JPH0739618B2 - Alloying of low level additives to heat processed Nd-Fe-B magnets - Google Patents

Description

Detailed Description of the Invention

FIELD OF THE INVENTION This invention relates to alloys of permanent magnets and methods of making these alloys. In particular, the invention relates to permanent magnet alloys having a high magnetic maximum coercivity at room temperature, for example EP-A-01.
No. 33758, a method for forming a magnetic alloy as extended to the preamble of claim 1.

[0002] Rapidly solidified neodymium, iron, boron (Nd-
The Fe-B) alloy produces an essentially isotropic permanent magnet material with high magnetic force, the main component of which is a tetragonal system.
It is the Nd ₂ Fe ₁₄ B phase. Ribbons or flakes produced by the rapid solidification process, i.e., melt spinning, can be heat-processed by pressing by isostatic pressing at elevated temperatures, giving them essentially the same magnetic properties as the original ribbon. Produces a full-density, ie hot-pressed, magnet that has. Further processing, specifically, die-upsetting (d
ie-upsetting) results in approximately 50% higher remanence (Br) and approximately 200% higher energy product compared to hot-pressed precursors.
ucts) [(BH) max] produces magnetically-matched magnets.

The process of magnetic matching achieved during die-upset has been described as a mechanism of diffusion slip which requires a small grain size of approximately 50 nm (nanometers) and a ductile grain boundary phase. Only a combination of small grain size and ductile grain boundary phase allows the c-axis orientation of grains along the pressing direction to occur during plastic deformation of the alloy. Since the c-axis is also the preferred orientation of magnetization,
The magnetic properties are enhanced along the pressing direction of the die-upset magnet.

Larger crystalline particles do not respond as well to smaller particles to the strain induced during die-upsetting, so that larger particles remain in a random orientation,
It is detrimental to the alloy as it reduces the remanence and energy product of the alloy. In addition, large particles, whether magnetically aligned or not, are also associated with a lower maximum magnetic coercivity in these materials. Therefore, it is desirable to use lower processing temperatures and shorter residence times at those temperatures to limit the growth of crystalline particles within the alloy during the hot working stage.

Another way to limit the growth of crystal grains is to introduce impurities or additives that collect at grain boundaries into the alloy. If the additive is a foreign substance to the 2-14-1 (referring to Nd ₂ Fe ₁₄ B) phase existing inside the crystal grain, the additive is a grain boundary as the size of the crystal grain grows. Migrate (should migrate, resulting in slow grain boundary migration and thereby slowing the growth of crystal grains.

In order to give a non-negligible effect on the intrinsic properties of the Nd ₂ Fe ₁₄ B phase, a relatively large concentration, ie,
Approximately 10 atomic percent of the substituents are typically required, but much smaller additive concentrations, ie approximately 1 atomic percent, have a considerable impact on the hard magnetic properties of the magnet. The reason is that the grain boundary phase, which plays a crucial role in the mechanism of grain growth and domain wall pinning, is selectively occupied by the additives that locally produce high additive concentrations inside the alloy. This is because that.

Previous work has shown that die-upset Nd-Fe- whose composition is given as Nd ₁₄ Fe ₇₇ B ₈ M _1.
This has been done for the effect of low level additives in B magnets. This previous work showed that gallium (in this case M = Ga in the above composition) has a maximum increase in the maximum magnetic coercivity, ie approximately 2 compared to the composition without additives (in this case M = Fe).
It was concluded to give 1.1 kilo Oersted. The latter exhibited a minimum magnetic maximum coercivity of approximately 7.6 kilo Oersteds. Other additives also increased the maximum magnetic coercivity, but to a lesser extent than gallium. However, the remanence reported for all of these magnets was 15 percent lower than that of magnets without additives.

The features of the method for producing an alloy with permanent magnet properties at room temperature are indicated by the features indicated in the characterizing part of claim 1.

To the knowledge of the current state of the art, it is concluded that the Nd ₂ Fe ₁₄ B type 1 magnet additive must be added to the alloy at the time of melting and casting of the ingot prior to melt spinning and heat-processing. . However, the method of the present invention introduces additives into the magnet alloy during the hot pressing stage, thus making it possible to adjust the additives and their concentrations during this final stage. The relatively low temperatures used for heat-processing, as compared to either the melt-spinning method or the sintering method, are probably the neodymium-rich particles that are believed to have the greatest effect on the growth of the crystalline particles and thus on the maximum magnetic coercivity. It may help limit the migration of additives to the world.

