High-permeability cold-resistant nanocrystalline strip as well as preparation method and application thereof

Abstract

The invention discloses a high-permeability cold-resistant nanocrystalline strip as well as a preparation method and application thereof, and relates to the field of magnetically soft alloys. The preparation method of the nanocrystalline strip comprises the steps of mother alloy preparation, low-temperature pretreatment, single-roller rapid quenching and magnetic field assisted isothermal annealing. The mother alloy comprises, by mass, 11%-12.5% of Si, 7.8%-9.2% of B, 1.0%-1.4% of Cu, 2.3%-3.5% of Nb, 0.4%-0.9% of Ti, 0.1%-0.3% of Nd and the balance Fe. The master alloy is subjected to heat preservation at-20 to-10 DEG C for 12-24 h during low-temperature pretreatment; and during magnetic field assisted isothermal annealing, a 0.2-0.4 T direct-current magnetic field is applied, the temperature is increased to 380-420 DEG C firstly, heat preservation is conducted for 30-40 min, then the temperature is increased to 540-580 DEG C, and heat preservation is conducted for 90-150 min. According to the preparation method, the nanocrystalline strip with high magnetic conductivity and strong cold resistance is obtained through cooperation of the mother alloy and a specific process.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of soft magnetic alloys, in particular to a high permeability cold-resistant nanocrystalline strip and a preparation method and application thereof. BACKGROUND

[0002] Iron-based nanocrystalline alloys have excellent soft magnetic properties, including high saturation magnetic induction and initial permeability, low coercivity and loss, and good frequency stability, and are widely used in the field of power electronics. However, the commonly used iron-based nanocrystalline soft magnetic alloy is Fe-Si-B nanocrystalline strip, and one of the obvious shortcomings of the nanocrystalline alloy in use is poor cold resistance, especially in a low temperature environment of-60℃, the brittleness of the Fe-Si-B nanocrystalline strip increases, and the magnetic properties seriously decay. SUMMARY

[0003] In order to improve the problem of poor cold resistance of the nanocrystalline strip in the related art, the present application provides a high permeability cold-resistant nanocrystalline strip and a preparation method and application thereof.

[0004] In a first aspect, the present application provides a preparation method of a high permeability cold-resistant nanocrystalline strip, which adopts the following technical scheme: The preparation method of the high permeability cold-resistant nanocrystalline strip comprises the following steps: Master alloy preparation: the raw materials are mixed according to the proportion and then vacuum smelting to obtain a master alloy; in the master alloy, the mass percentage of each component is as follows: Si 11%~12.5%, B 7.8%~9.2%, Cu 1.0%~1.4%, Nb 2.3%~3.5%, Ti 0.4%~0.9%, Nd 0.1%~0.3%, and Fe balance; Low-temperature pretreatment: the master alloy is placed in a low-temperature box at-20~-10℃ for 12~24h, and then naturally warmed to room temperature; Single-roller rapid quenching: the master alloy after low-temperature pretreatment is formed into an amorphous strip through a single-roller rapid quenching process; Magnetic field assisted isothermal annealing: under the protection of inert gas, a direct current magnetic field of 0.2~0.4T is applied, first heated to 380~420℃ at a heating rate of 5-10℃ / min and kept for 30~40min, then heated to 540~580℃ at a heating rate of 5-10℃ / min and kept for 90~150min, and then cooled to room temperature in the furnace to obtain a high permeability cold-resistant nanocrystalline strip.

[0005] The key of the high permeability cold-resistant nanocrystalline strip of the present application lies in: 1. Control the ratio of Fe, Si, B, Cu, Nb, Ti, Nd and other elements in the master alloy, so that each element is mutually coordinated to lay the foundation for obtaining high permeability and cold resistance. Specifically, Cu as nucleating agent, promotes the nucleation process of nanocrystalline, increases the number of nucleation. Nb is segregated at the grain boundary, hinders atomic diffusion, inhibits grain growth, is beneficial to obtain fine and uniform nanocrystalline, avoids the aggravation of low temperature brittleness. Ti ensures the lattice cold stability, Nd optimizes the low temperature activity of magnetic domain, both of which inhibit the attenuation of low temperature magnetic properties. Si and B can increase the resistivity of the material, reduce the eddy current loss, and help to maintain good magnetic permeability under high frequency magnetic field; in addition, the specific ratio of Fe and Si cooperates to ensure the ferromagnetic matrix, while reducing the magnetic crystal anisotropy of the alloy at low temperature, providing the basis for cold resistance.

