Additive manufacturing powder material and method for manufacturing additive manufacturing powder material

Abstract

The present invention relates to an additive manufacturing powder material, which comprises Fe alloy particles each having an oxide film on the surface, wherein the Fe alloy particles satisfy d≤15 and I / d≤0.025, where d [nm] represents the thickness of the oxide film, and the peak intensity ratio I represents the peak intensity ratio at 1,309 cm in a Raman spectrum. ‑1 to 1,329cm ‑1 The Raman shift of peak B in region B is at 657.5 cm ‑1 to 677.5cm ‑1 The intensity ratio IB / IA of peak A in the Raman shift region A is shown in FIG.

Description

Technical Field

[0001] The present invention relates to an additive manufacturing powder material and a method for manufacturing the additive manufacturing powder material. More particularly, the present invention relates to a powder material formed of an Fe-based alloy that can be used as a raw material in additive manufacturing and a method for manufacturing the powder material. Background Art

[0002] Additive manufacturing (AM) technology has recently attracted significant attention as a new technology for producing three-dimensional objects. One type of AM involves solidifying powdered materials through energy beam irradiation. Two representative AM methods using metal powders are powder bed fusion and powder deposition.

[0003] Specific examples of powder bed fusion methods include selective laser melting (SLM) and electron beam melting (EBM). In these methods, a powder material formed of metal is supplied to a base material serving as a base to form a powder bed, and an energy beam such as a laser beam or an electron beam is irradiated to predetermined positions of the powder bed based on three-dimensional design data. The powder material on the irradiated portion is solidified by melting and resolidification, thereby forming a formed body. The supply of powder material to the powder bed and the shaping by energy beam irradiation are repeated, and the formed body is stacked layer by layer to form a three-dimensional formed body.

[0004] On the other hand, specific examples of powder deposition methods include laser metal deposition (LMD), in which metal powder is ejected from a nozzle toward a location where a three-dimensional structure is to be formed while being irradiated with a laser beam, thereby obtaining a three-dimensional formed body having a desired shape.

[0005] When using the additive manufacturing method described above to produce a three-dimensional formed body made of a metal material, the resulting three-dimensional formed body may contain structures with uneven distribution of the component materials, such as voids and defects. It is desirable to minimize the occurrence of such uneven structures. In additive manufacturing methods using metal materials, several factors are believed to contribute to the uneven distribution of the component materials within the resulting three-dimensional formed body. One such factor is the state of the powder material before energy beam irradiation, which can significantly affect the state of the resulting three-dimensional formed body.

[0006] For example, in a powder bed fusion method, when a powder material can be smoothly supplied to a base material to stably form a powder bed in which the powder material is evenly spread, or when the powder bed can be filled with powder material at a high density, a three-dimensional formed body with high uniformity can be easily obtained by irradiating the powder bed with an energy beam. In addition, in a powder deposition method, a three-dimensional formed body can be stably formed by smoothly and uniformly supplying powder material from a nozzle. In an additive manufacturing method, since the powder material used as the raw material of the three-dimensional formed body has a high fluidity, this smooth supply and high-density filling of the powder material can be facilitated. As a result, a three-dimensional formed body with high uniformity can be obtained by irradiating with an energy beam.

[0007] The improvement of the fluidity of the powder material can be achieved by, for example, reducing the adhesion (attractive interaction) between the particles. As a means for this purpose, a method of forming a compound film such as a metal oxide film on the surface of the metal particles is often used. For example, as a metal powder material with high fluidity, Patent Document 1 discloses a metal powder material comprising particles having an average particle size of 500 nm or more, and comprising an internal region formed of a metal and a coating formed of an insulating inorganic compound, which covers the surface of the internal region and has a thickness of 15 nm or more. Here, examples of the insulating inorganic compound constituting the coating include metal oxides containing at least one metal constituting the internal region. In addition, Patent Document 2 discloses a method for manufacturing an additive manufacturing powder material capable of maintaining fluidity for a long time, wherein a powdered base material as an iron material is heated in an oxygen-containing atmosphere within a predetermined temperature range so that its oxygen content increases by more than 0.0025 wt % to less than 0.0100 wt % relative to the base material, thereby forming an oxide film on the surface of the base material.

[0008] Patent Document 1: JP-A-2019-183199

[0009] Patent Document 2: JP-A-2020-59902 Summary of the Invention

[0010] As mentioned above, in order to improve the fluidity of the powder material, it is effective to form an oxide film composed of a metal oxide on the surface of the metal particles. Patent Document 1 stipulates a lower limit for the coating thickness, so when the oxide film is formed to a certain thickness, the effect of improving fluidity is enhanced. However, in the case of manufacturing a three-dimensional molded body by an additive manufacturing method, when the raw material powder contains a large amount of oxide, the oxide acts as an impurity in the three-dimensional molded body, and there is a possibility that the quality of the three-dimensional molded body will deteriorate. From this point of view, it can be said that it is desirable to form a thin oxide film on the surface of the metal particles.

[0011] On the other hand, oxides can assume various chemical states (oxidation values) depending on the type of metal. In this case, each oxide in each chemical state may contribute differently to improving the fluidity of the powder material. Therefore, by appropriately selecting the type of oxide, a high fluidity improvement effect can be achieved even when the oxide film is thin.

[0012] An object of the present invention is to provide an additive manufacturing powder material that exhibits high fluidity even when an oxide film formed on the surface of metal particles is thin, and a production method capable of obtaining such an additive manufacturing powder material.

