JP7797859B2 - Metal powder for molding and method for producing metal powder for molding - Google Patents

Description

The present invention relates to metal powder for molding and a method for manufacturing metal powder for molding.

In recent years, additive manufacturing using metal powder has become increasingly popular as a technology for creating three-dimensional objects. Known methods for creating three-dimensional objects, depending on the solidification principle, include selective laser sintering (SLS), binder jetting, and fused deposition molding (FDM).

Of these, powder sintering additive manufacturing and binder jetting involve a process of leveling metal powder into layers to form a powder layer, and a process of solidifying part of the powder layer. These processes are repeated to create a three-dimensional object.

Fused deposition modeling is a technology that creates three-dimensional objects by repeating the process of softening resin containing metal powder with heat and extruding it from a nozzle, and then stacking the extruded resin and solidifying it.

Patent Document 1 discloses a metal powder for manufacturing as a powder to be used in such additive manufacturing methods. This metal powder for manufacturing is characterized by the ratio of particles having a circularity of less than 0.80 to the total number of particles being 10% or less, and the ratio of particles having a circularity of 0.95 or more to the total number of particles being 50% or more.

These characteristics result in a metal powder for molding with excellent fluidity and packing properties. Therefore, by using this metal powder for molding, molded bodies with excellent strength can be obtained.

Japanese Patent Application Laid-Open No. 2016-102229

The metal powder for manufacturing described in Patent Document 1 leaves room for improvement in terms of manufacturing performance. In particular, sufficient consideration is not given to preventing the inclusion of irregularly shaped particles. Irregularly shaped particles can cause manufacturing defects in additive manufacturing. Furthermore, a shaped body manufactured using the metal powder for manufacturing becomes a metal sintered body when subjected to a sintering process. However, the aforementioned manufacturing defects can cause a decrease in the sintered density and surface properties of the metal sintered body.

The present invention is applied to powder sintering layered manufacturing, binder jetting, and fused deposition modeling.
The metal powders that can be used for molding are:
The metal particles are stainless steel , and when D50 is the particle diameter at which the cumulative frequency of the metal particles is 50% in the particle size distribution on a volume basis of the metal particles, D50 is 3.0 μm or more and 30.0 μm or less.
m or less,
The particle diameter at which the cumulative frequency is 90% in the particle size distribution on a volume basis of the metal particles is defined as D9
0, the ratio of D90/D50 is 2.00 or less,
The volume ratio of the metal particles having a circularity of 0.60 or less is 2.0% or less.

The present invention is applied to powder sintering layered manufacturing, binder jetting, and fused deposition modeling.
The method for producing the metal powder for molding is as follows :
a preparation step of preparing a stainless steel raw material powder;
a submerged classification step of classifying the raw material powder in a liquid to extract particles having a D50 of 3.0 μm or more and 30.0 μm or less and a D90/D50 ratio of 2.00 or less, where D50 is the particle diameter at which a cumulative frequency of 50% in a volumetric particle size distribution is defined as D50 and D90 is the particle diameter at which a cumulative frequency of 90% in a volumetric particle size distribution is defined as D90;
The present invention is characterized by having the following.

1 is a cross-sectional view schematically illustrating a particle of a metal powder for molding according to an embodiment. FIG. 2 is a perspective view schematically showing secondary particles in which metal particles are bonded together. 1A to 1C are process diagrams illustrating a method for producing a metal powder for molding according to an embodiment.

The metal powder for molding and the method for manufacturing the metal powder for molding of the present invention will be described in detail below with reference to the accompanying drawings.

1. Metal Powder for Shaping First, the metal powder for shaping according to the embodiment will be described. Fig. 1 is a cross-sectional view schematically showing particles of the metal powder for shaping 1 according to the embodiment.

The metal powder for fabrication 1 shown in Figure 1 is a powder used in additive manufacturing. Examples of additive manufacturing methods include selective laser sintering (SLS), binder jetting, and fused deposition modeling (FDM). In selective laser sintering and binder jetting, a three-dimensional object is fabricated by repeatedly smoothing metal powder into layers to form a powder layer and solidifying a portion of the powder layer. In fused deposition modeling, a three-dimensional object is fabricated by repeatedly softening a resin containing metal powder with heat and extruding it from a nozzle, and stacking and solidifying the extruded resin.

As described below, the metal powder for molding 1 has been optimized in terms of particle size distribution and particle shape. Therefore, when used in the additive manufacturing method described above, it is possible to produce a dense molded body with excellent surface quality and few molding defects.

In the following description, particles of the metal powder for molding 1 will also be referred to as "metal particles 4." The metal particles 4 shown in Figure 1 include a core portion 2 and a coating film 3. Of these, the coating film 3 is provided so as to cover the surface of the core portion 2. Note that in this specification, "coated" is a concept that includes not only a state in which the entire surface of the core portion 2 is covered, but also a state in which only a portion of the surface is covered.

