Activation method

Abstract

The purpose of the present invention is to activate powder particles for use in powder-based 3D printers by achieving a balance between maintaining a spherical shape and reducing oxides. An activation method according to one embodiment of the present disclosure comprises: a supply step (S2) for supplying powder particles to a reaction vessel equipped with a plasma torch that generates a plasma flame by converting a working gas into plasma; and a plasma processing step (S3) for processing the powder particles with the plasma flame in a state in which the pressure inside the reaction vessel is in a pressure region in which the plasma flame behaves as a viscous fluid possessing flow, and the temperature of the plasma flame is within a temperature range in which the maximum temperature of the powder particles is equal to or higher than the melting point of the powder particles and the powder particles are not evaporated.

Description

Activation method

[0001] The present invention relates to an activation method for activating powder particles containing metal elements.

[0002] Powder bed fusion (PBF) 3D printers are devices that use raw material powder to create three-dimensional objects. They repeatedly melt and solidify thin layers of powder (powder bed) with a shape corresponding to the cross-section of the three-dimensional structure to be manufactured by irradiating them with a laser or electron beam, thereby building up the desired three-dimensional object layer by layer with high precision.

[0003] This device sinters the raw material powder using a laser or the like without using a mold, eliminating the need for molds and offering the significant advantage of being able to produce complex three-dimensional structures quickly and at low cost. However, because the process involves scanning a powder bed filled with raw material particles with a laser or the like to sinter them, there is a problem that, in principle, a large amount of residual material particles remain that are not incorporated into the fabricated object. Generally, these residual particles that are not incorporated into the fabricated object are reused in the next additive manufacturing batch without any special processing beyond sieving. The number of reuses varies depending on the raw material, additive manufacturing conditions, and the mechanical properties required of the product. Generally, after about 10 reuses, as described in Non-Patent Literature 1, the properties of the raw material particles deteriorate, and they are completely discarded.

[0004] During the process of reusing raw material particles about 10 times, sputter adhesion and heat effects cause the residual particles to change from spherical to irregularly shaped. At the same time, oxidation progresses on the surface of the residual particles that are affected by heat. When these irregularly shaped particles are used as raw material and spread on the powder bed, the raw material particles cannot be arranged neatly, resulting in uneven filling of the raw material particles. In this case, voids (such as blowholes) may be formed in the fabricated object during sintering with a laser, or the fabricated object may not turn out as designed, so irregularly shaped raw material particles must be removed. Furthermore, if the surface of the raw material particles is oxidized, it becomes difficult to melt them with a laser, resulting in defects in mechanical properties and the possibility of them becoming the starting point of fracture, so they should be removed as much as possible, and as a result, they are currently completely discarded after about 10 uses.

[0005] In this specification, raw material particles and residual material particles are collectively referred to as powder particles.

[0006] Yamaguchi et al., "Formation characteristics and sputtering behavior of nickel-based recycled powder in powder bed fusion bonding," Journal of the Japan Society for Precision Engineering Vol.90, No.11, 2024.

[0007] For example, when using aluminum (Al) alloy powder as raw material particles, the surface of the remaining Al particles oxidizes with repeated use, forming aluminum oxide (alumina). To reuse these remaining particles in a state close to the original raw material particles, a process is needed to restore the irregularly shaped spherical particles to their original highly spherical state, and a process is needed to remove or reduce these oxides and return them to a metallic surface. However, reducing the alumina formed by surface oxidation of Al alloy particles used as raw material particles requires a heat treatment that involves heating to a high temperature of over 2000°C in a carbon dioxide environment, as shown in the Ellingham diagram. This temperature far exceeds the melting point of Al and is near its boiling point. Therefore, if the remaining particles after use are heated in a crucible, all the particles will melt and the spherical shape will no longer be maintained. Furthermore, due to the heating to near the boiling point, the Al itself will partially vaporize and the material will be lost. In other words, maintaining the spherical shape and reducing the oxides simultaneously is recognized as an extremely difficult problem from a thermodynamic standpoint.

[0008] Furthermore, the raw material powders used in powder-based 3D printers are not limited to single compositions; alloy materials are also used. However, considering the need to collect and recycle leftover particles to leverage economies of scale, the different target metal components necessitate further adjustments and other labor-intensive processes. As a result, there are no economic advantages in terms of time, energy, or cost, and the current practice of complete disposal leads to high costs.

[0009] One aspect of the present invention aims to realize an activation method that can activate powder particles used in powder-based 3D printers while simultaneously maintaining a spherical shape and reducing oxides.

[0010] To solve the above problems, an activation method according to one aspect of the present invention is an activation method for activating powder particles containing a metal element, which are used as material for articles manufactured by a powder-forming 3D printer using a laser or electron beam, and includes a supply step of supplying the powder particles to a reaction vessel equipped with a plasma torch that generates a plasma flame by plasmaizing a working gas, and a plasma treatment step of processing the powder particles with the plasma flame while the pressure inside the reaction vessel is set to a pressure range in which the plasma flame becomes a flowing viscous fluid, and the temperature of the plasma flame is set to a temperature range in which the maximum temperature of the powder particles is above the melting point of the powder particles and the powder particles do not evaporate.

