Patent Grant
8287664
1. Field
Disclosed herein is a method for the production of magnetic powder composite cores pressed from a mix of alloy powder and binder. Also disclosed is a magnet core produced from a mix of alloy powder and binder and an inductive component containing such a magnet core.
2. Description of Related Art
In powder composite cores of this type, low hysteresis and eddy-current losses and low coercitive field strength are desired. The powder is typically supplied in the form of flakes provided by comminuting a soft magnetic strip produced using melt spinning technology. These flakes may, for example, have the form of platelets and are typically first provided with an electrically insulating coating and then pressed to produce a magnet core. While flakes of pure iron or iron/nickel alloys are so ductile that they are plastically deformed under the influence of the compacting pressure and result in pressed cores of high density and strength, flakes or powders of relatively hard and rigid materials cannot be pressed with just any pressure. Rigid flakes would break in unsuitable conditions, resulting not in the desired compaction, but only in a further reduction of particle size. In addition, the break-up of the flakes releases fresh surfaces without any electrically insulating coating, which can lead to a drastic reduction of the resistivity of the magnet core and thus to high eddy-current losses at high frequencies.
As described, for example, in DE 103 48 810 A1, it is possible to use powders with a multi-modal particle size distribution. A multi-modal size distribution permits a relatively dense packing of the particles, and thus permits the production of a relatively dense magnet core.
When using FeAlSi-based materials, the high energy input required for comminution results in structural damage in the production of fine-grain particle fractions, but such damage is healed virtually completely in the subsequent heat treatment process and hardly affects the magnetic properties of the finished magnet core. In mixes with ductile materials, packing density can be increased by increasing the ductile component, for example the pure iron component. This procedure is, for example, described in JP 2001-196216.
Problems are posed, however, by the production of dense magnet cores from amorphous FeBSi-based materials, which are favoured owing to their good magnetic properties. In the energy-intensive production of the fine-grain particle fractions, FeBSi-based materials form phases of iron borides, which represent permanent structural damage and adversely affect magnetic properties.
Disclosed herein is a method for the production of a powder composite core, which allows the production of particularly dense magnet cores from alloys produced in a rapid solidification process. Also disclosed herein is a particularly dense magnet core with low coercitive field strength.
One embodiment of a method described herein for the production of a magnet core comprises the following steps: First, at least one coarse-grain powder fraction is produced from an amorphous strip of a soft magnetic alloy. In addition, at least one fine-grain powder fraction is produced from a nanocrystalline strip, likewise of a soft magnetic alloy. Following comminution, the particle fractions may be sized in order to obtain an optimum particle size distribution. The particle fractions are then mixed to produce a multi-modal powder, the particles of the coarse-grain particle fraction having an amorphous structure, while the particles of the fine-grain particle fraction have a nanocrystalline structure. The multi-modal powder is then pressed to produce a magnet core.
The soft magnetic strip material is typically produced as amorphous strip in a rapid solidification process, the term “strip” in this context including a foil-like form or pieces of strip. To produce a nanocrystalline strip, the amorphous strip can then be subjected to heat treatment to obtain the nanocrystalline structure.
According to a basic concept of the invention, the aim is to minimise energy input in the comminution of the strip material to produce a powder. Energy input can be reduced by converting the strip into a nanocrystalline state prior to comminution, thus making it very brittle. In this brittle state, the fine-grain powder fractions can be produced without increasing energy input sufficiently for the formation of FeB phases. In this way, irreversible structural damage can be avoided. On the other hand, the production of the coarse-grain powder fraction from nanocrystalline strip is not advisable, because the flakes produced from nanocrystalline strip would also be nano-crystalline and therefore so brittle that they would not be compacted under pressure, but rather would disintegrate.
This problem can be solved by producing the fine-grain and the coarse-grain powder fractions by different means. By separately producing the fine-grain fractions from nanocrystalline strip and the coarse-grain fractions from amorphous strip, the roles played by the powder fractions in the production of the magnet core and their properties in the pressing process are taken into consideration. The production processes for the different powder fractions are “tailor-made” in a manner of speaking. As a result, the properties of the powder can be precisely adapted to pressing conditions and to the desired density of the finished magnet core before the pressing process.