[0013] In order to solve the above problems, the additive manufacturing powder material according to the present invention is an additive manufacturing powder material comprising Fe alloy particles each having an oxide film on the surface, wherein the Fe alloy particles satisfy d≤15 and I / d≤0.025, wherein d [nm] represents the thickness of the oxide film, and the Raman spectrum of the powder material has peaks A and B, and the maximum peak of peak A is located at 657.5 cm -1 to 677.5cm -1 The Raman shift is in region A, and the maximum peak of peak B is located at 1,309 cm -1 to 1,329cm -1 In the Raman shift region B, IA represents the integrated intensity of peak A in region A of the Raman spectrum, IB represents the integrated intensity of peak B in region B of the Raman spectrum, and the peak intensity ratio I represents the intensity ratio of peak B to peak A, IB / IA.

[0014] Here, the thickness of the oxide film preferably satisfies 8≤d≤15. The peak intensity ratio in the Raman spectrum preferably satisfies I≤0.30. In addition, the avalanche angle of the additive manufacturing powder material may be less than 40°.

[0015] The method for manufacturing an additive manufacturing powder material according to the present invention includes preparing Fe alloy particles by a gas atomization process, and then vacuum heating the Fe alloy particles to form an oxide film on the surface of the particles.

[0016] In the powder material containing Fe alloy particles, the maximum peak is located at 657.5 cm -1 to 677.5cm -1 Peak A in the Raman shift region is a characteristic peak of Fe3O4, and the maximum peak is located at 1,309 cm -1 to 1,329cm -1Peak B in the Raman shift region is a characteristic peak of Fe2O3. In other words, the smaller the value of the peak intensity ratio I calculated as IB / IA, the greater the ratio of Fe3O4 to Fe2O3 in the oxide film, where IA and IB are the integrated intensities of peaks A and B, respectively. The Hamaker constant of Fe3O4 is smaller than that of Fe2O3, which suppresses the adhesion between particles and is therefore very effective in improving fluidity. Therefore, controlling I / d to a low value of less than 0.025 causes the oxide film to contain a large amount of Fe3O4, thereby providing a high fluidity improvement effect even when the thickness d of the oxide film is as low as 15nm or less.

[0017] Here, when the thickness of the oxide film on the particle surface satisfies 8≤d≤15, the oxide film has a thickness sufficient to exhibit a high fluidity improvement effect, and the oxide film can be adjusted to a sufficiently low thickness so that it does not act as an impurity that deteriorates the quality of the three-dimensional formed body when additive manufacturing is performed.

[0018] When the peak intensity ratio in the Raman spectrum satisfies I ≤ 0.30, the oxide film contains a sufficiently large amount of Fe 3 O 4 relative to Fe 2 O 3 , making it easy to adjust I / d to below 0.025. This effectively improves the fluidity of the additive manufacturing powder material.

[0019] In addition, when the avalanche angle of the additive manufacturing powder material is less than 40°, it can be ensured that the additive manufacturing powder material has sufficiently high fluidity, so the additive manufacturing powder material can be suitable for use as a raw material for additive manufacturing.

[0020] In the method for manufacturing an additive manufacturing powder material according to the present invention, Fe alloy particles are prepared by a gas atomization process and then vacuum heated to form an oxide film on the surface of the particles. Only a small amount of oxide is formed on the surface of the Fe alloy particles prepared by the gas atomization method, and an oxide film is generated on the surface of the particles by heating. At this time, by performing vacuum heating, Fe3O4 can be preferentially formed on the oxide film compared to Fe2O3. The Hamaker constant of Fe3O4 is smaller than that of Fe2O3, so the adhesion between the particles is suppressed. Therefore, a powder material that has high fluidity and is suitable for additive manufacturing can be manufactured even when the thickness of the oxide film is thin. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Raman spectra of three powder materials are shown: Sample 0 represents the powder material before oxidation, Sample 1 represents the powder material oxidized in vacuum, and Sample 2 represents the powder material oxidized in the atmosphere.

[0022] Figures 2A to 2E For comparison Figure 1 Figures showing various properties of the three samples: As properties, Figure 2A The thickness d of the oxide film is shown in Figure 2B The oxygen value is shown in Figure 2C The peak intensity ratio I (=IB / IA) is shown in Figure 2D The film index (I / d) is shown in Figure 2E The avalanche angle is shown in .

[0023] Figure 3 Graph showing the relationship between the film index I / d and the avalanche angle for various powder materials. DETAILED DESCRIPTION

[0024] Hereinafter, the additive manufacturing powder material and the method for manufacturing the additive manufacturing powder material according to the embodiment of the present disclosure will be described in detail. Hereinafter, unless otherwise specified, various properties refer to values measured at room temperature in the atmosphere.

[0025] [Additive manufacturing powder materials]

[0026] The additive manufacturing powder material according to an embodiment of the present invention (hereinafter sometimes simply referred to as the powder material) includes Fe alloy particles each having an oxide film on the surface, and the thickness d of the oxide film, and the film index I / d obtained by the intensity ratio I of a predetermined peak in the Raman spectrum and the thickness d of the oxide film are within a predetermined range.

[0027] (1) Composition of additive manufacturing powder materials

[0028] As the material composition of the powder material according to the embodiment of the present invention, there is no particular limitation on the alloy composition as long as the alloy composition is an Fe alloy, that is, an alloy containing Fe as a main component. The specific alloy composition can be appropriately selected according to the alloy composition required for the three-dimensional formed body to be manufactured by additive manufacturing, and examples of the alloy composition include stainless steel, carbon steel, and tool steel. The powder material may contain particles of one Fe alloy, or may contain particles of two or more Fe alloys.

