JP7427919B2 - Manufacturing method of powder material - Google Patents

Description

The present invention relates to a method for producing a powder material, and more particularly, to a method for producing a powder material that can be used as a raw material in an additive manufacturing method.

As a new technology for manufacturing three-dimensional objects, additive manufacturing technology (AM) has made remarkable progress in recent years. One type of additive manufacturing technology is an additive manufacturing method that utilizes solidification of powdered materials by irradiation with energy rays. There are two typical additive manufacturing methods using metal powder materials: a powder lamination melting method and a powder deposition method.

Specific examples of the powder layered melting method include selective laser melting (SLM), electron beam melting (EBM), and the like. In these methods, a powder material made of metal is supplied onto a base material to form a powder bed, and based on three-dimensional design data, a laser beam or electron Irradiates energy rays such as rays. Then, the powder material in the irradiated area is melted and solidified, forming a modeled object. A three-dimensional object is obtained by repeatedly supplying powder material to a powder bed and modeling by irradiating energy rays, and sequentially stacking the objects in layers.

On the other hand, a specific example of the powder deposition method includes laser metal deposition (LMD). In this method, a nozzle is used to inject metal powder into a position where a three-dimensional object is to be formed, and at the same time a laser beam is irradiated to form a three-dimensional object having a desired shape.

When manufacturing three-dimensional objects made of metal materials using the above-mentioned additive manufacturing method, the resulting three-dimensional object may have a structure in which the distribution of constituent materials is uneven, such as voids or defects. may occur. It is desirable to suppress the generation of such non-uniform structures as much as possible. In the additive manufacturing method using metal materials, there are several possible causes of uneven distribution of constituent materials inside the manufactured three-dimensional model, but one of the reasons is that the powder before energy ray irradiation The condition of the material can have a large effect on the condition of the resulting three-dimensional structure.

For example, in the powder lamination melting method, if it is possible to smoothly supply powder material to a powder bed and stably form a powder bed in which the powder material is evenly spread, it is also possible to If it can be filled, a highly homogeneous three-dimensional structure can be easily obtained by irradiating the powder bed with energy rays. Also in the powder deposition method, a three-dimensional structure can be stably formed by smoothly supplying the powder material without clogging the nozzle. In this way, when manufacturing three-dimensional objects using additive manufacturing, the higher the fluidity of the powder material used as a raw material, the more smoothly the powder material can be supplied and the more densely packed it can be. Through irradiation with energy rays, a highly uniform shaped object can be obtained.

The inventors are thus conducting studies on powder materials with high fluidity that are suitable for use as raw materials for additive manufacturing. For example, Patent Document 1 discloses a metal powder material that includes metal particles having a particle size on the micron order and nanoparticles made of a metal or a metal compound attached to or mixed with the metal particles. By interposing the nanoparticles between the metal particles, a distance is maintained between the metal particles. This makes it possible to reduce the attractive force, mainly Van der Waals force, that acts between metal particles.

JP 2019-112699 Publication

As described in Patent Document 1, the fluidity of metal particles can be increased by attaching nanoparticles to the surfaces of metal particles. At this time, the higher the dispersibility of the nanoparticles, the more effective the improvement in fluidity can be exhibited. However, according to the inventors' research, nanoparticles may aggregate depending on the type of nanoparticles and the method of mixing metal particles and nanoparticles, and it is difficult to dissolve the agglomerated structure and disperse the nanoparticles. , which can be difficult. This makes it difficult to sufficiently increase the fluidity of the metal particles. Furthermore, if a powder material that still contains nanoparticle aggregates is used for additive manufacturing, the aggregates may cause defects that become fracture starting points in the obtained three-dimensionally constructed object. On the other hand, if an attempt is made to remove the generated nanoparticle aggregates from the powder material after the fact, the steps required to prepare the powder material will become complicated.

The problem to be solved by the present invention is to provide a method for producing a powder material that can easily produce a highly fluid powder material using metal particles and nanoparticles.

In order to solve the above problems, the method for producing a powder material according to the present invention involves preparing a raw material powder containing metal particles with an average particle size of 10 μm or more and 500 μm or less, and nanoparticles made of a metal or a metal compound. a dispersion step in which the raw material powder is introduced into a dispersion device that disperses the aggregated powder, a dispersion step in which the agglomeration of the nanoparticles is resolved, and the powder released from the dispersion device is introduced into a classification device, A classification step is performed in which the powder is classified and particles formed by the dispersed nanoparticles adhering to the metal particles are separated.

Here, it is preferable that the nanoparticles are not surface-treated with an organic substance.

The dispersion device may be an airflow dispersion device. In this case, the classification device is an airflow classification device, and after the dispersion step is completed, the powder released from the airflow dispersion device along with the airflow is directly introduced into the airflow classification device to classify the powder. It is a good idea to carry out the process.