In this way, an alloy capable of nanocrystallisation can be used even for the amorphous strip, provided it is still in a amorphous state at the time of pressing. However, the initially amorphous alloy capable of nanocrystallisation can be converted into a nanocrystalline alloy by heat treatment. As a result, a variety of alloy combinations can be used for the coarse- and fine-grain fractions: The fine-grain fraction is produced from an alloy capable of nanocrystallisation, which is already in a nanocrystalline state in the pressing process. The coarse-grain fraction, on the other hand, can be produced either from an alloy not capable of nanocrystallisation or from an alloy capable of nanocrystallisation, and in the latter case, the alloy can be converted into a nanocrystalline state after pressing.
The particles representing the fine-grain powder fraction advantageously have a diameter between 20 and 70 μm, while the particles representing the coarse-grain powder fraction have a diameter between 70 and 200 μm. With particles in this size range, relatively dense packing and, therefore, dense magnet cores can be obtained.
In one embodiment of the method, the amorphous strip is pre-embrittled by heat treatment at a pre-embrittling temperature Tembrittle prior to the production of the coarse-grain powder fraction in order to simplify comminution, the pre-embrittling temperature Tembrittle and the crystallisation temperature Tcrystal of the amorphous strip having the relationship Tembrittle<Tcrystal. The pre-embrittling temperature Tembrittle is therefore chosen so that it is low enough to avoid (nano-) crystallisation. It is further chosen to be low enough, and the duration of the heat treatment is chosen to be short enough, to make the particles produced from the strip ductile enough to avoid break-up in the pressing process. The pre-embrittling temperature Tembrittle advantageously is 100° C.≦Tembrittle≦400° C., preferably 200° C.≦Tembrittle≦400° C. The duration of the heat treatment may be 0.5 to 8 hours.
In an alternative embodiment of the method, the amorphous strip is comminuted to produce the coarse-grain powder fraction without any preceding heat treatment for pre-embrittling in the “as cast” state, i.e. in the state in which it is following the rapid solidification process. The amorphous strip is advantageously comminuted to produce the coarse-grain powder fraction at a grinding temperature Tmill of −196° C.≦Tmill≦20° C.
The nanocrystalline strip used to produce the fine-grain powder fraction is, for example, comminuted in a cutting mill. Using a cutting mill instead of, for example, a ball mill reduces energy input to a minimum and avoids irreversible structural damage.
In one embodiment of the method, the same alloy is used for the amorphous strip and for the nanocrystalline strip. In this case, the strip used to produce the fine-grain powder fraction is nanocrystallised by heat treatment following the rapid solidification process, while the strip used to produce the coarse-grain powder fraction is left in its amorphous state.
It is, however, alternatively possible to use different alloys. The first soft magnetic alloy for the amorphous strip may, for instance, be an alloy which is particularly suitable for processing in the amorphous state and which is sufficiently ductile, while the second soft magnetic alloy for the nanocrystalline strip may be an alloy which can be nanocrystallised particularly easily.
In view of these considerations, suitable soft magnetic alloys for both the amorphous and the nanocrystalline strip are soft magnetic iron-based alloys.
In one embodiment, the amorphous particles have the alloy composition MαYβZγ, wherein M is at least one element from the group including Fe, Ni and Co, wherein Y is at least one element from the group including B, C and P, wherein Z is at least one element from the group including Si, Al and Ge, and wherein α, β and γ are specified in atomic percent and meet the following conditions: 70≦α≦85; 5≦β≦20; 0≦γ≦20, wherein up to 10 atomic percent of the M component may be replaced by at least one element from the group including Ti, V, Cr, Mn, Cu, Zr, Nb, Mo, Ta and W and up to 10 atomic percent of the (Y+Z) component may be replaced by at least one element from the group including In, Sn, Sb and Pb.
