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
  • H01F1/12—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 soft-magnetic materials
  • H01F1/14—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 soft-magnetic materials metals or alloys
  • H01F1/147—Alloys characterised by their composition
  • H01F1/153—Amorphous metallic alloys, e.g. glassy metals
  • H01F1/15308—Amorphous metallic alloys, e.g. glassy metals based on Fe/Ni
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F3/00—Cores, Yokes, or armatures

Definitions

• This invention relates to iron-rich metallic glass alloys having high saturation induction that evidence particularly superior soft ferromagnetic properties when subjected to high magnetization rates.
• Glassy metal alloys are metastable materials lacking any long range order. They are
• pulse power applications Applications for soft magnetic cores, in a particular class that is now receiving increased attention, are generically referred to as pulse power applications.
• a low average power input with a long acquisition time, is converted to an output that has high peak power delivered in a short transfer time.
• very fast magnetization reversals ranging up to 100 T/ ⁇ s (or 100 MT/s)
• pulse power applications include saturable reactors for magnetic pulse compression and for protection of circuit elements during turn on, and pulse transformers in linear induction particle accelerators.
• Metallic glasses are very well suited for pulse power applications because of their high resistivities and thin ribbon geometry, which allow low losses under fast
• metallic glass materials have led to their use as core materials in various pulse power applications: in high power pulse sources for linear induction particle accelerators, as induction modules for coupling energy from the pulse source to the beam of these accelerators, as magnetic switches in power generators, in inertial confinement fusion research, and in magnetic modulators for driving exciraer lasers.
• the core material is initially "parked” in, or biased into, a specific magnetic state through the imposition of
• the application of a large, negative d.c. field will place the core material in a negatively saturated state.
• the direction in which the core material will be driven into saturation during the application is referred to as the positive direction.
• a subsequent removal of this field will position the core material at negative remanence.
• the former procedure allows for a maximum flux swing of twice the saturation induction in the core material but, as a matter of convenience, the latter procedure, known as the pulse reset, is most commonly employed.
• the maximum flux swing is then the sum of the remanent and saturation inductions.
• the term "maximum flux swing" connotes a value that is determined by the sum of the remanent and saturation inductions.
• Metallic glasses may easily be annealed to yield a value for B r , the remanent
• the core material should, preferably, also possess a low induced magnetic anisotropy energy.
• a low magnetic anisotropy energy leads to lower core losses, by facilitating the establishment of an optimal ferromagnetic domain structure, and therefore allow the cores to operate with greater efficiency.
• the saturation induction of this glassy alloy is about 1.75 T.
• the high cobalt content in this alloy imparts a high value for the magnetic anisotropy energy and, consequently, high core losses.
• a metallic glass alloy that contains no cobalt is METGLAS 2605SC (nominal composition:
• a metallic glass alloy that offered a combination of high induction (large flux swings) and low magnetic anisotropy energy would be highly desirable for the purpose of pulse power applications.
• An additional advantage would be derived if such an alloy were to offer economy in production costs.
• the present invention provides iron-rich magnetic alloys that are at least about 80% glassy and are
• the glassy metal alloys of the invention have a composition described by the formula
• alloys may, optionally, contain up to about 1 atom percent of Mn.
• the metallic glasses of the invention when suitable annealed, additionally evidence large values for the dc swing from negative remanence to positive saturation.
• the saturation induction ranges from about 1.55 T to about 1.75 T
• the magnetic anisotropy energy ranges between about 300 J/m 3 and 400 J/m 3
• the above mentioned dc swing typically ranges from about 2.9 T to about 3.2 T.
• the metallic glasses of this invention are especially suitable for use in large magnetic cores used in various pulse power applications requiring high magnetization rates.
• Representative of such applications are high-power pulse sources for linear induction particle accelerators, induction modules for coupling energy from the pulse source to the beam of these accelerators, magnetic
• switches in power generators in inertial confinement fusion research and magnetic modulators for driving excimer lasers Other uses include cores of airborne transformers, current transformers, ground fault