The metal particles are preferably made of titanium alloy, nickel alloy, cobalt alloy, or iron alloy. The nanoparticles are preferably made of a metal compound containing at least a part of the metal elements contained in the metal particles, or a metal compound containing at least one light metal element selected from Si, Al, and Ti.

According to the method for producing a powder material according to the above invention, it is possible to produce a powder material in which nanoparticles are attached to the surface of metal particles having a particle size on the order of microns. 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 improved.

In addition, in the dispersion process, raw material powder containing metal particles and nanoparticles is introduced into a dispersion device and the powder is dispersed. It is possible to eliminate aggregation between nanoparticles and improve the dispersibility of nanoparticles. Furthermore, in the classification process, the powder that has undergone the dispersion process is introduced into a classifier, and particles formed by nanoparticles attached to metal particles are separated, thereby eliminating nanoparticles that are not attached to metal particles and remaining particles. The removal of unintended particles, such as the removal of aggregates of nanoparticles, and the adjustment of the particle size of the powder material can be performed at the same time. In this way, it is possible to easily produce a powder material with high fluidity, which is composed of an aggregate of nanoparticle-attached metal particles having a desired particle size, and has a reduced content of nanoparticle aggregates. The obtained powder material can be suitably used as a raw material for additive manufacturing by taking advantage of its high fluidity.

Here, if the nanoparticles have not been surface-treated with an organic substance, aggregation between the nanoparticles is likely to occur, but by performing the dispersion process, aggregation between the nanoparticles can be prevented. This can be effectively eliminated, and the fluidity of the produced powder material can be sufficiently improved. By using nanoparticles that have not been surface-treated with organic substances, when using powder materials for additive manufacturing, it is possible to reduce the influence of organic substances on the additive manufacturing process and on the manufactured additively manufactured objects. , can be reduced.

When the dispersion device is an airflow dispersion device, the airflow effectively disperses nanoparticle aggregates, making it easier to obtain a powder material in which the dispersed nanoparticles are attached to the surfaces of metal particles.

In this case, the classification device is an airflow classification device, and after the dispersion process is completed, the powder released from the airflow dispersion device along with the airflow is directly introduced into the airflow classification device to carry out the classification process. According to the above, by using an air classifier as a classification device, it is possible to both sort metal particles with a desired particle size attached to nanoparticles and remove unintended particles such as nanoparticles not attached to metal particles. This can be done with high efficiency. Furthermore, by using an air flow dispersion device in the dispersion process and an air flow classifier in the classification process, the powder released from the air flow dispersion device along with the air flow is directly introduced into the air flow classification device. It becomes possible to perform the steps continuously. Thereby, a highly fluid powder material can be manufactured more easily and with a simple device configuration.

When the metal particles are made of titanium alloy, nickel alloy, cobalt alloy, or iron alloy, the powder material to be produced can be three-dimensionally made of these alloys, which are in high demand for production using additive manufacturing. It can be suitably used as a raw material for products.

When the nanoparticles are made of a metal compound containing at least a part of the metal elements contained in the metal particles, or a metal compound containing at least one light metal element selected from Si, Al, and Ti, the nanoparticles are nanoparticles. By attaching the particles to the metal particles, the fluidity of the powder material can be effectively increased. In particular, when the nanoparticles are made of a metal compound containing at least a part of the metal elements contained in the metal particles, the presence of the nanoparticles can be detected when the obtained powder material is used as a raw material for additive manufacturing. , in the layered manufacturing process and the resulting layered product.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing an example of a powder material manufacturing apparatus capable of implementing a powder material manufacturing method according to an embodiment of the present invention, together with a schematic diagram of powder to be processed. FIG. 2 is a schematic diagram showing a powder material obtained by the above manufacturing method. This is a photograph taken of the state of the powder material. (a) shows sample #2 in which the material to which nanoparticles were added was subjected to dispersion and classification, and (b) shows sample #3 in which only mixing was performed to the material to which nanoparticles were added. . It is a figure which shows the particle size distribution and circularity of a powder material. The figure shows the measurement results for sample #1 which does not contain nanoparticles and sample #2 in which the material to which nanoparticles are added is dispersed and classified. Particle images used for particle shape evaluation are shown for sample #1 and sample #2 in a particle size range of 20±2 μm. A SEM observation image of sample #2 is shown. High-magnification images are shown in the order of (a), (b), and (c). The results of elemental analysis by EDX are shown for positions P1 and P2 in FIG. 6(c), respectively. FIG. 3 is a diagram showing the bulk density normalized shear adhesion force for samples #1 to #3.

Hereinafter, a method for manufacturing a powder material according to an embodiment of the present invention will be described in detail with reference to the drawings. As shown in FIG. 2, the powder material produced by this production method includes metal particles P1 having a particle size on the micron order and nanoparticles P2 made of a metal or a metal compound. Nanoparticles P2 are attached to the surface of metal particles P1. Such a powder material can be suitably used as a raw material for manufacturing a three-dimensional structure by irradiation with energy rays in the additive manufacturing method.

