Additive manufacturing of FeCo alloy

Abstract

To provide a laminate molding made of an FeCo-based alloy and exhibiting excellent soft magnetic properties.SOLUTION: The laminate molding is laminated and molded by using metal powder comprising, by mass, 45.0 to 55.0% C, 0 to 2.5% V, and the balance Fe with inevitable impurities, and is characterized in that a B2 regular phase and an α phase are included in a configuration phase.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an additively manufactured object using an FeCo-based alloy suitable for the rapid melting and rapid solidification process of a three-dimensional additive manufacturing method. [Background technology]

[0002] Permendur, whose representative composition is Fe49Co2V (values ​​are in mass%), is an FeCo-based alloy known as a soft magnetic material with low coercive force and high saturation magnetic flux density. Permendur is used in small, high-output motors, solenoid valves that require high magnetic force, pole pieces for electronic devices, etc. Permendur is a difficult-to-process material that becomes embrittled due to the precipitation of the B2 ordered phase, so it is not easy to process steel containing the B2 ordered phase into parts.

[0003] It would be convenient to manufacture parts in near-net shape by metal additive manufacturing, but simply additive manufacturing with the component composition of permendur does not bring out the inherent soft magnetic properties. For example, in a summary of research presentations on the application of metal additive manufacturing to Fe50Co (see Non-Patent Document 1), X-ray diffraction data of the additive manufacturing product is shown, and although unidentified peaks other than the α phase are observed, the B2 ordered phase is not recognized in the peaks, and the soft magnetic properties of the ingot material of permendur are not exhibited, which cannot be said to be sufficient. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Tetsuji Kuze et al. "Effects of Forming and Heat Treatment Conditions on the Properties of Soft Magnetic Materials" Abstracts of the Japan Society of Powder and Powder Metallurgy Lectures 2-29A (Spring 2023 Meeting) Summary of the Invention [Problem to be solved by the invention]

[0005] The problem to be solved by the present invention is to provide a metal additive manufacturing product made of an FeCo-based alloy that exhibits excellent soft magnetic properties. The FeCo alloy is an alloy whose main components are Fe and Co, with the remainder consisting of unavoidable impurities. The FeCo alloy of the present invention may further contain a small amount of V as an optional additive component.

[0006] Permendur is a soft magnetic material with low coercivity and high saturation magnetic flux density, and the B2 ordered phase is involved in improving the soft magnetic properties. However, if the B2 ordered phase is included in the metal structure, it will be brittle and have poor toughness, making it difficult to process in practice. Therefore, from the viewpoint of mechanical properties such as toughness, heat treatment is performed in the ingot material to control the formation of the B2 ordered phase, and attempts are being made to control the content of the B2 ordered phase by actively adding V.

[0007] Since additive manufacturing is a method suitable for forming complex three-dimensional shapes, it is possible to create objects using additive manufacturing methods that can be processed in near net shapes in advance. This would make it easier to lower the weight of consideration for toughness in the processing phase.

[0008] However, when additive manufacturing is attempted using powder of components with the permendur composition, the B2 ordered phase is not included, as described in Non-Patent Document 1. Then, in an additive manufacturing body produced by an additive manufacturing method in which the component composition itself is the same as permendur, and the additive manufacturing method involves rapid solidification and rapid cooling, it is difficult to exhibit the expected excellent soft magnetic properties, even though it uses nearly 50% expensive Co, and it cannot be said that the desired soft magnetic properties are sufficient.

[0009] Even if the component composition is the same, objects manufactured by metal additive manufacturing have a different crystal structure from ingot materials, and because the objects are manufactured by repeatedly performing a step of rapidly cooling locally melted powder, the objects are manufactured without the formation of the B2 ordered phase by simply additive manufacturing.

[0010] Incidentally, the peaks not identified in Non-Patent Document 1 are considered to be due to either the γ phase, the oxide phase, or a peak derived from strain specific to the metal lamination, and are different from the B2 ordered phase.

