DE2050688A1 - Process for producing a rare earth permanent magnetic material - Google Patents

Description

Western Electric Company, Incorporated Chin, GY 6-28-5-18 Hew York, NY 10007, V.St.A.

Process for producing a rare earth permanent magnetic material

The invention relates to high coercivity, high 3H product permanent magnetic materials which _{include copper-thinned Co 1} -Ce and related compositions of other stoichiometry, as well as those compositions which contain different diluent media and "anions".

In Applied Physics Letters, Volume 12, p. 361 (1968) a number of permanent magnetic materials are described which contain rare earths. As described there, this work is based on the knowledge that fine particles of a number of compounds such as Co ₁ -Ce have excellent permanent magnetic properties in particle form, but lose these properties when they are produced as a solid body. The article also describes the dilution of such compounds with certain non-magnetic elements such as copper. The material modified in this way can be cast in solid form and retains the permanent magnetic properties.

As these compositions coercive force values and energy products that were previously only achieved by the expensive composition PtCo, this article has great things Experience interest. Subsequent work then related

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to the development of methods for the production of thin layers and for at least experimental use in numerous Devices.

Attempts to further improve the properties of these compositions make use of the fact that the copper-rich precipitates in the cast blank are large (on the order of 10 micrometers). The size of similar areas was reduced by a homogenization procedure in which a high temperature heat treatment close to the melting point, followed by a put quench in oil, is provided; See Permanent Magnets and Their Application, John Wiley and Sons, Inc. (1962), p. 70. There, such a method was applied to a different copper-containing permanent magnet Material was applied, resulting in an improvement in magnetic properties. This procedure resulted in his Application to the rare earth containing compositions actually lead to a reduction in the average Size of the failed copper-rich areas, but did not lead to a significant improvement in the magnetic Properties.

According to the invention, there is now a considerable improvement in the magnetic properties when subjected to a heat treatment at high temperatures of the rare earth-containing compositions of interest here, such as these in the above

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a critical slow cool-down program instead of rapid quenching, which follows The size reduction of the copper-rich areas is not significantly different compared to that which is located with an identical high temperature heat treatment followed by a quick quench. While probably this improvement - at least in part - can be attributed to homogenization, the kinematics of the System to require a minimum cooling rate in order to enable the introduction of suitable nucleation centers- " chen. The improvement according to the invention is only achieved with such a cooling rate.

The method according to the invention is specified in the claims and explained in detail below with reference to the drawings; show it:

Fig. 1 in double coordinate scales the magnetization B and the magnetization minus the applied field strength BH, in Gauss, about the listed on the abscissa λ transmitted field strength of the applied field H, in Oersteds, showing the relation here between both untreated compositions as also for compositions treated according to the invention and

2 shows the magnetization B in Gauss over the energy product BH plotted on the abscissa, in Gauss times

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Oerstedt to illustrate the relationship between these for treated and untreated materials.

The results of the invention are generally of the entire class of previously reported transition metal magnetic materials and. "Associated with rare earths. The more significant of these materials are generally described using intermetallic compounds that have the approximate stoichiometry Μ, -RE. the "Cation" position denoted by M is primarily or exclusively of one or both of the elements cobalt and Iron ingested. Dilution media that have been found to be suitable are copper, nickel and aluminum. Useful Properties are obtained when the dilution in the 14th place is between two and 98 atomic percent. The rare ones Earths (RE) are samarium, cerium, gadolinium, praseodymium, lanthanum, yttrium, neodymium and holmium; they can be individually or in any Combination can be used. The highest coercive forces were found with samarium, cerium, and praseodymium in that order obtain. This rare earth skid is therefore preferred. Mixtures which are found to be particularly advantageous include cerium and samarium, as well as any two or more of them three preferred items.

While the M ₁ -RE stoichiometry and approximations thereof are preferred, useful magnetic properties have also been reported for the HLRt-RE stoichiometric composition

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been; therefore, the magnetic contributions may come from compositions that go up to this value ^{with their "cation 11" content.}

The wide compositional range can therefore be expressed by the general formula

Mean therein

χ a value between about 5 and about 8.5 y the atomic fraction of 0.02x to 0.98x M at least one of the elements cobalt and iron M ¹ one or more of the elements copper, nickel and aluminum

RE as defined above.

