Powder materials

Abstract

To provide a powder material that has high flowability and high packing density suitable for manufacturing a three-dimensional molding in a laminate molding method.SOLUTION: A powder material contains a metallic particle. A 10% grain size d10 in a cumulative grain size distribution of the metallic particle is less than 16 μm, and a 90% grain diameter d90 is larger than 35 μm. A value obtained by normalizing specific energy obtained by dividing flow energy measured as energy acting on a blade conducting a screw motion upward in the powder by the mass of the powder by the bulk density of the powder is less than 0.47 mJ ml / g2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to powder materials, and more particularly to powder materials suitable for use in additive manufacturing, where a powder bed is formed and an energy beam such as a laser beam is irradiated to manufacture a three-dimensional object. [Background technology]

[0002] Additive Manufacturing (AM) is a new technology for manufacturing three-dimensional objects, and its development has been remarkable in recent years. One type of additive manufacturing is additive manufacturing, which utilizes the solidification of powder materials by energy ray irradiation. Powder bed fusion is a typical example of additive manufacturing using metal powder materials.

[0003] Specific examples of powder bed melting include selective laser melting (SLM) and electron beam melting (EBM). In these methods, a powder material made of metal is supplied onto a base substrate to form a powder bed, and based on three-dimensional design data, an energy beam such as a laser beam or electron beam is irradiated onto a predetermined location on the powder bed. The powder material in the irradiated area then solidifies through melting and re-solidification, forming a three-dimensional object. By repeatedly supplying powder material to the powder bed and irradiating it with energy beams, the object is built up in layers, and a three-dimensional object is obtained.

[0004] When manufacturing three-dimensional objects made of metal materials using the additive manufacturing method described above, the resulting three-dimensional objects may have structures with uneven distribution of constituent materials, such as voids and defects. It is desirable to suppress the generation of such uneven structures as much as possible. There are several possible causes for uneven distribution of constituent materials within three-dimensional objects manufactured using additive manufacturing methods with metal materials, but one factor is that the state of the powder material before energy ray irradiation can have a significant impact on the state of the resulting three-dimensional object.

[0005] For example, in additive manufacturing, if the powder material has excellent fluidity, the supply of the powder material can be carried out smoothly, and a uniformly packed powder bed can be stably formed. Thus, when manufacturing three-dimensional objects by additive manufacturing, if the powder material used as a raw material has high fluidity, it becomes easier to obtain a highly uniform object when energy rays are irradiated onto the powder bed formed using that powder material. For example, Patent Document 1 attempts to improve the fluidity of the powder material by limiting the proportion of fine particles with a particle size of 20 μm or less to a small amount of 15 percent or less, based on electron microscope observation. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2018-172739 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] In conventional methods, including those disclosed in Patent Document 1, powder materials used as raw materials for additive manufacturing are often classified to remove as much fine powder as possible in order to increase fluidity. However, in additive manufacturing, in order to obtain a powder bed in which powder material is uniformly packed, which can produce a high-quality three-dimensional object with a suppressed non-uniform distribution of constituent materials, it is important that the powder material not only has high fluidity but also exhibits high packing density. Powder materials whose fluidity has been increased by classification do not necessarily exhibit high packing density.

[0008] The problem that this invention aims to solve is to provide a powder material with high fluidity and high packing density that is suitable for manufacturing three-dimensional objects using additive manufacturing. [Means for solving the problem]

[0009] To solve the above problems, the powder material according to the present invention is a powder material containing metal particles, wherein the 10% particle size d of the mass-based cumulative particle size distribution of the metal particles 10 The particle size is less than 16 μm, and the 90% particle size is d 90 Furthermore, the specific energy obtained by dividing the flow energy, which is measured as the energy acting on a blade moving spirally upward through the powder, by the mass of the powder, normalized by the bulk density of the powder, is 0.47 mJ·ml / g 2 It means it is less than [a certain value].

[0010] Here, the powder material is preferably of an avalanche angle of less than 40°.

[0011] The aforementioned powder material should preferably have a packing density of 57% or higher.

[0012] Furthermore, the powder material may contain nanoparticles made of metal or metal oxide in addition to the metal particles.

[0013] The aforementioned metal particles may consist of an iron-based alloy or a nickel-based alloy.

