Powder material

Abstract

To provide a powder material which has high fluidity and has reduced influence by the presence of organic substances.SOLUTION: There is provided a powder material which is composed of an iron-based alloy and contains metal particles P1 having an average particle diameter of 10 μm or more and 500 μm or less and nanoparticles P2 which are composed of a metal or a metal compound and are not subjected to a surface treatment with organic substances. The nanoparticles P2 are preferably adhered to the metal particles P1. In addition, in the powder material, an aggregate having a particle diameter of 1 μm or more which is composed of the nanoparticles P2 is preferably not present between the metal particles P1. The nanoparticles P2 are preferably silica particles.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a powder material, and more particularly to a powder material that can be used as a raw material in a layer manufacturing method.

Background Art

[0002] As a new technology for manufacturing three-dimensional objects, the development of additive manufacturing technology (AM) has been remarkable in recent years. As a type of additive manufacturing technology, there is a layer manufacturing method that utilizes solidification by irradiating a powder material with an energy beam. As layer manufacturing methods using a metal powder material, two typical methods are the powder bed fusion method and the powder deposition method.

[0003] Specific examples of the powder bed fusion method include methods such as 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 an electron beam is irradiated at a predetermined position on the powder bed. Then, the powder material at the irradiated site solidifies by melting and re-solidification, and a shaped object is formed. By repeating the supply of the powder material to the powder bed and the shaping by energy beam irradiation, and sequentially laminating the shaped objects in layers, a three-dimensional object can be obtained.

[0004] On the other hand, a specific example of the powder deposition method is the laser metal deposition (LMD). In this method, while injecting a metal powder using a nozzle at a position where a three-dimensional object is to be formed, at the same time, irradiation with a laser beam is performed to form a three-dimensional object having a desired shape.

[0005] When manufacturing a three-dimensional object made of a metal material using the above-described additive manufacturing method, the resulting three-dimensional object may have a structure in which the distribution of the constituent materials, such as voids and defects, is non-uniform. It is desirable to suppress the generation of such non-uniform structures as much as possible. In the additive manufacturing method using a metal material, there are multiple possible causes for the non-uniform distribution of the constituent materials inside the manufactured three-dimensional object. As one of the factors, the state of the powder material before energy beam irradiation can have a significant impact on the state of the resulting three-dimensional object.

[0006] For example, in the powder bed fusion method, if the powder material can be smoothly supplied to the powder bed and a powder bed with the powder material evenly spread can be stably formed, and if the powder material can be filled at a high density in the powder bed, a three-dimensional object with high homogeneity is likely to be obtained after irradiating the powder bed with an energy beam. Also, in the powder deposition method, a three-dimensional object can be stably formed by smoothly supplying the powder material without clogging the nozzle. Thus, when manufacturing a three-dimensional object by the additive manufacturing method, the higher the fluidity of the powder material used as the raw material, the more it can promote the smooth supply and high-density filling of the powder material, and a highly uniform object can be obtained after irradiation with an energy beam.

[0007] The inventors have been studying a powder material with high fluidity suitable for use as a raw material for additive manufacturing. For example, Patent Document 1 discloses a metal powder material containing metal particles having a particle size on the micron order and nanoparticle made of a metal or metal compound attached to or mixed with the metal particles. By interposing the nanoparticles between the metal particles, the distance between the metal particles is maintained. Then, the attractive force mainly composed of the van der Waals force acting between the metal particles can be reduced. Patent Document 1 gives, as a preferred example, a form in which a hydrophobic group such as a hydrocarbon group represented by a phenyl group is bonded to the surface of the metal oxide nanoparticles. By interposing nanoparticles surface-modified with a hydrophobic group between the metal particles, the adhesion force between the metal particles via water can be reduced, and the fluidity of the metal powder material can be increased.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] As described in Patent Document 1, when adding nanoparticles to metal particles, by hydrophobically treating the surface of the nanoparticles with an organic substance, the effect of improving the fluidity by the nanoparticles can be enhanced. On the other hand, the presence of the organic substance on the nanoparticle surface may affect the quality of the product manufactured from the powder material and the manufacturing process of the product. For example, when using the powder material as a raw material for additive manufacturing, if an organic substance layer is formed on the surface of the nanoparticles, when the nanoparticles melt in the additive manufacturing process, hydrocarbon-based gases derived from the organic substance are generated. As a result, pores may be generated in the structure of the obtained three-dimensional structure. If such pore formation can be prevented, the effect of obtaining a three-dimensional structure having a highly uniform structure by improving the fluidity of the powder material by adding nanoparticles is expected to be further enhanced.

[0010] The problem to be solved by the present invention is to provide a powder material having high fluidity and reduced influence due to the presence of an organic substance.

Means for Solving the Problems

[0011] To solve the above problems, the powder material according to the present invention is made of an iron-based alloy and includes metal particles having an average particle diameter of 10 μm or more and 500 μm or less, and nanoparticles made of a metal or a metal compound and not subjected to surface treatment with an organic substance.

[0012] Here, the nanoparticles may be attached to the metal particles. In the powder material, aggregates having a particle size of 1 μm or more composed of the nanoparticles may not be present between the metal particles. In this case, furthermore, the powder material may not contain aggregates having a particle size of 1 μm or more composed of the nanoparticles in a state attached to the metal particles.

[0013] The iron-based alloy constituting the metal particles may be a precipitation hardening type stainless steel. The nanoparticles may be silica particles. A plurality of the nanoparticles may form an aggregate in which they are fused together.

Advantages of the Invention

[0014] The powder material according to the above invention contains, in addition to metal particles, nanoparticles. By interposing the nanoparticles between the metal particles, a distance is ensured between the metal particles. Then, the attractive force acting between the metal particles is reduced, and the fluidity of the powder material can be enhanced. Further, since the nanoparticles are not surface-treated with an organic substance, when the powder material is used as a raw material for additive manufacturing, the influence of the presence of the organic substance, such as the formation of voids due to the generation of gas derived from the organic substance, is reduced. As a result, combined with the effect of enhancing the fluidity of the powder material by adding the nanoparticles, a three-dimensional molded article having a highly uniform and dense structure can be easily obtained.

