Metal ribbon, method for producing an amorphous metal ribbon and method for producing a nanocrystalline metal ribbon

Abstract

Metal strip comprising a casting wheel side that has solidified on an outer surface of a heat sink, an opposite air side, a total volume, a microstructure that is at least 80 volume percent amorphous, and a surface layer, wherein the air side has a surface crystallization fraction greater than 0% and less than 23%, and wherein the surface layer occupies between 0.01% and 5% of the total volume of the metal strip, wherein crystalline grains are located in the surface layer that constitute the surface crystallization fraction, wherein 80 volume percent of the crystalline grains of the surface crystallization located in the surface layer have a mean grain size greater than 100 nm.

Description

[0001] The invention relates to a metal strip, a method for producing an amorphous metal strip and a method for producing a nanocrystalline metal strip.

[0002] Amorphous metal ribbons can be produced using a rapid solidification technology, such as a centrifugal melting process, if an alloy with a suitable content of glass-forming elements, also called metalloids, is used.

[0003] Iron-based soft magnetic alloys made of Fe 100-a-b-w-x-y-z T a M b Si w B x P y C zThese materials can also be produced in the form of amorphous ribbons using rapid solidification technology. These rapidly solidified amorphous iron-based metal ribbons possess good soft magnetic properties and can therefore be used either directly or as a starting material for nanocrystalline materials, for example as iron cores for inductive components or as shielding films, as disclosed, for example, in US 2012 / 262266 A1 and DE 10 2013 103268 B4. Furthermore, in their amorphous state, they also possess particularly good and interesting mechanical properties, such as a relatively low modulus of elasticity and high hardness, and can therefore be used as spring materials or for knives or razor blades.

[0004] The demands placed on amorphous and nanocrystalline metal strips are constantly increasing, with even better properties desired at even smaller thicknesses and in even greater lengths. To improve the economic viability of these amorphous metal strips in particular, the more reliable production of longer strip lengths, for example, with a continuous length of several kilometers, is desirable.

[0005] The task, therefore, is to meet this need by providing an improved amorphous metal strip.

[0006] According to the invention, a metal strip is provided comprising a casting wheel side that has solidified on the outer surface of a heat sink, i.e., a casting wheel, an opposing air side, and a microstructure that is at least 80 volume percent amorphous, or that comprises at least 80 volume percent nanocrystalline grains and amorphous residual matrix, of which at least 80 percent of the nanocrystalline grains have a mean grain size of less than 50 nm and exhibit random orientation. The air side has a surface crystallization fraction of less than 23%.

[0007] The metal strip is thus produced using a rapid solidification technology in which a molten metal solidifies on the outer surface of the casting wheel. In one embodiment, the microstructure is at least 80% amorphous by volume. The metal strip with this amorphous microstructure can therefore be described as being in its cast state.

[0008] In one embodiment, the metal strip comprises at least 80% by volume nanocrystalline grains and an amorphous residual matrix, of which at least 80% of the nanocrystalline grains have a mean grain size of less than 50 nm and a random orientation. The nanocrystalline grains are typically generated by annealing the amorphous metal strip, so that the metal strip with at least 80% by volume nanocrystalline grains and an amorphous residual matrix, of which at least 80% of the nanocrystalline grains have a mean grain size of less than 50 nm and a random orientation, can be described as being in the annealed nanocrystalline state.

[0009] A metal strip can also be called metal foil.

[0010] The casting wheel side and the air side of the metal strip differ in their properties due to the manufacturing process and are therefore distinguishable in the finished strip. The casting wheel side and the air side of the metal strip can also be distinguished with the naked eye. The air side typically appears metallic and shiny, while the casting wheel side appears more matte.

[0011] It was surprisingly discovered that rapidly solidified amorphous metal strips and the nanocrystalline metal strips produced from them by heat treatment are affected by the occurrence of surface crystallization, and that this unexpectedly occurring surface crystallization has an influence on the mechanical and magnetic properties and consequently on the reliability with which good properties, such as mechanical properties and, in the case of magnetic alloys, also magnetic properties, can be achieved.

[0012] Surface crystallization refers to the formation of crystalline grains on the surface of the ribbon, i.e., within a surface layer of the ribbon. For example, more than 80% by volume of the crystalline grains in the surface layer have a mean grain size greater than 100 nm.

[0013] These crystalline grains have a mean grain size that, in the case of a nanocrystalline metal strip, is larger than the mean grain size of the nanocrystalline grains within the strip itself, and are therefore distinguishable from them. For example, the crystalline grains of the surface layer have a mean grain size of more than 100 nm, while the nanocrystalline grains have a mean grain size of at most 50 nm.

[0014] In some embodiments, the crystalline grains of the surface crystallization exhibit a texture.

[0015] In some embodiments, the crystalline grains of the surface crystallization can be distinguished from the nanocrystalline grains by this texture, if the nanocrystalline grains have a random orientation and no texture.

[0016] Amorphous metal strips possess an inherent ductility due to their amorphous structure, which makes the production of continuous strips possible. This inherent ductility is also utilized in some applications. Elongation at break is a mechanical property used to determine the ductility of the amorphous metal strip.

[0017] However, the occurrence of surface crystallization can impair this ductility, which can lead to strip breaks during production, for example, since the strip is continuously wound after rapid solidification of the melt to form it. It should be noted that production speeds of 10 to 50 meters per second are common in large-scale plants, so that even the slightest irregularity in the mechanical properties of the amorphous metal strip can lead to strip breaks. Consequently, according to the invention, the surface crystallization fraction on the air side, and in some embodiments also on the casting wheel side, of the amorphous metal strip is limited to less than 23% in each case to ensure good ductility and uniform mechanical properties, including ductility and elongation at break.

[0018] It was found that the cooling rate of the melt influences the observed surface crystallization, with lower cooling rates favoring surface crystallization. Furthermore, it was found that in conventional manufacturing processes, the cooling rate can vary over the course of a casting process, thus favoring the formation of surface crystallization, at least temporarily.

[0019] This variation in the cooling rate and the associated variation in the surface crystallization fraction can lead to a variation in the mechanical properties, including the ductility of the amorphous metal ribbon along the length of the ribbon.

[0020] In order to achieve good mechanical and soft magnetic properties, the invention aims to avoid a crystalline structure on the surface as completely as possible.

[0021] In the case of nanocrystalline metal ribbons, the random orientation of the many small crystallites with grain sizes in the range of a few tens of nanometers—significantly below the exchange interaction length—is desirable to achieve good soft magnetic properties. The exchange interaction is responsible for the collective ordering of the magnetic moments in the material, and the exchange interaction length describes the maximum distance between two magnetic moments that allows them to still influence each other. If the grain size is below the exchange interaction length and the crystalline orientation of the grains is randomly distributed, potential crystal anisotropy due to the exchange interaction is prevented.

[0022] The surface crystallization fraction can be determined by X-ray powder diffraction using copper Kα radiation. The surface crystallization fractions given herein are determined as follows. For an amorphous film, the surface fraction is determined by the quotient of the area fraction of a characteristic reflection of a crystalline phase, i.e., the crystalline phase of the surface crystallization, divided by the sum of the area fraction of a halo characteristic of an amorphous phase and the area fraction of the characteristic reflection of the crystalline phase.

[0023] The characteristic reflection of the crystalline phase of surface crystallization depends on the structure and composition of the crystalline phase. For example, a (400) reflection is used for silicon-containing phases when, as in the present cases, they are strongly textured in the (100) direction.

[0024] Since in the present cases the surface crystallization was almost always strongly textured in the (100) direction, the proportion of surface crystallization in a nanocrystalline sample can be determined as follows: First, the area fraction of a second characteristic reflection, which is characteristic of the nanocrystalline phase, is determined.

[0025] The area fraction of a first characteristic reflection, which is characteristic of the crystalline phase of the surface crystallization, is then determined. This area fraction must be reduced by the contribution of the nanocrystalline phase to this reflection. For pure iron, this is 20% of the second characteristic reflection, and for Fe3Si, it is 12.8%. Since the exact silicon content is not readily known, 20% was always deducted, which can lead to a slight underestimation of the surface crystallization fraction in silicon-containing alloys.

