DE69810551T2 - Magnetic cores of the body or laminated type - Google Patents

Description

The present invention relates to a solid magnetic core and a laminated magnetic core made of a soft magnetic glassy alloy and suitable for use in transformers, choke coils, magnetic sensors and the like.

Magnetic cores made of 50% Ni-Fe permalloy, magnetic cores made of 80% Ni-Fe permalloy and magnetic cores made of silicon steel have been used for transformers, choke coils, magnetic sensors and the like. However, the magnetic cores made of these magnetic materials have a problem that they cause a large core loss, especially in a high frequency range, and a sharp temperature rise at a frequency of several tens of kHz or more. Such magnetic cores are therefore generally not usable in this frequency range.

In order to overcome the above problem, a specific laminated magnetic core has recently been used, which is constructed from a magnetic core body formed by torically winding a Co-based amorphous alloy tape having a small core loss and a high angle ratio, or a Fe-based amorphous alloy tape having a high saturation magnetic flux density and a high maximum magnetic permeation, or by punching such a tape into a given shape and then laminating the formed However, during winding or laminating of the tape, a gap of the order of 3 µm is likely to occur between adjacent tapes because the tape is concave or convex on both sides.

The volume occupied by an alloy ribbon in relation to the volume of a magnetic core body is called the lamination factor. In the above example, the lamination factor is calculated as follows:

20(um)/(20 + 3(um)) · 100 = 87%

This equation shows that the volume of a gap is large with respect to a magnetic core body, which means that it is not possible to make a smaller magnetic core.

Therefore, a magnetic core made by laminating an amorphous alloy ribbon remains a problem that a leakage of magnetic flux between two ribbons occurs more frequently, possibly resulting in an increase in core loss.

In addition, a technique has been developed in which a powder material obtained by crushing the above alloy ribbon is sintered and the sintered material is then solidified in a solid form. This technique requires that the powder material is sintered at a relatively low temperature so as to prevent it from crystallizing, which makes it difficult to manufacture a magnetic core. with a high density. The finished magnetic core may have an increased core loss.

To eliminate the above-mentioned problems of the prior art, the present invention provides a solid magnetic core having a minimized core loss. The invention further provides a laminated magnetic core having a minimized core loss and enabling downsizing.

According to the invention, there is provided a magnetic core which is produced by spark plasma sintering at a temperature rise rate of more than 1000/min and under a pressure of more than 2.94 x 10⁸ Pa, with a magnetic core body which is produced by sintering a powdery material made of a soft magnetic glassy alloy, the glassy alloy having a composition according to the following formula:

(Fe1-a-bCoaNib)100-x-y-zMxByTz

wherein 0 ≤ a ≤ 0.29, 0 ≤ b ≤ 0.43, 5 at.% ≤ x ≤ 20 at.%, 10 at.% ≤ y ≤ 22 at.%, and 0 at.% ≤ z ≤ 5 at.% are satisfied, M represents one or more elements selected from the group consisting of Zr, Nb, Ta, Hf, Mo, Ti and V, and T represents one or more elements selected from the group consisting of Cr, W, Ru, Rh, Pd, Os, Ir, Pt, Al, Si, Ge, C and P; the glassy alloy has a temperature interval ΔTx of 50°C or more in its supercooled liquid region, ΔTx is represented by the equation ΔTx = Tx - Tg, wherein Tx is a crystallization temperature and Tg is a glass transition temperature.

Alloys of the above type have been described in A. Inoue et al., Appl. Phys. Lett 71(4) (1997) 464-466.

Preferably, ΔTx may be greater than 60°C, wherein the value of a, regarded as a composition ratio of Co, may be 0.042 ≤ a ≤ 0.29 and the value of b, regarded as a composition ratio of Ni, may be 0.042 ≤ b ≤ 0.043.

The element M can be represented by the formula (M'1-cM"c) where M' is either one or both of Zr and Hf , M" is one or more elements selected from the group consisting of Nb, Ta, Mo, Ti and V, and the ratio c is 0 ≤ c ≤ 0.6.

The soft magnetic glassy alloy can have a ratio c of 0.2 ≤ c ≤ 0.4 or 0 ≤ c ≤ 0.2.

The magnetic core body can be manufactured by heat treating the soft magnetic glassy alloy at 427 to 627ºC.

Preferably, the soft magnetic glassy alloy may have a ΔTx of 50ºC or more and have a composition corresponding to the following formula:

(Fe1-a-bCoaNib)100-x-y-zMxByTz

wherein 0 < a < 0.29, 0 < b < 0.43, 0 at.% < z < 5 at.% are satisfied, M represents one or more elements selected from the group consisting of Zr, Nb, Ta, Hf, Mo, Ti and V, and T represents one or more elements selected from the group consisting of Cr, W, Ru, Rh, Pd, Os, Ir, Pt, Al, Si, Ge, C and P.

Preferably, ΔTx is greater than 60°C, the value of a, considered as a composition ratio of Co, is 0.042 < a < 0.29, and the value of b, considered as a composition ratio of Ni, is 0.042 < b < 0.043. The element M can be represented by the formula (M'1-cM"c) wherein M' is either one or both of Zr and Hf, M" is one or more elements selected from the group consisting of Nb, Ta, Mo, Ti and V, and the ratio c is 0 < c < 0.6.

The magnetic core body can be manufactured by heat treating the soft magnetic glassy alloy at 427 to 627ºC.

Element B can be replaced by C in an amount not exceeding 50%.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is an exploded view of the solid magnetic core according to the present invention.