[0011] Therefore, the problem that the present invention aims to solve is to provide a laminated body made of an FeCo alloy formed by an additive manufacturing method, which exhibits excellent soft magnetic properties. [Means for solving the problem]

[0012] The inventors have further investigated based on the findings that, since the B2 ordered phase of an FeCo-based alloy is formed when cooling is slow, in a body formed by an additive manufacturing method in which fine powder is rapidly cooled and solidified, the B2 ordered phase does not form if the body is simply cooled rapidly, and since the structure immediately after additive manufacturing is fine, the body in the rapidly solidified state immediately after manufacturing has an excessively high coercive force, making it difficult to obtain soft magnetic properties equivalent to those of permendur, a general ingot material.As a result of further investigation, the inventors have found that, by devising the heat treatment conditions, an additive manufacturing body can be obtained that contains the B2 ordered phase and the α phase in the constituent phases that form the metal structure, even in an additive manufacturing body using an FeCo-based alloy powder (which may contain V as an optional additional component) formed by an additive manufacturing method in which rapid solidification is performed, and that a body exhibiting excellent soft magnetic properties equivalent to those of original permendur can be obtained.

[0013] In other words, the inventors discovered that in FeCo-based alloys, generally the finer the crystal grains, the higher the coercive force, and so if the alloy is left to undergo rapid solidification, it will form a fine structure and will not exhibit its inherent magnetic properties. However, by annealing the additively manufactured body at a high temperature from above 1000°C, which is the gamma single phase region, the crystal grains will become coarse and a structure containing the B2 ordered phase will be obtained, resulting in an additively manufactured body with excellent soft magnetic properties comparable to those of ingot permendur.

[0014] The first means for solving the problems of the present invention is an additively manufactured body produced by additive manufacturing using an alloy powder made of an FeCo-based alloy, characterized in that the constituent phases include a B2 ordered phase and an α-phase. Note that the FeCo-based alloy referred to here refers to an alloy whose main components are Fe and Co, which may contain a small amount of V as an optional component, and the remainder being unavoidable impurities.

[0015] The second means is the layered product according to the first means, characterized in that, when the layered product is measured by X-ray diffraction using a Co tube, the peak intensity ratio between the (100) plane of the B2 ordered phase and the (200) plane of the α phase satisfies B2(100) / α(200)≧2.5%.

[0016] The third aspect is the layered product according to the first or second aspect, characterized in that the FeCo-based alloy is an alloy containing, in mass%, 45.0-55.0% Co, 0-2.5% V, and the remainder Fe and unavoidable impurities, where V is an optional component and may be 0%.

[0017] The fourth aspect of the present invention is the layered object according to any one of the first to third aspects, in which the average crystal grain size of the layered object is 15 μm or more. Effect of the Invention

[0018] According to the above-mentioned means, even if the shaped body is made by additive manufacturing, it is possible to obtain a metal additive manufacturing product of an FeCo-based alloy having high saturation magnetic flux density, low coercive force, and excellent soft magnetic properties. As shown in FIG. 2, since the additive manufacturing process does not contain the B2 ordered phase, the addition of V is optional for the additive manufacturing process by rapid solidification and rapid cooling. For example, by devising the heat treatment conditions, the B2 ordered phase can be contained by annealing, so that soft magnetic properties close to those of the ingot material can be obtained, and mechanical properties such as toughness can also be appropriately adjusted. [Brief description of the drawings]

[0019] [Figure 1]This graph shows the results of X-ray diffraction measurements using a Co tube on an additive manufacturing body that was annealed from 1100°C after additive manufacturing using an FeCo-based alloy powder of the present invention. The horizontal axis shows 2θ, and the vertical axis shows intensity on a logarithmic scale. [Diagram 2] This is a graph showing the results of X-ray diffraction measurement using a Co tube for an as-produced body produced by additive manufacturing using an FeCo-based alloy powder of the present invention. The horizontal axis shows 2θ, and the vertical axis shows intensity on a logarithmic scale. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The additive manufacturing object obtained by additive manufacturing of the FeCo alloy powder according to the present invention is produced by metal additive manufacturing using an FeCo alloy (which may optionally contain V) as the material. After annealing the additive manufacturing object, it is possible to obtain an object that contains the B2 ordered phase in addition to the α phase by slow cooling.

[0021] [Powder] The powder for additive manufacturing used for the additive manufacturing body made of the FeCo-based alloy of the present invention will be described. The FeCo-based alloy powder used for additive manufacturing can be obtained by various methods, such as water atomization, single roll quenching, twin roll quenching, gas atomization, disk atomization, and centrifugal atomization, but gas atomized powder is preferable from the viewpoint of spheroidization. In addition, from the viewpoint of the fluidity and packing rate of the powder used for additive manufacturing, it is desirable that the average particle size of the FeCo-based alloy powder is 10 μm or more and 100 μm or less on a volume average. Therefore, the following will be described using gas atomized powder as an example.

