Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
  • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
  • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
  • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
  • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
  • H01F1/047—Alloys characterised by their composition
  • H01F1/053—Alloys characterised by their composition containing rare earth metals
  • H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
  • H01F1/0555—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 pressed, sintered or bonded together
  • H01F1/0557—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 pressed, sintered or bonded together sintered

Definitions

• a known method which is based on such a composition consists of compacting a powder of said alloy under high pressure, at the same timeapplying to it an orientating magnetic field, then applying a thermal treatment to the pieces obtained, comprising fritting at a temperature of about 1100C.
• a pre-fritting operation at a temperature of between 600 and l000C and preferably around 750C is included in the abovementioned thermal treatment.
• the effect of this pre-fritting is to increase the density of the residual induction of the end product. It is moreover known that an annealing operation carried out after cooling the fritted pieces improves their intrinsic coercive field and induction and that the magnetic characteristics of the end product depend to a large extent on the greater or lesser rapidity with which the pieces are removed from the annealing furnace. In practice, the annealing operation will be, after rapid removal of the pieces, immediately followed by sudden water quenching.
• the coercive field of the end product is therebyconsiderably improved.
• An alloy made up of samarium and cobalt is prepared, the latter material having a purity of about 99.95 percent.
• the samarium is in the form of fibres and it is first remelted to form a compact bar.
• the initial proportions are between 35 and 42 percent of samarium by weight, the preferred samarium content being around 37 percent.
• a charge of 700 g. comprising 259 g of Sm and 441 g of Co is treated. Melting is done in an induction furnace supplying 30 kW power at a frequency of 4 KHz, preferably in accordance with the method described in US. Pat. application filed on December 10, 1971 under the Ser. No. 206,732 by the inventor. for: Method and device for manufacturing alloys of transition elements and rare earth group metals intended for the production of materials for permanent magnets.
• This method consists of first melting the Co, placed 'in a recrystallized alumina crucible, by heating to about 1500C, leaving it to cool to about 1 C, then lowering a bar of Sm into contact with the contents of the crucible: Sm diffuses in Co.
• the alloying operation is finished, the alloy is reheated for about one minute to liquefy and homogenize it, then it is cast in a graphite ingot-mould.
• the material obtained is then pounded, then crushed into a powder whose grain size, measured by means of a FlSHER SUB-SIEVE instrument, is about 4 microns.
• the intrinsic coercive field of this powder measured after saturation in a 95,000-Oersted field, is about 10,000 Oersteds.
• This powder is mixed with a lubricant to facilitate its subsequent compression, then premagnetized in a pulse field in accordance with the method described in French Patent application filed on Oct. 29, 1970 under the serial number 7039028 by SOCIETE DETUDES ET DE RECHERCHES MAG- NETlQUES.for: Improvement to the methods of manufacturing materials for permanent magnets.”
• the material is then shaped into a cylinder by compressing the powder under a pressure of about 2T/cm in the presence of a magnetic field parallel to the direction of compression, with an intensity of 10 to 15 Koersteds.
• the compressed pieces are piled in a refractory shuttle made e.g. of stainless steel and coated with a powder of an auxiliary samarium alloy with a melting point higher than that of the basic alloy in accordance with the method described in US. Pat. application filed on Dec. 21, 1971, Ser. No. 210,583 for: Method of manufacturing fritted permanent magnets on basis of cobalt and rare earths, by the Inventor.
• the shuttle is then inserted into a refractory tube (e.g. made of quartz) sealed at one end and the other end of which is connected to a pumping unit.
• a refractory tube e.g. made of quartz
• This quartz tube is emptied of its air until a primary vacuum is obtained, keeping it at a temperature of about 200C, then an inert gas is introduced into it, such as helium or argon, under a pressure of l atmosphere.
• a pre-fritting operation is then carried out in the following way:
