JP2021123745A - Method for producing powder material - Google Patents

Abstract

To provide a method for producing a powder material capable of suppressing the inclusion of excessively generated fine particles when producing a powder material having fine particles adhered on the surface of the metal particle through a thermal plasma treatment.SOLUTION: There is provided a method for producing a powder material, including: a plasma treatment step of performing thermal plasma treatment to raw material particles M consisting of metal to produce metal particles P1 having a higher circularity than the raw material particles M and fine particles P2 and P3 which comprise at least a part of metal elements constituting the metal particles P1 and have a particle size smaller than that of the metal particles P1, and then producing plasma-treated particles P' in which at least a part of the fine particles P2 is attached to the surface of the metal particles P1; and a grain cracking step of separating and removing a part of the fine particles P3 from the surface of the metal particles P1 of the plasma-treated particles P' using shearing by an air flow to fractionate the composite particles in which the remaining fine particles P2 are attached to the surface of the metal particles P1, in this order.SELECTED DRAWING: Figure 1

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 a laminated molding method.

In recent years, the development of additive manufacturing technology (AM) has been remarkable as a new technology for manufacturing three-dimensional shaped objects. As a kind of additional manufacturing technology, there is a laminated molding method using solidification of a powder material by irradiation with energy rays. Two typical methods of additive manufacturing using a metal powder material are the powder additive manufacturing method and the powder deposition method.

Specific examples of the powder laminating melting method include a selective laser melting method (SLM) and an electron beam melting method (EBM). 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 and electrons are placed at a predetermined position on the powder bed. Irradiate energy rays such as lines. Then, the powder material of the irradiated portion is solidified by melting and re-solidification, and a modeled object is formed. A three-dimensional model can be obtained by repeating the supply of the powder material to the powder bed and the modeling by irradiation with energy rays, and sequentially laminating the model in layers.

On the other hand, as a specific example of the powder deposition method, a laser metal deposition method (LMD) can be mentioned. In this method, a three-dimensional model having a desired shape is formed by injecting a metal powder at a position where a three-dimensional model is desired to be formed and at the same time irradiating a laser beam.

When a three-dimensional model made of a metal material is manufactured using the above-mentioned laminated modeling method, the resulting three-dimensional model has a structure in which the distribution of constituent materials such as voids and defects is uneven. May occur. It is desirable to suppress the formation of such a non-uniform structure as much as possible. In the laminated modeling method using a metal material, there are multiple possible causes for uneven distribution of the constituent materials inside the three-dimensional model to be manufactured, but one of the factors is the powder before irradiation with energy rays. The state of the material can have a great influence on the state of the resulting three-dimensional model.

For example, in the powder laminating and melting method, if the powder material can be smoothly supplied to the powder bed and a powder bed in which the powder material is uniformly spread can be stably formed, and in the powder bed, the powder material can be produced at a high density. If it can be filled, it is easy to obtain a highly homogeneous three-dimensional model by irradiating the powder bed with energy rays. Even in the powder deposition method, a three-dimensional model can be stably formed by smoothly supplying the powder material without blocking the nozzle. In this way, when a three-dimensional model is manufactured by the laminated modeling method, the higher the fluidity of the powder material used as a raw material, the smoother the supply of the powder material and the higher the density of filling can be promoted. , A highly uniform model can be obtained through irradiation with energy rays.

The inventors are studying a powder material having high fluidity suitable for use as a raw material for laminated molding, and a method capable of producing such a powder material. For example, in Patent Document 1, by heating raw material particles made of metal by thermal plasma treatment, the surface of the metal particles having a higher circularity than the raw material particles is more than at least a part of the metal elements constituting the metal particles. A manufacturing method is disclosed in which a metal powder material to which nanoparticles of a constituent metal or a metal compound are attached is manufactured. By improving the circularity of the metal particles and forming the nanoparticles, the fluidity of the obtained powder material can be increased and the filling property can be improved. As a result, the obtained powder material can be suitably used for laminated modeling.

JP-A-2019-112700

As described in Patent Document 1, by subjecting the metal particles to thermal plasma treatment, the circularity of the metal particles is improved, and fine particles are generated on the surface of the metal particles, and the fine particles are formed between the metal particles. It plays a role in securing a distance and improving the fluidity of the powder material. However, in plasma treatment, fine particles are likely to be excessively generated. For example, as the fine particles generated excessively, dust-like fine particles containing a metal oxide as a main component can be mentioned. If the produced powder material contains a large amount of metal oxide, it may affect the quality of the obtained three-dimensional model when the powder material is used as a raw material for laminated modeling. Therefore, in the powder material produced through the plasma treatment, it is preferable that the content of an excessive amount of fine particles such as soot-like fine particles is reduced as much as possible.

The problem to be solved by the present invention is a method for producing a powder material capable of suppressing the content of excessively generated fine particles when producing a powder material in which fine particles are adhered to the surface of metal particles through thermal plasma treatment. Is to provide.

In order to solve the above problems, the method for producing a powder material according to the present invention includes metal particles having a higher circularity than the raw material particles by subjecting the raw material particles made of metal to thermal plasma treatment, and the above-mentioned metal particles having a higher circularity than the raw material particles. Plasma-treated particles containing at least a part of metal elements constituting the metal particles and having a particle size smaller than that of the metal particles, and having at least a part of the fine particles adhered to the surface of the metal particles. A part of the fine particles is separated and removed from the surface of the metal particles of the plasma-treated particles by utilizing the plasma treatment step of producing the above and the shearing by the air flow, and the remaining fine particles are left on the surface of the metal particles. The pulverization step of separating the composite particles to which the particles are attached is carried out in this order.

Here, it is preferable to perform the pulverization step using an air flow classifier. In this case, it is advisable to classify the composite particles at the same time in the pulverization step.

In the composite particles, the average particle size of the metal particles is 10 μm or more and 500 μm or less, and the fine particles remaining on the surface of the metal particles are preferably nanoparticles. The average particle size refers to the particle size (d50) at which the integrated fraction under the sieve in the mass reference distribution is 50%.