[0011] According to one aspect of the present invention, in powder particles used in a powder-based 3D printer, it is possible to activate the powder particles while simultaneously maintaining a spherical shape and reducing oxides.

[0012] This is a schematic diagram showing the configuration of an activation device according to one embodiment of the present invention. This is a flowchart showing an example of the processing of the activation method according to one embodiment of the present invention. This is an SEM image of AlSi10Mg to be activated in Example 1. This is an enlarged SEM image of a part of AlSi10Mg shown in Figure 3. This is an SEM image of AlSi10Mg after plasma treatment in Example 1. This is an SEM image of Scalmallory to be activated in Example 2. This is an enlarged SEM image of a part of Scalmallory shown in Figure 6. This is an SEM image of Scalmallory after plasma treatment in Example 2. This is an SEM image of Cu particles to be activated in Example 3. This is an enlarged SEM image of a part of Cu particles shown in Figure 9. This is an SEM image of Cu particles after plasma treatment in Example 3. This is an SEM image of Cu1.5Cr0.5Zr particles to be activated in Example 4. This is an SEM image of Cu1.5Cr0.5Zr particles after plasma treatment in Example 4. This is an SEM image of the Fe-Ni-Co alloy particles to be activated in Example 5. This is an SEM image of the Fe-Ni-Co alloy particles after plasma treatment in Example 5. This is an SEM image of the Fe-Ni-Co-Mo alloy particles to be activated in Example 6. This is an SEM image of the Fe-Ni-Co-Mo alloy particles after plasma treatment in Example 6.

[0013] One embodiment of the present invention will be described in detail below. Figure 1 is a schematic diagram showing the configuration of an activation device 1 used to perform the activation method in this embodiment. The activation method in this embodiment is a method for activating powder particles 2 containing metal elements, which are used as material for articles manufactured by a powder-based 3D printer using a laser or electron beam. In this specification, "activation" means that the surface oxygen concentration may be reduced to the same level as or below that of unused raw material particles, and / or that the shape of the particles may be made to the same level as or better than that of unused raw material particles in terms of sphericity.

[0014] The powder particles 2 to be activated by the activation method of this embodiment contain a metal element. The powder particles 2 may contain Al as a metal element, for example, an alloy containing Al, Si and Mg, an alloy containing Al, Mg, Sc and Zr, or an alloy containing Ti, Al and V. Alternatively, the powder particles 2 may contain Cu, or an alloy containing Cu and Cr. An alloy containing Cu may be, for example, Cu1.5Cr0.5Zr. Alternatively, the powder particles 2 may be stainless steel such as SUS. Alternatively, the powder particles 2 may be an alloy containing Nb. Alternatively, the powder particles 2 may be an alloy containing Ni. Alternatively, the powder particles 2 may be an alloy containing Fe. An alloy containing Fe may be, for example, an Fe-Ni-Co alloy or an Fe-Ni-Co-Mo alloy.

[0015] The powder particles 2 before activation in this embodiment may be leftover particles that have been used multiple times (for example, about 10 times) in a powder-based 3D printer using a laser or electron beam, but were not used to manufacture an article. Such leftover particles have low sphericity and high surface oxidation concentration due to deformation caused by thermal effects during use in the powder-based 3D printer, and the adhesion of fine particles (spatter) that melt and scatter due to laser irradiation.

[0016] As shown in Figure 1, the activation device 1 comprises a hybrid plasma torch 3 (plasma torch), a powder supply unit 20, a reaction vessel 30, a cooling unit 40, and a recovery unit 50. In the activation device 1, the hybrid plasma torch 3 and the reaction vessel 30 are arranged in series, with the hybrid plasma torch 3 on the upper side and the reaction vessel 30 on the lower side.

[0017] The hybrid plasma torch 3 is installed in the reaction vessel 30. The hybrid plasma torch 3 generates a plasma flame 11. The hybrid plasma torch 3 comprises a DC plasma torch 10 and a high-frequency coil 70.

[0018] The DC plasma torch 10 has a cathode electrode and an anode electrode connected to a DC power supply, and a flow path for circulating working gas between the two electrodes. When working gas is supplied to the gas flow path and a DC voltage is applied between the two electrodes, the DC plasma torch 10 generates a DC plasma by converting the working gas into plasma through a discharge that occurs between the two electrodes.

[0019] The high-frequency coil 70 is a high-frequency induction coil that is wound around the outer circumference of an insulating tube through which the working gas flows and is connected to a high-frequency power supply. When a high-frequency current is applied to the high-frequency coil 70, the working gas is converted into plasma by electromagnetic induction, generating high-frequency plasma.