[0029] Specific examples of the composition of the exemplary alloy composition described above include the following compositions: Compositions described with only upper limits of the composition mean that these components are not essential and may not be included.

[0030] Stainless steel: (by mass%) C≤0.40%, Si≤1.0%, Mn≤1.0%, Ni

[0031] ≤15.0%, 10.0%≤Cr≤20.0%, Mo≤3.0%, Cu≤5.0% and Nb≤0.7%, with the balance being Fe and unavoidable impurities.

[0032] Tool steel: (in mass %) C ≤ 0.50%, Si ≤ 1.50%, Mn ≤ 0.60%, 4.0% ≤ Cr ≤ 6.0%, 0.90% ≤ Mo ≤ 1.50% and 0.20% ≤ V ≤ 1.30%, the balance being Fe and unavoidable impurities.

[0033] Maraging steel: (in mass %) C ≤ 0.03%, Si ≤ 0.10%, Mn ≤ 0.10%, 17.0% ≤ Ni ≤ 19.0%, 8.0% ≤ Co ≤ 10.0%, 4.0% ≤ Mo ≤ 6.0%, 0.50% ≤ Ti ≤ 0.80%, 0.05% ≤ Al ≤ 0.15%, the balance being Fe and unavoidable impurities.

[0034] There are no particular restrictions on the particle size of the Fe alloy particles, but from the perspective of suitability as a raw material for additive manufacturing, the Fe alloy particles preferably have a particle size in the micrometer range. Specifically, the average particle size (d50) of the Fe alloy particles can be between 10 μm and 500 μm. An average particle size of between 10 μm and 100 μm is particularly preferred. The average particle size (d50) refers to the particle size at which the cumulative undersize fraction in a mass-based distribution is 50%.

[0035] Preferably, the powder material according to the embodiment of the present invention contains only Fe alloy particles, excluding inevitable impurities, and is used for additive manufacturing in a state of only the Fe alloy particles. However, other types of particles can be appropriately added and used. Examples of other types of particles include nanoparticles. Nanoparticles can be located between adjacent metal particles to ensure the distance between the metal particles, thereby reducing the attractive force acting between the metal particles. As a result, the fluidity of the powder material containing metal particles can be improved. Metal oxide particles, in particular oxide particles of light metal elements such as Si, Al or Ti, can be appropriately used as nanoparticles. Nanoparticles do not substantially affect the three-dimensional formed body to be manufactured due to their small volume, but the amount of nanoparticles added can be adjusted to less than 0.1% by mass based on the Fe alloy particles. In the powder material according to the embodiment of the present invention, since the film index I / d of the metal particles is adjusted to below the predetermined upper limit, the powder material exhibits sufficiently high fluidity even without adding nanoparticles.

[0036] Preferably, the powder material contains only metal particles having a micron-sized particle size that are formed from an Fe alloy and have an oxide film thickness d and a film index I / d that fall within the predetermined ranges described below. However, particles formed from alloys other than Fe alloys may be added to the Fe alloy particles. In this case, the content of the particles other than Fe alloys is preferably less than that of the Fe alloy particles, and the oxide film thickness d on the surface of the particles formed from the alloy other than Fe alloys preferably satisfies the predetermined ranges described below. Preferably, excluding unavoidable impurities, the powder material does not contain other Fe alloy particles whose oxide film thickness d and film index I / d do not meet the predetermined ranges described below.

[0037] (2) Thickness of oxide film

[0038] In the Fe alloy particles included in the powder material according to the embodiment of the present invention, the thickness d [nm] of the oxide film formed on the surface of the particle is less than 15 nm (d ≤ 15). Here, the thickness of the oxide film is the average value of the thickness of the oxide film in each particle. The thickness of the oxide film can be estimated by a detection method such as micro-Auger electron spectroscopy, by which the depth distribution of element abundance can be known. For example, the average value of the thickness of the oxide film in five randomly selected particles can be evaluated. At this time, the depth at which the oxygen concentration is half of the oxygen concentration of the outermost surface can be estimated and used as the thickness of the oxide film.

[0039] In the powder material, the thickness of the oxide film is adjusted to 15 nm or less. This makes it less likely that the oxide will act as an impurity that degrades the quality of the obtained three-dimensional formed body when it is formed by additive manufacturing. From the perspective of the reinforcing effect, the thickness of the oxide film is more preferably 13 nm or less, and even more preferably 12 nm or less.

[0040] There is no particular lower limit on the thickness of the oxide film in the powder material. However, because the oxide film reduces the adhesion between particles in the powder material, thereby improving fluidity, it is preferable to form an oxide film having a thickness that is equal to or greater than the detection limit of a detection method such as Auger electron spectroscopy. More preferably, the oxide film has a thickness of 8 nm or greater, further preferably 9 nm or greater, and even more preferably 10 nm or greater.

[0041] (3) Chemical state of oxide film

[0042] It is known that Fe oxides have various chemical states (oxidation values), so the oxide film on the surface of the Fe alloy particles may also contain Fe in various chemical states. The chemical state of the oxide film has a significant influence on the fluidity of the powder material.

[0043] In the powder material according to the embodiment of the present invention, the chemical state of the oxide film on the surface of the Fe alloy is determined from the Raman spectrum obtained by Raman spectrometry. Figure 1 The Raman spectra of three Fe alloy powders are shown. Two characteristic peaks are observed in the shown region. These peaks will be described with reference to Sample 2 as an example.