The composite particles have a reduced shear adhesion force standardized by bulk density and an internal friction angle as compared with the raw material particles, and have a reduced oxygen concentration as compared with the plasma-treated particles. It is good. Further, it is preferable that the composite particles have a smaller shear adhesion force standardized by bulk density than the plasma-treated particles.

As the raw material particles, any of titanium alloy, nickel alloy, cobalt alloy, and iron alloy particles may be used. In this case, the raw material particles are made of an alloy containing an additive metal element selected from at least one of aluminum, magnesium, copper, and tin, and the metal particles constituting the composite particles and the additive metal elements are added to the fine particles. May be contained.

In the method for producing a powder material according to the above invention, in the plasma treatment step, the plasma-treated particles are formed as composite particles in which the fine particles are adhered to the surface of the metal particles whose circularity is improved by subjecting the raw material particles to thermal plasma treatment. However, in the plasma treatment step, fine particles are excessively generated, and the excess fine particles tend to adhere to the surface of the metal particles. The fine particles adhering to the surface of the metal particles improve the fluidity and filling property of the powder material, but the excessively generated fine particles do not show a high effect on improving the fluidity of the powder material, while the powder. It may increase the oxygen concentration of the material and affect the quality of products manufactured using powdered materials, such as three-dimensional shaped objects produced by the laminated molding method.

However, after the plasma treatment step, a pulverization step is carried out, leaving only some of the fine particles in a state of being attached to the surface of the metal particles, and separating and removing the other fine particles to start with soot-like fine particles. A powder material that does not contain excess fine particles can be produced. The composite particles constituting this powder material have fine particles adhered to the surface of the metal particles having an increased circularity, and due to the high circularity and the effect of securing the distance between the metal particles by the fine particles. , Shows high fluidity. Since the content of excess fine particles such as soot-like fine particles is reduced, the oxygen concentration of the powder material is suppressed to a small value, and the quality of products manufactured using the powder material is deteriorated. It is possible to suppress the influence of. Therefore, the produced powder material can be suitably used as a raw material for laminated modeling and the like.

Further, in this production method, by separating and removing excess fine particles by a pulverization step using shearing by an air flow, the obtained composite particles are less likely to be crushed or deformed, and plasma treatment is performed. It is easy to maintain the structure of the composite particles in which the fine particles are attached to the surface of the metal particles having a high circularity obtained in the step even after the pulverization step. Further, the separation / removal of excess fine particles can be carried out as a simple process without using a substance other than gas.

Here, when the pulverization step is performed using an air flow classifier, the separation of the fine particles excessively generated on the surface of the metal particles and the removal of the separated fine particles should be carried out effectively and easily. Can be done.

In this case, in the pulverization step, the classification of the composite particles can be performed at the same time. Then, a powder material having a controlled particle size distribution can be easily produced.

In the composite particles, when the average particle size of the metal particles is 10 μm or more and 500 μm or less and the fine particles remaining on the surface of the metal particles are nanoparticles, it is considered as a plasma treatment step. By the grain process, composite particles in which fine particles are attached to the surface of metal particles can be efficiently produced. In addition, the produced powder material can be suitably used for producing a three-dimensional model by a laminated modeling method.

When the shear adhesion force standardized by bulk density and the internal friction angle are reduced in the composite particles as compared with the raw material particles, and the oxygen concentration is reduced as compared with the plasma-treated particles. , The powder material has acquired high fluidity by improving the circularity and generating fine particles through the plasma treatment step and the pulverization step, and the oxygen concentration has been reduced by separating and removing excess fine particles. This is shown as the physical characteristics of the powder material, and the produced powder material can be suitably used for the production of a three-dimensional modeled product by a laminated modeling method or the like.

Furthermore, in the case of composite particles, when the shear adhesion force standardized by bulk density is smaller than that of plasma-treated particles, the fluidity of the powder material is due to the separation and removal of excess fine particles by the pulverization step. It is shown as the physical characteristics of the powder material that the powder material is further enhanced, and the produced powder material can be particularly preferably used for the production of a three-dimensional modeled product by the laminated modeling method.

When any of titanium alloy, nickel alloy, cobalt alloy, and iron alloy particles is used as the raw material particles, the powder material to be produced is a tertiary material composed of those alloys that are in great demand for production using the laminated molding method. It can be suitably used as a raw material for the original model.

In this case, if the raw material particles are made of an alloy containing an additive metal element selected from at least one of aluminum, magnesium, copper, and tin, the sublimation of the additive metal element contained in the raw material particles in the plasma treatment step. Then, composite particles containing the above-mentioned additive metal element are likely to be formed in the metal particles and the fine particles.

It is a figure explaining the plasma processing process in the manufacturing method of the powder material which concerns on one Embodiment of this invention. It is a figure explaining the pulverization process in the manufacturing method of the said powder material. It is a schematic diagram which shows the powder material obtained by the said manufacturing method, (a) shows the plasma-treated particle obtained by the plasma processing step, and (b) shows the composite particle further obtained through a pulverization step. It is a figure which shows the measurement result of the particle size distribution and the circularity of a powder material. Sample # 1 is a raw material particle, sample # 2 is a plasma-treated particle that has undergone a plasma treatment step, and sample # 3 is a composite particle that has undergone a further pulverization step. For samples # 1 to # 3, particle images used for evaluating the particle shape are shown in the range of particle size 20 ± 2 μm. An SEM observation image is shown for sample # 1. An SEM observation image is shown for sample # 2. The images are high-magnification in the order of (a), (b), and (c). An SEM observation image is shown for sample # 3. The images are high-magnification in the order of (a), (b), and (c). It is a figure which shows the measurement result of the bulk density standardized shear adhesion force about samples # 1 to # 3. It is a figure which shows the measurement result of the internal friction angle about samples # 1 to # 3. It is a figure which shows the measurement result of the oxygen value about samples # 1 to # 3. It is a figure which shows the measurement result of the specific surface area about samples # 1 to # 3.

Hereinafter, a method for producing a powder material according to an embodiment of the present invention will be described in detail with reference to the drawings. In this production method, a powder material containing composite particles P having a predetermined structure is produced from raw material particles M made of metal.