The metal powder 1 for fabrication containing such metal particles 4 has excellent fluidity and packing properties. Therefore, for example, in powder sintering layer fabrication or binder jet fabrication, when the metal powder 1 for fabrication is leveled in layers to form a powder layer, a smooth powder layer with few irregularities or voids is obtained. Furthermore, for example, in fused deposition modeling, when a resin containing the metal powder 1 for fabrication is extruded from a nozzle to form a deposited layer, it can be extruded while minimizing defects and discontinuities, resulting in a smooth deposited layer with few irregularities or voids. Furthermore, by sintering a shaped body obtained using such a powder layer or deposited layer, i.e., a green body before sintering, a dense sintered body with minimal surface roughness can be produced.

1.1 Metal Particles The constituent material of the metal particles 4 is not particularly limited and may be any metal material. Examples include simple elements such as Fe, Ni, Co, and Ti, as well as alloys and intermetallic compounds containing these as main components.

Examples of Fe-based alloys include stainless steels such as austenitic stainless steel, martensitic stainless steel, and precipitation-hardened stainless steel, as well as low-carbon steel, carbon steel, heat-resistant steel, die steel, high-speed tool steel, Fe-Ni alloys, and Fe-Ni-Co alloys.

Examples of Ni-based alloys include Ni-Cr-Fe-based alloys, Ni-Cr-Mo-based alloys, and Ni-Fe-based alloys.

Examples of Co-based alloys include Co-Cr-based alloys, Co-Cr-Mo-based alloys, and Co-Al-W-based alloys.

Examples of Ti-based alloys include alloys of Ti with metal elements such as Al, V, Nb, Zr, Ta, and Mo, such as Ti-6Al-4V and Ti-6Al-7Nb.

The metal particles 4 may be composed of a composite material of a metallic material and a non-metallic material. Examples of non-metallic materials include ceramic materials such as oxides, nitrides, carbides, and sulfides, inorganic materials such as silicon materials and carbon materials, and organic materials such as organic compounds. In composite materials, the volume ratio of the metallic material is set to be large.

In the metal powder for molding 1 shown in Figure 1, the core portion 2 is made of a metallic material, and the coating film 3 is made of a non-metallic material. Note that the coating film 3 may be provided as needed and may be omitted.

In the particle size distribution of metal particles 4 on a volume basis, when the particle diameter at which the cumulative frequency is 50% is defined as D50, the particle diameter D50 is 3.0 μm or more and 30.0 μm or less, preferably 4.0 μm or more and 20.0 μm or less, and more preferably 5.0 μm or more and 14.0 μm or less. When the particle diameter D50 of metal particles 4 is within this range, when metal powder for molding 1 is leveled to form a powder layer or when resin containing metal powder for molding 1 is extruded to form a deposited layer, the packing ability of metal particles 4 is improved, and the gaps between metal particles 4 can be sufficiently small. By creating a shaped body using such a powder layer or deposited layer and sintering it, it is possible to produce a dense sintered body with low surface roughness.

If the particle diameter D50 of the metal particles 4 is below the lower limit, the metal particles 4 will aggregate and the fluidity of the metal powder for molding 1 will decrease. As a result, when the metal powder for molding 1 is smoothed into a layer, unevenness and cavities are likely to occur in the powder layer, and when a resin containing the metal powder for molding 1 is extruded, unevenness and cavities are likely to occur in the deposited layer. On the other hand, if the particle diameter D50 of the metal particles 4 exceeds the upper limit, the gaps between the metal particles 4 will become larger. Therefore, depending on the shape of the metal particles 4, unevenness and cavities are likely to occur in the powder layer or deposited layer.

When the particle size distribution of metal particles 4 on a volume basis is defined as the particle size at which the cumulative frequency is 90%, the ratio of D90/D50 is 2.00 or less, preferably 1.75 or less, and more preferably 1.50 or less. When the ratio of D90/D50 is within this range, the content of coarse particles is low, and the particle size distribution can be said to be sufficiently narrow. Therefore, in a metal powder for molding 1 containing such metal particles 4, the deterioration of flowability and filling ability due to coarse particles is suppressed. Note that coarse particles refer to particles with a particle size of 50 μm or more, for example.

If the D90/D50 ratio exceeds the upper limit, the proportion of coarse particles increases, resulting in a decrease in the fluidity and fillability of the metal powder for molding 1. While there is no specific lower limit for the D90/D50 ratio, it is preferable to set it at 1.2 or higher, considering the balance between production costs and fluidity and fillability.

The volumetric particle size distribution of the metal particles 4 can be obtained, for example, using a laser diffraction particle size distribution measuring device.

The cross-sectional shape of the metal particles 4 is not particularly limited and may be, for example, circular, elliptical, polygonal, etc., but is preferably circular.