[0020] The hybrid plasma torch 3 generates a hybrid plasma (plasma frame 11) by superimposing a DC plasma generated by the DC plasma torch 10 and a high-frequency plasma generated by the high-frequency coil 70.

[0021] The hybrid plasma torch 3, although not shown in the diagram, is connected to a power supply, a working gas supply unit, a refrigerant supply unit, and a control unit. The power supply applies current and voltage to the hybrid plasma torch 3. The working gas supply unit supplies working gas to the hybrid plasma torch 3. The working gas is, for example, Ar gas and H ２ A gas mixture is used. The refrigerant supply unit cools the hybrid plasma torch 3 using a refrigerant. For example, water is used as the refrigerant. The control unit is electrically connected to the power supply, the working gas supply unit, and the refrigerant supply unit, and controls and monitors the current, voltage, amount of working gas supplied, flow rate of working gas, pressure in the reaction vessel 30, amount of refrigerant supplied, and temperature of the refrigerant. The hybrid plasma torch 3 receives working gas from the working gas supply unit and has current and voltage applied from the power supply, which turns the working gas into plasma and generates a high-temperature plasma flame 11. ２ The amount of gas added (supply) is within the range that allows for the stable generation of the plasma flame 11, and H ２The total amount of molecules and dissociated H radicals is adjusted to be approximately the same as the total amount of oxygen atoms on the surface of powder particles 2 per unit time, taking into account the rate at which powder particles 2 are introduced. The average velocity of the plasma flame 11 is several tens of m / sec. The plasma flame 11 is introduced into the reaction vessel 30.

[0022] The temperature of the plasma flame 11 decreases as it moves from the generation section 12 to the tail flame section 13. The generation section 12 of the plasma flame 11 has a temperature range above the melting point of the powder particles 2.

[0023] In this embodiment, the activation device 1 uses a hybrid plasma torch 3 to generate a plasma flame 11, but the activation device of this disclosure is not limited to this. In one aspect of this disclosure, the activation device may not include a DC plasma torch 10 and may generate the plasma flame 11 using only a high-frequency coil 70. In this case, a water-cooled tube capable of supplying powder particles called probes is inserted into the reaction vessel 30, and powder particles 2 are supplied into the reaction vessel 30 from the water-cooled tube.

[0024] The reaction vessel 30 has an upper part 31, a lower part 32 facing the upper part 31, and a side part 33 connecting the upper part 31 and the lower part 32. The upper part 31 is a disc-shaped lid provided at the upper end of the side part 33. A hybrid plasma torch 3 is provided in the center of the upper part 31. The lower part 32 is a bottomed cylindrical container with an open top. A gate valve 34 is installed at the top of the lower part 32, and at the end of the plasma treatment, the gate valve 34 can be sealed, allowing the lower part 32, which is the container, to be transported while maintaining a vacuum. The reaction vessel 30 is water-cooled and can be cooled under vacuum. The side part 33 is composed of a cylindrical part 33a connected to the upper part 31 and a conical part 33b connected to the lower part 32.

[0025] A pump 80 is connected to the side 33 of the reaction vessel 30 via a pressure regulating valve 90, allowing the pressure inside the reaction vessel 30 to be adjusted.

[0026] The reaction vessel 30 has its upper part 31 connected to the hybrid plasma torch 3, and the plasma flame 11 is introduced from the hybrid plasma torch 3. The temperature of the plasma flame 11 introduced into the reaction vessel 30 decreases from top to bottom.

[0027] The powder supply unit 20 is provided at the upper part of the reaction vessel 30 inside the reaction vessel 30. The opening of the powder supply unit 20 is arranged toward the central axis of the plasma. The number of openings can be selected, such as 4, 8, 12, etc., so that the powder can be uniformly supplied to the entire high-temperature region of the columnar plasma flame. The powder supply unit 20 supplies the powder particles 2 of the powder containing metal elements to the plasma flame 11 generated in the reaction vessel 30. In this embodiment, the powder supply unit 20 uses a plasma gas to supply the powder particles 2 of the powder into the plasma flame 11 in the reaction vessel 30. As the plasma gas, for example, a mixed gas such as Ar, H ２ , N ２ , O ２ , CH ４ , C ２ H ２ is used. The powder particles 2 supplied from the powder supply unit 20 to the plasma flame 11 come into contact with the plasma flame 11 and are processed by the plasma flame 11.

[0028] The cooling unit 40 cools the powder particles 2 processed by the plasma flame 11. The cooling unit 40 is provided inside the reaction vessel 30. The cooling unit 40 is connected to a cooling gas supply unit (not shown), and introduces a cooling gas containing no oxygen supplied from the cooling gas supply unit into the inside of the reaction vessel 30 and blows it onto the lower part of the plasma flame 11. In the activation device of one aspect of the present disclosure, the powder particles 2 processed by the plasma flame 11 may be cooled by ejecting a cooling gas from a nozzle to the plasma flame 11 from the side surface of the reaction vessel 30.

