id O
~
.u U u1 0 0 0o O
rl W y0 M M M 111 M
CJ M
.. .. .. ..
.. ..
..
O . ..
O .
If1 N
+~ N O
~ p' 1I1 N ~l1 O O O O
t11 r Q; w lf1 r 10 rl 10 10 ri M
N
O O O
O O O O
dp O W N ~ tf1 -ri O ~ tff ~ ~
' ' ~O tt7 tt7 d aT d ~ G7 G7 N
aJ v! N (~
a .p ,p .O
ld O O O
H JJ y y!
~ ~
W W W
x O O O
i O O O
C U U U
~ O~ O~ tr~
C C p .-i .a .-1 a a7 ~ Ca +~ Ca ~
a .C .C x O ~! .-1 V' .-1 Q' .-I
rl 3 rl 3 ri 3 ~ a 3 a~ ~ ~ E ~ E
a ~ ai N ~ N
.
~ NE U NE U NH U
W O O O
'Cf sr 'O H b a 'C3 "p 'C1 .C7 'C1 .t7 xx a xx ~ xx to ~
O O ri N M W t1 x M M M M M M
- 2a~~~~1 As seen from the above table, when using the fine alloy powder in which the ratios of Ni and Co in TM
are higher than those of RE2TMIqB powder as a powder to be mixed, the more improvement of the corrosion resistance is attained.
INDUSTRIAL APPLICABILITY
According to the invention, the rare earth metal-transition metal series magnets having improved corrosion resistance and magnetic properties can be produced as compared with the conventional production method. Particularly, the corrosion resistance is improved, so that the considerable improvement of reliability as an industrial material is realized.
Claims (10)
1. A corrosion-resistant rare earth metal-transition metal series permanent magnet consisting essentially of:
RE: not less than 10 at% but not more than 25 at% (in which RE is one or more of Y, Sc and lanthanide), B: not less than 2 at% but not more than 20 at%, and the remainder being essentially TM (in which TM is one or more of Fe, Co and Ni), wherein the magnet has a texture comprised of:
(i) a phase of RE2TM14B (in which TM is one or more Fe, Co and Ni) having Nd2Fe14B structure, and (ii) a phase of at least one member selected from the group consisting of an RE-TM series intermetallic compound (in which TM is Ni or a mixture of Ni and Fe or Co), an RE-TM
series eutectic structure (in which TM is Ni or a mixture of Ni and Fe or Co) and RE-TM-B series intermetallic compound (in which TM is Ni or a mixture of Ni and Fe or Co), each having a melting point lower than that of the RE2TM14B phase, at a ratio of the phase (i) to the phase (ii) of 95:5 to 40:60 as a formula unit.
RE: not less than 10 at% but not more than 25 at% (in which RE is one or more of Y, Sc and lanthanide), B: not less than 2 at% but not more than 20 at%, and the remainder being essentially TM (in which TM is one or more of Fe, Co and Ni), wherein the magnet has a texture comprised of:
(i) a phase of RE2TM14B (in which TM is one or more Fe, Co and Ni) having Nd2Fe14B structure, and (ii) a phase of at least one member selected from the group consisting of an RE-TM series intermetallic compound (in which TM is Ni or a mixture of Ni and Fe or Co), an RE-TM
series eutectic structure (in which TM is Ni or a mixture of Ni and Fe or Co) and RE-TM-B series intermetallic compound (in which TM is Ni or a mixture of Ni and Fe or Co), each having a melting point lower than that of the RE2TM14B phase, at a ratio of the phase (i) to the phase (ii) of 95:5 to 40:60 as a formula unit.
2. The permanent magnet according to claim 1, wherein the content of Ni or Co or both of Ni and Co in TM in the low melting point RE-TM series and RE-TM-B series phases is higher than that of the RE2TM14B phase.
3. The permanent magnet according to claim 1 or 2, wherein RE in the RE2TM14B phase (i) is Nd or Pr or a combination thereof.