[0026] For a nanocrystalline film, the surface area fraction is now determined by the quotient of the area fraction of a first characteristic reflection of a crystalline phase, i.e., the crystalline phase of the surface crystallization, but reduced by the contribution of the nanocrystalline phase to this reflection, divided by the sum of the area fraction of a second characteristic reflection, which is characteristic of the nanocrystalline phase, and the total area fraction of the first characteristic reflection of the crystalline phase.

[0027] For example, for silicon-containing phases, a (400) reflection is used as the first characteristic reflection of surface crystallization and the (220) reflection as the second characteristic reflection of the nanocrystalline phase.

[0028] If the surface crystallization is not textured, its proportion can only be determined in the cast amorphous ribbon, as described above for amorphous films. In the nanocrystalline state, the proportion of surface crystallization and the nanocrystalline phase are no longer distinguishable by powder diffractometry due to the lack of texture in the surface crystallization. However, since the surface crystallization grows into a continuous layer under heat treatment, the proportion of surface crystallization in the nanocrystalline sample is always equal to or greater than in the amorphous sample.

[0029] The air side and the casting wheel side exhibit a surface crystallization content of less than 23% in the cast state.

[0030] According to the invention, the metal strip has a surface crystallization content on the air side of the metal strip of less than 23% in order to provide good properties such as soft magnetic properties.

[0031] The formation of crystalline grains on the air-side surface of the metal strip was observed more frequently in practice than the formation of crystalline grains on the casting wheel-side surface of the metal strip. This observation could, for example, be the result of a faster cooling rate on the casting wheel side of the metal strip, since the casting wheel side is in direct contact with the heat sink, i.e., the casting wheel.

[0032] In one embodiment, the air side has a surface crystallization fraction of less than 5%. Preferably, this surface crystallization fraction is kept as small as possible and can even be 0, so that no surface crystallization fraction is measurable at all.

[0033] In one embodiment, the casting wheel side has a surface crystallization fraction of less than 23%, preferably less than 5%. Preferably, the casting wheel side has no surface crystallization, so that the surface crystallization fraction is 0%.

[0034] In one embodiment, the metal strip has a surface layer that is between 0.01% and 5% of the total volume, in which crystalline grains are located, forming the surface crystallization fraction.

[0035] This embodiment relates to metal strips that have crystalline grains, i.e., the surface crystallization fraction is greater than 0%, including metal strips in the cast state.

[0036] In one embodiment, the metal strip has a surface layer that is between 0.01% and 5% of the total volume, in which crystalline grains are located, forming the surface crystallization fraction.

[0037] This embodiment relates to metal strips which, in the nanocrystallized state, have crystalline grains on the surface that were already present in the cast state, i.e., the surface crystallization fraction is greater than 0%.

[0038] In one embodiment, the crystalline grains have a grain size greater than 100 nm. They can also be larger than 250 nm. In one embodiment, at least 80% by volume (vol%) of the crystalline grains have a mean grain size greater than 100 nm. The crystalline grains can thus be distinguished from the smaller nanocrystalline grains, which have a mean grain size of at most 50 nm.

[0039] In one embodiment, the casting wheel side and the air side of the metal strip each have an area of ​​at least 100m². 2 on and the surface crystallization fraction of this area, each determined on several approx. 1cm2 For large samples from this area, the surface crystallization fraction is less than 23%, preferably less than 15%. In one embodiment, the surface crystallization fraction on the casting wheel side and / or the air side is less than 23%, preferably less than 15%, over a length of at least 2 km. A large-area or long metal strip is thus provided with a low surface crystallization fraction. This allows components such as inductive devices to be reliably manufactured commercially with the desired properties.

[0040] In one embodiment, an area of ​​1 cm² is used. 2 The surface crystallization fraction of this area is less than 23%, preferably less than 15%, and is examined from both the casting wheel side and the air side of the metal strip.

[0041] The formation of surface crystallization can act as a defect or fracture point, potentially leading to strip breakage during the manufacturing process or in subsequent processing steps, such as continuous heat treatment. The amorphous metal strip according to the invention can be produced in a continuous length of up to 8 km, preferably up to 50 km, and particularly preferably up to over 100 km, in a single casting operation, since strip breaks are more effectively avoided due to the absence or low degree of surface crystallization.

[0042] The metal strip can have a width of 2 mm to 300 mm, preferably 40 mm to 200 mm, and / or a thickness of less than 50 µm, preferably less than 25 µm, preferably less than 20 µm, preferably between 10 µm and 18 µm.

[0043] It has been found that another factor influencing the occurrence of surface crystallization is the purity of the metal strip, particularly the purity of the melt from which the metal strip is produced using rapid solidification technology. The purity of the melt can also affect the cooling rate, which in turn influences the occurrence of surface crystallization. In one embodiment, the metal strip has a titanium content of less than 0.25 atomic percent, an aluminum content of less than 0.4 atomic percent, a manganese content of less than 0.4 atomic percent, and a sulfur content of less than 0.35 atomic percent in order to reduce the degree of surface crystallization.

[0044] It was found that for iron-based metal strips, for example with a composition of Fe 100-a-b-w-x-y-z T a M b Si w B x P y C z Components with high µ dynThese values ​​can only be reliably achieved with a surface crystallization content of less than 23%. In one embodiment, the metal strip or the component made from the metal strip thus has a µ dyn > 100,000, preferably 150,000.

[0045] In one embodiment, the casting wheel side of the metal strip has a surface roughness with an arithmetic mean value, Ra, of less than 0.8 µm, preferably less than 0.7 µm. A low surface roughness is also advantageous for increasing the fill factor in wound or stacked components, as it results in smaller gaps between adjacent layers.

[0046] In one embodiment, the metal strip (Fe,T) a M band up to 1 atomic% impurities, where 70 atomic% ≤ a ≤ 90 atomic% and 10 atomic% ≤ b ≤ 30 atomic%, T is one or more of the elements Co, Ni, Cu, Cr, Zn, Sn and V, and M is one or more of the elements Nb, Mo, Zr, Ta, B, Si, C and P.

[0047] In one embodiment, the metal strip Fe 100-a-b-w-x-y-z T a M b Si w B x P y C z (in atomic %) and up to 1 atomic % impurities, wherein T is one or more of the group consisting of Co, Ni, Cu, Cr, Zn, Sn and V, M is one or more of the group consisting of Nb, Mo, Zr and Ta and 0 ≤ a ≤ 80 0 ≤ b ≤ 10 0 ≤ w ≤ 25 3 ≤ x ≤ 20 0 ≤ y ≤ 7 0 ≤ z ≤ 2 applies.

[0048] Furthermore, the metal strips can contain up to 1 atomic percent of common impurities.

[0049] The amorphous metal ribbon and the nanocrystalline ribbon can also be a copper-based alloy such as VITROBRAZE 2255 (nominal composition in atomic % Cu). 76,2 Ni7Sn9,3 P 6,5 Zn1), or a nickel-based alloy such as VITROBRAZE 2150 (nominal composition in atomic % Ni) 73,35 Cr 18,2 Si 7,3 B 1,15 ), or a cobalt-based alloy such as VITROVAC 6025 (nominal composition in atomic % Co) 68 Fe4Mo2Si 16 B 10 ) or a nanocrystallizable alloy such as VITROPERM 800 (nominal composition in atomic % Fe) 73,9 Cu1Nb3Si 15,5 B 6,6 ) be.

[0050] A method for producing an amorphous metal ribbon using rapid solidification technology is also provided, which includes the following: Providing a melt of an iron-based, cobalt-based, nickel-based, or copper-based alloy with a metalloid content of 10 to 30 atomic percent, Continuously pressing a rolling device against the outer surface of a cooling sink with sufficient pressure to smooth the outer surface of the cooling sink while the melt is poured onto the moving outer surface of the cooling sink. Pouring the molten metal onto the moving outer surface of the moving cooling element, whereby the molten metal solidifies on the outer surface and forms an amorphous metal ribbon.