[0014] The 10% particle size of the metal particles 10 The particle size is less than 15 μm, and the 90% particle size d 90 It would be even better if it were larger than 40 μm.

[0015] The powder material according to the present invention is manufactured by a process that includes manufacturing the metal particles by a gas atomization method.

[0016] Here, it is preferable not to perform a classification process to remove the smaller diameter particles in the particle size distribution after producing the metal particles by the gas atomization method. [Effects of the Invention]

[0017] The powder material according to the above invention has a particle size distribution of d 10is less than 16 μm, that is, the ratio of particles less than 16 μm is more than 10%, and the content of finer particles (fine powder) is larger than that of conventional powder materials such as those described in Patent Document 1. On the other hand, d 90 is more than 35 μm, and the inclusion of relatively large-sized particles is also ensured. Thus, d 10 The inclusion of small-diameter particles defined by the distribution with <16 μm and d 90 Both metal particles of large-diameter particles defined by the distribution with >35 μm are included, so that the effect of improving the packing density due to the small-diameter particles entering the gaps between the large-diameter particles can be obtained. That is, the powder material according to the above invention has a wide particle size distribution, and when the powder material is spread as a powder bed, the packing density in the powder bed is improved, and a highly uniform powder bed is likely to be obtained. In addition, in the above powder material, the specific energy obtained as a value obtained by dividing the flow energy measured as the energy acting on the blade that spirally moves upward in the powder by the mass of the powder is normalized by the bulk density of the powder, and the value is less than 0.47 mJ·ml / g 2 is less than. The specific energy indicates the energy required to disperse the aggregates of metal particles in an environment where the movement of the powder is not restricted, such as during low-pressure filling. That is, the value obtained by normalizing the specific energy by the bulk density is an index indicating the fluidity of the powder material, and the smaller this value is, the better the fluidity of the powder material. Note that the specific energy is represented as Specific Energy (SE), the bulk density is represented as ρ b , and the value obtained by normalizing the specific energy by the bulk density is represented as SE / ρ b value, and will be described later.

[0018] The powder material according to the above invention contains a large number of small-diameter metal particles as defined by d 10 <16 μm, which has the effect of increasing the packing density, but may also be a factor in reducing the fluidity. However, SE / ρ bBy keeping the value low, sufficiently high fluidity can be ensured. Thus, the powder material according to the above invention achieves both high fluidity and packing density, and can smoothly form a powder bed with high packing density. As a result, it becomes a raw material powder that can produce three-dimensional objects with a highly uniform structure through additive manufacturing.

[0019] Here, if the avalanche angle of the powder material is less than 40°, high fluidity can be ensured in the powder material. The avalanche angle is the angle at which the powder causes an avalanche when it is placed in a rotating drum and rotated at a low speed (the angle between the slope and the horizontal plane of the powder deposit layer), and the higher the fluidity of the powder, the smaller the avalanche angle.

[0020] When the packing density of the powder material is 57% or higher, a high-density powder bed can be formed, and a homogeneous laminated object can be obtained.

[0021] When a powder material contains nanoparticles made of metal or metal oxide in addition to metal particles, the interposition of nanoparticles between adjacent metal particles makes it easier to improve the fluidity of the powder material.

[0022] When the metal particles consist of an iron-based alloy or a nickel-based alloy, the powder material can be suitably used as a raw material for three-dimensional molded objects made of iron-based alloys or nickel-based alloys, for which there is a large demand for manufacturing using additive manufacturing.

[0023] 10% particle size of metal particles d 10 The particle size is less than 15 μm, and the 90% particle size is d 90 When the particle size exceeds 40 μm, the powder material has an even wider particle size distribution, which further enhances the effect of improving the packing efficiency.

[0024] The method for manufacturing metal particles according to the above invention includes a step of manufacturing metal particles by gas atomization. By manufacturing metal particles by gas atomization, it is easy to produce particles with a particle size on the order of microns and high circularity that exhibit high fluidity for various alloy compositions. Furthermore, by using the gas atomization method, nanoparticles may be simultaneously generated on the surface of the metal particles using the constituent components of the metal particles as raw materials during the manufacturing process. These nanoparticles can contribute to improving the fluidity of the powder material. In particular, by generating nanoparticles attached to the surface of the metal particles, the effect of improving fluidity can be obtained stably.