[Metal particles and nanoparticles]
Before explaining the method for producing the powder material, the metal particles P1 and nanoparticles P2, which are used as raw materials for producing the powder material and constitute the powder material, will be explained. The metal particles P1 are particles made of metal having a particle size on the micron order, and when a powder material is used for additive manufacturing, they become the main material constituting the three-dimensionally shaped object. The nanoparticles P2 are particles made of a metal or a metal compound and have a particle size on the order of nanometers, and play the role of reducing the interparticle attraction of the metal particles P1 in the powder material and increasing the fluidity of the powder material. Fulfill.

(1) Metal particles The metal particles P1 have a particle size on the micron order, and the average particle size (d50) can be 10 μm or more and 500 μm or less. From the viewpoint of suitably using it as a raw material for additive manufacturing, it is particularly preferable that the average particle size is 10 μm or more and 100 μm or less. In the powder material to be manufactured, from the viewpoint of obtaining high fluidity, it is preferable that the metal particles P1 have a shape that can be regarded as spherical. For example, it is preferable that the circularity of the metal particles P1 is 0.90 or more, more preferably 0.95 or more in terms of the average particle size, that is, for particles whose particle size is equal to the average particle size.

The metal species constituting the metal particles P1 is not particularly limited, and examples thereof include titanium alloys, nickel alloys, cobalt alloys, iron alloys, and the like. Three-dimensional objects made of these alloys are in high demand for production using additive manufacturing, so powder materials using metal particles P1 made of these alloys are preferably used as raw materials for three-dimensional objects. be able to.

Although the method for manufacturing the metal particles P1 is not particularly limited, they can be suitably manufactured by an atomization method. Although various methods such as a gas atomization method and a disk atomization method can be applied, the gas atomization method is particularly suitable from the viewpoint of manufacturing efficiency of the metal particles P1.

(2) Nanoparticles The particle size of the nanoparticles P2 is not particularly limited as long as it is on the order of nanometers, but preferred examples include cases where the particle size is 1 nm or more and 100 nm or less. . The shape of the nanoparticles P2 is also not particularly limited, and may have any shape such as a substantially spherical shape, a polyhedral shape, an irregular shape, or the like. Preferably, it is approximately spherical.

The nanoparticles P2 may be made of a metal or a metal compound, but from the viewpoint of effectively reducing the attractive force between the metal particles P1 in the powder material to be produced, the nanoparticles P2 are made of a metal compound. It is preferable. Examples of the metal compound include metal oxides, metal nitrides, metal carbides, and the like. Among these, metal oxides are preferred from the viewpoint of low activity and ease of obtaining nanoparticles. The metal species constituting the metal compound is not particularly limited, but it is preferable to use a light metal element such as Si, Al, or Ti. Nanoparticles of oxides of these elements (SiO ₂ , Al ₂ O ₃ , TiO _{2 ,} etc.) have established manufacturing methods, are easily available, and can be incorporated into three-dimensional objects made of metal. Even if it is included, it is unlikely to cause serious effects.

Furthermore, if the nanoparticles P2 made of a metal compound containing at least a part of the metal elements contained in the metal particles P1 are used, products manufactured using powder materials such as additively manufactured objects, and the manufacturing process of the products can be used. In this case, the influence of the nanoparticles P2 can be suppressed to a small level. Among these, it is preferable that the metal element that is the main component of the metal particles P1 be the main component of the metal elements that constitute the nanoparticles. For example, when metal particles P1 made of a titanium alloy are used, nanoparticles P2 made of titanium oxide can be used.

The nanoparticles P2 may contain components other than the main component metal or metal compound, or may be surface-treated with an organic substance or the like. By performing surface treatment with an organic substance or the like, the surface of the nanoparticles P2 can be made hydrophobic and the attractive interaction between the nanoparticles P2 via water molecules can be reduced. As a result, aggregation of nanoparticles P2 and aggregation of metal particles P1 to which nanoparticles P2 are attached can be easily suppressed. However, in this manufacturing method, even if aggregates of nanoparticles P2 are contained in the raw material powder, such aggregates can be dissolved and removed through a dispersion process and a classification process, as will be explained later. can be achieved effectively. From the viewpoint of enjoying high effects in dissolving and removing aggregates through these steps, it is preferable that the nanoparticles P2 are not surface-treated with an organic substance or the like. Since the nanoparticles P2 do not contain organic substances, it is possible to suppress the influence of organic substances on products manufactured using powder materials, such as layered products, and on the manufacturing process of the products.

[Powder material manufacturing equipment]
Here, a powder material manufacturing apparatus capable of implementing a powder material manufacturing method according to an embodiment of the present invention will be described. FIG. 1 shows a powder material manufacturing apparatus 1 according to an example.

