Patent Application
20150243421
The present invention relates to an ultrafine-crystalline alloy ribbon which can be wound and rewound without fracture, a fine-crystalline, soft-magnetic alloy ribbon obtained by heat-treating it, and a magnetic device comprising the fine-crystalline, soft-magnetic alloy ribbon.
Soft-magnetic materials used for various reactors, choke coils, pulse power magnetic devices, antennas, cores of transformers, motors and power generators, current sensors, magnetic sensors, electromagnetic wave-absorbing sheets, etc. include silicon steel, ferrite, Co-based, amorphous, soft-magnetic alloys, Fe-based, amorphous, soft-magnetic alloys, and Fe-based, fine-crystalline, soft-magnetic alloys. Though silicon steel is inexpensive and has a high magnetic flux density, it suffers large loss at high frequencies, and is difficult to be made thin. Because ferrite has a low saturation magnetic flux density, it is easily saturated magnetically in high-power applications operable with large magnetic flux densities. Because the Co-based, amorphous, soft-magnetic alloys are expensive and have as low saturation magnetic flux densities as 1 T or less, parts made of them for high-power applications are inevitably large, and their loss increases with time due to thermal instability. Though the Fe-based, amorphous, soft-magnetic alloys have as high saturation magnetic flux densities as about 1.5 T, they are not sufficient, and their coercivity is not sufficiently low.
On the other hand, the Fe-based, fine-crystalline, soft-magnetic alloys have high saturation magnetic flux densities and excellent soft-magnetic properties. An example of Fe-based, fine-crystalline, soft-magnetic alloys is disclosed in WO 2007/032531. This Fe-based, fine-crystalline, soft-magnetic alloy has a composition represented by the formula of Fe100-x-y-zCuxByXz, wherein X is at least one element selected from the group consisting of Si, S, C, P, Al, Ge, Ga and Be, and x, y and z are numbers meeting the conditions of 0.123 x≦3, 8≦y≦20, 0<z≦10, and 10<y+z≦24 by atomic %, and a structure comprising crystal grains having an average particle size of 60 nm or less dispersed in a proportion of 30% or more by volume in an amorphous matrix; and having as high saturation magnetic flux density as 1.7 T or more and low coercivity.
This Fe-based, fine-crystalline, soft-magnetic alloy is produced by quenching an Fe-based alloy melt to form an ultrafine-crystalline alloy ribbon comprising fine crystal grains having an average particle size of 30 nm or less dispersed in a proportion of less than 30% by volume in an amorphous matrix, and subjecting this ultrafine-crystalline alloy ribbon to a high-temperature, short-time heat treatment or a low-temperature, long-time heat treatment. The quenched alloy ribbon is peeled from a cooling roll, wound around a reel with its tip end attached thereto, and if necessary, rewound.
Though ultrafine-crystalline alloy ribbons inherently have poor windability because of low toughness and thus easy fracture, they should be wound to a neatly laminated coil shape in mass production. To this end, reels with flanges are used. It has been found, however, that side portions of the ribbon come into contact with flanges of a winding reel in rewinding, making it likely that the ultrafine-crystalline alloy ribbon is frequently fractured. Such problems do not occur in amorphous alloy ribbons having relatively high toughness.
Accordingly, an object of the present invention is to provide an ultrafine-crystalline alloy ribbon, which can be wound and rewound without frequent fracture even when a conventional winding reel with flanges is used.
Another object of the present invention is to provide a fine-crystalline, soft-magnetic alloy ribbon obtained from this ultrafine-crystalline alloy ribbon, which has a high saturation magnetic flux density and excellent soft-magnetic properties.
A further object of the present invention is to provide a magnetic device comprising the above fine-crystalline, soft-magnetic alloy ribbon.
As a result of intensive research in view of the above objects, the inventors have found that in the production of an ultrafine-crystalline alloy ribbon by a liquid-quenching method, the formation of ultrafine crystal grains-depleted regions having a lower number density of ultrafine crystal grains in both side portions enables the ultrafine-crystalline alloy ribbon to exhibit sufficient fracture resistance due to the toughness of the ultrafine crystal grains-depleted regions, thereby extremely lowering the frequency of fracture due to contact with the reel flanges. The present invention has been completed based on such finding.
Thus, the ultrafine-crystalline alloy ribbon of the present invention has a structure, in which ultrafine crystal grains having an average particle size of 30 nm or less are dispersed in a proportion of more than 0% and less than 30% by volume in an amorphous matrix; an ultrafine crystal grains-depleted region having a smaller number density of ultrafine crystal grains than in a center portion of the ribbon being formed in a region of 0.2 mm in width from each side of the ribbon; and the number density of ultrafine crystal grains having particle sizes of 3 nm or more being less than 500/μm2 in the ultrafine crystal grains-depleted region.
In the ultrafine crystal grains-depleted regions, the number density of ultrafine crystal grains having particle sizes of 3 nm or more is preferably 100/μm2 or less. In a center portion other than the ultrafine crystal grains-depleted regions, the number density of ultrafine crystal grains having particle sizes of 3 nm or more is preferably 500/μm2 or more. The upper limit of the number density of ultrafine crystal grains in the center portion is preferably 3000/μm2.
The total width of both ultrafine crystal grains-depleted regions is preferably 5% or less of the entire width of the ultrafine-crystalline alloy ribbon.
The ribbon is preferably made of a magnetic alloy having a composition represented by the general formula of Fe100-x-y-zAxByXz, wherein A is Cu and/or Au, X is at least one element selected from the group consisting of Si, S, C, P, Al, Ge, Ga and Be, and x, y and z are numbers meeting the conditions of 0<x≦5, 8≦y≦22, 0≦z≦10, and x+y+z≦25 by atomic %.