[0006] When the Nb content is insufficient, the grain is easy to coarsen from the target 18~25nm to 35~50nm during annealing, the magnetic domain structure becomes coarse, the magnetic domain wall motion resistance increases, the room temperature permeability decreases from ≥2.0×10 4 H / m to 1.2×10 4 ~1.5×10 4 H / m, the-60℃ permeability attenuation rate increases from ≤8% to 18%~25%, and the internal grain boundary bonding force of the strip is weakened, the bending radius, and the fracture problem is easy to occur during installation. When the Nb content is excessive, excessive Nb will form Fe-Nb-Si brittle phase (such as Nb3Fe) with Fe and Si, which has no magnetism and hinders the movement of magnetic domain, the room temperature permeability directly drops below 1.0×10 4 H / m, losing the application value of "high permeability" material; the strip is easy to crack during single roll rapid quenching, the yield rate decreases from more than 85% to less than 50%, losing the industrialization feasibility. And the-60℃ tensile strength of the strip decreases from ≥900MPa to 700~750MPa, which cannot withstand long-term use in extreme environment; at the same time, Nb is a high-value metal, and the content exceeding 3.5% will increase the raw material cost.

[0007] The insufficient Ti content will weaken the magnetic domain wall pinning effect at low temperature, the-60℃ permeability attenuation rate of the strip increases from ≤8% to 22%~30%, which cannot meet the demand of power equipment in high latitude area for magnetic field conduction stability. And Ti and Nb have a "synergistic crystal inhibition" effect, insufficient Ti will weaken the crystal inhibition effect of Nb, the grain is easy to coarsen from 18~25nm to 32~40nm after annealing, the room temperature permeability decreases from ≥2.0×10 4 H / m to 1.3×10 4 ~1.6×10 4H / m, breaking through the core indicator of high magnetic permeability. Simultaneously, Ti improves grain boundary bonding; when Ti content is insufficient, the bending radius of the strip at -60℃ increases from ≤18mm to 26~32mm, making the strip prone to brittle cracking during low-temperature installation or in vibration environments. When Ti content is excessive, excess Ti will form brittle intermetallic compounds such as Fe2Ti and FeTi with Fe. These non-magnetic phases hinder magnetic domain movement, causing the room temperature magnetic permeability to drop below 1.0×10⁻⁶. 4 The high permeability (H / m) compromises the core application value of "high magnetic permeability" materials. Secondly, the brittle Ti-Fe phase is prone to microcracks during temperature cycling from -60°C to 80°C, and the strip shows a significant risk of fracture after only 20-25 cycles, making it unsuitable for long-term use in extreme low-temperature environments. Furthermore, excessively high Ti content increases the alloy's melting point, requiring an additional 100-150°C heating for vacuum melting, increasing energy consumption by 15%-20%. Simultaneously, surface cracks easily appear during rapid quenching, reducing the yield from over 85% to below 60%, thus losing its economic viability for industrialization.

[0008] When the Nd content is below 0.1%, its optimizing effect on magnetic properties cannot be fully utilized, resulting in insufficient magnetic permeability and relatively high coercivity in the strip. This affects the strip's application performance in electromagnetic equipment, increasing energy loss and reducing efficiency. Excessive Nd content, on the other hand, leads to the formation of Nd₂Fe in the alloy. 14 The reduced exchange coupling between boron grains leads to a decrease in remanent magnetic polarization. Furthermore, Nd is a relatively expensive element; excessively high Nd content increases production costs and may negatively impact the processing performance of the strip, making it more difficult to manufacture.