Fig. 2 is a cross-sectional view showing important parts of the design of a spark plasma sintering apparatus for Use in the manufacture of the solid magnetic core of the invention.

Fig. 3 is a view showing a shape of a pulse current wave applied to the powder material by the spark plasma sintering device.

Fig. 4 is an exploded view of the laminated magnetic core according to the present invention.

Fig. 5 is an exploded view showing a modified form of the laminated magnetic core according to the present invention.

Fig. 6 is a graphical representation of the DSC curves of the ribbon grades of the glassy alloys composed of Fe₆₀Co₃Ni₇Zr₁₀B₆₀, Fe₅�6Co₃Ni₇Zr₁₀B₆₀, Fe₅�6Co₃Ni₇Zr₁₀B₆₀, Fe₄₉Co₁₄Ni₇Zr₁₀B₆₀, and Fe₄₆Co₁₇Ni₇Zr₁₀B₆₀, respectively.

Fig. 7 is a triangular diagram showing the dependence of ΔTx (= Tx - Tg) on the contents of Fe, Co and Ni with respect to the composition (Fe1-a-bCoaNib)₇₀₀Zr₁₀₀B₂₀.

Fig. 8 is a graphical representation of the X-ray diffraction patterns of quenched ribbons with variable layer thicknesses with respect to a composition Fe₅₆Co₇Ni₇Zr₄Nb₆B₂₀.

Fig. 9 is a graphical representation of the dependence of magnetic saturation flux density (Bs), magnetic remanence (Hc), magnetic permeability (ue) at 1 kHz and Magnetostriction (λs) on the content of Nb with respect to the composition types Fe₅₆Co₇Ni₇Zr10-xNbxB₂₀, where x is 0, 2, 4, 6, 8 and 10 at.%.

Fig. 10 is a graphical representation of the core loss of the solid magnetic cores made from magnetic core bodies of a composition Fe₅₆Co₇Ni₇Zr₈Nb₂B₅₀.

Fig. 11 is a graphical representation of the relationship between the layer thickness and the lamination factor with respect to the glassy alloy according to the invention.

Fig. 12 is a graph showing the relationship between the core loss and Bm with respect to each of the laminated magnetic cores made from ribbons having a composition of Fe56Co7Ni7Zr8Nb2B20.

Fig. 13 is a graph showing the relationship between the core loss and Bm with respect to each of the laminated magnetic cores made from ribbons having a composition of Fe62Co7Ni7Zr8Nb2B14.

Now, the solid magnetic core according to an embodiment of the present invention will be described.

The solid magnetic core of the invention can be made in a ring shape, for example. This ring-shaped solid magnetic core can be made from a magnetic core body obtained by sintering a powder material of a soft magnetic glassy alloy described below. or by pouring a hot melt of such a glassy alloy into a predetermined mold, followed by cooling the hot melt to a solid form. The magnetic core body is then covered with, for example, an epoxy resin or is encapsulated in a resin case for insulation protection.

In the manufacture of a solid magnetic core for use in an EI core, a magnetic core body is made by sintering a powder material of a soft magnetic glassy alloy to form an E core and an I core, and then bringing them together and integrally bonding them.

The resulting magnetic core body is covered with, for example, an epoxy resin at a specific portion for insulating protection of that specific portion or encapsulated in a resin case, thereby making the solid magnetic core for the EI core.

In Fig. 1, a preferred embodiment of the ring-shaped solid magnetic core 1 according to the present invention is shown. A solid magnetic core 1 is manufactured using a magnetic core body 3 obtained by sintering a powder material of a soft magnetic glassy alloy described below or by pouring a hot melt of such a glassy alloy into a given mold, followed by cooling the hot melt into a solid shape, and fitting the magnetic core body 3 into a hollow ring-shaped case 2 made of a resin.

The housing 2 may preferably be molded from polyacetal resin, polyethylene terephthalate resin or the like.

An adhesive 4 is applied to an inner surface of a bottom portion 2a of the housing 2 at two separate locations, as can be seen in Fig. 1, in order to stably connect the magnet core body 3 to the housing 2. Preferably, the number of locations coated with the adhesive is in the range of 2 to 4.

The adhesive 4 is selected from epoxy resin, silicone rubber and the like.

A method for producing the solid magnetic core 1 of the present invention by means of spark plasma sintering is described below.

Fig. 2 shows important parts of the embodiment of a spark plasma sintering apparatus suitable for use in the manufacture of the solid magnetic core 1 according to the invention. This embodiment of a spark plasma sintering apparatus consists essentially of a cylindrical hollow mold 11, an upper punch 12 and a lower punch 13, both punches being inserted in the hollow mold 11, a punch electrode 14 arranged to support the lower punch 13 and to act as an electrode on one side, wherein a pulse current described later flows, a punch electrode 15 arranged to press the upper punch 12 downwards and to act as an electrode on the other side, wherein the Pulse current flows, and a thermocouple 17 which is arranged to measure the temperature of a starting powder 16 which is present as a sandwich layer between the upper and lower punches 12, 13.

In the front sides of the upper and lower punches 12, 13, which are opposite each other, shapes are defined that correspond to the shape of a magnetic core body to be formed.

In addition, the above-mentioned important parts of the spark plasma sintering apparatus are housed in a chamber not shown. This chamber is connected to an evacuation system not shown and to an ambient gas supply system not shown, such that the starting powder (powder material) 16 to be filled between the upper and lower punches 12, 13 can be kept in a desired atmosphere, for example, an inert gas atmosphere or the like.