[0051] The amorphous metal strip produced in this way has a casting wheel side that has solidified on the outer surface of a heat sink, an opposing air side, and a microstructure that is at least 80% amorphous by volume. The air side and the casting wheel side have a surface crystallization fraction of less than 23%, preferably less than 5%.

[0052] In this process, the surface of the heat sink is continuously smoothed during casting. The outer surface is contacted by the rolling device as the heat sink moves. The rolling device is used to repeatedly prepare the outer surface before the molten metal solidifies on it. The outer surface can be rolled and thus reshaped by the rolling device, resulting in a smooth outer surface.

[0053] In this context, "reformed" is understood to mean the redistribution of material. Removing material from the outer surface, as can be done with a brush, is not the purpose of using the roller device. Therefore, no chips, virtually no abrasion, and no dust are produced that could negatively affect the manufacturing process.

[0054] The pressure required to deform the outer surface depends on the material and condition of the heat sink and its outer surface. Less pressure is used for a soft material like copper than for a hard material such as a high-alloy copper alloy or molybdenum.

[0055] In particular, the rolling device is pressed against a point on the outer surface of the movable cooling element located between the point where the strip detaches from the cooling element and the casting surface, i.e., the point on the cooling element where the molten metal meets the cooling element. Consequently, after the strip has solidified and before its next contact with the molten metal, the outer surface can be reshaped by the rolling device. This point on the outer surface where the molten metal meets the metal forms part of the so-called casting track on the outer surface of the movable cooling element.

[0056] This smoothing of the heat sink surface through surface reshaping also serves to ensure that the cooling rate of the melt solidification remains uniform throughout the casting process. This helps to better prevent the occurrence of increased surface crystallization in sections of a strip or variations in the degree of surface crystallization along the strip's length.

[0057] In one embodiment, the rolling device can be pressed against the outer surface of the movable cooling element in such a way that the outer surface is smoothed by the rolling device. Consequently, the roughness of the outer surface after contact with the rolling device, or after forming by the rolling device, is lower than before contact. This has the advantage that the roughness of the strip, and in particular the surface roughness of the strip caused by solidification on the outer surface of the movable cooling element, can be kept low. As a result, the homogeneity of the strip is ensured over greater lengths.

[0058] This in turn allows for a longer casting process, meaning that the casting process is not interrupted or does not need to be interrupted at a casting track, so that longer continuous metal strips can be produced and manufacturing costs can be reduced.

[0059] Furthermore, low surface roughness can improve various properties of the manufactured strip. For example, the surface roughness of some magnetic alloys influences their magnetic properties. By producing a long strip with a homogeneous and low surface roughness, multiple magnetic cores can be manufactured from a single casting process, resulting in more homogeneous properties. This can reduce manufacturing costs due to lower losses.

[0060] In one embodiment, the solidified film is continuously fed onto a spool.

[0061] In one embodiment, the rolling device is designed to continuously contact the outer surface of the movable cooling element while the molten metal is poured onto this surface. This arrangement allows the area on which the molten metal solidifies to be reshaped and smoothed before it comes into contact with the molten metal again. This results in a more homogeneous outer surface and consequently the production of rapidly solidifying strips with lower surface roughness and a lower degree of surface crystallization.

[0062] In another embodiment, the rolling device is designed such that it reduces the roughness of the outer surface of the movable cooling element by reshaping the outer surface while the melt is being poured onto the outer surface of the movable cooling element. The reshaping of the outer surface thus results in a reduced surface roughness.

[0063] In one embodiment, the movable heat sink is rotatable about a rotational axis; that is, the movement is a rotation. To achieve a desired cooling rate and strip thickness, the peripheral speed of the heat sink is adjusted accordingly. With increasingly higher peripheral speeds, the strip thickness is progressively reduced. A typical cooling rate is greater than 10 5 K / s. The circumferential speed can be from 10 m / s to 50 m / s.

[0064] The heat sink can have the shape of a wheel or a roller, with the molten metal being applied to the circumferential surface of the wheel or roller. The axis of rotation is therefore perpendicular to the center of the circular end of the wheel.

[0065] In one embodiment, the rolling device is movable parallel to the axis of rotation of the movable cooling element. The parallelism is adjusted as precisely as technically feasible and with reasonable effort. This arrangement allows the rolling device to be brought into contact with different areas of the cooling element's width, such as only a portion of the circumferential surface of the casting wheel. This can be advantageous when multiple casting tracks are present on a single cooling element. One casting track can be reshaped by the rolling device to follow another, enabling multiple castings to be performed with the same cooling element but with different casting tracks, without having to replace the cooling element. This can reduce production time and, consequently, production costs.

[0066] The rolling device can also be movable perpendicular to the outer surface of the movable cooling element. If the outer surface moves in the z-direction, the rolling device can be movable in the x-direction and / or the y-direction. Movement in the x-direction can, for example, allow different strip-shaped areas of the outer surface to be formed. Movement in the y-direction can be used to adjust the pressure with which the rolling device is pressed against the outer surface.

[0067] In one embodiment, the rolling device has a roller that is rotatable and can be pressed against the outer surface of the movable cooling element. The roller of the rolling device thus contacts the outer surface of the movable cooling element to repeatedly prepare this surface. The rolling device can also have a holder for the roller so that the roller is rotatably mounted and movable relative to the outer surface, for example, parallel to the axis of rotation of the movable cooling element and / or parallel to the outer surface of the movable cooling element. Roughness and irregularities in the outer surface can be generated by the contact between the melt and the outer surface. Since the outer surface comes into contact with the melt multiple times, its quality deteriorates progressively with increasing casting time.

[0068] These irregularities can be smoothed out with the rolling device, so that a smooth outer surface is returned to the melt. Consequently, the surface roughness of the lower surface of the strip, which forms on the outer surface as the melt solidifies, can be kept more homogeneous along the length of the strip.

[0069] In one embodiment, the rolling device has a rotatably mounted roller.

[0070] The cooling element can be provided in the form of a rotatable casting wheel, with the molten metal being poured onto the rim of the wheel. The roller of the rolling device can be arranged to form a rolling mill together with the rim, which shapes and smooths the surface of the rim.

[0071] If a rotatable roller is provided as the rolling device, this roller can be driven in a first direction of rotation and the cooling element in a second direction of rotation, with the first direction of rotation being opposite to the second. The cooling element can drive the roller due to the friction between the roller and the cooling element. Thus, two opposite directions of rotation are achieved. The roller can also be driven independently with a separate control system.

[0072] In one embodiment, the roller is moved across the outer surface as parallel as technically possible and with reasonable effort to the second axis of rotation of the heat sink while the heat sink moves, so that the outer surface is contacted and deformed in a spiral pattern. This embodiment can be used to reduce irregularities across the entire width of the outer surface.

[0073] In one embodiment, the casting wheel side has a surface crystallization content of less than 23%, preferably less than 5%.

[0074] In one embodiment, during the pouring of the molten metal onto the moving outer surface of the moving cooling element, the outer surface is protected by organic material, at least at the point where the molten metal strikes it. This better prevents the formation of surface irregularities and holes in the metal strips, which could serve as nuclei for the formation of crystalline phases. Thus, the formation of crystalline grains on the surface can be more effectively prevented.

[0075] In one embodiment, the heat sink is made of a material with a thermal conductivity greater than 200 W / mK. In another embodiment, the heat sink has a material with a thermal conductivity greater than 200 W / mK and a Vickers hardness of less than 280 HV, but greater than 130 HV. This combination of material parameters promotes the reduction of surface crystallization because the higher thermal conductivity helps to increase the cooling rate, and the hardness allows for improved smoothing of the heat sink surface. A higher cooling rate should result in less surface crystallization.

[0076] The metal strip produced using one of the embodiments described herein can be provided with the following properties.