[0044] When observing the Raman spectrum of sample 2, it was observed that at 657.5 cm -1 to 677.5cm -1 Raman shift region (region A) and 1,309 cm -1 to 1,329cm -1 A clear peak structure with a maximum peak in the Raman shift region (region B) is observed. These peaks are referred to as Peak A and Peak B. Compared to the standard spectrum of the pure substance, Peak A is unique to Fe₃O₄, while Peak B is unique to Fe₂O₃. Similar to Peak B, the broad peak (Peak C) at the lower wavenumber side of Peak A also originates from Fe₂O₃.

[0045] Since Peak A and Peak B are attributed to Fe₃O₄ and Fe₂O₃, respectively, the intensity ratio of Peak A to Peak B is an indicator reflecting the abundance ratio of Fe₃O₄ to Fe₂O₃ in the oxide film. The higher the intensity of Peak B relative to Peak A, the higher the proportion of Fe₂O₃ in the oxide film. Therefore, in an embodiment of the present invention, the integrated intensity IA of Peak A and the integrated intensity IB of Peak B are estimated, and the intensity ratio I of Peak B to Peak A is calculated (I=IB / IA). This intensity ratio I is used as an indicator of the chemical state of the oxide film.

[0046] When estimating the peak ratio, it is preferred to obtain a Raman spectrum by Raman spectrometry using a laser having a wavelength of 532 nm as excitation light. In particular, it is preferred to obtain a Raman spectrum of each particle by micro-Raman spectrometry. In the obtained Raman spectrum, the background (baseline) is removed, and then the spectrum intensity is integrated to obtain the integrated intensity IA of Peak A and the integrated intensity IB of Peak B. For Peak A, the integration range is 657.5 cm -1 to 677.5cm -1 The Raman shift region (region A) and for peak B, the integration range is 1,309 cm -1 to 1,329cm -1In the Raman spectrum of the Fe alloy particle, peaks A, B, and C are separated from each other to a certain extent, and regions A and B are set to sufficiently avoid regions where these peaks overlap. Therefore, when calculating the integrated intensities IA and IB, it is not necessary to use curve fitting for peak separation, and the spectral intensity itself can be integrated within the respective predetermined integration ranges in the Raman spectrum minus the background.

[0047] Once the integrated intensities IA and IB of Peak A and Peak B are obtained, the peak ratio I can be calculated as the ratio of the integrated intensity IB to the integrated intensity IA (I = IB / IA). When using micro-Raman spectroscopy, measurements can be performed on a plurality of randomly selected particles, and the intensity ratio I can be estimated as an average. For example, the background-removed Raman spectra of a plurality of particles can be averaged, and the integrated intensities IA and IB can be estimated from the average spectrum, and the peak ratio I can be calculated.

[0048] In the embodiment of the present invention, the value of I / d obtained by dividing the peak ratio I obtained by Raman spectroscopy by the thickness d [nm] of the above oxide film is used as a film index to define the state of the oxide film. In the powder material according to the embodiment of the present invention, the value of the film index is limited to 0.025 or less (I / d≤0.025).

[0049] As shown in the following examples, the present inventors have found that, in a powder material formed of Fe alloy particles, the smaller the value of the film index I / d, the higher the fluidity of the powder material. Figure 1 For Samples 1 and 2, whose Raman spectra are shown in Figure 2, the oxide film thicknesses are substantially the same, but as is apparent from visual evaluation of the spectra, Peak B appears stronger in Sample 2, resulting in a greater peak ratio I in Sample 2. In other words, the film index I / d in Sample 2 is greater than that in Sample 1. In fact, as described in detail in the Examples below, when evaluating each film index, the film index in Sample 1 is 0.025 or less, while the film index in Sample 2 exceeds 0.025. Thus, Sample 1 exhibits higher fluidity than Sample 2.

[0050] As the adhesion (attractive interaction) between particles decreases, the fluidity of the powder material improves. It is known that the adhesion between particles is proportional to the Hamaker constant. According to a reference, in water as the medium, the Hamaker constant for Fe₃O₄ is smaller than that for Fe₂O₃, with the Hamaker constant for Fe₂O₃ being 39 zJ, while the Hamaker constant for Fe₃O₄ is 33 zJ (reference: B. Faure, "Particle Interactions at the Nanoscale," PhD thesis, Stockholm University (2012)). This means that in a powder material formed from Fe alloy particles, with the same oxide film thickness, the powder material exhibits higher fluidity as the ratio of Fe₃O₄ to Fe₂O₃ in the oxide film increases. In the case of a thick oxide film, the fluidity of the powder material is more likely to improve due to the influence of the oxide film thickness. Therefore, in the case of a thick oxide film, even when the abundance ratio of Fe₃O₄ to Fe₂O₃ is low, a high fluidity improvement effect can be easily achieved compared to a thin oxide film. On the contrary, in the case where the oxide film is thin, the abundance ratio of Fe3O4 to Fe2O3 must be increased compared to the case where the oxide film is thick in order to sufficiently improve the fluidity of the powder material.

[0051] In other words, the abundance ratio of Fe3O4 required to fully improve the fluidity of the powder material depends on the thickness of the oxide film. The greater the thickness, the smaller the abundance ratio of Fe3O4 to Fe2O3 can be. Therefore, in an embodiment of the present invention, rather than using the peak ratio I of the Raman spectrum itself, which directly reflects the abundance ratio of Fe3O4 to Fe2O3 in the oxide film, as the film index, the value I / d, obtained by dividing the peak ratio I by the thickness d of the oxide film, is used as the film index. When the value of the film index I / d decreases due to a decrease in the peak ratio I or an increase in the thickness, the fluidity of the powder material is improved.