Specifically, the metal powder 1 for molding has a ratio of metal particles 4 with a circularity of 0.60 or less of 2.0% or less, preferably 1.8% or less, and more preferably 1.5% or less. In such metal powder 1 for molding, the ratio of metal particles 4 with a relatively low circularity is kept sufficiently low, and the ratio of metal particles 4 with a relatively high circularity is relatively high. Such metal particles 4 with a high circularity have low rolling resistance. In addition, the gaps between metal particles 4 when they are close to each other can be kept particularly small. Therefore, if the ratio of metal particles 4 with a circularity of 0.60 or less is within the above range, the fluidity and filling properties of the metal powder 1 for molding are improved.

If the proportion of metal particles 4 with a circularity of 0.60 or less exceeds the upper limit, the proportion of metal particles 4 with a relatively low circularity will increase, resulting in a decrease in the fluidity and filling ability of the metal powder for molding 1.

The circularity CI of the metal particle 4 is defined by the following formula (1).
CI=4πS/L ² ...(1)
In the above formula (1), S represents the projected area of the metal particle 4 , and L represents the circumferential length of the metal particle 4 .

The circularity of the metal particles 4 is measured by performing the following image processing on an image of the metal particles 4.

First, an image of multiple metal particles 4 taken with a scanning electron microscope (SEM), optical microscope, or the like is subjected to image processing to detect contours. This identifies the particle image. Next, the area and perimeter of the particle image are measured. The circularity CI is then calculated based on the above formula (1). Next, the circularity CI is determined for each of the multiple metal particles 4. Then, the proportion of metal particles 4 in one image that have a circularity CI of 0.60 or less is calculated. It is preferable to use measurement values for 100 or more particles to calculate the proportion.

Image processing to identify particle images from images can be performed using, for example, the image processing system ImageJ developed by the National Institutes of Health.

The metal powder for molding 1 may be powder produced by any method. Examples of production methods include various atomization methods such as water atomization, gas atomization, and rotary water flow atomization, as well as reduction, carbonyl, and pulverization. Of these, water atomization is preferred. That is, the metal particles 4 are preferably particles containing water-atomized particles. Water-atomized particles are small, highly spherical, and have a relatively uniform particle size. In addition, water-atomized particles have a high density of hydroxyl groups on their surfaces. These hydroxyl groups serve as a base for the coating film 3, which will be described later, and therefore improve adhesion between the core portion 2 and the coating film 3. Therefore, water-atomized particles are useful as particles for the metal particles 4.

In the metal powder for molding 1, the metal particles 4 may be bonded together to form secondary particles. Figure 2 is a perspective view schematically showing secondary particles 6 in which the metal particles 4 are bonded together.

The secondary particles 6 shown in Figure 2 are formed by metal particles 4 being bound together. For binding, an organic binder such as a resin material or an inorganic binder is used. The secondary particles 6 are produced using a suspension containing the metal particles 4 and various granulation methods such as spray drying, tumbling granulation, and fluidized bed granulation. The secondary particle 6 form increases the apparent sphericity, so even if the metal particles 4 contain a relatively high proportion of irregularly shaped particles or have a relatively low circularity, a metal powder for molding 1 with excellent fluidity and packing properties can be achieved.

The average particle size of the secondary particles 6 is not particularly limited, but is preferably between 2 and 20 times the particle size D50 of the metal particles 4, and more preferably between 3 and 10 times. Secondary particles 6 with such an average particle size result in a metal powder for molding 1 with superior fluidity and packing properties.

1.2. Coating Film The coating film 3 covers the surface of the core portion 2. This allows various properties to be imparted to the core portion 2 made of a metal material. Note that the coating film 3 is not essential and may be omitted.

Examples of materials constituting the coating film 3 include compounds derived from coupling agents. Coupling agents are organic compounds containing organic reactive groups and hydrolyzable groups. Using a coupling agent allows the organic reactive groups to be positioned on the surface of the core portion 2. Providing such a coating film 3 can suppress aggregation of the metal particles 4. Furthermore, because organic reactive groups have a high affinity with resin components, they can enhance the wettability of the metal particles 4 with binders used in binder jetting and resins used in fused deposition modeling. These effects can improve the fluidity and packing ability of the metal powder 1. Furthermore, the coating film 3 also contributes to improving the moisture resistance and rust resistance of the metal powder 1. By improving the moisture resistance and rust resistance, deterioration of the metal powder 1 due to moisture absorption and rust development can be suppressed.

Examples of coupling agents include silane coupling agents, titanium coupling agents, and zirconium coupling agents. Of these, silane coupling agents are preferred. In other words, the coating film 3 preferably contains a compound derived from a silane coupling agent. Silane coupling agents have alkoxysilyl groups as hydrolyzable groups, and because these alkoxysilyl groups are highly reactive, they can form a coating film 3 with excellent adhesion. Furthermore, even if compounds derived from silane coupling agents are ultimately incorporated into the molded body or sintered body, they are unlikely to adversely affect the properties of the molded body or sintered body.