[0077] In one embodiment, the amorphous metal strip has a width of 2 mm to 300 mm and / or a thickness of less than 50 µm.

[0078] In one embodiment, the metal strip has a surface layer that is between 0.01% and 5% of the total volume, in which crystalline grains are located that form the surface crystallization fraction.

[0079] In one embodiment, the crystalline grains have a grain size greater than 100 nm. However, they can also be larger than 250 nm. In another embodiment, at least 80% by volume (vol%) of the crystalline grains have a mean grain size greater than 100 nm.

[0080] In one embodiment, the casting wheel side and the air side each have an area of ​​at least 100m². 2 The surface crystallization fraction of this area is less than 23%, preferably less than 15%. The surface crystallization fraction is measured at several approximately 1 cm². 2 large test pieces were taken from this area.

[0081] As mentioned above, an iron-based metal strip can be produced using the method according to one of the embodiments described herein.

[0082] In one embodiment, the metal strip (Fe,T) a M b and up to 1 atomic% impurities, where 70 atomic% ≤ a ≤ 90 atomic% and 10 atomic% ≤ b ≤ 30 atomic%, T is one or more of the elements Co, Ni, Cu, Cr, Zn, Sn and V and M is one or more of the elements Nb, Mo, Zr, Ta, B, Si, C and P.

[0083] In one embodiment, the metal strip Fe 100-a-b-w-x-y-z T a M b Si w B x P y C z (in atomic %) and up to 1 atomic % impurities, wherein T is one or more of the group consisting of Co, Ni, Cu, Cr, Zn, Sn and V, M is one or more of the group consisting of Nb, Mo, Zr and Ta and 0 ≤ a ≤ 80 0 ≤ b ≤ 10 0 ≤ w ≤ 25 3 ≤ x ≤ 20 0 ≤ y ≤ 7 0 ≤ z ≤ 2 applies.

[0084] Furthermore, the metal strips can contain up to 1 atomic percent of common impurities.

[0085] A method for producing a nanocrystalline metal strip is also provided. An amorphous metal strip produced by a method according to one of the embodiments described herein is heat-treated at a temperature Ta, where 400°C ≤ Ta ≤ 750°C, to generate a nanocrystalline structure in the foil in which at least 80 vol% of the grains have a mean size of less than 50 nm.

[0086] The nanocrystalline structure may lack texture, for example in embodiments where at least 80 vol% of the grains have a mean size smaller than 50 nm and a random orientation.

[0087] For cobalt-based alloys, the temperature Ta can range between 400°C and 750°C. For iron-based alloys, 450°C ≤ Ta ≤ 750°C is possible.

[0088] In one embodiment, the strip is heat-treated in a continuous furnace. In this embodiment, the strip is drawn through the furnace at a speed s such that the residence time of the strip in a temperature zone of the furnace with temperature Ta is between 2 seconds and 2 minutes.

[0089] In one embodiment, the strip is heat-treated continuously under a tensile stress of 5 MPa to 1000 MPa.

[0090] In one embodiment, a desired value of the anisotropic field strength, Ha, or the permeability and optionally a maximum value of a remanence ratio, J, are specified. r / J s , of less than 0.02, and / or a maximum value of a coercive field strength, H c , which are less than 1% of the anisotropic field strength, H a, and / or is less than 10 A / m, and a permissible deviation range for each of these values ​​is predetermined, and the magnetic properties of the strip are continuously measured as it leaves the continuous furnace, and if deviations from the permissible deviation ranges of the magnetic properties are detected, the tension on the strip is adjusted accordingly to bring the measured values ​​of the magnetic properties back within the permissible deviation ranges.

[0091] According to the invention, an amorphous metal strip with the lowest possible degree of surface crystallization is provided to ensure good mechanical properties. Furthermore, the metal strip can be produced on an industrial scale in continuous lengths of up to 8 km, preferably up to 50 km, and particularly preferably up to over 100 km. This can be achieved by maintaining a sufficiently high cooling rate during the solidification of the melt throughout the entire casting process. This can be achieved by reshaping and smoothing the surface of the cooling element and protecting it from dust and other impurities, and / or by using a suitable material for the surface of the cooling element, and / or by ensuring that the melt has a suitable proportion of glass-forming elements and few impurities, in particular Ti, Al, Mn, and S.

[0092] The metal strip according to one of the embodiments described herein can be used in many different technical fields.

[0093] The metal strip according to one of the embodiments described herein can be used in a soft magnetic core or an inductive component. For example, the metal strip can be wound into a coil that serves as the core or soft magnetic component of a component such as an inductive component.

[0094] The metal strip according to one of the embodiments described herein can be used as a soft magnetic core in antenna or sensor applications.

[0095] The mechanical properties of the metal strip can be used in applications such as blades, as an amorphous spring, or as the blade of a knife.

[0096] In other applications, the metal strip can be used as a solder foil in brazing according to one of the embodiments described herein.

[0097] The metal strip according to one of the embodiments described herein can also be used as a layer of a laminate. For example, the metal strip can be arranged on a substrate and fixed to the substrate, for example, with adhesive. Several layers of the metal strip can be stacked on top of each other to form a laminate.

[0098] The metal strip according to one of the embodiments described herein can be used as a shielding foil for an object with components for wireless charging or as a shielding foil for an object with components to be shielded. In these embodiments, the metal strip has a soft magnetic alloy.

[0099] The components to be shielded can be one or more of the group consisting of electronic components, cables, sensor areas, and cavities.

[0100] The invention will now be explained in more detail using the drawings and examples. Fig. Figure 1 shows a schematic time-temperature conversion graph diagram. Fig. Figure 2a shows a dark-field TEM image of an amorphous sample with surface crystallization. Fig. Figure 2b shows a dark-field TEM image of the same sample in the heat-treated, nanocrystalline state. Fig. Figure 3 shows a diffractogram of an amorphous sample. Fig. Figure 4 shows a diffractogram of a nanocrystalline sample. Fig. Figure 5a shows a diffractogram of an amorphous sample with little surface crystallization. Fig. Figure 5b shows a diffractogram of an amorphous sample with very pronounced surface crystallization. Fig. Figure 6 shows a diffractogram of a nanocrystalline sample with pronounced surface crystallization. Fig. Figure 7 shows a diffractogram of an amorphous sample with surface crystallization, which in this case is untextured. Fig. Figure 8 shows a graph of the proportion of surface crystallization in comparison for the free side and the side facing the casting wheel of a metal strip. Fig. Figure 9 shows a graph of coercive field strength as a function of grain size. Fig. Figure 10 shows a graph of AC permeability at two-way sinusoidal control with 1.5 A / m and 50 Hz µDyn (a) and at sinusoidal control with 0.3 A / m and 100 kHz µ100kHz (b) as a function of surface crystallization. Fig. Figure 11 shows a graph of surface crystallization as a function of the mean band thickness.

[0101] An example of a rapid solidification technology is centrifugal melting. In centrifugal melting, a glass-forming metal alloy is melted in a crucible, typically made primarily of oxide ceramic (e.g., aluminum oxide) or graphite. Depending on the reactivity of the melt, the melting process can take place in air, vacuum, or a protective gas such as argon. After the alloy has melted to temperatures well above its liquidus temperature, the molten metal is injected through a nozzle, which usually has a slotted outlet, onto a rotating heat sink, such as a roller or wheel made of a copper alloy. The nozzle is positioned very close to the surface of the rotating heat sink, at a distance of approximately 50 µm to 500 µm.The molten metal, which passes through the nozzle outlet and hits the moving surface of the heat sink, solidifies there at cooling rates of approximately 10. 4 K / min up to 10 6 K / min. The rotational movement of the roller transports the solidified melt as a continuous ribbon, releases it from the cool roller and winds it onto a winding device.

[0102] The amorphous metal strips are produced in the centrifugal melting process with thicknesses between approximately 10 µm and approximately 30 µm. Common widths range from 5 mm to 200 mm.