[0029] Next, the details of the conditions for activating the powder particles 2 by the activation device 1 in this embodiment will be described. In the activation device 1, the pressure inside the reaction vessel 30 is set to a pressure range in which the plasma flame 11 becomes a flowing viscous fluid, and the temperature of the plasma flame 11 is set to a temperature range in which the maximum temperature of the powder particles 2 is above the melting point of the powder particles 2, and the powder particles 2 do not evaporate, and the powder particles 2 are processed by the plasma flame 11.

[0030] To set the pressure inside the reaction vessel 30 to a pressure range in which the plasma flame 11 becomes a flowing viscous fluid, for example, the pressure inside the reaction vessel 30 may be set to 0.1 to 400 Torr (0.0133 to 53.2 kPa). The pressure range in which the plasma flame 11 becomes a flowing viscous fluid is the pressure range in which the plasma flame 11 becomes a mesoplasma.

[0031] The "temperature range in which the maximum temperature of the powder particles 2 is above the melting point of the powder particles 2, and the powder particles 2 do not evaporate" refers to a temperature just above the melting point of the powder particles 2. The temperature of the plasma flame 11 is set appropriately depending on the type of powder particles 2. For example, the plasma temperature on the streamlines of the plasma flame 11 where the powder particles are carried by the plasma flow changes depending on the size of the powder particles 2 and the supply rate of the powder particles 2 to the reaction vessel 30, but is always adjusted so that the particle temperature of the powder particles 2 is above the melting point of the powder particles 2 and below the boiling point of the powder particles 2. In particular, for powder particles 2 in which the metal elements constituting the powder particles 2 have low melting and boiling points, mesoplasma conditions can be suitably used, which allow the gas temperature to be kept low and the plasma length to be extended.

[0032] For example, if the powder particles 2 are an alloy containing Al, and the particle size is about 20 to 70 μm, which is a typical particle size commonly used in powder bed fusion bonding using a laser or electron beam, and the supply rate of the powder particles 2 introduced into the plasma is about 50 to 200 g / min, the maximum temperature of the plasma flame 11 may be about 1000°C to 3000°C. As another example, if the powder particles 2 are Ti or an alloy containing Ti, the maximum temperature of the plasma flame 11 may be 2000°C to 5000°C. If the powder particles 2 are an alloy containing Fe or an alloy containing Ni, the maximum temperature of the plasma flame 11 may be 2000°C to 5000°C.

[0033] Furthermore, in the activation device 1 of this embodiment, depending on the scale of the activation device 1, the power supplied to the plasma torch may be 5 kW or more. This makes it easier to adjust the pressure in the reaction vessel 30 and the temperature of the plasma flame 11 to desired conditions. In the case of a hybrid plasma torch having a DC plasma torch 10 and a high-frequency coil 70, such as the hybrid plasma torch 3 of this embodiment, the power supplied to the plasma torch refers to the sum of the power supplied to the DC plasma torch 10 and the power supplied to the high-frequency coil 70. Typically, the power supplied to the DC plasma torch 10 is 3 to 5 kW, and the power supplied to the high-frequency coil 70 is 10 kW or more.

[0034] The power supplied to the hybrid plasma torch 3 depends on the process pressure, the plasma gas flow rate, the amount of powder particles 2 supplied, and the speed of the pump 80. The powder temperature of the powder particles 2 is approximately just above the melting point, and H is supplied to the surface of the powder particles 2. ２ Ya H ２ The settings are adjusted so that the flux of dissociated H radicals is sufficiently high to obtain an etching effect. For example, add 20 slm of Ar to the plasma and H ２Introduce about 5 slm of gas, maintain the pressure at about 1 to 10 Torr, and input about 10 kW into the hybrid plasma torch 3, then a relatively low-temperature mesoplasma with a flow can be generated at a plasma temperature of about 1000 to 2000 °C. When it is desired to increase the processing speed (supply amount) of the powder particles 2, increase the Ar gas input into the plasma to 40 slm and H ２ Increase the gas to about 10 slm. To maintain the pressure at 1 to 10 Torr in the low-pressure region of the mesoplasma, adjust to increase the power input into the hybrid plasma torch 3 to about 20 kW. When performing the treatment at 100 to 200 kPa in the high-pressure region of the mesoplasma, even if about 100 slm of Ar gas is introduced into the plasma, the treatment is possible with a power input of 20 kW into the hybrid plasma torch 3. In any of the above cases, it is necessary to increase the exhaust speed of the exhaust pump 80 for exhaust and to increase the length of the reaction vessel 30 for stable activation regeneration treatment.

