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
• • 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
  • H01F1/058—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IVa elements, e.g. Gd2Fe14C

Definitions

• the invention relates to a boron-free hard magnetic material on the basis of neodymium, iron and carbon, which comprises a hard magnetic tetragonal phase.
• the invention also relates to a method of manufacturing such a material.
• a known material of this type comprises Nd2Fe14B having a tetragonal crystal structure as a hard magnetic phase. It is known that in this compound a partial substitution of boron by carbon leads to an increased magnetic anisotropy (see, for example, Journal de Physique Colloque C6, supplpir au no. 9, T. 46, Sept. 1985, page C6-305/308: " Magnetic Anisotropy of Carbon Doped Nd2Fe14B" by Bolzoni, Leccabue, Pareti and Sanchez). In this article it is stated on page 306 that when boron is completely replaced by carbon it is impossible to obtain a tetragonal phase which is required to obtain the desired hard magnetic properties.
• this object can be achieved by a material having the following overall composition, 11.2 to 15.2 at.% of Nd, 74.8 to 84.8 at.% of Fe and 4 to 10 at.% of C, a finely crystalline tetragonal phase having a grain size of 0.2 ⁇ m or smaller and having the Nd2Fe14C structure being present in the material.
• This composition range comprises material compositions having coercive forces ⁇ o H c of 0.6 T or larger. It should be noted that materials having the highest coercive force are obtained if the composition of the materials is selected as follows: Nd: 12 - 15 at.%, Fe: 75 - 84 at.% and C: 4.8 - 10 at.%.
• the magnetic properties of the material improve, however, if the composition of the material is selected as follows, Nd: 12.0 - 14.2 at.%, Fe: 76.6 - 83.2 at.% and C: 4.8 - 9.2 at.%, the Curie temperature of these materials being in general 260°C or higher. However, sometimes the material also contains a second soft magnetic phase. Substantially single-phase materials in general have the following composition, Nd: 12 - 14 at.%, Fe: 78 - 81 at.% and C: 6 - 8 at.%.
• the compositions of the materials of the present invention possess the known property of the Nd2Fe14B material that substitution of part of the iron by cobalt increases the Curie temperature.
• Finely crystalline is to be understood to mean herein that at least 90% of the crystallites in the hard magnetic phase have a dimension of 0.2 ⁇ m or smaller.
• the hard magnetic material according to the invention can be obtained by melting together the starting elements, followed by melt spinning on a chill surface, for example the surface of a rapidly rotating copper disc, which moves rapidly relative to the orifice.
• a method of manufacturing a hard magnetic material in the form of a ribbon is known from European Patent Application EP-A 108 474.
• the moving chill surface is formed by the circumferential surface of a disc of a material having a high thermal conductivity such as copper coated with chromium.
• the ribbons or flakes formed comprise a microcrystalline phase having a structure which resembles that of Nd2Fe17; the material is not hard magnetic. It must be assumed that part of the carbon present is dissolved in this phase. In this respect, the material according to the invention clearly differs from boron-­containing materials. Boron is substantially insoluble at the temperatures used in the Nd2Fe17 phase.
• the desired hard magnetic properties can be obtained if immediately after melt spinning the material is subjected to a recrystallizing annealing treatment of short duration at a relatively low temperature.
• the annealing treatment is carried out at a temperature between 675 and 750°C, preferably at a temperature between 685°C and 730°C.
• On heating to a temperature of 720°C the desired finely crystalline tetragonal phase Nd2Fe14C is formed within a minute after attaining the said temperature.
• the annealing duration necessary for the crystallization can be established readily in an experimental way at any annealing temperature in the indicated temperature range.
• a suitable annealing treatment consists in that the material is maintained in a furnace for 1 to 5 minutes, the furnace being at a temperature of 720°C. In practice, a dwell time of 2 to 3 minutes was found to be suitable. The material thus obtained has suitable permanent magnetic properties.
• a saturation magnetization ⁇ o M sat of > 1.2 T, a remanence ⁇ o M r of > 0.50 T and a coercive force ⁇ o H c of > 1.0 T were measured.
• a marked grain growth occurs when it is heated for a long time (360 hours) at 800°C, the grains being formed having a dimension between 0.2 and 0.6 ⁇ m. In this process the coercive force decreases to 0.2 T.
• a further increase of the dimensions of the grains was observed when they were heated at 850°C and 900°C for 15 days. Then, the most important phase is still the Nd2Fe14C phase.
• the material in the form of flakes is compressed in a hot condition, for example at 650°C, if necessary, after it has been powdered or ground.
• the material in the form of flakes may alternatively be bound with a synthetic resin, if necessary after it has been powdered or ground, and formed into a magnet.
• An advantage of the new magnetic material is that during its manufacture it cannot form toxic boron-containing compounds when it contacts water and/or hydrogen.
• the flakes obtained were introduced into a furnace which was heated to a temperature of 720°C, and they were maintained therein for 3 minutes.
• the material thus obtained had, predominantly, a finely crystalline tetragonal structure (Nd2Fe14C). Crystallite dimension (more than 90%): 0.2 ⁇ m.
• the following magnetic properties were measured: Coercive force ⁇ o H c ) : 1.02 T Saturation magnetization ⁇ o M sat ) : 1.34 T Remanence ⁇ o M r : 0.72 T Curie temperature : 269°C

Landscapes

• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Hard Magnetic Materials (AREA)
• Carbon And Carbon Compounds (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=19851074

Family Applications (1)

Country Status (5)

Cited By (1)

Families Citing this family (1)

• 1987
  • 1987-12-11 NL NL8702992A patent/NL8702992A/nl not_active Application Discontinuation
• 1988
  • 1988-12-05 EP EP88202783A patent/EP0320063A1/de not_active Withdrawn
  • 1988-12-08 KR KR1019880016306A patent/KR890010945A/ko not_active Withdrawn
  • 1988-12-08 CN CN88108566A patent/CN1033495A/zh active Pending
  • 1988-12-08 JP JP63308976A patent/JPH01192714A/ja active Pending

Non-Patent Citations (4)

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