[0025] Here, if a classification process is not carried out to remove the smaller diameter particles in the particle size distribution, the metal particles constituting the powder material will have a broad particle size distribution, and as a result, it will be easier to increase the packing density of the powder material. Also, d 10 Achieving a particle size distribution of <16 μm may eliminate the need for particle size adjustment through the addition of small-diameter particles from external sources, thus simplifying the powder material manufacturing process. By producing metal particles using the atomization method, it is possible to easily obtain highly circular metal particles and nanoparticles, resulting in metal particles with high fluidity. This makes it possible to easily and inexpensively manufacture powder materials with excellent fluidity and packing properties. [Brief explanation of the drawing]

[0026] [Figure 1] The images show an SEM image of metal particles contained in the powder material in an embodiment of the present invention (left figure; scale bar indicates 10 μm) and a magnified image of the surface of the metal particles (right figure; scale bar indicates 100 nm). [Modes for carrying out the invention]

[0027] The powder material according to embodiments of the present invention will be described in detail below. The powder material according to embodiments of the present invention can be used as a raw material for manufacturing a three-dimensional object by irradiating it with energy rays, by forming a powder bed in additive manufacturing.

[0028] The composition of the powder material according to embodiments of the present invention, the properties of the powder material, and the method for producing the powder material will be described.

[0029] The powder material according to this embodiment has a 10% particle size d in the mass-based cumulative particle size distribution. 10 The particle size is less than 16 μm, and the 90% particle size is d 90 The powder material contains metal particles having a particle size distribution in which the particle size is larger than 35 μm. In addition to such metal particles, the powder material also contains nanoparticles. The powder material according to this embodiment has the above particle size distribution and a predetermined SE / ρ ratio, which will be described later. b Insofar as the values ​​are met, the product may contain components other than metal particles and optionally included nanoparticles. However, it is preferable not to include components other than metal particles and nanoparticles, except for unavoidable impurities.

[0030] (1) Metal particles In the mass-based cumulative particle size distribution of metal particles contained in the powder material according to this embodiment, d 10 is less than 16 μm, and d 90 It is larger than 35 μm. 10 <16μm means that the overall particle size distribution contains many small-diameter particles with a particle size of about 10μm. On the other hand, d 90A particle size distribution of >35μm means that the inclusion of relatively large particles is ensured. Thus, a wide particle size distribution allows the powder material to achieve a high packing density. If the powder material consisted only of large-diameter metal particles, voids would form where the metal particles are adjacent during the powdering process, reducing the packing density of the powder bed. However, as with the metal particles in this embodiment, a wide particle size distribution allows for filling the voids between large-diameter particles with small-diameter particles (fine powder), thereby improving the packing density of the powder bed. From the viewpoint of broadening the particle size distribution of the powder material and enhancing the effect of improving packing density, the particle size distribution of the powder material should have a d 10 It is less than 15 μm, and d 90 A size greater than 40 μm is preferable.

[0031] From the standpoint of the fluidity of powder materials, d 10 The lower limit is not particularly limited, but if the particles are too small, it becomes difficult to improve the packing density, so it is preferable to set it to, for example, 1 μm or larger. 90 The upper limit is not particularly limited, but considering the particle size of metal powders commonly used as raw materials for additive manufacturing, it is preferable to set it to, for example, 200 μm or less. Furthermore, from a similar viewpoint, the average particle size d, which is the 50% particle size in the mass-based cumulative particle size distribution, is also appropriate. 50 It is preferable that the particle size is 10 μm or more and 150 μm or less.

[0032] The powder material has the above particle size distribution, and the SE / ρ described later b While the metal constituting the metal particles is not particularly limited as long as it provides a value, iron-based alloys, nickel-based alloys, cobalt-based alloys, and titanium-based alloys can be suitably used. More preferably, iron-based alloys or nickel-based alloys are used. Iron-based alloys and nickel-based alloys are in high demand in additive manufacturing, and powder materials mainly composed of iron-based alloys or nickel-based alloys can be suitably used as raw materials for additive manufacturing. As for iron-based alloys, those having a component composition equivalent to various stainless steels and tool steels can be particularly suitably used.