[0015] Here, when the nanoparticles are attached to the metal particles, the reduction of the attractive force between the metal particles can be stably and highly achieved.

[0016] In the powder material, when aggregates having a particle size of 1 μm or more composed of the nanoparticles are not present between the metal particles, the nanoparticles are attached to or mixed with the metal particles in a highly dispersed state. Therefore, a high effect is exhibited in improving the fluidity of the powder material. Further, by reducing the content of aggregates of coarse nanoparticles, it is possible to suppress the formation of defects caused by the aggregates of nanoparticles in the three-dimensional molded article obtained through additive manufacturing.

[0017] In this case, furthermore, if the powder material does not contain aggregates with a particle size of 1 μm or more composed of nanoparticles in a state of adhering to the metal particles, that is, not only those existing between the metal particles but also in a state of adhering to the metal particles, if aggregates of nanoparticles with a particle size of 1 μm or more are not formed, each of the above effects can be further enhanced. That is, the effect of improving the fluidity of the powder material and the effect of suppressing defects in the three-dimensional shaped object become even higher.

[0018] When the iron-based alloy constituting the metal particles is a precipitation-hardening stainless steel, the demand for the powder material as a raw material for laminated manufacturing is large, and through laminated manufacturing, it can provide a three-dimensional shaped object excellent in characteristics such as hardness.

[0019] When the nanoparticles are silica particles, the nanoparticles exhibit a high effect in enhancing the fluidity of the powder material. In addition, the influence of adding the nanoparticles on the three-dimensional shaped object obtained through laminated manufacturing can be suppressed to a small extent.

[0020] When the nanoparticles constitute a fused body in which a plurality are fused, the nanoparticles have a high effect in improving the fluidity of the powder material.

Brief Description of the Drawings

[0021]

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[0022] Hereinafter, with reference to the drawings, a powder material according to an embodiment of the present invention will be described in detail. In this specification, for a certain component and for particles having a certain particle size and form, the state of "not containing" shall include not only the state of not containing those components and particles at all, but also the state of containing those components and particles as inevitable impurities.

[0023] [Powder Material] As shown in FIG. 1, the powder material according to one embodiment of the present invention is made of an iron-based alloy and includes metal particles P1 having a particle size on the micron order and nanoparticle P2 made of a metal or a metal compound. Nanoparticles P2 are attached to the surface of the metal particles P1, constituting nanoparticle-attached metal particles P. The nanoparticles P2 are not surface-treated with an organic substance.

[0024] Here, the fact that the nanoparticles P2 are attached to the metal particles P1 means a state in which the attractive force acting between the nanoparticles P2 and the metal particles P1 is at least greater than the attractive force acting between the metal particles P1 when the nanoparticles P2 are not included. In the powder material, the nanoparticles P2 do not necessarily have to be attached to the metal particles P1, and a part or all of the nanoparticles P2 may be present in the powder material in a state simply mixed with the metal particles P1. However, from the viewpoints of the stability of the retention of the nanoparticles P2 and the enhancement of the effects by the addition of the nanoparticles P2, etc., it is preferable that the nanoparticles P2 are attached to the metal particles P1. Hereinafter, the form in which the nanoparticles P2 are attached to the metal particles P1 will be mainly described.

[0025] This powder material containing the nanoparticles P2 in addition to the metal particles P1 can be suitably used, for example, as a raw material for additive manufacturing. From the viewpoint of avoiding the inclusion of impurities and the formation of defects in the three-dimensional object obtained by additive manufacturing, it is preferable that this powder material does not contain components other than the metal particles P1 and the nanoparticles P2, excluding inevitable impurities. It is also preferable not to contain components for increasing the fluidity of the powder material, other than the nanoparticles P2 such as lubricants. Hereinafter, the respective configurations of the metal particles P1 and the nanoparticles P2 will be described.

[0026] (1) Metal particles The metal particles P1 have a particle size on the micron order, and the particle size can be 10 μm or more and 500 μm or less in terms of the average particle size (d50). From the viewpoint of being suitably used as a raw material for additive manufacturing, it is particularly preferable if the average particle size is 10 μm or more and 100 μm or less. In the powder material, from the viewpoint of obtaining high fluidity, the metal particles P1 preferably have a shape that can be regarded as spherical. For example, it is preferable that the circularity of the metal particles P1 is 0.85 or more, and further 0.90 or more, at the average particle size, that is, for particles having a particle size equal to the average particle size. Note that the average particle size (d50) refers to the particle size at which the cumulative undersize fraction in the mass-based distribution is 50%.

[0027] The metal particles P1 are composed of an iron-based alloy. Iron-based alloys are in great demand in additive manufacturing, and powder materials mainly composed of iron-based alloys can be suitably used as raw materials for additive manufacturing. In particular, it is preferable to use stainless steel as the iron-based alloy. Among them, it is preferable to use a precipitation-hardening stainless steel such as SUS630 alloy. The metal particles P1 made of a precipitation-hardening stainless steel will give a three-dimensional shaped object excellent in properties such as hardness through the additive manufacturing process.

[0028] In addition to the metal component as the main component, the metal particles P1 may contain metal compounds such as oxides and carbides. Examples of such compounds include compound films such as oxide films that are inevitably formed on the surface of the metal particles P1. Further, the metal particles P1 may contain organic substances. Examples of such organic substances include those derived from the manufacturing process of the metal particles P1, such as residues of raw material compounds, and those disposed on the surface of the metal particles P1 as surface treatment agents. However, from the viewpoint of enhancing the effect of improving fluidity by adding the nanoparticles P2, and from the viewpoint of reducing the influence of organic substances on the additive manufacturing process and the resulting additive manufactured object, it is preferable that the metal particles P1 do not contain intentionally added organic substances such as surface treatment films.

[0029] The method for producing the metal particles P1 is not particularly limited, but can be preferably produced by an atomization method. Various methods such as gas atomization method and disk atomization method are applicable, but in particular, the gas atomization method is preferable from the viewpoint of the production efficiency of the metal particles P1 and the like.

[0030] (2) Nanoparticles The particle size of the nanoparticles P2 is not particularly limited as long as it is on the order of nanometers, but cases where it is 1 nm or more and 100 nm or less can be exemplified as preferable ones.