The particles capable of nanocrystallisation may have the alloy composition (Fe1-aMa)100-x-y-z-α-β-γCuxSiyBzM′αM″βXγ, wherein M is Co and/or Ni, wherein M′ is at least one element from the group including Nb, W, Ta, Zr, Hf, Ti and Mo, wherein M″ is at least one element from the group including V, Cr, Mn, Al, elements of the platinum group, Sc, Y, rare earths, Au, Zn, Sn and Re, wherein X is at least one element from the group including C, Ge, P, Ga, Sb, In, Be and As, and wherein a, x, y, z, α, β and γ are specified in atomic percent and meet the following conditions: 0≦a≦0.5; 0.1≦x≦3; 0≦y≦30; 0≦z≦25; 0≦y+z 35; 0.1≦α≦30; 0≦β≦10; 0≦γ≦10.
As an alternative, the particles capable of nanocrystallisation may have the alloy composition (Fe1-a-bCoaNib)100-x-y-z MxByTz, wherein M is at least one element from the group including Nb, Ta, Zr, Hf, Ti, V and Mo, wherein T is at least one element from the group including Cr, W, Ru, Rh, Pd, Os, Ir, Pt, Al, Si, Ge, C and P, and wherein a, b, x, y and z are specified in atomic percent and meet the following conditions: 0≦a≦0.29; 0≦b≦0.43; 4≦x≦10; 3≦y≦15; 0≦z≦5.
For the strip capable of nanocrystallisation, one or more of the alloys Fe73.5Nb3Cu1Si15.5B7, Fe73.5Nb3Cu1Si13.5B9, Fe86Cu1Zr7B6, Fe91Zr7B3 and Fe84Nb7B9 can be used.
The multi-modal powder obtained by mixing coarse- and fine-grain powder fractions is advantageously pressed at a pressing temperature Tpress of Tpress>Tembrittle to produce a magnet core. This ensures that the coarse-grain particles, in particular, behave in a very ductile manner and that there is no further mechanical comminution during the pressing process.
After pressing, the magnet core is advantageously subjected to heat treatment at a heat treatment temperature Tanneal in order to relieve mechanical stresses introduced into the magnet core by pressing and to obtain good magnetic properties, in particular a low coercitive field strength. The heat treatment temperature Tanneal is expediently chosen such that the heat treatment temperature Tanneal and the crystallisation temperature Tcrystal of the first soft magnetic alloy have the relationship Tanneal Tcrystal. This results in the nanocrystallisation of the coarse-grain particles which still have an amorphous structure at this point. For this purpose, the heat treatment temperature is typically set above 500° C.
As an alternative, the heat treatment temperature Tanneal may be chosen such that the heat treatment temperature Tanneal and the crystallisation temperature Tcrystal of the first soft magnetic alloy have the relationship Tanneal≦Tcrystal. In this case, the nano-crystallisation of the amorphous particle fraction is avoided. The only purpose of the heat treatment in this case is the relief of mechanical stresses, and typically 400° C. Tanneal≦450° C.
All heat treatment processes are advantageously conducted in a controlled atmosphere to prevent corrosion and thus the premature ageing of the magnet core combined with a deterioration of its magnetic properties.
Prior to pressing, in certain embodiments, processing aids such as binders and/or lubricants are advantageously added to the multi-modal powder. In other embodiments, particles representing the coarse- and/or fine-grain powder fractions may be pickled in an aqueous or alcohol solution prior to pressing to apply an electrically insulating coating and then dried. An electrically insulating coating may also be applied by different means. It is used to reduce the resistivity of the magnet core and to reduce eddy-current losses.
A magnet core described herein comprises a soft magnetic powder made from particles, the particle size distribution being multi-modal. It can further comprise processing aids such as binders. In certain embodiments, the powder comprises at least one coarse-grain powder fraction with particles with an amorphous structure and at least one fine-grain powder fraction with particles with a nanocrystalline structure.
A magnet core of this type may combine an exceptionally high density with a low coercitive field strength, because the multi-modal particle size distribution permits a particularly dense packing of the particles, while the particle surfaces suffer only minor deformation and structural damage.
The magnet core according to the invention can be used in inductive components such as storage chokes, PFC chokes (chokes for power factor correction), switching power supplies, filter chokes or smoothing chokes.