[0022] [molding] The method for producing the molded object includes a rapid melting and rapid solidification process, which is a process of melting and solidifying a metal powder. Specific examples of this process include a three-dimensional additive manufacturing method, a thermal spraying method, a laser coating method, and a cladding method. In particular, the FeCo-based alloy powder of the present invention is suitable for a three-dimensional additive manufacturing method using a powder bed fusion bonding method, and can form a large-sized molded object at a high density.

[0023] As a three-dimensional additive manufacturing method, for example, a 3D printer can be used, and a near-net-shape modeled body with a complex three-dimensional shape can be obtained. In the powder bed fusion method (powder bed method) among the additive manufacturing methods, a laser beam or an electron beam is irradiated to the spread FeCo-based alloy powder of the present invention. The particles are rapidly heated and melted by the irradiation. The melted particles then rapidly solidify. The particles are bonded to each other by this melting and solidification. The irradiation is selectively performed on a part of the spread FeCo-based alloy powder. The part of the spread powder that is not irradiated does not melt. A bonding layer is formed only in the irradiated part.

[0024] A thin layer of FeCo alloy powder is spread on the bonding layer. A laser beam or an electron beam is irradiated to a portion of the FeCo alloy powder. The irradiation causes the particles to melt rapidly. The molten particles then rapidly solidify. This melting and solidification bonds the particles in the powder together, forming a new bonding layer. The new bonding layer also bonds to the existing bonding layer.

[0025] By repeating the bonding by irradiation, the aggregate of bonding layers gradually grows. This growth results in a three-dimensional object. This additive manufacturing method makes it easy to obtain objects with complex shapes.

[0026] [Heat treatment] When using FeCo-based alloy powder, the formed unheat-treated object is not used as is, but rather, the unheat-treated object is subjected to an annealing heat treatment process to obtain an additive manufacturing object with the desired characteristics of the present invention.

[0027] That is, by setting the cooling rate during annealing to 2000°C / hr or less, a laminated product containing the B2 ordered phase can be obtained for the FeCo alloy. In addition, by lowering the cooling rate, the amount of the B2 ordered phase can be increased, improving the soft magnetic properties. The cooling rate is preferably 600°C / hr or less, and more preferably 100°C / hr or less.

[0028] When used in conventional processes such as forging, FeCo alloys are annealed at a temperature of 900°C or less, which is in the α single phase region. However, the laminated body produced by the laminated manufacturing method involving rapid solidification has a fine structure due to rapid solidification in the as-produced state, and therefore has too high a coercive force. Therefore, by annealing at a temperature of 900°C or more, it is possible to obtain excellent soft magnetic properties with low coercive force by coarsening the crystal grains. In addition, annealing at a temperature of 1000°C or more, which is in the γ single phase region, can promote the precipitation of the B2 ordered phase. The annealing temperature is cooled from the γ single phase region, and is preferably 1000°C or more, more preferably 1050°C or more, and even more preferably 1100°C or more.

[0029] [X-ray diffraction peak intensity ratio of B2 ordered phase (100) plane to α phase (200) plane] When measured by X-ray diffraction using a Co tube, the peak intensity ratio between the (100) plane of the B2 ordered phase and the (200) plane of the α phase: B2(100) / α(200)≧2.5% From the data obtained by X-ray diffraction using a Co tube, the peak intensity ratio of B2(100) / α(200) was calculated to quantify the content of the B2 ordered phase. Since FeCo alloys containing the B2 ordered phase exhibit excellent soft magnetic properties, the B2(100) / α(200) peak intensity ratio is preferably 2.2% or more, more preferably 3.3% or more, and even more preferably 3.9% or more.

[0030] [Crystal grain size] A molded body produced by additive manufacturing using fine metal powder tends to have a fine crystal grain size and a higher coercive force than a normal ingot material, but the larger the crystal grain size, the lower the coercive force and the better the soft magnetic properties. Therefore, by making the average crystal grain size 15 μm or more by heat treatment, excellent soft magnetic properties can be obtained. The average crystal grain size of the additively molded body is preferably 21 μm or more, more preferably 42 μm or more, and even more preferably 81 μm or more.