4. The permanent magnet according to any one of claims 1 to 3, wherein TM in the RE2TM14B phase (i) consists of 10 to 73 at% of Fe, 7 to 50 at% of Co and 5 to 30 at% of Ni.
5. The permanent magnet according to any one of claims 1 to 3, wherein TM in the RE2TM14B phase (i) consists of Fe alone.
6. The permanent magnet according to any one of claims 1 to 3, wherein TM in the RE2TM14B phase consists of Fe and Co.
7. The permanent magnet according to any one of claims 1 to 6, wherein RE in the low melting point phase (ii) of the RE-TM series or the RE-TM-B series contains at least one light rare earth element selected from the group consisting of La, Ce, Pr and Nd.
8. The permanent magnet according to any one of claims 1 to 7, wherein the low melting point phase (ii) contains Ni as TM in an amount of at least 8 at%.
9. The permanent magnet according to any one of claims 1 to 8, which has such corrosion resistance that a rusted surface area ratio is no more than 11% after a 48 hour exposure test in air at a temperature of 70°C and a humidity of 95%.
10. A method of producing the corrosion-resistant rare earth metal-transition metal series magnet as claimed in any one of claims 1 to 9, which comprises:
subjecting a mixture of (i) powder composed essentially of RE2TM14B series intermetallic compound (in which TM is one or more of Fe, Co and Ni) and (ii) powder having a melting point lower than that of the above powder (i) and composed essentially of at least one member selected from the group consisting of the RE-TM series intermetallic compound (in which TM is Ni or a mixture of Ni and Fe or Co), the RE-TM
series eutectic structure (in which TM is Ni or a mixture of Ni and Fe or Co) and the RE-TM-B series intermetallic compound (in which TM is Ni or a mixture of Ni and Fe or Co) to a compression molding to form a molded body; and then sintering the molded body, wherein the powders have a particle size of from 0.5 to 5 µm.
subjecting a mixture of (i) powder composed essentially of RE2TM14B series intermetallic compound (in which TM is one or more of Fe, Co and Ni) and (ii) powder having a melting point lower than that of the above powder (i) and composed essentially of at least one member selected from the group consisting of the RE-TM series intermetallic compound (in which TM is Ni or a mixture of Ni and Fe or Co), the RE-TM
series eutectic structure (in which TM is Ni or a mixture of Ni and Fe or Co) and the RE-TM-B series intermetallic compound (in which TM is Ni or a mixture of Ni and Fe or Co) to a compression molding to form a molded body; and then sintering the molded body, wherein the powders have a particle size of from 0.5 to 5 µm.
Applications Claiming Priority (7)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP263,946/89 | 1989-10-12 | ||
| JP26394689 | 1989-10-12 | ||
| JP335,028/89 | 1989-12-26 | ||
| JP33502889 | 1989-12-26 | ||
| JP2269635A JP2675430B2 (en) | 1989-10-12 | 1990-10-09 | Corrosion resistant rare earth-transition metal magnet and method of manufacturing the same |
| JP269,635/90 | 1990-10-09 | ||
| PCT/JP1990/001315 WO1991006107A1 (en) | 1989-10-12 | 1990-10-11 | Corrosion-resistant, rare earth-transition metal magnet and method of production thereof |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2044171A1 CA2044171A1 (en) | 1991-04-13 |
| CA2044171C true CA2044171C (en) | 2000-12-12 |
Family
ID=27335262