[0031] The shape of the nanoparticles P2 is also not particularly limited and can be any shape such as substantially spherical, polyhedral shape, irregular shape, etc. Preferably, from the viewpoint of effectively improving the fluidity of the powder material, it is preferably substantially spherical. Alternatively, the nanoparticles P2 are preferably in the form of an aggregate in which a plurality of primary particles having a shape such as a substantially spherical shape are fused. Here, the fusion between primary particles means adhesion by an atomic bond formed through melting, and unlike aggregation, it cannot be easily eliminated by dispersion or classification described later. The shape of the aggregate is not limited, but it is preferably dendritic, in which the rows of fused primary particles extend in various directions. When the nanoparticles P2 are in the form of an aggregate, particularly a dendritic aggregate, compared with the case where they exist in the form of primary particles, as will be described in detail later, a distance is provided between the metal particles P1, and the effect of reducing the attractive force acting between the metal particles P1 and improving the fluidity can be greatly exerted even with a small amount of addition. The particle size of the primary particles constituting the aggregate is preferably 1 nm or more and 100 nm or less as described above, and the particle size of the aggregate as a whole (the length of the longest straight line across the aggregate) is preferably 25 nm or more and 500 nm or less.

[0032] The nanoparticle P2 may be made of a metal or a metal compound. However, from the viewpoint of effectively reducing the attractive force between the metal particles P1 in the powder material, it is preferably made of a metal compound. Examples of the metal compound include metal oxides, metal nitrides, metal carbides, etc. Among them, from the viewpoints of low activity and ease of obtaining the nanoparticles, etc., it is preferably a metal oxide. The metal species constituting the metal compound is not particularly limited, but a form using light metal elements such as Si, Al, Ti, etc. is suitable. Oxides (SiO 2 , Al 2 O 3 , TiO 2 , etc.) of these nanoparticles have established manufacturing methods, can be easily obtained, and are less likely to have a profound impact even when contained in a three-dimensional shaped object made of metal through a laminated shaping process.

[0033] In particular, it is preferable to use an oxide of Si (silica) as the nanoparticle P2. The nanoparticle P2 made of silica is excellent in the effect of reducing the attractive force between the metal particles P1 and is also easily available. In addition, the nanoparticle P2 made of silica exhibits a certain degree of high dispersibility even without surface treatment.

[0034] The nanoparticle P2 is not subjected to surface treatment with an organic substance. That is, the surface of the nanoparticle P2 is not coated with an organic substance except for the inevitable organic components such as residues derived from the manufacturing raw materials and those adhered from the environment. Therefore, the metal or metal compound constituting the nanoparticle P2 is exposed on the surface of the nanoparticle P2. The nanoparticle P2 may contain components other than the main component metal or metal compound as long as it is outside the organic substance layer covering the surface, but it is preferably that the content of the organic component in the whole nanoparticle P2 is reduced as much as possible. It is better that the whole nanoparticle P2 does not contain organic components other than inevitable ones.

[0035] (3) Characteristics of the powder material In the powder material according to this embodiment, the nanoparticles P2 adhere to the surface of the metal particles P1, resulting in metal particles with adhered nanoparticles P, or the nanoparticles P2 are mixed into the metal particles P1. As a result, the nanoparticles P2 are interposed between adjacent metal particles P1, and a distance equal to or greater than the particle size of the nanoparticles P2 (or their fused bodies) is maintained between the metal particles P1. The attractive forces acting between the metal particles P1, such as van der Waals forces and electrostatic attractions, decrease as the distance between the metal particles P1 increases. That is, the presence of the nanoparticles P2 ensures a distance between the metal particles P1, thereby reducing the attractive force between the metal particles P1. As a result, the shear adhesion force (τ s ) of the powder composed of the metal particles P1 is reduced, and as a result, the fluidity of the powder material can be enhanced.

[0036] For example, due to the adhesion of the nanoparticles P2, the shear adhesion force of the powder composed of the metal particles P1 can be reduced to 55% or less, and further to 50% or less, compared to the case without the nanoparticles P2. Also, the shear adhesion force (τ s ) normalized by the bulk density (ρ) of the powder material, i.e., the bulk density-normalized shear adhesion force (τ s / ρ), can be made 0.07 (m / s) 2 or less, and further 0.05 (m / s) 2 or less.

[0037] Since the powder material has high fluidity, it can be suitably used as a raw material for additive manufacturing. For example, when performing powder bed fusion methods such as the SLM method or the EBM method among additive manufacturing methods, the powder material is supplied from a hopper and spread on a substrate to form a powder bed. At this time, due to the high fluidity of the powder material, the powder material can be stably discharged from the hopper. Also, when using a recoater or the like to spread the powder material to form a powder bed, it becomes easier to spread the powder material densely and homogeneously. Thus, the high fluidity of the powder material is important for stably forming a powder bed with high uniformity and density. Then, by irradiating an energy beam onto the powder bed with high uniformity and density and performing additive manufacturing, it becomes easier to form a three-dimensional object that is homogeneous and has few defects. Also, in additive manufacturing by powder deposition methods including the LMD method, by using a powder material with excellent fluidity, the powder material can be stably supplied to the nozzle. Further, when injecting the powder material together with an air current from the nozzle toward the location where manufacturing is performed, clogging of the nozzle can be suppressed and manufacturing can proceed stably.

[0038] Furthermore, in the powder material according to the present embodiment, the nanoparticles P2 are not surface-treated with an organic substance, which also enhances the suitability of using the powder material as a raw material for additive manufacturing. If the nanoparticles P2 are surface-treated with an organic substance, in the additive manufacturing process, when the powder material is irradiated with an energy beam and the nanoparticles P2 are melted together with the metal particles P1, hydrocarbon-based gas will be generated due to the organic substance coating the nanoparticles P2. Then, in the three-dimensional object manufactured through additive manufacturing, voids that are not occupied by the metal material may be formed at the locations where the gas is generated. When such voids are formed, a non-uniform distribution will occur in the structure of the three-dimensional object, and the effect of enhancing the fluidity of the powder material to improve the homogeneity of the resulting object will be diminished. However, if nanoparticles P2 without surface treatment with an organic substance are used, the possibility of voids being formed in the additive manufactured object due to the presence of the organic substance on the surface of the nanoparticles P2 can be eliminated. As a result, when the powder material is used as a raw material for additive manufacturing, together with the effect of enhancing the fluidity of the powder material, a highly uniform and dense structure can be easily obtained in the resulting additive manufactured object.