[0103] To produce an amorphous metal ribbon, in addition to the aforementioned high cooling rates, a non-metallic component, known as a metalloid or glass former, is required in the alloy to disrupt the formation of a crystalline structure. Common elements used as metalloids include boron, silicon, phosphorus, and niobium, with the total proportion typically ranging from 10 at.% to 30 at.%. Iron, nickel, and cobalt are primarily used as metals due to their ferromagnetic order at room temperature, but copper is also suitable. Typical alloys and their production are described, for example, in EP 0 271 657 A.

[0104] It has been found that both the magnetic properties, in the case of a magnetic alloy, and the processability of the films can be significantly affected and even disrupted by manufacturing-related surface crystallization. This process involves the formation of crystallites directly beneath the surface, with a grain size typically several hundred nanometers. In the case of iron-based alloys, these are, for example, body-centered cubic α-Fe or Fe3Si grains. A possible explanation for this observation is related to… Fig. 1 explained.

[0105] The present invention is based on the new finding that partial crystallinity in the vicinity of the surface of rapidly solidified ribbons generally arises when the heat cannot be dissipated quickly enough during the production of the ribbon to create a completely amorphous structure, and that the cooling rate can vary due to various factors.

[0106] The required cooling rate is determined, among other things, by the metalloid content of the alloy. The greater this proportion of structure-disrupting atoms, i.e., the higher the metalloid content, the lower the cooling rates required for completely amorphous solidification.

[0107] Fig. Figure 1 schematically shows a time-temperature transformation (TTT) diagram for metallic glasses. Possible cooling curves are shown. Depending on the cooling rate, the material transitions from the melt to either the glassy or the crystalline state, with crystallization starting locally at so-called nucleation sites, such as structural defects in the material.

[0108] Curve A, with the highest cooling rate, clearly produces an amorphous structure. Curve B, corresponding to the medium cooling rate, just barely produces an amorphous structure and could easily be transformed into a semi-crystalline structure, for example, by crystallization nuclei. The lowest cooling rate, C, unequivocally leads to a crystalline state. The presence and number of crystallization nuclei thus have a significant influence on the crystallization of the supercooled melt.

[0109] According to the invention, crystallization nuclei are thus to be avoided. In order to maintain a high cooling rate and thus better prevent the crystallization of the supercooled melt, the following measures are investigated and implemented.

[0110] In the chosen centrifugal melting process, surface crystallinity can develop, since a surface always represents a disruption in the structure and thus acts as a nucleation site. Furthermore, heat dissipation occurs via a copper casting wheel on which the strip rests, meaning that the surface opposite the casting wheel, i.e., the air side of the metal strip, exhibits lower heat dissipation. This effect can be further amplified if exothermic oxidation occurs at this exposed surface with the oxygen in the surrounding air, as the additional heat of oxidation must also be dissipated in this case.

[0111] Surface crystallization is not observed exclusively on the free surface. Less frequently, the side facing the casting wheel, i.e., the casting wheel side of the metal strip, can also exhibit surface crystallization, as crystalline copper can act as a very good nucleation site. Therefore, in the following, both sides—the free surface and the surface facing the casting wheel—of the rapidly solidified metallic strips are always examined. All four cases were observed: surface crystallization occurs only on the air side, only on the casting wheel side, on both sides, or on neither side.

[0112] In order to maintain the outstanding soft magnetic properties and the good mechanical processability of rapidly solidified metallic strips even under the increasing requirements described above for greater widths, higher saturation inductions, lower raw material costs and decreasing thicknesses, a strip with largely surface crystallization-free properties is cast.

[0113] Impurities in the melt are kept to a minimum, as these can serve as nucleation sites for crystallization. Furthermore, impurities that tend to form highly exothermic oxides in air, such as aluminum or titanium, are particularly detrimental because they promote surface crystallization. This can occur due to the exothermic nature of the oxide formation, which leads to a locally reduced cooling rate. However, it can also happen via heterogeneous nucleation if these elements are already present as oxides.

[0114] Furthermore, the influence of the casting wheel on surface crystallization is investigated, as it affects this process. This includes the thermal conductivity of the copper alloy, as well as the geometric dimensions of the casting wheel and its surface finish. Wear of this surface during the casting process leads to the formation of cavities that transport process gas beneath the molten droplets and cause contact problems between the melt or strip and the roller. This significantly reduces the cooling rate, at least locally. To minimize wear of the casting wheel, a high-strength material is selected. However, the properties of strength and thermal conductivity are generally inversely related in commonly used copper alloys used in melt metallurgy.

[0115] Another parameter that can be used to influence the cooling rate is the material of the casting wheel surface.

[0116] It was observed that strips produced with a casting wheel surface made of a copper-nickel-silicon alloy exhibiting a high strength of 200 HV (HV30) show a significantly higher proportion of strips with surface crystallization than the average of approximately 50% produced with a casting wheel surface made of a CuBe alloy. This is due to the alloy's low thermal conductivity of only 150 W / mK.

[0117] The tendency to form surface crystallinity was significantly improved when using beryllium-alloyed copper materials with a thermal conductivity above 200 W / mK. With these materials, the thermal conductivity increases with decreasing beryllium content. By far the best results were achieved with a material possessing a thermal conductivity of 330 W / mK. Low beryllium contents are also advantageous from an occupational safety perspective, as beryllium dust is toxic. Therefore, the addition of beryllium should be limited to 2 wt%, preferably 1 wt%.

[0118] Depending on the beryllium content, beryllium-alloyed copper materials exhibit hardnesses between 130 HV and 250 HV (HV30). However, the material with the highest thermal conductivity has the lowest hardness of 130 HV.

[0119] To ensure consistently good thermal contact between the melt or strip and the roller with these soft materials, and to enable their long-term use in the casting process of amorphous strips, it is advantageous to guarantee uniform treatment of the contact surface even during the actual manufacturing process. This is intended to maintain a consistent roughness of the casting wheel surface.

[0120] However, material-removing processes, such as polishing or brushing, can lead to local contact problems or gas formation due to processing residues (e.g., polishing agents, dust, bristles) on the casting wheel, with the negative effects on the local cooling rate and an increased surface crystallization rate described above. To prevent surface crystallization, a forming process, as described in DE 10 2010 036 401 A1, is therefore used according to the invention to process the surface of the cooling element, in particular the surface of the casting track onto which the melt is poured.

[0121] In summary, an amorphous metal strip with a low degree of surface crystallization is provided, even over longer continuous lengths, exhibiting good and uniform mechanical properties, particularly ductility and elongation at break. In the case of magnetic alloys, the amorphous metal strip also displays good and uniform magnetic properties, depending on the composition and, if necessary, after the required nanocrystallization.

[0122] When the amorphous metal strip is heat-treated to produce the nanocrystalline metal strip, this nanocrystalline metal strip exhibits good and uniform mechanical properties and, in the case of magnetic alloys, additionally good and uniform magnetic properties.

[0123] Examples of metal strips according to the invention are summarized in Table 1. Table 1 shows the width B (mm), the thickness D (pm), the composition, the thermal conductivity of the casting wheel material (W / mK), the determined proportion of surface crystallization (%), and the measured µ. Dyn Various examples of metal strips. The surface crystallization fraction was determined by powder diffractometry.

[0124] The strips are manufactured using rapid solidification technology, whereby during the casting process the surface of the casting track on the casting wheel is reshaped and smoothed by means of a roller.