[0033] (2) Nanoparticles The powder material according to this embodiment contains nanoparticles. The inclusion of nanoparticles in the powder material has the effect of improving the fluidity of the powder material, and the interposition of nanoparticles between metal particles reduces the attractive interaction between metal particles, thereby reducing the adhesion force between metal particles.

[0034] Nanoparticles may be attached to the surface of metal particles or dispersed independently of the metal particles in the space between them. Preferably, they are attached to the surface of the metal particles, from the viewpoint of stabilizing the distribution of nanoparticles. It is preferable that the nanoparticles are composed of metal or metal oxide. Nanoparticles may be generated from the constituent components of the metal particles as described above, or they may be added separately from the metal particles. As an example of when nanoparticles are generated from the constituent components of metal particles, as will be described later as a method for manufacturing metal particles, when metal particles are formed by atomization, nanoparticles derived from the constituent components of the metal particles are generated attached to the surface of the metal particles. When nanoparticles are composed of metal oxides, suitable metal oxides include SiO2, Al2O3, and TiO2. These metal oxides are unlikely to have a serious impact even if they are included in a three-dimensional object made of metal after the additive manufacturing process. Nanoparticles made of metal oxides may be prepared separately from the metal particles and added to the metal particles.

[0035] The particle size of the nanoparticles is not particularly limited as long as it is on the order of nanometers, but examples of preferred sizes are 1 nm or larger and 100 nm or smaller. The shape of the nanoparticles is also not particularly limited and can take any particle shape, such as approximately spherical, polyhedral, or irregular. In particular, when nanoparticles are added separately from metal particles, it is preferable that they be approximately spherical in shape from the viewpoint of effectively improving the fluidity of the powder material. The amount of nanoparticles contained in the powder material is not particularly limited, but for example, from the viewpoint of obtaining a high effect of improving fluidity, it is preferable to have 0.001% by mass or more based on the mass of the metal particles. Also, from the viewpoint of avoiding the impact on the quality of the three-dimensional molded product due to the inclusion of excessive nanoparticles, it is preferable to have 0.1% by mass or less. Note that, due to their small particle size, the nanoparticles do not substantially affect the mass-based particle size distribution of the powder material.

[0036] (3) Properties of powder materials In the powder material according to this embodiment, the specific energy (SE: mJ / g) indicating the fluidity of the powder material is expressed as the bulk density (ρ) of the powder material. b The value obtained by dividing by (g / ml) (SE / ρ b :mJ·ml / g 2 ) is used as an indicator of the fluidity of the powder material, SE / ρ b The value is 0.47 mJ·ml / g 2 It is kept below a certain level. SE is the energy required to disperse aggregates of metal particles in a powder material by shear in a low-stress environment. More specifically, it is calculated from the shear force applied to a blade when a vane-shaped blade rotates upward in a helical motion within the powder material in an environment where the powder is not constrained, such as during low-pressure filling. When strong aggregation occurs between the particles of the powder material and the fluidity of the powder material is low, the specific energy (SE) becomes large.

[0037] A powder flowability analyzer can be used to measure the SE value of powder materials. A specific example of such an analyzer is the FT4 powder rheometer manufactured by Freeman Technology.

[0038] Thus, SE / ρ b The value serves as an indicator of the fluidity of the powder material; a smaller value indicates higher fluidity of the powder material. In the powder material according to this embodiment, SE / ρ b The value is 0.47 mJ·ml / g 2 By being less than this, the adhesive force (attractive force) acting between particles is kept low, and the powder material has high fluidity. . powder SE / ρ of the raw material b The value is 0.47 mJ·ml / g 2 By being less than SE / ρ, the powder material according to this embodiment has good fluidity. This allows for smooth supply of the powder material to the powder bed and smooth spreading of the powder material on the powder bed during the additive manufacturing process, resulting in a homogeneous and high-density powder bed. As a result, it becomes possible to obtain high-quality three-dimensional objects. b The means to keep the value low are not particularly limited, but examples include adding nanoparticles to the metal particles as described above, improving the circularity of the metal particles, and removing moisture. SE / ρ b While there is no need to specify a lower limit for the value, for metal powders such as iron-based alloys, it is generally around 0.3 mJ·ml / g. 2 That concludes the explanation.