[0039] The powder material according to this embodiment preferably does not contain aggregates of coarse nanoparticles P2. It is preferable that it does not contain aggregates of nanoparticles P2 at least at a level recognizable by the naked eye. If coarse aggregates of nanoparticles P2 are contained in the powder material, such aggregates may reduce the fluidity of the powder material. This is because the nanoparticles P2 constituting the aggregates are interposed between individual metal particles and cannot contribute to reducing the attractive force between the metal particles P1 and enhancing the fluidity. Rather, the amount of nanoparticles P2 that can adhere to the surface of the metal particles P1 decreases by the amount of nanoparticles P2 consumed in the formation of the aggregates, so that the effect of reducing the attractive force between the metal particles P1 and enhancing the fluidity is reduced. Furthermore, the aggregates of nanoparticles P2 are likely to form defects that act as fracture initiation points in the laminated molded article. Therefore, if the content of aggregates of nanoparticles P2 is reduced in the powder material, it becomes easier to manufacture a three-dimensional molded article having a homogeneous structure with few defects through the laminated molding process from the viewpoints of both ensuring the fluidity of the powder material and eliminating fracture initiation points.

[0040] Preferably, in the powder material, it is preferable that aggregates having a particle size of 1 μm or more composed of the nanoparticles P2 do not exist between the metal particles P1. In other words, it is preferable that the powder material does not contain aggregates of the nanoparticles P2 having a particle size of 1 μm or more in a state (isolated state) where they are not attached to the metal particles P1. Then, as described above, the effect of improving the fluidity of the powder material and eliminating the fracture initiation points in the three-dimensional shaped article becomes higher. More preferably, aggregates of the nanoparticles P2 having a particle size of 1 μm or more are not contained in the powder material even in a state other than the isolated state, including the state where they are attached to the metal particles P1. Thereby, the above-described effects of improving fluidity and eliminating fracture initiation points become even higher. Furthermore, it is preferable that aggregates having a particle size smaller than 1 μm are not contained in the powder material either in an isolated state or in another state. The presence or absence and particle size of the aggregates may be evaluated by observing the powder material using a scanning electron microscope (SEM). The particle size of the aggregates can be measured as the length of the longest straight line crossing the aggregates in the SEM image. The nanoparticles P2 preferably do not form aggregates, or even if they do form aggregates, the smaller the aggregation diameter, the better. Therefore, there is no lower limit for the particle size of the aggregates. However, if the particle size is about 500 nm or less, even if aggregates are formed, it does not significantly affect the fluidity of the powder material, and the labor required for completely eliminating the aggregates can be saved.

[0041] In the powder material according to the present embodiment, since the nanoparticles P2 are not surface-treated with an organic substance, aggregation between the nanoparticles P2 via water may easily occur. However, by sufficiently eliminating such aggregation, the characteristics of the powder material as a raw material for laminated shaping can be enhanced. For example, as described below, when manufacturing the powder material, by performing a dispersion step and a classification step, even if the nanoparticles P2 are not surface-treated with an organic substance, a powder material in which the nanoparticles P2 are dispersed with aggregation eliminated and attached to the surface of the metal particles P1 can be efficiently manufactured.

[0042] In the powder material, the particle size and shape of the metal particles P with attached nanoparticles are substantially maintained as those of the metal particles P1 alone. When the powder material is used as a raw material for laminated manufacturing, the average particle size of the metal particles P with attached nanoparticles is preferably about 10 to 100 μm. Also, the circularity is preferably 0.85 or more, and more preferably 0.90 or more, at the average particle size.

[0043] [Manufacturing method of powder material] Here, an example of the method for manufacturing the above powder material will be described. Here, a raw material preparation step, a dispersion step, and a classification step are carried out in this order. As described above, in this powder material, the contained nanoparticles P2 are not surface-treated with an organic substance and may aggregate between particles. However, by carrying out the dispersion step and the classification step, the aggregation of the nanoparticles P2 can be eliminated. Hereinafter, the manufacturing apparatus used for manufacturing the powder material and each manufacturing step will be described in order.

[0044] (1) Manufacturing apparatus FIG. 2 shows an example of a powder material manufacturing apparatus 1 that can be used for manufacturing the powder material. The powder material manufacturing apparatus 1 includes a dispersion apparatus 10 and a classification apparatus 20. The dispersion apparatus 10 is an apparatus that can disperse aggregated powder. The classification apparatus 20 is an apparatus that can classify the powder, that is, select the particle size. With respect to the flow of the powder, the dispersion apparatus 10 is provided upstream and the classification apparatus 20 is provided downstream, and the powder discharged from the dispersion apparatus 10 is introduced into the classification apparatus 20.

[0045] Both the dispersion device 10 and the classification device 20 may be in any form for dispersing and classifying powder respectively, and the connection form between the dispersion device 10 and the classification device 20 is not particularly limited. However, it is preferable to use an air flow dispersion device as the dispersion device 10 and an air flow classification device as the classification device 20. And it is preferable to directly connect the discharge port 13 of the dispersion device 10 to the supply port 21 of the classification device 20, and introduce the powder discharged together with the air flow from the discharge port 13 of the dispersion device 10 directly into the supply port 21 of the classification device 20 without contacting the external environment.

[0046] As the dispersion device 10, for example, it is preferable to use an air flow dispersion device as disclosed in Japanese Patent Application Laid-Open No. 4-330957. In this type of air flow dispersion device 10, a high-speed air flow is ejected from the ring nozzle 12. Then, the powder supplied from the supply port 11 is sucked by the negative pressure generated by the air flow, and the sucked powder is collided with the high-speed air flow. The powder is accelerated by the air flow, and the agglomerated state between the particles is eliminated and dispersed by particle-to-particle collision, collision with the device wall surface, and application of shear force. The dispersed powder is discharged from the discharge port 13 together with the air flow.