The fine-crystalline, soft-magnetic alloy ribbon of the present invention, which is obtained by heat-treating the above ultrafine-crystalline alloy ribbon, has a structure, in which fine crystal grains having an average particle size of 60 nm or less are dispersed in a proportion of 30% or more by volume in an amorphous matrix; grain-grown regions comprising fine crystal grains having larger particle sizes than the average particle size being formed in both side portions; and the total width of both grain-grown regions being 5% or less of the entire width of the fine-crystalline, soft-magnetic alloy ribbon.
The magnetic device of the present invention comprises the above fine-crystalline, soft-magnetic alloy ribbon.
[1] Ultrafine-Crystalline Alloy Ribbon
(1) Ultrafine Crystal Grains-Depleting Region
The ultrafine-crystalline alloy ribbon is heat-treated to accelerate the growth of ultrafine crystal grains, thereby obtaining an fine-crystalline, soft-magnetic alloy ribbon comprising 30% or more by volume of fine crystal grains having an average particle size of 60 nm or less, which are dispersed in an amorphous matrix. The term “ultrafine crystal grains” used herein means crystal nuclei precipitated in an amorphous matrix of an ultrafine-crystalline alloy obtained by quenching an alloy melt, and the term “fine crystal grains” means crystal grains grown from the ultrafine crystal grains by heat treatment.
The soft-magnetic properties of the fine-crystalline, soft-magnetic alloy ribbon is influenced by the particle size and volume fraction of fine crystal grains, which can be adjusted to some extent by a heat treatment process. What is important to obtain desired particle size and volume fraction is to adjust the number density of ultrafine crystal grains in the secondary cooling process. With respect to the ultrafine crystal grains and the fine crystal grains, the “volume fraction” is determined from a photomicrograph by a lineal intercept method, and the “number density” is the number of crystal grains counted per a unit area on a photomicrograph.
As described above, Cu clustering occurs in the secondary cooling process, and the number density of ultrafine crystal grains changes depending on the cooling speed particularly in a range of about 300-500° C. It has conventionally been considered desirable that the number density of ultrafine crystal grains is uniform in the entire ribbon. However, an ultrafine-crystalline alloy ribbon containing ultrafine crystal grains has low toughness, likely suffering fracture at the time of winding and rewinding. Paying attention to the fact that the starting points of fracture are substantially in both side portions, intensive research has revealed that the reduction of the number density of ultrafine crystal grains in side portions, namely the formation of ultrafine crystal grains-depleted regions in side portions, makes it possible to prevent fracture at the time of winding and rewinding. The ultrafine crystal grains-depleted region has a structure close to an amorphous phase, preferably having a substantially amorphous phase.
A high cooling speed (good cooling efficiency) forms an amorphous phase, resulting in a low number density of ultrafine crystal grains. As shown in
Because the width of each region 1b, 1b having a reduced number density of ultrafine crystal grains is not necessarily constant in a longitudinal direction, a region 15 of 0.2 mm in width from each side 12, 14 within the region 1b, 1b, in which decrease in the number density of ultrafine crystal grains is clearly observed, is defined as an “ultrafine crystal grains-depleted region.” To secure toughness necessary for mass production, the number density of ultrafine crystal grains 13 having particle sizes of 3 nm or more (confirmed by the naked eye in a TEM photograph having magnification of 20,000 times) should be less than 500/μm2 in the ultrafine crystal grains-depleted region 15. A structure comprising ultrafine crystal grains 13 at a number density of less than 500/μm2 has toughness substantially close to that of an amorphous phase. Because the ultrafine crystal grains-depleted region 15 is formed substantially continuously in a longitudinal direction in the ultrafine-crystalline alloy ribbon, the ultrafine-crystalline alloy ribbon has improved fracture resistance.
In the ultrafine crystal grains-depleted region 15 having a reduced number density of ultrafine crystal grains, grain growth easily occurs by heat treatment. Accordingly, the ultrafine crystal grains-depleted region 15 becomes a “grain-grown region” after heat treatment. Coarse crystal grains reduce magnetic saturability in a low magnetic field. Paying attention to a ratio B80/B8000, in which B80 is a magnetic flux density in a low magnetic field (80 A/m), and B8000 is a magnetic flux density in a high magnetic field (8000 A/m) (substantially equal to a saturation magnetic flux density Bs), B80/B8000 tends to become smaller as crystal grains become coarser. B800/B8000 is substantially equal to B80/BS. When regions with poor magnetic saturability are 5% or less of the entire ribbon, B80/B8000 is as high as 95%, indicating that the ribbon has good magnetic saturability. Accordingly, when the total width of the ultrafine crystal grains-depleted regions 15 is 5% or less of the entire width of the ribbon, the ribbon has magnetic saturability within an acceptable range. For example, when the ribbon is as wide as 25 mm, the width of each ultrafine crystal grains-depleted region (grain-grown region) 15 may be 25×0.05/2=0.625 mm or less. A percentage of the total width of the grain-grown regions to the entire width of the ribbon is preferably 4% or less, more preferably 2% or less. With the grain-grown regions having such width, the ribbon has improved fracture resistance (toughness) necessary for rewinding, etc., while securing enough magnetic saturability at low frequencies.
(2) Structure
The ultrafine-crystalline alloy ribbon has a structure, in which ultrafine crystal grains having an average particle size of 30 nm or less are dispersed in a proportion of more than 0% and 30% or less by volume in an amorphous matrix. When the ultrafine crystal grains have an average particle size of more than 30 nm, fine crystal grains become coarse after heat treatment, resulting in poor soft-magnetic properties. The lower limit of the average particle size of ultrafine crystal grains is about 0.5 nm from the measurement limit, and it is preferably 1 nm or more, more preferably 2 nm or more. To obtain excellent soft-magnetic properties, the average particle size of ultrafine crystal grains is preferably 5-25 nm, more preferably 5-20 nm. In the Ni-containing composition, the average particle size of ultrafine crystal grains is preferably about 5-15 nm. The volume fraction of ultrafine crystal grains is more than 0% by volume in the ultrafine-crystalline alloy ribbon. With a volume fraction exceeding 30% by volume, however, the average particle size of ultrafine crystal grains tends to be more than 30 nm, providing the ribbon with such insufficient toughness that it cannot easily be handled in subsequent steps. On the other hand, without ultrafine crystal grains (if completely amorphous), coarse crystal grains would be easily formed by a heat treatment. The volume fraction of ultrafine crystal grains is preferably 5-30%, more preferably 10-25%, in the ultrafine-crystalline alloy ribbon.