[0039] In powder materials, SE / ρ b When the value is small, the avalanche angle (Φ) tends to be small. The avalanche angle is a value obtained by observing the flow behavior of powder that is pulled upward as a cylindrical container containing a predetermined amount of powder is slowly rotated. It represents the angle of the powder (the angle between the slope and the horizontal plane of the powder deposit layer) just before an avalanche occurs due to an imbalance between the adhesive force between particles and gravity. SE / ρ b When the value is small and the adhesive force between particles is small, the fluidity of the powder improves, resulting in a smaller avalanche angle (Φ).

[0040] The avalanche angle (Φ) of the powder material in this embodiment is preferably less than 40°, and more preferably less than 35°. Having an avalanche angle (Φ) of less than 40° provides excellent fluidity, which in turn allows processes affected by the fluidity of the powder material, such as the supply of the powder material, to proceed smoothly in additive manufacturing. This also facilitates improvements in the density of the powder bed and the smoothness of the powder bed surface, resulting in the production of high-quality three-dimensional objects. While there is no specific lower limit for the avalanche angle of the powder material, for this type of metal powder composed of iron-based alloys or nickel-based alloys, it is generally 15° or higher.

[0041] As described above, the powder material according to this embodiment is d 10 As specified by <16 μm, it exhibits a high packing density due to the inclusion of many small-diameter particles. Packing density is equal to bulk density (ρ b ) is true density (ρ t The value obtained by dividing by (ρ) b / ρ t It can be quantitatively evaluated as (x100%). In the powder material according to this embodiment, it is preferable that the packing density is 57% or more. This sufficiently increases the packing density of the powder material in the powder bed formed by the powder material, and effectively contributes to improving the spatial uniformity of the constituent materials in the three-dimensional object obtained by additive manufacturing. There is no particular upper limit set for the packing density, but in this type of metal powder composed of iron-based alloys or nickel-based alloys, it is generally 90% or less.

[0042] The powder material is d 10 <16μm, and d 90 >35μm particle size distribution and 0.47mJ·ml / g 2 SE / ρ less than b Having a specific value results in high fluidity and high packing density, making powder materials suitable for use as raw materials in additive manufacturing. For example, when performing powder bed fusion methods such as SLM or EBM, powder material is supplied from a hopper and spread on the substrate to form a powder bed. In this case, the SE / ρ of the powder materialb A value of less than 0.47 indicates that the powder material has high fluidity, allowing for stable discharge of the powder material from the hopper. Furthermore, when spreading the powder material to form a powder bed using a recoater or similar device, the high fluidity of the powder material facilitates smooth spreading. In addition, as mentioned above, the particle size distribution of the powder material, which broadly includes fine powder, makes it easier to spread the powder material at high density and uniformly. Thus, high fluidity and high packing ability of the powder material are important for stably forming a uniform and dense powder bed. Increased fluidity and packing ability of the powder material allow for dense and smooth spreading of the powder material, resulting in high packing efficiency when forming a powder bed. Then, by irradiating an energy ray onto a uniform and dense powder bed and performing additive manufacturing, it becomes easier to form a uniform three-dimensional object with few defects.

[0043] (4) Method for producing powder materials The method for producing the powder material according to this embodiment described above is not particularly limited, but it can be suitably produced using the method for producing the powder material according to the embodiment of the present invention described below.

[0044] First, it is necessary to prepare metal particles, which will be the raw materials for the powder material. The method for producing metal particles is not particularly limited, but gas atomization is preferred. In gas atomization, metal nanoparticles are obtained by spraying molten alloy into a vacuum and blowing an inert gas such as nitrogen gas or argon gas onto the sprayed molten alloy. In gas atomization, it is easy to make the shape of the metal particles close to a sphere, and furthermore, the particle size and the state of the particle surface can be controlled by conditions such as the dimensions of the nozzle that sprays the molten alloy (opening angle, etc.) and the gas pressure. For example, if the component composition of the molten alloy includes metal elements that sublimate more easily than other component metal elements (such as Fe), in gas atomization, these metal elements can be sublimated and solidified on the surface of the metal particles, making it possible to produce metal particles with a desired micron-order particle size, along with nanoparticles derived from the metal particle components attached to the surface of the metal particles. Conditions that promote the sublimation of the constituent components of metal particles can be achieved, for example, by selecting the type of gas nozzle used (such as the opening angle) or by maintaining a low pressure in the area where the molten metal is pulverized within the apparatus. In this way, by producing metal particles using the gas atomization method, highly spherical metal particles can be formed, and furthermore, by appropriately promoting the generation of nanoparticles, powder materials with high fluidity can be easily manufactured.