[0035] In the activation device 1 in this embodiment, by treating the powder particles 2 with the plasma frame 11 under the above conditions, a part of the powder particles 2 can be melted and the surface of the powder particles 2 can be etched by constituting the plasma frame 11. Thereby, by one process performed at a low temperature, the powder particles 2 can be spheroidized and at the same time, the surface oxygen concentration of the powder particles 2 can be reduced by etching. As a result, the powder particles 2 that have become unusable as a raw material for the powder molding type 3D printer due to structure defects that deteriorate the mechanical properties by the oxidized particles can be activated and reused as a raw material for the powder molding type 3D printer. According to the activation method in this embodiment, the surface oxygen concentration of the powder particles 2 can be made equal to that of the unused raw material particles or slightly lower than that of the unused raw material particles.

[0036] In the activation device 1 according to one aspect of the present embodiment, if necessary, the plasma-treated powder is collected in a container that can be non-exposed and sealed, and the collected container is transferred in a glove box filled with argon gas, and it is possible to transfer it to a storage container or the like inside the glove box. Therefore, oxidation of the powder particles 2 after plasma treatment can be suppressed.

[0037] In the activation device 1 according to one aspect of the present disclosure, in a state where the activation device 1 is tilted, a rotary device is arranged below the inside of the reaction vessel 30, and the powder particles 2 that have fallen downward are transferred upward by the rotary device, and the particles are repeatedly plasma-treated by plasma. It may be configured to perform plasma treatment by a rotary kiln method.

[0038] Next, an activation method using the activation device 1 in the present embodiment will be described while referring to FIG. 2. FIG. 2 is a flowchart showing an example of the processing of the activation method in the present embodiment.

[0039] As shown in FIG. 2, the activation method in the present embodiment first generates a plasma frame 11 in the reaction vessel 30 by plasmaizing the working gas with the hybrid plasma torch 第3 (step S1).

[0040] Next, powder particles 2 are supplied to the reaction vessel 30 (step S2, supply step). At this time, the pressure inside the reaction vessel 30 is set to a pressure range (for example, 0.1 to 400 Torr) where the plasma frame 11 becomes a viscous fluid having a flow, and the temperature of the plasma frame 11 is such that the maximum temperature of the powder particles is equal to or higher than the melting point of the powder particles 2 and the powder particles 2 are not evaporated.

[0041] Next, the powder particles 2 are exposed to the plasma frame in the above state, and the powder particles 2 are processed by the plasma frame 11 (step S3, plasma treatment step).

[0042] Finally, cooling gas is introduced from the cooling unit 40 into the reaction vessel 30 to cool the powder particles 2 processed by the plasma flame 11 (step S4, cooling step). By immediately cooling the powder particles 2 processed by the plasma flame 11 to room temperature in a vacuum atmosphere using the cooling unit 40, the formation of a re-oxidation film on the surface of the powder particles 2 can be suppressed. The cooled powder particles 2 are collected in a container that constitutes the lower part 32 of the reaction vessel 30.

[0043] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0044] [Summary] An activation method according to Embodiment 1 of the present disclosure is an activation method for activating powder particles containing a metal element, which are used as material for articles manufactured by a powder-forming 3D printer using a laser or electron beam, and includes a supply step of supplying the powder particles to a reaction vessel equipped with a plasma torch that generates a plasma flame by plasmaizing a working gas, and a plasma treatment step of processing the powder particles with the plasma flame while the pressure inside the reaction vessel is set to a pressure range in which the plasma flame becomes a flowing viscous fluid, and the temperature of the plasma flame is set to a temperature range in which the maximum temperature of the powder particles is above the melting point of the powder particles and the powder particles do not evaporate.

[0045] The activation method according to Embodiment 2 of the present disclosure further includes a cooling step of cooling the powder particles after the plasma treatment step, in Embodiment 1.

[0046] The activation method according to embodiment 3 of this disclosure is characterized in that, in embodiment 1 or 2 above, the pressure inside the reaction vessel is set to 0.1 to 400 Torr in the plasma treatment step.

[0047] The activation method according to embodiment 4 of this disclosure is characterized in that, in any of embodiments 1 to 3 above, the power supplied to the plasma torch in the plasma processing step is 5 kW or more.

[0048] The activation method according to embodiment 5 of the present disclosure, in any of embodiments 1 to 4 above, wherein in the plasma processing step, the plasma frame spheres the powder particles and simultaneously reduces the surface oxygen concentration of the powder particles by etching.

[0049] The activation method according to embodiment 6 of this disclosure is characterized in that, in any of embodiments 1 to 5 above, the powder particles contain Al as the metal element.

[0050] The activation method according to embodiment 7 of this disclosure is characterized in that, in any of embodiments 1 to 6 above, the powder particles are an alloy containing Al, Si, and Mg.

[0051] The activation method according to embodiment 8 of the present disclosure is, in any of embodiments 1 to 6 above, an alloy containing Al, Mg, Sc, and Zr.

[0052] The activation method according to aspect 9 of this disclosure is characterized in that, in any of aspects 1 to 6 above, the powder particles are Cu.