In order to manufacture the solid magnetic core 1 by using the spark plasma sintering apparatus shown above, a powder material 16 to be molded is first prepared. The powder material 16 can be obtained by melting a soft magnetic glassy alloy of a given composition described later and then pouring the melt, quenching using a single roll or a twin roll, solution spinning or solution extraction, or spraying with a high pressure gas, thereby molding the melt into various shapes including solid, ribbon-like, linear, powder-like or other shapes. and further granulating the non-powdery forms.

The soft magnetic glassy alloy for use in the present invention has a temperature interval Tri above 20°C when supercooled to a liquid, or above 40°C or above 50°C, depending on the alloy composition used. This temperature interval is unique and surprising with respect to the alloys known in the prior art. Moreover, such a soft magnetic glassy alloy has excellent soft magnetic properties at room temperature, which is not yet known and thus new.

Then, the powder material 16 prepared above is placed between the upper and lower punches 12, 13 of the spark plasma sintering apparatus shown in Fig. 2, and the chamber is evacuated on the inside thereof. The powder material 16 is formed by the pressure exerted upward and downward by the two punches 12, 13, and at the same time, it is heated by the flow of a pulse current illustrated in Fig. 3, thereby forming a magnetic core body 3 having a desired shape.

This spark plasma sintering apparatus enables the powder material 16 to be heated at a predetermined rate by means of a current flow, and further enables the temperature of such material to be precisely controlled according to the value of the current flow. Thus, temperature control can be carried out with a much higher accuracy than in the case of heating under Use of a heater so that sintering can take place under almost ideal, pre-designed conditions.

In carrying out the present invention, it is necessary that the sintering temperature is 300°C or more so as to form the powder material 16 into a solid shape. However, since the soft magnetic glassy alloy for use as the powder material 16 has a large temperature interval ΔTx (Tx - Tg) when supercooled to a liquid, the magnetic core body 3 can be advantageously produced with a high density by the pressure sintering in such a specific temperature range.

However, when the sintering temperature is close to a crystallization temperature, magnetic anisotropy tends to occur due to crystalline nucleation (structural order in a short range) and crystallization, which degrades the resulting soft magnetic properties.

Due to the mechanism of the spark plasma sintering device, the sintering temperature to be monitored is a temperature read from the thermocouple 17 attached to the die 11. The temperature read in this way is lower than that to which the powder material 16 is heated.

For these reasons, the sintering temperature in the invention should preferably be within the range T ≤ Tx, where Tx is the crystallization temperature and T is the sintering temperature.

According to the present invention, the rate of temperature rise for sintering is preferably greater than 10°C/min. Lower rates of temperature rise lead to development of undesirable crystalline phases.

The sintering pressure is greater than 2.94 · 10⁸ PA [3 t/cm²]. At lower pressures, the formation of the magnetic core body fails.

The formed magnetic core body 3 may be heat-treated, with the result that its magnetic properties can be improved. The temperature in the heat treatment is higher than the Curie temperature, but lower than a temperature at which crystals are formed which would be responsible for deteriorating the magnetic properties. In particular, the heat treatment temperature is preferably 427 to 627°C, more preferably 477 to 527°C.

The magnetic core body 3 produced in this way has the same composition as the soft magnetic glassy alloy used as powder material 16 and thus has the best soft magnetic properties at room temperature. In such a magnetic core body, the magnetic properties can be further improved by heat treatment.

Because the magnetic core body 3 is inserted, the solid magnetic core 1 has excellent soft magnetic properties and can therefore be used in a wide range of applications as a magnetic core for transformers, choke coils and magnetic sensors. Magnetic cores can thus be produced whose Properties are better than those of conventional magnetic cores.

The foregoing description relates to a magnetic core body 3, which is manufactured by spark plasma sintering the powder material 16 composed of the soft magnetic glassy alloy. Without being limited to this sintering method, such a magnetic core body can be suitably obtained by a sintering method in which pressure is applied by extrusion.

In addition, the magnetic core body 1 of the present invention can be obtained by using a magnetic core body 3 which is prepared by pouring a hot melt of the above soft magnetic glassy alloy and then cooling the melt into a solid form.

This hot melt can be prepared by weighing starting materials such as pure metals Fe, Co, Ni and Zr, pure crystalline boron and the like in their respective given amounts and then melting these materials in an Ar atmosphere and in vacuum by, for example, a high frequency induction heater, an arc furnace, a trough furnace, a reflection furnace or the like.

The resulting hot alloy melt is poured into a mold having a given shape, followed by gradual cooling of the melt to a solid state, thereby forming a magnetic core body 3 having a desired shape.

The magnetic core body 3 thus obtained, like that produced by sintering the powder alloy, has a high density and excellent soft magnetic properties and is thus useful as a magnetic core for use in transformers, choke coils, magnetic sensors and the like.

Next, the laminated magnetic core according to the present invention will be described with reference to the drawings.

The laminated magnetic core of the invention can be obtained, for example, in a ring shape. This ring-shaped laminated magnetic core can be made of a magnetic core body which is made by molding a tape of a soft magnetic glassy alloy, which will be described later, and then torically winding the tape, or by press-punching the tape into a plurality of rings and then laminating the rings in a given number. The formed magnetic core body is further covered with, for example, an epoxy resin, or is encapsulated in a resin case for insulation protection.

In the manufacture of a laminated magnetic core for use in an EI core, a magnetic core body is manufactured by press-punching the above soft magnetic glassy alloy ribbon into a plurality of E-type layers or a plurality of I-type layers, laminating the E-layers together, or laminating the I-layers together, thereby forming an E-core or an I-core. and then integrally bonding the E and I cores together. The formed magnetic core is covered with, for example, an epoxy resin at a certain portion, or is encapsulated in a resin case for insulation protection of a certain portion, thereby producing the laminated magnetic core for the EI core.

