JPH05152119A - Hot-worked rare earth element-iron-carbon magnet - Google Patents

Abstract

PURPOSE: To obtain an anisotropic permanent magnet having a high coercive force, by a method wherein the composition of a molten material, which consists of Nd or Pr, Fe and C or C and B, is rapidly solidified to turn the composition into a fine granularity of powder, and this powder is hot-pressed or is subjected to closed upsetting die forging after a hot press. CONSTITUTION: A magnet is an anisotropic permanent magnet, which contains one kind of a rare-earth element or more than one kind of rare-earth elements which is or are chosen from the mixture, whose rate occupying in the whole rare-earth elements is 40% or lower, of Nd with Pr or of Nd or Pr with one kind of other rare-earth element or more than one kind of other rare-earth elements, Fe or the mixture of Fe with Co, C and B. The magnet consists of the main phases of flat fine grains, which consist of a tetragonal system crystalline phase RE2 TM14 CXB1- X (The RE is one kind of a rare-earth element or more than one kind of rare-earth elements, the TM is Fe or the mixture of Fe and Co and the (x) is 0.2 to 1.0) and are aligned by a hot processing, and a grain boundary semimicrophase and is one containing grains of the mean largest diameter of 1000 mm or smaller. As a result, the magnet having a high coercive force is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rare earth element and iron permanent magnet. More particularly, the present invention relates to permanent magnets of iron, neodymium and / or praseodymium, and carbon, as described in the preamble of claim 1. Such magnets are disclosed, for example, in US Pat. No. 4,849,035.

[0002]

_2. Description of the Related Art Permanent magnets having a RE ₂ Fe ₁₄ B type structure are widely used. Such magnets can be manufactured by sintering, and a melt of the appropriate composition is rapidly solidified and bonded magnets from the quenched material, hot pressed. It can also be made by manufacturing magnets or hot pressed and then hot worked magnets.

Recently, rare earth-iron-carbon compositions have
It is formed of an E ₂ Fe ₁₄ C structure. This structure is similar to the iron-rare earth element-boron structure described above. Stadelmaier and Liu in US Pat. No. 4,849,035 disclose: That is, the cast iron-dysprosium-carbon composition and iron-dysprosium-neodymium-carbon-boron undergo a long annealing cycle at 900 ° C. in the ingot form to yield a magnetically hard tetragonal system 2-14-1.
It became a structure. The casting exhibited the properties of a permanent magnet. The casting was pulverized to produce particles. The finely ground particles have been disclosed as suitable for bonded magnets. Such materials showed a favorable coercivity, but at the same time a relatively low remanence.

Koehun et al., Journal of Applied P
hysics (Published January 15, 1989, Volume 62, Issue 2, 704-709
P.) “Nd ₂ Fe ₁₄ prepared by melt spinning method
C Permanent Magnetic Materials Bas
ed on Nd ₂ Fe ₁₄ C Prepared by Melt Spinning), it was announced that melt-spun ribbon particles composed of neodymium, iron and carbon were produced. Such particles became permanent magnets with a 2-14-1 structure when annealed at the appropriate temperature. Such particles can also be used to make resin bonded magnets.

[0005]

The anisotropic permanent magnet of the present invention has the characteristics described in claim 1.

It is an object of the present invention to provide a hot-worked magnet having a Nd ₂ Fe ₁₄ C-type structure, such as a hot-pressed magnet or a hot-pressed and then die-upset.
Is to provide a magnet. Here, the magnet is composed of very fine particles, has permanent magnet characteristics, and is magnetically anisotropic. Another object of the present invention is to provide a method of manufacturing such hot-worked magnets.

[0007]

According to the preferred embodiment of the present invention, these and other objects and advantages are achieved as follows.

The melt was made of neodymium and / or praseodymium, iron and carbon, (or carbon and boron). Such compositions are suitable for forming a 2-14-1 type structure having one or more secondary phase sub-portions after hot working. The composition of this melt is solidified very rapidly by a method such as melt spinning,
Amorphous compositions or very fine particle size compositions are produced, eg compositions having an average particle size of about 40 nm or less. Melt spun material is initially a brittle, magnetically isotropic piece of ribbon. Such pieces can be easily broken into powders suitable for hot pressing and / or other hot working in the die cavity.