[0125] Table 1 also shows the relationship between the presence of pronounced surface crystallization and the deterioration of soft magnetic properties based on the dynamic AC permeability µ. Dyn (< 100000) represents. Table 1 B [mm] D [µm] Fe [Wt.] Nb [Weight] Ti [Weight] Al [Weight] Thermal conductivity of casting wheel material [W / mK] Percentage of surface crystallization [%] µ Dyn 1* 46 17.98 82.95 5.47 0.007 0.006 150 76 78353 2* 58 19.25 85.53 2.87 0.007 0.004 290 93 - 3* 58 20.12 86.02 4.69 0.004 0.002 230 65 - 4* 58 20.29 82.98 5.42 0.006 0.007 290 53 81982 5 25 18.63 82.97 5.47 0.004 0.002 290 1 193549 6 46 18.10 82.97 5.46 0.002 0.004 290 6 115467 7 58 18.22 83.06 5.42 0.005 0.003 290 12 152960 8 46 18.69 83.39 4.21 0.007 0.003 290 4 - 9 58 22.90 85.94 4.35 0.005 0.002 330 0 - 10 58 17.40 86.01 4.34 0.005 0.002 330 1 - 11 108 - 82,98 5,43 0,005 0,002 290 0 138708 * Comparative examples

[0126] Examples 1 to 4 in Table 1 are comparative examples and show that surface crystallinity occurs more frequently in wide (> 50 mm), thick (> 19 µm) bands with increased iron content (> 85 wt.%) and reduced niobium content (< 5 wt.%) supported by titanium or aluminum impurities, as well as in cases of poor thermal conductivity of the casting wheel material (< 200 W / mK).

[0127] Examples 5 and 6 according to the invention exhibit the opposite behavior to Examples 1 to 4. They are rather narrow, thin bands with low iron and high niobium content, as well as very small amounts of titanium and aluminum impurities. Even with a medium thermal conductivity of the casting wheel material, low levels of surface crystallization of less than 10% are observed.

[0128] Examples 7 and 8 according to the invention show that, with a suitable manufacturing process and suitable machining of the casting wheel surface during production, it is also possible to produce wide strips and also strips with reduced niobium content.

[0129] Examples 9 to 11 of the invention illustrate that, with the highest thermal conductivities of the casting wheel material and with a sufficiently low amount of impurities, it is also possible to produce wide, thick strips with increased iron content and reduced niobium content.

[0130] As mentioned above, surface crystallization is characterized by the formation of crystalline grains that differ from the amorphous and nanocrystalline structure of the metal strip's core. These crystalline grains can be detected, for example, using transmission electron microscopy.

[0131] Fig.Figure 2a shows a dark-field transmission electron microscope image of a sample of an amorphous metal ribbon with surface crystallization. The area of ​​the image below the blue line, labeled "Pt," is simply a platinum layer applied for the necessary sample preparation. In the upper part of the image, the amorphous structure of the sample appears as a uniform gray color. Below this, on the surface of the sample, two individual crystalline grains with a grain size of approximately 140 nm can be identified, embedded in the amorphous structure. The arrows indicate the crystalline orientation of the grains, which was determined by electron diffraction measurements.

[0132] Two crystalline grains with a grain size of approximately 140 nm are clearly visible directly below the surface.

[0133] Fig.Figure 2b shows a dark-field TEM image of the same sample in the heat-treated, nanocrystalline state. Subjecting this amorphous sample to a suitable heat treatment results in the nanocrystalline structure that can be found in Fig. 2b is clearly visible. The grains on the surface, however, grow together to form a continuous layer approximately 150 nm (one grain) deep, with grain sizes of up to 300 nm. The nanocrystalline structure is visible in the upper part of the image, where each small dot corresponds to a grain with a size of approximately 15 nm. Note the different length scales of the two images. A continuous crystalline layer is now visible on the sample surface, extending exactly one grain length deep, and thus approximately 150 nm, into the sample. The grain size of this layer is approximately 300 nm.

[0134] While transmission electron microscopy can detect surface crystallization, it requires complex and time-consuming sample preparation. Therefore, powder diffractometry is evaluated and used as a detection method for measuring the surface crystallization of metal strips.

[0135] Similar to a powder, a polycrystalline material exhibits statistically distributed crystal orientations in its individual grains, so that it can be treated as such.

[0136] Measurements were taken using Kα radiation from a copper anode in a Bragg-Brentano configuration and within an angular range of 2Θ = 20° to 2Θ = 125°. The measurement spot is approximately ten millimeters in diameter and is taken directly on the untreated strip surface. The copper Kα radiation, with a wavelength of 1.54 Å, has a significantly lower energy than, for example, the molybdenum Kα radiation with a wavelength of 0.71 Å, so that the penetration depth for measuring surface crystallization is not too great.

[0137] Estimating the penetration depth of copper-Kα radiation for Fe3Si yields d(1 / e) = 6.29 µm, meaning that after approximately 6 µm, the radiation has dropped to a fraction of 1 / e. For molybdenum, the penetration depth is d(1 / e) = 46.22 µm. With a foil thickness of approximately 20 µm, this radiation thus covers the entire sample volume within the illuminated area of ​​about one square centimeter. However, since the crystalline surface layer comprises only a maximum of about 1.5% of the total volume (2 x 0.15 µm), it cannot be resolved when measuring the entire sample volume. This differs from copper-Kα, where only the near-surface volume contributes to the material response. The fact that surface crystallization can only be observed using powder diffractometry when using suitable radiation could explain the lack of studies on this important material property.

[0138] A completely amorphous sample shows no sharp reflections in its diffractogram, but only smeared reflections, which roughly correspond to the strongest reflection positions of the related crystalline structure. Fig. Figure 3 shows such a diffractogram for a sample of VITROPERM 800 (nominal composition in atomic % Fe). 73,9 Cu1Nb3Si 15,5 B 6,6 ).

[0139] In the diffractogram of the Fig. Figure 3 shows the smeared, amorphous halo at a scattering angle of 2Θ = 44.7°. Furthermore, a second, significantly smaller halo can even be seen at approximately 2Θ = 82°. The so-called amorphous halo for a typical nanocrystalline iron-based alloy is located at a scattering angle of 2Θ = 44.7°.

[0140] Fully crystalline, body-centered cubic α-iron exhibits the strongest reflection, belonging to the (110) plane, at 2Θ = 44.674° (100%), followed by the reflections of the (211) plane at 2Θ = 82.335° (30.0%) and the (200) plane at 2Θ = 65.023° (20.0%). The body-centered cubic Fe3Si also exhibits the strongest reflection of the (220) plane at 2Θ = 45.237° (100%), followed by the reflections of the (422) plane at 2Θ = 83.536° (21.3%) and the (400) plane at 2Θ = 65.902° (12.8%).

[0141] Fig. Figure 4 shows a typical diffractogram for a completely nanocrystalline sample in which approximately 80% of the volume consists of statistically oriented nanocrystallites. The amorphous component can only be identified as a slight broadening in the trailing edges of the reflections. This amorphous component can be separated, for example, using the methods described in EP 1260812.

[0142] In the diffractogram of the Fig.Figure 4 shows the sharp reflections typical of a polycrystalline, body-centered cubic crystal structure with a statistical grain distribution. The amorphous component can only be recognized as a slight broadening at the trailing edges of the reflections. The strongest reflections for Fe3Si are located at ( 220 ) − Ebene: 2 Θ = 45.237 ° ( 100 % ) , <?page 16=""?> ( 422 ) − Ebene: 2 Θ = 83.536 ° ( 21.3 % ) and ( 400 ) − Ebene: 2 Θ = 65.902 ° ( 12.8 % ) .

[0143] Fig. Figure 5a shows a diffractogram of an amorphous sample with little surface crystallization and in Fig. 5b a diffractogram of an amorphous sample with very pronounced (b) surface crystallization.

[0144] In Fig. 5a is, besides the amorphous halo, as already described in Fig.As shown in Figure 3, a strong, crystalline reflection was visible at 2Θ = 65.9°. This corresponds to body-centered cubic crystallites oriented entirely in the (100) direction. This is referred to as the texture of the material.

[0145] Fig. Figure 5b shows an amorphous sample with surface crystallization. In this diffractogram, only the (400) reflection is visible in addition to the amorphous structure. The surface crystallites are therefore highly textured in the (100) direction. This is confirmed by electron diffraction measurements. For this reason, it is easy to separate the crystalline and amorphous components.

[0146] These examples exclusively involve alloys containing silicon. However, the considerations also apply to silicon-free alloys.