When an average distance between ultrafine crystal grains (average distance between their centers of gravity) is 50 nm or less, the magnetic anisotropy of fine crystal grains is preferably averaged, resulting in reduced effective crystal magnetic anisotropy. When the average distance is more than 50 nm, the magnetic anisotropy is less averaged, resulting in high effective crystal magnetic anisotropy and poor soft-magnetic properties.
(3) Composition
A magnetic alloy used in the present invention preferably has a composition represented by the general formula of Fe100-x-y-zAxByXz, wherein A is Cu and/or Au, X is at least one element selected from the group consisting of Si, S, C, P, Al, Ge, Ga and Be, and x, y and z are numbers meeting the conditions of 0<x≦5, 8≦y≦22, 0≦z≦10, and x+y+z≦25 by atomic %. Of course, the magnetic alloy may contain inevitable impurities. To have a saturation magnetic flux density Bs of 1.7 T or more, it has a fine-crystalline (nano-crystalline) structure of bcc-Fe. To obtain this structure, the Fe content should be high. Specifically, the Fe content is 75 atomic % or more, preferably 77 atomic % or more, more preferably 78 atomic % or more.
When 0.1≦x≦3, 10≦y≦20, 0≦z≦10, and 10<y+z≦24, in the above composition range, the saturation magnetic flux density Bs is 1.7 T or more. When 0.1≦x≦3, 12≦y≦17, 0<z≦7, and 13≦y+z≦20, the saturation magnetic flux density Bs is 1.74 T or more. Also, when 0.1≦x≦3, 12≦y≦15, 0<z≦5, and 14≦y+z≦19, the saturation magnetic flux density Bs is 1.78 T or more. Further, when 0.1≦x≦3, 12≦y≦15, 0<z≦4, and 14≦y+z≦17, the saturation magnetic flux density Bs is 1.8 T or more. With the preferred composition ranges of elements described below, the soft-magnetic properties and productivity can be improved.
To have good soft-magnetic properties, specifically coercivity of 24 A/m or less, preferably 12 A/m or less, and a saturation magnetic flux density Bs of 1.7 T or more, the ultrafine-crystalline alloy contains a nucleus-forming element A (Cu and/or Au) insoluble in Fe, in an Fe—B-based basic composition stably providing an amorphous phase even at a high Fe content. Specifically, Cu and/or Au insoluble in Fe are added to an Fe—B-based alloy containing 88 atomic % or less of Fe, which stably provides a main amorphous phase, to precipitate ultrafine crystal grains. The ultrafine crystal grains uniformly grow by a subsequent heat treatment.
When the amount x of the element A is too little, the precipitation of ultrafine crystal grains is difficult. With more than 5 atomic % of the element A, quenching provides a brittle ribbon having an amorphous phase as a main phase. From the aspect of cost, the element A is preferably Cu. Because soft-magnetic properties tend to be poor with more than 3 atomic % of Cu, the amount x of Cu contained is preferably 0.3-2 atomic %, more preferably 1-1.7 atomic %, most preferably 1.2-1.6 atomic %. When Au is contained, it is preferably 1.5 atomic % or less.
B (boron) is an element promoting the formation of an amorphous phase. Less than 8 atomic % of B makes it difficult to obtain an ultrafine-crystalline alloy ribbon having an amorphous phase as a main phase, and more than 22 atomic % of B provides an alloy ribbon with a saturation magnetic flux density of less than 1.7 T. Accordingly, the amount y of B contained should meet the condition of 8≦y≦22. The amount y of B contained is preferably 11-20 atomic %, more preferably 12-18 atomic %, most preferably 12-17 atomic %.
The element X is at least one element selected from the group consisting of Si, S, C, P, Al, Ge, Ga and Be, particularly Si. Because the addition of the element X makes higher a temperature of precipitating Fe—B or Fe—P (when P is added) having large crystal magnetic anisotropy, a heat treatment temperature can be elevated. A high-temperature heat treatment increases the percentage of fine crystal grains, resulting in increased Bs, and improved squareness of a B—H curve, while suppressing the degeneration or discoloration of a ribbon surface. Though the lower limit of the amount z of the element X may be 0 atomic %, 1 atomic % or more of the element X can form an oxide layer of the element X on the ribbon surface, sufficiently suppressing the oxidation of the ribbon. When the amount z of the element X exceeds 10 atomic %, Bs becomes less than 1.7 T. The amount z of the element X is preferably 2-9 atomic %, more preferably 3-8 atomic %, most preferably 4-7 atomic %.
Among the element X, P is an element improving the capability of forming an amorphous phase, suppressing the growth of fine crystal grains, and the segregation of B to an oxide coating. Thus, P is preferable to achieve high toughness, high Bs and good soft-magnetic properties. When S, C, Al, Ge, Ga or Be is used as the element X, magnetostriction and magnetic properties can be adjusted.