In silane coupling agents, hydrolyzable groups such as alkoxysilyl groups are hydrolyzed to produce silanols. The silanols react with hydroxyl groups generated on the surface of the core portion 2, causing the silane coupling agent to adhere to the surface of the core portion 2. The silane coupling agent then undergoes a dehydration condensation reaction, resulting in a coating film 3 bonded to the surface of the core portion 2.

Examples of organic reactive groups include cyclic structure-containing groups, fluoroalkyl groups, fluoroaryl groups, amino groups, acrylic groups, and methacrylic groups. Of these, cyclic structure-containing groups, fluoroalkyl groups, and fluoroaryl groups are preferred. These groups have relatively good heat resistance and hydrophobicity, making them stable even in high-temperature environments and maintaining the effect of suppressing aggregation of metal particles 4. For this reason, they are useful as organic reactive groups for coupling agents used with metal particles 4 that are subjected to heating and drying.

A cyclic structure-containing group is a functional group with a cyclic structure. Examples of cyclic structure-containing groups include aryl groups such as phenyl, tolyl, xylyl, and naphthyl groups, and cyclic ether groups such as epoxy, 3,4-epoxycyclohexyl, and oxetanyl groups.

A fluoroalkyl group is an alkyl group having 1 to 16 carbon atoms and substituted with one or more fluorine atoms. It is particularly preferred that the fluoroalkyl group be a perfluoroalkyl group.

A fluoroaryl group is an aryl group having 6 to 20 carbon atoms and substituted with one or more fluorine atoms. It is particularly preferred that the fluoroaryl group is a perfluoroaryl group.

The coating film 3 may also be a laminated film including multiple layers made of different types of compounds.

The average thickness of the coating film 3 is preferably 1 nm or more and 100 nm or less, and more preferably 3 nm or more and 50 nm or less. This allows the volume ratio of the coating film 3 to the metal powder for molding 1 to be reduced while fully ensuring the functions of the coating film 3 described above.

If the average thickness of the coating film 3 is below the lower limit, depending on the material of the coating film 3, the coverage rate of the coating film 3 may decrease, and the fluidity and fillability of the metal powder for manufacturing 1 may not be sufficiently improved. On the other hand, if the average thickness of the coating film 3 is above the upper limit, depending on the material of the coating film 3, the coating film 3 may be prone to peeling, or the volume ratio of the coating film 3 to the metal powder for manufacturing 1 may increase more than necessary.

The average thickness of the coating film 3 is measured, for example, by magnifying and observing the cross-section of the metal particle 4. Specifically, the metal particle 4 is cut with a focused ion beam to prepare a cross-sectional thin section sample. The obtained cross-sectional thin section sample is then observed with a scanning transmission electron microscope, and the thickness of the coating film 3 is measured at five or more locations per metal particle 4. The measured values are then averaged, and the calculated result is used as the average thickness of the coating film 3.

The constituent elements of the coating film 3 can be identified, for example, by EDX analysis (energy dispersive X-ray analysis), Auger electron spectroscopy, etc.

1.3. Ceramic Particles The metal powder for manufacturing 1 according to this embodiment includes ceramic particles 5 in addition to metal particles 4. The ceramic particles 5 are not essential and may be omitted. The average particle size of the ceramic particles 5 is smaller than that of the metal particles 4. Therefore, the ceramic particles 5 are more likely to be distributed on the surfaces of the metal particles 4, and are interposed between the metal particles 4, suppressing the aggregation of the metal particles 4. This further improves the fluidity and packing ability of the metal powder for manufacturing 1.

Examples of materials constituting the ceramic particles 5 include oxide-based ceramics such as aluminum oxide, magnesium oxide, titanium oxide, zirconium oxide, silicon oxide, iron oxide, potassium oxide, sodium oxide, calcium oxide, chromium oxide, and niobium oxide; nitride-based ceramics such as boron nitride and silicon nitride; and silicon carbide; and one or more of these may be used.

Of these, it is preferable that the constituent material of the ceramic particles 5 contains silicon oxide. Silicon oxide is chemically stable and, even when finally incorporated into a shaped body or a sintered body, is unlikely to adversely affect the properties of the shaped body or the sintered body. Examples of silicon oxide include _SiO , _SiO2 , _Si2O3 , _Si2O , _Si3O , and a mixture of two or more of these.

The average particle size of the ceramic particles 5 is preferably 1 nm or more and 100 nm or less, more preferably 3 nm or more and 50 nm or less, and even more preferably 5 nm or more and 20 nm or less. When the average particle size of the ceramic particles 5 is within this range, the ceramic particles 5 are particularly likely to be distributed on the surfaces of the metal particles 4. The ceramic particles 5 distributed on the surfaces of the metal particles 4 can then roll or otherwise enhance the sliding between the metal particles 4. As a result, frictional resistance between the metal particles 4 is reduced, thereby improving the fluidity and packing properties of the metal powder for molding 1. Furthermore, even when ceramic particles 5 with such an average particle size are incorporated into a sintered body, their particle size as inclusions is sufficiently small to minimize the impact on the surface texture and mechanical properties of the sintered body.