[0047] As the classification device 20, for example, it is preferable to use an air flow classification device such as a forced vortex type air flow classifier disclosed in Japanese Patent Application Laid-Open No. 2003-145052. In this type of air flow classification device 20, the dispersion blade 22 is rotated to generate an air flow, and the powder introduced from the supply port 21 is supplied to the classification zone 23 provided with the classification blade 25 in a state of being dispersed by the shear force of the air flow. In the classification zone 23, the powder is subjected to the centrifugal force by the high-speed rotating classification rotor 24 and the resistance by the air flow. At this time, classification is performed by the centrifugal force and resistance corresponding to the particle size acting on the particles. The large-diameter particles on which the centrifugal force acts greatly move to the coarse powder region 26, while the small-diameter particles on which the resistance acts greatly move to the fine powder region 27. By selecting the operating conditions of the classification device 20, particles having a desired particle size can be separated in the coarse powder region 26.

[0048] By using both the dispersing device 10 and the classifying device 20 as air-flow type devices, the discharge port 13 of the dispersing device 10 and the supply port 21 of the classifying device 20 can be directly connected by appropriately using the piping member 30. Then, the powder discharged together with the air flow from the dispersing device 10 will be directly introduced into the classifying device 20. As a result, the process of dispersing the powder by the dispersing device 10 and the process of classifying the powder by the classifying device 20 can be continuously carried out.

[0049] (2) Raw material preparation process When manufacturing the powder material, before performing the dispersion and classification by the above-mentioned powder material manufacturing apparatus 1, a raw material preparation process is carried out to prepare the raw material powder for manufacturing the powder material. The raw material powder contains metal particles P1 and nano particles P2. As the metal particles P1 and the nano particles P2, the particles as described above may be prepared respectively. At this time, the particle size distributions of the metal particles P1 and the nano particles P2 may be appropriately adjusted. In particular, for the metal particles P1, it is preferable to perform classification and select the metal particles P1 having a desired particle size according to the use of the powder material, such as laminated molding. As described above, as the nano particles P2, it is preferable to use a fused body. The fused body can be manufactured, for example, by a method of forming nano particles by a dry method and colliding them in a state where the surface is melted by a flame or the like as appropriate. In the dispersion process described later, since the nano particles P2 are highly dispersed and mixed and adhered to the metal particles P1 with high uniformity, when mixing the metal particles P1 and the nano particles P2 in this raw material preparation process, it is not necessary to enhance the uniformity of the mixing so much. For example, stirring by hand may be sufficient.

[0050] By mixing, at least a part of the nano particles P2 adheres to the surface of the metal particles P1, constituting the metal particles P with nano particles attached. On the other hand, another part of the nano particles P2 has aggregated with each other to form an aggregate before mixing with the metal particles P1, and may maintain its aggregated state even after passing through the mixing with the metal particles P1. Furthermore, during the mixing with the metal particles P1, new aggregates may be formed between the nano particles P2.

[0051] The addition amount of the nanoparticles P2 in the raw material powder may be appropriately selected according to the degree of improvement in fluidity required in the powder material to be produced, etc. However, from the viewpoint of sufficiently obtaining the effect of reducing the van der Waals force between the metal particles P1 and improving the fluidity, a form in which it is 0.001% by mass or more, and further 0.003% by mass or more based on the mass of the metal particles P1 can be exemplified as a preferable one. On the other hand, from the viewpoint of suppressing the formation of aggregates due to an excessive amount of the nanoparticles P2, its content may be, for example, suppressed to 0.5% by mass or less, and further 0.1% by mass or less. When an excessive amount of the nanoparticles P2 is added, not only does the effect of reducing the van der Waals force between the metal particles P1 saturate, but also an adhesive force acts between the nanoparticles P2 attached to the adjacent metal particles P1, and in some cases, the fluidity of the powder material may decrease instead. Note that the content ratio of the nanoparticles P2 in the raw material powder is substantially maintained even after passing through the subsequent dispersion step and classification step.

[0052] (3) Dispersion step In the dispersion step, the raw material powder prepared in the above raw material preparation step is introduced into the dispersion device 10 to eliminate the aggregation of the nanoparticles P2 in the raw material powder.

[0053] In the above powder material manufacturing apparatus 1, the raw material powder may be charged into the supply port 11 of the airflow dispersion device 10 (arrow a1 in the figure). In the dispersion device 10, when an airflow is jetted onto the raw material powder, the constituent particles of the raw material powder are dispersed and mixed with each other. At the same time, due to particle-particle collisions, collisions with the device wall surface, and the application of shear force by the airflow, the aggregated state of the aggregates of the nanoparticles P2 contained in the raw material powder is eliminated. As a result, the nanoparticles P2 are in a highly dispersed state, and at least a part of them is dispersed and mixed with the metal particles P1 and further adheres to the surface of the metal particles P1.

[0054] (4) Classification step In the classification step, the powder discharged from the dispersion device 10 through the above dispersion step is introduced into the classification device 20 to classify the powder. By classification, the nanoparticle-attached metal particles P in which the nanoparticles P2 are attached to the metal particles P1 are selected and separated.

[0055] In the above-described powder material manufacturing apparatus 1, the discharge port 13 of the airflow dispersing apparatus 10 and the supply port 21 of the airflow classification apparatus 20 are connected, and the powder that has completed the dispersion process is directly introduced into the classification apparatus 20 together with the airflow (arrow a2 in the figure) and undergoes classification by the classification apparatus 20. After the dispersion process is completed, the powder introduced from the dispersion apparatus 10 into the classification apparatus 20 includes, in addition to the nanoparticle-attached metal particles P in which the nanoparticles P2 are attached to the surface of the metal particles P1, a dispersion of the nanoparticles P2 that are not attached to the surface of the metal particles P1, that is, the aggregated nanoparticles P2 that have been deaggregated, may inevitably be included. However, by passing through the classification process, the dispersion of the nanoparticles P2 that are not attached to the surface of the metal particles P1 moves to the fine powder region 27 and is separated from the nanoparticle-attached metal particles P. Furthermore, even if aggregates of the nanoparticles P2 that have not completely eliminated the aggregated state are mixed in the powder after passing through the dispersion process, such aggregates can also be separated from the nanoparticle-attached metal particles P. In this way, the nanoparticle-attached metal particles P can be separated from components with different particle sizes such as the dispersion and aggregates of the nanoparticles P2 and collected from the coarse powder region 26.