[0031] [Coercive force] Since FeCo alloys are used as soft magnetic materials, it is preferable that they have a low coercive force. Therefore, the preferred coercive force is 280 [A / m] or less. More preferably, the coercive force is 181 [A / m] or less, and even more preferably, the coercive force is 75 [A / m] or less.

[0032] [component] Next, before describing the embodiments of the present invention, the reasons for specifying the preferred composition of the FeCo alloy will be described. Note that % in the composition is by mass %.

[0033] Co: 45.0-55.0% Co is a basic component for obtaining a magnetic body. Therefore, in the present invention, Co is set to 45.0 to 55.0%. If Co is less than 45%, the magnetic permeability is low and the coercive force is high. From this viewpoint, the lower limit of Co is preferably 47.0% or more, more preferably 48.0% or more, and even more preferably 49.0% or more. On the other hand, if Co exceeds 55%, the saturation magnetic flux density is low and the coercive force is high. From this viewpoint, the upper limit of Co is preferably 53.0% or less, more preferably 52.0% or less, and even more preferably 51.0% or less.

[0034] V: 0~2.5% V is a component that can be added to the present invention as an optional component for improving workability, but V may be 0%. If the B2 ordered phase is excessive, toughness is deteriorated and workability is deteriorated, so adding V improves workability. However, if V is excessive, not only does the saturation magnetic flux density decrease, but the coercive force also increases. Therefore, the addition of V is set to 0 to 2.5% or less (V includes 0%).

[0035] In addition, since the present invention is a shaped body by the additive manufacturing method, a near-net shape can be formed in advance, and therefore the amount of V added can be reduced by prioritizing soft magnetic properties over processability. From this viewpoint, V is 2.0% or less, more preferably 1.0% or less, and even more preferably 0.5% or less. V may also be 0%.

[0036] Remainder: Fe and unavoidable impurities Fe is generally a component with a high saturation magnetic moment, and by adding Co, it is possible to realize an excellent saturation magnetic flux density as an FeCo-based alloy.

[0037] [Example] The chemical compositions of the powders used in the examples and comparative examples of the present invention are shown in Tables 1 and 2. The compositions of the layered objects made using these powders are almost the same.

[0038] (Creating powder) The powder was produced by the vacuum melting inert gas atomization method. Specifically, in a vacuum, raw materials having the prescribed compositions shown in Tables 1 and 2 were heated and melted in an alumina crucible by high-frequency induction heating, and the molten metal was dropped from a nozzle with a diameter of 5 mm located under the crucible, and high-pressure argon gas was sprayed onto the molten metal to obtain a powder, which was then classified using a -63 μm sieve.

[0039] (About Additive Manufacturing) Using these powders as raw materials, additive manufacturing was carried out using a three-dimensional additive manufacturing device (EOS-M280), and an additive manufacturing body consisting of a 10 x 10 x 10 mm rectangular parallelepiped was obtained. The additive manufacturing was carried out using the standard device parameters MS1 (layer thickness 40 μm) as the base, but with the output changed to 300 W and the scanning speed changed to 1100 mm / s. This additive manufacturing body was used as a test piece for measuring the coercive force.

[0040] (Heat treatment conditions) The heat treatment conditions for the layered objects of the examples and comparative examples are shown in Tables 1 and 2. Annealing was performed under the conditions of furnace cooling in a vacuum atmosphere, gas cooling in an Ar atmosphere, and water cooling in an air atmosphere, and the difference in cooling rate was evaluated.

[0041] [B2(100) / α(200) X-ray intensity ratio] The heat-treated molded body (10 x 10 x 10 mm) was cut on a plane perpendicular to the lamination direction, mechanically polished, and X-ray diffraction measurements were performed on the polished surface. X-ray diffraction measurements were performed using a Rigaku RAPID II with a Co tube. The ratio of the maximum reflection peak of the (200) plane of the α phase (PDF number: 01-087-0722) to the reflection peak of the (100) plane of the B2 ordered phase (PDF number: 01-071-5029) was taken as the B2(100) / α(200) X-ray intensity ratio.

[0042] [Structural observation: Determination of grain size] The heat-treated molded body (10 x 10 x 10 mm) was cut on a plane perpendicular to the lamination direction, mechanically polished, and the polished surface was then subjected to aqua regia etching treatment, after which the center of the embedded sample was observed under an optical microscope at a magnification of 400. Observations were performed at five randomly selected locations, and the average value of the crystal grain size calculated by the line segment method was regarded as the average crystal grain size of the sample.

