Anisotropic soft magnetic additive fabricated product and method for manufacturing the same

Abstract

To provide a laminate molded object exhibiting different soft magnetic properties that vary depending on directions.SOLUTION: The present invention relates to an anisotropic soft magnetic laminate molded object comprising an iron-based alloy. The iron-based alloy includes an alloy composition containing 1.5 to 7.5 mass% of Si based on the total, and a metallographic structure having crystal grains oriented in the <001> direction. The iron-based alloy may contains 0.1 to 2.5 mass% of Al, and the C content is preferably 0.1 mass% or less. The crystal grains are preferably, for example, columnar crystals grown while being oriented in the <001> direction. The iron-based alloy having such metallographic structure can be obtained by, for example, directed energy deposition (DED). When conventional electromagnetic steel sheet laminates (core, yoke, or the like) are replaced with the anisotropic soft magnetic laminate molded object of the present invention, the performance and efficiency of electromagnetic apparatuses can be improved.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an anisotropic soft magnetic laminated shaped object or the like having different magnetic properties depending on the direction.

Background Art

[0002] Unlike conventional removal processing (cutting, grinding, cutting, etc.) and forming processing (casting, forging, pressing, etc.), additive manufacturing (AM: Additive Manufacturing), which can obtain a desired shaped object without the need for a dedicated mold or a large machine tool, has attracted attention. By additive manufacturing (referred to as "laminated shaping") that repeats lamination, a shaped object (referred to as a "laminated shaped object") that was difficult to manufacture by conventional manufacturing methods can be obtained.

[0003] Additive manufacturing (laminated shaping) is roughly classified into seven types (ASTM standard). Specifically, there are methods such as directed energy deposition (DED: Directed Energy Deposition), powder bed fusion bonding (PBF: powder bed fusion), binder jetting, material jetting, material extrusion, vat photopolymerization, and sheet lamination.

[0004] Among these, according to DED and PBF, practical shaped objects made of metal or ceramic can be obtained. Both DED and PBF are common in that they melt and solidify (bond) raw material powder (including mixed powder) with a high-energy beam (a heat source such as a laser or an electron beam) to obtain a shaped object. In particular, DED can suppress the amount of raw material powder used and increase the degree of freedom of shaping conditions compared to PBF. Many proposals regarding such laminated shaping have been made. For example, there are descriptions related to the following documents.

Prior Art Documents

Non-Patent Documents

[0005] [Non-Patent Document 1] Takayuki Nakano, Additive Manufacturing Processes for Titanium and Titanium Alloys, Materia, Vol. 58 (2019), pp. 181-187. [Non-Patent Document 2] K. Sofinowski et. al; Encoding data into metal alloys using laser powder bed fusion, Additive Manufacturing, Vol. 52 (2022), 102683. [Non-Patent Document 3] Kanemaru et al., Proceedings of the 2021 Autumn Meeting of the Japan Society for Precision Engineering, (2021), p. 326. [Non-Patent Document 4] Hideaki Ikehata, et. al; Grain refinement of Fe-Ti alloys fabricated by laser powder bed fusion, Materials &Design, Volume 204, 2021, 109665, [Overview of the project] [Problems that the invention aims to solve]

[0006] Non-patent document 1 reports on additively manufactured products made of Ti-based alloys used in artificial bones. Non-patent document 2 reports on additively manufactured products made of stainless steel.

[0007] Non-patent document 3 reports on the effects of heat input and heat treatment on the magnetic properties of FeSi and FeCoV fabricated using DED. However, non-patent document 3 does not disclose specific alloy compositions and only deals with soft magnetic fabricated materials consisting of isotropic crystal grains.

[0008] Non-patent document 4 reports that, in order to improve the mechanical properties of additively manufactured products made of iron-based alloys, the crystal grains generated by PBF (L-PBF) or DED (L-DED) using a laser as a heat source are changed from columnar to fine isotropic. However, non-patent document 4 does not contain any description regarding the magnetic properties of additively manufactured products.