From the standpoint of coercive force, best results are obtained with a value for y between about 0.1x and 0.8x. As also indicated, the preferred value of χ is about 5. The limits for χ and y are largely experimental, but can be expanded based on the discussion above. The \ limits for χ refer to the stoichiometric range, which is known to make a magnetic contribution in the undiluted systems. When y increases beyond a certain limit, the magnetic saturation decreases and the coercive force increases. The M ¹ containing compound is required to maintain coercive force and the range for the y values is mainly dictated by this consideration.

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The above work in Applied Physics Letters, 1968, was based on the assumption that the massive ensemble was theirs permanent magnetic properties of a polyphase structure, in which effectively isolated small areas of the magnetic composition. Subsequent tests have largely verified this assumption. Accordingly it is while the above description reproduces the essential part of the composition exactly, possible to make modifications, which provide isolated areas of magnetic "connection".

The known manufacturing conditions for the compositions concerned have been described elsewhere. In general, the elementary materials or other reactants, the ar desired composition lead, mixed and heated to the melting point under protective gas. That Protective gas, which can be argon, nitrogen, or helium, is used to oxidize the rare earth elements in particular to prevent. An arc fusing apparatus was often used for fusing, and therefore cooling was rapid.

According to the invention, the significant process sequence comprises a high-temperature or homogenization heat treatment, followed from a "slow" cooling. This invention Process steps can be carried out after the initial reaction or at any later time. During the Influence of any heat treatment at low temperatures before the process steps provided according to the invention

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does not show any consequences, custom-made magnetic properties can be obtained if appropriate Heat treatments at low temperatures follow the sequence of steps according to the invention.

The temperature range over which the VafahrensBchrittfolge runs, going from about 800 ⁰ C to about 5 ⁰ C below the melting point. While temperatures below 800 ⁰ C v may be irksam /, the kinematics of the system is such that excessively long heat treatment may be required. The upper limit is only intended to provide a safety margin from the melting point. It has no other use.

The heat treatment time over the prescribed temperature range is between about one minute and about 1000 minutes. Measurable results can be achieved with any combination of time and temperature can be maintained within the prescribed ranges. However, deliver shorter times - as expected is - more pronounced results in conjunction with the higher temperatures within the range.

The heat treatment described above leads to homogenization, i. H. to a size reduction of the copper-rich Areas in the final product. However, the improvement in magnetic properties on which the invention is based is only available if a certain critical cooling of

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(the minimum value of the annealing region) is reduced to a temprature of about 50O ⁰ C or less is performed at a temperature of at least 800 ⁰ C. Above this range, the cooling rate ranges from 0.01 ⁰ C per second to 100 ⁰ C per second, and a preferred Abkuhlgeschwindigkeitsbereich is between about 0.1 ⁰ C per second and about 10 ⁰ C per second. Exceeding the rate of about 100 ⁰ C per second to an appreciable extent is a Abschrekkung the same, and then obtains no significant improvement of the magnetic properties more. Cooling at a rate that is appreciably lower than 0.01 ^° C. per second does not lead to adverse effects, but is impractical from an economic point of view and can moreover lead to significant agglomeration of the magnetic areas or non-magnetic areas, which leads to a there is a marked loss in coercive force. The preferred limits for the cooling rate are based on optimizing the magnetic properties and on economic considerations.

It has been indicated that heat treatment at low temperatures has heretofore been beneficial to the compositions concerned was applied. While it is believed that optimal results are obtained through precise control of temperature and Time can be obtained at high temperatures, as has been explained in the previous section, the at lower temperatures, reduced kinetics allow more accurate targeting of the properties. Accordingly, a

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Tempering at low temperatures in the range from about 30O ⁰ C to about 50O ⁰ C (or the final temperature of the previous cooling cycle) lead to a certain improvement in the coercive force. In general, the times effective for this tempering at lower temperatures are between a few minutes and a day. A setting that results from a treatment at low temperatures after the high temperature treatment can also be achieved within the range from a few minutes to about a day, for example at 400 ^° C. The results tend to be predictable and due to a phase failure mechanism.