[0009] 2. Low-temperature pretreatment improves magnetic permeability and cold resistance. The principle behind low-temperature pretreatment improving magnetic permeability is as follows: ① Low-temperature pretreatment can slowly release more than 80% of residual stress, eliminating "obstruction points" on magnetic domain walls, making domain movement smoother, and reducing room temperature magnetic permeability from 1.8 × 10⁻⁶. 4 H / m increased to 2.0×10 4H / m or higher; ② During the low-temperature pretreatment process, the atoms of the amorphous phase inside the baseband will undergo slight rearrangement to form a more uniform short-range ordered structure, reducing magnetocrystalline anisotropy caused by uneven atomic distribution (the core influencing factor of magnetic permeability). This structural optimization makes the magnetic domains easier to orient under the action of a magnetic field, further improving the stability of magnetic permeability. The principle behind the improved cold resistance through low-temperature pretreatment is as follows: ① Low-temperature pretreatment is equivalent to subjecting the strip to a "mild low-temperature environment in advance," allowing internal stress to relax slowly under non-low-temperature conditions. When the strip actually enters a -60℃ environment, the stress variation is reduced, the permeability attenuation rate drops from 15% to below 8%, and the bending radius remains stably maintained at ≤18mm. ② Low-temperature pretreatment promotes slight segregation of Cu and Nb elements, forming 5-8nm pre-nucleation particles. This guides the uniform refinement of grains within the 15-20nm range after annealing, providing microstructural support for cold resistance. ③ During pretreatment, Cu, Nb, and other elements slightly diffuse towards the grain boundaries, forming a denser grain boundary segregation layer, enhancing the grain boundary's crack resistance at low temperatures. This prevents the grain boundaries from becoming brittle due to reduced atomic thermal motion at low temperatures, making the strip less prone to fracture when bent at -60℃, and significantly improving its cold resistance and toughness.

[0010] 3. During annealing, a gradient temperature increase is used. First, the rapid quenching stress is slowly released at 380~420℃, and then the uniform precipitation of nanocrystals is induced at 540~580℃, avoiding grain coarsening caused by direct high-temperature annealing. At the same time, a DC magnetic field is applied to guide the nanocrystals to preferentially oriented along the magnetic field direction, reducing the resistance to magnetic domain movement at low temperatures and further reducing the temperature sensitivity of saturation magnetic induction. In this step, the heating rate needs to be controlled. An improper heating rate can cause uneven grain size distribution, affecting the consistency of material properties. If the heating is too slow, it can easily lead to excessive grain growth, destroying the unique fine and uniform structure of nanocrystals.

[0011] In some specific implementations, during vacuum melting, the vacuum degree is ≤3×10 -3 Pa, melting temperature is 1580~1680℃, melting time is 45~65min, holding time is 20~30min.

[0012] This application ensures that the raw materials are fully and uniformly mixed by controlling the above-mentioned vacuum melting parameters, reducing the impurity content and improving the purity of the alloy, thereby improving the magnetic properties of the strip.

[0013] In some specific embodiments, during single-roll rapid quenching, the master alloy is crushed, heated to 1380~1480℃ to melt, and the molten master alloy is sprayed onto the surface of the copper roller through a nozzle. The rotation speed of the copper roller is controlled at 32~40m / s, and the cooling rate of the master alloy is 4×10⁻⁶ m / s. 5 ~6×10 5 ℃ / s.

[0014] This application utilizes single-roller rapid quenching technology to solidify the alloy liquid at an extremely fast cooling rate, forming an amorphous structure, which provides a good foundation for subsequent crystallization treatment.

[0015] In some specific embodiments, the thickness of the amorphous ribbon is 25~35μm.

[0016] In this application, the thickness of the amorphous ribbon is controlled at 25~35μm, which can ensure mechanical strength and improve the yield of single-roll rapid quenching.

[0017] In some preferred embodiments, the mass percentage of each component in the master alloy is: Si 11.5%~12%, B 8.5%~9.0%, Cu 1.0%~1.4%, Nb 2.3%~3.5%, Ti 0.4%~0.6%, Nd 0.1%~0.3%, and Fe balance.

[0018] Secondly, the high magnetic permeability cold-resistant nanocrystalline ribbon provided in this application adopts the following technical solution: A high-permeability cold-resistant nanocrystalline ribbon is prepared by any one of the above-described methods for preparing a high-permeability cold-resistant nanocrystalline ribbon.

[0019] In some specific implementations, within the temperature range of -60 to 25°C, the rate of change of saturation magnetic induction (relative to 25°C) is ≤2.5%, the coercivity fluctuation (relative to 25°C) is ≤5 A / m, and the fracture toughness is ≥12 MPa·m. 1 / 2 .

