US3839102A - Permanent magnet - Google Patents

Abstract

Permanent magnet material having a high coercive force and a high residual flux density is constituted by an alloy of cerium (15 to 20 mol percent), cobalt (52 to 77 mol percent) and copper (8 to 30 mol percent). The cerium can be replaced by Cemischmetal in an amount providing the equivalent quantity of cerium. The material has a novel microstructure. The material can be prepared by melting together the ingredient materials and furnace-cooling to room temperature. Superior results are obtained with specially scheduled heat-treatments including controlled cooling rates. It is not necessary to use a fine particle magnet material.

Description

Tawara et al.

[ 4] PERMANENT MAGNET [75] Inventors: Yoshio Tawara; Harufumi Senno,

both of Osaka, Japan [73] Assignee: vMatsushita Electric Industrial Co.,

Ltd., Osaka, Japan [22] Filed: Nov. 10, 1970 [21] Appl. No.: 88,479

Related U.S. Application Data [62] Division of Ser. No. 775,651, Nov. 14, 1968.

[30] Foreign Application Priority Data Mar. 18, 1968 Japan 43-18154 [52] U.S. Cl. 148/102, 148/31.57 [51] Int. Cl. Hlf l/02 [58] Field of Search 148/100, 101, 102, 103,

[56] References Cited 0 UNITED STATES PATENTS 3,211,592 10/1965 Masumoto et al. 148/121 [4 1 Oct. 1, 1974 3,350,240 /1967 Higuchi et al. 148/121 3,421,889 1/1969 Ostertag et a1. 75/170 3,424,578 l/l969 Strnat et al. 75/213 3,523,836 8/1970 Buschow et al 148/31.57 3,546,030 12/1970 Buschow et al 148/3l.57 3,560,200 2/1971 Nesbitt et al. 75/122 Primary Examiner-Walter R. Satterfield Attorney, Agent, or Firm-Wenderoth, Lind & Ponack 5 7 ABSTRACT Permanent magnet material having a high coercive force and a high residual flux density'is constituted by an alloy of cerium (15 to mol percent), cobalt (52 to 77 mol percent) and copper (8 to mol percent). The cerium can be replaced by Ce-mischmetal in an amount providing the equivalent quantity of cerium. The material has a novel microstructure. The material can be prepared by melting together the ingredient materials and furnace-cooling to room temperature. Superior results are obtained with specially scheduled heat-treatments including controlled cooling rates. It is not necessary to use a fine particle magnet material.

3 Claims, 4 Drawing Figures sum 1 or 4 PAIENTEnnm nan PATENTED 0ST 1 I974 3.839.102 sum 2m 4 IIYISI (30) e010; aA roJaoo ogsupnuy sumaord m u50 oumu mc oou oow ooi

uaungseds go alnqeledmaq PAIENTEBDCT um sum w is I I 1 Q1 0) e910; aA'golaog 1 2 PERMANENT MAGNET is a Ce-rich metal and is widely used in industry be- This application is a division of Ser. No. 775,651, cause of the lower cost than that of pure Ce metal. As filed Nov. 14, 1968. is well known, the Ce-mischmetal contains, as a main This invention relates to a permanent magnet mateingredient, Cc. rare earth metals such as La, Pr and Nd rial characterized by a high coercive force and a high in a small amount, and other metals such as Fe, Mg and residual flux density and to a manufacturing method A] m a y Small amountth f Ce-mischmetal, in the present specification, refers to It has been suggested that the alloy composed of a an alloy havmg composltlon whims to Table Table 1 Ce La Pr Nd other rare Fe Mg Al earth metal Ce-mischmetal 40-94 3-30 01-4 0.l-l.5 0.ll.0 0.1-2.0 0-1.0 0-I.0

rare earth metal and a transition metal such as YCo,-, is The alloy specimens of the present invention have an a promising candidate for a fine particle magnet mateinteresting microstructure which has not been found in rial. It has been a problem, however, how to make a any other similar magnetic alloy consisting of any other fine and chemically stable particle of the material. In a combination of rare earth metals and transition metals. general, a mechanically crushed particle of the material The microstructure consists of a fiber-like structure as is liable to be oxidized in air and the oxidation is accelshown in FIG. 1. It is observed with a conventional mierated by the coexistence of moisture even at room croscope on tha flat surface of specimens etched by temperature. Therefore, it is desired to make a magnet conc. HCl for a few minutes. It has been discovered of the material without using the pulverized form that a high coercive force is closely related to the mithereof. crostructure. In a specimen having a high coercive An object of the invention is to provide a novel magforce, quite definite and fine fiber structure are found, netic material characterized by a high coercive force whereas, in a specimen with a low coercive force, such and a highresidual flux density. a structure as above mentioned is hardly found.