[0056] As described above, even if aggregates of the nanoparticles P2 are contained in the raw material powder, by sequentially passing through the dispersion process and the classification process, the aggregated structure of the nanoparticles P2 is eliminated, and a powder material containing the finely dispersed nanoparticles P2 attached to the surface of the metal particles P1 with high purity can be manufactured. For the manufactured powder material, it is not necessary to perform operations such as sieving afterwards to remove the aggregates of the nanoparticles P2. As described above, by performing the dispersion process and the classification process on the raw material powder in which the metal particles P1 and the nanoparticles P2 are mixed, a powder material that does not contain coarse aggregates with a particle size of 1 μm or more that are not attached to the metal particles can be preferably manufactured.

Example

[0057] Hereinafter, the present invention will be described more specifically using examples. Here, it was examined how the state and properties of the powder material change by adding nanoparticles.

[0058] (Preparation of Samples) Metal particles composed of an Fe-17Cr-4Ni-4Cu-0.3Nb alloy (the coefficients are concentrations in mass %) corresponding to the SUS630 alloy were prepared by the gas atomization method. Then, classification was performed at +15 / -45 μm. The obtained metal powder was designated as Sample #1.

[0059] To the metal powder of Sample #1, SiO 2 nanoparticles (TECNAN's "TECNAPOW-SIO2" with an average primary particle size of 10 - 15 nm) that were not surface-treated were mixed to obtain raw material powder. The SiO 2 nanoparticles used here are those in which substantially spherical primary particles form dendritic aggregates. The addition amount of the nanoparticles was 0.010 mass% based on the mass of the metal particles. The obtained raw material powder was fed into a powder material manufacturing apparatus connected with an air flow dispersing device (a ring nozzle jet type disperser "DN-155" manufactured by Nisshin Engineering Co., Ltd.) and an air flow classification device (a turbo classifier "TC-15" manufactured by the same company) similar to that shown in Fig. 2 for dispersion and classification. Metal particles adhered with nanoparticles were separated and designated as Sample #2. For Sample #2, samples with the addition amount of nanoparticles changed were also prepared for those classified at +15 / -45 μm and those classified at -45 μm of the metal particles. Further, the mixture of the metal powder of Sample #1 and the above-mentioned SiO 2 nanoparticles by a shaking type powder mixer was designated as Sample #3.

[0060] (Evaluation of Powder Materials) First, in order to confirm the state of the metal particles added with nanoparticles, the particle size distribution was evaluated for Sample #1 and Sample #2. At this time, the particle shape was evaluated using a particle image analyzer. Based on the particle shape, the particle size distribution was evaluated and the circularity of the particles was measured. Also, in order to confirm the state of the nanoparticles in the powder material, visual observation, digital camera photography, and SEM observation were performed for Sample #2 and Sample #3, and elemental analysis was performed on a narrow region of the surface of the metal particles by energy dispersive X-ray spectroscopy (EDX) using SEM.

[0061] Furthermore, the change in the fluidity of the powder material due to the addition of nanoparticles was investigated. Specifically, for Samples #1, #2, and #3, the bulk density-normalized shear adhesion force (τ s / ρ) was measured. When measuring, in accordance with JIS Z 8835, using a rotational cell type shear test apparatus, the shear stress (τ) generated when applying pressure (σ) to the powder material was measured. And, as the y-intercept when plotting σ on the x-axis and τ on the y-axis, the shear adhesion force (τ s ) was obtained. Also, the bulk density (ρ) was measured in accordance with JIS Z 2504, using a bulk specific gravity measuring instrument for metal powders. Each measurement was carried out under the conditions of an air temperature of 23°C and a relative humidity of RH24%. For Sample #2, similar measurements were performed for each sample with a varying amount of added nanoparticles.

[0062] (Evaluation Results) (1) State of the Powder Material Figure 3 shows the evaluation results of the particle size distribution and the roundness for each particle size of Sample #1 composed of metal particles without added nanoparticles and Sample #2 with added nanoparticles to the metal particles. Also, Table 1 shows the parameters related to the particle size distribution. Furthermore, Figure 4 shows, as an example of the particle images used to obtain the roundness shown in Figure 3, the particle images at a particle size of 37 μm ± 3 μm corresponding to the average particle size for Samples #1 and #2. The average values of the roundness obtained from these particle images were 0.89 for Sample #1 and 0.92 for Sample #2. The roundness for each particle size shown in Figure 3 was similarly calculated as the average value in the particle size range of ±3 μm.

[0063] [Table 1]

[0064] According to Fig. 3, for sample #1 without added nanoparticles and sample #2 with added nanoparticles, the particle size distributions are very similar in terms of median and width. The representative values shown in Table 1 are also very close for both. That is, sample #1 and sample #2 have substantially the same particle size distribution, and it is confirmed that the particle size distribution of the sample particles has not changed substantially after the addition of nanoparticles.

[0065] And when comparing the particle images in Fig. 4 for sample #1 and sample #2, for many particles, there is no significant difference in particle shape between the two samples. As described above, the average value of the circularity estimated from these particle images is also almost the same for both samples. Furthermore, according to Fig. 3, in the entire particle size range, almost the same degree of circularity is obtained between the two samples. That is, it is confirmed that the circularity has not changed substantially after the addition of nanoparticles.

[0066] Fig. 5 shows the SEM image of sample #2. According to the low-magnification image in (a), metal particles that match the particle shape and particle size observed in the particle image of Fig. 4 are observed. Furthermore, in the high-magnification image obtained by magnifying the surface of the metal particles in (b), a large number of deposits with sizes ranging from several tens of nanometers to several hundreds of nanometers are seen, such as the location indicated as A2.