As shown in FIG. 3B, the powder material produced by this production method contains composite particles P in which fine particles P2 having a particle size smaller than that of the metal particles P1 are attached to the surface of the metal particles P1. Such a powder material can be suitably used as a raw material or the like for producing a three-dimensional model by irradiating an energy ray in a laminated modeling method.

[Manufacturing method of powder material]
In the method for producing a powder material according to an embodiment of the present invention, the raw material preparation step, the plasma treatment step, and the granulation step are carried out in this order. Hereinafter, each step will be described in order.

(1) Raw material preparation step In the raw material preparation step, raw material particles M for producing a powder material are prepared. The raw material particles M are made of metal. The raw material particles M preferably have a particle size on the order of microns.

Since the metal material constituting the raw material particles M is a powder material produced while maintaining the alloy composition substantially, and further, a metal material constituting a product manufactured using the powder material such as a three-dimensional modeled product. , Raw material particles M may be prepared as metal particles having a desired alloy composition in a product manufactured by using a powder material. The alloy composition is not particularly limited, but titanium alloys, nickel alloys, cobalt alloys, and iron alloys can be exemplified as suitable examples of the alloys constituting the raw material particles M. This is because there is a great demand for producing three-dimensional shaped objects using these alloys as raw materials by the laminated molding method. Further, the alloy constituting the raw material particles M preferably contains a metal element (added metal element) that easily sublimates, such as aluminum, magnesium, copper, and tin. This is because these elements are metals that easily cause sublimation, and in the subsequent plasma treatment step, fine particles P2 are easily formed on the surface of the metal particles P1 by sublimation. As an example of a suitable composition of the raw material particles M, a Ti-Al alloy represented by a Ti-6Al-4V alloy can be mentioned.

The raw material particles M have substantially no fine particles on the surface. It may have fine particles, but even in that case, the amount of the fine particles is suppressed to a negligible level as compared with the amount of the fine particles P2 adhering to the metal particles P1 obtained through the plasma treatment step. Further, the raw material particles M may contain a metal compound such as a metal oxide or an organic component as a part of the composition, but the content of these components is included in the subsequent production process or the obtained composite particle P. The raw material particles M are preferably made of only metal, except for the raw material residue, the components in the atmosphere, the components unavoidably contained due to the manufacturing process, and the like so as not to affect the characteristics.

The method for producing the raw material particles M is not particularly limited, but it is preferable to use the atomizing method. The atomizing method obtains metal particles by solidifying the molten alloy in the form of minute droplets. A gas atomization method that generates minute droplets by injecting molten alloy into a vacuum and spraying an inert gas onto the injected molten alloy, or dropping droplets on a disk that rotates at high speed and using centrifugal force to create minute particles. A disk atomizing method that produces various droplets can be applied. In the atomizing method, metal particles having a particle size on the order of microns can be efficiently obtained. The atomizing method can be applied to various alloy compositions. Further, since it has a particle size on the order of microns and it is easy to obtain metal particles having a high degree of circularity to some extent, it is suitable for use in the production of raw material particles M in the production method according to the present embodiment. In particular, the gas atomizing method is suitable from the viewpoint of production efficiency and convenience of metal particles.

The raw material particles M produced by the atomizing method or the like may be appropriately classified to adjust the particle size distribution. The composite particles P obtained through the subsequent plasma treatment step and the pulverization step have an average particle size similar to that of the raw material particles M. The particle size distribution of the raw material particles M may be adjusted based on the desired average particle size. The classification of the raw material particles M can be performed, for example, by using an air flow classifier similar to that used in the subsequent pulverization step.

(2) Plasma treatment step In the next plasma treatment step, the raw material particles M prepared in the raw material preparation step are subjected to thermal plasma treatment.

As shown in FIG. 1, the thermal plasma treatment can be performed by the plasma processing apparatus 10. In the plasma processing apparatus 10, a plasma arc PL is generated by applying a high frequency from the high frequency induction coil 11 to the plasma gas G. By increasing the output of the plasma arc PL, thermal plasma can be generated, and the substance passing through the plasma can be instantly heated to a high temperature.

In the plasma processing step, the raw material particles M are passed through the plasma arc PL generated by the plasma processing apparatus 10. The raw material particles M are instantly heated to a high temperature by the plasma arc PL to eliminate agglutination between the metal particles and cause melting or sublimation on the surface of the metal particles P1. Then, it is rapidly cooled at a position where it has passed through the plasma arc PL, and as shown in FIG. 3A, it becomes plasma-treated particles P'having fine particles P2 on the surface of the metal particles.

The raw material particles M obtained by the atomizing method often cause agglomeration. However, by heating the raw material particles M by thermal plasma treatment or the like, the agglutination is eliminated. As a result, the obtained metal particles P1 have an improved circularity as compared with the raw material particles M.

When the raw material particles M are further heated, the structure at least near the surface of the raw material particles M is melted or sublimated. By causing melting or sublimation, the particle shape and surface structure initially possessed by the raw material particles M are temporarily eliminated. When the raw material particles M are rapidly cooled, the melted or sublimated material is re-solidified, and at that time, the specific surface area is reduced and the surface is smoothed by the effect of the surface free energy. As a result, metal particles P1 having a higher circularity than the raw material particles M are generated.

Further, when the structure near the surface of the raw material particles M is melted or sublimated and rapidly cooled and solidified on the surface of the raw material particles M, the melted or sublimated material is used as a raw material on the surface of the metal particles P1 obtained by recoagulation. , Fine particles P2 are generated. The fine particles P2 are formed as particles containing at least a part of the metal elements constituting the metal particles P1 and having a particle size smaller than that of the metal particles P1. The generated fine particles P2 are attached to the surface of the metal particles P1.