• Figure 1 is a schematic representation of the dynamic magnetization curve obtained when a ferromagnetic material is subjected to very high magnetization rates, wherein H a is the applied field and ⁇ B is the total change in induction;
• Figure 2 is a plot, on a log-log scale, of the core loss as a function of the magnetization rate, (dB/dt), for a preferred metallic glass of the invention, illustrating the beneficial effects on the core which result from coating the ribbon surfaces;
• Figure 3 in a similar plot, compares the losses obtained from a preferred metallic glass of the invention against the losses obtained from two prior art metallic glasses that are now commercially used in cores for pulse power applications, all data for this figure being derived from coated and annealed ribbons;
• Figure 5 is a plot, on a log-log scale, of the core loss obtained from various preferred metallic glasses of the invention, as a function of the magnetization rate, (dB/dt); and.
• iron-rich magnetic metallic glass alloys that are at least about 80% glassy and are characterized by a combination of high saturation induction and low magnetic anisotropy energy.
• the glassy metal alloys of the invention have a composition described by the formula Fe a Co b B c Si d Ce. where "a" - "e" are
• alloys in atom percent, “a” ranges from about 72 to about 84, “b” ranges from about 2 to about 8, “c” ranges from about 11 to about 16, “d” ranges from about 1 to about 4, and “e” ranges from 0 to about 4.
• These alloys may, optionally, contain up to about 1 atom percent of Mn.
• the purity of the above compositions is that found in normal commercial practice.
• the metallic glasses of the invention when suitably annealed, additionally evidence large values for the dc swing from negative remanence to positive
• saturation induction ranges from about 1.55 T to about 1.75 T
• the magnetic anisotropy energy ranges between about 300 J/m 3 and 400 J/m 3
• the above mentioned dc swing typically ranges from about 2.9 T to about 3.2 T.
• the alloys of the invention are preferably at least 90% glassy, and most preferably 100% glassy, as established by X-ray diffraction. Furthermore, the glassy alloys of the invention that evidence a saturation induction of at least about 1.6 T are to be especially preferred from the point of view of pulse power applications.
• Examples of metallic glasses of the invention include
• the magnetic core of a given cross-sectional area will "hold off" a known amount of Vs from the output. Therefore, under a fixed input voltage level, the hold-off time is greater when the core material has a greater saturation induction.
• Co in the alloys serves to increase the saturation induction level.
• Cobalt contents of less than about 2 at.% provide only marginal increases in saturation induction levels over alloys containing no cobalt.
• the rate of increase of saturation induction due to the presence of Co reduces substantially above about 8 at.% Co, and higher levels of Co are therefore not desired because of the substantial cost of the element.
• alloys of the invention that contain carbon are preferred alloys of the invention, for a variety of reasons: First, the introduction of C in the alloys has been found to increase even further the saturation
• alloys containing between about 11 and 14 at.% boron especially notable in alloys containing between about 11 and 14 at.% boron. For this reason, alloys of the invention having a B content ranging between about 11 at.% and about 14 at.% are more preferred.
• the maximum amount of about 4 at.% for C in the alloys of the invention offers an acceptable compromise between the loss of saturation induction levels and the improvements in melt handling characteristics. It will be noted from Table I that the saturation induction of an alloy with 4 at.% C is approximately the same as in an alloy without any carbon,
• the magnetic anisotropy energy of a ferromagnetic material is a measure of the energy required to rotate the magnetic moments in the material away from an established, preferred direction of alignment. The magnitude of this energy dictates the ease with which a particular domain structure may be
• FIG. 1 This figure is a schematic representation of the dynamic magnetization curves ("B-H loops") obtained from ferromagnetic materials which are subjected to high magnetization rates; H a is the applied magnetic field on the core material and ⁇ B is the flux swing obtained from the core material. As noted in the figure, this magnetization curve may be broken down to five regions (or parts) of magnetic response from the core material.
• region I after a rapid increase usually limited by stray inductances, H reaches a maximum and then actually decreases in many cases.
• This peak in region II is associated with the establishment of bar shaped
• the area enclosed by the dynamic magnetization curve and the ordinate axis in Figure 1 represents the core loss of the magnetic core material.