The particles of such powders are amorphous or a number of very fine, substantially spherical particles. The particles are magnetically isotropic. For example, about 700
Hot-press at a suitable high temperature of ~ 900 ° C for a time of 20-30 seconds to a few minutes to obtain a sufficiently dense, fine-grained Nd ₂
An Fe ₁₄ C type tetragonal crystal structure is formed. The hot pressed product is then further hot worked at a high temperature, for example 750 to 900 ° C., to promote the growth of platelet-like particles and to plastically deform the particles to form platelet-like particles. , The C axes are generally parallel and the resulting particles are magnetically anisotropic. The particles are flat and aligned, but they are more finely grained. The preferred direction of magnetization is the pressing direction, ie the direction perpendicular to the direction of material flow during hot working. In general,
The maximum average size of the flat particles is about 1000 nm or less, and the thickness is preferably 200 nm or less. The microstructure of the hot-worked material is dominated by the flat 2-14-1 grains, and further by the intergranular material.
Is characterized by having one or more minor phases consisting of Currently, the material typically consists of iron and rare earth elements.

A mixture of iron and cobalt may be used as the transition metal element, but iron is preferred. Up to 40% of the total amount of rare earth elements may contain rare earth elements other than neodymium and praseodymium, but neodymium and / or praseodymium are preferably used as rare earth elements. Carbon or a mixture of carbon and boron is 2-1
Preferred for the third component of the 4-1 structure. In the practice of the present invention, the proportion of iron (or iron and cobalt), rare earth elements and carbon is such that the preferential crystalline phase formed is 2-14-.
The balance must be such that it has a tetragonal structure. If this crystal structure did not form, the hot worked product would have a low coercivity, ie, no permanent magnet properties.

The invention and how it may be implemented are described in more detail below with reference to the accompanying drawings.

The product of the present invention is a permanent magnet. The magnet has a coercivity greater than 1000 Oe.

[0013]

【Example】

Example 1 13.75 atom% neodymium, 80.25 atom% iron,
And an ingot having a composition of 6 atomic% carbon were prepared. This material is 6.89-20.68kPa (1-3ps
i) redissolved by induction heating in a quartz crucible under an atmosphere of argon above atmospheric pressure, and has a diameter of 254 mm rotating at a speed of 28 m / sec.
Melt spinning was performed by extruding the molten material on the outer surface of a (10 in) chrome plated copper wheel through a 0.65 mm orifice located at the bottom of the crucible. The extruded flow of molten metal collided with the rim of the spinning wheel and separated from the outer peripheral surface in the form of ribbon-like fragments.

X-ray diffraction analysis of the ribbon particles confirmed that the ribbon particles were substantially amorphous. Ribbon pieces were ground into powder to facilitate processing. A portion was then placed in the cavity of a 12.7 mm (0.5 in) diameter graphite die. The ribbon pieces were reheated therein to 450 ° C. under vacuum. The die temperature was then raised to 750 ° C. Die temperature is 6
When above 40 ° C., pressure was applied with a boron nitride-lubricant containing tungsten carbide-titanium carbide punch. A cycle of pressure was applied so that the load pressure increased rapidly up to 100 MPa. The sample was extruded by pulling out a punch after fully compressing the debris, holding it at maximum load for 30 seconds.
The whole process was performed in vacuum. As a result, a completely dense cylindrical product was obtained.

The resulting hot pressed product has a density of about 7.74 g / cc and contains a tetragonal crystal phase of Nd ₂ Fe ₁₄ C and is believed to be primarily neodymium and iron. It also contained a small amount of grain boundary phase with an undetermined composition. The parameters of the crystal lattice of this tetragonal system were measured to be a = 8.797Å, c = 12.0.
It turned out to be 01Å.

The magnetic properties of the hot pressed product were obtained from the demagnetization curve measured using a hysteresis graph. The compressed body showed anisotropy. The same characteristics in the direction parallel to the pressed direction are as follows. That is, B _r = 7.7 kG, H _ci = 10.7 kOe,
And (BH) _max = 11.4 MGOe. In the direction perpendicular to the pressed direction, the magnetic characteristic is B _r = 6.8k.
G, H _ci = 11.3 kOe, and (BH) _max = 8.1 MGOe
Met.