[0009] This invention has been made in view of these circumstances, and aims to provide anisotropic soft magnetic additively fabricated products and the like. [Means for solving the problem]

[0010] As a result of diligent research, the inventors succeeded in obtaining additively fabricated materials with soft magnetic properties (referred to as "soft magnetic properties" or simply "magnetic properties") that differ depending on the direction. By further developing this result, the present invention described below was completed.

[0011] Anisotropic soft magnetic additive manufacturing The present invention relates to an alloy composition containing 1.5 to 7.5% by mass of Si in total, <001> This is an anisotropic soft magnetic additive fabrication material made of an iron-based alloy having a metallic structure with oriented crystal grains.

[0012] The anisotropic soft magnetic additive manufacturing product of the present invention (also simply referred to as "the manufactured product") has crystal grains that are in the easy magnetization direction. <001> The material has a metallic structure oriented in a specific direction, exhibiting anisotropy where its soft magnetic properties differ depending on the direction. This fabricated material enables the realization of highly efficient magnetic circuits with a high degree of freedom, making it possible to provide high-performance soft magnetic components. Furthermore, since the fabricated material of the present invention is made of an iron-based alloy (Fe-based alloy) containing Si, it can achieve high magnetic permeability and low iron loss.

[0013] 《Manufacturing method》 The present invention can also be understood as a method for manufacturing anisotropic soft magnetic additively fabricated objects (additive fabrication method). For example, the above-mentioned fabricated objects can be obtained by manufacturing methods such as directed energy deposition (DED) or powder bed fusion (PBF).

[0014] The powder used in that case may be a single type of alloy powder or a mixed powder formulated to a desired composition. The heat source for melting the powder is a laser beam, an electron beam, a plasma arc, or the like. In this specification, for the sake of convenience, L-DED (LMD) or L-PBF using a laser beam, which is a typical heat source, will be taken up and described.

[0015] 《Others》 (1) As used in this specification, "additive manufacturing" or "additively manufactured object" includes cases where a part of another member is modified, repaired, or built up on a part of another member.

[0016] The specific degree of the (soft) magnetic properties of the iron-based alloy being different depending on the direction (anisotropic soft magnetism) is not questioned. The magnetic properties are indicated by the saturation magnetic flux density, the magnetic flux density (or magnetization) when a predetermined magnetic field is applied, the permeability, the coercive force (residual magnetization), and the like. Anisotropic soft magnetism may be indicated using ratios, differences, etc. regarding a specific direction or two orthogonal directions of such magnetic properties.

[0017] (2) Unless otherwise specified, "x to y" as used in this specification includes the lower limit value x and the upper limit value y. A new range such as "a to b" can be newly established with any numerical value included in the various numerical values or numerical ranges described in this specification as a new lower limit value or upper limit value. Also, "x to y μm" as used in this specification means x μm to y μm. The same applies to other unit systems.

Brief Description of Drawings

[0018] <偶 [Figure 1] IPF related to the metal structure of Sample 1. [Figure 2A] IPF related to the metal structure of Sample A. [Figure 2B] IPF related to the metal structure of Sample B. [Figure 2C] a IPF related to the metal structure of Sample C. [Figure 3] Graph showing the relationship between the magnetic flux density and the magnetizing force for Sample 1 and Sample C. [Figure 4A] IPF related to the metal structure of Sample 2. [Figure 4B] It is the IPF related to the metallographic structure of Specimen 3. [Figure 5] They are the Fe-Si phase diagram and the Fe-Al phase diagram. [Figure 6] It is the B-H curve showing the relationship between the crystal orientation and magnetic properties of the iron-based alloy.

Embodiments for Carrying Out the Invention

[0019] One or more components arbitrarily selected from this specification can be added to the components of the present invention. The content described in this specification is applicable not only to the raw material powder but also to the laminated manufacturing method using the raw material powder, the laminated manufactured product, etc. as appropriate.

[0020] 《Alloy Composition》 (1) The iron-based alloy contains Si, for example, 1.5 to 7.5%, 2 to 6%, 2.5 to 5% or 3 to 4% with respect to its entirety (100%). In addition, the alloy composition referred to in this specification is the mass ratio with respect to the entire iron-based alloy (100% by mass) to be observed, and is indicated only by “%” or a numerical value.