• This core loss is really a "half-cycle" loss, in that only one-half of a conventional hysteresis loop is being traversed by the material.
• the magnetic anisotropy energy of metallic glasses in the Fe-B-Si system may be reduced by the addition of suitable amounts of a fourth element.
• carbon is one such element
• examples of other such elements include Mo, Nb, V, and Cr. lt has been unexpectedly found, however, that, in the Fe-Co-B-Si system of metallic glasses, C is the only elemental addition that increases the saturation induction level of the "parent" alloy. All other attempted
• the effect of Si in the alloys of the invention is to reduce the saturation induction but increase the thermal stability of the glassy state of the alloys by increasing their crystallization temperatures.
• the maximum level of about 4 at.% Si in the alloys of this invention defines an acceptable balance between these two effects of Si.
• Coated ribbons were obtained by dipping as-cast ribbons in a diluted solution of colloidal silica. The host solution was isopropanol in the commercially available colloid, and methanol was used for dilution.
• Polyimide may be employed to achieve similar or greater reductions in the core loss of the materials of this invention. Similarly, it would also be apparent that, depending on the coating material, the ribbon may be annealed prior to being coated.
• Figure 3 compares the losses obtained from the same alloy of Figure 2 with the losses obtained from two prior art metallic glasses that are now commercially used in cores for pulse power applications, as a function of the magnetization rate. Fifty millimeter wide ribbons of all three alloys referred in this figure were coated as
• H (ave.) the average field
• dB/dt the measured core loss
• compositions described in the examples are nominal
• Patent No. 4,142,571 the disclosure of which is hereby incorporated by reference thereto. All casts were made in a vacuum chamber, using 0.025 to 0.100 kg melts comprising constituent elements of high purity. The resulting ribbons, typically 25 to 30 ⁇ m thick and about 6 mm wide, were determined to be free of crystallinity by x-ray diffractometry using Cu-K ⁇ radiation and differential scanning calorimetry. Some of the alloys were also cast separately as 50 mm wide ribbons, to facilitate a direct comparison with commercial alloys. Each of the alloys was at least 80% glassy, most of them more than 90% glassy and, in many instances, the alloys were 100% glassy.
• Ribbons of these glassy metal alloys were strong, shiny, hard and ductile.
• a commercial vibrating sample magnetometer was used for the measurement of the saturation magnetic moment of these alloys. As-cast ribbon from a given alloy was cut into several small squares (approximately 2 mm X 2 mm), which were randomly oriented about a direction normal to their plane, their plane being parallel to a maximum applied field of about 755 kA/m. By using the measured mass density, the saturation induction, B s , was then calculated. The density of many of these alloys was measured using standard techniques invoking Archimedes' Principle.
• the core losses were measured on closed-magnetic path toroidal samples.
• the toroidal samples were prepared by winding continuous ribbons of the glassy metal alloys onto ceramic bobbins (about 40 mm O.D.), so that the mean magnetic path length was about 0.13 m.
• Each toroidal sample contained between about 0.002 kg and 0.01 kg of ribbon. All toroids were annealed prior to the loss measurements. The anneal temperatures ranged between about 573 K and 623 K, the anneal times ranged between about 900 s and 3600 s, and an external field ranging in strength from about 400 A/m to about 1600 A/m was imposed on the toroids throughout the anneal cycle.
• the toroids were driven by discharging a low
• inductance capacitor bank through a set of insulated primary windings, numbering from about 3 to about 10.
• the current in the primary windings was measured using a commercial current probe.
• a one turn secondary winding provided a voltage proportional to (dB/dt), the
• the voltage and current waveforms were digitized at 20 ns per point and recorded on a

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Chemical & Material Sciences (AREA)
• Dispersion Chemistry (AREA)
• Soft Magnetic Materials (AREA)
• Hard Magnetic Materials (AREA)
• Glass Compositions (AREA)

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• 1990
  • 1990-06-20 EP EP90911005A patent/EP0482064B1/de not_active Expired - Lifetime
  • 1990-06-20 JP JP2510372A patent/JPH0689438B2/ja not_active Expired - Lifetime
  • 1990-06-20 WO PCT/US1990/003472 patent/WO1991001563A1/en active IP Right Grant
  • 1990-06-20 DE DE90911005T patent/DE69004962T2/de not_active Expired - Fee Related
  • 1990-06-20 CA CA002059267A patent/CA2059267C/en not_active Expired - Fee Related

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