[0052] The greater the thickness of the oxide film on the surface of the Fe alloy particles, the higher the effect of improving fluidity. On the other hand, from the viewpoint of reducing the amount of oxides that may affect the quality of the three-dimensional formed body to be manufactured when additive manufacturing is performed using powder materials, it is desirable to adjust the thickness of the oxide film on the surface of the Fe alloy particles to be as small as possible. In fact, in an embodiment of the present invention, as described above, the thickness of the oxide film is limited to 15 nm or less. Therefore, in the powder material according to an embodiment of the present invention, it is desirable to include a sufficient proportion of Fe3O4 in the oxide film to help improve fluidity, while adjusting the thickness of the oxide film to be as small as possible, and using the film index I / d as an indicator, taking into account the contribution of both the thickness of the oxide film and the chemical state of the oxide film, thereby obtaining sufficiently high fluidity.

[0053] Specifically, by setting the upper limit of the film index I / d to 0.025, the fluidity of the powder material can be ensured even when the oxide film is thinned. As shown in the following examples, when the film index I / d is 0.025 or less, the fluidity level of the powder material is high and it is suitable for use as a raw material for additive manufacturing (especially additive manufacturing by powder bed fusion). The film index I / d is preferably 0.020 or less, and more preferably 0.015 or less, because this can more effectively improve the fluidity of the powder material. Although there is no particular lower limit for the film index I / d, considering the Fe alloy particles that can be actually manufactured, the film index I / d is about 0.005 or more.

[0054] As described above, when the thickness d of the oxide film changes, the abundance ratio of Fe3O4 required to fully improve the fluidity of the powder material also changes. Therefore, as long as the film index I / d is adjusted to 0.025 or less, the value of the peak ratio I itself in the Raman spectrum is not particularly limited. However, when the oxide film contains a large amount of Fe3O4 relative to Fe2O3 to obtain a low peak ratio I, the film index I / d tends to be a smaller value, and the fluidity of the powder material is easily improved. For example, the peak ratio I is preferably 0.30 or less, and more preferably 0.25 or less. Although there is no particular lower limit for the peak ratio I, considering the Fe alloy particles that can be actually manufactured, the peak ratio I is about 0.05 or more.

[0055] In the embodiment of the present invention, there is no particular limitation on the oxygen content of the oxide film, as long as the thickness d of the oxide film in the Fe alloy particles is adjusted to 15 nm or less and the film index I / d is adjusted to 0.025 or less. However, from the perspective of enhancing the effect of improving fluidity by forming oxides, the oxygen value (the proportion of oxygen atoms in the entire powder material) is preferably 0.035 mass% or more. On the other hand, from the perspective of suppressing the formation of large amounts of oxides, the oxygen value is preferably 0.050 mass% or less.

[0056] As described above, by reducing the film index I / d, the fluidity of the powder material can be improved. The fluidity of the powder material can be evaluated by using (for example) the avalanche angle as an indicator. Powder materials with smaller avalanche angles exhibit higher fluidity. When the film index I / d is less than 0.025 as described above, the avalanche angle of the powder material can be adjusted to less than 40°, which is a level that can provide sufficiently high fluidity in additive manufacturing. The avalanche angle is preferably less than 35°. There is no particular restriction on the lower limit of the avalanche angle, but in Fe alloy particles that can be actually manufactured, the avalanche angle is generally above 25°.

[0057] In the powder material according to the embodiment of the present invention, the chemical state of the oxide film is defined by the abundance ratio of Fe3O4 to Fe2O3, and it is preferred that, among the Fe oxides contained in the film formed on the surface of the Fe alloy particles, only Fe3O4 and Fe2O3 are contained, except for unavoidable impurities. However, it is not prohibited to contain Fe oxides in other oxidation states in the film. In addition, in addition to Fe oxide, the film may contain chemical substances other than Fe oxide, such as oxides of metals other than Fe, or carbides of Fe or other metals. Even in these cases, the film index I / d calculated by the peak intensity ratio I focused on Fe3O4 and Fe2O3 should be 0.025 or less. It is preferred that the film does not contain chemical substances other than Fe3O4 and Fe2O3 in a larger amount than Fe3O4, so as not to significantly damage the fluidity improvement effect exhibited by Fe3O4.

[0058] [Manufacturing method of powder material for additive manufacturing]

[0059] Next, a method for producing an additive manufacturing powder material according to an embodiment of the present invention will be described. By the method according to an embodiment of the present invention, the powder material according to the embodiment of the present invention described in detail above can be appropriately produced.

[0060] When producing a powder material, Fe alloy particles are first prepared by gas atomization. An inert gas such as Ar can be used as the atomizing gas. Fe alloy particles prepared by gas atomization do not undergo excessive surface oxidation; typically, the thickness of the oxide film is adjusted to 10 nm or less, and the oxygen content is adjusted to 0.035 mass % or less.

[0061] Next, the particles produced by gas atomization are oxidized to form an oxide film on the surface. The oxide film is formed by heating the particles in a vacuum (under reduced pressure). Heating in the atmosphere tends to produce a large amount of Fe2O3 with a high oxidation number, but vacuum heating can increase the proportion of Fe3O4 produced.