Specific embodiments are described in greater detail below in order to further illustrate and exemplify the method and magnet core disclosed herein, without limiting the scope of the appended claims.
From a strip with the nominal composition Fe73.5Nb3Cu1Si15.5B7, particle fractions with the following particle diameters were produced: The nanocrystalline particles of the first fraction had diameters between 28 and 50 μm, the amorphous particles of the second fraction had diameters between 80 and 106 μm, and the likewise amorphous particles of the third fraction had diameters between 106 and 160 μm. The press-ready powder mix consisted of 29% flakes of the first fraction, 58% flakes of the second fraction and 10% flakes of the third fraction in addition to 2.8% binder mix and 0.2% lubricant. The mix was pressed at a pressure of 8 t/cm2 and a temperature of 180° C. to produce a magnet core. After pressing, the core had a density of 67 percent by volume. After pressing, the magnet core was subjected to a heat treatment lasting one hour in a controlled atmosphere at 560° C. The finished magnet core had a static coercitive field strength of 51.6 A/m.
From a strip with the nominal composition Fe73.5Nb3Cu1Si15.5B7, particle fractions with the following particle diameters were produced: The nanocrystalline particles of the first fraction had diameters between 40 and 63 μm, and the amorphous particles of the second fraction had diameters between 80 and 106 μm. The press-ready powder mix consisted of 48.5% flakes of the first fraction, 48.5% flakes of the second fraction and 2.8% binder mix and 0.2% lubricant. The mix was pressed at a pressure of 8 t/cm2 and a temperature of 180° C. to produce a magnet core. After pressing, the core had a density of 68.3 percent by volume. After pressing, the magnet core was subjected to a heat treatment lasting one hour in a controlled atmosphere at 560° C. The finished magnet core had a static coercitive field strength of 55.4 A/m.
For comparison, magnet cores were produced in the conventional way from purely amorphous powders.
From a strip with the nominal composition Fe73.5Nb3Cu1Si15.5B7, purely amorphous particles with particle diameters between 80 and 106 μm were produced. The press-ready powder mix consisted of 97% of these amorphous particles and 2.8% binder mix and 0.2% lubricant. The mix was pressed at a pressure of 8 t/cm2 and a temperature of 180° C. to produce a magnet core. After pressing, the core had a density of 61.7 percent by volume. After pressing, the magnet core was subjected to a heat treatment lasting one hour in a controlled atmosphere at 560° C. The finished magnet core had a static coercitive field strength of 71.0 A/m.
From a strip with the nominal composition Fe73.5Nb3Cu1Si15.5B7, purely amorphous particle fractions with the following particle diameters were produced: The particles of the first fraction had diameters between 40 and 63 μm, and the particles of the second fraction had diameters between 80 and 106 μm. The press-ready powder mix consisted of 48.5% flakes of the first fraction, 48.5% flakes of the second fraction and 2.8% binder mix and 0.2% lubricant. The mix was pressed at a pressure of 8 t/cm2 and a temperature of 180° C. to produce a magnet core. After pressing, the core had a density of 63.2 percent by volume. After pressing, the magnet core was subjected to a heat treatment lasting one hour in a controlled atmosphere at 560° C. The finished magnet core had a static coercitive field strength of 100.5 A/m.
These examples show that high densities can be combined with low coercitive field strengths of the magnet cores when using the method described herein. The low coercitive field strength in the magnet cores from examples 1 and 2 is due to the fact that the fine-grain particles, as a result of their production from a nanocrystalline material, do not suffer any significant irreversible structural damage caused by the formation of FeB phases.
As a result of the separate production of coarse-grain amorphous and fine-grain nano-crystalline powder fractions, the resulting powder mix meets all requirements: It is multi-modal and allows, even when using FeBSi-based alloys capable of nano-crystallisation, a very dense packing of the particles, resulting in a high density of the magnet core. Owing to their amorphous structure, the coarse-grain particles are ductile enough not to break up in the pressing process. And finally, being produced from a nanocrystalline starting material, the fine-grain particles are not irreversibly damaged by the formation of iron boride phases which would adversely affect the magnetic properties of the core.