If the average particle size of the ceramic particles 5 is below the lower limit, the ceramic particles 5 will have difficulty rolling. As a result, the above-mentioned effects may not be achieved. On the other hand, if the average particle size of the ceramic particles 5 exceeds the upper limit, the ceramic particles 5 will have difficulty distributing on the surfaces of the metal particles 4. Furthermore, inclusions derived from the ceramic particles 5 may be more likely to inhibit sintering of the shaped body (green body).

The average particle size of the ceramic particles 5 is preferably 0.01% to 5.0% of the average particle size (particle size D50) of the metal particles 4, more preferably 0.05% to 1.0%, and even more preferably 0.10% to 0.50%. This makes it easier for the ceramic particles 5 to be distributed on the surfaces of the metal particles 4, and ensures that the particle size of inclusions formed in the sintered body is sufficiently small.

The ratio of the total mass of ceramic particles 5 to the sum of the total mass of metal particles 4 and the total mass of ceramic particles 5 is not particularly limited, but is preferably 0.01% by mass or more and 1.00% by mass or less, more preferably 0.03% by mass or more and 0.50% by mass or less, and even more preferably 0.05% by mass or more and 0.30% by mass or less. By setting the ratio of ceramic particles 5 within this range, the effects of adding ceramic particles 5 can be fully enjoyed, while minimizing the impact of inclusions derived from ceramic particles 5.

The average particle size of ceramic particles 5 is measured as follows. First, ceramic particles 5 are observed at a magnification of 100x or more. Then, the area of the particle image of ceramic particles 5 in the observed image is measured. Next, the diameter of a perfect circle having the same area as that measured is calculated. The calculated diameter is used as the particle size of that particle image. In this way, particle sizes are determined for 10 or more particle images, and the average value is calculated. The calculated average value is used as the average particle size of ceramic particles 5.

The ceramic particles 5 may be surface-treated as needed. Examples of surface treatments include hydrophobic treatment, coupling agent treatment, and organosilazane treatment. By subjecting the ceramic particles 5 to hydrophobic treatment, adsorption of moisture onto the ceramic particles 5 is suppressed. This suppresses aggregation between the ceramic particles 5, and therefore more effectively suppresses aggregation between the metal particles 4.

1.4. Effects of the Metal Powder for Metal Shaping According to the Embodiment As described above, the metal powder for metal shaping 1 according to this embodiment has metal particles 4, a particle diameter D50 of 3.0 μm or more and 30.0 μm or less, a D90/D50 ratio of 2.00 or less, and a volume ratio of metal particles 4 having a circularity of 0.60 or less of 2.0% or less. D50 is the particle diameter at which the cumulative frequency in the particle size distribution on a volume basis of the metal particles 4 is 50%. D90 is the particle diameter at which the cumulative frequency in the particle size distribution on a volume basis of the metal particles 4 is 90%.

This configuration results in a metal powder 1 for molding with high fluidity and packing properties. By using this metal powder 1 for molding, powder layers and deposition layers with few irregularities or voids can be easily formed in additive manufacturing. This makes it possible to obtain a molded body (green body) with the desired shape, which is dense and has little surface roughness. In other words, the metal powder 1 for molding is a powder with excellent moldability. Then, by sintering this molded body, a sintered body with high sintered density and excellent surface properties can be produced.

Furthermore, as described above, in the metal powder for molding 1 according to this embodiment, it is preferable that the metal particles 4 include water-atomized particles. This allows for metal particles 4 to be obtained that have a narrow particle size distribution, i.e., a sufficiently small D90/D50 ratio, even if the particle diameter D50 is smaller. Furthermore, it allows for metal particles 4 to be obtained that have excellent adhesion between the core portion 2 and the coating film 3, and that have excellent agglomeration resistance, moisture resistance, rust prevention, etc.

Furthermore, as described above, in the metal powder for molding 1 according to this embodiment, the metal particles 4 include a core portion 2 made of a metal material and a coating film 3 that coats the surface of the core portion 2.

This configuration allows various properties to be imparted to the core portion 2, which is made of a metal material. For example, if the coating film 3 contains a compound derived from a coupling agent, the organic reactive groups of the coupling agent can be disposed on the surface of the core portion 2. This suppresses aggregation of the metal particles 4 and improves the fluidity and filling ability of the metal powder for molding 1. In addition, the hydrolyzable groups of the coupling agent can react with the surface of the core portion 2. This results in a coating film 3 with excellent adhesion.

Furthermore, the metal powder for molding 1 according to this embodiment contains, in addition to metal particles 4, ceramic particles 5 whose average particle size is smaller than that of the metal particles 4.

With this configuration, the ceramic particles 5 suppress the aggregation of the metal particles 4. This further improves the fluidity and filling properties of the metal powder for molding 1.