In Fig. 4, a preferred embodiment of the laminated magnetic core in a ring shape according to the present invention is shown. A laminated magnetic core 21 is formed using a magnetic core body 24 which is made by toroidally winding a tape 23 of a soft magnetic glassy alloy, which will be described later, and fitting the magnetic core body 24 into a case 22 which is made of a resin in a hollow ring shape.

Preferably, the housing 22 may be molded from, for example, polyacetal resin, polyethylene terephthalate resin, or the like.

As shown in Fig. 4, an adhesive 25 is applied at two separate locations on an inner surface of a bottom portion 22a of the housing 22 in order to fix the magnetic core body 24 in a stable position on the housing 22. The number of locations to be coated with the adhesive 25 is preferably in the range of 2 to 4.

The adhesive 25 is selected from epoxy resin, silicone rubber and the like.

Fig. 5 shows another embodiment of the laminated magnetic core in ring form.

The magnetic core 31 is constructed with a magnetic core body 33, which is made by laminating rings punched out of the tape 23 of the soft magnetic glassy alloy, which will be described later, fitting the magnetic core body 33 into a case 32 molded from a resin in a hollow ring shape, and fitting a sheath 34 to the case 32 after the magnetic core body 33 is fitted into the case 32. The case 32 and the sheath 34 are preferably molded from polyacetal resin, polyethylene terephthalate resin, or the like.

Fe system alloys composed of Fe-P-C system, Fe-P-B system, Fe-Ni-Si system and the like have so far been known to have a glass transition. However, these alloys cannot be practically formed into glassy alloys because they have an extremely small temperature width ΔTx in their supercooled liquid regions.

In contrast, the soft magnetic glassy alloy according to the present invention contains one or more of Fe, Co and Ni as main components and has a unique temperature range ΔTx of greater than 20°C in its supercooled liquid region, which is represented by the equation ΔTx = Tx - Tg (wherein Tx is a crystallization temperature and Tg is a glass transition temperature), or a temperature interval of 25 to 60°C or more depending on the composition of the alloy used. This makes it It is possible to cast such a glassy alloy by gradual cooling and to cast it into a ribbon-like or linear shape with a relatively large cross-sectional thickness.

In order to achieve an increased lamination factor, the amorphous alloy layers used for the laminated magnetic cores 21 may have a large thickness.

Conventional amorphous alloys have a very small ΔTx in their supercooled liquid regions, as already stated above. In the case where a hot melt with a given composition of such an amorphous alloy is rapidly cooled by solution quenching to form a ribbon, it is necessary that such a ribbon be no more than 50 µm in order to prevent its magnetic properties from deteriorating. This suggests a limitation on the improved lamination factor.

The soft magnetic glassy alloy according to the present invention can provide a tape ranging in its layer thickness from 100 to 200 µm. The magnetic core bodies 23, 33, which can be produced by winding or laminating such tapes, have such a high lamination factor that miniaturization is possible. Furthermore, the tape is capable of reducing its core loss in comparison with the same layer thicknesses of the conventional amorphous alloys because of its high specific resistance.

The soft magnetic glassy alloy 23 for use in the laminated magnetic core can be produced, for example, by preparing the contained elements as powder, mixing powders in the above-mentioned composition range, melting the resulting mixture in an inert gas atmosphere such as an Ar gas and using a melting device such as a crucible to obtain a hot melt of the selected composition, and then quenching the hot melt by a single roll method. The single roll method referred to here refers to a method in which a hot melt is rapidly cooled by spraying it onto a rotating metal roll to form a glassy metal having a ribbon-like shape.

One of the soft magnetic glassy alloys for use in the above-described solid and laminated magnetic cores is composed of one or more elements selected from the group consisting of Fe, Co and Ni as main components and is further provided with one or more elements selected from the group consisting of Zr, Nb, Ta, Hf, Mo, Ti and V, and B in their given amounts.

One of the soft magnetic glassy alloys is given by the following formula

(Fe1-a-bCoaNib)100-x-yMxBy

where 0 ≤ a ≤ 0.29, 0 ≤ b ≤ 0.43, 5 at.% ≤ x ≤ 20 at.% and 10 at.% ≤ y ≤ 22 at.% are preferred, and M is one or more Elements selected from the group consisting of Zr, Nb, Ta, Hf, Mo, Ti and V.

Incidentally, the above composition should have a temperature interval ΔTx of greater than 20ºC in its supercooled liquid region, where ΔTx is represented by the equation ΔTx = Tx - Tg, where Tx is a crystallization temperature and Tg is a glass transition temperature.

It is advantageous for the above composition that Zr or Hf necessarily be present and that ΔTx is higher than 25ºC.

More preferably, in the above composition, ΔTx may be higher than 60°C, the ratio a may be 0.042 ≤ a ≤ 0.29, and the ratio b may be 0.042 ≤ b ≤ 0.43, and satisfy the formula (Fe1-a-bCoaNib)100-x-yNxBy defined above.

