JPH0682574B2 - Method of manufacturing permanent magnet with excellent corrosion resistance - Google Patents

Description

TECHNICAL FIELD The present invention relates to a rare earth / boron / iron alloy having improved corrosion resistance of a permanent magnet containing R (R is at least one of rare earth elements including Y), B and Fe as main components. The present invention relates to a method for manufacturing a permanent magnet.

BACKGROUND ART Currently, typical permanent magnet materials are alnico, hard ferrite and rare earth cobalt magnets. 20-30 wt% of cobalt due to the destabilization of the situation of cobalt raw material in recent years
%, The demand for Alnico magnets has decreased, and inexpensive hard ferrite, which is mainly composed of iron oxide, has become the mainstream of magnet materials. On the other hand, rare earth cobalt magnets are very expensive because they contain 50-60 wt% of cobalt and use Sm that is rarely contained in rare earth ores, but they have much higher magnetic properties than other magnets. , Mainly used for small size and high value added magnetic circuits.

The present applicant has previously proposed an Fe-BR system permanent magnet (R is at least one of rare earth elements including Y) as a new high-performance permanent magnet that does not contain expensive Sm or Co (Japanese Patent Application No. Sho-200-200).
57-145072 (JP-A-59-46008). This permanent magnet is an excellent permanent magnet which uses Rd, which is a resource-rich light rare earth mainly as N, and which has Fe as a main component and has an extremely high energy product of 25 MGOe or more.

However, Fe-B having the above-mentioned excellent magnetic properties
Since the R-type permanent magnet contains iron and a rare earth element that are easily oxidized in the air as main components, when it is incorporated in a magnetic circuit, the oxide generated on the surface of the magnet lowers the output of the magnetic circuit and reduces the magnetic force. There was a problem of causing variations between circuits and contamination of peripheral devices due to the dropping of surface oxide.

Therefore, in order to improve the corrosion resistance of the Fe-BR permanent magnet, the applicant has previously proposed a permanent magnet whose surface is coated with a corrosion-resistant metal plating layer by electroless plating or electrolytic plating (Japanese Patent Application No. 58-162350 (Japanese Patent Laid-Open No. 60-54406)
And a permanent magnet whose surface is coated with a corrosion resistant resin layer by spraying or dipping (Japanese Patent Application No. 58-1).
No. 71907 (JP-A-60-63901).

However, in the former plating method, when the permanent magnet body is a sintered body, since the sintered body is porous, the acidic solution or alkaline solution remains in this hole during the plating pretreatment, and it is generated over time. There is a risk of rusting, and because the magnet body has poor chemical resistance, the magnet surface is corroded during plating, resulting in poor adhesion.
There was a problem of poor anticorrosion properties.

In addition, since the latter method of resin coating has directionality, it takes a lot of steps and labor to form a uniform resin coating on the entire surface of the object to be treated, especially for irregularly shaped magnets with complicated shapes. It is difficult to apply a thick coating, and the dipping method causes the resin coating to have a non-uniform thickness, resulting in poor product dimensional accuracy.

The object of the present invention is to improve the corrosion resistance of a new permanent magnet mainly composed of rare earth, boron and iron. It does not use corrosive chemicals or the like and does not remain, and has excellent adhesion and corrosion resistance. It is an object of the present invention to provide a method for manufacturing a permanent magnet, in which a thin film can be provided on the surface of a magnet body with a uniform thickness.

Structure and effect of the present invention This invention, R (R is at least one of rare earth elements including Y) constituting the cathode 8 atomic% to 30 atomic%, B2 atomic% to 28 atomic%, Fe42 atomic% to 90 atomic %, The main phase is a tetragonal phase permanent magnet body, and the coating material that constitutes the anode is housed in a decompression container, and reverse sputtering is performed in the presence or absence of a reactive gas. After that, the coating material that constitutes the anode is heated to atomic form,
The ionized particles, which are in the form of molecules or fine particles, are ionized by colliding them with thermoelectrons and traveling due to the electric field distribution, and increased by colliding with other vaporized particles, which constitute the cathode, A method for producing a permanent magnet having excellent corrosion resistance, which comprises depositing a corrosion-resistant thin film of a coating substance on the surface of the permanent magnet to form a coating.