Example 2 The hot pressed cylinder obtained in Example 1 was
In the same direction, in vacuum, the cylinder is 750-800 ° C
The oversized graphite (19.0) that enables plastic deformation up to about 40% of the original height at the die temperature.
Pressed using a 5 mm (0.75 in) ID die. Vibrating sample mag
The resulting die upset forged flat, cylindrical magnet was cut with a high speed diamond saw to make a 2mm cube for magnetic property measurements with a netometer. The cube was cut so that two opposite faces were perpendicular to the pressed and die upset forging direction and the other four faces were parallel to the pressed and die upset forging direction.

The neodymium-iron-carbon die upset forged magnet has a remanent magnetism (Br = 1.
7kG), the residual magnetism (Br =
12.3kG) was higher. This magnetic anisotropy indicates that the c-axes of individual particles that have been die upset forged are aligned along the pressing direction. The coercivity of the sample is 2.
It was 8 kOe.

1 and 2 are two SEMs of the same region of the fracture surface of the die upset forged sample taken at different magnifications.
It is a photograph. The particles consisting of Nd ₂ Fe ₁₄ B tetragonal crystals appear to be arranged in a flat platelet. The particles are about 100 nm thick and have a maximum dimension of about 700-800 nm or less. The short dimension of the particles, the c-axis, the preferred direction of magnetization lies along the direction of the applied pressure.

Example 3 Four alloy groups were produced so as to have the following compositions. That is, Nd _13.75 Fe _80.25 (B _1-X C _X ).
₆ , in four alloys, X is 0.2,
Compositions were made that were 0.4, 0.6 and 0.8.

The four samples were each melt-spun and
Pieces of amorphous ribbon, such as those made in Example 1, were formed. Following the procedure used in Example 1, large pieces of ribbon of each of the four samples were milled and hot pressed into cylinders. They contained fine particles of the tetragonal phase Nd ₂ Fe ₁₄ C _x B _1-X . Here, the value of X is as shown above. The density and magnetic characteristics of the cylindrical magnet are as follows.

[0022]

[Table 1]

Example 4 The high deformation resistance and relatively low coercivity of die upset forged Nd _13.75 Fe _80.25 C ₆ magnets suggested that higher Nb concentrations were required. Some alloys with Nd
A composition of _{13.75 + X} Fe _80.25-X C ₆ was prepared as detailed in Example 1. 30m / s for each composition
Was melt spun as detailed in Example 1 except that a wheel with the following speeds was used. Hot press the sample,
Most of them were die upset forged. Such hot working steps were performed as detailed in Example 1 using a graphite die and a tungsten carbide-titanium carbide punch.

The general process parameters used to hot press these Nd-Fe-C ribbons are shown in FIG. The ribbon was heated to 650 ° C in the place of pressure for about 5.75 minutes (panels A and B of Figure 3).
Please refer to. ). The time interval required to achieve sufficient density (or close to it) is 2 at the bottom of FIG.
1 at maximum pressure (about 65 MPa), as shown by two panels
It was ~ 2 minutes. Final hot press temperature is Nd
The -Fe-B magnet has a temperature of about 800 ° C, while the carbide magnet has a temperature of about 850 ° C.

The hot pressed magnet was removed from the die and allowed to cool to room temperature. The measurement of magnetic properties was performed as detailed below. The data are listed in Table 2.
Some of the hot pressed magnets were then tested in Example 2
Reheated in a larger die and die upset forged as detailed in.

After heating for about 8.25 minutes, the temperature reached 700 ° C. An initial die upsetting pressure of about 15 MPa was applied at about 800 ° C. This pressure was maintained until the height of the sample was reduced by at least about 5%. The height decreased by about 5% when the pressure increased to 20-25 MPa. 15 MPa
By starting with, the precursor could be deformed without cracking. However, 15MP
The strain rate at a was also slow. 20 to pressure
By increasing to 25 MPa, the strain rate is Nd
The strain rate was increased to a level comparable to the strain rate of the -Fe-B alloy (about 1 min ^-1 ). Higher temperatures are required to produce fully die upset forged carbides. The final temperature (about 900 ° C) was about 50-100 ° C higher than the temperature used for die upset forged boride magnets.
The height of all die upset forged magnets detailed herein was reduced to 45% of their original height. (Ie 55
% Die upset forging. )

The magnetic properties of hot-pressed and then die upset forged magnets were measured using Walker-type MH.
This was done using the 5020 hysteresis graph. The results are shown in Table 2.
And 3 are shown. After annealing at 700 ° C. for about 30 minutes, the X-ray (Cu K) diffraction pattern of the powder ribbon was observed.