A further object of the invention is to provide a per- The alloy body of the invention as heated is polished manent magnet material comprising Ce, Co and Cu. at one surface thereof with a suitable abrasive such as A still further object of the invention is to provide a SiC powder or Cr O powder in a particle size of 0.5 to composition of the alloy consisting of Ce, Co and Cu. 10p. in order that it may be provided with a flat surface. which gives a high coercive force, without pulverizing The surface is etched by a I2N HCl solution (aqueous) the alloy. for several minutes at room temperature 15 to 30C). A further object of the invention is to provide a per- The etched surface shows an etch pattern when obmanent magnet material comprising Ce-mischmetal inserved microscopically as shown in FIG. 1. Said etch eluding Fe, La, Pr and Nd as minor constituents, Co pattern is composed of many etch fibers 2, with a charand Cu. acteristic fineness defined as the average distance be- Another object of the invention is to provide a 4n tween two adjacent points 4 and 6 on a straight line 3 method of manufacturing a permanent magnet matetaken on the etch pattern, crossed by the etch fibers. In rial. order to determine the fineness of the fiber-like struc- These and other objects which are achieved by the ture, it is convenient to measure the same on a micropresent invention will be apparent upon consideration scopic photograph. It can be made by drawing a suffiof the following detailed description taken together ciently long straight line on the microscopic photowith the accompanying drawings wherein: graph in an arbitrary direction, so that there will be FIG. 1 is a schematic drawing which shows a strucmany cross points of the line with the etch fibers. The

ture, enlarged by 200 times, of the alloy according to average distance is obtained by dividing the line length the present invention; by the number of all such cross points on the line.

FIG. 2 shows the relation between the intrinsic coer- 5i According to the Present invention, the Small the cive force in oersteds and the fineness of the fiber-like fineness of the alloy, the higher the coercive force structure in microns, which is characteristic of the reof. The alloy having a fineness larger than 100p. alloy of the present invention; has a poor coercive force such as lower than 500 Oe re- FIG. 3 shows an example of cooling rate applicable gardless of the composition. A coercive force higher to the method of manufacturing the magnet material of than 2000 Oe is obtained with an alloy having a finethe invention; ness smaller than 20,u.. FIG. 2 shows the relation be- FIG. 4 is a graph showing the relation bet th tween intrinsic coercive force and the fineness of the intrinsic coercive force and the aging time according to r-like Structure of various specimens of the invenone example of the invention. tion. It is clearly seen from FIG. 2 that the finer the According to the present invention, an alloy which r cture the higher is the coercive force.

consists of proper amounts of C e, Co and Cu has excel- T e alloy according to the present invention with the lent magnetic properties for use as a permanent ma ZlfOItBCIBSCIibQd structure WZIS crushed t0 1 fine particle net. A novel composition of ferromagnetic alloy ac- Size and examined y y P diffractometrycording to the invention comprises 15 to 20 mol pereXample 0f he analysis for the alloy having a composicent of Ce, 52 to 77 mol percent of Co and 8 to 30 mol tiOh 0f mol P rc t Cc. mol percent Co and 8.3 percent of Cu. The 15 to 20 mol percent of Ce can be mol W Cu is Shown in Table In h u replaced by the less expensive Ce-mischmetal without {nefih Fe'Kamdilltion generated in an y tube Work" impairing the magnetic properties. The Ce-mischmctal "2 at anode Voltage of 35 kv and anode Current of 8 mA through a Mn filter was used as X-ray source. The diffracted X-ray from the specimen was counted by a conventional counter at a counting rate of 400 c/s and a scanning velocity of l/min. and recorded at a *uk. unknown, weak. in medium. s strung. ss \er strong The observed diffraction angles. 20, are listed in the first column of Table 2. In the second column, is shown the line intensity. The interplanar spacings [d] corresponding to each line are shown in the third column. Some of the diffraction lines can be indexed as shown in the fourth column, assuming that the crystal phase has a CaCu -type structure which is well verified in the case of many RCo,-, compounds. The other lines. however. remain unexplained. The most intense ones among these unexplained lines appear at slightly lower angles than the main lines of (111) and (110). This looks like a splitting of the main line into two lines. Although the origin'of these extra lines are unknown at present, it should be noted that these lines are characteristic of the alloy of the present invention.