In addition, as shown in Figure 2, the metal powder for manufacturing 1 may have secondary particles 6 in which metal particles 4 are bonded together. The secondary particles 6 have a high apparent sphericity due to the aggregation of the metal particles 4. Therefore, the fluidity and filling ability of the metal powder for manufacturing 1 can be improved regardless of the particle shape of the metal particles 4.

2. Manufacturing Method of Metal Powder for Shaping Next, a manufacturing method of a metal powder for shaping according to an embodiment will be described. Fig. 3 is a process diagram for explaining a manufacturing method of a metal powder for shaping according to an embodiment.

The manufacturing method for metal powder for molding shown in Figure 3 includes a preparation process S102, a submerged classification process S104, and a coating film formation process S106.

In the preparation step S102, a raw material powder is prepared. The raw material powder may be a commercially available product, or may be a powder produced by the atomization method, pulverization method, or other production method.

Atomization methods are divided into water atomization, rotary water jet atomization, gas atomization, etc., depending on the type of coolant and the configuration of the equipment. Atomization is a method of producing raw material powder by pulverizing and cooling molten metal by colliding it with a liquid or gas jet sprayed at high speed.

In the water atomization method, molten metal is split in the air by a large negative pressure, forming fine droplets. These droplets are then rapidly cooled and solidified by a high-speed water jet, yielding the raw material powder.

For example, in the atomization method, the circularity CI can be adjusted depending on the amount and temperature of the molten metal colliding with the liquid or gas, the flow velocity of the liquid or gas colliding with the molten metal, etc. Although it will vary somewhat depending on the composition of the molten metal, for example, reducing the amount of molten metal colliding with the liquid or gas, increasing the temperature, or slowing the flow velocity of the liquid or gas colliding with the molten metal tends to increase the circularity CI of the raw material powder.

In the submerged classification step S104, the raw material powder is classified in a liquid. This extracts particles having a particle diameter D50 of 3.0 μm or more and 30.0 μm or less and a D90/D50 ratio of 2.00 or less. In this way, the core portion 2 described above is obtained.

Classification in liquid is also called wet classification. In contrast, classification in air is also called dry classification. While dry classification classifies particles in air by utilizing differences in mechanical behavior, wet classification in liquid uses centrifugal force, gravity, etc. to classify particles in liquid. Therefore, wet classification in liquid can classify small particles with greater precision, and can also suppress particle aggregation during classification more effectively than dry classification.

Specifically, the submerged classification process preferably includes placing the raw material powder in a liquid and classifying it using centrifugal force or gravity. High classification accuracy can be achieved using either a centrifugal field or a gravitational field.

From the perspective of more precise classification, it is more preferable to include a gravity classification operation. Gravity classification is a classification operation that takes advantage of the fact that the settling speed in a liquid varies depending on the particle size (particle diameter), and can be carried out using, for example, an upright cylindrical wet classifier. Alternatively, by determining the settling speed for each particle size in advance and collecting particles from the classifier according to the settling time, particles with the desired particle diameter can be obtained. This makes it possible to extract particles with a particularly narrow particle size distribution.

When classifying raw material powder in a liquid, it is preferable that the liquid contain a dispersant. Adding a dispersant can suppress aggregation of particles in the liquid, allowing the raw material powder to be classified more accurately. Examples of dispersants include carboxylate-based dispersants and sulfonate-based dispersants.

The amount of dispersant added is not particularly limited, but is preferably 0.1 to 5.0 parts by mass, and more preferably 0.2 to 3.0 parts by mass, per 100 parts by mass of raw material powder.

By carrying out the above classification procedure, the particle diameter D50 can be adjusted to fall within the above range. Furthermore, by removing coarse particles, the D90/D50 ratio can be adjusted to fall within the above range.

2.3. Coating Film Formation Step In the coating film formation step S106, a coating film is formed on the particle surface of the particles extracted in the submerged classification step S104. This results in a metal powder for molding. Note that this step may be performed as needed or may be omitted.

As mentioned above, various coupling agents are used to form the coating film, and a silane coupling agent is preferably used. A coating film can be formed on the surface of the particles (cores) extracted in the submerged classification step S104 by methods such as placing the extracted particles and coupling agent in a reactor and heating, spraying the coupling agent onto the extracted particles, or placing the particles in a solution containing a coupling agent and drying them.

After forming the coating film, the resulting coating film may be subjected to heat treatment if necessary. The heat treatment conditions are, for example, a temperature of 50°C or higher and 300°C or lower, and a time of 10 minutes to 24 hours or lower. This can remove any hydrates remaining in the coating film, remove any unreacted coupling agent, and improve the adhesion of the coating film.

In addition, a classification step separate from the submerged classification step S104 may be performed between the preparation step S102 and the submerged classification step S104. In this classification step, coarse particles contained in the raw material powder are removed in advance. This can improve the classification accuracy in the submerged classification step S104.

In addition, in the above description, the coating film formation process S106 is performed after the submerged classification process S104, but this order may be reversed.