[0053] The activation method according to embodiment 10 of the present disclosure is characterized in that, in any of embodiments 1 to 6, the powder particles are Cu1.5Cr0.5Zr.

[0054] The activation method according to embodiment 11 of the present disclosure is characterized in that, in any of embodiments 1 to 6 above, the powder particles are an Fe-Ni-Co alloy.

[0055] The activation method according to embodiment 12 of this disclosure is characterized in that, in any of embodiments 1 to 6 above, the powder particles are an Fe-Ni-Co-Mo alloy.

[0056] An embodiment of the present invention is described below. In this embodiment, the activation method of the present disclosure was applied to powder particles having the composition of AlSi10Mg. Figure 3 is a Scanning Electron Microscope (SEM) image of the AlSi10Mg to be activated in this embodiment. The particles shown in Figure 3 are leftover particles that were used 14 times in a powder-based 3D printer but were not used to manufacture articles. Figure 4 is a magnified SEM image of a part of the AlSi10Mg shown in Figure 3. As shown in Figures 3 and 4, the AlSi10Mg to be activated in this embodiment included elliptical particles and had low sphericity. In addition, some particles had minute particles attached to their surface.

[0057] For the AlSi 10Mg shown in Figure 3, after removing fine particles using a sieve with a mesh size of 45 μm, the plasma treatment according to this disclosure was performed under the following conditions: • Plasma torch: Hybrid plasma torch having a DC plasma torch and a high-frequency coil • Supply rate of powder particles to the reaction vessel: 50 g / min • Power supplied to the DC plasma torch: 3.4 kW • Power supplied to the high-frequency coil: 17.5 kW • Pressure in the reaction vessel: 30 kPa (226 Torr) • Plasma gas: Ar • Flow rate of plasma gas: 12 slm • H ２ Gas supply volume: 1 slm

[0058] The pressure in the reaction vessel described above is the pressure range in which the plasma flame generated inside the pressure vessel becomes a flowing, viscous fluid. Furthermore, each of the above conditions is designed to set the temperature of the plasma flame to a temperature range in which the maximum temperature of the powder particles is above the melting point of AlSi10Mg, and where the AlSi10Mg does not evaporate.

[0059] For AlSi10Mg before plasma treatment and AlSi10Mg after plasma treatment, the average particle size, sphericity, average volume, average surface area, specific surface area, oxygen concentration, and average oxide film thickness were measured or calculated.

[0060] The average particle size was measured using an FE-SEM (JEOL Ltd., JSM-IT800SHL).

[0061] Sphericity, average volume, average surface area, and specific surface area were calculated from quantitative image evaluation of SEM photographs. Oxygen concentration was measured using an EMGA-930 from Horiba, Ltd.

[0062] The average oxide film thickness was determined by converting the oxygen concentration measured by EMGA into the thickness of the aluminum oxide, under the assumption that single-crystal aluminum oxide (alumina) is formed on the outermost surface of the particles, which are the average size measured from SEM images.

[0063] Table 1 shows the measured or calculated average particle size, sphericity, average volume, average surface area, specific surface area, oxygen concentration, and average oxide film thickness. The specific surface area is expressed as a ratio to the specific surface area before plasma treatment (specific surface area ratio). As shown in Table 1, the change in average particle size before and after plasma treatment was small. Figure 5 is an SEM image of AlSi10Mg after plasma treatment. As shown in Table 1 and Figure 5, the sphericity of AlSi10Mg after plasma treatment was higher than that of AlSi10Mg before plasma treatment. Also, as shown in Table 1, the specific surface area decreased after plasma treatment. Also, as shown in Table 1, the oxygen concentration of AlSi10Mg after plasma treatment was significantly lower than that of AlSi10Mg before plasma treatment. These results demonstrate that by treating AlSi10Mg with the activation method of this disclosure, it is possible to achieve both the maintenance of spherical shape and the reduction of oxides, thereby increasing sphericity and reducing surface oxygen concentration.

[0064] In this embodiment, we conducted an investigation using leftover material particles that were not used to manufacture articles after being used 14 times with a powder-based 3D printer. We confirmed that even when the plasma treatment of the present invention is applied to unused raw material particles created using the gas atomization method, it is possible to make them more spherical and reduce surface oxidation.

[0065] Other embodiments of the present invention are described below. In this embodiment, the activation method of the present disclosure was applied to powder particles made of an alloy containing Al, Mg, Sc, and Zr called Scalmallory. Figure 6 is an SEM image of the Scalmallory to be activated in this embodiment. The particles shown in Figure 6 are leftover particles that were used 14 times with a powder-based 3D printer but were not used to manufacture articles. Figure 7 is an enlarged SEM image of a part of the Scalmallory shown in Figure 6. As shown in Figures 6 and 7, no large, flattened particles were observed in the Scalmallory to be activated in this embodiment.