[0147] The surface crystallinity is measured by the area fraction of the crystalline reflection relative to the total area fraction of the amorphous halo and the crystalline reflection, considering only the main halo of the amorphous structure. While the result theoretically corresponds to a volume fraction, this is strongly influenced by the illuminated volume and is therefore only comparable for an identical measurement setup.

[0148] The assessment of surface crystallization in the nanocrystalline band is somewhat less precise. Fig. Figure 6 shows a diffractogram of a nanocrystalline sample with pronounced surface crystallization. This diffractogram corresponds to the one from Fig.4, however, the (400) reflection is significantly enhanced. This is due to the textured, crystalline component in the considered volume, which is caused by surface crystallization. The reflections to the left of the (220) and (400) reflections are measurement artifacts (due to insufficient filtering of the Kβ radiation).

[0149] The significantly increased (400) reflection is clearly visible. A measure of surface crystallinity can also be defined from this by calculating the area fraction of the (400) reflection minus 20%, based on the total area of ​​the (220) reflection and the total (400) reflection. This measure is comparable to the measure defined for the amorphous state, but less precise, because, firstly, only the strongest reflection is used to calculate the total area; the contribution of the other reflections in the diffractogram is neglected. Secondly, the 20% subtraction is strictly applicable only to silicon-free samples. For silicon-containing samples, the contribution of surface crystallinity is correspondingly underestimated, depending on the silicon content of the resulting crystalline grains.

[0150] Fig. Figure 7 shows the diffractogram of an amorphous sample with surface crystallization. The amorphous sample had the composition Fe 81,1 CO4CU 0,8Si 0,5 B 9,54 P 3,94 C 0,12 on (values ​​in atomic %) with a sulfur impurity of 0.005 atomic %. This diffractogram corresponds in its execution to the one from Fig.4a, however, no texture of the surface crystallization is present here. Therefore, the strongest crystalline reflection of the surface crystallization is the (220) reflection, which coincides with the amorphous halo, as would be expected with a statistical orientation distribution. The (422) and (400) reflections can be discerned. The contribution of the surface crystallization is determined in this case as well by determining the respective area fraction of the (220) peak and the amorphous halo. To fit the curves, the folding of the two peaks, which overlap in this case, is taken into account. It should be noted that determining the contribution of surface crystallization in the nanocrystalline state would not be possible here, since it does not differ crystallographically from the untextured surface crystallization in this case.

[0151] These powder diffractometry methods are used to examine several samples in order to investigate the influence of different manufacturing parameters on the surface crystallization fraction.

[0152] Fig. Figure 8 shows a graph of the proportion of surface crystallization comparing the free side and the side facing the casting wheel. The complete diagram is shown at the top, and a section is shown below, allowing for better resolution of the area below 0.15. Fig. Figure 8 shows the normalized number of over 400 samples examined, each exhibiting a corresponding proportion of surface crystallization. The compositions of these 400 samples ranged from amorphous soft magnetic alloys to nanocrystalline compositions and solder alloys, all within the range specified above.

[0153] It can be seen that no proportions greater than 35% were measured on the side facing the casting wheel, while proportions of up to 100% were found on the side facing the air. A slightly larger number of samples (76.2%) were free of surface crystallization on the side facing the casting wheel than (69.5%) on the side facing the air. Furthermore, no proportions greater than 35% were found on the side facing the casting wheel, whereas surface crystallization of up to 100% was observed on the side facing the air. Overall, surface crystallization occurred in approximately half of the samples examined (46.8%).

[0154] In their amorphous state, rapidly solidified metallic strips exhibit very good mechanical properties. For example, in two-point bending tests, they show elongations at break of up to 100% and hardnesses of approximately 10 GPa, measured using a nanoindenter with a three-sided diamond Synton-Berkovich tip. It has been found that the elongation at break decreases by up to two orders of magnitude when crystallization begins within the material. This embrittlement can also be observed in the presence of surface crystallization in otherwise amorphous material, although not to such a pronounced extent. For this reason, surface crystallization should be avoided to ensure trouble-free further mechanical processing of the strips.

[0155] Amorphous and nanocrystalline materials possess a small coercive field, as required for good soft magnetic materials, provided the grain sizes of any crystalline regions are below the exchange interaction length and the orientation of the crystallites is statistically distributed. In this case, the crystal anisotropy averages out and exerts no disruptive macroscopic influence.

[0156] Fig. Figure 9 shows a diagram of the dependence of the coercive field strength on the grain size from the book "Handbook of magnetic materials" by G. Herzer, Vol. 10, Chapter 3. It can be seen that the highest coercive field strengths are measured for grain sizes between 100 nm and 300 nm. This corresponds to the grain size of a typical surface crystallization, which in this case is also usually highly textured.

[0157] Thus, good magnetic properties can be reliably ensured if the surface crystallization content is limited and, preferably, surface crystallization is avoided as completely as possible.

[0158] Fig. Figure 10 shows the AC permeability measured with a two-wave sine wave at 1.5 A / m at 50 Hz, the so-called dynamic permeability µDyn, and the dynamic permeability measured with a sine wave at 0.3 A / m at 100 kHz as a function of surface crystallinity, using the maximum value from the air and casting wheel sides. Although both the measure of surface crystallinity and the determination of the dynamic permeability are subject to large measurement uncertainties, the negative influence of surface crystallinity on the magnetic properties of the material can be observed.

[0159] The image above shows that it is still possible to achieve a dynamic permeability greater than 150000 for a surface crystallization fraction of 23%.

[0160] Out of Fig. Figure 9 indicates that a surface crystallization level of up to 23% is tolerable without significant impairment of soft magnetic performance. Brittleness tests confirm this result, with the 23% figure referring to the measurement method described above using X-ray powder diffractometry with copper Kα radiation.

[0161] Fig.Figure 11 shows a graph of surface crystallization as a function of the mean strip thickness. It can be seen that surface crystallization increases with increasing strip thickness. Due to its low metalloid content in general, and its low niobium content in particular, the present alloy tends to exhibit strong surface crystallization. It was chosen to demonstrate the relationship between thickness and surface crystallization even at typical thicknesses around 20 µm. The two green dots correspond to embodiments 9 and 10 and show that, with high thermal conductivity of the casting wheel material and optimized manufacturing, this alloy can also be produced without surface crystallization at typical thicknesses.

[0162] In summary, an amorphous or nanocrystalline metal ribbon is provided that has a surface crystallization fraction of less than 23%, preferably less than 5%, preferably 0%, wherein the surface crystallization fraction is determined using the powder diffractometry methods described above. Such an amorphous ribbon is produced using rapid solidification technology. A nanocrystalline ribbon can be produced from the amorphous ribbon by heat-treating the amorphous ribbon.

[0163] During the production of the amorphous metal strip, the cooling rate of the molten metal solidification is adjusted and maintained throughout the casting process to prevent crystallization on the surface of the metal strip, particularly in a surface layer on the air side, across its entire length and width. This allows for the reliable large-scale production of longer amorphous metal strips with dependable mechanical properties and, depending on the composition, also magnetic properties. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 2012262266 A1

[0003] DE 102013103268 B4

[0003] EP 0271657 A

[0103] DE 102010036401 A1

[0120] EP 1260812

[0141]