In particular, when the component composition of the raw material particles M contains a metal element such as Al, Mg, Cu, Sn, which is more easily sublimated than other component metal elements, the metal that is easily sublimated or the original The alloy having a higher concentration of the metal that easily sublimates than the component composition of the raw material particles M preferentially sublimates from the raw material particles M. Then, when resolidifying on the surface of the metal particles P1 having an increased circularity, fine particles P2 are likely to be formed on the surface of the metal particles P1 due to the difference in behavior regarding resolidification with other component metals. In this case, in the produced composite particle P, the element that easily sublimates is contained in both the metal particle P1 and the generated fine particles P2. As the titanium alloys, nickel alloys, cobalt alloys, and iron alloys listed above as examples of the metal species constituting the raw material particles M, those containing easily sublimable metal elements such as Al, Mg, Cu, and Sn are known. Is.

In the fine particles P2 formed by sublimating the metal material constituting the raw material particles M from the surface by the plasma treatment step, the state taken by the metal element is not particularly limited, and even if it is in the metal state, at least one state is taken. The part may be in the state of a metal compound. In the plasma arc PL, the generated metal fine particles are immediately oxidized, and at least the surface portion of the fine particles P2 tends to become a metal oxide.

In the plasma-treated particles P'obtained through the plasma treatment step, as described above, the fine particles P2 are generated by adhering to the surface of the metal particles P1, and as will be described in detail later, the attractive forces acting between the metal particles P1 are mutual. It plays a role in reducing the action and improving the fluidity of the powder material, but in the plasma treatment process, an excess amount of fine particles (excess fine particles) P3 is generated in excess of the amount sufficient to play such a role. May be done. Similar to the fine particles (adhered fine particles) P2 attached to the surface of the metal particles P1, at least a part of the metal elements constituting the raw material particles M is sublimated and resolidified in the plasma arc PL in the excess fine particles P3. It is a fine particle to be produced, has a particle size smaller than that of the metal particle P1, and is in a state of at least a part of a metal oxide.

In some cases, there is no clear difference between the adhered fine particles P2 on the surface of the metal particles P1 and the excess fine particles P3 in various properties such as component composition, shape, size, and interaction with the metal particles P1. However, while the adhered fine particles P2 are generated in a state of being firmly adhered to the surface of the metal particles P1, the excess fine particles P3 have a weaker adhesive force to the metal particles P1 than the adhered fine particles P2, and are dust-like fine particles. Often generated as. In this case, as shown in a later example, the excess fine particles P3 are weakly bound to the metal particles P1 so as to be deposited on the outside of the adhered fine particles P2 firmly attached to the surface of the metal particles P1. Easy to generate with. Further, a part of the excess particles P3 is contained in the plasma-treated particles P'in a form of being mixed with the composite particles P to which the fine particles P2 are attached to the metal particles P1 without adhering or accumulating on the surface of the metal particles P1. In some cases.

As described above, by performing the thermal plasma treatment on the raw material particles M, the metal particles P1 having a high circularity and the fine particles P2 and P3 having a particle size smaller than the metal particles P1 are generated, and the plasma-treated particles. P'is obtained. In the plasma-treated particles P', at least a part of the fine particles generated by heating by the plasma arc PL is firmly adhered to the surface of the metal particles P1 as the adhered fine particles P2, and the excess fine particles are excessively generated fine particles. It also contains P3.

(3) Dissolution Step The plasma-treated particles P'obtained in the plasma treatment step are then subjected to the granulation step. In the pulverization step, excess fine particles P3 are separated and removed by utilizing shearing due to an air flow.

In the pulverization step, the specific method is not particularly limited as long as the excess fine particles P3 can be separated from the surface of the metal particles P1 by pulverization and removed by utilizing shearing by an air flow. .. However, as shown in FIG. 2, it is preferable to carry out the pulverization step using the air flow classifier 20.

The airflow classifier 20 is originally a device used for classifying powder materials, that is, selecting particle sizes using airflow, but depending on the selection of operating conditions or the like, shearing of aggregates of particles, that is, aggregation The structure can be eliminated. As the airflow classifier 20, it is preferable to use a forced vortex type airflow classifier as disclosed in Japanese Patent Application Laid-Open No. 2003-145502.

This type of airflow classification device is provided with a classification rotor 24 that rotates at high speed and a dispersion blade 22, and when the classification rotor 24 is rotated, a shear flow is generated in the gap 23 between the casing 21 and the dispersion blade 22. appear. When the powder material is put into the shear flow from the supply port 21a, the powder material is pulverized by the shearing force while passing through the void 23. The particles after pulverization receive the centrifugal force of the classification rotor 24 and the drag force of the air flow from the classification blade 55. At this time, the coarse powder and the fine powder are separated by the centrifugal force and the drag force acting on the particles according to the particle size. Large-diameter particles (coarse powder) having a large centrifugal force move to the coarse powder region 26, while small-diameter particles (fine powder) having a large drag force move to the fine powder region 27.

In the granulation step of the manufacturing method according to the present embodiment, the powder containing the plasma-treated particles P'released from the plasma treatment apparatus 10 through the above-mentioned plasma treatment step is charged into the airflow classifier 20 together with air. do. The plasma-treated particles P'injected into the airflow classifier 20 from the supply port 21a receive shearing force due to the airflow while passing through the gap 23 between the dispersion blade 22 and the casing 21, and cause granulation. As a result, the excess fine particles P3 are pulverized and separated from the surface of the metal particles P1 and move to the fine powder region 27. On the other hand, the adhered fine particles P2 maintain the state of being adhered to the surface of the metal particles P1 as shown in FIG. 3B, and maintain the state of forming the composite particles P together with the metal particles P1. The composite particle P moves to the coarse powder region 26. In this way, the excess particles P3 can be separated / removed from the surface of the metal particles P1 and the composite particles P can be separated from the coarse powder region.

As described above, the excess fine particles P3 are in the state of soot-like fine particles and the like, and in many cases, the adhesive force to the metal particles P1 is weaker than that of the adhered fine particles P2. The adhered fine particles P2 can easily separate and remove excess fine particles P3 from the surface of the metal particles P1 while maintaining the state of being attached to the surface of the metal particles P1. Even if there is no large difference between the adhered fine particles P2 and the excess fine particles P3 in the interaction with the metal particles P1, it is manufactured by adjusting the operating conditions of the airflow classifying machine 20 such as the rotation speed of the classifying rotor 24. The remaining fine particles can be removed from the surface of the metal particles P1 as excess fine particles P3 while leaving an amount of fine particles necessary for improving the fluidity of the powder material as attached fine particles P2 on the surface of the metal particles P1. .. The metal particles P1 are substantially unaffected by airflow such as crushing and deformation, and substantially maintain the structure taken by the plasma-treated particles P'.