[0062] From the perspective of efficiently generating Fe3O4, the heating temperature when forming the oxide film is preferably in the range of 100°C to 150°C. In addition, by adjusting the heating temperature within this range, the generation ratio of Fe3O4 to Fe2O3 can be changed. The higher the heating temperature, the higher the proportion of Fe2O3 tends to be, that is, the peak intensity ratio I in the Raman spectrum tends to be larger. The heating time can be appropriately selected and can be, for example, in the range of 5 minutes to 120 minutes. When the heating time is extended, the thickness d of the oxide film tends to increase.

[0063] There are no particular restrictions on the degree of vacuum during heating, but reducing the pressure to below -0.05 MPa relative to atmospheric pressure is sufficient. Furthermore, there are no particular restrictions on the specific configuration of the heating apparatus, as long as vacuum heating is possible. From the perspective of forming a highly uniform oxide film of a certain thickness and chemical state on the surface of each particle, it is preferable to use an apparatus that can vibrate the powder in a vacuum while heating it, such as a vibration dryer.

[0064] Example

[0065] Hereinafter, the present invention will be described in more detail with reference to Examples. Herein, the relationship between the state of the oxide film of the Fe alloy particles and the fluidity of the powder material was studied. Hereinafter, unless otherwise specified, various evaluations were performed in the atmosphere at room temperature.

[0066] [1] Comparison of oxide film state and fluidity

[0067] First, for powder materials prepared under typical conditions, the state and fluidity of the oxide film were evaluated.

[0068] (Sample Preparation)

[0069] Fe alloy particles were prepared by gas atomization using Ar gas. The composition of the Fe alloy included, by mass%, 0.42% C, 1.0% Si, 0.4% Mn, 5.0% Cr, 1.2% Mo, 1.0% V, and 0.03% O, with the balance being Fe and unavoidable impurities. The average particle size (d50) of the Fe alloy particles was 35 μm. A powder material formed from the Fe alloy particles thus obtained was used as Sample 0.

[0070] Sample 0 obtained by the gas atomization method was oxidized under different conditions to produce Sample 1 and Sample 2. Sample 1 was obtained by vacuum heating of Sample 0. Specifically, Sample 0 was heated while vibrating in a vacuum (-0.1 MPa based on atmospheric pressure) using a vibration dryer capable of reducing pressure ("VU-45 Model" manufactured by Chuo Kakohki Co., Ltd.). As for the heating temperature and heating time, the sample was maintained at 125°C for 1 hour.

[0071] Sample 2 was obtained by heating Sample 0 in the atmosphere. Specifically, Sample 0 was heated in a constant temperature dryer while being allowed to remain in the atmosphere. The heating temperature and heating time were 125° C. for 1 hour.

[0072] (Evaluation of sample status)

[0073] (1) Thickness

[0074] For each sample, the oxide film thickness was estimated by micro-Auger electron spectroscopy. The depth profile of the O and Fe concentrations was evaluated using depth profiling using Ar sputtering. After confirming that the surface layer primarily consisted of Fe and O, the thickness at which the O concentration was half that of the outermost surface was estimated and used as the oxide film thickness. The film thicknesses of five randomly selected particles were obtained and averaged, with the average value used as the thickness value for each sample.

[0075] (2) Chemical state

[0076] For each sample, the chemical state of the oxide film on the particle surface was evaluated by Raman spectroscopy. Raman spectra of each particle were measured using a micro Raman spectrometer. As the excitation light, a laser with a wavelength of 532 nm (intensity: 0.7 mW) was used. 15 randomly selected particles were measured. In the Raman spectrum of each particle obtained, the background (baseline) was removed, and then the Raman spectra of the 15 particles were averaged. Then, in the average Raman spectrum, the 657.5 cm -1 to 677.5cm -1 The spectral intensity in the Raman shift region of 1,309 cm was integrated to obtain the integrated intensity IA of peak A, and the -1 to 1,329cm -1 The spectral intensity in the Raman shift region is integrated to obtain the integrated intensity IB of Peak B. When determining the integrated intensity, peak separation is not performed, and the intensity values of the Raman spectrum averaged after background removal are integrated. The peak ratio I is then calculated as I = IB / IA. Furthermore, the peak ratio I value is divided by the thickness d estimated by micro-Auger electron spectroscopy to obtain the film index I / d.

[0077] (3) Oxygen value

[0078] The oxygen value of each sample was measured by an inert gas fusion infrared absorption method using a TC600 nitrogen and oxygen analyzer manufactured by LECO in accordance with JIS G1239:2014.

[0079] (4) Avalanche Corner

[0080] The avalanche angle of each sample was evaluated using a rotating drum powder flowability tester. The powder material was placed in a transparent drum, and the drum was rotated at a speed of 0.6 rpm while the state of the powder material was photographed from the outside of the drum. The angle of the powder material when avalanche occurred (the angle formed by the inclined surface of the powder material and the horizontal surface) was then recorded as the avalanche angle.

[0081] (Evaluation Results)

[0082] first, Figure 1The Raman spectra obtained for samples 0 to 2 are shown. For each sample, the spectrum obtained by removing the background from the spectra measured for 15 particles and averaging the spectra is shown. As most notably shown in the spectrum of sample 2, two clear peaks, peak A and peak B, appear in each spectrum, with the maximum peak of peak A at 657.5 cm. -1 to 677.5cm -1 The Raman shift region is in the range of 1,309 cm, and the maximum peak of peak B is located at 1,309 cm -1 to 1,329cm -1 Compared with the standard spectrum, peak A at low wavenumbers can be attributed to Fe3O4, while peak B at high wavenumbers can be attributed to Fe2O3. The broad peak C seen at the lower wavenumber side of peak A is attributed to Fe2O3.