That is, the present invention provides R (R is at least one of rare earth elements including Y) 8 atom% to 30 atom% and B2 atom% to
A metal such as Al, Ni, Cr, Cu, Co or the like was formed by ion plating on the surface of a permanent magnet body containing 28 atomic% and 42 atomic% to 90 atomic% Fe as the main components and the main phase being a tetragonal phase. This is a method for producing a permanent magnet having excellent corrosion resistance, which is characterized in that an alloy or a corrosion-resistant thin film layer of SiO ₂ , Al ₂ O ₃ , Cr ₂ O ₃ , TiN, AlN, TiC, etc. is extendedly coated.

This invention is a manufacturing method for forming a uniform, strong and stable corrosion-resistant thin film layer on the surface of the present permanent magnet in order to suppress oxides generated on the surface, and by the corrosion-resistant thin film formed by the present invention, Oxidation of the magnet surface is suppressed, and
Since corrosive chemicals, etc. are not used or left, there is an advantage that the magnetic characteristics are not deteriorated and stable for a long period of time.

The ion plating method according to the present invention is, for example, a vacuum chamber having a degree of vacuum of 10 ⁻⁴ to 10 ⁻⁷ Torr, containing a coating material required for forming a thin film together with a permanent magnet body constituting a cathode, and performing reverse sputtering. After that, it is heated to make the substance into atomic, molecular, and fine particles, which are ionized by thermionic electrons colliding with them, and the ionized particles of the coating material traveling by the electric field distribution collide with other evaporated particles. The ionized particles thus increased are condensed on the surface of the magnet body constituting the cathode to form and coat a thin film.

The heating method of the substance to be ionized includes a resistance heating method such as a crucible method and a direct resistance heating method, a high frequency induction heating method, an electron beam heating method, and the like, and the composition and thickness of the coating material to be formed and deposited in any of these methods, It can be appropriately selected and applied according to the shape of the adherend side permanent magnet body and workability.

The coating substance that is the substance to be evaporated is Al, Ni, Cr, Cu, Co.
Such as metal or its alloy or SiO ₂ , Al ₂ O ₃ , Cr ₂ O ₃ , T
iN, AlN, TiC and other metals, alloys, ceramics, metal nitrides, etc. that can improve the corrosion resistance of this system permanent magnet,
Oxide or carbide compounds are preferred.

In the present invention, when a nitride film, an oxide film, or a carbonized film is formed on the surface of the permanent magnet body, it is possible to introduce a reactive gas such as O ₂ , N ₂ , CO ₂ acetylene into the vacuum container. Preferably, and when forming an alloy coating,
By providing a plurality of evaporation sources for each alloy component and allowing a constant ratio during evaporation, it is possible to form an alloy film having a constant composition.

In the present invention, the thickness of the corrosion-resistant thin film on the surface of the Fe-BR permanent magnet formed by the above-mentioned ion plating means is preferably 30 μm or less in consideration of magnetic characteristics and corrosion resistance.

Reason for limitation of permanent magnet The rare earth element R used in the permanent magnet of the present invention is 8 atom%
It is preferable to contain at least one of Nd, Pr, Ho and Tb of -30 atom% or at least one of La, Sm, Ce, Er, Eu, Pm, Tm, Yb, Lu and Y. .

Usually, one kind of R is sufficient, but in practice, a mixture of two or more kinds (Misch metal, didymium, etc.) can be used for the reasons of availability, and Sm, Y, La, Ce, Ge
Etc. can be used as a mixture with other R, especially Nd, Pr, etc.

It should be noted that this R does not have to be a pure rare earth element, and may contain an impurity that is unavoidable in manufacturing within the industrially available range.