The powder material manufacturing apparatus 1 includes a dispersion device 10 and a classification device 20. The dispersion device 10 is a device capable of dispersing aggregated powder. The classifier 20 is a device that can classify powder, that is, sort the particle size. A dispersion device 10 is provided upstream and a classifier 20 is provided downstream with respect to the flow of powder, and the powder released from the dispersion device 10 is introduced into the classifier 20.

Both the dispersion device 10 and the classification device 20 may have any form for dispersing and classifying powder, respectively, and the connection form between the dispersion device 10 and the classification device 20 is also particularly limited. isn't it. However, it is preferable to use an airflow dispersion device as the dispersion device 10 and to use an airflow classification device as the classification device 20. Then, the discharge port 13 of the dispersion device 10 is directly connected to the supply port 21 of the classifier 20, and the powder released from the discharge port 13 of the dispersion device 10 along with the airflow is brought into direct contact with the external environment. It is preferable that the liquid be introduced into the supply port 21 of the classifier 20 without any separation.

As the dispersion device 10, there are known devices that disperse powder based on various principles, such as an airflow type, an impeller type, or an orifice type, and any of them may be applied, but the present powder material manufacturing method In the apparatus 1, as mentioned above, it is preferable to use the airflow type dispersion apparatus 10. As the airflow dispersion device 10, for example, one disclosed in Japanese Patent Laid-Open No. 4-330957 can be used. In this type of airflow distribution device 10, a high-speed airflow is ejected from a ring nozzle 12. Then, the powder supplied from the supply port 11 is suctioned by the negative pressure generated by the airflow, and the suctioned powder is caused to collide with the high-speed airflow. The powder is accelerated by the airflow, collided with the particles, collided with the wall surface of the device, and applied shear force, whereby the agglomeration state between the particles is resolved and the powder is dispersed. The dispersed powder is discharged from the discharge port 13 along with the airflow.

Although the classification device 20 may be based on any principle, it is preferable to use a dry classification device using air current. For example, it is preferable to use a forced vortex air classifier, such as the one disclosed in JP-A No. 2003-145052. In this type of air classifier 20, the dispersing blades 22 are rotated to generate an air current, and the powder introduced from the supply port 21 is dispersed by the shear force of the air current before passing through the classification blades 25. It is supplied to a classification zone 23 equipped with the same. In the classification zone 23, the powder is subjected to centrifugal force from the classification rotor 24 rotating at high speed and drag from the airflow. At this time, classification is performed by applying centrifugal force and drag force to the particles depending on the particle size. Large diameter particles, on which a large centrifugal force acts, move to the coarse powder region 26, while small diameter particles, on which a large drag force acts, move to the fine powder region 27. By selecting the operating conditions of the classifier 20, it is possible to separate particles having a desired particle size in the coarse powder region 26.

By using airflow type devices as both the dispersion device 10 and the classification device 20, the discharge port 13 of the dispersion device 10 and the supply port 21 of the classification device 20 can be directly connected using the piping member 30 as appropriate. Can be done. Then, the powder released from the dispersion device 10 along with the airflow is directly introduced into the classification device 20. Thereby, the process of dispersing the powder using the dispersion device 10 and the process of classifying the powder using the classifier 20 can be performed continuously.

[Method for producing powder material]
Next, a method for manufacturing a powder material according to an embodiment of the present invention will be described. This manufacturing method can be suitably implemented using the powder material manufacturing apparatus 1 described above. In this manufacturing method, a raw material preparation step, a dispersion step, and a classification step are performed in this order. Each step will be explained in order below.

(1) Raw material preparation process In the raw material preparation process, raw material powder for manufacturing the powder material is prepared. The raw material powder contains metal particles P1 having a particle size on the micron order and nanoparticles P2 made of a metal or a metal compound. As the metal particles P1 and the nanoparticles P2, particles as described above may be prepared respectively. At this time, the particle size distribution of the metal particles P1 and nanoparticles P2 may be adjusted as appropriate. In particular, it is preferable to classify the metal particles P1 to select metal particles P1 having a desired particle size according to the application of the powder material such as additive manufacturing. The classification method is not particularly limited, and for example, the classification device 20 that constitutes the powder material manufacturing device 1 may be used.

In the raw material preparation step, the metal particles P1 and nanoparticles P2 that have been prepared are mixed to prepare a raw material powder. In the dispersion step described below, the nanoparticles P2 are highly dispersed and are mixed and attached to the metal particles P1 with high uniformity, so in this raw material preparation step, when mixing the metal particles P1 and the nanoparticles P2, It is not necessary to increase the uniformity of the mixing very much. For example, manual stirring may be sufficient.