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002044171A Expired - Fee Related CA2044171C (en) | 1989-10-12 | 1990-10-11 | Corrosion-resistant rare earth metal-transition metal series magnets and method of producing the same |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0447567B1 (en) |
| JP (1) | JP2675430B2 (en) |
| KR (1) | KR960013029B1 (en) |
| CA (1) | CA2044171C (en) |
| DE (1) | DE69027201T2 (en) |
| WO (1) | WO1991006107A1 (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5405455A (en) * | 1991-06-04 | 1995-04-11 | Shin-Etsu Chemical Co. Ltd. | Rare earth-based permanent magnet |
| DE69202515T2 (en) * | 1991-06-04 | 1995-09-21 | Shinetsu Chemical Co | Process for the production of two-phase permanent magnets based on rare earths. |
| JP2782024B2 (en) * | 1992-01-29 | 1998-07-30 | 住友特殊金属株式会社 | Method for producing raw material powder for R-Fe-B-based permanent magnet |
| US5387291A (en) * | 1992-03-19 | 1995-02-07 | Sumitomo Special Metals Co., Ltd. | Process for producing alloy powder material for R-Fe-B permanent magnets and alloy powder for adjusting the composition therefor |
| CN1044940C (en) * | 1992-08-13 | 1999-09-01 | Ybm麦格奈克斯公司 | Method of manufacturing a permanent magnet on the basis of ndfeb |
| EP0583041B1 (en) * | 1992-08-13 | 1997-02-05 | Koninklijke Philips Electronics N.V. | Method of manufacturing a permanent magnet on the basis of NdFeB |
| US5482575A (en) * | 1992-12-08 | 1996-01-09 | Ugimag Sa | Fe-Re-B type magnetic powder, sintered magnets and preparation method thereof |
| CN1934283B (en) | 2004-06-22 | 2011-07-27 | 信越化学工业株式会社 | R-Fe-B-based rare earth permanent magnet material |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2700643B2 (en) * | 1987-04-11 | 1998-01-21 | 株式会社トーキン | Manufacturing method of rare earth permanent magnet with excellent oxidation resistance |
| DE3783413T2 (en) * | 1986-09-16 | 1993-05-27 | Tokin Corp | METHOD FOR PRODUCING A RARE-EARTH IRON BOR PERMANENT MAGNET WITH THE AID OF A QUARKED ALLOY POWDER. |
| JPH0621324B2 (en) * | 1986-10-04 | 1994-03-23 | 信越化学工業株式会社 | Rare earth permanent magnet alloy composition |
| JPS63127505A (en) * | 1986-11-17 | 1988-05-31 | Taiyo Yuden Co Ltd | Magnet and manufacture thereof |
| JPH063763B2 (en) * | 1986-12-26 | 1994-01-12 | 信越化学工業株式会社 | Rare earth permanent magnet manufacturing method |
| JP2948223B2 (en) * | 1987-03-31 | 1999-09-13 | 住友特殊金属 株式会社 | High performance permanent magnet with excellent corrosion resistance and method of manufacturing the same |
| US5015307A (en) * | 1987-10-08 | 1991-05-14 | Kawasaki Steel Corporation | Corrosion resistant rare earth metal magnet |
-
1990
- 1990-10-09 JP JP2269635A patent/JP2675430B2/en not_active Expired - Lifetime
- 1990-10-11 KR KR1019910700606A patent/KR960013029B1/en not_active IP Right Cessation
- 1990-10-11 CA CA002044171A patent/CA2044171C/en not_active Expired - Fee Related
- 1990-10-11 EP EP90914967A patent/EP0447567B1/en not_active Expired - Lifetime
- 1990-10-11 DE DE69027201T patent/DE69027201T2/en not_active Expired - Fee Related
- 1990-10-11 WO PCT/JP1990/001315 patent/WO1991006107A1/en active IP Right Grant
Also Published As
| Publication number | Publication date |
|---|---|
| EP0447567B1 (en) | 1996-05-29 |
| KR920701999A (en) | 1992-08-12 |
| WO1991006107A1 (en) | 1991-05-02 |
| DE69027201T2 (en) | 1996-10-10 |
| CA2044171A1 (en) | 1991-04-13 |
| JP2675430B2 (en) | 1997-11-12 |
| KR960013029B1 (en) | 1996-09-25 |
| EP0447567A4 (en) | 1992-05-20 |
| JPH03250607A (en) | 1991-11-08 |
| DE69027201D1 (en) | 1996-07-04 |
| EP0447567A1 (en) | 1991-09-25 |
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