R (at least one of rare earth elements including Y) is an essential element in the novel permanent magnet, and if it is less than 8 atom%, the crystal structure becomes a cubic crystal structure having the same structure as α-iron. Therefore, high magnetic characteristics, especially high coercive force cannot be obtained,
If it exceeds 30 atomic%, the R-rich non-magnetic phase increases,
The residual magnetic flux density (Br) decreases, and a permanent magnet with excellent characteristics cannot be obtained. Therefore, the rare earth element is 8 atom% to 30
The range is atomic%.

B is an essential element in the novel permanent magnets, and if it is less than 2 atomic%, a rhombohedral structure is formed, and a high coercive force (iHc) cannot be obtained. An excellent permanent magnet cannot be obtained because the magnetic phase increases and the residual magnetic flux density (Br) decreases. Therefore, B is 2
The range is from atomic% to 28 atomic%.

Fe is an essential element in the above new permanent magnets, and if the content is less than 42 atomic%, the residual magnetic flux density (Br) decreases, and
If the atomic percentage is exceeded, high coercive force cannot be obtained, so Fe is
The content is 42 atom% to 90 atom%.

Further, in the permanent magnet alloy according to the present invention, substituting a part of Fe with Co can improve the temperature characteristics without impairing the magnetic characteristics of the obtained magnet, but the Co substitution amount is If it exceeds 50% of Fe, the magnetic properties are deteriorated, which is not preferable.

Further, the permanent magnet according to the present invention can tolerate the presence of impurities unavoidable in industrial production in addition to R, B and Fe, but a part of B is 4.0 atom% or less of C, 3.5 atom% or less of P, 2.5 atom%
By substituting at least one of the following S and Cu of 3.5% or less with a total amount of 4.0 atom% or less, it is possible to improve the manufacturability of the permanent magnet and reduce the cost.

Further, at least one of the following additional elements is RB-
It is added to Fe-based permanent magnets because it is effective in improving the coercive force, etc., improving the manufacturability, and lowering the price. However, the residual magnetic flux density (B
Since it causes a decrease in r), it is desirable to add in a range that is equal to or higher than the residual magnetic flux density of the conventional hard ferrite magnet.

9.5 atomic% or less Al, 4.5 atomic% or less Ti, 9.5 atomic% or less V, 8.5 atomic% or less Cr, 8.0 atomic% or less Mn, 5 atomic% or less Bi, 12.5 atomic% or less Nb, 10.5 Ta less than atomic%, Mo less than 9.5 atomic%, W less than 9.5 atomic%, Sb less than 2.5 atomic%, Ge less than 7 atomic%, Sn less than 3.5 atomic%, Zr less than 5.5 atomic%, 6.0 atomic % Or less of Ni, 5.0 at% or less of Si, and 5.5 at% or less of Hf at least one kind is added and contained. However, when two or more kinds are contained, the maximum content is the maximum value of the added elements. However, if the content of the permanent magnet is not more than atomic%, the coercive force of the permanent magnet can be increased.

In the crystal phase of this Fe-BR permanent magnet, it is essential that the main phase is tetragonal, and a sintered permanent magnet having magnetic characteristics superior to those of fine and uniform alloy powder can be obtained.

Therefore, the permanent magnet of the present invention mainly uses resource-rich light rare earths such as Nd and Pr as R, Fe, B,
By using R, as a main component, an excellent permanent magnet having an extremely high energy product of 25 MGOe or more, a high residual magnetic flux density, a high coercive force, and high corrosion resistance can be obtained at low cost.

Further, the permanent magnet of the present invention is characterized by containing a nonmagnetic phase (excluding oxide phase) of 1% to 50% by volume, and in the case of a sintered magnet, the crystal grain size is 1 to 100 μm. A compound having a tetragonal crystal structure in the range is the main phase.

Further, the permanent magnet of the present invention can be magnetically anisotropic magnet obtained by press molding in a magnetic field, and can be magnetically isotropic magnet by press molding in a non-magnetic field.