[0021] Si is a ferrite stabilizing element and suppresses the austenite transformation of the iron-based alloy. Also, Si can increase the electrical resistivity (also referred to as “specific resistance”) and magnetic properties (permeability) of the iron-based alloy.

[0022] When Si is too little, austenite transformation occurs during the cooling process of the solidified phase, and the orientation of crystal grains deteriorates. Also, when Si is too little, the iron loss of the manufactured product increases. When Si is too much, the iron-based alloy becomes brittle, and cracks and the like are likely to occur in the manufactured product due to thermal shock, thermal stress, etc.

[0023] (2) The iron-based alloy may contain Al, for example, 2.5% or less, 2% or less, or 1.8% or less. Its lower limit value, if we have to say, may be, for example, 0.001% or more, 0.01% or more, 0.1% or more, 0.5% or more, or 1% or more.

[0024] Al, like Si, is a ferrite-stabilizing element. Al contributes to the formation of a protective film (oxide film) on the surface of the fabricated object. Excessive Al, like Si, can lead to embrittlement of the iron-based alloy and ultimately cracking of the fabricated object.

[0025] (3) In addition to impurities, the iron-based alloy may contain modifying elements (e.g., Mo, W, Ti, Nb, V) that can improve the orientation of the metallic structure and magnetic properties. The total amount of such elements may be, for example, 2% or less, 1% or less, 0.5% or less, or 0.2% or less.

[0026] For example, the content of carbon (C), which forms carbides and degrades magnetic properties, should ideally be 0.2% or less, or 0.1% or less. Similarly, the content of oxygen (O), which forms oxides and degrades magnetic properties, should ideally be 0.2% or less, or 0.1% or less.

[0027] The main component (the remainder) of iron-based alloys, Fe, is present in amounts of, for example, 90% or more, 96% or more, or 95% or more.

[0028] 《Metal structure》 Iron-based alloys have a crystal orientation. <001> It is preferable that the metal structure consists of many crystal grains oriented in the desired direction. Iron-based alloys mainly consist of a body-centered cubic (BCC) ferrite phase (α phase), <001> This is the easy magnetization direction (easy magnetization axis).

[0029] The grain orientation ratio (degree of crystal orientation) should ideally be, for example, 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, and even 93% or more. The degree of crystal orientation can be determined, for example, based on the inverse pole figure orientation map (simply called "IPF") obtained by analyzing the metal structure using electron backscattered diffraction (EBSD). Specifically, within the field of view of the IPF, the crystal orientation is <001> The degree of crystal orientation (area) may be defined as the value (%) obtained by dividing the total area of ​​crystal grains that fall within a ±15° range by the total area of ​​the field of view. The area of ​​each crystal grain and their total area can be determined, for example, using image analysis software attached to the EBSD device.

[0030] The degree of crystal orientation may also be indicated using the magnetic properties of the iron-based alloy. For example, the degree of crystal orientation (magnetism) may be indicated by comparing the magnetic flux density (B5, B8, B10, etc.) with the saturation magnetic flux density (Bs) when magnetic fields of 500 A / m, 800 A / m, 1000 A / m, etc. are applied. To give a specific example, if B8 / Bs is, for example, 80% or more, 85% or more, or even 90% or more, <001> The crystal orientation is pronounced. Furthermore, if the difference between the two orthogonal directions is, for example, 10% or more, or even 15% or more, the anisotropy of the soft magnetic properties is pronounced.

[0031] In additive manufacturing processes such as DED and PBF, where the melting (formation of a molten pool) and solidification of powder are repeatedly performed locally, a special temperature field is formed near the molten pool, making it possible to achieve very large solidification rates and temperature gradients. Therefore, by adjusting the fabrication conditions (heat input conditions, cooling conditions, scanning conditions, etc.), it is possible to produce, for example, highly oriented crystal grains that undergo directional solidification.