The materials according to the present invention have a residual flux density higher than 3500 G, a coercive force higher than 600 Oe, and a maximum energy product higher than 1.3 MGzOe. The best results are obtained with compositions consisting essentially of 17.1 to 17.4 mol percent of Ce. 64 to 72.6 mol percent of Co and 10.3 to 18.57 mol percent ofCu in which the fine fiber-structure is easily formed. It is possible to replace Ce with Ce-mischmetal so that the amount of total rare earth elements in said Ce-Mischmetal is equivalent to that of said Ce. without impairing the resultant magnetic properties. The material of said optimal composition with a markedly developed fiberstructure has a residual flux density higher than 4250 G, a coercive force higher than 1500 O0, and a maximum energy product higher than 4.0 MGtOe.

The magnetic alloys according to the invention can be prepared by a conventional metallurgical method. For example, the ingredient metals are melted together in an alumina crucible in air at 10' mmHg using a graphite heater. and the molten alloy is furnace-cooled to room temperature. The alloy thus prepared has a more or less developed fiber-structure. However, in order to obtain a clearly and finely developed fiberstructure with the alloy materials and accordingly a high coercive force, it is effective to give the materials specially scheduled heat-treatments.

According to one manufacturing method of the present invention. the mixed ingredient metals are melted at a temperature higher than l200C. said melt is solidified at a temperature slightly lower than the melting point of the desired alloy. the solidified alloy is maintained at a temperature between the solidifying temperature and about 1000C to obtain a homogenized alloy,

the homogenized alloy is cooled to a temperature of 650 to 250C at an average rate of 35 to 3C per minute, and then the resultant alloy is quenched to room temperature. The homogenizing treatment. although not necessary, has a favorable effect on the magnetic properties.

An important feature of the process is the controlled cooling after the homogenizing heat treatment inorder to obtain superior magnetic properties. The magnetic properties are highly dependent on the said cooling rate from 1 C to 250C.

The cooling rate should be higher in a relatively high temperature region than in a relatively low temperature region. The most important process feature is the controlledcooling from 1000C to 650C of which-the average rate should be 35 to 10C per minute.

An example ofa proper cooling rate which is realized during the furnace cooling process is shown in FIG. 3.

According to an alternative method of producing the magnet material of the invention, the mixed ingredient metals are melted at a temperature higher than 1200C. said melt is quenched to room temperature, for instance, in a metal mold cooled by a cooling means such as water, the quenched alloy is aged at a temperature of 400 to 650C for 20 minutes to 10 hours, and then the aged alloy is cooled to room temperature.

The quenched alloy exhibits a low coercive force value such as about 200 Oe. The coercive force. however. increases to value as high as 1250 Oe during the aging period of l to 5 hours at a temperature of 400 to 650C. An aging treatment below 400C requires too prolonged a period to obtain a sufficiently high coercive force value. In some cases for a higher aging temperature, for example of 700C, the coercive force value decreases.

Illustrative embodiments of the invention are as follows:

Example 1 The alloy of 16.67 mol percent of Ce-mischmetal. 75.0 mol percent of Co and 8.33 mol percent of Cu was melted at 1670C, maintained for 30 minutes at I000C. cooled to 400C according to the cooling curve shown in FIG. 3 and then rapidly cooled to room temperature. A sphere of about 3 mm in diameter was prepared from the ingot. The demagnetization curve was measured by means of a conventional vibrating specimen magnetometer. The magnetic properties were:

temperature. A sphere of about 3 mm in diameter was prcparedfrom the ingot. The demagnetization curve was measured by means of a conventional vibrating specimen magnetometer. The magnetic properties were:

Br 5960 G bHc 3240 Oe (BH)max 8.0 MG'Oe Example 3 The alloy of 16.67 mol percent of Ce-mischmetal, 66.7 mol percent of Co and 16.63 mol percent of Cu was melted at 1670C, maintained for 30 minutes at 1000C,'cooled to 400C according to the cooling curve shown in FIG. 3 and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

was carried out by the same method as in the previous examples. The magnetic properties were:

Br 3700 G bHc 1250 Oe (BH)max 1.3 MG-Oe The influence of the Cu-content in the Ce-mischmetal- Co-Cu alloy system is shown explicitly from the above examples.