The permanent magnet according to the present invention exhibits a coercive force iHc ≧ 1 kOe and a residual magnetic flux density Br> 4 kG, and the maximum energy product (BH) max is equal to or higher than that of hard ferrite. In the most preferable composition range, (BH) max ≧ 10MGOe , The maximum value is 25MGOe
Reach above

Further, the main component of R of the alloy powder for permanent magnets of the present invention is
R12 atom% ~ 2 when light rare earth metal occupies 50% or more
When 0 atomic%, B4 atomic% to 24 atomic% and Fe65 atomic% to 82 atomic% are the main components, magnetically anisotropic sintered magnets show the best magnetic characteristics, especially light rare earth metals In the case of Nd, the maximum value of (BH) max reaches 35MGOe or more.

Examples Example 1 As a starting material, electrolytic iron having a purity of 99.9%, ferroboron alloy containing B19.4% with the balance being Fe and Al, Si, C and other impurities, and Nd having a purity of 99.7% or more are used. These were melted by high frequency and then cast in a water-cooled copper mold to obtain an ingot having a composition of 15Nd-8B-77Fe.

After that, the ingot was roughly pulverized by a stamp mill and then finely pulverized by a ball mill to obtain a fine powder having a particle size of 3 μm.

Insert this fine powder into the mold, orient in a magnetic field of 12 kOe,
It was molded in a direction parallel to the magnetic field with a pressure of 1.5 t / cm ² .

The obtained molded body was sintered under the conditions of 1100 ° C. for 1 hour in Ar, then allowed to cool, and further subjected to an aging treatment in Ar at 600 ° C. for 2 hours to produce a permanent magnet.

From the obtained permanent magnet, outer diameter 20 mm × inner diameter 10 mm × thickness 1.5 mm
A test piece was cut into a size.

Next, the above test piece was placed in a vacuum container having a vacuum degree of 5 × 10 ^-5 Torr, and reverse sputtering was performed at a voltage of 400 V for 1 minute in 0.8 Torr Ar gas. After heating for 30 minutes, the temperature is lowered to 300 ℃ and the coating material is 3-5
mmφ granular fused silica is used, and this is heated, and thermoelectrons are collided with the molten fused silica that has become a molecular state to be ionized, and SiO ₂ ionized particles traveling due to the electric field distribution collide with other evaporated particles, and further SiO ₂ ionized particles were increased, and these ionized particles were attracted to an electric field to attach the test piece constituting the cathode to form a SiO ₂ thin film. The thickness of the thin film formed on the surface of the test piece was 5 μm.

The above ion plating conditions are as follows:
The ionization voltage was 100 V, 80 to 90 mA, and the treatment was for 40 minutes.

The test piece was subjected to a corrosion resistance test and a density strength test of the thin film after the corrosion resistance test. In addition, the magnetic properties before and after the corrosion resistance test were measured. The test results and measurement results are shown in Table 1.

For comparison, the test pieces were solvent degreased with trichlene for 3 minutes, alkali degreased with 5% NaOH at 60 ° C for 3 minutes, and then pickled with 2% HCl at room temperature for 10 seconds. In the bath, under the condition of current density 4A / dm ² , bath temperature 60 ℃, 20 minutes,
Electroless nickel plating was performed to obtain a comparative test piece (comparative example) having a nickel plating layer with a thickness of 10 μm on the surface. This test piece was subjected to the same tests and measurements as in Example 1 above, and the results are also shown in Table 1.

The corrosion resistance test was evaluated by the appearance of the test piece when the test piece was left in an atmosphere of 60 ° C. and a humidity of 90% for 500 hours.

In addition, the adhesion strength test, the test piece after the corrosion resistance test,
The adhesive tape was used to pull the grid portion at 1 mm intervals, and it was evaluated whether the thin film layer was peeled off (No peeled grid / number of front grid).