Claims

[1] metal band that a casting wheel side that has solidified on an outer surface of a heat sink, an opposite side of the air and a structure that is at least 80 volume percent amorphous, or that has at least 80 volume percent nanocrystalline grains and amorphous residual matrix, of which at least 80 percent of the nanocrystalline grains have a mean grain size of less than 50 nm and a random orientation, where the air side has a surface crystallization fraction of less than 23%. [2] Metal strip according to claim 1, wherein the air side has a surface crystallization fraction of less than 5%. [3] Metal strip according to claim 1 or claim 2, wherein the casting wheel side has a surface crystallization content of less than 23%, preferably less than 5%. [4] Metal strip according to any one of claims 1 to 3, wherein the metal strip has a surface layer which is between 0.01% and 5% of the total volume in which crystalline grains are located which form the surface crystallization fraction. [5] Metal strip according to claim 3, wherein 80 volume % of the crystalline grains of the surface crystallization have a mean grain size greater than 100 nm. [6] Metal strip according to claim 4 or claim 5, wherein the crystalline grains of the surface crystallization have a texture. [7] Metal band according to any one of claims 1 to 6, which a width of 2 mm to 300 mm, preferably 40 mm to 200 mm, and / or has a thickness of less than 50 µm, preferably less than 25 µm, preferably less than 20 µm, preferably between 10 µm and 18 µm. [8] Metal strip according to any one of claims 1 to 7, having a titanium content of less than 0.25 atom%, an aluminium content of less than 0.4 atom%, a manganese content of less than 0.4 atom% and a sulfur content of less than 0.35 atom%. [9] Metal strip according to any one of claims 1 to 8, wherein the metal strip (Fe,T) a M b and contains up to 1 atomic% impurities, where 70 atomic% ≤ a ≤ 90 atomic% and 10 atomic% ≤ b ≤ 30 atomic%, T is one or more of the elements Co, Ni, Cu, Cr, Zn, Sn and V, and M is one or more of the elements Nb, Mo, Zr, Ta, B, Si, C and P. [10] Metal band according to any one of claims 1 to 8, wherein the metal band Fe 100-a-b-w-x-y-z T a M b Si w B x P y C z (in atomic %) and contains up to 1 atomic % impurities, wherein T is one or more of the group consisting of Co, Ni, Cu, Cr, Zn, Sn and V, M is one or more of the group consisting of Nb, Mo, Zr and Ta and 0 ≤ a ≤ 80 0 ≤ b ≤ 10 0 ≤ w ≤ 25 3 ≤ x ≤ 20 0 ≤ y ≤ 7 0 ≤ z ≤ 2 applies. [11] Metal strip according to claim 9 or claim 10, comprising a µ dyn > 100000, preferably 150000. [12] Metal strip according to any one of claims 9 to 11, wherein the casting wheel side of the metal strip has a surface roughness with an arithmetic mean value, Ra, which is less than 0.8µm, preferably less than 0.7µm. [13] Method for producing an amorphous metal ribbon using a rapid solidification technology comprising: Providing a melt from an alloy, Continuously pressing a rolling device onto the outer surface of the cooling element while the melt is poured onto the moving outer surface of the cooling element, with a pressure sufficient to smooth the outer surface of the cooling element. Pouring the molten metal onto a moving outer surface of a moving heat sink, whereby the molten metal solidifies on the outer surface and forms an amorphous metal ribbon, wherein the amorphous metal strip is a casting wheel face that has solidified on the outer surface of a heat sink, an opposite side of the air and has a structure that is at least 80 percent amorphous by volume, wherein the air side has a surface crystallization content of less than 23%, preferably less than 5%. [14] Method according to claim 13, wherein the casting wheel side has a surface crystallization fraction of less than 23%, preferably less than 5%. [15] Method according to claim 13 or claim 14, wherein the amorphous metal strip has a width of 2 mm to 300 mm and / or a thickness of less than 50 µm. [16] Method according to any one of claims 13 to 15, wherein the metal strip has a surface layer which is between 0.01% and 5% of the total volume in which crystalline grains are located which form the surface crystallization fraction. [17] Method according to claim 16, wherein 80 volume % of the crystalline grains of the surface crystallization have a mean grain size greater than 100 nm. [18] Method according to any one of claims 13 to 17, wherein the rolling device is pressed against the outer surface of the cooling body in such a way that it continuously reduces the roughness of the outer surface of the cooling body while the melt is poured onto the outer surface of the cooling body. [19] Method according to any one of claims 13 to 18, wherein a rotatable roller is provided as a rolling device, and the surface of the rotating roller is pressed onto the outer surface of the rotating cooling body with such pressure that the outer surface of the cooling body is reshaped. [20] Method according to any one of claims 13 to 19, wherein a rotatable roller is provided as the rolling device and the roller is driven with a first direction of rotation and the cooling element with a second direction of rotation, wherein the first direction of rotation is opposite to the second direction of rotation. [21] Method according to any one of claims 13 to 20, wherein the roller is moved parallel to the second axis of rotation of the cooling body over the outer surface of the cooling body, so that the outer surface of the cooling body is contacted in a spiral manner. [22] Method according to any one of claims 13 to 21, wherein during the pouring of the melt onto the moving outer surface of the moving cooling element the outer surface is protected from organic material at least at the point where the melt meets the outer surface. [23] Method according to any one of claims 13 to 22, wherein the heat sink has a material with a thermal conductivity of more than 200 W / mK. [24] Method according to any one of claims 13 to 23, wherein the metal strip (Fe,T) a M band contains up to 1 atomic% impurities, where 70 atomic% ≤ a ≤ 90 atomic% and 10 atomic% ≤ b ≤ 30 atomic%, T is one or more of the elements Co, Ni, Cu, Cr, Zn, Sn and V and M is one or more of the elements Nb, Mo, Zr, Ta, B, Si, C and P. [25] Method according to any one of claims 13 to 23, wherein the metal strip Fe 100-a-b-w-x-y-z T a M b Si w B x P y C z (in atomic %) and contains up to 1 atomic % impurities, wherein T is one or more of the group consisting of Co, Ni, Cu, Cr, Zn, Sn and V, and M is one or more of the group consisting of Nb, Mo, Zr and Ta and 0 ≤ a ≤ 80 0 ≤ b ≤ 10 0 ≤ w ≤ 25 3 ≤ x ≤ 20 0 ≤ y ≤ 7 0 ≤ z ≤ 2 applies. [26] Method for producing a nanocrystalline film comprising: Heat-treating an amorphous film produced by the method according to one of claims 11 to 25 at a temperature Ta, wherein 400°C ≤ Ta ≤ 750°C, to produce a nanocrystalline structure in the film in which at least 80 vol% of the grains have a mean size less than 50 nm and a random orientation. [27] Method according to claim 26, wherein the strip is heat-treated in a continuous furnace. [28] Method according to claim 27, wherein the belt is drawn through the continuous oven at a speed s such that the residence time of the belt in a temperature zone of the continuous oven with temperature Ta is between 2 seconds and 2 minutes. [29] Method according to any one of claims 26 to 28, wherein the strip is heat-treated continuously under a tensile stress of 5 MPa to 1000 MPa. [30] Method according to any one of claims 26 to 29, wherein a desired value of the anisotropy field strength, Ha, or of the permeability and optionally a maximum value of a remanence ratio, J r / J s , of less than 0.02, and / or a maximum value of a coercive field strength, H c , which are less than 1% of the anisotropic field strength, H a , and / or is less than 10 A / m, and a permissible deviation range for each of these values ​​is predetermined, and The magnetic properties of the strip are continuously measured as it leaves the continuous furnace, and If deviations from the permitted deviation ranges of the magnetic properties are detected, the tensile tension on the band is adjusted accordingly to bring the measured values ​​of the magnetic properties back within the permitted deviation ranges. [31] Use of the metal strip according to any one of claims 1 to 12 in a soft magnetic core, or an inductive component. [32] Use of the metal strip according to any one of claims 1 to 12 as a soft magnetic core of antennas or sensors. [33] Use of the metal band according to any one of claims 1 to 12 in a blade, in an amorphous spring, as the blade of a knife. [34] Use of the metal strip according to any one of claims 1 to 12 as a solder foil in brazing. [35] Use of the metal strip according to any one of claims 1 to 12 as a layer of a laminate. [36] Use of the metal strip according to any one of claims 1 to 12 as a shielding foil in an object with components for wireless charging. [37] Use of the metal tape according to any one of claims 1 to 12 as a shielding foil in an object with components to be shielded. [38] Use according to claim 37, wherein the component to be shielded is one or more of the group consisting of electronic components, cables, sensor areas and cavities.

Images