[0067] Furthermore, for position A1 in Fig. 5(b) where there are no deposits and position A2 where there are deposits, the results of elemental analysis by EDX are shown in Fig. 6(a) and (b), respectively. According to this, at position A1 where it is considered that the surface of metal particles composed of Fe-17Cr-4Ni-4Cu-0.3Nb alloy without attached nanoparticles is being observed, only the elements constituting the alloy are detected as the main existing elements. At position A2 where nanoparticles are attached, the same elements as at position A1 are detected, but the concentrations of O and Si are significantly higher compared to position A1. This is considered to be due to SiO 2 derived from the nanoparticles. That is, the deposits observed in the SEM image are SiO attached to the surface of the metal particles. 2can be attributed to the nanoparticles. As confirmed by the SEM image of Fig. 5(b), the SiO 2 nanoparticles are attached to the surface of the metal particles in a highly dispersed state. From this, it is confirmed that by adding the nanoparticles to the metal particles and performing the dispersion and classification steps, a powder material in which the nanoparticles are dispersed and attached to the surface of the metal particles can be produced.

[0068] Thus, it is confirmed that SiO 2 nanoparticles are dispersed and attached to the surface of the metal particles, but a form in which the SiO 2 nanoparticles form coarse aggregates is not observed in the SEM image. If the nanoparticles form coarse aggregates with a particle size of 1 μm or more and exist in an isolated state without adhering to the metal particles, such aggregate particles should be observed in the space between the metal particles in the low-magnification image of Fig. 5(a) (see Fig. 10(a)). However, such particles are not seen in the actual SEM image of Fig. 5(a). Such coarse aggregates do not exist even when attached to the surface of the metal particles. In the SEM image of Fig. 5(a), there are also a plurality of metal particles with irregularly shaped protrusions with a scale of several to dozens of microns formed on the surface, but these protrusions are derived from the metal particles. From the above results, it is confirmed that the SiO 2 nanoparticles do not exist at least in an isolated state in the form of aggregates with a particle size of 1 μm or more, and it can be said that they do not exist in states other than the isolated state.

[0069] As described above, even after adding nanoparticles, the particle size and roundness of the particles constituting the powder material have not substantially changed, and it is confirmed that the addition of nanoparticles and the dispersion and classification processes do not affect the particle shape and particle size of the metal particles. Furthermore, from the results of SEM observation, it is confirmed that the added nanoparticles are dispersed and adhered to the surface of the metal particles without forming coarse aggregates. Next, in the properties of the powder material such as the shear adhesion force showing the evaluation results, it is confirmed that the changes occurring when adding nanoparticles are not due to changes in particle shape and particle size, but are the result of the addition of nanoparticles itself.

[0070] (2) Flowability of powder material Figure 7 shows the measurement results of the bulk density-normalized shear adhesion force (τ s / ρ) for Sample #1 and Sample #2. The unit is (m / s) 2 .

[0071] According to Figure 7, compared with Sample #1 without added nanoparticles, the value in Sample #2 with added nanoparticles has decreased by nearly 40%. This result is considered to be due to the fact that in Sample #2, the nanoparticles are interposed between the metal particles, reducing the attractive force between the metal particles and improving the flowability. Although uncoated nanoparticles are used, even so, the nanoparticles exhibit a high effect in improving the flowability of the powder material. The measurement results of Sample #3 will be described later.

[0072] (3) Nanoparticle addition amount and flowability Figure 8 shows the bulk density-normalized shear adhesion force (τ sThe results of measuring ( / ρ) are shown. The horizontal axis represents the addition amount of nanoparticles based on the mass of metal particles, expressed in mass%. According to this, in any classification condition, in the region up to at least an addition amount of 0.003 mass%, and further in the region up to about 0.010 mass%, as the addition amount increases, the bulk density-normalized shear adhesion force decreases rapidly. However, it is particularly remarkable under the classification condition of -45 μm. In the region where the addition amount is from 0.010 mass% to about 0.020 mass%, the decrease in the addition amount has saturated. And when the addition amount further increases, the bulk density-normalized shear adhesion force turns to a gentle increasing trend. Under the classification condition of -45 μm, the bulk density-normalized shear adhesion force takes a minimum value at around an addition amount of 0.015 mass%.

[0073] In the region where the addition amount is small, the rapid decrease in the bulk density-normalized shear adhesion force with respect to the addition amount of nanoparticles is because when the density of nanoparticles intervening between metal particles increases, the distance between metal particles increases, reducing the van der Waals force between metal particles. In the region where the addition amount of nanoparticles is larger, the decrease in the bulk density-normalized shear adhesion force has saturated with the increase in the addition amount because due to the effect of the presence of nanoparticles, contact between metal particles hardly occurs, and it is interpreted that even if the density of nanoparticles is increased further, the distance between metal particles cannot be increased any more. In the region where the addition amount of nanoparticles is larger, the fact that the bulk density-normalized shear adhesion force turns to a gentle increase is interpreted as because an adhesion force acts between the nanoparticles themselves attached to adjacent metal particles, reducing the fluidity of the metal particles to which the nanoparticles are attached. Note that although the difference in classification conditions affects the magnitude of the bulk density-normalized shear adhesion force, it does not have a significant impact on the tendency of the behavior with respect to the addition amount.

[0074] (4) Influence of the manufacturing method on the state of the powder material As described above, in the powder material of sample #2 manufactured through the dispersion and classification process, the nanoparticles are dispersed and adhered to the surface of the metal particles. We confirmed how the dispersion and classification process affects the state of the powder material.

[0075] Figures 9(a) and (b) respectively show the results of photographing the powder materials of Samples #2 and #3 with a digital camera. First, for the powder material that has only undergone mixing by the powder mixer in Fig. 9(b), granular bodies that are brightly photographed are scattered among the finely powdered aggregates that are observed darkly. The diameter of this granular body is about 1 mm, and from color comparison etc., it can be associated with aggregates of SiO 2 nanoparticles. The SiO 2 nanoparticles had formed an aggregated structure before mixing with the metal particles, and it is considered that the aggregated structure was not completely eliminated only by passing through the mixing by the powder mixer.