Since the pulverization step is carried out by using the airflow classifier 20 which is supposed to sort the particle size of the particles as the original use, it is performed at the same time as the separation / removal of the excess fine particles P3 using shearing by the airflow. The classification of the composite particles P in which the adhered fine particles P2 are attached to the metal particles P1, that is, the adjustment of the particle size distribution can be performed at the same time. Specifically, by selecting the operating conditions of the airflow classifier 20 such as the rotation speed of the classifying rotor 24, the excess fine particles P3 are pulverized and separated from the plasma-treated powder P'to generate composite particles P, and the composite particles P are generated. Among the produced composite particles P, those having a desired particle size can be selected, guided to the coarse powder region 26, and sorted.

As described above, in the pulverization step, excess fine particles P3 corresponding to a part of fine particles are separated and removed from the surface of the metal particles P1 constituting the plasma-treated particles P'by utilizing shearing by the air flow. The composite particles P to which the adhered fine particles P2, which are the remaining fine particles, are attached to the surface of the metal particles P1 can be separated. At the same time, the composite particles P can be classified.

In the form described above, the pulverization step is performed by using the airflow classifying machine 20, but the airflow classifying machine 20 may be used instead of the airflow classifying machine 20 or in combination with the airflow classifying machine 20. .. The airflow disperser uses a ring nozzle or the like to generate a high-speed airflow and collide with the powder. The powder is accelerated by the air flow, and the agglomerated state between the particles is eliminated and dispersed by the collision between the particles, the collision with the wall surface of the device, and the application of the shearing force. Even if such an air flow disperser is used, the excess fine particles P3 can be separated and removed from the surface of the metal particles P1 in the plasma-treated particles P'.

The pulverization step may be performed using only the airflow disperser, but it is preferable to arrange the airflow disperser in front of the airflow classifier 20. That is, the plasma-treated particles P'may be first passed through the airflow disperser, and the powder released from the airflow disperser may be introduced into the airflow classifier 20. The air flow disperser separates the excess fine particles P3 from the surface of the metal particles P1 constituting the plasma-treated particles P'. Then, the powder containing the separated excess fine particles P3 together with the composite particles P is released from the air flow disperser. By introducing the powder released from this air flow disperser into the air flow classifier 20, the separation of the excess fine particles P3 from the surface of the metal particles P1 is further promoted, and the composite particles P from which the excess fine particles P3 have been removed are produced. , The composite particle P can be separated by spatially separating it from the excess fine particle P3. Further, the composite particle P can be classified. When the airflow disperser is provided in front of the airflow classifier 20, the discharge port from which the processed powder material is discharged from the airflow disperser and the supply port 21a for charging the powder material into the airflow classifier 20 are directly connected. It is good to do it. Then, the powder discharged from the airflow disperser together with the airflow is introduced into the airflow classifier 20 directly, that is, without coming into contact with the external environment. The processing according to 20 can be continuously performed.

[Powder material to be manufactured]
As shown in FIG. 3B, the powder material produced by the production method according to the present embodiment contains composite particles P to which fine particles P2 are attached to the surface of metal particles P1 having a shape close to a sphere. .. The powder material does not contain excess fine particles P3 except for unavoidable components that could not be completely removed in the granulation step.

The metal particles P1 constituting the composite particles P have substantially the same particle size as the primary particle size of the raw material particles M, and have substantially the same component composition as the raw material particles M. The particle size of the metal particles P1 is substantially equal to the particle size of the composite particles P as a whole, and the average particle size is preferably 10 μm or more from the viewpoint of suitability as a raw material for laminated molding. Further, it is preferably 500 μm or less, particularly preferably 100 μm or less. The average particle size refers to the particle size (d50) at which the integrated fraction under the sieve in the mass reference distribution is 50%.

The metal particles P1 have a higher circularity than the raw material particles M, have a highly symmetric shape, and have a smooth surface after being melted and resolidified on the surface portion by a plasma treatment step. Since the metal particles P1 have a high circularity, the internal friction angle (φ) in the powder material becomes small due to the effect of the shape. Then, the easiness of collapsing of the aggregate of the powder material is improved, and the fluidity of the powder material is increased. Further, when the metal particles P1 are spread as a powder bed or the like, the powder material can be densely filled, and the filling property is improved. Preferably, the circularity of the composite particles P is 0.90 or more, more preferably 0.95 or more, in terms of average particle size.

When the plasma treatment step is carried out using the raw material particles M having a particle size on the order of micron, nanoparticles are likely to be formed as adhered fine particles P2 on the surface of the metal particles P1 having a particle size on the order of micron. Specifically, the adhered fine particles P2 having an average particle size of 1 nm or more and 200 nm or less are likely to be formed.

As described above, the metal element constituting the adhered fine particles P2 is composed of at least one of the raw material particles M and the metal elements constituting the metal particles P1 that have undergone thermal plasma treatment. Since the metal element contained in the adhered fine particles P2 is the same as at least a part of the metal element contained in the metal particles P1, the metal particles are produced in a product manufactured by using a powder material such as a three-dimensional model. It does not contain any metal elements other than those constituting P1. The shape of the adhered fine particles P2 is not particularly limited, but it is likely to take an irregular shape because it is formed through melting or sublimation and resolidification of the constituent materials of the raw material particles M.

Due to the presence of the adhered fine particles P2 on the surface of the metal particles P1, the adhered fine particles P2 are interposed between the metal particles P1 and a distance equal to or larger than the particle size of the fine particles 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 attractive force becomes smaller as the distance between the metal particles P1 increases. That is, due to the presence of the adhered fine particles P2, the attractive force between the metal particles P1 is reduced by securing the distance between the metal particles P1. As a result, 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 increased.