Part of Fe may be substituted by at least one element D selected from the group consisting of Ni, Mn, Co, V, Cr, Ti, Zr, Nb, Mo, Hf, Ta and W. The amount of the element D contained is preferably 0.01-10 atomic %, more preferably 0.01-3 atomic %, most preferably 0.01-1.5 atomic %. Among the element D, Ni, Mn, Co, V and Cr have an effect of moving a high-B-concentration region toward the surface, providing a near-surface region with a structure close to the matrix, thereby improving the soft-magnetic properties (magnetic permeability, coercivity, etc.) of the soft-magnetic alloy ribbon. Because the element D predominantly enters an amorphous phase remaining after a heat treatment together with such metalloid elements as the element A, B, Si, etc., it suppresses the growth of fine crystal grains having a high Fe content, to reduce their average particle size, thereby improving the saturation magnetic flux density Bs and the soft-magnetic properties.
Particularly when part of Fe is substituted by Co or Ni soluble in Fe together with the element A, the amount of the element A that can be added increases to make a crystal structure finer, thereby improving soft-magnetic properties. The amount of Ni is preferably 0.1-2 atomic %, more preferably 0.5-1 atomic %. Less than 0.1 atomic % of Ni provides an insufficient effect of improving handleability (cuttability and windability), and more than 2 atomic % of Ni reduces BsB80 and Hc. The amount of Co is preferably 0.1-2 atomic %, more preferably 0.5-1 atomic %.
Ti, Zr, Nb, Mo, Hf, Ta and W also predominantly enter an amorphous phase remaining after a heat treatment together with the element A and metalloid elements, contributing to improvement in a saturation magnetic flux density Bs and soft-magnetic properties. On the other hand, when these elements having large atomic weights are too much, the amount of Fe per a unit weight is low, resulting in poor soft-magnetic properties. The total amount of these elements is preferably 3 atomic % or less. Particularly in the case of Nb and Zr, their total amount is preferably 2.5 atomic % or less, more preferably 1.5 atomic % or less. In the case of Ta and Hf, their total amount is preferably 1.5 atomic % or less, more preferably 0.8 atomic % or less.
Part of Fe may be substituted by at least one element selected from the group consisting of Re, Y, Zn, As, Ag, In, Sn, Sb, platinum-group elements, Bi, N, O, and rare earth elements. The total amount of these elements is preferably 5 atomic % or less, more preferably 2 atomic % or less. To obtain a particularly high saturation magnetic flux density, the total amount of these elements is preferably 1.5 atomic % or less, more preferably 1.0 atomic % or less.
[2] Production Method of Ultrafine-Crystalline Alloy Ribbon
(1) Alloy Melt
An alloy melt used for the ultrafine-crystalline alloy ribbon preferably has a composition represented by the above the general formula of Fe100-x-y-zAxByXz, wherein A is Cu and/or Au, X is at least one element selected from the group consisting of Si, S, C, P, Al, Ge, Ga and Be, and x, y and z are numbers meeting the conditions of 0<x≦5, 8≦y≦22, 0≦z≦10, and x+y+z≦25 by atomic %. Taking for example a case where the element A is Cu in the above composition, a method for producing an ultrafine-crystalline alloy ribbon by a single-roll method will be explained in detail below, of course without intention of restricting the present invention thereto.
(2) Quenching of Melt
In the case of quenching by a single-roll method, the temperature of the alloy melt is preferably higher than the melting point of the alloy by 50-300° C. For example, in the case of producing a ribbon of several tens of micrometers in thickness in which ultrafine crystal grains are precipitated, a melt at about 1300-1400° C. is preferably ejected from a nozzle onto a cooling roll. An atmosphere in the single-roll method is air or an inert gas (Ar, nitrogen, etc.) when the alloy does not contain an active metal, or an inert gas (Ar, He, nitrogen, etc.) or vacuum when it contains an active metal. To form an oxide coating on the surface, the quenching of a melt is conducted preferably in an oxygen-containing atmosphere (for example, air).
Materials for the cooling roll are suitably high-thermal-conductivity, pure copper, or copper alloys such as Cu—Be, Cu—Cr, Cu—Zr, Cu—Zr—Cr, etc. In the case of mass production, or in the case of producing thick and/or wide ribbons, the cooling roll is preferably cooled with water. Because the cooling of the roll with water affects the volume fraction of ultrafine crystal grains, it is effective to keep the cooling capability of the cooling roll, which may be called “cooling speed,” from the start to end of casting. Because the cooling capability of the cooling roll is correlated with the temperature of cooling water in a mass production line, it is effective to keep the cooling water at a predetermined temperature or higher.
(3) Width and Position of Ultrafine-Crystalline Alloy Ribbon on Cooling Roll
To form ultrafine crystal grains with a sufficient number density in a center portion of the ultrafine-crystalline alloy ribbon, and ultrafine crystal grains-depleted regions 15 with a low number density in both side portions, it is necessary (a) to optimize the cooling conditions (a material for the cooling roll, the structure of cooling water paths, the amount of cooling water, etc.) affecting the volume fraction of ultrafine crystal grains, and (b) to optimize the relation between a cooling roll width and a ribbon width, and the position of the ribbon on the cooling roll.
In a center portion of the ultrafine-crystalline alloy ribbon, the ribbon should be exposed to a temperature of 300° C. to 500° C. for 0.01 second or more in the secondary cooling process. When the ribbon temperature is lower than the above temperature range before the secondary cooling process, or when the cooling time is shorter than described above, too rapid quenching takes place, resulting in a low number density of ultrafine crystal grains. This occurs when the cooling roll is too wide relative to the ribbon as shown in
When a ribbon 1 having a proper width is located substantially in a center region of the cooling roll 2 as shown in
Intensive research has revealed that when a ribbon 1 has a width W of 5-250 mm, which is 50% or less of the width L of a cooling roll 2, and when with the distance S is 30-150 mm, a 1-mm-wide region extending from each side 12, 14 of the ribbon 1 is cooled about 100-300° C. lower than in a center portion of the ribbon in the primary cooling process, resulting in a good ultrafine crystal grains-depleted region 15. In the case of a ribbon 1 having a width W of 5-250 mm, which is more than 50% of the width L of the cooling roll 2, temperature elevation is remarkable in the entire cooling roll 2, so that the distance S should be 50-200 mm.