[0020] In some specific embodiments, the grain size of the high magnetic permeability cold-resistant nanocrystalline ribbon is 10-25 nm.

[0021] In some preferred embodiments, the grain size of the high magnetic permeability cold-resistant nanocrystalline ribbon is 15-20 nm.

[0022] Thirdly, this application provides an application of a high magnetic permeability cold-resistant nanocrystalline ribbon in power equipment, especially power equipment in extremely cold environments.

[0023] In summary, this application includes at least the following beneficial technical effects: This application utilizes a master alloy with a specific composition to prepare nanocrystalline ribbons. Furthermore, it incorporates a low-temperature pretreatment process and a magnetic field-assisted isothermal annealing process with a temperature gradient, building upon traditional nanocrystalline ribbon preparation techniques. This results in a room-temperature permeability of ≥2.0 × 10⁻⁶ for the nanocrystalline ribbons. 4The nanocrystalline ribbon exhibits high yield with single-roll rapid quenching, and within the temperature range of -60 to 25℃, the saturation magnetic induction intensity change rate (relative to 25℃) is ≤2.5%, the coercivity fluctuation value (relative to 25℃) is ≤5A / m, and the fracture toughness is ≥12MPa·m. 1 / 2 With a bending radius of ≤18mm, it can be used in power equipment in extremely cold environments. Detailed Implementation

[0024] The following section provides further explanation of this application in conjunction with specific experiments. Example

[0025]

Example 1

[0026] In this embodiment, the preparation method of the high magnetic permeability cold-resistant nanocrystalline ribbon includes the following steps: Master alloy preparation: After mixing the raw materials according to the specified ratio, the mixture is placed into a vacuum induction furnace, and the vacuum degree of the induction furnace is controlled to be ≤3×10. -3 Pa, melting temperature 1600℃, melting for 60 min, to obtain the master alloy; Low-temperature pretreatment: The master alloy was placed in a -15℃ low-temperature chamber for 20 hours and then naturally heated to room temperature; Single-roll rapid quenching: After the low-temperature pretreated master alloy is crushed, it is heated to 1400℃ to melt. The molten master alloy is sprayed onto the surface of a copper roller through a nozzle. The rotation speed of the copper roller is controlled at 35 m / s, and the cooling rate of the master alloy is 5 × 10⁻⁶ m / s. 5 At ℃ / s, an amorphous ribbon with a thickness of 25-35μm is formed; Magnetic field-assisted isothermal annealing: Under inert gas protection, a 0.3T DC magnetic field is applied, and the temperature is first raised to 400℃ at a heating rate of 5℃ / min and held for 35min. Then, the temperature is raised to 555℃ at a heating rate of 5℃ / min and held for 120min. The material is then cooled to room temperature in the furnace to obtain a high magnetic permeability cold-resistant nanocrystalline ribbon.

[0027] Comparative Example Comparative Example 1 A nanocrystalline ribbon material, which differs from [Example 1] in that Ti and Nd are replaced by Fe of equal mass.

[0028] Comparative Example 2 A nanocrystalline ribbon material, which differs from [Example 1] in that the low-temperature pretreatment step is omitted.

[0029] Comparative Example 3 A nanocrystalline ribbon material differs from [Example 1] in that the magnetic field-assisted isothermal annealing step is different. In this comparative example, the magnetic field-assisted isothermal annealing step is as follows: Under inert gas protection, a 0.3T DC magnetic field is applied, the temperature is raised to 420℃ and held for 30 minutes, and then cooled to room temperature in the furnace to obtain nanocrystalline ribbon.

[0030] Comparative Example 4 A nanocrystalline ribbon material differs from [Example 1] in that the magnetic field-assisted isothermal annealing step is different. In this comparative example, the magnetic field-assisted isothermal annealing step is as follows: Under inert gas protection, a 0.3T DC magnetic field is applied, the temperature is raised to 580℃ and held for 90 minutes, and then cooled to room temperature in the furnace to obtain nanocrystalline ribbon.

[0031] Performance testing 1. Single-roll rapid quenching yield: Record the yield of the single-roll rapid quenching step in each embodiment and comparative example, wherein the yield = total weight of qualified nanocrystalline ribbon / total weight of master alloy ingot * 100%.