Other soft magnetic glassy alloys are given by the following formula

(Fe1-a-bCoaNib)100-x-y-zMxByTz

wherein 0 ≤ a ≤ 0.29, 0 ≤ b ≤ 0.43, 5 at.% ≤ x ≤ 20 at.% and 10 at.% ≤ y ≤ 22 at.% and 0 at.% ≤ z ≤ 5 at.% are satisfied, M is one or more elements selected from the group consisting of Zr, Nb, Ta, Hf, Mo, Ti and V, and T is one or more elements selected from the group consisting of Cr, W, Ru, Rh, Pd, Os, Ir, Pt, Al, Si, Ge, C and P. In the above formula (Fe1-a-bCoaNib)100-x-y-zMxByTz, according to the invention, the ratio a 0.042 ≤ a ≤ 0.29 and the ratio b 0.042 ≤ b ≤ be 0.43.

The above element M can be represented by the formula (M'1-cM"c) wherein M' is either one or both of Zr and Hf, M" is one or more elements selected from the group consisting of Nb, Ta, Mo and V, and the ratio c 0 ≤ c ≤ 0.6.

The ratio c in the above composition may further be 0 ≤ c ≤ 0.4 or 0 ≤ c ≤ 0.2.

Moreover, the ratio a can be 0.042 ≤ a ≤ 0.25 and the ratio b can be 0.042 ≤ b ≤ 0.1.

The soft magnetic glassy alloy can be heat treated at a temperature of 427ºC (700 K) to 627ºC (900 K). This heat treatment enables a high magnetic permeability to be achieved. In addition, the element B can be replaced by an element C in an amount of 50% or less in the above composition.

An explanation will be given of the reasons for the above-mentioned compositions of the soft magnetic glassy alloy in the practice of the present invention.

The elements Fe, Co and Ni for use as main components in the invention are necessary to achieve magnetic properties and to obtain high saturation magnetic flux density and soft magnetic properties.

In particular, the ratio a as a composition ratio of Co may preferably be selected be such that 0 ≤ a ≤ 0.29, and the ratio b may be selected as a composition ratio of Ni such that 0 ≤ b ≤ 0.43 to ensure a ΔTx of 50 to 60ºC. The ratio a as a composition ratio of Co may preferably be such that 0 ≤ a ≤ 0.29, and the ratio b may be selected as a composition ratio of Ni such that 0 ≤ b ≤ 0.43 to ensure a ΔTx of 50 to 60ºC. To achieve a ΔTx greater than 60ºC, the ratio a may be set to 0.042 ≤ a ≤ 0.29 and the ratio b may be set to 0.042 ≤ b ≤ 0.43.

Regarding the above compositions, it is desired that the ratio a as a composition ratio of Co is 0.042 ≤ a ≤ 0.25 to obtain good soft magnetic properties, and that the ratio b as a composition ratio of Ni is 0.042 ≤ b ≤ 0.1 to obtain a high saturation magnetic flux density.

M is one or more elements selected from Zr, Nb, Ta, Hf, Mo, Ti and V. These elements are effective to make the final alloy amorphous and may preferably be in the range between greater than 5 at.% and less than 20 at.%. To achieve even better magnetic properties, this range may be between greater than 5 at.% and less than 15 at.%. In particular, Zr is effective among these elements. A part of Zr may be replaced by an element such as Nb or the like, and in such a case the ratio c 0 ≤ c ≤ 0.6 may be used to achieve a high ΔTx. To enable a ΔTx of 80°C or higher, the ratio may preferably be 0.2 ≤ c ≤ 0.4.

B has the ability to provide amorphism, and this element is added in an amount between greater than 10 at.% and less than 22 at.%. Amounts less than 10 at.% reduce ΔTx and prevent the production of a magnetic core body 3 with a high density, while amounts greater than 22 at.% make the magnetic core body formed brittle. In order to achieve a better ability to provide amorphism and good magnetic properties, the content of B may more preferably be above 16 at.% but below 20 at.%.

The compositions specified above may further comprise one or more elements expressed by T selected from Cr, W, Ru, Rh, Pd, Os, Ir, Pt, Al, Si, Ge, C and P.

These elements are added in amounts between more than 0 at.% and less than 5 at.%. They are used to significantly improve corrosion resistance. Deviations from this range are responsible for reduced magnetic properties and a poorer ability to form amorphism.

The soft magnetic glassy alloys of the above specified compositions can have magnetic properties at room temperature and can show further improvement in such properties after heat treatment.

With respect to the process for producing the soft magnetic glassy alloy according to the invention, It should be mentioned that a suitable cooling rate is determined from the composition of the alloy used, the processing means used, the size of a product to be obtained, the shape of a product to be obtained and other parameters. In general, a range of 10² to 10⁶ ºC/s or the like can be taken as a measure of cooling rates.

In the solid magnetic core 1 described above, according to the present invention, a solid magnetic core body 3 can be manufactured with a high density by sintering a powder material of a soft magnetic glassy alloy by means of spark plasma sintering, the soft magnetic glassy alloy having a temperature interval ΔTx of greater than 20°C in its supercooled liquid region, ΔTx being represented by the equation ΔTx = Tx - Tg, where Tx is a crystallization temperature and Tg is a glass transition temperature. Thus, a reduced core loss is achieved.

In addition, in the solid magnetic core 1, the sintering temperature is optionally selected from a temperature range satisfying the relationship T ≤ Tx, where Tx is a crystallization temperature and T is a sintering temperature. This results in a magnetic core body 3 having the same composition as the soft magnetic glassy alloy for use as a starting material and exhibiting a high saturation magnetic flux density and an excellent magnetic permeability with a consequent reduction in core loss.

A heat treatment of the sintered magnetic core body 3 enabled such core bodies to develop a higher magnetic saturation flux density and a higher magnetic permeability.

In the solid magnetic core 1, the magnetic core body 3 can be formed by a so-called casting process in addition to a spark plasma sintering process, in which a hot melt of an alloy is solidified by cooling. The solid magnetic core 1 can thus be produced with cost savings.