By mixing, at least a portion of the nanoparticles P2 adhere to the surfaces of the metal particles P1, forming nanoparticle-attached metal particles P. On the other hand, another part of the nanoparticles P2 aggregates with each other to form an aggregate before mixing with the metal particles P1, and maintains the aggregated state even after mixing with the metal particles P1. There are cases. Furthermore, during mixing with the metal particles P1, new aggregates may be formed between the nanoparticles P2.

The amount of nanoparticles P2 added to the raw material powder may be appropriately selected depending on the degree of fluidity improvement required for the powder material to be manufactured. A preferred example is a configuration in which the amount is 0.001% by mass or more based on the mass of P1. On the other hand, from the viewpoint of suppressing the formation of aggregates due to an excessive amount of nanoparticles P2, the content is preferably suppressed to, for example, 0.5% by mass or less.

(2) Dispersion process In the dispersion process, the raw material powder prepared in the raw material preparation process described above is introduced into the dispersion device 10 to eliminate aggregation of nanoparticles P2 in the raw material powder.

When using the powder material manufacturing apparatus 1 described above, raw material powder may be introduced into the supply port 11 of the air flow dispersion apparatus 10 (arrow a1 in the figure). In the dispersion device 10, the constituent particles of the raw material powder are mutually dispersed and mixed by injecting an air stream onto the raw material powder. At the same time, the agglomerated state of the nanoparticles P2 contained in the raw material powder is dissolved by interparticle collisions, collisions with the device wall surface, and application of shear force by airflow. As a result, the nanoparticles P2 are in a highly dispersed state, and at least a portion thereof is mutually dispersed and mixed with the metal particles P1, and further adheres to the surface of the metal particles P1.

(3) Classification process In the classification process, the powder released from the dispersion device 10 through the above-mentioned dispersion process is introduced into the classification device 20, and the powder is classified. By classification, nanoparticle-adhered metal particles P, which are formed by adhering nanoparticles P2 to metal particles P1, are sorted out and fractionated.

When using the powder material manufacturing apparatus 1 described above, the discharge port 13 of the airflow dispersion device 10 and the supply port 21 of the airflow classification device 20 are connected, and the powder that has completed the dispersion process is transferred to the classification device 20 along with the airflow. (arrow a2 in the figure), and is classified by the classifier 20. After the dispersion process is completed, the powder introduced from the dispersion device 10 to the classifier 20 includes, in addition to the nanoparticle-attached metal particles P having the nanoparticles P2 attached to the surface of the metal particles P1, A dispersion of unattached nanoparticles P2, ie, deagglomerated nanoparticles P2, may inevitably be included. However, through the classification process, the dispersion of nanoparticles P2 that is not attached to the surface of the metal particles P1 moves to the fine powder region 27 and is separated from the metal particles P to which the nanoparticles are attached. Furthermore, even if aggregates of nanoparticles P2 whose agglomerated state could not be completely resolved even after the dispersion process are mixed in the powder, such aggregates can also be separated from the metal particles P attached to the nanoparticles. can do. In this way, the nanoparticle-attached metal particles P can be separated from components having different particle sizes, such as dispersions and aggregates of the nanoparticles P2, and fractionated from the coarse powder region 26.

As described above, even if the raw material powder contains aggregates of nanoparticles P2, by going through the dispersion process and the classification process in order, the agglomerated structure of nanoparticles P2 is dissolved, and the nanoparticles are finely dispersed. A powder material containing highly purified nanoparticle-attached metal particles P in which P2 is attached to the surface of the metal particle P1 can be produced. There is no need to perform subsequent operations such as sieving on the manufactured powder material in order to remove aggregates of nanoparticles P2. Therefore, a powder material made of nanoparticle-attached metal particles P can be easily produced. In particular, by using airflow type devices as both the dispersion device 10 and the classification device 20, and by continuously performing the dispersion step and the classification step, it is possible to further improve the simplicity of the manufacturing process and the manufacturing device. can.

[Produced powder material]
In the powder material manufactured by this manufacturing method, as shown in FIG. 2, nanoparticles P2 are dispersed and adhered to the surfaces of metal particles P1, forming nanoparticle-attached metal particles P. Here, the fact that the nanoparticle P2 is attached to the metal particle P1 means that the attractive force acting between the nanoparticle P2 and the metal particle P1 is at least the attractive force acting between the metal particles P1 when the nanoparticle P2 is not included. It refers to a state that is larger than.

Since the nanoparticles P2 are attached to the surface of the metal particles P1, the nanoparticles P2 are interposed between the metal particles P1, and a distance equal to or larger than the particle size of the nanoparticles P2 is maintained between the metal particles P1. Become. The attractive force acting between the metal particles P1, such as van der Waals force and electrostatic attraction, becomes smaller as the distance between the metal particles P1 becomes larger. In other words, the presence of the nanoparticles P2 ensures a distance between the metal particles P1, thereby reducing the attractive force between the metal particles P1. Thereby, the shear adhesion force (τ _s ) acting between the metal particles P1 can be reduced, and as a result, the fluidity of the powder material can be improved. For example, by adhering the nanoparticles P2, the shear adhesion force between the metal particles P1 can be made 50% or less, or even 40% or less, of the case where the nanoparticles P2 are not included.