• the quartz tube is introduced into a furnace maintained at a temperature of between 600 and l000C and preferably around 750C for a period of 2 to 60 minutes, preferably 20 minutes.
• This operation makes it possible to obtain a higher final density after fritting and a higher residual induction than those obtained in the standard way, without pre-fritting.
• a piece fritted at l l 15C for 30 min., without pre-fritting has the following characteristics:
• This pre-fritting thus constitutes an important characteristic of the method in accordance with the invention. Moreover, it gives a material which is already cohesive enough to allow it to be machined. Machining can therefore be done at this stage of manufacture more easily than in the final stage, where the pieces have much greater density.
• fritting carried out in the following way.
• the temperature of the quartz tube is raised, in about 10 minutes, from 750 to a value of between l050 and 1 150C. More specifically, this is achieved by moving the quartz tube slowly from one area to another in the same furnace. The pieces are maintained at fritting temperature (second furnace area) for 10 to 60 minutes. The quartz tube is then quickly brought out into the ambient air and left to cool naturally.
• the pieces are again coated with the abovementioned auxiliary alloy and the shuttle, after primary pumping, is placed in'a helium atmosphere in a refractory stainless steel tube.
• This tube is introduced into a furnace and maintained for a period of 5 to 48 hours preferably 24 hours at a temperature lower than the fritting temperature, e.g. 900C.
• the refractory stainless steel tube is quickly removed from the annealing furnace and suddenly quenched in water contained in a container in which stirring takes place.
• the alloy of the above mentioned composition theoretically has two phases Sm C0,, and Sm C0 However, as casting comprises sudden cooling, it is probable that these two phases coexist, but in an unco-ordinated way, at the time when thermal treatment begins,
• the effect of pre-fritting would thus be to coordinate these two phases, the Sm Co, phase surrounding the grains of Sm Co
• the 8m C0 phase is at a temperature close to its melting point, so that fritting is carried out with this material, which has a low melting point (and is thus in a pasty state) present at the grain boundaries, and is thus facilitated; the density is there: fore improved.
• the presence of Sm C0 around Sm C0 prevents the evaporation of Sm and thus the formation of Sm Co the more so because the increase from the pre-fritting temperature to the fritting temperature, as well as the fritting operation itself, are fairly rapid.
• the crystalline structure of the fritted product will be essentially the same as that of the Sm C0 alloy. the presence of 5m Co, only constributing uncoordinated defects. The result is that the saturation magnetization of the end product is very close to the ideal value defined by the Sm C0 structure.
• a process of manufacturing a permanent magnet material based on samarium and cobalt comprising the steps of: (a) preparing a powder of an alloy of samarium and cobalt, having a samarium content between 35 and 42 percent by weight and a cobalt content of between 65 and 58 percent by weight; (b) compacting the powder formed in step (a) under high pressure, while concurrently applying to the compact a magnetic field orienting the magnetic particles in the alloy; (c) sintering the compressed powder in an inert atmosphere; and (d) annealing the sintered compressed powder, the improvement comprising intermediate compacting step (b) and sintering step (c), the additional step of prefritting the compacted body of step (b) at a temperature of between 600 and l000 C for a period of between 2 and 60 minutes to increase the density and residual induction properties of the final product.

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• Chemical & Material Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Hard Magnetic Materials (AREA)
• Powder Metallurgy (AREA)

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Publications (1)

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Cited By (3)

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Citations (5)

Family Cites Families (3)

• 1972
  • 1972-05-02 FR FR7215499A patent/FR2182635B1/fr not_active Expired
• 1973
  • 1973-04-10 CH CH516173A patent/CH573653A5/xx not_active IP Right Cessation
  • 1973-04-18 GB GB1877873A patent/GB1392915A/en not_active Expired
  • 1973-04-19 US US00352695A patent/US3844851A/en not_active Expired - Lifetime
  • 1973-04-19 DE DE2320122A patent/DE2320122C2/de not_active Expired
  • 1973-04-27 NL NLAANVRAGE7305987,A patent/NL182847C/xx not_active IP Right Cessation
  • 1973-05-02 IT IT23609/73A patent/IT993556B/it active

Patent Citations (5)

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