When the width L of the cooling roll 2 is too large relative to the width W of the ribbon 1 as shown in
(4) Adjustment of Gap
In the casting of a ribbon by a single-roll method, the thickness, cross section shape, surface undulation, etc. of the ribbon can be controlled by adjusting the puddle. To adjust the puddle, the control of a distance (gap) between the nozzle and the cooling roll, and the adjustment of the pressure and weight of an ejected melt are effective. Because the pressure and weight of an ejected melt may change depending on parameters such as the remaining amount and temperature of the melt, their control is difficult. On the contrary, the gap can be relatively easily adjusted by always monitoring the distance between the cooling roll and the nozzle, and feedbacking it. Accordingly, it is preferable to control the thickness, cross section shape, surface undulation, etc. of the ultrafine-crystalline alloy ribbon by adjusting the gap.
In general, a wider gap provides a better melt flow, effective for making the ribbon 1 thicker and preventing the puddle from collapsing. However, too wide a gap provides the ribbon 1 with a semioval cross section having a thicker center portion and thinner side portions, generating a cooling speed difference due to the thickness difference, and thus precipitating different amounts of ultrafine crystal grains. To form good ultrafine crystal grains-depleted regions in both side portions, the gap is preferably as relatively wide as 150-400 μm, with a low ejecting pressure of an alloy melt onto the cooling roll 2. The gap is more preferably 200-300 μm.
(5) Peripheral Speed of Cooling Roll
To control the cooling speed of the ribbon 1, which has a close relation to the formation of ultrafine crystal grains, the peripheral speed of the cooling roll 2 is preferably controlled. A higher peripheral speed of the cooling roll 2 provides a smaller number of ultrafine crystal grains, and a lower peripheral speed increases ultrafine crystal grains. To promote the formation of ultrafine crystal grains in a center portion 1a of the ribbon 1, the peripheral speed of the cooling roll is preferably 15-50 m/s, more preferably 20-40 m/s, most preferably 25-35 m/s. It has been found that the peripheral speed of the cooling roll 2 affects the formation of ultrafine crystal grains-depleted regions 15. A higher peripheral speed of the cooling roll 2 provides a higher cooling speed of the ribbon 1, promoting the formation of ultrafine crystal grains-depleted regions 15. When an ultrafine-crystalline alloy ribbon 1 of 10-40 μm in thickness and 5-250 mm in width is formed by a single-roll method, the peripheral speed of the cooling roll 2 having a width meeting the above condition is preferably 15-50 m/second, more preferably 20-40 m/second.
(6) Peeling Temperature
With an inert gas (nitrogen, etc.) blown from a nozzle to a gap between an ultrafine-crystalline alloy ribbon obtained by quenching and the cooling roll, the ribbon is peeled from the cooling roll. The peeling temperature (correlated with the cooling time) of the ribbon also affects the volume fraction of ultrafine crystal grains. The peeling temperature of the ribbon, which can be adjusted by changing the position of a nozzle blowing an inert gas (peeling position), is generally 170-350° C., preferably 200-340° C., more preferably 250-330° C. With the peeling temperature of lower than 170° C., the ribbon is excessively quenched, making the alloy structure substantially amorphous. On the other hand, when the peeling temperature is higher than 350° C., crystallization by Cu proceeds excessively, making the ribbon too brittle. With a proper cooling speed, ultrafine crystal grains are not formed in a ribbon surface region with a reduced amount of Cu by quenching, but many ultrafine crystal grains are precipitated inside the ribbon by a relatively slow cooling speed.
The peeled ultrafine-crystalline alloy ribbon is wound directly around a reel by a synchronous winding machine in many cases. Because the temperature is relatively high inside the ribbon, the ribbon is desirably cooled sufficiently before winding to prevent further crystallization. For example, an inert gas (nitrogen, etc.) is preferably blown to the peeled ribbon to cool it to substantially room temperature, and the ribbon is then wound.
[3] Fine-Crystalline, Soft-Magnetic Alloy Ribbon
The ultrafine-crystalline alloy ribbon is heat-treated to obtain a fine-crystalline, soft-magnetic alloy ribbon having a structure, in which fine crystal grains having a body-centered cubic (bcc) structure and an average particle size of 60 nm or less are dispersed in a volume fraction of 30% or more, preferably 50% or more, in an amorphous phase. Of course, fine crystal grains have a larger average particle size than that of ultrafine crystal grains which are not subjected to the heat treatment. The average particle size of fine crystal grains is preferably 15-40 nm.
(1) Heat Treatment Method
(a) High-Temperature, Short-Time Heat Treatment
The ultrafine-crystalline alloy ribbon of the present invention may be subjected to a high-temperature, high-speed heat treatment, by which the ribbon is heated to the highest temperature at a temperature-elevating speed of 100° C./minute or more, and kept at the highest temperature for 1 hour or less. An average temperature-elevating speed up to the highest temperature is preferably 100° C./minute or more. Because a temperature-elevating speed in a high-temperature region of 300° C. or higher largely affects the magnetic properties of the ribbon, the average temperature-elevating speed at 300° C. or higher is preferably 100° C./minute or more. The highest temperature in the heat treatment is preferably equal to or higher than (TX2−50)° C., wherein TX2 is a precipitation temperature of a compound, specifically 430° C. or higher. With the highest temperature of lower than 430° C., sufficient precipitation and growth of fine crystal grains do not occur. The upper limit of the highest temperature is preferably 500° C. (TX2) or lower. Even if the highest temperature is kept for more than 1 hour, fine crystallization does not further proceed, resulting in low productivity. The keeping time of the highest temperature is preferably 30 minutes or less, more preferably 20 minutes or less, most preferably 15 minutes or less. Such high-temperature heat treatment can suppress the growth of crystal grains and the formation of a compound as long as it is conducted in a short period of time, resulting in low coercivity, an improved magnetic flux density in a low magnetic field, and reduced hysteresis loss.