As described above, in the production method according to the present embodiment, the raw material particles M are heated by thermal plasma treatment to form composite particles P in which fine particles P2 are attached to the surface of the metal particles P1 having improved circularity, thereby forming a circular shape. Due to the effects of both the improvement of the degree and the adhesion of the fine particles P2, the shear adhesion force (τ _s ) acting between the metal particles P1 is reduced as compared with the original raw material particles M. In addition, the internal friction angle (φ) is also reduced. As a result, the fluidity of the powder material is improved. In addition, the filling property of the powder material is also improved. For example, in the composite particles P (after the granulation step is performed) obtained through the plasma treatment step, the bulk density standardized shear adhesion force (bulk density standardized shear adhesion force), which is a value obtained by standardizing the shear adhesion force by the bulk density as compared with the raw material particles M. τ _s / ρ) can be reduced to 60% or less, and further to 55% or less. Further, the internal friction angle (φ) can be reduced to 90% or less of the raw material particles M with tanφ.

By improving the fluidity and filling property of the powder material, the powder material can be suitably used as a raw material for laminated modeling. For example, in the additive manufacturing method, when the powder layered melting method such as the SLM method or the EBM method is carried out, the powder material is supplied from the hopper and spread on the base material to form a powder bed. At this time, since the powder material has high fluidity, the powder material can be stably discharged from the hopper. Further, when the powder material is spread using a recorder or the like to form a powder bed, the powder material has high fluidity and filling property, so that the powder material can be spread with high density and homogeneity. It will be easier to do. By increasing the packing density of the powder bed, the homogeneity of the obtained three-dimensional model is also improved. Even in the laminated molding by the powder deposition method such as the LMD method, the powder material can be stably supplied to the nozzle by using the powder material having excellent fluidity. Further, when the powder material is injected together with the air flow from the nozzle to the portion to be modeled, the nozzle can be suppressed from being blocked and the modeling can be stably advanced.

Further, in the powder material obtained by the production method according to the present embodiment, the excess fine particles P3 generated in the plasma treatment step are pulverized and separated from the composite particles P by undergoing the pulverization step utilizing shearing by the air flow. , Has been removed. When the raw material particles M made of metal are subjected to thermal plasma treatment, excess fine particles P3 such as soot-like fine particles are inevitably generated. The excess fine particles P3 can be separated and removed while maintaining the structure of the particles P.

As described above, by interposing the fine particles P2 between the metal particles P1, the attractive force between the metal particles P1 is reduced and the fluidity of the powder material is improved. The effect of improving sex is saturated. Rather, the excessive presence of fine particles containing a metal compound such as an oxide may affect the quality of a metal product produced from a powder material by laminated molding or the like through the generation of impurities or the like. However, in the powder material obtained by this production method, excess fine particles P3 are separated and removed, and the excess fine particles P3 such as soot-like fine particles are not contained except for unavoidable components, so that the oxide in the powder material is not contained. The content of the metal compound such as the above can be suppressed, and the influence on the quality of the product due to the excessive content of the metal compound can be reduced.

For example, in the composite particles P obtained through the pulverization step after the plasma treatment step, the oxygen concentration in the powder material (as compared with the plasma-treated particles P'containing the excess fine particles P3 before the pulverization step, Oxygen value) can be reduced to 90% or less. The removal of the excess fine particles P3 can also be evaluated by the specific surface area of the powder material, and the specific surface area can be reduced to 70% by performing the pulverization step on the plasma-treated particles P'containing the excess fine particles P3. It can be reduced to:

In this production method, since the pulverization step is carried out by using shearing by an air flow, separation / removal of excess fine particles P3 is sufficiently achieved in the produced powder material, while the adhered fine particles P2 are circular. The structure of the composite particles P adhering to the surface of the metal particles P1 having a high degree of degree is maintained almost unaffected even after the pulverization step. The excess fine particles P3 may be separated / removed by using mechanical means such as a jet mill or a rotating body. In such a case, the adhered fine particles to be left on the surface of the metal particles P1. It is difficult to maintain the structure of the composite particle P because there is a possibility that the metal particles P2 may be removed, and further, the metal particles P1 may be affected by crushing or deformation. In the case of shearing due to an air flow, a violent mechanical stimulus is not applied to the composite particles P, so avoid these situations and provide the composite particles P in which the fine particles P2 are attached to the surface of the metal particles P1 having a high circularity. It becomes a thing. Further, the excess fine particles P3 separated from the composite particles P can be separated by a wet method such as ultrasonic vibration, but in that case, it is necessary to use a medium, and the excess fine particles P3 separated from the composite particles P need to be used. Unless the medium containing the fine particles P3 is removed by filtration or the like, the composite particles P cannot be obtained in the form of powder. However, by separating the excess fine particles P3 by shearing with an air flow, a substance other than a gas to be introduced into the air flow classifier 20 together with the plasma-treated particles P', such as a liquid medium, for separating and removing the excess fine particles P3. It is not necessary to use the above, and a powder material containing the composite particles P in high purity can be obtained without performing steps such as filtration and purification after the separation of the excess fine particles P3.

Due to the fact that the structure of the composite particle P does not change or the mixture of other substances does not occur due to the pulverization step, the fluidity and filling property of the composite particle P improved through the plasma treatment step are pulverized. It will be maintained at a high level even after going through the process. That is, in the plasma treatment step, the circularity of the metal particles P1 is improved and the adhered fine particles P2 are generated, so that the shear adhesive force (τ _s ) and the internal friction angle (φ) of the powder material are reduced, but the particles are pulverized. Even after the step, the shear adhesion force (τ _s ) and the internal friction angle (φ) are maintained in a state of being reduced as compared with the raw material particles M through the plasma treatment step. Further, the value of the bulk density normalized shear adhesion force (τ _s / ρ) may be further reduced by passing through the pulverization step as compared with the case where only the plasma treatment step is passed. It is considered that this is because among the fine particles generated in the plasma treatment step, those that do not substantially contribute to the improvement of the shear adhesion force but rather show a high adhesion force are removed.