The examples and embodiments described herein are provided to illustrate, rather than limit the scope of, the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 032 520 | Jul 2006 | DE | national |
This application claims benefit of the filing date of DE 10 2006 032 520.6, filed on Jul. 12, 2006, and of U.S. Provisional Application Ser. No. 60/820,222, filed on Jul. 24, 2006.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB2007/052771 | 7/11/2007 | WO | 00 | 4/10/2009 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2008/007345 | 1/17/2008 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 3255512 | Lochner et al. | Jun 1966 | A |
| 4076861 | Furukawa et al. | Feb 1978 | A |
| 4201837 | Lupinski | May 1980 | A |
| 4472334 | Gallimard | Sep 1984 | A |
| 4543208 | Horie et al. | Sep 1985 | A |
| 4601765 | Soileau et al. | Jul 1986 | A |
| 4743311 | Schultz et al. | May 1988 | A |
| 4891079 | Nakajima et al. | Jan 1990 | A |
| 4923533 | Shigeta et al. | May 1990 | A |
| 4985089 | Yoshizawa et al. | Jan 1991 | A |
| 5160379 | Yoshizawa et al. | Nov 1992 | A |
| 5252148 | Shigeta et al. | Oct 1993 | A |
| 5258473 | Niessner et al. | Nov 1993 | A |
| 5509975 | Kojima et al. | Apr 1996 | A |
| 5522948 | Sawa et al. | Jun 1996 | A |
| 5594397 | Uchikoba et al. | Jan 1997 | A |
| 5751207 | Poess | May 1998 | A |
| 5762967 | Sagawa et al. | Jun 1998 | A |
| 6001272 | Ikuma et al. | Dec 1999 | A |
| 6028353 | Nakano et al. | Feb 2000 | A |
| 6189204 | Shikama et al. | Feb 2001 | B1 |
| 6373368 | Shikama et al. | Apr 2002 | B1 |
| 6392525 | Kato et al. | May 2002 | B1 |
| 6425960 | Yoshizawa et al. | Jul 2002 | B1 |
| 6478889 | Kanekiyo et al. | Nov 2002 | B2 |
| 6710692 | Kato et al. | Mar 2004 | B2 |
| 6749767 | Mitani et al. | Jun 2004 | B2 |
| 6750723 | Yoshida et al. | Jun 2004 | B2 |
| 6791445 | Shibata et al. | Sep 2004 | B2 |
| 6814776 | Kanekiyo et al. | Nov 2004 | B2 |
| 6827557 | Kim | Dec 2004 | B2 |
| 6946097 | Deevi et al. | Sep 2005 | B2 |
| 7172660 | Song et al. | Feb 2007 | B2 |
| 7175716 | Tunnicliffe et al. | Feb 2007 | B2 |
| 7175717 | Song et al. | Feb 2007 | B2 |
| 7265651 | Brunner | Sep 2007 | B2 |
| 7532099 | Brunner | May 2009 | B2 |
| 20010015239 | Kanekiyo | Aug 2001 | A1 |
| 20020124914 | Kim | Sep 2002 | A1 |
| 20020158540 | Lindquist et al. | Oct 2002 | A1 |
| 20030156000 | Brunner | Aug 2003 | A1 |
| 20040045635 | Bandyopadhyay et al. | Mar 2004 | A1 |
| 20040079449 | Kanekiyo et al. | Apr 2004 | A1 |
| 20040089377 | Deevi et al. | May 2004 | A1 |
| 20040183643 | Brunner | Sep 2004 | A1 |
| 20050028889 | Song et al. | Feb 2005 | A1 |
| 20050034787 | Song et al. | Feb 2005 | A1 |
| 20050236071 | Koshiba et al. | Oct 2005 | A1 |