Example 5 The alloy of 15.25 mol percent of Ce-mischmetal. 67.8 mol percent of Co and 16.95 mol percent of Cu was melted at 1670C. maintained for 30 minutes at 1000C. cooled to 400C according to the cooling curve shown in FIG. 3 and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 4250 G bHc' 1200 O0 (BH)max 3.4 MG'Oe Example 6 The alloy of 16.67 mol percent of Ce-mischmetal, 66.7 mol percent of Co and 16.63 mol percent of Cu was melted at l670C. maintained for 30 minutes at 1000C. cooled to 400C according to the cooling curve shown in FIG. 3 and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 4750 G bHt' 2900 Oe (BH)max 5.0 MG'Oe Example 7 The alloy of 19.35 mol percent of Ce-mischmetal.

64.52 mol percent of Co and 16.13 mol percent of Cu was melted at 1670C, maintained for 30 minutes at 1000C, cooled to 400C according to the cooling curve shown in FIG. 3 and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 3600 G bHc 750 Oe (BH)max 1.7 MG-Oe The influence of the Ce-mischmetal content in the Ce-mischmetal-Co-Cu alloy system is shown explicitly from the preceding three examples.

Examples 8 The alloy of 16.67 mol percent of Ce-mischmetal,

66.7 mol percent of Co and 16.63 mol percent of Cu was melted at 1550C, maintained for 30 minutes at 1000C, cooled to 300C according to the cooling curve shown in FIG. 3 and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

bHL 2750 Oe (BH)max 3.8 MG'Oe Example 9 The alloy of 16.67 mol percent of Ce-mischmetal. 66.7 mol percent of Co and 16.63 mol of Cu was melted at 1550C. maintained for 30 minutes at 1000C. cooled to 400C according to the cooling curve shown in FIG. 3 and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 4750 G hHc' 2900 De (BH)max 5.0 MG-Oe Example 10 The alloy of 16.67 mol of Ce-mischmetal, 66.67 mol percent of Co and 16.63 mol of Cu was melted at 1550C maintained for 30 minutes at 1000C, cooled to 530C according to the cooling curve shown .in FIG. 3 and then rapidly cooled to room temperature.

was carried out by the same method as in the previous examples. The magnetic properties were:

Br 5050 G bl-lc 2000 Oe (BH)max 4.3 MGOe Example 12 The alloy of 16.67 mol percent of Ce-mischmetal, 66.7 mol percent of Co and 16.63 mol percent of Cu was melted at 1550C, maintained for 30 minutes at 1000C, cooled to 790C according to the cooling curve shown in FIG. 3 and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 4650 G bl-lc 150 Oe (BH)max 0.25 MG'Oe It is apparent from the preceding five examples that the temperature at which the sample is taken out from the electric furnace influences explicitly the magnetic properties.

Example 13 The alloy of 17.4 mol percent of Ce, 66.1 mol percent of Co and 16.5 mol percent of Cu was melted at 1550C. maintained for 30 minutes at 1000C. cooled to 400C at the average rate of 28C/min. between l000C and 650C and at the overall rate of 16.5C/min. and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 4550 G bHe 800 Oe (BH)max 2.4 MG'Oe Example 14 The alloy of 17.4 mol percent of Ce. 66.1 mol percent of Co and 16.5 mol percent of Cu was melted at 1550C. maintained for 30 minutes at 1000C. cooled to 400C at the average rate of 24C/min. between 1000C and 650C and the overall average rate of l3.2C/min. and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 4720 G bHc 2300 Oe (BH)max 3.8 MG'Oe Example The alloy of 17.4 mol percent of Ce, 66.1 mol percent of Co and 16.5 mol percent of Cu was melted at 1550C, maintained for minutes at 1000C. cooled to 400C at the average cooling rate of l9.5C/min. between 1000C and 650C and at the overall average rate of 10.5C/min. and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 6050 G bHc 2570 Oe (BH)max 7.1 MG'Oe Example 16 The alloy of 17.4 mol percent of Ce, 66.1 mol percent of Co and 16.5 mol percent of Cu was melted at 1550C. maintained for 30 minutes at 1000C, cooled to 400C at an average cooling rate of 12C/minbetween 1000C and 650C and at the overall average rate of 4C/min. and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 6500 G bHc 900 Oe (BH)max 1.6 MG'Oe It is apparent from the preceding four examples that cooling rate influences the magnetic properties of the materials.