The form of the relationship shown in FIGS. 1 and 2 applies to all of the compositions in question. The specially reproduced coordinate values are of the composition Co * RCuFe ₀ cCe. In FIG. 1, the parameters are plotted in the alternative coordinate units for B and BH. The former curves are solid, while the latter \ are drawn in dashed lines. The lower curve corresponds to in each case a cast blank which melted at present, the special case in the arc and was subsequently subjected to a four-hour low temperature tempering at 400 ⁰ C. The remaining induction for this special sample was about 5000 Gauss as indicated. The coercive force was about 3500 oersted. The upper curves, the solid and dashed lines, were made on the basis of measurements on the identical composition, but the

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has been subjected to a high temperature treatment at 1000 ^° C. for 20 minutes, followed by cooling at a rate of 1 ^° C. per second to a temperature below about 500 ^° C. In this particular case, for comparison purposes, this sample was also subjected to a subsequent four-hour low-temperature heat treatment at 400.degree. The residual induction increased to a value of about 6000 Gauss, while the coercive force increased to about 5600 Oersted. The value of ^ Hq (defined as the value of H at BH = O) increased from about 5500 to about 7300 Oersted by the high temperature heat treatment.

The two curves in Fig. 2 also show the ratios for the same composition, Co-, ^ CuFeQ cCe. the Coordinate values are as written. The first curve has a maximum at an energy product of around 5 million Gauss times Oersted, it corresponds to the cast blank, while the second curve has a maximum at around 9 million Gauss times Oersted has the same composition, but after the high-temperature heat treatment has been carried out, as this has been explained in connection with FIG. For comparison purposes, both samples were made the same Subsequent treatment at low temperatures.

While the individual coordinate values vary in a known manner from composition to composition within the

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change the affected area, the shape of the curves shown remains unchanged in both figures. In all cases the maximum values of the residual induction, the coercive force and the energy product increase when the high temperature V / arm treatment is applied according to the invention.

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Claims (7)

- 12 patent to sp rtich e 1. A method of making a permanent magnetic material of approximate composition where M equals at least one of the elements cobalt and iron M ^{1 is} equal to at least one of the elements copper, nickel and aluminum RE equals at least one of the elements samarium, cerium, gadolinium, praseodymium, lanthanum, yttrium, neodymium and holmium, χ equal to a value between about 5 and about 8.5 y equal to the atomic fraction from 0.02x to 0.98x, in which the ingredients are mixed in the composition required for the material, the mixture into a body is brought into the desired shape and the body is fired and subsequently subjected to a heat treatment, thereby characterized in that the heat treatment in the temperature range from a temperature of about 5 ⁰ C below the melting point the composition is carried out up to 800 ^° C. for a period of time from 1 minute to 1000 minutes and that the heat-treated body with a speed between 100 ⁰ C per second and 0.01 ⁰ C per second over the temperature range from the heat treatment temperature to at least 500 C is cooled. 1 0982Q / 1 345 2. The method according to claim 1, characterized in that a cooling rate between 1O ⁰ C per second and 0.1 ⁰ C per second is used. 3. The method according to claim 1 or 2, characterized in that the composition is subsequently subjected to tempering at temperatures ranging from about 300 ⁰ C to the end temperature of the cooling process. 4. The method according to claim 3 »characterized in that the tempering is carried out for a few minutes to about 24 hours will. 5. The method according to any one of claims 1 to 4, characterized in that a composition is assumed for which the ratio of the total M and M ¹ ions present to the RE ions is between 5 and 8.5. 6. The method according to any one of claims 1 to 5, characterized in that that the RE ions of cerium, samarium and their mixtures are selected. 7. Magnetic body, characterized by its production according to the method according to one or more of the preceding claims. 109820/1345 Blank page