As described above, the method for producing metal powder for molding according to this embodiment includes a preparation step S102 and a submerged classification step S104. In the preparation step S102, raw material powder is prepared. In the submerged classification step S104, the raw material powder is classified in liquid, and particles having a D50 of 3.0 μm or more and 30.0 μm or less and a D90/D50 ratio of 2.00 or less are extracted. Note that D50 refers to the particle size at which the cumulative frequency in the volumetric particle size distribution is 50%, and D90 refers to the particle size at which the cumulative frequency in the volumetric particle size distribution is 90%.

With this configuration, classification in liquid allows for highly accurate extraction of particles with optimized D50 and D90/D50 ratios. Metal powder for molding containing classified particles with highly precisely controlled particle size distribution has excellent moldability, and by sintering the resulting molded body, a sintered body with high sintering density and excellent surface properties can be produced. In other words, with the above configuration, it is possible to produce metal powder for molding that exhibits these effects.

The metal powder for molding and the method for manufacturing the metal powder for molding of the present invention have been described above based on preferred embodiments, but the present invention is not limited to these.

For example, the metal powder for molding of the present invention may be one in which any desired component has been added to the above-described embodiment. Furthermore, the method for manufacturing a metal powder for molding of the present invention may be one in which any desired process has been added to the above-described embodiment.

Next, specific examples of the present invention will be described.
3. Preparation of Metal Powder for Molding 3.1. Example 1
First, a powder of stainless steel SUS316L produced by water atomization was prepared. The obtained stainless steel powder was then classified in a liquid using gravity. The classification method is described in detail below.

In the classification method using gravity in liquid, 30 g of raw material powder was first placed in 400 mL of pure water and dispersed using ultrasound to create a raw material powder dispersion. This raw material powder dispersion was then slowly poured into 1,600 mL of pure water to form a slurry, which was then left to stand for 330 minutes before being classified by gravity. 600 mL of slurry was then collected from the liquid surface using a siphon. The collected slurry was then heated and dried at 85°C for 120 minutes to evaporate the water, and the classified particles were extracted. This resulted in the production of a metal powder for molding.

The volumetric particle size distribution of the classified particles was then obtained using a laser diffraction/scattering particle size distribution analyzer. Based on the obtained particle size distribution, the particle diameters D50 and D90 were determined. The ratio of D90/D50 was also calculated. The calculation results are shown in Table 1.

Furthermore, the circularity CI of the classified particles was measured from images observed using a scanning electron microscope. The proportion of particles with a circularity CI of 0.60 or less was then calculated. The calculation results are shown in Table 1.

Example 2
First, a powder of stainless steel SUS316L produced by water atomization was prepared. Next, the obtained stainless steel powder was classified in a liquid using centrifugal force. The classification method is described in detail below.

In the classification method using centrifugal force in liquid, the raw material powder was first placed in pure water and dispersed at a content of 7% by mass to create a raw material powder dispersion. This raw material powder dispersion was then classified using a wet rotary classifier. The resulting classified raw material powder was then heated and dried at 85°C for 120 minutes to volatilize the water and extract the classified particles. This resulted in the production of a metal powder for molding.

Then, in the same manner as in Example 1, the particle diameters D50 and D90 were measured, and the D90/D50 ratio and the proportion of particles with a circularity CI of 0.60 or less were calculated. The measurement and calculation results are shown in Table 1.

Example 3
First, a powder of stainless steel SUS316L produced by gas atomization was prepared. The resulting stainless steel powder was then classified using the method shown in Table 1, and the classified particles were extracted. This resulted in a metal powder for molding having the particle size characteristics shown in Table 1.

Example 4
First, a powder of stainless steel SUS316L produced by water atomization was prepared. The resulting stainless steel powder was then classified using the method shown in Table 1, and the classified particles were extracted. This resulted in a metal powder for molding having the particle size characteristics shown in Table 1.

Example 5
First, a powder of stainless steel SUS316L produced by water atomization was prepared. Next, the obtained stainless steel powder was classified by the method shown in Table 1, and the classified particles were extracted.

The classified particles were then treated with a silane coupling agent. This resulted in a metal powder for molding with a coating layer. Phenyltrimethoxysilane was used as the silane coupling agent.

3.6 Example 6
The stainless steel powder was classified using the method shown in Table 1, the classified particles were extracted, and a metal powder for molding having a coating layer was obtained in the same manner as in Example 5, except that 3-glycidoxypropyltrimethoxysilane was used as the silane coupling agent.

3.7. Comparative Example 1
First, a powder of stainless steel SUS316L manufactured by gas atomization was prepared. The resulting stainless steel powder was then classified in air using an airflow. Specifically, the raw powder was classified using a cyclone classifier. The classified metal particles were extracted, yielding a metal powder for molding having the particle size characteristics shown in Table 1.

3.8. Comparative Examples 2 to 6
First, a powder of stainless steel SUS316L produced by water atomization was prepared. The resulting stainless steel powder was then classified in air using an airflow, and the classified metal particles were extracted. This resulted in a metal powder for molding having the particle size characteristics shown in Table 1.