(b) Low-Temperature, Long-Time Heat Treatment
Another heat treatment is a low-temperature, low-speed heat treatment, by which the ribbon is kept at the highest temperature of about 350° C. or higher and lower than 430° C. for 1 hour or more. From the aspect of mass production, the keeping time of the highest temperature is preferably 24 hours or less, more preferably 4 hours or less. To suppress increase in coercivity, an average temperature-elevating speed is preferably 0.1-200° C./minute, more preferably 0.1-100° C./minute. This heat treatment provides a fine-crystalline, soft-magnetic alloy ribbon having high squareness.
(c) Heat Treatment Atmosphere
Though a heat treatment atmosphere may be air, the oxygen concentration of the heat treatment atmosphere is preferably 6-18%, more preferably 8-15%, most preferably 9-13%, to form an oxide coating having a desired layer structure by diffusing Si, Fe, B and Cu toward the surface. The heat treatment atmosphere is preferably a mixed gas of an inert gas such as nitrogen, Ar, helium, etc., and oxygen. The dew point of the heat treatment atmosphere is preferably −30° C. or lower, more preferably −60° C. or lower.
(d) Heat Treatment in Magnetic Field
To provide the fine-crystalline, soft-magnetic alloy ribbon with good induction magnetic anisotropy by a heat treatment in a magnetic field, a magnetic field having sufficient intensity to saturate the soft-magnetic alloy is preferably applied, in a period in which the heat treatment temperature is 200° C. or higher (preferably 20 minutes or more), during temperature elevation, in a period in which the highest temperature is kept, and/or during cooling. Though different depending on the shape of the ribbon, the magnetic field intensity is preferably 8 kA/m or more, in any case where it is applied in a width direction of the ribbon (height direction in the case of an annular core) or in a longitudinal direction of the ribbon (circumferential direction in the case of an annular core). The magnetic field may be a DC magnetic field, an AC magnetic field, or a pulse magnetic field. The heat treatment in a magnetic field provides a fine-crystalline, soft-magnetic alloy ribbon having a high or low squareness ratio in a DC hysteresis loop. In the case of a heat treatment with no magnetic field, the fine-crystalline, soft-magnetic alloy ribbon has a moderate squareness ratio in a DC hysteresis loop.
(2) Surface Treatment
The fine-crystalline, soft-magnetic alloy ribbon may be provided with an oxide coating such as SiO2, MgO, Al2O3, etc., if necessary. With a surface treatment during the heat treatment, the resultant oxide has a high bonding strength. A core of this ribbon may be impregnated with a resin, if necessary.
(3) Matrix Structure of Fine-Crystalline, Soft-Magnetic Alloy Ribbon
In the heat-treated amorphous matrix, fine crystal grains having an average particle size of 60 nm or less and a body-centered cubic (bcc) structure are dispersed at a volume fraction of 30% or more. When the average particle size of fine crystal grains exceeds 60 nm, the ribbon has poor soft-magnetic properties. When the volume fraction of fine crystal grains is less than 30%, the ribbon is too amorphous, having a low saturation magnetic flux density. The average particle size of fine crystal grains after the heat treatment is preferably 40 nm or less, more preferably 30 nm or less. The lower limit of the average particle size of fine crystal grains is generally 12 nm, preferably 15 nm, more preferably 18 nm. The volume fraction of fine crystal grains after the heat treatment is preferably 50% or more, more preferably 60% or more. With the average particle size of 60 nm or less and the volume fraction of 30% or more, the alloy ribbon has lower magnetostriction and better soft magnetic properties than those of Fe-based amorphous alloys. Though Fe-based amorphous alloy ribbons having the same composition have relatively large magnetostriction due to a magnetic volume effect, the fine-crystalline, soft-magnetic alloy, in which bcc-Fe-based fine crystal grains are dispersed, has much smaller magnetostriction due to a magnetic volume effect, exhibiting a larger noise reduction effect.
[4] Magnetic Device
A magnetic device formed by the fine-crystalline, soft-magnetic alloy ribbon has a high saturation magnetic flux density, suitable for high-power applications in which it is important to avoid magnetic saturation. Such applications include, for example, large-current reactors such as anode reactors; choke coils for active filters; smoothing choke coils; pulse power magnetic devices used in laser power supplies, accelerators, etc.; cores for transformers, communications pulse transformers, motors and power generators; yokes; current sensors; magnetic sensors; antenna cores; electromagnetic wave-absorbing sheets, etc. Pluralities of alloy ribbons may be laminated and wound to form step-lapped or overlapped cores for transformers.
The present invention will be explained in more detail by Examples below without intention of restricting the present invention thereto. In each Example and Comparative Example, the peeling temperature of a ribbon, the average particle size, volume fraction number and density of fine crystal grains, and the distance of cutting without fracture from a side by scissors (cutting fracture test) were measured by the following methods.
(1) Measurement of Peeling Temperature of Ribbon
The temperature of an ultrafine-crystalline alloy ribbon when it was peeled from the cooling roll by a nitrogen gas blown from a nozzle was measured as a peeling temperature by a radiation thermometer (FSV-7000E available from Apiste).