The above soft magnetic glassy alloy is composed of one or more elements selected from Fe, Co and Ni as main components, one or more elements selected from Zr, Nb, Ta, Hf, Mo, Ti and V and B, so that the temperature interval ΔTx in its supercooled liquid region can be made larger. This means that the powder material of the alloy can be sintered at a higher temperature, and the magnetic core body 3 can thus be obtained with a higher density. The core loss is therefore small with respect to the solid magnetic core 1.

The solid magnetic core 1 of the invention is provided with a magnetic core body 3 composed of a soft magnetic glassy alloy having a ΔTx higher than 50°C, a composition represented by the following formula, high magnetic permeability, low magnetic susceptibility and excellent soft magnetic properties. Smaller core loss is thus possible.

(Fe1-a-bCOaNib)100-x-yMxBy

where 0 ≤ a ≤ 0.29, 0 ≤ b ≤ 0.43, 5 at.% ≤ x ≤ 20 at.% and 10 at.% ≤ y ≤ 22 at.% and 0 at.% ≤ z ≤ 5 at.% are satisfied, M is one or more elements selected from the group consisting of Zr, Nb, Ta, Hf, Mo, Ti and V, or

(Fe1-a-bCoaNib)100-x-y-zMxByTz

wherein 0 ≤ a ≤ 0.29, 0 ≤ b ≤ 0.43, 5 at.% ≤ x ≤ 20 at.% and 10 at.% ≤ y ≤ 22 at.% and 0 at.% ≤ z ≤ 5 at.% are satisfied, M is one or more elements selected from the group consisting of Zr, Nb, Ta, Hf, Mo, Ti and V, and T is one or more elements selected from the group consisting of Cr, W, Ru, Rh, Pd, Os, Ir, Pt, Al, Si, Ge, C and P.

The laminated magnetic cores 21, 31 described above are provided with a magnetic core body 24 made by torically winding a tape of a soft magnetic glassy alloy having a temperature interval ΔTx of greater than 20°C in its supercooled liquid region, where ΔTx is represented by the equation ΔTx = Tx - Tg, where Tx is a crystallization temperature and Tg is a glass transition temperature, or with a magnetic core body 33 made by laminating such a tape. Thus, a magnetic core can be made from a tape having a higher layer thickness so that the lamination factors of the laminated magnetic cores 21, 33 are large. This ensures a reduced core loss and a downsized product.

The above soft magnetic glassy alloy is composed of one or more elements selected from Fe, Co and Ni as main components, one or more elements selected from Zr, Nb, Ta, Hf, Mo, Ti and V and B, so that the temperature interval ΔTx in its supercooled liquid region can be made larger. Accordingly, the laminated magnetic cores 21, 31 can be manufactured from a tape having an increased layer thickness with an improved lamination factor and with a reduced core loss.

The laminated magnetic cores 21, 31 are provided with magnetic core bodies 24, 33 composed of a soft magnetic glassy alloy with a temperature interval ΔTx of greater than 50ºC, which has a composition represented by the following formula, a high magnetic permeability, a low magnetic susceptibility, a high saturation magnetic flux density and excellent soft magnetic properties. A low core loss is thus possible.

(Fe1-a-bCoaNib)100-x-yMxBy

where 0 ≤ a ≤ 0.29, 0 ≤ b ≤ 0.43, 5 at.% ≤ x ≤ 20 at.% and 10 at.% ≤ y ≤ 22 at.% are satisfied, M is one or more elements, selected from Zr, Nb, Ta, Hf, Mo, Ti and V, or

(Fe1-a-bCoaNib)100-x-y-zMxByTz

where 0 ≤ a ≤ 0.29, 0 ≤ b ≤ 0.43, 5 at.% ≤ x ≤ 20 at.% and 10 at.% ≤ y ≤ 22 at.% and 0 at.% ≤ z ≤ 5 at.% are satisfied, M is a or more elements selected from Zr, Nb, Ta, Hf, Mo, Ti and V, and T is one or more elements selected from Cr, W, Ru, Rh, Pd, Os, Ir, Pt, Al, Si, Ge, C and P.

EXAMPLES example 1

Pure metals. Fe, Co, Ni and Zr and pure crystalline boron were mixed in an Ar gas atmosphere and melted by an arc to produce a matrix alloy.

Subsequently, this matrix alloy was melted using a quartz nozzle and subjected to a single roll process in which the melt was quenched by being sprayed onto a copper roller rotating at 40 m/s in an Ar gas atmosphere from a hole of 0.4 mm diameter formed at a lower end of the nozzle at a spray pressure of 0.39 10⁵ Pa. Thus, glassy alloy ribbon grades having a width of 0.4 to 1 mm and a thickness of 13 to 22 µm were prepared. The resulting grades were examined by differential scanning calorimetry (DSC).

Fig. 6 shows the DSC curves of the glassy alloy ribbons composed of Fe₆₀Co₃Ni₇Zr₁₀B₂₀, Fe₅�6Co₃Ni₇Zr₁₀B₂₀, Fe₅�6Co₃N₇Zr₁₀B₂₀, Fe₄₋₃Co₃N₇Zr₁₀B₂₀, and Fe₄₋₃Co₃Ni₇Zr₁₀B₂₀, respectively.