Example 7
First, a powder of stainless steel SUS316L produced by water atomization was prepared. Next, the obtained stainless steel powder was classified in a liquid using gravity. The classified particles were then extracted.

Next, silica particles were added as ceramic particles to the classified particles. This resulted in a metal powder for molding. The average particle size of the added silica particles, their particle size ratio to the classified particles, and the silica particle addition ratio are shown in Table 2.

3.10. Examples 8 to 13
A metal powder for molding was obtained in the same manner as in Example 7, except that the manufacturing method of the stainless steel powder, the classification method, the particle size characteristics of the stainless steel powder, the conditions for adding the ceramic particles, etc. were changed as shown in Table 2.

As shown in Tables 1 and 2, in each example, the particle diameter D50, the D90/D50 ratio, and the proportion of metal particles with a circularity CI of 0.60 or less were all within the specified ranges.

4. Preparation of Sintered Body Using the metal powders for shaping obtained in each Example and Comparative Example, a shaped body was prepared by the binder jet method, consisting of 50 layers stacked together. A stearic acid emulsion was used as the binder solution.

The resulting molded body was then degreased and sintered in a furnace. The sintering conditions were 1300°C for 3 hours in an argon atmosphere. This resulted in a sintered body.

5. Evaluation of Sintered Compacts 5.1. Relative Density Next, the density of the resulting sintered compacts was measured. The relative value of the measured density relative to the true density of the metal powder used for molding, i.e., the relative density, was calculated. The calculation results are shown in Tables 1 and 2.

5.2. Surface roughness Next, the surface roughness of the obtained sintered body was measured. The surface roughness refers to the arithmetic mean roughness Ra, and was measured in accordance with the method specified in JIS B 0671-1:2002. The measurement results are shown in Tables 1 and 2.

As is clear from Tables 1 and 2, the sintered bodies produced using the metal powders for molding in each Example had higher relative densities and lower surface roughness than the sintered bodies produced using the metal powders for molding in each Comparative Example.

Although not shown in Tables 1 and 2, a shaped body was produced by laminating 50 layers using the metal powders for shaping obtained in each Example and Comparative Example using the fused deposition modeling method. The produced shaped body was then subjected to a degreasing process and then sintered. The relative density and surface roughness of the resulting sintered body were measured, and the evaluation results showed the same trends as those in Tables 1 and 2.

It was therefore found that by using the metal powder for molding according to the present invention in additive manufacturing, it is possible to produce molded bodies with high moldability, i.e., with few molding defects. Furthermore, it was found that by sintering the resulting molded bodies, it is possible to produce sintered bodies with high sintering density and excellent surface properties.

1... Metal powder for molding, 2... Core, 3... Coating film, 4... Metal particles, 5... Ceramic particles, 6... Secondary particles, S102... Preparation process, S104... Submerged classification process, S106... Coating film formation process

Claims (9)

having stainless steel metal particles,
The particle diameter at which the cumulative frequency is 50% in the particle size distribution on a volume basis of the metal particles is defined as D5.
When the D50 is 0, D50 is 3.0 μm or more and 30.0 μm or less,
The particle diameter at which the cumulative frequency is 90% in the particle size distribution on a volume basis of the metal particles is defined as D9
0, the ratio of D90/D50 is 2.00 or less,
A metal powder for manufacturing used in powder sintering additive manufacturing, binder jet manufacturing, and fused deposition modeling , characterized in that the volume ratio of the metal particles having a circularity of 0.60 or less is 2.0% or less. The metal powder for molding according to claim 1, wherein the metal particles include water-atomized particles. The metal powder for molding according to claim 1 or 2, wherein the metal particles each include a core portion made of a metal material and a coating film that coats the surface of the core portion. The metal powder for molding according to claim 3 , wherein the coating film contains a compound derived from a silane coupling agent. 5. The metal powder for molding according to claim 1, further comprising ceramic particles having an average particle size smaller than that of said metal particles. The metal powder for shaping according to claim 1 , wherein the metal powder comprises secondary particles in which the metal particles are bonded together. a preparation step of preparing a stainless steel raw material powder;
a submerged classification step of classifying the raw material powder in a liquid to extract particles having a D50 of 3.0 μm or more and 30.0 μm or less and a D90/D50 ratio of 2.00 or less, where D50 is the particle diameter at which a cumulative frequency of 50% in a volumetric particle size distribution is defined as D50 and D90 is the particle diameter at which a cumulative frequency of 90% in a volumetric particle size distribution is defined as D90;
The powder sintering layer manufacturing method, the binder jet method, and the fused deposition modeling method are characterized by having
A method for producing the metal powder used for molding. The method for producing a metal powder for shaping according to claim 7 , wherein the submerged classification step includes placing the raw material powder in a liquid and classifying the raw material powder by centrifugal force or gravity. The method for producing metal powder for molding described in claim 8, wherein the liquid contains a dispersant.