[0032] The morphology (shape, size) of the crystal grains is not a concern, but for example, <001> Columnar crystals that grow while being oriented can significantly increase the degree of crystal orientation in the metal microstructure and the anisotropy of the iron-based alloy. As the crystal grains become larger, the coercivity decreases and the soft magnetic properties can improve. Columnar crystals should ideally grow beyond the thickness of the stacked layers or the size of the molten pool (usually less than 500 μm). Specifically, the maximum length of the columnar crystals should ideally be, for example, 500 μm or more (or greater), 750 μm or more, 1 mm or more, or 5 mm or more. There is no upper limit, but if we were to specify one, it would be, for example, 100 mm or less or 50 mm or less. Such large columnar crystals are thought to arise from repeated directional solidification or epitaxial growth.

[0033] In this specification, "epitaxial growth" refers to a mode in which solidification progresses in a molten pool irradiated with a high-energy beam while maintaining the crystal structure and crystal orientation, or a mode in which crystal grains generated by directed solidification grow while aligning their crystal orientations. Such epitaxial growth is considered to be largely unaffected by the surface state (crystal structure, etc.) of the substrate (substrate) on which the additively manufactured product is formed. For this reason, in this invention, the material and crystal structure of the substrate are not restricted as long as additive manufacturing is possible.

[0034] Furthermore, the orientation direction of the metal structure (crystal grains) does not necessarily have to coincide with the fabrication direction (scanning direction or layering direction) or the directional solidification direction. The orientation direction can also be controlled by adjusting or selecting the fabrication conditions.

[0035] 《Raw material powder》 (1) The raw material powder used in additive manufacturing does not matter in terms of type, manufacturing process, or form (shape, size), as long as it forms a substantially uniform liquid phase in the irradiation area (molten pool) of the high-energy beam. For example, it may be a single alloy powder, a mixed powder or granulated powder consisting of multiple types of powders. It may also be atomized powder or pulverized powder.

[0036] The particle size of the raw material powder may be adjusted or selected as appropriate. For example, the particle size of the raw material powder may be 5 to 150 μm or 20 to 105 μm. The particle size as used herein is defined, for example, by a sieving method that classifies using a sieve of a predetermined mesh size. Powder with particle size "x to y" consists of particles that do not pass through a sieve with a mesh size of x (μm) but pass through a sieve with a mesh size of y (μm). "Less than y" consists of particles that pass through a sieve with a mesh size of y (μm).

[0037] Anisotropic soft magnetic additive manufacturing (1) The fabricated object may have no restrictions on the number of layers, layer thickness, form (shape, size), or application. The fabricated object may be a soft magnetic component such as a yoke or core. The soft magnetic component may be all or part of a rotor or stator of an electric motor (including a generator), or a core for a transformer. The electric motor may be of any type, such as a synchronous motor or DC motor equipped with permanent magnets, or an induction motor or switched reluctance motor (SR motor) without permanent magnets.

[0038] According to the present invention, it is also possible to obtain a soft magnetic member in which the orientation direction of the crystal grains is varied in parts or sections (regions). Therefore, by replacing a soft magnetic member made of a laminate of non-oriented electrical steel sheets or oriented electrical steel sheets with the fabricated product of the present invention, the performance and efficiency of electromagnetic equipment can be further improved. [Examples]

[0039] Various samples (additive-formed objects) made of iron-based alloys were manufactured using LMD (L-DED), and their microstructure and properties were evaluated. The present invention will be described in more detail based on these specific examples.

[0040] [First Embodiment] Sample preparation (1) Raw material powder Pure Fe powder, pure Si powder, and alloy powders (Fe-3Si, Fe-3.5Si-1.5Al, Fe-6.5Si-1.5Al) were prepared. The numerical values ​​indicating the component composition of the alloy powders are given as mass % of the total powder (remainder: Fe).

[0041] For pure Fe powder (Fe source powder), gas atomized powder (particle size: 45-105 μm) was used. For pure Si powder, pulverized powder (particle size: -300 μm) was used. For alloy powder, gas atomized powder was used. The particle sizes were 45-105 μm for Fe-3Si powder and Fe-3.5Si-1.5Al powder, and 25-105 μm for Fe-6.5Si-1.5Al powder.

[0042] According to the desired alloy composition, each powder was weighed and blended to create a mixed powder (rotary mixing at 45 rpm for 1 hour), which was then subjected to additive manufacturing.