[0045] Furthermore, in the powder material of this embodiment, it is preferable not to perform classification on the metal particles obtained by the gas atomization method described above, as is done in conventional manufacturing processes. In conventional manufacturing processes, the fluidity of the powder material is improved by removing fine particles through classification. However, as explained above, the powder material according to this embodiment is d 10As exemplified by a particle size distribution of <16μm, the inclusion of a large amount of fine powder enables high packing efficiency. By omitting the removal of fine powder through classification in the manufacturing process, it becomes easier to obtain a particle size distribution with a high proportion of such fine powder. Eliminating the fine powder removal process reduces costs and improves yield. Furthermore, there is no need for a process of adding separately prepared fine powder to powder materials containing a large amount of large-diameter particles.

[0046] Furthermore, after the production of metal particles by atomization or other methods, heating such as thermal plasma treatment may be performed as appropriate from the viewpoint of adjusting the particle size distribution and promoting the generation of nanoparticles. In some cases, secondary aggregation may occur in the metal particles obtained by atomization, but this aggregation is resolved by heating. When the metal particles are further heated, the structure near the surface of the metal particles melts or sublimes, and when the surface of the metal particles rapidly cools and solidifies, nanoparticles are generated on the surface of the metal particles by re-solidification, using the molten or sublimated material as raw material.

[0047] Furthermore, nanoparticles made of metal oxides or the like may be added separately after the production of metal particles by atomization and / or after heat treatment. The flowability of the powder material can be further improved by generating nanoparticles derived from metal particles and / or by adding metal oxide nanoparticles from an external source. [Examples]

[0048] The present invention will be described in more detail below using examples. Here, the particle size distribution and SE / ρ of the powder material will be described. b The relationship between the values ​​and fluidity, packability, and tiling properties was investigated. Each evaluation was performed in air at room temperature. The present invention is not limited to the following examples.

[0049] [1] Relationship between the state and properties of powder materials (Sample preparation) Metal particles were prepared using a gas atomization method with iron-based alloys and nickel-based alloys as raw materials. During the gas atomization process, the nozzle opening angle and gas pressure were adjusted to control the pressure of the recirculation zone formed by the atomized gas to less than -55 kPaG, thereby adjusting the particle size and allowing nanoparticles to adhere to the surface. The metal particles obtained in this manner had an average particle size in the range of 20 μm to 50 μm. No classification was performed on the obtained metal particles. Several powder material samples were prepared in this manner (Samples 1 to 8). The following studies were conducted on the above-prepared samples.

[0050] (Evaluation of particle size distribution) JIS Z 8825 :2013 In accordance with the standards, the particle size distribution of each powder material was measured using a laser diffraction / scattering analyzer.

[0051] (Evaluation of the form of powdered materials) The fabricated metal particles were observed using a scanning electron microscope (SEM). Figure 1 shows the observed image of a representative sample. The sample used for the observation in Figure 1 is sample 3 in Table 1, and d 10 The value is 13.8 μm, and SE / ρ b The value is 0.45 mJ·ml / g 2 This is a sample. The raw material is JIS SKD-61 Tool steel (JIS G4404:2015) That is the case.

[0052] (SE / ρ b (Value evaluation) SE / ρ b The value is the specific energy (SE) value multiplied by the bulk density (ρ). b It is evaluated by dividing by ). SE and ρ bThe measurement was performed using a Freeman Technology "Powder Rheometer FT4". A 23.5 mm diameter blade and a 25 mm cylindrical split container were used for the measurement. Each sample of metal powder material was filled into the cylindrical split container, the blade was rotated upwards, and the shear force applied from the blade to the powder material was measured and defined as SE. The measurement environment was an indoor temperature of 15°C to 30°C and a humidity of less than 20%. The SE measured as described above was defined as ρ b Divide by SE / ρ b It was set as the value.