(2) Measurement of Average Particle Size and Volume Fraction of Fine Crystal Grains
The average particle size of fine crystal grains (and ultrafine crystal grains) was determined by measuring the major diameters DL and minor diameters DS of arbitrarily selected fine crystal grains in the number of n (30 or more) on a transmission electron photomicrograph (TEM photograph), etc. of each sample, and averaging them by the formula of Σ(DL+DS)/2n. Also, with an arbitrary straight line (length: Lt) drawn on a TEM photograph, etc. of each sample, the total length Lc of portions of fine crystal grains crossing the straight line was measured to calculate the percentage of crystal grains LL (=Lc/Lt) along the straight line. This operation was repeated on five straight lines, and the resultant data of LL were averaged to determine the volume fraction of fine crystal grains. The volume fraction VL=Vc/Vt, wherein Vc was the total volume of fine crystal grains, and Vt was the volume of a sample, was approximated to VL≈Lc3/Lt3=LL3.
(3) Measurement of Number Density of Ultrafine Crystal Grains
On TEM photographs (magnification: 20,000 times) of a 0.2-mm-wide ultrafine crystal grains-depleted region extending from a side of each ribbon surface and a center portion of the ribbon, the number of ultrafine crystal grains having particle sizes of 3 nm or more, which were confirmable by the naked eye, was counted, to calculate the number density ρ0.2 of ultrafine crystal grains per a unit area (μm2) in the ultrafine crystal grains-depleted region, and the number density ρc of ultrafine crystal grains per a unit area (μm2) in the center portion.
(4) Cutting Fracture Test
Though brittle fracture does not occur when an amorphous phase is cut by scissors, brittle fracture occurs when a phase containing ultrafine crystal grains is cut by scissors. Accordingly, when an ultrafine-crystalline alloy ribbon is cut by scissors, the width of an ultrafine crystal grains-depleted region can be presumed from the distance of fracture from a side of the ribbon. Thus, 10 side portions of an ultrafine-crystalline alloy ribbon were cut by scissors to measure fracture distances from the side. With their averaged value rc, the width of the ultrafine crystal grains-depleted region was evaluated by the following standard.
(6) Measurement of DC Magnetic Properties
A 120-mm single plate sample was measured with respect to a magnetic flux density B80 at 80 A/m and a magnetic flux density B8000 at 8000 A/m (substantially equal to a saturation magnetic flux density Bs) by an automatic DC magnetization recorder (available from Metron, Inc.), to determine a ratio of B80/B8000.
An alloy melt (1300° C.) having a composition of FebalCu1.4Si5B13 (atomic %) was quenched in the air, by a single-roll method using a copper-alloy-made cooling roll (width: 168 mm, peripheral speed: 27 m/s, temperature of entering cooling water: about 60° C., temperature of exiting cooling water: about 70° C.), with a gap of 200 μm between a nozzle and the cooling roll, and the resultant ultrafine-crystalline alloy ribbon of 25 mm in width, about 23 μm in thickness and about 10 km in length was peeled at a temperature of 250° C. from the cooling roll, and wound without fracture. A melt-ejecting position was substantially in a center portion of the cooling roll, with as sufficiently large distance as about 72 mm between a side of the ribbon and a side of the cooling roll.
As a result of rewinding the cooled ribbon by the same apparatus and conditions as conventional ones, the ribbon was not fractured even after contact with flanges of a winding reel. It is considered that the toughness of ultrafine crystal grains-depleted regions on both sides contributed to improving the fracture resistance of the ribbon.
A ribbon was produced from the same alloy melt under the same conditions as in Example 1, except that a melt-ejecting position was shifted toward one side to have a distance S of about 30 mm between a side of the ribbon and a side of the cooling roll. Fracture did not occur by winding during the melt ejection.
When the cooled ribbon was rewound in the same manner as in Example 1, the ribbon was fractured several times by contact with flanges of a winding reel. This appears to be due to the fact that good ultrafine crystal grains-depleted regions were not formed in both side portions of the ribbon.
Each alloy melt (1300° C.) having a composition of Febal.Cu1.3Si4B14 (atomic %) shown in Table 1 was quenched in the air by a single-roll method using a copper-alloy-made cooling roll (width: 168 mm or 280 mm, peripheral speed: 23-36 m/s, temperature of entering cooling water: 25-60° C., temperature of exiting cooling water: 30-70° C.), with a gap of 180-250 μm between a nozzle and the cooling roll. In this case, with a melt-ejecting position on the cooling roll changed, a distance S (shorter one) between a side of the ribbon and a side of the cooling roll was changed as shown in
With respect to each ribbon of Examples 1-12 and Comparative Examples 1-5, the number density ρ0.2 of ultrafine crystal grains having particle sizes of 3 nm or more in a 0.2-mm-wide region extending from a side, and the number density ρc of ultrafine crystal grains having particle sizes of 3 nm or more in a center portion were measured.
Because a higher number density of ultrafine crystal grains provides a ribbon with higher Vickers hardness, a position at which the number density of ultrafine crystal grains was ½ of the number density ρc of ultrafine crystal grains in a center portion (expressed by a distance r1/2 from a side) was determined from the Vickers hardness distribution of the ribbon in a width direction.
The cooled ribbon was rewound around a reel having flanges, to examine the number v of fracture (the number of winding after fracture and reconnection) per a unit length (1 km) of the ribbon. If the number of fracture were 5 or less, production efficiency would be little influenced. The wound ribbon was subjected to a cutting fracture test, to measure a fracture-free cutting distance by scissors from a side.
A 120-mm-long, single-plate sample obtained from each ultrafine-crystalline alloy ribbon was charged into a heat treatment furnace, and subjected to a low-temperature, long-time heat treatment comprising heating to 410° C. over about 15 minutes and keeping that temperature for 1 hour, thereby forming a fine-crystalline, soft-magnetic alloy ribbon. With respect to each fine-crystalline, soft-magnetic alloy ribbon, the average particle size and volume fraction of fine crystal grains were measured. As a result, it was confirmed that the fine-crystalline, soft-magnetic alloy ribbon had a structure comprising fine crystal grains having an average particle size of 60 nm or less dispersed in a proportion of 30% or more by volume.