The powder material produced by this production method does not substantially contain aggregates of nanoparticles P2 or nanoparticles P2 not attached to metal particles P1, other than nanoparticle-attached metal particles P. is preferable, and preferably does not contain aggregates of nanoparticles P2, at least at a level that can be visually recognized. If aggregates of nanoparticles P2 are contained in the powder material, the nanoparticles P2 constituting such aggregates are interposed between individual metal particles and are separated between metal particles P1. It cannot contribute to reducing the attractive force and increasing fluidity. Rather, the amount of nanoparticles P2 that can be attached to the surface of metal particles P1 decreases by the amount of nanoparticles P2 spent forming aggregates, which reduces the attractive force between metal particles P1 and increases fluidity. It becomes low. By reducing the aggregation of the nanoparticles P2 as much as possible, the fluidity of the manufactured powder material can be improved. By dissolving and removing aggregates of nanoparticles P2 through a dispersion process and a classification process, the shear adhesion force between metal particles P1 can be reduced to, for example, 80% or less compared to the case without these processes. It can be done.

Since the powder material has high fluidity, the powder material can be suitably used as a raw material for additive manufacturing. For example, when implementing a powder lamination melting method such as an SLM method or an EBM method among additive manufacturing methods, powder material is supplied from a hopper and spread over a base material to form a powder bed. At this time, since the powder material has high fluidity, the powder material can be stably flowed out from the hopper. Further, when spreading the powder material to form a powder bed using a recoater or the like, it becomes easier to spread the powder material densely and uniformly. Thus, it is important that the powder material has high fluidity in order to stably form a powder bed with high uniformity and density. Then, by irradiating the powder bed with high uniformity and density with energy rays and performing additive manufacturing, it becomes easier to form a homogeneous three-dimensional structure with fewer defects. Even in additive manufacturing using a powder deposition method such as the LMD method, by using a powder material with excellent fluidity, the powder material can be stably supplied to the nozzle. Moreover, when the powder material is injected along with the airflow from the nozzle toward the location where modeling is performed, clogging of the nozzle can be suppressed, and modeling can proceed stably.

In this way, in the powder material, the nanoparticles P2 are dispersed and attached to the surface of the metal particles P1, and the content of aggregates of the nanoparticles P2 is reduced, thereby increasing the fluidity of the powder material. be able to. As a result, when the powder material is used as a raw material for additive manufacturing, the additive manufacturing process can proceed smoothly and a three-dimensionally shaped object having a highly uniform structure can be obtained. Furthermore, if aggregates of nanoparticles P2 are contained in the powder material, such aggregates not only reduce the fluidity of the powder material but also cause defects that act as fracture starting points in the additively manufactured product. easy to form. In other words, eliminating the agglomerated structure of the nanoparticles P2 in the powder material is important when using the powder material as a raw material for additive manufacturing, both from the viewpoint of ensuring the fluidity of the powder material and eliminating the origin of fracture. This increases suitability.

In the manufactured powder material, the particle size and shape of the nanoparticle-attached metal particles P are substantially the same as those of the metal particles P1 used as the raw material powder. When a powder material is used as a raw material for additive manufacturing, the average particle size of the nanoparticle-attached metal particles P is preferably about 10 to 100 μm. Further, the circularity is preferably 0.90 or more, more preferably 0.95 or more in terms of average particle size.

Hereinafter, the present invention will be explained more specifically using Examples. Here, we investigated how the state and properties of the powder material change through the manufacturing process described above.

(Preparation of sample)
Metal particles made of a Ti-6Al-4V alloy (an alloy containing 6% by mass of Al and 4% by mass of V, with the remainder consisting of Ti and unavoidable impurities) were produced by a gas atomization method. Then, classification was performed at 15/45 μm. The obtained metal powder was designated as sample #1.

TiO ₂ nanoparticles (“TECNAPOW-TIO2” manufactured by TECNAN, average particle size 10 to 15 nm) without surface treatment were mixed with the metal powder of sample #1 to obtain a raw material powder. The amount of nanoparticles added was 0.02% by mass based on the mass of metal particles. The obtained raw material powder was passed through an air flow dispersion device (ring nozzle jet disperser "DN-155" manufactured by Nisshin Engineering Co., Ltd.) and an air flow classification device (turbo classifier "TC-" manufactured by Nisshin Engineering Co., Ltd.) similar to those shown in Fig. 1. 15'') was supplied to a powder material manufacturing apparatus connected to the powder material manufacturing apparatus for dispersion and classification. The metal particles to which the nanoparticles were attached were separated and designated as sample #2.