[0043] (2) Additive manufacturing The raw material powder (mixed powder) placed in the powder feeder (powder box) of the LMD device (laser processing test machine manufactured by Enshu Co., Ltd.) was supplied to the powder nozzle using a carrier gas (Ar).

[0044] Using the LMD apparatus, a roughly cubic block (10mm x 10mm x 10mm) was fabricated on a substrate (SS400 / 100 x 100 x t10mm) in a room-temperature, atmospheric environment.

[0045] The irradiation conditions for the laser (YLS-4000CW manufactured by IPG Corporation) were as follows: output: 750W or 600W, beam diameter (spot diameter): 2.0mm, scanning speed: 40mm / s. Powder supply rate: 0.08g / s, scanning pitch (x direction): 0.5mm, layer pitch (z direction / building direction): 0.3mm, carrier gas (Ar) flow rate: 25L / min. 33 layers were required to fabricate the block.

[0046] In this way, a sample with the following alloy composition (mass%) was obtained. Sample 1: Fe-3.5Si-1.5Al (Output: 750W) Sample A: Fe-1Si (Output: 750W) Sample B: Fe-6.5Si-1.5Al (Output: 600W)

[0047] (3) Welded and manufactured materials For reference, sample C was also prepared, which was a molten material having the same alloy composition as sample 1, but which was plastically deformed. The molten material was a casting made by pouring molten alloy (1650°C) into a mold and air-cooling and solidifying it in an Ar atmosphere. After swaging this casting (around 300°C), the grain size was refined by heat treatment (800°C × 3hr).

[0048] "observation" (1) The metallographic structure of the test specimens cut from the sample was analyzed using an EBSD device (MSC-2200, manufactured by TSL Solutions Co., Ltd.). The obtained inverse pole figure orientation maps (IPFs) are shown in Figure 1 (Sample 1), Figure 2A (Sample A), Figure 2B (Sample B), and Figure 2C (Sample C), respectively. For Sample 1 and Sample B, the IPF perpendicular to the fabrication direction and the IPF in the fabrication direction (layering direction) are shown. Note that "perpendicular" in this example does not necessarily refer to the scanning direction.

[0049] (2) As is clear from each IPF, the metallographic structure of sample 1 is <001> It was formed as large columnar crystals (maximum length of 5 mm or more) that grew while being oriented. The degree of crystal orientation (area) for each sample was approximately 99.5% for sample 1, 15.4% for sample A, 2.4% for sample B, and 23.4% for sample C. The degree of crystal orientation is determined by the crystal orientation. <001> The total area of ​​crystal grains within ±15° of the direction was calculated by dividing it by the total area of ​​the field of view (IPF). This calculation was performed using OIM (Orientation Imaging Microscopy)-Analysis7 (manufactured by TSL Solutions Co., Ltd.). Except for sample C, the calculation was based on the IPF in the direction perpendicular to the fabrication direction.

[0050] (3) As is clear from the comparison of Sample 1, Sample A, and Sample B, it was found that a metallic structure in which the crystal grains are oriented in a specific direction can be obtained by adopting an appropriate alloy composition and fabrication conditions.

[0051] "measurement" (1) The magnetic properties (magnetization curves) of sample 1 and sample C were measured using a vibrating sample magnetometer (VSM-35-15, manufactured by Toei Kogyo Co., Ltd.). For sample 1, measurements were taken in both the direction parallel and perpendicular to the molding direction. The obtained results are shown in Figure 3.

[0052] Table 1 summarizes the magnetic flux density (B5) when a magnetic field of 500 A / m is applied, the magnetic flux density (B8) when a magnetic field of 800 A / m is applied, the magnetic flux density (B10) when a magnetic field of 1000 A / m is applied, as well as the remanent magnetization (HC) and the degree of crystal orientation (magnetic). The degree of crystal orientation (B8 / Bs) is expressed as the ratio (%) of B8 to the saturation magnetic flux density (Bs = 1.93 T).