[0076] On the other hand, for Sample #2 in which dispersion and classification were performed on the powder material, as shown in Fig. 9(a), fine dark-colored powder is uniformly observed throughout the image, and no granular bodies that are brightly photographed as seen in Fig. 9(b) are confirmed. That is, in Sample #2, a highly uniform powder material is produced. This indicates that through the dispersion and classification process, the aggregated state of the aggregates of SiO 2 nanoparticles in the raw material powder was eliminated, and the dispersibility of the nanoparticles was enhanced.

[0077] Thus, from the appearance of the powder material, it is confirmed that in Sample #3 that has not undergone dispersion and classification, SiO 2 nanoparticles form coarse aggregates on the order of millimeters, but on a smaller scale, SiO 2The state of the nanoparticles was confirmed by SEM observation. Figure 10 shows the SEM image of Sample #3. Looking at the low-magnification image in Figure 10(a), metal particles having the same shape and size as those seen in the image of Sample #2 in Figure 5(a) are observed. However, in Figure 10(a), as indicated by the arrows, particles smaller in diameter than those metal particles are distributed between those metal particles. The particle size of those small-diameter particles is generally 1 μm or more and 5 μm or less. The particle size of the particles indicated by the arrows is 2.8 μm. Such small-diameter particles are not seen in the image of Sample #2 in Figure 5(a).

[0078] Figure 11(a) shows an enlarged observation image of the small-diameter particles pointed by the arrow in Figure 10(a). According to this, the particles are almost spherical and have a shape with minute irregularities on the surface, and as described above, the particle size is 2.8 μm. Figure 11(b) shows the result of elemental analysis by EDX obtained for the vicinity of the center of this particle. According to this, although various elements considered to be derived from the metal particles are also present in small amounts, strong peaks of Si and O are observed. From this, it can be said that the observed small-diameter particles are derived from SiO 2 nanoparticles. The primary particle size of the nanoparticles used as the raw material is 10 to 15 nm, and the particle size of the fused bodies is at most on the order of 100 nm, so the observed small-diameter particles are considered to be aggregates formed by the aggregation of a large number of SiO 2 nanoparticles (fused bodies). From the results of the above SEM observation and EDX analysis, it can be seen that in Sample #3, SiO 2 nanoparticles form aggregates with a particle size of 1 μm or more and are dispersed without adhering to the metal particles. That is, SiO 2 nanoparticles form aggregates not only in the millimeter-order aggregates seen in Figure 9(b) but also in the micron-order.

[0079] Figures 10(b) and (c) also show SEM images of magnified observations of different regions on the surface of the metal particles for Sample #3. In at least the region observed in Figure 10(b), almost no nanoscale deposits like those seen on the surface of the metal particles of Sample #2 in Figure 5(b) are visible. Even in the region of Figure 10(c), only a few deposits are seen. That is, in Sample #3, it can be said that the attachment of SiO 2 nanoparticles to the surface of the metal particles hardly occurs, and even if it does occur, the attachment density is significantly lower compared to the case of Sample #2. This can be interpreted as meaning that in Sample #3, the SiO 2 nanoparticles are consumed in the formation of aggregates on the millimeter or micron order, resulting in fewer nanoparticles available for attachment to the surface of the metal particles.

[0080] As described above, in Sample #3 where only the metal particles and SiO 2 nanoparticles were mixed by a powder mixer, the SiO 2 nanoparticles form aggregates with a particle size of 1 μm or more and are distributed in the powder material in an isolated state without adhering to the metal particles. The density of SiO 2 nanoparticles adhering to the surface of the metal particles is very low. On the other hand, as described above, in Sample #2 manufactured through the dispersion process and the classification process, the aggregation of SiO 2 nanoparticles is eliminated in the dispersion and classification processes, so the SiO 2 nanoparticles do not form aggregates with a particle size of 1 μm or more and exist in an isolated state, but are finely dispersed and adhered to the surface of the metal particles.

[0081] Finally, the fluidity of the powder materials is compared between Sample #2 and Sample #3. Figure 7 shows the bulk density-normalized shear adhesion force (τ s / ρ) of Samples #1, #2, and #3. Compared to Sample #1 without the addition of nanoparticles, in Sample #3 with the addition of nanoparticles and only mixed by a powder mixer, the value is reduced to about 90%. This is presumably because at least part of the nanoparticles are interposed between the metal particles, reducing the attractive force between the metal particles and improving the fluidity.

[0082] Furthermore, in Sample #2 where nanoparticles were added and the dispersion and classification processes were carried out, as already explained, compared with Sample #1, the bulk density-normalized shear adhesion force has decreased by nearly 40%. Even when compared with Sample #3, the value has become about 45% smaller. From this, it can be seen that by simply adding and mixing nanoparticles to metal particles, although the effect of improving the fluidity of metal particles can be obtained, by carrying out the dispersion and classification processes, the nanoparticles can reduce the attractive force between the particles of metal particles and exhibit a higher effect in improving the fluidity.

[0083] 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.

Explanation of Reference Numerals

[0084] P Metal particles with attached nanoparticles P1 Metal particles P2 Nanoparticles 1 Powder material manufacturing apparatus 10 (Airflow) dispersion device 11 Supply port 13 Discharge port 20 (Airflow) classification device 21 Supply port 26 Coarse powder region 27 Fine powder region

Claims

1. It consists of an iron-based alloy, and contains metal particles with an average particle size of 10 μm or more and 500 μm or less, and nanoparticles consisting of a metal or a metal compound and not subjected to surface treatment with an organic substance, a plurality of the nanoparticles constitute an aggregate fused together, a powder material, wherein the particle size of the whole aggregate defined as the length of the longest straight line crossing the aggregate is 25 nm or more and 500 nm or less.

2. The powder material according to claim 1, wherein the nanoparticles are attached to the metal particles.

3. The powder material according to claim 1 or 2, wherein in the powder material, aggregates having a particle size of 1 μm or more composed of the nanoparticles do not exist between the metal particles.

4. The powder material according to claim 3, wherein the powder material does not contain aggregates having a particle size of 1 μm or more composed of the nanoparticles in a state of being attached to the metal particles.

5. The powder material according to any one of claims 1 to 4, wherein the iron-based alloy constituting the metal particles is a precipitation hardening stainless steel.

6. The powder material according to any one of claims 1 to 5, wherein the nanoparticles are silica particles.

Images