For comparison, a sample #3 was obtained by adding the same type and amount of TiO ₂ nanoparticles as those of sample #2 to the metal powder of sample #1 and only mixing them. Mixing was performed using a shaking powder mixer.

(Evaluation of powder materials)
First, in order to confirm the dispersion state of metal particles and nanoparticles, the state of the powder material was visually observed for sample #2 and sample #3. The condition of the sample was recorded by photography.

In addition, in order to confirm the state of the metal particles to which nanoparticles were added, the particle size distribution of Sample #1 and Sample #2 was evaluated. 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.

Furthermore, regarding sample #2, the state of the particles was observed using a scanning electron microscope (SEM). Further, elemental analysis was performed on a narrow region on the surface of the metal particles by energy dispersive X-ray spectroscopy (EDX) using SEM.

Finally, we investigated changes in the fluidity of the powder material depending on whether nanoparticles were added or not and how they were added. Specifically, the bulk density normalized shear adhesion force (τ _s /ρ) was measured for each of samples #1 to #3. For measurement, shear stress (τ) generated when pressure (σ) was applied to the powder material was measured using a rotating cell type shear test device in accordance with JIS Z 8835. Then, the shear adhesion force (τ _s ) was determined as the vertical axis intercept when σ was plotted on the horizontal axis and τ was plotted on the vertical axis. Moreover, the bulk density (ρ) was measured using a bulk specific gravity meter for metal powders in accordance with JIS Z 2504. Each measurement was performed under conditions of an air temperature of 24° C. and a relative humidity of 23%.

(Evaluation results)
(1) Dispersibility of nanoparticles Figures 3(a) and 3(b) show photographs of the state of the powder materials of samples #2 and #3, respectively. First, regarding the powder material that has been mixed only by the powder mixer shown in FIG. 3(b), granules that are photographed brightly are scattered among the aggregates of fine powder that are observed darkly. The diameter of this granule is approximately 1 mm, and can be associated with an aggregate of TiO ₂ nanoparticles based on color comparison. It is thought that the _TiO2 nanoparticles used as a raw material had formed an agglomerated structure before being mixed with the metal particles, and that the agglomerated structure was not completely eliminated only by mixing with a powder mixer. .

On the other hand, for sample #2, in which the powder material was dispersed and classified, dark-colored fine powder was uniformly observed over the entire image, as shown in Figure 3(a). The brightly photographed granules seen in 3(b) are not observed. In other words, in sample #2, a highly uniform powder material was produced. This indicates that through the dispersion/classification step, the agglomerated state of the TiO ₂ nanoparticle aggregates contained in the raw material powder was resolved, and the dispersibility of the nanoparticles was improved.

(2) Particle size distribution and circularity Figure 4 shows the particle size distribution of sample #1 made of metal particles without added nanoparticles and sample #2 made of metal particles with nanoparticles added and subjected to a dispersion/classification process. , and evaluation results of circularity for each particle size. Table 1 also shows parameters related to particle size distribution. Further, FIG. 5 shows particle images for samples #1 and #2 at a particle size of 20 μm±2 μm corresponding to the average particle size, as an example of the particle image used to obtain the circularity shown in FIG. 4. The average value of circularity obtained from these particle images was 0.96 for both samples #1 and #2. The circularity for each particle size shown in FIG. 4 is similarly calculated as an average value in the particle size range of ±2 μm.

According to FIG. 4, the particle size distributions of sample #1 to which no nanoparticles were added and sample #2 to which nanoparticles were added were very similar in terms of median value and width. The representative values shown in Table 1 are also almost the same for both. In other words, sample #1 and sample #2 have almost the same particle size distribution, and the particle size distribution of the sample particles has not changed substantially through the addition of nanoparticles and the dispersion/classification process. is confirmed.

When the particle images in FIG. 5 are compared between sample #1 and sample #2, there is no significant difference in particle shape between the two samples for many of the particles. As mentioned above, the average value of circularity is also 0.96, which is the same for both samples. Furthermore, according to FIG. 4, approximately the same degree of circularity is obtained in the entire grain size region. In other words, it is confirmed that the circularity does not change substantially through the addition of nanoparticles and the dispersion/classification process.

As described above, even after the addition of nanoparticles and the dispersion/classification process, the particle size and circularity of the particles constituting the powder material do not substantially change, and the dispersion/classification process It is confirmed that this does not affect the particle shape or size of the particles. Furthermore, the changes that occur when nanoparticles are added in properties of powder materials, such as shear adhesion, which will be evaluated later, are not due to changes in particle shape or particle size, but are the result of the addition of nanoparticles themselves. This is confirmed.

(3) Structure of metal particles to which nanoparticles are attached Figure 6 shows the results of SEM observation of the particles of sample #2. According to the low magnification image (scale bar: 20 μm) in FIG. 6(a), particles having a shape close to a sphere with a diameter of about 20 μm are observed. In other words, it is confirmed that most of the metal particles having a shape close to a sphere are dispersed without causing mutual aggregation.