As described above, the powder material produced by the production method according to the present embodiment is a composite particle composed of metal particles P1 whose circularity has been increased through a plasma treatment step and fine particles P2 adhering to the metal particles P1. By containing P, it is excellent in fluidity and filling property. Further, by passing through the pulverization step, the excess amount of fine particles P3 generated in the plasma treatment step is separated and removed while maintaining the structure of such composite particles P, so that the increase in oxygen content is suppressed. Has been done. Therefore, the produced powder material can be suitably used for producing a three-dimensional model by the laminated modeling method.

Hereinafter, the present invention will be described in more detail with reference to Examples. Here, it was investigated how the state and properties of the powder material change by going through each of the manufacturing processes 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 and the balance 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 used as sample # 1.

The metal powder of sample # 1 was subjected to thermal plasma treatment using a plasma treatment device, and the obtained plasma-treated particles were used as sample # 2. Further, the sample # 2 was subjected to a pulverization treatment using an air flow classifier, and the pulverization and the classification were performed. The composite particles in which the fine particles were attached to the metal particles were separated and used as sample # 3.

(Evaluation of powder material)
First, in order to confirm the state of the metal particles in each sample, the particle size distribution was evaluated for the samples # 1 to # 3. 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, for each sample, the state of the particles was observed using a scanning electron microscope (SEM).

Furthermore, the characteristics and chemical state of samples # 1 to # 3 were evaluated. Each evaluation was performed under the conditions of a temperature of 24 ° C. and a relative humidity of 23%. As the characteristics of each sample, first, the bulk density normalized shear adhesion force (τ _s / ρ) and the internal friction angle (φ) were evaluated. In the measurement, the shear stress (τ) generated when pressure (σ) was applied to the powder material was measured using a rotary cell type shear test device in accordance with JIS Z 8835. _{Then, the shear adhesion force (τ s} ) was obtained as the vertical intercept when σ was plotted on the horizontal axis and τ was plotted on the vertical axis. The bulk density (ρ) was measured using a bulk specific gravity measuring device for metal powder in accordance with JIS Z 2504. Further, the internal friction angle (φ) was calculated by using a plot with σ on the horizontal axis and τ on the vertical axis, which was used for measuring _{the shear adhesion force (τ s), and the slope of the approximate straight line as tanφ.}

As an evaluation of the chemical state, the oxygen value was measured. At this time, the oxygen concentration in each sample (the ratio of the mass of oxygen atoms to the total mass of the sample) was measured by the gas analysis method and used as the oxygen value. Furthermore, the specific surface area was measured for each sample. The specific surface area was measured by the BET adsorption method using Kr as the adsorption gas.

(Evaluation results)
(1) Particle size distribution and circularity Figure 4 shows a sample # 1 composed of raw material particles, a sample # 2 in which the raw material particles were subjected to thermal plasma treatment, and a sample # in which the raw material particles were further pulverized using an air flow classifier. For No. 3, the particle size distribution and the evaluation result of the circularity for each particle size are shown. In addition, Table 1 below summarizes the parameters related to the particle size distribution and the values of circularity at a particle size of 20 μm ± 2 μm corresponding to the average particle size. Further, FIG. 5 shows, as an example of the particle image used for obtaining the circularity shown in FIG. 4, a representative example of the particle image having a particle size of 20 μm ± 2 μm for each sample.

According to the particle size distribution in FIG. 4 and the particle size values in Table 1, the particle size distributions of the sample # 1 corresponding to the raw material particles and the sample # 2 subjected to the thermal plasma treatment are similar in terms of median value and width. It has become. On the other hand, the circularity has been improved through thermal plasma treatment. In particular, the improvement in circularity is remarkable in a region where the particle size is large. Looking at the particle image of FIG. 5, in sample # 1, two particles having the same diameter are attached to each other like the third image from the left, or the sixth image from the left. In addition, relatively many particles having a distorted shape are observed, such as particles having a diameter of about 10 μm and small particles having a diameter of about several μm attached to the particles. On the other hand, in sample # 2, the irregularity of the particle shape is reduced. From these results, it is confirmed that the circularity of the metal particles is improved by the thermal plasma treatment.

Further, when the sample # 2 and the sample # 3 that has undergone the pulverization treatment are compared, in the particle size distribution of FIG. 4, the distribution on the small diameter side decreases and the distribution shifts to the slightly larger diameter side in the sample # 3. You can see that. The distribution width is also small. The particle size values in Table 1 also have an increased d10 value in sample # 3, which is consistent with the tendency seen in FIG. The roundness shows a slight improvement. As a result of these results, the metal powder of sample # 2 that had undergone the plasma treatment step contained a large amount of fine powder formed as excess fine particles, whereas the metal powder was pulverized using an airflow classifier. Therefore, in sample # 3, it is interpreted that these fine particles have been removed.

(2) Structure of metal particles Figures 6 to 8 show the results of SEM observation of the particles of samples # 1 to # 3, respectively. The observation magnification is 5,000 times in FIGS. 6 and 7 (a) and 8 (a). Further, (b) of FIGS. 7 and 8 is 10,000 times, and (c) is 100,000 times.

First, comparing the SEM images of sample # 1 in FIG. 6 and sample # 2 in FIG. 7, the particles in sample # 1 have a slightly distorted shape, whereas in sample # 2, the overall shape of the particles. However, it is approaching a sphere. This is also in agreement with the results obtained in the above circularity evaluation. Then, in sample # 2, a large number of nano-order convex structures are distributed on the surface of the particles, and it is confirmed that the formation of fine particles has occurred on the surface of the metal particles through the thermal plasma treatment.

Further, when the SEM images of the sample # 2 of FIG. 7 and the sample # 3 of FIG. 8 are compared, it can be seen that the density of the fine particles on the surface of the metal particles in the sample # 3 is lower than that in the sample # 2. In particular, when comparing the high-magnification image of (c), in sample # 2, many structures are formed such that other fine particles are piled up on the outside where the fine particles are attached to the surface of the metal particles. On the other hand, in sample # 3, the structure in which the fine particles are piled up is almost eliminated, and most of the remaining fine particles are in a state of being directly attached to the surface of the metal particles. From this, it is confirmed that a part of the fine particles generated by the thermal plasma treatment is removed from the surface of the metal particles through the pulverization step using the air flow classifier. In particular, it can be said that the fine particles that are not firmly adhered to the surface of the metal particles are preferentially removed.