Each variety has been shown to have a wide range of supercooled liquid when the temperature, and that it crystallized when the temperature exceeded the supercooled liquid region. The temperature interval ΔTx in the supercooled liquid region is represented by the equation ΔTx = Tx - Tg, and the value of Tx - Tg of each variety is beyond 60ºC and in the range of 64 to 68ºC, as can be seen from Fig. 6. A substantial equilibrium state of a supercooled liquid region was obtained in a wide range from 596ºC (869 K) a little below a temperature indicating crystallization due to an exothermic peak, to 632ºC (905 K).

Fig. 7 is a triangular diagram of the dependence of ΔTx (= Tx - Tg) on the contents of Fe, Co and Ni with respect to the composition (Fe1-a-bCoaNib)₇₀₀Zr₁₀₀B₂₀.

As is obvious from Fig. 7, the value of Tx beyond 25°C is in all ranges of the composition of (Fe1-a-bCoaNib)₇₀₀Zr₁₀₀B₂₀.

With respect to the value of Tg, it has been shown that Tg increases monotonically as Co is increased in a range from about 7 at.% to about 50 at.%. On the other hand, with respect to ΔTx, it has also been shown that the value of 17 is large in an Fe-rich composition, as can be seen from Fig. 7, and that to achieve a ΔTx of greater than 60°C, the content of Co is preferably in the range between above 3 at.% and below 20 at.%, and that the content of Ni is preferably in the range between above 3 at.% and below 30 at.%.

The above composition is expressed by the ratios of Fe, Co and Ni as (Fe1-a-bCoaNib)₇₀₋Zr₁₀₋B₂₋. Thus, for Co having a content of more than 3 at.%, the ratio a of Co is above 0.042, and for Co having a content of less than 20 at.%, the ratio a of Co is below 0.29 because (Fe1-a-bCoaNib) is 70 at.%. For Ni having a content of more than 3 at.%, the ratio b of Ni is above 0.042, and for Ni having a content of less than 30 at.%, the ratio b is below 0.43.

Example 2

Pure metals of Fe, Co, Ni and Zr and pure crystalline boron were mixed in an Ar gas atmosphere and melted by an arc to produce a matrix alloy Fe56Co7Ni7Zr4B20.

Subsequently, this matrix alloy was melted using a quartz nozzle and subjected to a single roll process in which the melt was quenched by spraying it onto a copper roll rotating at 40 m/s in an Ar gas atmosphere. In this way, glassy alloy strips were produced.

Alloy ribbons with a layer thickness of 20 to 195 µm were manufactured with appropriate settings for the opening of a nozzle, for the distance between a nozzle tip and a roll surface (gap), for the revolutions of a roll, for the injection pressure and for the atmospheric pressure.

The varieties were examined by X-ray diffraction, with the results shown in Fig. 8.

As is evident from these figures, each of the varieties was found to have a hollow pattern at 2Θ = 38 to 52º and thus an amorphous structure at a single layer.

Example 3

The procedure of Example 1 was repeated except that the compositions Fe56Co7Ni7Zr10-xNbxB20, where x is 0, 2, 4, 6, 8 and 10 at.% were used. Grades of glassy alloy ribbons were thus obtained.

The resulting species were then heat treated at 527ºC (800 K) for 5 minutes.

Fig. 9 shows the dependence of the saturation magnetic flux density (Bs), the coercivity (Hc), the magnetic permeability (ue) at 1 kHz and the magnetostriction (λs) on the content of Nb with respect to the grades.

The saturation magnetic flux density (Bs) decreased in both a rapidly cooled and a heat-treated grade with the addition of Nb. A Nb-free grade was more than 0.9 (T), while a grade containing 2 at.% Mb was about 0.75 (T).

The magnetic permeability (ue) was 5.031 in a quenched grade which did not contain Nb, and 2.228 in a quenched grade containing 10 at.% Nb. The permeability dropped in a quenched grade containing 10 at.% Nb. However, heat treatment resulted in a greatly improved permeability (ue) and was 25.000, particularly in a grade containing 2 at.% Nb.

The magnetic remanence (Hc) was low at 50 A/m (= 0.625 Oe) in both a Nb-free grade and a grade containing 2 at.% Nb. In particular, a grade containing less than 2 at.% Nb showed a remarkably good value, of about 5 A/m (= 0.625 Oe). Heat treatment ensures excellent magnetic remanence (Hc) even in a grade containing more than 4 at.% Nb.

It has been found, as stated above, that Nb should be added in an amount between above 0 at.% and below 2 at.% in order to obtain good soft magnetic properties in the alloy grades of the foregoing composition. Accordingly, a solid magnetic core and a laminated magnetic core composed of a soft magnetic glassy alloy having a high saturation magnetic flux density, a low magnetic remanence and a high magnetic permeability can be manufactured. In case of manufacturing a transformer using such a magnetic core, a finished transformer with a low core loss and with a good power transmission efficiency is possible.

Example 4 (Example of the invention)

The procedure of Example 1 was repeated except that a composition Fe56Co7Ni7Zr8Nb2B20 was used. In this way, glassy alloy ribbons were prepared.

These ribbons were then granulated in atmosphere by using a rotor mill. The resulting powder was sieved into a powder with a particle diameter of 53 to 105 µm and used as starting powder in the following steps.

Approximately 2 g of the starting powder was filled into a mold made of WC using a hand press and molded into the shape shown in Fig. 2. The powder was pressed by the upper and lower punches in a chamber having an atmosphere of 3.99 x 10-3 Pa [3 x 10-5 Torr] and was heated by flowing a pulse wave from a power supply system. As shown in Fig. 3, the pulse waveform was set to flow 12 pulses and pause for 2 pulses. The powder was heated with a current supply of 4,700 to 4,800 A maximum.