[0032] Table 1

[0033] Based on the test data in Table 1, it can be seen that in Comparative Example 1, the yield of amorphous ribbons with a thickness of 25-35 μm decreased when Ti and Nd were not added to the nanocrystalline ribbons. In Comparative Example 2, omitting the low-temperature pretreatment step of the master alloy also led to a decrease in the yield of amorphous ribbons with a thickness of 25-35 μm.

[0034] 2. Grain size: The grain size of the nanocrystalline ribbon was measured / analyzed using SEM images and recorded in Table 2 below: Table 2

[0035] Based on the test data in Table 2, it can be seen that: in Comparative Example 1, when Ti and Nd are not added to the nanocrystalline ribbon, the grain size of the nanocrystalline ribbon increases and the uniformity decreases; in Comparative Example 2, when the low-temperature pretreatment step is omitted from the master alloy, the grain size of the nanocrystalline ribbon also increases significantly and the uniformity decreases; in Comparative Examples 3 and 4, when the amorphous ribbon is subjected to non-gradient isothermal annealing, the grain size of the nanocrystalline ribbon also increases significantly and the uniformity decreases.

[0036] (3) Using a BH analyzer (MATS-2010SA), the saturation magnetic induction intensity Bs (T), the rate of change of saturation magnetic induction intensity Bs (relative to 25℃), the coercivity Hc (A / m), and the Hc fluctuation value (relative to 25℃) of the nanocrystalline tape in Example 1 were tested at -60℃, -40℃, -20℃, and 25℃ (room temperature control). After holding at each temperature point for 30 minutes, the tape was tested to ensure that it reached a thermal equilibrium state. At the same time, the fracture toughness of the high magnetic permeability cold-resistant nanocrystalline tape was tested according to ASTM E399- "Standard Test Method for Plane Strain Fracture Toughness of Metallic Materials" and recorded in Table 3 below. Among them, the rate of change of saturation magnetic induction intensity Bs (relative to 25℃) = -(Bs corresponding to 25℃ - Bs corresponding to the test temperature) / Bs corresponding to 25℃ * 100%; the Hc fluctuation value (relative to 25℃) = Hc corresponding to the test temperature - Hc corresponding to 25℃.

[0037] Table 3 Performance test parameters of the high magnetic permeability cold-resistant nanocrystalline ribbon in Example 1

[0038] Based on the test data in Table 3, it can be seen that the nanocrystalline ribbon in Example 1 can maintain a saturation magnetic induction intensity change rate (relative to 25℃) ≤2.5%, a coercivity fluctuation value (relative to 25℃) ≤5A / m, and a fracture toughness ≥12MPa·m in an environment of -60℃ to 25℃. 1 / 2 .

[0039] (4) Using a BH analyzer (MATS-2010SA), the saturation magnetic induction intensity Bs(T) of the nanocrystalline ribbons in Comparative Examples 1-4 in environments of -60℃ and 25℃ was tested, and the rate of change of saturation magnetic induction intensity Bs (relative to 25℃) was calculated. The results are recorded in Table 4 below.

[0040] Table 4

[0041] Based on the test data in Table 4, it can be seen that the saturation magnetic induction intensity change rate (relative to 25℃) of the nanocrystalline ribbons in Comparative Examples 1-4 is much greater than 2.5%, which means that the nanocrystalline ribbons in Comparative Examples 1-4 have poor cold resistance stability.

[0042] 4. Five samples were randomly selected from the nanocrystalline ribbons in each embodiment and comparative example. These samples were then subjected to 50 cycles of temperature cycling from -60°C to 25°C in a high-low temperature test chamber (LCR Meter ZX8516B 30 Ω 1K 1V in series). The permeability of the samples after the 25°C and variable-temperature cycling tests was measured using an inductance meter. The permeability decay rate was calculated, and the results are recorded in Table 5 below. The permeability decay rate is calculated as follows: (Permeability of the sample at 25°C - Permeability of the sample after the variable-temperature cycling test) / Permeability of the sample at 25°C * 100%.