Therefore, what is needed is a method for making permanent magnet alloys in which additives are introduced into the alloy prior to the heat-processing step.

It is an object of the invention to provide a Nd ₂ Fe ₁₄ B type magnet.

It is another object of this invention to form such a magnet by the method of introducing a metal additive into the magnet just prior to heat-processing.

In accordance with the preferred embodiment of the present invention, these and other objects and advantages are achieved as follows.

Applicants have diffusion-alloyed the metal additives into the magnet alloy during hot forging, thus improving the additive and its concentration, and thus the magnetic properties, during this final processing step. Be the first to adjust. Neodymium, whose relatively low temperatures used in hot working as compared to other techniques such as melt spinning or sintering, can have the greatest effect on the growth of crystal grains and thus also on the maximum coercivity of magnetism. -Helps limit the migration of additives to rich grain boundaries. Prior to hot pressing the alloy, the elemental additives are introduced into the alloy by agitating the fine powder of the additive into a milled, rapidly solidified ribbon. Pure elements were used, but it is envisaged that compounds may also be used, as well as other techniques of adding additives, such as plating or spraying.

It was determined that the eleven metal element additives were completely diffused through the Nd-Fe-B magnet, thereby obtaining a homogenous magnetic alloy throughout everywhere. With these additives, cadmium, copper, gold, iridium, magnesium, nickel, palladium, platinum,
Ruthenium, silver and zinc. Other elemental additives have also been tested, but they tend to diffuse only short distances (approximately 100 micrometers) and / or react with the Nd-Fe-B matrix to form intermetallic phases. Only formed.

The first inventive feature of the present invention is Nd-Fe-B.
Through magnets about 0.1 to about 10 weight percent
Diffusion-alloying zinc at concentrations in the range of weight percent. Two other powder additives, copper and nickel, both at concentrations of approximately 0.5 weight percent, were used to
It was also successfully diffused-alloyed into the d-Fe-B alloy. The resulting magnetic alloy is characterized by having enhanced magnetism compared to Nd-Fe-B magnets formed by conventional methods.
For example, the addition of each of these elements to a rapidly solidified ribbon increased the maximum magnetic coercivity of the alloy by 100 percent when die-upsetting the magnetic alloy.

Other objects and advantages of the present invention will be better appreciated from the following detailed description of the invention.

The invention and its implementation will be described hereinafter with particular reference to the accompanying drawings.

_Grinded ribbon flakes of rapidly solidified material with approximately the following composition, Nd _13.7 Fe _81.0 B _5.3, were used as starting materials. The rapidly solidified ribbon was formed using conventional techniques. First, a mixture consisting of neodymium, iron and boron is formed, then each component is melted into a homogeneous melt, and finally the homogeneous mixture is formed into an alloy ribbon having an extremely fine crystal microstructure. Quenched at a rate sufficient to form. Hot pressed magnets grind these ribbons, add the required amount of metal additives to the milled ribbons, and then add the resulting mixture in vacuum to about 750-800.
Formed from these ribbons by rapid heating to 0 ° C. and pressing by isostatic pressing at approximately 100 megapascals. The die-upset magnets were prepared by adding these hot pressed precursors in a large die at 750 ° C.
It was prepared by hot pressing until the initial height of the precursor was reduced by approximately 60 percent. Graphite dies were used in both thermal processing steps and boron nitride was used as a lubricant for the die walls.

The magnet was sliced (sliced) using a high-speed diamond saw, and (1) a cross section for microscopic analysis and (2) a cube of 50 mg for demagnetization measurement by a sample vibrating magnetometer (VSM). made. All samples were pre-magnetized in a pulsed magnetic field of 120 kilo Oersted (kOe), then V
The magnetic force was measured using the SM in both directions parallel and perpendicular to the pressing direction. The geometry-based correction of the sample was performed with a self-demagnetization factor of 1/3. Unless otherwise specified, all values of remanence (Br), magnetic maximum coercive force (Hci) and magnetic energy [(BH) max] given throughout this specification are measured values in the press direction and parallel direction. Refers to. The density of the alloy was also measured using the standard water displacement method.