| 20070193657 | Brunner | Aug 2007 | A1 |
| 20080001702 | Brunner | Jan 2008 | A1 |
| 20090206975 | Nuetzel et al. | Aug 2009 | A1 |
| 20100194507 | Brunner | Aug 2010 | A1 |
| Number | Date | Country |
|---|---|---|
| 502063 | Jul 1930 | DE |
| 694374 | Jul 1940 | DE |
| 1740491 | Dec 1956 | DE |
| 1564643 | Jan 1970 | DE |
| 2816173 | Oct 1979 | DE |
| 3422281 | Dec 1984 | DE |
| 19608891 | Sep 1997 | DE |
| 69810551 | Mar 1999 | DE |
| 19844132 | Apr 1999 | DE |
| 19860691 | Mar 2000 | DE |
| 198 37 630 | May 2000 | DE |
| 19908374 | Sep 2000 | DE |
| 199 42 939 | Mar 2001 | DE |
| 100 64 024 | Jun 2001 | DE |
| 10024824 | Nov 2001 | DE |
| 100 31 923 | Jan 2002 | DE |
| 103 48 808 | Mar 2005 | DE |
| 103 48 810 | Mar 2005 | DE |
| 602 05 728 | Mar 2006 | DE |
| 10 2006 008 2 | Aug 2007 | DE |
| 0 216 457 | Apr 1987 | EP |
| 0299498 | Jan 1989 | EP |
| 0 302 355 | Feb 1989 | EP |
| 0455 113 | Nov 1991 | EP |
| 0271657 | May 1992 | EP |
| 0 502 397 | Sep 1992 | EP |
| 0 794 538 | Sep 1997 | EP |
| 0824755 | Feb 1998 | EP |
| 0899 753 | Mar 1999 | EP |
| 0 936 638 | Aug 1999 | EP |
| 1 371 434 | Dec 2003 | EP |
| 51092097 | Feb 1975 | JP |
| 57-039516 | Mar 1982 | JP |
| 57-187357 | Nov 1982 | JP |
| 59177902 | Oct 1984 | JP |
| 59179729 | Oct 1984 | JP |
| 61058450 | Mar 1986 | JP |
| 61-166902 | Jul 1986 | JP |
| 61-172709 | Aug 1986 | JP |
| 62-226603 | Oct 1987 | JP |
| 62-232103 | Oct 1987 | JP |
| 63-21807 | Jan 1988 | JP |
| 64-053404 | Mar 1989 | JP |
| 1-139702 | Jun 1989 | JP |
| 02-047812 | Feb 1990 | JP |
| 4-048005 | Feb 1992 | JP |
| 41-65605 | Jun 1992 | JP |
| 04-213804 | Aug 1992 | JP |
| 05-097907 | Apr 1993 | JP |
| 05-283238 | Oct 1993 | JP |
| 05-299232 | Nov 1993 | JP |
| 53-04018 | Nov 1993 | JP |
| 06-224023 | Aug 1994 | JP |
| 82-55717 | Oct 1996 | JP |
| 83-18542 | Dec 1996 | JP |
| 9-306715 | Nov 1997 | JP |
| 10-092623 | Apr 1998 | JP |
| 10-097913 | Apr 1998 | JP |
| 10-208923 | Aug 1998 | JP |
| 2000-182845 | Jun 2000 | JP |
| 2000-277357 | Oct 2000 | JP |
| 2001-068324 | Mar 2001 | JP |
| 2001-196216 | Jul 2001 | JP |
| 2004-063798 | Jul 2002 | JP |
| 2003-534656 | Nov 2003 | JP |
| 2004-179270 | Jun 2004 | JP |
| 2004-349585 | Dec 2004 | JP |
| 2005-150257 | Jun 2005 | JP |
| 2005-171275 | Jun 2005 | JP |
| 2006-118040 | May 2006 | JP |
| 338550 | May 1972 | SU |
| WO 0010755 | Mar 2000 | WO |
| WO 0025326 | May 2000 | WO |
| WO 0028556 | May 2000 | WO |
| WO 0030132 | May 2000 | WO |
| WO 0118828 | Mar 2001 | WO |
| WO 0191141 | Nov 2001 | WO |
| WO 03088281 | Oct 2003 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20110056588 A9 | Mar 2011 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60820222 | Jul 2006 | US |