Sintering was carried out by heating the grades from room temperature to a sintering temperature at a pressure of 6.37 x 10⁸ Pa [6.5 t/cm2] and then holding them at the latter temperature for approximately 5 minutes. The rate of temperature rise was 100°C/min.

A hollow cylindrical grade with an outer diameter of 10 mm and an inner diameter of 6 mm and a thickness of 2 mm, as shown in Fig. 1, was manufactured by spark wire forming, whereby a magnetic core body was obtained.

This magnetic core body was fitted into a case made of a polyacetal resin as shown in Fig. 1. In this example, a bottom portion of the case was coated with an adhesive on an inner surface at two separate locations so that the magnetic core body was permanently attached to the case. Three solid magnetic cores were manufactured by the same treatment.

The core losses of the solid magnetic cores according to the present invention are shown in Fig. 8.

In Fig. 10, the relationship between the working magnetic flux density (Bm) and the core loss is shown with respect to a comparable magnetic core formed by laminating a silicon layer (Si 3.5%).

As can be seen from Fig. 10, both the three magnetic cores of the invention and the comparison magnetic core show an increase in core loss as the working magnetic flux densities decrease. However, the three magnetic cores shown by the invention always have a smaller core loss than the comparison magnetic core in the range of the measured working magnetic flux density.

Example 5

In the same manner as in Example 1, strips were prepared from a glassy alloy with variable layer thicknesses of a composition Fe₅₆Co₇Ni₇Zr₄Nb₆B₂₀.

Subsequently, each tape was punched into a ring shape, after which the rings were laminated in a given number. An epoxy or polyimide resin was placed between the layers to provide insulation between the layers and bonding between the layers. In this way, a laminated magnetic core of ring shape with an outer diameter of 12 mm, inner diameter of 4 mm and a thickness of 5 mm was manufactured as shown in Fig. 5. isr.

Fig. 11 shows the relationship between the layer thickness and the lamination factor with respect to the laminated magnetic core obtained above. The lamination factor was determined by a cross-sectional observation using a microscope.

As is obvious from Fig. 11, the lamination factor improves with increasing layer thickness and becomes almost constant at or above 97% when the layer thickness exceeds 100 µm. A laminated magnetic core composed of the soft magnetic glassy alloy according to the invention causes no drop in the soft magnetic properties as stated above. Thus, a laminated magnetic core with a low core loss can be obtained.

On the other hand, a known amorphous alloy of Fe78Si9B13 only gives a band of the order of 20 µm. In such a case, the lamination factor is only 87%.

Since the conventional amorphous alloy has a small ΔTx, it is necessary to form a ribbon with a thickness of not more than 50 µm so as not to impair the soft magnetic properties in the manufacture of such a ribbon by rapidly cooling a hot melt of an alloy with a given composition by a solution quenching process. Because thicknesses greater than 50 µm lead to a reduction in the soft magnetic properties, an increased lamination factor and improved soft magnetic properties cannot be obtained in a well-balanced manner. This fails to produce a laminated magnetic core with a reduced core loss.

Example 6

In the same manner as in Example 1, a 20 µm thick ribbon of a glassy alloy Fe₅₆Co₇Ni₆Zr₈Nb₂B₅₀ and a 20 µm thick ribbon of a glassy alloy Fe₆₂Co₇Ni₆Zr₈Nb₂B₁₄ were prepared. Each such ribbon was punched into a ring shape and the rings were laminated as in Example 5. The resulting laminate was heat treated at 527°C (800 K) for 5 minutes.

Thereafter, the laminate was impregnated with a polyimide resin as in Example 5, thereby preparing a laminated magnetic core.

Fig. 12 and Fig. 13 show the relationship between the working magnetic flux density (Bm) and the core loss with respect to the laminated magnetic cores prepared above.

For comparison purposes, the core loss of a laminated magnetic core made of silicon steel (Si 6.5%) is also shown in both figures.

In Fig. 12 and Fig. 13 the results of three different varieties formed by the same treatment are shown.

The laminated magnetic cores of the invention, as is clear from Fig. 12 and Fig. 13, have a smaller core loss than the comparative magnetic core.

Claims (2)

1. A magnetic core manufactured by spark plasma sintering at a temperature rise rate of more than 10ºC/min and under a pressure of more than 2.94 x 10⁸ Pa (3 t/cm²), with a magnetic core body manufactured by sintering a powdery material of a soft magnetic glassy alloy, wherein the glassy alloy has a composition corresponding to the following formula: (Fe1-a-bCOaNib)100-x-y-zMxByTz wherein 0 ≤ a ≤ 0.29, 0 ≤ b ≤ 0.43, 5 at.% ≤ x ≤ 20 at.%, 10 at.% ≤ y ≤ 22 at.%, and 0 at.% ≤ z ≤ 5 at.% are satisfied, M represents one or more elements selected from the group consisting of Zr, Nb, Ta, Hf, Mo, Ti and V, and T represents one or more elements selected from the group consisting of Cr, W, Ru, Rh, Pd, Os, Ir, Pt, Al, Si, Ge, C and P; the glassy alloy has a temperature interval ΔTx of 50ºC or more in its supercooled region, ΔTx is represented by the equation ΔTx = Tx - Tg, where Tx is a crystallization temperature and Tg is a glass transition temperature. 2. A magnetic core produced by spark plasma sintering according to claim 1, wherein ΔTx is greater than 60ºC, wherein the Value of a, regarded as a composition ratio of Co, is 0.042 ≤ a ≤ 0.29, and value of b, regarded as a composition ratio of Ni, is 0.042 ≤ b ≤ 0.043.