[0043] Table 5

[0044] Based on the test data in Table 5, the room temperature magnetic permeability of the nanocrystalline ribbon in Example 1 is greater than 2.0 × 10⁻⁶. 4 After 50 cycles of temperature cycling from -60°C to 25°C, the magnetic permeability decay rate of the nanocrystalline ribbon is less than 3%, indicating that the nanocrystalline ribbon in Example 1 has excellent cold resistance. The magnetic permeability of the nanocrystalline ribbons in Comparative Examples 1-4 is lower than that in Example 1, and the magnetic permeability decay rate of the nanocrystalline ribbons in Comparative Examples 1-4 is much greater than that in Example 1, indicating that the cold resistance stability of the nanocrystalline ribbons in Comparative Examples 1-4 is poor.

[0045] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a high-permeability, cold-resistant nanocrystalline ribbon, characterized in that, Includes the following steps: Master alloy preparation: The raw materials are mixed according to the formula and then vacuum melted to obtain the master alloy; the mass percentage of each component in the master alloy is: Si 11%~12.5%, B 7.8%~9.2%, Cu 1.0%~1.4%, Nb 2.3%~3.5%, Ti 0.4%~0.9%, Nd 0.1%~0.3%, Fe balance; Low-temperature pretreatment: The master alloy is kept at -20~-10℃ for 12~24h, and then naturally heated to room temperature; Single-roll rapid quenching: The pretreated master alloy is subjected to a low-temperature rapid quenching process to form an amorphous ribbon; Magnetic field-assisted isothermal annealing: Under the protection of inert gas, a DC magnetic field of 0.2~0.4T is applied. The temperature is first raised to 380~420℃ at a heating rate of 5-10℃ / min and held for 30~40min. Then, the temperature is raised to 540~580℃ at a heating rate of 5-10℃ / min and held for 90~150min. The material is then cooled to room temperature in the furnace to obtain a high magnetic permeability cold-resistant nanocrystalline ribbon.

2. The method for preparing a high-permeability, cold-resistant nanocrystalline ribbon according to claim 1, characterized in that: During vacuum melting, the vacuum degree is ≤3×10 -3 Pa, melting temperature is 1580~1680℃, melting time is 45~65min, holding time is 20~30min.

3. The method for preparing a high-permeability, cold-resistant nanocrystalline ribbon according to claim 1, characterized in that: During single-roll rapid quenching, the master alloy is crushed, heated to 1380~1480℃ to melt, and the molten master alloy is sprayed onto the surface of the copper roller through a nozzle. The rotation speed of the copper roller is controlled at 32~40m / s, and the cooling rate of the master alloy is 4×10⁻⁶ m / s. 5 ~6×10 5 ℃ / s.

4. The method for preparing a high-permeability, cold-resistant nanocrystalline ribbon according to claim 1, characterized in that: The thickness of the amorphous ribbon is 25~35μm.

5. The method for preparing a high-permeability, cold-resistant nanocrystalline ribbon according to claim 1, characterized in that: The mass percentage of each component in the master alloy is as follows: Si 11.5%~12%, B 8.5%~9.0%, Cu 1.0%~1.4%, Nb 2.3%~3.5%, Ti 0.4%~0.6%, Nd 0.1%~0.3%, and Fe balance.

6. A high-permeability, cold-resistant nanocrystalline ribbon, characterized in that: It is prepared by the method of any one of claims 1-5 for preparing a high magnetic permeability cold-resistant nanocrystalline ribbon.

7. The high magnetic permeability cold-resistant nanocrystalline ribbon according to claim 6, characterized in that: Within the temperature range of -60 to 25°C, the fracture toughness of the high-permeability cold-resistant nanocrystalline ribbon is ≥12 MPa·m. 1 / 2， The high permeability cold-resistant nanocrystalline ribbon exhibits a saturation magnetic induction intensity change rate of ≤2.5% relative to 25℃, and a coercivity fluctuation value of ≤5A / m relative to 25℃.

8. The high magnetic permeability cold-resistant nanocrystalline ribbon according to claim 6, characterized in that: The grain size of the high magnetic permeability cold-resistant nanocrystalline ribbon is 15-20 nm.

9. An application of the high magnetic permeability cold-resistant nanocrystalline ribbon as described in any one of claims 6-8, characterized in that: In electrical equipment used in extremely cold environments.

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