[0053] (Avalanche angle assessment) The avalanche angle (Φ) was evaluated using the "Revolution Powder Analyzer" manufactured by Mercury Scientific. This device consists of a cylindrical rotating drum containing the powder material and a CCD camera that captures images of the inside of the drum and continuously records the behavior of the powder material. When a predetermined amount of powder material is placed in the rotating drum and rotated at a low speed (0.6 rpm), the powder deposit is pulled upward along with the rotation, but an avalanche occurs when the balance between the adhesive force between particles and gravity is disrupted. The state when an avalanche occurs was recorded with the CCD camera, and the avalanche angle (Φ) of the powder material at the time of the avalanche (the angle between the slope of the powder deposit and the horizontal plane) was defined as the avalanche angle to evaluate the fluidity of the powder material.

[0054] (Evaluation of packing density) Packing density (hereafter, packing density will be ρ) f (as stated) is bulk density (ρ b ) / true density(ρ t The true density (ρ) was calculated as follows: t The values ​​used were calculated using Sente Software's material property calculation software (JMatPro). Bulk density (ρ b ) is the above SE / ρ b The same value used to calculate the value was used.

[0055] (Evaluation results) <State of metal particles> Figure 1 shows an SEM image of a typical prepared sample. From the image, it can be seen that the shape of the metal particles contained in the powder material is almost spherical, and furthermore, as shown in the magnified view, a large number of nanoparticles are attached to the surface of the metal particles. The shape of the metal particles is approximately spherical, corresponding to the use of the gas atomization method in the preparation of the metal particles. Furthermore, the attachment of nanoparticles to the surface of the metal particles is thought to be due to the fact that metals that are easily sublimated among the metals contained in the raw material of the metal particles sublimated during the gas atomization process and solidified on the surface of the metal particles. The sample used to obtain the SEM image in Figure 1 is sample 3.

[0056] <Properties of powdered materials> Of all the samples, d 90 Regarding the sample that was >35μm, d 10 and SE / ρ b The values, avalanche angle (Φ), and packing density (ρ) f The following measurements were taken and summarized in Table 1 for each of the samples 1 to 8. [Table 1]

[0057] Table 1 shows that in the particle size distribution of powder materials, d 10 The size is less than 16 μm, and SE / ρ b The value is 0.47 mJ·ml / g 2 Samples 1-4, which are below this value, all have an avalanche angle (Φ) of less than 40° and a packing density (ρ f ) is 57% or more. On the other hand, as shown in samples 5 to 8, the d of the powder material 10 Even if the value is less than 16 μm, SE / ρ b If the value is not less than 0.47, it is not possible to obtain a small avalanche angle of less than 40° and a high packing density of 57% or more. Therefore, in the particle size distribution of powder material, d 10 is less than 16 μm, and d 90 Furthermore, the size is greater than 35 μm, and also, SE / ρ b 0.47 mJ·ml / g 2If it is less than that, it can be seen that a powder material having high fluidity suitable for additive manufacturing, giving a small avalanche angle, and increasing the packing density in the powder bed can be obtained.

[0058] [2] Spreading property of powder material When the powder material has d in the particle size distribution 10 less than 16 μm and SE / ρ b value of 0.47 mJ·ml / g 2 When having the above characteristics, for the purpose of evaluating whether the powder material can be properly spread, the spreading property of the powder material was evaluated as shown below.

[0059] (Method for evaluating spreading property of powder material) Using Sample 2, Sample 4, and Sample 8 shown in Table 1, a powder bed was actually created with an additive manufacturing apparatus, and the spreading property was evaluated. Sample 2 and Sample 4 have d 10 less than 16 μm and SE / ρ b value of less than 0.47 mJ·ml / g 2 and Sample 8 is a sample that does not satisfy the above range. The evaluation results are summarized in Table 2 show . From the perspective of supplementing the evaluation of the spreading property, in addition to the above Samples 2, 4, and 8, a commercially available powder material was separately prepared as a reference sample, and for these reference samples, the avalanche angle and packing density were measured according to the same measurement method as in the above test [1], and the spreading property was evaluated.