Example 17 The alloy of 18.03 mol percent of Ce-mischmetal, 55.32 mol percent of Co and 26.65 mol percent of'Cu was melted at 1550C. and quenched in water. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 2300 G hHc 260 Oe Example 18 The alloy of 18.03 mol percent of Ce-mischmetal, 55.32 mol percent of Co and 26.65 mol percent of Cu was melted at 1550C. quenched in water, aged for 1 hour at 300C and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 2600 G bHc 490 Oe Example 19 The alloy of 18.03 mol percent of Ce-mischmetal, 55.32 mol percent of Co and 26.65 mol percent of Cu was melted at 1550C, quenched in water, aged 'for 1 hour at 400C and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 2900 G bHe 890 Oe Example 20 The alloy of 18.03 mol percent of Ce-misehmetal, 55.32 mol percent of Co and 26.65 mol percent of Cu was melted at 1550C, quenched in water, aged for 1 hour at 520C and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 3000 G bHc 1250 Oe Example 21 The alloy of 18.03 mol percent of Ce-mischmetal, 55.32 mol percent of Co and 26.65 mol percent of Cu was melted at 1550C, quenched into water, aged for 1 hour at 600C and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 3000 G bl-lc 970 Oe Example 22 Br 2500 G bHc 260 Oe The influence of aging temperature is explicitly confirmed from the six preceding examples.

Example 23 The alloy of 18.03 mol percent Ce-mischmetal, 55.32

mol percent of Co and 26.65 mol percent of Cu which was prepared by melting the ingredient metals at 1550C and quenching in water, was heated at 520C for various times. The intrinsic coercive force ,H,. of thus obtained alloy is plotted against the aging time in FIG. 4.

The intrinsic coercive force increased rapidly with increasing the aging time in the range from about 20 min. to 1 hour, and was followed by a gradual increase up to the aging time of about 8 hours, then by a gradual decrease with the aging time over 10 hours.

What is claimed is:

1. A method for making a permanent magnet material having a fiber-like microstructure of fineness smaller than 20 microns and having a maximum energy product of at least 1.3 MG.oe, comprising heating a mixture of 15 to'20 mol percent of Ce or Ce mischmetal, 52 to 77 mol percent of Co and 8 to 30 mol percent of Cu to a melt at a temperature higher than 1200C, quenching said melt to room temperature, aging the quenched alloy at a temperature of 400C to 650C for 20 minutes to 10 hours and then rapidly cooling the aged alloy to room temperature.

2. A method for making a permanent magnet material according to claim 1, wherein Ce-mischmetal is employed.

3. A method for making a permanent magnet material according to claim 1 wherein Ce is employed.

Claims (3)

1. A METHOD FOR MAKING A PERMANENT MAGNET MATERIAL HAVING A FIBER-LIKE MICROSTRUCTURE OF FINENESS SMALLER THAN 20 MICRONS AND HAVING A MAXIMUM ENERGY PRODUCT OF AT LEAST 1,3 MG.OE, COMPRISING HEATING A MIXTURE OF 15 TO 20 MOL PERCENT OF CE OR CE MISCHMETAL, 52 TO 77 MOL PERCENT OF CO AND 8 TO 30 MOL PERCENT OF CU TO A METAL AT A TEMPERATURE HIGHER THAN 1200*C, QUENCHING SAID METAL TO ROOM TEMPERATURE, AGING THE QUENCHED ALLOY AT A TEMPERATURE OF 400*C TO 650*C FOR 20 MINUTES TO 10 HOURS AND THE RAPIDLY COOLING THE AGED ALLOY TO ROOM TEMPERATURE.

2. A method for making a permanent magnet material according to claim 1, wherein Ce-mischmetal is employed.

3. A method for making a permanent magnet material according to claim 1 wherein Ce is employed.

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