Each single-plate sample was measured with respect to B80/B8000. The results of the above measurements are shown in Table 1.
(1)The gap between the nozzle and the cooling roll.
(1) The number density of ultrafine crystal grains having particle sizes of 3
(2) The number density of ultrafine crystal grains having particle sizes of 3
It was confirmed that in Examples 2-12, ultrafine crystal grains-depleted regions (substantially amorphous) were formed in a range of 0.2 mm from both sides of the ribbon. The results of Examples 2-10 indicate that ribbons comprising ultrafine crystal grains-depleted regions containing ultrafine crystal grains at number densities ρ0.2 of less than 500 μm2 in regions of 0.2 mm from both sides could be rewound without fracture, and if any, the number of fracture was within 5, resulting in good operation efficiency. Also, fracture seldom occurred in the cutting fracture test, indicating high toughness. Even in Examples in which cutting of 0.2 mm or more could be made in the cutting fracture test, the width of the ultrafine crystal grains-depleted region was within 5% of the entire width of the ribbon. Examples in which cutting of 0.1-0.2 mm could be made exhibited relatively good ratios of B80/B8000 despite several numbers of fracture. It was found that with ultrafine crystal grains-depleted regions of 0.1 mm or more in width, fracture could be extremely reduced at the time of rewinding.
In Examples 11 and 12, complete amorphous phases were formed on both sides, resulting in no fracture when rewound. However, the positions of fracture exceeded 5% of the entire width, resulting in regions having coarse crystal grains after the heat treatment, and relatively low ratios of B80/B8000. However, this does not particularly cause any problems in high-frequency applications such as choke coils, reactors, etc.
It was confirmed that the heat-treated structure was a structure, in which ultrafine crystal grains having an average particle size of about 40-60 nm were dispersed in a proportion of about 50% by volume in an amorphous matrix at position of 0.2 mm from a side of the ribbon, the average crystal particle size being larger in side portions corresponding to the ultrafine crystal grains-depleted regions than in a center portion. This appears to be due to the fact that grain growth was more promoted by a heat treatment in side portions having a small number density (low density). Regions having larger particle sizes were not wider than the ultrafine crystal grains-depleted regions. Because coarse crystal grains affect coercivity, the regions having larger particle sizes should have the same structure of the center portion, preferably within 5% of the entire width at least like the ultrafine crystal grains-depleted regions.
In any of Comparative Examples 2-5, the number density of ultrafine crystal grains ρ0.2 in a 0.2-mm-wide region extending from a side was 500/μm2 or more, indicating that necessary ultrafine crystal grains-depleted regions were not formed. As a result, several tens of fracture occurred in rewinding, failing to conduct efficient winding. Also, fracture occurred in a short distance of cutting in the cutting fracture test, and the distance r1/2 was about 0.1 mm presumably by the brittleness of ultrafine crystal grains. This appears to be due to the fact that because there was no sufficient distance S between a side of the ribbon and a side of the cooling roll, or because the ribbon was too wide relative to the cooling roll, heat conduction with proper side cooling could not be achieved.
Each alloy melt (1300° C.) having a composition (atomic %) shown in Table 2 was quenched in the air by a single-roll method using a copper-alloy-made cooling roll (width: 168 mm or 280 mm, peripheral speed: 23-36 m/s, temperature of entering cooling water: 25-60° C., temperature of exiting cooling water: 30-70° C.), with a gap of 180-250 μm between a nozzle and the cooling roll. By changing a melt-ejecting position on the cooling roll, a distance S (shorter one) between a side of the ribbon and a side of the cooling roll was changed as shown in
The cooled ribbon was rewound around a reel having flanges, to examine the number v of fracture (the number of winding after fracture and reconnection) per a unit length (1 km) of the ribbon. If the number of fracture were 5 or less, production efficiency would be little influenced. Each ultrafine-crystalline alloy ribbon was subjected to a cutting fracture test, to measure a fracture-free cutting distance rc by scissors from a side.
A 120-mm-long, single-plate sample obtained from each ultrafine-crystalline alloy ribbon was charged into a heat treatment furnace, and subjected to a low-temperature, long-time heat treatment comprising heating to 410° C. over about 15 minutes and keeping that temperature for 1 hour, thereby forming a fine-crystalline, soft-magnetic alloy ribbon. With respect to each fine-crystalline, soft-magnetic alloy ribbon, the average particle size and volume fraction of fine crystal grains were measured. As a result, it was confirmed that the fine-crystalline, soft-magnetic alloy ribbon had a structure comprising fine crystal grains having an average particle size of 60 nm or less dispersed in a proportion of 30% or more by volume.
A single-plate sample of each fine-crystalline, soft-magnetic alloy ribbon was measured with respect to B80/B8000. The results of the above measurements are shown in Table 2.
As shown in Table 2, the number of fracture in rewinding was within an acceptable range with good B80/B8000 in any Example. This appears to be due to the fact that with a preferred heat conduction model obtained in the production of the ribbon, suitable ultrafine crystal grains-depleted regions were formed in both side portions of the ribbon.
The composition of the alloy is not restricted to those in Examples above, but may be within the present invention as long as non-uniform ultrafine crystallization can be achieved in an amorphous matrix.
Because an ultrafine crystal grains-depleted region having a smaller number density of ultrafine crystal grains than in a center portion of the ribbon is formed in each side portion, and because the ultrafine crystal grains-depleted region has toughness closer to that of an amorphous phase, the ultrafine-crystalline alloy ribbon of the present invention exhibits high fracture resistance when wound or rewound. As a result, the ultrafine-crystalline alloy ribbon is less broken or fractured in handling such as cutting, winding, etc., so that it can be stably mass-produced.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-198087 | Sep 2012 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2013/074351 | 9/10/2013 | WO | 00 |