[0053] (2) As is clear from Figure 3 and Table 1, it was confirmed that the additively fabricated sample 1 had different magnetic properties in the direction parallel to and perpendicular to the fabrication direction, i.e., it exhibited magnetic anisotropy. On the other hand, the melted sample C had no difference in magnetic properties depending on the direction and was isotropic.

[0054] [Second Example] Samples 2 and 3 were also fabricated, with variations in the powder alloy composition and fabrication conditions.

[0055] Sample 2 had the same alloy composition as Sample 1 (Fe-3.5Si-1.5Al) and was fabricated with a laser output of 500W and a scanning speed of 5mm / s. Sample 3 consisted of Fe-3Si and was fabricated with a laser output of 500W and a scanning speed of 5mm / s.

[0056] The IPF of each sample is shown in Figures 4A and 4B. The crystal grains of sample 2 are oriented at approximately 90° to the fabrication direction. <001> The grains were oriented. The crystal grains of sample 3 were oriented at approximately 45° to the fabrication direction. <001> It was oriented.

[0057] From these, we can see that in addition to the direction of the shape... <001> It was confirmed that oriented metallic structures can be formed, meaning that the orientation direction can be controlled.

[0058] "supplement" (1) Phase diagram The Fe-Si and Fe-Al phase diagrams, created using thermodynamic analysis software (Thermo-Calc, database TCFE6), are shown together in Figure 5.

[0059] When a solid-state transformation (γ phase → α phase) occurs, grain refinement and equiaxation progress, and the crystal orientation becomes random. In other words, the crystal grains become less likely to orient, and the magnetic properties become isotropic. As is clear from Figure 5, by keeping the alloy composition within a predetermined range, the solid-state transformation via the γ phase is avoided, and the crystal orientation becomes random. <001> This enables the formation of an α-phase (ferrite) consisting of crystal grains that are preferentially oriented.

[0060] (2) Crystal orientation and magnetic properties The relationship between crystal orientation and magnetic properties is shown in Figure 6 (Source: HJ Williams; Magnetic Properties of Single Crystals of Silicon Iron, Phys. Rev., vol. 52(1937), pp.747-751). Figure 6 shows the magnetization curves for each crystal orientation for a single crystal made of Fe-3.85Si. As is clear from Figure 6, iron-based alloys containing an appropriate amount of Si exhibit the easy magnetization direction. <001> In this regard, it exhibits the best soft magnetic properties (permeability, saturation magnetic flux density, remanent magnetization, etc.).

[0061] From the above, it has been confirmed that the additively fabricated material of the present invention exhibits different soft magnetic properties depending on the direction.

[0062] [Table 1]

Claims

1. The alloy composition contains 1.5 to 7.5 mass% of Si, with the remainder being Fe and impurities. A metal structure having crystal grains oriented in <001>, An anisotropic soft magnetic additive fabricated object made of an iron-based alloy equipped with [a specific feature].

2. The anisotropic soft magnetic additive fabricated product according to claim 1, wherein the alloy composition further comprises 0.001 to 2.5 mass% of Al.

3. The anisotropic soft magnetic additive manufacturing product according to Claim 1, wherein the metal structure has a crystal orientation degree of 50% or more, which is the ratio of the total area of ​​crystal grains located within ±15° from <001> to the total area of ​​the field of view of the inverse pole figure orientation map, or a crystal orientation degree of 80% or more, which is the ratio (B8 / Bs) of the magnetic flux density (B8) when a magnetic field of 800 A / m is applied to the saturation magnetic flux density (Bs).

4. The anisotropic soft magnetic additive fabricated product according to claim 1, wherein the crystal grains are columnar crystals.

5. The anisotropic soft magnetic additive fabricated product according to claim 4, wherein the columnar crystals have a maximum length of 500 μm or more.

6. The anisotropic soft magnetic additive fabricated product according to any one of claims 1 to 5, wherein the metallic structure is a directional solidification structure.

7. A manufacturing method for obtaining an anisotropic soft magnetic additive manufacturing product according to any one of Claims 1 to 5 by a directed energy deposition method for melting and solidifying raw material powder.

8. A method for manufacturing an anisotropic soft magnetic additive manufacturing product according to claim 7, accompanied by epitaxial growth of crystal grains.

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