(3) Characteristics and chemical state of powder material Fig. 9 shows the measurement results of _{bulk density normalized shear adhesion force (τ s / ρ) for samples # 1 to # 3.} The unit is (m / s) ² . According to this, the value of the bulk density normalized shear adhesion force is reduced to about 53% from sample # 1 to sample # 2 through thermal plasma treatment. This is associated with the fact that the attractive force between the metal particles is reduced by forming fine particles on the surface of the metal particles through the thermal plasma treatment.

Even after the pulverization step from sample # 2 to sample # 3, the value of bulk density normalized shear adhesion did not increase. This suggests that the structure of the composite particles in which the fine particles are attached to the surface of the metal particles is maintained even after the pulverization step using the air flow classifier. Rather, in sample # 3, the bulk density standardized shear adhesion force is further reduced, although it is about 5% with respect to sample # 2. It is presumed that this is because the fine powder with high adhesive force was removed by the pulverization process using the air flow classifier.

Further, FIG. 10 shows the measurement results of the internal friction angle (φ) for the samples # 1 to # 3. According to this, the internal friction angle is reduced to about 86% in tanφ from sample # 1 to sample # 2 through thermal plasma treatment. This is interpreted as a result of the improvement in the circularity of the metal particles by the thermal plasma treatment.

The value of the internal friction angle did not increase even after the pulverization step from sample # 2 to sample # 3. This suggests that the metal particles do not undergo changes such as crushing and deformation even after undergoing the pulverization step using the air flow classifier.

FIG. 11 shows the measurement results of oxygen values for samples # 1 to # 3. According to this, when the sample # 1 to the sample # 2 are subjected to the thermal plasma treatment, the oxygen value of the powder is greatly increased. This means that a large amount of fine particles made of metal oxides were generated by the thermal plasma treatment.

After undergoing the pulverization step using the air flow classifier from sample # 2 to sample # 3, the oxygen value is reduced to about 87%. This corresponds to the fact that some of the oxide-containing fine particles generated by the thermal plasma treatment were removed in the granulation step, which is in agreement with the above SEM observation results.

Further, FIG. 12 shows the measurement results of the specific surface area of the samples # 1 to # 3. According to this, the specific surface area of the particles is greatly increased from the sample # 1 to the sample # 2 when the thermal plasma treatment is performed. According to the particle size distribution of FIG. 4, the specific surface area of the particles is increased even though the particle size is almost unchanged, which is caused by a large amount on the surface of the metal particles by the thermal plasma treatment. It is interpreted that this is due to the formation of fine particles and the formation of fine uneven shapes on the surface of the particles.

When the sample # 2 to the sample # 3 are subjected to the pulverization step using the air flow classifier, the specific surface area is reduced to 65% or less. It is interpreted that a part of the fine particles generated by the thermal plasma treatment is removed in the pulverization step to reduce the unevenness of the particle surface. This result is also in agreement with the above-mentioned SEM observation result and oxygen value measurement result. By using the specific surface area as an index, it can be confirmed that the excess fine particles have been removed more clearly than when the oxygen value is used as an index.

Based on the above test results, it was confirmed that by subjecting the raw material particles made of metal to thermal plasma treatment, composite particles having fine particles adhered to the surface of the metal particles having improved circularity were formed. At this time, an excess amount of fine particles is generated, but by performing a pulverization treatment using an air flow classifier, the excessively generated fine particles can be separated from the surface of the metal particles and removed. At this time, the structure of the composite particles in which the fine particles are attached to the surface of the metal particles having a high circularity is maintained. By improving the circularity of the metal particles and adhering the fine particles to the surface thereof, the shear adhesion force and the internal friction angle of the metal particles are reduced, and high fluidity and filling property can be obtained in the produced powder material. In addition, the removal of excess particulates, which is identified as a reduction in oxygen levels and specific surface area, can reduce the effects of oxide content in the powder material produced.

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.

10 Plasma processing device 20 Air flow classifier M Raw material particles P Composite particles P'Plasma processing particles P1 Metal particles P2 (Adhesion) Fine particles P3 Excess fine particles

Claims (8)

By performing thermal plasma treatment on the raw material particles made of metal, the metal particles having a higher circularity than the raw material particles and at least a part of the metal elements constituting the metal particles are contained, and the raw material particles are more than the metal particles. A plasma treatment step of producing fine particles having a small particle size and producing plasma-treated particles in which at least a part of the fine particles is attached to the surface of the metal particles.
A part of the fine particles is separated and removed from the surface of the metal particles of the plasma-treated particles by utilizing shearing by an air flow, and the composite particles in which the remaining fine particles are attached to the surface of the metal particles are separated. A method for producing a powder material, in which the pulverization step is carried out in this order. The method for producing a powder material according to claim 1, wherein the pulverization step is performed using an air flow classifier. The method for producing a powder material according to claim 2, wherein in the pulverization step, classification of the composite particles is also performed at the same time. In the composite particles, the average particle size of the metal particles is 10 μm or more and 500 μm or less, and the fine particles remaining on the surface of the metal particles are nanoparticles, according to claim 1. The method for producing a powder material according to any one of claims 3. Compared with the raw material particles, the composite particles have a reduced shear adhesion force standardized by bulk density and an internal friction angle, and also have a reduced internal friction angle.
The method for producing a powder material according to any one of claims 1 to 4, wherein the oxygen concentration is reduced as compared with the plasma-treated particles. The method for producing a powder material according to claim 5, wherein the composite particles have a smaller shear adhesion force standardized by bulk density as compared with the plasma-treated particles. The method for producing a powder material according to any one of claims 1 to 6, wherein particles of a titanium alloy, a nickel alloy, a cobalt alloy, or an iron alloy are used as the raw material particles. The raw material particles are made of an alloy containing an additive metal element selected from at least one of aluminum, magnesium, copper and tin.
The method for producing a powder material according to claim 7, wherein the metal particles constituting the composite particles and the fine particles contain the additive metal element.

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