Example 2 The above test piece was placed in a vacuum vessel having a degree of vacuum of 1 × 10 ⁻⁵ Torr and reverse sputtered in N ₂ gas of 10 ⁻² Torr at a voltage of 400 V for 1 minute, and then as a pretreatment. After heating to 350 ℃ for 30 minutes, cool it down to 300 ℃ and use 5mmφ ×
Using a 3 mm Ti piece with a purity of 99.99%, this is heated, the thermoelectrons are collided with the atomized Ti to ionize, and the TiN ionized particles traveling due to the electric field distribution collide with other evaporated particles, Further, the TiN ionized particles were increased, and these ionized particles were attracted to an electric field and adhered to the test piece constituting the cathode to form a TiN thin film. The thickness of the thin film formed on the surface of the test piece was 5 μm.

The above ion plating conditions are as follows:
The ionization voltage was 100 V, 40-60 mA, and the treatment was for 20 minutes.

The test piece was subjected to the same corrosion resistance test as in Example 1 and the adhesion strength test of the thin film after the corrosion resistance test, and the magnetic properties before and after the corrosion resistance test were measured. The test and measurement results are the first
Shown in the table.

Example 3 The above test piece was put in a vacuum container having a degree of vacuum of 1 × 10 ⁻⁵ Torr, and reverse sputtering was performed in a CO ₂ gas of 10 ⁻² Torr at a voltage of 400 V for 1 minute, and then as a pretreatment. After heating to 350 ℃ for 30 minutes, cool it down to 300 ℃ and use 5mmφ ×
3mm purity Ti piece of 99.99% was used, this was heated, and thermal electrons were made to collide with atomic atomized Ti to be ionized, and TiC ionized particles traveling due to electric field distribution collided with other evaporated particles, Further, TiC ionized particles were increased, and these ionized particles were attracted to an electric field and adhered to the test piece constituting the cathode to form a TiC thin film. The thickness of the thin film formed on the surface of the test piece was 5 μm.

The above ion plating conditions are as follows:
The ionization voltage was 100 V, 40-60 mA, and the treatment was for 20 minutes.

The test piece was subjected to the same corrosion resistance test as in Example 1 and the density strength test of the thin film after the corrosion resistance test, and the magnetic characteristics before and after the corrosion resistance test were measured. The test and measurement results are the first
Shown in the table.

As is clear from the test and measurement results in Table 1, the corrosion-resistant thin film according to the present invention has a required film thickness and remarkably excellent uniformity as compared with the comparative example. It can be seen that the oxidization of No. 1 is reliably prevented, the magnetic characteristics are not deteriorated, and the magnetic characteristics are remarkably improved as compared with the comparative example.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁵ Identification number Internal reference number for FI Technical indication H01F 41/02 G 8019-5E (56) Reference JP-A-49-86896 (JP, A) Special features Kai 56-94705 (JP, A) JP 59-138311 (JP, A) JP 50-18364 (JP, A) JP 59-46008 (JP, A) JP 61-163266 ( JP, A) JP-A-49-115368 (JP, A) "Thin Film Handbook" December 10, 1983, published by Ohmsha, Inc. 121

Claims (1)

[Claims] 1. A main component comprising 8% by atom to 30% by atom of R (R is at least one of rare earth elements including Y), B2% by atom to 28% by atom, and 42% by atom to 90% by atom of Fe constituting a cathode. The permanent magnet body having a tetragonal phase as the main phase and the coating material forming the anode are housed in a decompression container, and after reverse sputtering in the presence or absence of a reactive gas, the anode is used. Heating the coating material that constitutes
The ionized particles, which are in the form of molecules or fine particles, are ionized by colliding them with thermoelectrons and traveling due to the electric field distribution, and increased by colliding with other vaporized particles, which constitute the cathode, A method for producing a permanent magnet having excellent corrosion resistance, which comprises depositing a corrosion-resistant thin film of a coating substance on the surface of a permanent magnet to form a coating.