[0043] [Coercive force measurement] The coercivity was measured using a coercivity meter (HC-1031, manufactured by Denshijiki Kogyo Co., Ltd.) The heat-treated molded body (10 × 10 × 10 mm) was placed in the coercivity meter, and a magnetic field was applied to the surface perpendicular to the lamination direction to measure the coercivity.

[0044] [Saturation magnetic flux density measurement] The saturation magnetic flux density was measured using a vibrating sample magnetometer (VSM). A magnetic field was applied to the surface perpendicular to the lamination direction of the heat-treated molded body (2 x 2 x 2 mm), and the saturation magnetic flux density was measured.

[0045] The results of each measurement are shown in Tables 1 and 2. In Table 2, the underlined parts indicate that the component composition and peak intensity ratio are outside the range of the present invention's means, and that the action and effect are inferior.

[0046] [Table 1]

[0047] [Table 2]

[0048] The examples of the present invention were annealed from a high temperature of 1000°C or more, and were slowly cooled, resulting in the observation of the B2 ordered phase as shown in Figure 1. In the examples, the coercive force was 200 [A / m] or less, which showed excellent coercive force. In addition, the saturation magnetic flux density was 2.10 T or more, which showed excellent soft magnetic properties.

[0049] In addition, in Example 6, the B2(100) / α(200) intensity ratio [%] was low at 2.2, which was below the peak intensity ratio of 2.5 or more specified in the second means, and therefore the B2 content was somewhat low, and the coercive force was somewhat higher than that of the other Examples.

[0050] In the examples of the present invention, no unidentifiable peaks were observed other than the α phase described in Non-Patent Document 1. In Non-Patent Document 1, the B2 ordered phase was not observed, and the layer thickness during molding was 20 μm, whereas in the present invention, different molding conditions were applied, with a layer thickness of 40 μm, and therefore the difference in thermal history during rapid solidification caused a difference in the constituent phases. In addition, while the non-patent literature describes annealing in the α single phase region below 1000°C, the present invention describes annealing in the γ single phase region, and this high-temperature annealing also promotes the precipitation of the B2 ordered phase. The present invention has a different constituent phase from that of Non-Patent Document 1, and contains a B2 ordered phase, so that the coercive force is 200 [A / m] or less. Therefore, in the present invention, it was confirmed that the soft magnetic properties of bulk permendur in the ingot material can be realized in the additive manufacturing material.

[0051] On the other hand, the coercive force of the comparative examples all exceeded 300 [A / m], which was not excellent.The saturation magnetic flux density was also lower than that of the examples, at 2.08 T or less. In Comparative Example 1, the amount of V was too large, the coercive force was too high, and the saturation magnetic flux density was low. In Comparative Example 2, the amount of Co was too little, the coercive force was too high, and the saturation magnetic flux density was low. In Comparative Example 3, the amount of Co was excessive, the coercive force was too high, and the saturation magnetic flux density was low. In Comparative Example 4, since water cooling was used, the B2 ordered phase, which would not form unless cooling was slow, was not included in the constituent phases, and therefore the coercive force was high and the saturation magnetic flux density was low. [Industrial Applicability]

[0052] The additively manufactured material using the FeCo-based alloy according to the present invention exhibits excellent soft magnetic properties and can therefore be used in components such as small, high-output motors, solenoid valves that require high magnetic force, and pole pieces for electronic devices.

Claims

1. An additively manufactured body produced by additive manufacturing using only alloy powder made of an FeCo-based alloy, the additively manufactured body being characterized in that the constituent phases include a B2 ordered phase and an α phase.

2. 2. The layered product according to claim 1, characterized in that, when the layered product is measured by X-ray diffraction using a Co tube, the peak intensity ratio between the (100) plane of the B2 ordered phase and the (200) plane of the α phase satisfies B2(100) / α(200)≧2.5%.

3. The layered product according to claim 1 or 2, characterized in that the FeCo-based alloy is an alloy consisting of, in mass%, Co: 45.0 to 55.0%, V: 0 to 2.5%, and the remainder: Fe and unavoidable impurities.

4. The layered product according to claim 1 or 2, wherein the average crystal grain size of the layered product is 15 μm or more.

5. The layered product according to claim 3 , wherein the average crystal grain size of the layered product is 15 μm or more.

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