[0083] When comparing the Raman spectra of samples 0 to 2, in sample 0 before oxidation treatment, the intensities of peak A and peak B are relatively low. Compared with sample 0, in sample 1 oxidized in vacuum, peak B does not increase substantially, while peak A increases significantly. In other words, in sample 1, although the amount of Fe2O3 does not increase substantially, the generation of Fe3O4 is enhanced. On the other hand, in sample 2 oxidized in the atmosphere, peak A and peak B both increase significantly compared with sample 0. That is, in sample 2, both Fe2O3 and Fe3O4 are generated. When comparing sample 1 and sample 2, the intensity of peak A is substantially the same in sample 1 and sample 2, while the intensity of peak B is significantly higher in sample 2. In other words, compared with sample 1, sample 2 has a larger abundance ratio of Fe2O3 to Fe3O4. This result becomes clearer when obtaining the peak intensity ratio I.

[0084] Figures 2A to 2E The evaluation results of Samples 0 to 2 obtained by the respective evaluation methods are summarized. Figure 2A shows the film thickness d of the oxide film, Figure 2B shows the oxygen value, Figure 2C shows the peak intensity ratio I (=IB / IA), Figure 2D The membrane index (I / d) is shown, and Figure 2E shows the avalanche angle. First, when comparing Figure 2A When comparing the thickness of the oxide film in the sample 0, the thickness of both samples 1 and 2 increased after oxidation. The thickness of sample 1 was almost the same as that of sample 2. The oxygen values of both samples 1 and 2 increased after oxidation of sample 0. There was no significant difference between the oxygen values of sample 1 and sample 2. In other words, the amount of oxygen atoms constituting the Fe oxide in sample 1 and sample 2 was not significantly different.

[0085] However, when observing Figure 2CAs shown in the peak intensity ratio 1 based on Raman spectroscopy, the peak intensity ratio of sample 2 is significantly increased to about 1.7 times the peak intensity ratio of sample 0 before oxidation, while the peak intensity ratio of sample 1 does not change. Figure 1 As mentioned above, since the thickness of the oxide film in sample 1 and sample 2 is almost the same, the Figure 2D Similarly, the film index I / d shows a relationship in which the peak intensity ratio I value of Sample 2 is greater than that of Sample 1. These results confirm that the abundance ratio of Fe2O3 to Fe3O4 in Sample 2 is significantly greater than that in Sample 1. In other words, in Sample 1, which was oxidized in vacuum, the relative amounts of Fe2O3 and Fe3O4 are suppressed, while the formation of Fe3O4 is promoted. The film index I / d value of Sample 1 is 0.025 or less, while the values of the film index I / d for Samples 0 and 2 exceed 0.025.

[0086] Next, when comparing Figure 2E The measured avalanche angle values for each sample are shown. While Samples 1 and 2 both have smaller avalanche angles than Sample 0, the reduction in the avalanche angle for Sample 1 is more significant. The smaller the avalanche angle, the higher the flowability of the powder material. In other words, while both Samples 1 and 2 have improved flowability compared to Sample 0 before oxidation, Sample 1, after vacuum oxidation, has significantly improved flowability compared to Sample 2.

[0087] Summarizing the above results, the peak intensity ratio I and film index I / d of Sample 1, oxidized in a vacuum, were smaller than those of Sample 2, oxidized in air. In other words, the ratio of Fe₃O₄ to Fe₂O₃ in the oxide film of Sample 1 was greater than that of Fe₃O₄ to Fe₂O₃ in the oxide film of Sample 2. Furthermore, Sample 1 exhibited higher fluidity than Sample 2. These findings confirm that Fe₃O₄ has a greater effect on improving the fluidity of powder materials than Fe₂O₃.

[0088] [2] Relationship between the state of the oxide film and fluidity

[0089] Next, the number of samples will be further increased, and the relationship between the state of the oxide film and its fluidity will be studied in detail.

[0090] (Sample Preparation)

[0091] Samples 1a to 1e were prepared by vacuum heating the powder material of sample 0 prepared in the above-mentioned test [1] in the same manner as sample 1, except that the heating temperature and / or heating time were changed. In addition, samples 2a to 2f were prepared by heating the powder material of sample 0 in the atmosphere in the same manner as sample 2, except that the heating temperature and / or heating time were changed. In each of samples 1a to 1e and samples 2a to 2f, the thickness and chemical state of the oxide film were changed by changing the heating temperature and / or heating time. The heating temperature mainly affects the chemical state (oxidation value) of the oxide film, and increasing the heating temperature makes it easier to generate Fe2O3 than Fe3O4. The heating time mainly affects the thickness of the oxide film, and as the heating time is extended, a thick oxide film is more likely to be formed.

[0092] (Evaluation of sample status)

[0093] For each of the prepared samples, the film thickness d, chemical state (peak intensity ratio I based on Raman spectroscopy), and avalanche angle of the oxide film were evaluated in the same manner as in the above-mentioned test [1].

[0094] (Evaluation Results)

[0095] Table 1 below summarizes the values of the thickness d, peak intensity ratio I, film index I / d, and avalanche angle of the oxide films of samples 0 to 2 prepared in the above experiment [1], newly prepared samples 1a to 1e, and samples 2a to 2f.