The powdered elemental additives used were characterized by the size of the particles. That is, zinc was 75 micrometers or less, copper and manganese were 45 micrometers or less, and nickel was 10 micrometers or less. The powdered elemental additives were individually added (in weight percent) to rapidly solidified and ground Nd-Fe-B ribbons. Thus, for example, 1 weight percent zinc additive corresponds to a mixture containing about 1 weight percent powdered zinc and 99 weight percent ground Nd-Fe-B ribbon.

Die-upset Nd-Fe-B magnets were made from hot-pressed precursors containing various elemental additives as described in the above method. The densities and magnetism of the die-swept zinc-containing magnets are summarized in Table I below.

TABLE I Die-upset Nd-Fe-B magnets made from hot-pressed Nd-Fe-B precursors containing diffusion-alloyed zinc at density and magnetism (magnetism parallel and perpendicular to the press direction) position. (Measured) Zinc density Br (BH) max Hci wt% g / cc kG MGOe kOe 0.0 7.57 12.1 (3.5) 30.9 (2.3) 7.9 (10.2) 0.1 7.62 12.3 (3.4) 34.1 (2.1) 10.9 (9.8) 0.2 7.60 12.2 (3.6) 33.4 (2.5) 14.0 (11.6) 0.5 7.58 12.0 (3.6) 32.4 (2.2) 15.3 (11.2) 0.8 7.57 11.9 (3.7) 31.4 (2.6) 15.8 (12.6) 1.0 7.60 11.7 (4.1) 30.6 (3.2) 13.6 (12.8) 2.5 7.58 11.5 (3.8) 25.6 (2.6) 7.4 (9.2) 5.0 7.55 11.0 (4.2) 22.4 (2.7) 7.8 (7.7) 10 7.56 9.2 (3.9) 9.7 (0.8) 3.7 (2.1)

From the results shown in Table I, the optimum amount of zinc additive in the Nd-Fe-B precursor was about 0.5-0.8 weight percent, which is shown in Figures 1A, 1B, 1C and 2A. And 2
This corresponds to the result shown in B. 1A, 1B and 1C illustrate the relationship between various magnetic properties and the weight percentage of zinc in a die-upset Nd-Fe-B magnet. In particular,
FIG. 1A shows a plot of magnetic maximum coercivity (Hci) vs. weight percent zinc; FIG. 1B shows remanence (Br) v.
FIG. 1C shows the energy product [(BH) max] vs. weight percent zinc relationship.
For comparison, the corresponding magnetic properties of the zinc-free Nd-Fe-B magnets are shown by the dashed lines in each figure.

Nd containing about 0.5-0.8 weight percent zinc
-In the case of Fe-B magnet, the maximum magnetic coercive force of the magnet was 15.3kOe and 15.8kOe, respectively, as shown in FIGS. . At higher concentrations, the maximum magnetic coercivity gain (increase) was reversed and all magnetic properties were significantly degraded when about 10 weight percent zinc was added. Magnets containing 0.5 weight percent zinc and magnets without zinc have essentially the same remanence Br = 12 kG and the same energy product (BH) max = 3
Had 1-32 MGOe.

Further, as shown in FIGS. 2A and 2B,
The inflection point of the degaussing curve occurred in a reversing magnetic field which increased proportionally in the zinc-containing magnet. 2A and 2B show demagnetization curves for a die-swept Nd-Fe-B magnet.
FIG. 2A is a magnet containing about 0.5 weight percent zinc, FIG.
B is a magnet containing no zinc. The measurement was performed parallel (par.) And perpendicular (perp.) With respect to the press direction. Again, for comparison, Nd-Fe-B containing 0.5 weight percent zinc.
The broken line corresponding to the measured value of the maximum magnetic coercive force of the magnet in the parallel direction is inserted.