[0060] When evaluating the spreading property of each sample, as an additive manufacturing apparatus, "Metal 3D Printer M2" manufactured by Concept Laser was used, a predetermined amount of powder material was put into the apparatus, and at a speed of 100 mm / s RecorderLeveling was performed to create a leveling section (powder bed) of 245 mm × 245 mm. The powder layer thickness was 50 μm, and an amount corresponding to twice the layer thickness was supplied to the powder bed for leveling. The surface of the powder bed was photographed with a built-in camera of the device, and the leveling property was evaluated using a 220 mm × 220 mm area within the captured image as the measurement area. In the obtained captured image, since the areas where the powder material is densely filled are photographed with higher brightness, the areas with brightness above the standard corresponding to the leveling density that allows for seamless additive manufacturing are regarded as the areas where the powder material is sufficiently leveled (area a), and the areas with brightness less than the above threshold are regarded as the areas where the leveling of the powder material is insufficient (area b). After binarization, the area of each region was estimated. Furthermore, the effective area ratio (%) was calculated using the following formula. When the effective area ratio is 98% or more, it is evaluated as "〇" for "good leveling property", and when it is less than 98%, it is evaluated as "×" for "poor leveling property" and shown in Table 1. Effective area ratio (%) = Area of area a × 100 / Area of measurement area

[0061] (Evaluation result: Leveling property) Using the powder materials of Sample 2, Sample 4, Sample 8 in Table 1, as well as Reference Sample 1 and Reference Sample 2 prepared separately, a powder bed was actually formed, and whether the powder materials of each sample in the powder bed were uniformly filled was evaluated by the above method. The results are shown in Table 2. For the samples of Sample 2 and Sample 4 in Table 2, both have d 10 less than 16 μm in the particle size distribution of the powder material, and the SE / ρ b value is less than 0.47 mJ·ml / g 2 , while for Sample 8, Reference Sample 1, and Reference Sample 2, all have SE / ρ b values of 0.47 mJ·ml / g 2 or more. For Samples 2 and 4 with SE / ρ b values less than 0.47 mJ·ml / g 2 , the leveling properties are both evaluated as "〇" for "good", while for Sample 8, Reference Sample 1, and Reference Sample 2 with SE / ρ b values of 0.47 mJ·ml / g 2 or more, the leveling properties are evaluated as "×" for "poor".

[0062] The differences in packing properties described above can be attributed to the fluidity and packing density of the powder material. As explained in Test [1], both Sample 2 and Sample 4 have a small avalanche angle of less than 40° and a high packing density of 57% or more, indicating high fluidity and high packing density in the powder bed. On the other hand, Sample 8, Reference Sample 1, and Reference Sample 2 have an avalanche angle greater than 40° and a packing density of less than 57%. Therefore, the powder material has a d particle size distribution. 10 The size is less than 16 μm, and SE / ρ b The value is 0.47 mJ·ml / g 2 This results in a small avalanche angle and high packing density, and accordingly, the powder material exhibits high packing properties when forming the powder bed, ensuring uniform filling. [Table 2]

[0063] 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.

Claims

1. A powder material containing metal particles, 10% particle size d in the mass-based cumulative particle size distribution of the metal particles １０ The particle size is less than 16 μm, and the 90% particle size d ９０ It is larger than 35 μm, The specific energy, obtained by dividing the fluid energy (measured as the energy acting on a blade moving spirally upward through the powder) by the mass of the powder, is expressed in units of mJ / g. This specific energy is then normalized by dividing it by the bulk density of the powder (expressed in units of g / ml), resulting in a value of 0.47 mJ·ml / g. ２ It is less than, The aforementioned metal particles are a powder material manufactured by a gas atomization method and have not undergone classification to remove particles on the smaller diameter side of the particle size distribution.

2. The powder material according to claim 1, wherein the avalanche angle is less than 40°.

3. The powder material according to claim 1 or claim 2, wherein the packing density is 57% or more.

4. The powder material according to any one of claims 1 to 3, wherein the powder material contains nanoparticles made of metal or metal oxide in addition to the metal particles.

5. The powder material according to any one of claims 1 to 4, wherein the metal particles consist of an iron-based alloy or a nickel-based alloy.

6. The 10% particle size d of the aforementioned powder material １０ The powder material according to any one of claims 1 to 5, wherein the particle size is less than 15 μm, and the 90% particle size d90 is greater than 40 μm.

7. A method for producing a powder material according to any one of claims 1 to 6, wherein after producing the metal particles by a gas atomization method, a classification step is not performed to remove the particles on the smaller diameter side of the particle size distribution.

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