[0096] [Table 1]

[0097]

[0098] According to Table 1, it can be seen that the vacuum-oxidized sample group 1 (sample 1 and samples 1a to 1e) has a smaller avalanche angle and higher fluidity than the sample group 2 (sample 2 and samples 2a to 2f). In addition, in general, the peak intensity ratio I of sample group 1 tends to be smaller than the peak intensity ratio I of sample group 2. That is, it can be seen in general that in samples with a smaller peak intensity ratio I, the avalanche angle tends to be smaller. However, although samples 1d, 1e, and 2a to 2c show very close peak intensity ratios I within 0.24 to 0.26, their avalanche angles are widely distributed in the range of 33° to 50°. That is, the correlation between the peak intensity ratio I and the avalanche angle is not always high.

[0099] On the other hand, when focusing on the film index I / d obtained by dividing the peak intensity ratio I by the thickness d [nm] of the oxide film, it can be clearly seen that the value of the film index I / d of sample group 1 is smaller than that of sample group 2, and that a high correlation with the avalanche angle is exhibited. This trend becomes even clearer when expressed in a graph. Figure 3The relationship between the film index I / d and the avalanche angle of all samples shown in Table 1 is plotted. The data of sample group 1 are represented by circle marks (○), and the data of sample group 2 are represented by cross marks (×). In addition, the data of unoxidized sample 0 are represented by triangle marks (Δ).

[0100] according to Figure 3 , clearly showing a monotonically increasing trend in the avalanche angle as the film index I / d increases. Furthermore, the data points for Sample Group 1 and Sample Group 2 smoothly follow one another and exhibit a monotonically increasing trend. These results demonstrate a high correlation between the film index I / d and the avalanche angle. When the film index I / d is small, it can be confirmed that the avalanche angle is also small, and the powder material has high fluidity.

[0101] When the avalanche angle of the powder material is less than 40°, it can be considered that the powder material has high enough fluidity to be used in additive manufacturing. Figure 3 As shown by the dotted line in the figure, an avalanche angle of less than 40° is achieved in the region where the film index I / d is 0.025 or less. In Sample Group 1, which employed vacuum oxidation, the film index I / d reached 0.025 or less. It can be said that vacuum oxidation enables efficient production of Fe₃O₄ even when the oxide film thickness d is low, in terms of its ratio relative to Fe₂O₃.

[0102] The embodiments and examples of the present invention have been described above. The present invention is not particularly limited to these embodiments and examples, and various modifications can be made.

[0103] This application is based on Japanese patent application No. 2021-197469 filed on December 6, 2021, the contents of which are incorporated herein by reference.

Claims

1. An additive manufacturing powder material comprising: Fe alloy particles each having an oxide film on the surface, wherein The Fe alloy particles satisfy d≤15 and I / d≤0.025, Wherein d represents the thickness of the oxide film, and the unit of d is nm, The Raman spectrum of the powder material has peak A and peak B, and the maximum peak of peak A is located at 657.5 cm -1 to 677.5cm -1 The Raman shift region A is the largest peak of peak B, and the maximum peak is located at 1,309 cm -1 to 1,329cm -1 In the Raman shift region B, IA represents the integrated intensity of the peak A in the region A of the Raman spectrum, IB represents the integrated intensity of the peak B in the region B of the Raman spectrum, and The peak intensity ratio I represents the intensity ratio IB / IA of the peak B to the peak A. The thickness of the oxide film was estimated by micro-Auger electron spectroscopy, and the depth distribution of the concentrations of O and Fe was evaluated by depth analysis using Ar sputtering to perform the measurement. After confirming that the surface layer mainly contained Fe and O, the thickness at which the O concentration was half of the O concentration on the outermost surface was estimated and used as the thickness of the oxide film. Raman spectra of each particle were measured using a micro-Raman spectrometer. As the excitation light, a laser with a wavelength of 532 nm and an intensity of 0.7 mW was used. When determining the integrated intensity, no peak separation was performed, and the intensity value of the Raman spectrum averaged after removing the background was integrated.

2. The additive manufacturing powder material according to claim 1, satisfying 8≤d≤15.

3. The additive manufacturing powder material according to claim 1 or 2, further satisfying I≤0.

30. 4 . The additive manufacturing powder material according to claim 1 , wherein the avalanche angle of the additive manufacturing powder material is less than 40°.

5. The additive manufacturing powder material according to any one of claims 1 to 4, wherein the oxygen value of the powder material is 0.035 mass % or more, wherein the oxygen value is defined as the proportion of oxygen atoms in the entire powder material. 6 . The powder material for additive manufacturing according to claim 1 , wherein the Fe alloy particles have an average particle size d50 of 10 μm to 500 μm. 7 . The powder material for additive manufacturing according to claim 1 , further comprising nanoparticles in an amount of 0.1 mass % or less based on the Fe alloy particles.

8. A method for producing an additive manufacturing powder material, wherein the additive manufacturing powder material is the additive manufacturing powder material according to any one of claims 1 to 7, comprising: preparing Fe alloy particles by a gas atomization process; and vacuum heating the Fe alloy particles to form an oxide film on the surface of each Fe alloy particle, When the Fe alloy particles are heated in vacuum, the Fe alloy particles are heated at a temperature ranging from 100° C. to 150° C. for 5 minutes to 120 minutes. 9 . The method for producing a powder material for additive manufacturing according to claim 8 , wherein when the Fe alloy particles are vacuum-heated, the pressure is reduced to −0.05 MPa or less based on atmospheric pressure.

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