Surprisingly, the magnetic properties of the hot pressed magnets when the carbon concentration is above 6 atom% and the neodymium concentration is above 14.5 atom% are comparable to those of similar boride compositions. It deteriorated rapidly. Due to the formation of the phase Nd ₂ Fe ₁₇ , the coercivity disappears as a whole with Nd ₁₆ Fe ₇₈ C ₆ . The main diffraction peaks can be easily explained by comparing with the calculated 2-17 phase pattern. As reported by others studying annealed ingots, it is highly possible that the observed 2-17 phase contains dissolved carbon.

In order to suppress the formation of the 2-17 phase, Nd
A composition with ₁₆ Fe _78-y C _{6 + y} was used to try to make a magnet with a higher carbon concentration. The saturation of hot pressed magnets increased sharply with increasing carbon levels, exceeding 12 kOe at carbon concentrations of 9% or higher. The X-ray diffraction pattern of the annealed Nd ₁₆ Fe ₇₅ C ₉ ribbon powder is a = 0.8803 nm and c =
1. Tetragonal system with lattice parameter of 2010 nm 2-
The 14-1 phase showed strong strength. The observed diffraction is Nd ₂
By comparing with the calculated pattern of Fe ₁₄ C, 2
It was found that the -14-1 phase is the main phase, but that phase does not always exist. In addition to the possibility that a small amount of the 2-17 phase is present, iron (α-
There are also signs that Fe) is present.

Α-Fe and 2- in these alloys
The presence of phases such as 17 is more apparent by adjusting the neodymium concentration while maintaining high carbon levels of 9% and 10%. Neodymium level 16%
Up to about 17%), the coercivity of these hot pressed magnets decreased and the X-ray diffraction pattern of the reannealed ribbons showed the presence of the 2-17 phase. Neodymium levels below 16% (about 14
%), The coercivity also decreased. Such a decrease may be due to α-Fe.

The demagnetization properties of the Nd _{13.75 + X} Fe _80.25-X C ₆ and Nd ₁₆ Fe _78-y C _{6 + y} alloys of the present invention are shown in Table 2 below.

[0032]

[Table 2]

Three hot pressed magnets with high coercivity (≧ 12 kOe) were die upset forged using the process parameters described (see Table 3 showing composition). The demagnetization curves for the three die upset forged magnets and their hot pressed precursors are shown in FIG. In each case, die upsetting increased the remanence to exactly over 40%. More importantly, the coercivity of these die upset forged magnets makes it possible to obtain significantly higher energy products than those with lower neodymium and carbon concentrations (see Example 2). Want).

[0034]

[Table 3]

In accordance with the method of the present invention, a rapidly solidified composition of rare earth elements, iron (or iron and cobalt), and carbon (or carbon and boron) is hot worked to obtain a fully dense, finely grained composition. Form an object. The fine-grained material is processed to a magnetic degree of alignment such that the magnets are magnetically anisotropic. Hot working means hot pressing, hot die upsetting, extruding, hot isostatic pressing, or rolling, as long as a specific hot worked microstructure is obtained as a result. Generally, if the hot worked process consists of more than one step, such as a combination of hot process and die upset forging, it is necessary to perform an intermediate cooling step when performing all steps. Not.

For a given composition, a method of rapid solidification, and a method of rapid solidification and hot working, the magnetic phase Re ₂ ™ with a small portion whose resulting microstructure consists essentially of grain boundary material.
Controlled and performed to consist of ₁₄ C _X B _1-X . Hot working aligns fine, platelet-like particles consisting of a major phase in which the c-axes of the particles are aligned and the resulting product is magnetically anisotropic. The melt-spun (rapidly solidified) material is preferably amorphous, or very fine granules with an average particle size of about 40 nm or less are suitable. Flattened particles were obtained after severe hot working. It is preferred that their largest dimension is on average about 1000 nm or less.