[0066] The plasma treatment of the Scalmalloy shown in Figure 6 was performed under the following conditions: • Plasma torch: Hybrid plasma torch having a DC plasma torch and a high-frequency coil • Supply rate of powder particles to the reaction vessel: 100 g / min • Power supplied to the DC plasma torch: 3.4 kW • Power supplied to the high-frequency coil: 21 kW • Pressure in the reaction vessel: 30 kPa (226 Torr) • Plasma gas: Ar • Flow rate of plasma gas: 12 slm • H ２ Gas supply volume: 1 slm

[0067] The pressure in the reaction vessel described above is the pressure range in which the plasma flame generated inside the pressure vessel becomes a flowing, viscous fluid. Furthermore, each of the above conditions is necessary to set the temperature of the plasma flame to a temperature range in which the maximum temperature of the powder particles is above the melting point of Scalmalloy, and Scalmalloy does not evaporate.

[0068] For both the Scalemallory samples before and after plasma treatment, the average particle size, sphericity, average volume, average surface area, specific surface area, oxygen concentration, and average oxide film thickness were measured or calculated. The measurement and calculation methods were the same as those used in Example 1.

[0069] Table 2 shows the measured or calculated average particle size, sphericity, average volume, average surface area, specific surface area, oxygen concentration, and average oxide film thickness. Figure 8 is an SEM image of Scalelloy after plasma treatment. As shown in Table 2 and Figure 8, the sphericity of Scalelloy after plasma treatment was higher than that of Scalelloy before plasma treatment. Also, as shown in Table 2, the specific surface area decreased after plasma treatment. Furthermore, as shown in Table 2, the oxygen concentration of Scalelloy after plasma treatment was significantly lower than that of Scalelloy before plasma treatment. These results demonstrate that by treating Scalelloy with the activation method of this disclosure, it is possible to achieve both the maintenance of spherical shape and the reduction of oxides, thereby increasing sphericity and reducing surface oxygen concentration.

[0070] Other embodiments of the present invention are described below. In this embodiment, the activation method of the present disclosure was applied to Cu particles. Figure 9 is an SEM image of the Cu particles to be activated in this embodiment. The particles shown in Figure 9 are leftover particles that were used 14 times with a powder-based 3D printer but were not used to manufacture articles. Figure 10 is an enlarged SEM image of a part of the Cu particles shown in Figure 9. As shown in Figures 9 and 10, the Cu particles to be activated in this embodiment included elliptical particles and had low sphericity.

[0071] The plasma treatment according to this disclosure was performed on Cu particles shown in Figure 9 under the following conditions: • Plasma torch: Hybrid plasma torch having a DC plasma torch and a high-frequency coil • Supply rate of powder particles to the reaction vessel: 720 g / min • Power supplied to the DC plasma torch: 3.4 kW • Power supplied to the high-frequency coil: 12 kW • Pressure in the reaction vessel: 30 kPa (226 Torr) • Plasma gas: Ar • Flow rate of plasma gas: 300 slm • H ２ Gas supply: 3 slm

[0072] The pressure in the reaction vessel described above is the pressure range in which the plasma flame generated inside the pressure vessel becomes a flowing, viscous fluid. Furthermore, each of the above conditions is designed to set the temperature of the plasma flame to a temperature range in which the maximum temperature of the powder particles is above the melting point of the Cu particles, and where the Cu particles do not evaporate.

[0073] The average particle size, sphericity, and oxygen concentration were measured or calculated for Cu particles before and after plasma treatment. The measurement and calculation methods were the same as those used in Example 1.

[0074] Table 3 shows the measured or calculated average particle size, sphericity, and oxygen concentration. Figure 11 is an SEM image of Cu particles after plasma treatment. As shown in Table 3 and Figure 11, the Cu particles after plasma treatment had higher sphericity than the Cu particles before plasma treatment. Also, as shown in Table 3, the oxygen concentration of the Cu particles after plasma treatment was significantly reduced compared to the Cu particles before plasma treatment. These results demonstrate that by treating Cu particles with the activation method of this disclosure, it is possible to achieve both the maintenance of spherical shape and the reduction of oxides, thereby increasing sphericity.

[0075] Other embodiments of the present invention are described below. In this embodiment, the activation method of the present disclosure was applied to Cu1.5Cr0.5Zr particles. Figure 12 is an SEM image of the Cu1.5Cr0.5Zr particles to be activated in this embodiment. The particles shown in Figure 12 are leftover particles that were used 14 times with a powder-based 3D printer but were not used to manufacture articles. As shown in Figure 12, the Cu1.5Cr0.5Zr particles to be activated in this embodiment included elliptical particles and had low sphericity. In addition, some particles had minute particles attached to their surface.