FIG. 3 is for three different die-upset Nd-Fe-B magnets, each containing 0.5 weight percent of different additives: copper (solid line), nickel (dashed line), manganese (dotted line). A demagnetization curve is illustrated. The measurements were made parallel to the press direction. As in the case of zinc, the maximum magnetic coercive force of the die-upset Nd-Fe-B magnet was 14.0 kOe for each when adding about 0.5 weight percent of copper and nickel powder.
And increased to 12.1 kOe. In contrast, when manganese powder is used as an additive, the maximum magnetic coercive force Hci = 12.
The 7kOe had no noticeable effect. The copper-containing magnet had a larger remanence, Br = 12.7 kG, than the magnet containing zinc, nickel or manganese. The remanence of the latter was roughly equal to 12 kG. However, the most likely cause of this was variation in pressing conditions and did not appear to be due to additives.

Using electron probe analysis to locate the additive elements in the Nd-Fe-B magnet alloy, heat containing about 0.5 weight percent each of zinc, copper, nickel and manganese- The polished surface of the wrought sample was inspected. It was determined that almost all of the zinc powder had reacted with the ribbon matrix. However, some zinc was present between the ribbons, that is, inside the grain boundary phase, with a composition of Zn ₄ Nd ₃₁ Fe ₆₅ . Also again
Zinc is a less obvious intermetallic phase in the boundary region.
It may have existed in the metallic phase). However, most of the zinc diffused into the ribbon, or the crystalline particles themselves. Still, because the additive was small,
The ribbons or particles are believed to consist primarily of the tetragonal Nd ₂ Fe ₁₄ B phase.

Copper and nickel diffused throughout the magnet as did zinc. However, the diffusion of manganese is 10% of that of the original crystal grains of the powder additive even when the amount added is about 0.5 weight percent.
It was limited to the area within 0 to 200 micrometers. Without the ability of diffusion, manganese was unlikely to affect the maximum magnetic coercivity of the magnet.

The zinc concentration varied from ribbon to ribbon and showed a strong correlation with the neodymium concentration. Among the ribbons rich in neodymium, the zinc concentration was higher. The variation in neodymium concentration was probably due to the manufacturing process. For some reason, this pattern was also observed in magnets without zinc. Since zinc diffuses into the neodymium-rich intergranular boundaries, and neodymium-rich ribbons should account for a large volume percentage of this boundary phase, in the case of zinc, a larger percentage of these ribbons. It is thought to be gathered in.

It should be noted that gallium, which gave the largest increase in the maximum magnetic coercive force when added to the ingot, was difficult to obtain as a powder and was difficult to handle as a powder because of its low melting point. . However, early tests with coarse gallium powder showed that although gallium diffused close to the ribbon, most gallium was confined as an intermetallic phase, and just as with manganese, the addition of gallium did not lead to alloying. It was revealed that the maximum magnetic coercive force was not changed significantly.

The diffusion-alloying method is performed by hot working Nd-Fe-B.
It has been shown to be an effective way to introduce low levels of additives into magnets. Although similar maximum magnetic coercive forces were previously obtained by adding elements to the initial ingot, the method of diffusion-alloying during hot working has made the final chemistry of the magnet more detailed. In short, it allows grain boundaries to be determined during the final processing stage. Elements such as zinc, copper, and nickel that diffuse into the matrix enhance the maximum magnetic coercivity by 100 percent in die-swept Nd-Fe-B magnetic alloys. Elements that did not diffuse easily, such as manganese, had little effect on the maximum magnetic coercivity. At the optimum level of about 0.5 to 0.8 weight percent, the additive did not reduce the remanence or magnetic energy product of the alloy.

Although the invention has been described with the aid of preferred embodiments, it will be apparent that other forms can be adopted by those skilled in the art. For example, using compound powders instead of elemental powder additives, or eleven elements believed to be completely diffused into Nd-Fe-B magnetic alloys,
That is, in order to replace any of cadmium, copper, gold, iridium, magnesium, nickel, palladium, platinum, ruthenium, silver, zinc with another, or to promote the diffusion into the grain boundaries of the alloy. Modifying heating and processing temperature etc. Furthermore, Nd-Fe-B alloys rapidly solidified by using techniques such as solution chemical plating, which results in homogeneous ion deposition of additives on the surface of individual ribbons, or plasma spraying or metal spraying. A method of introducing an additive into is also foreseen. Therefore, the scope of the invention should be determined solely by the appended claims.

[Brief description of drawings]

1A, 1B and 1C are diagrams illustrating various magnetic properties related to the weight percent of zinc in a die-upset Nd-Fe-B magnet, respectively.