According to the high magnification image (scale bar: 1 μm) in FIG. 6(b), a large number of particles of nano-order size are dispersed and attached to the surface of the spherical particles. FIG. 6(c) shows a higher magnification image (scale bar: 200 nm), and it can be seen that a large number of particles with dimensions of 100 nm or less are dispersed on the surface of the metal particles.

Furthermore, in FIG. 6(c), the elemental analysis results by EDX are shown in FIG. 7 for the position P1 where no nano-sized particles are present and the position P2 where nano-sized particles are present. According to this, C, O, Al, and Ti are detected at position P1, where no nanoparticles are attached and it is thought that the surface of metal particles made of Ti-6Al-4V alloy is observed. . Among these elements, Al and Ti correspond to the components of the metal particles. It is presumed that C originates from the carbon tape in which the sample powder was dispersed during SEM observation. It is thought that O originates from an oxide film inevitably formed on the surface of the metal particles.

Similarly to the position P1, C, O, Al, and Ti are detected at the position P2 where the nanoparticles are attached, but the concentration of O is significantly higher than that at the position P1. This is considered to be derived from _TiO2 nanoparticles. In other words, the nano-sized particles observed in the SEM image can be attributed to TiO ₂ nanoparticles attached to the surface of the metal particles. As confirmed in the SEM images of FIGS. 6(b) and 6(c), the TiO ₂ nanoparticles are highly dispersed and are distributed and attached to the entire surface of the metal particles. This confirms that by adding nanoparticles to metal particles and performing a dispersion/classification process, it is possible to produce a powder material in which the nanoparticles are dispersed and adhered to the surface of the metal particles.

(5) Fluidity of powder materials FIG. 8 shows the measurement results of bulk density normalized shear adhesion (τ _s /ρ) for samples #1 to #3. The unit is (m/s) ² . According to this, the value is about 48% smaller in sample #3, in which nanoparticles were added and only mixed using a powder mixer, compared to sample #1 to which nanoparticles were not added. . This is thought to be because at least some of the nanoparticles are interposed between the metal particles, reducing the attractive force between the metal particles and improving fluidity.

Furthermore, in sample #2 to which nanoparticles were added and the dispersion/classification process was performed, the bulk density normalized shear adhesion was reduced to 38% compared to sample #1. Even when compared with sample #3, the value is about 80% smaller. Therefore, by adding nanoparticles to metal particles and performing a dispersion/classification process in addition to mixing them, nanoparticles can reduce the attractive force between metal particles and improve fluidity. However, it can be seen that the effect is even higher.

Combining the above test results, we believe that by adding nanoparticles to metal particles with a particle size on the micron order and performing a dispersion/classification process, we can improve the dispersibility of the nanoparticles. It was confirmed that it could be attached to the surface of metal particles. The nanoparticles dispersed and attached to the surface of the metal particles are interposed between the metal particles, thereby reducing the attractive force between the metal particles and improving the fluidity of the powder material. By dispersing the nanoparticles through the dispersion/classification process, a large number of nanoparticles can adhere to the surface of the metal particles, which is considered to effectively contribute to reducing the attractive force between the metal particles.

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.

1 Powder material manufacturing device 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 P Nanoparticle-attached metal particles P1 Metal particles P2 Nanoparticles

Claims (5)

A raw material preparation step of preparing a raw material powder containing metal particles with an average particle size of 10 μm or more and 500 μm or less, and nanoparticles made of a metal oxide and not surface-treated with an organic substance ;
a dispersion step of introducing the raw material powder into an air flow dispersion device that disperses the agglomerated powder to eliminate agglomeration of the nanoparticles;
The powder material discharged with the air flow from the air flow dispersion device is directly introduced into an air flow classification device to classify the powder material and separate particles formed by the dispersed nanoparticles adhering to the metal particles. carrying out a classification process,
At a level that can be recognized visually, no granules consisting of aggregates of the nanoparticles are observed, and
A method for producing a powder material, wherein the nanoparticles are dispersed on the surface of the metal particles in the form of particles having a size of 100 nm or less . The method for producing a powder material according to claim 1 , wherein the metal particles are made of any one of a titanium alloy, a nickel alloy, a cobalt alloy, and an iron alloy. The nanoparticles are made of a metal oxide containing at least a part of the metal elements contained in the metal particles, or a metal oxide containing at least one light metal element selected from Si, Al, and Ti. A method for producing a powder material according to claim 1 or 2 . 4. The method for producing a powder material according to claim 3, wherein the nanoparticles are mainly composed of a metal element that is the main component of the metal particles. Any one of claims 1 to 4, wherein the content of the nanoparticles in the raw material powder is 0.001% by mass or more and 0.5% by mass or less based on the mass of the metal particles. The method for producing the powder material described in .

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