The overall composition of the anisotropic magnet of the present invention is 50.
Preferably, it consists of ˜90 atomic% iron, 6-20 atomic% neodymium and / or praseodymium, and 0.5-18 atomic% carbon or carbon and boron. It is particularly preferable that the content of neodymium and / or praseodymium is 13 to 17 atomic%, and the content of carbon is 6 to 12 atomic%. The composition formula of RE ₂ TM ₁₄ C _X B _1-X having a tetragonal structure in harmony with these ranges is as follows. That is, RE is neodymium and / or praseodymium, or a mixture of these rare earth elements and other rare earth elements, provided that the content of the other rare earth elements is about 40% or less of the total content of the rare earth elements. To do. TM is iron or a mixture of iron and cobalt, and X is a value in the range of 0.2 to 1.0. Cobalt may make up about half of the TM content of the alloy.

The hot-worked anisotropic magnet of the present invention can be finely pulverized into an anisotropic magnetic powder for bonded magnets. The finely ground powder is mixed with an epoxy resin or other suitable binder, magnetically aligned and further pressed or molded. The resin, if appropriate, cures when heated.

[Brief description of drawings]

FIG. 1 is a SEM (scanning electron microscope) photograph of the metallographic structure of the fracture surface of a die upset forged Nd _13.75 Fe _80.25 C ₆ magnet. FIG. 2 is an SEM photograph of the metallographic structure of the fracture surface of the die upset forged Nd _13.75 Fe _80.25 C ₆ magnet. FIG. 3 is a graph of three types of process parameters measured during hot pressing of a ribbon of molten yarn having a composition of Nd ₁₆ Fe ₇₈ C ₉ . FIG. 4 consists of three graphs of process parameters measured during die upset forging of a hot pressed precursor having a composition of Nd ₁₆ Fe ₇₈ C ₉ . FIG. 5 is a demagnetization curve of a magnet that was hot pressed and then die upset forged. The composition is shown in each panel under each curve.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01F 1/08 A 7371-5E

Claims (5)

[Claims] 1. Neodymium; praseodymium; or a mixture of neodymium and / or praseodymium with one or more other rare earth elements, the proportion of which is less than 40% of the total rare earth elements. 1
An anisotropic permanent magnet containing one or more rare earth elements, iron or a mixture of iron and cobalt, carbon and optionally boron: tetragonal crystalline phase R
Hot working of E ₂ TM ₁₄ C _X B _1-X (RE is one or more of the rare earth elements, TM is iron or a mixture of iron and cobalt, and the value of X is 0.2 to 1.0) Anisotropy, characterized in that it comprises a major phase of fine grains aligned in a flat phase and a minor grain boundary phase, and the flat grains have an average maximum dimension of 1000 nm or less. permanent magnet. 2. Iron of 50 to 90 atomic%, 6 to 20 atomic%.
Neodymium and / or praseodymium, and 0.5 to 1
The anisotropic permanent magnet according to claim 1, which is composed of 8 atom% of carbon. 3. X is 1 and the content of neodymium and / or praseodymium is in the range of about 13 to 17 atomic%,
The anisotropic permanent magnet according to claim 2, wherein the carbon content is about 6 to 12 atom%. 4. The method for producing a fine-grained anisotropic permanent magnet according to claim 1, comprising 40 to 90 atomic% of iron, 6 to 20 atomic% of neodymium and / or praseodymium, and 0.5 to Rapidly solidifying amorphous or very fine-grained particles of composition of 18 atomic% carbon are hot pressed at high temperature to solidify the particles to form a main phase with one or more grain boundary phases. Forming a substantially fully densified material consisting essentially of aligned and flat particles, and characterized in that the largest dimension of said particles is on average less than 1000 nm. Method for manufacturing anisotropic magnet. 5. The method for producing a fine-grained anisotropic permanent magnet according to claim 1, wherein the initially formed amorphous or very fine spherical-grained microstructure has a diameter of about 40 nm. Rapidly solidified particles having the following microstructure and having a composition of 40 to 90 atomic% iron, 6 to 20 atomic% neodymium and / or praseodymium, and 0.5 to 18 atomic% carbon at high temperature It is hot pressed to solidify to form a substantially fully densified product, which is further hot worked at elevated temperature by applying pressure in the same direction as the direction of hot pressing to be aligned and substantially flat. Comprising producing a microstructure consisting of said main phase of the particles and one or more grain boundary phases, and said particles having an average maximum dimension of 1000 nm or less, the resulting product being anisotropic permanent. Showing the properties of a magnet and And having a direction of parallel selective magnetization in the direction of the pressure applied during the during processing, manufacturing method of anisotropic permanent magnets of the fine particulate.