2A and 2B are diagrams illustrating demagnetization curves for the following two die-upset magnets, respectively: FIG. 2A: Nd-containing about 0.5 weight percent zinc.
Fe-B alloy; Figure 2B: Nd-Fe-B alloy without additives. However,
The two curve values are parallel (par) and perpendicular to the press direction, respectively.
Measured along both directions of (perp).

FIG. 3 illustrates the degaussing curves measured parallel to the press direction for three die-upset Nd-Fe-B magnets, each containing about 0.5 weight percent additive.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication location H01F 41/02 G 8019-5E (56) Reference JP-A-1-175705 (JP, A) Kaihei 1-196104 (JP, A)

Claims (10)

[Claims] 1. A method for producing an alloy having the properties of a permanent magnet at room temperature, which comprises forming a mixture of neodymium, iron and boron, and melting the mixture to form a homogeneous melt. Quenching the material at a rate to form an alloy having a very fine crystalline microstructure, adding powder of the metal additive to the alloy to form a powder mixture, heating the powder mixture, and Applying pressure to the heated mixture to near full density, in each step the metal additive comprises cadmium, copper, gold, iridium, magnesium, nickel, palladium, platinum, ruthenium, silver or zinc. Either and added in an amount up to 1% by weight of the mixture, and the mixture of alloy and metal additive is heated to a temperature of 750 to 800 ° C. during the heat compression step to add the metal addition. object Is diffused in the alloy. 2. The method comprises the following step, namely, the solidified alloy has a magnetic maximum coercive force of at least 10,000 Oersted (Oe) to introduce additional magnetic anisotropy into the solidified alloy. The method for producing an alloy having the properties of a permanent magnet at room temperature according to claim 1, further comprising the step of heat-processing the solidified alloy so as to have 3. The method for producing an alloy having the properties of a permanent magnet at room temperature according to claim 1, wherein the metal additive is a powder metal containing zinc, copper or nickel. 4. The metal additive comprises 0.5 to 0.8 weight percent powdered zinc and isobaric about 1 to the heated alloy.
The method for producing an alloy having the properties of a permanent magnet at room temperature according to claim 1, characterized in that the alloy is solidified to a near-complete density by applying a pressure of 00 megapascal. 5. The solidified alloy is subjected to a time sufficient to reduce the initial height of the solidified alloy by about 60 percent so that additional magnetic anisotropy is introduced into the solidified alloy. 5. The method for producing an alloy having permanent magnet properties at room temperature according to claim 4, further comprising the step of further thermally processing the solidified alloy by pressing at about 750 ° C. 6. About 0.5 weight percent powdered copper is added to said alloy; and a pressure of about 100 megapascals isobaric to said heated alloy to solidify said heated alloy to near full density. The method for producing an alloy having the properties of a permanent magnet at room temperature according to claim 1, wherein the alloy is added in a balanced manner. 7. The solidified alloy is subjected to a time sufficient to reduce the initial height of the solidified alloy by about 60 percent so that additional magnetic anisotropy is introduced into the solidified alloy. 7. The method for producing an alloy having permanent magnet properties at room temperature according to claim 6, further comprising the step of further heat-processing the solidified alloy by pressing at about 750 ° C. 8. About 0.5 weight percent of powdered nickel is added to the alloy; and a pressure of about 100 megapulses isobaric to the solidified alloy to solidify the heated alloy to near full density. The method for producing an alloy having the properties of a permanent magnet at room temperature according to claim 1. 9. The solidified alloy is subjected to a time sufficient to reduce the initial height of the solidified alloy by about 60 percent so that additional magnetic anisotropy is introduced into the solidified alloy. 9. The method for producing an alloy having permanent magnet properties at room temperature according to claim 8, further comprising the step of further heat-processing the solidified alloy by pressing at about 750 ° C. 10. A powdered alloy of neodymium, iron and boron, characterized by having a very fine-grained microstructure, and in amounts of up to about 1 weight percent cadmium, copper, An alloy having the properties of a permanent magnet at room temperature is formed by the method according to claim 1, containing one powder metal selected from gold, iridium, magnesium, nickel, palladium, platinum, ruthenium, silver or zinc. A suitable mixture to do.