[0076] The plasma treatment according to this disclosure was performed on Cu1.5Cr0.5Zr particles shown in Figure 12 under the following conditions: • Plasma torch: Hybrid plasma torch having a DC plasma torch and a high-frequency coil • Supply rate of powder particles to the reaction vessel: 228 g / min • Power supplied to the DC plasma torch: 3 kW • Power supplied to the high-frequency coil: 12 kW • Pressure in the reaction vessel: 30 kPa (226 Torr) • Plasma gas: Ar • Flow rate of plasma gas: 100 slm • H ２ Gas supply volume: 1 slm

[0077] The pressure in the reaction vessel described above is the pressure range in which the plasma flame generated inside the pressure vessel becomes a flowing, viscous fluid. Furthermore, each of the above conditions is designed to set the temperature of the plasma flame to a temperature range in which the maximum temperature of the powder particles is above the melting point of the Cu1.5Cr0.5Zr particles, and the Cu1.5Cr0.5Zr particles do not evaporate.

[0078] The average particle size, sphericity, and oxygen concentration were measured or calculated for both the Cu1.5Cr0.5Zr particles before plasma treatment and the Cu1.5Cr0.5Zr particles after plasma treatment. The measurement and calculation methods were the same as those used in Example 1.

[0079] Table 4 shows the measured or calculated average particle size, sphericity, and oxygen concentration. Figure 13 is an SEM image of Cu1.5Cr0.5Zr particles after plasma treatment. As shown in Table 4 and Figure 13, the Cu1.5Cr0.5Zr particles after plasma treatment had higher sphericity than the Cu1.5Cr0.5Zr particles before plasma treatment. Also, as shown in Table 4, the oxygen concentration of the Cu1.5Cr0.5Zr particles after plasma treatment was significantly reduced compared to the Cu1.5Cr0.5Zr particles before plasma treatment. These results demonstrate that by treating Cu1.5Cr0.5Zr particles with the activation method of this disclosure, it is possible to achieve both the maintenance of spherical shape and the reduction of oxides, thereby increasing sphericity.

[0080] Other embodiments of the present invention are described below. In this embodiment, the activation method of the present disclosure was applied to Fe-Ni-Co alloy particles, which are a superinvar material. Figure 14 is an SEM image of the Fe-Ni-Co alloy particles to be activated in this embodiment. The particles shown in Figure 14 are leftover particles that were used 14 times with a powder-based 3D printer but were not used to manufacture articles. As shown in Figure 14, no large, flattened particles were observed among the Fe-Ni-Co alloy particles to be activated in this embodiment.

[0081] The plasma treatment described in this disclosure was performed on Fe-Ni-Co alloy particles shown in Figure 14 under the following conditions: • Plasma torch: Hybrid plasma torch having a DC plasma torch and a high-frequency coil • Supply rate of powder particles to the reaction vessel: 206.6 g / min • Power supplied to the DC plasma torch: 3 kW • Power supplied to the high-frequency coil: 17 kW • Pressure in the reaction vessel: 30 kPa (226 Torr) • Plasma gas: Ar • Flow rate of plasma gas: 100 slm • H ２ Gas supply volume: 1 slm

[0082] The pressure in the reaction vessel described above is the pressure range in which the plasma flame generated inside the pressure vessel becomes a flowing, viscous fluid. Furthermore, each of the above conditions is designed to set the temperature of the plasma flame to a temperature range in which the maximum temperature of the powder particles is above the melting point of the Fe-Ni-Co alloy particles, and the Fe-Ni-Co alloy particles do not evaporate.

[0083] The average particle size, sphericity, and oxygen concentration were measured or calculated for Fe-Ni-Co alloy particles before and after plasma treatment. The measurement and calculation methods were the same as those used in Example 1.

[0084] Table 5 shows the measured or calculated average particle size, sphericity, and oxygen concentration. Figure 15 is an SEM image of Fe-Ni-Co alloy particles after plasma treatment. As shown in Table 5 and Figure 15, the Fe-Ni-Co alloy particles after plasma treatment had higher sphericity than the Fe-Ni-Co alloy particles before plasma treatment. Also, as shown in Table 5, the oxygen concentration of the Fe-Ni-Co alloy particles after plasma treatment was significantly reduced compared to the Fe-Ni-Co alloy particles before plasma treatment. These results demonstrate that by treating Fe-Ni-Co alloy particles with the activation method of this disclosure, it is possible to achieve both the maintenance of spherical shape and the reduction of oxides, thereby increasing sphericity.

[0085] Other embodiments of the present invention are described below. In this embodiment, the activation method of the present disclosure was applied to Fe-Ni-Co-Mo alloy particles. Figure 16 is an SEM image of the Fe-Ni-Co-Mo alloy particles to be activated in this embodiment. The particles shown in Figure 16 are leftover particles that were used 14 times with a powder-based 3D printer but were not used to manufacture articles. As shown in Figure 16, no large, flattened particles were observed among the Fe-Ni-Co-Mo alloy particles to be activated in this embodiment.

[0086] The plasma treatment described herein was performed on Fe-Ni-Co-Mo alloy particles shown in Figure 16 under the following conditions: • Plasma torch: Hybrid plasma torch having a DC plasma torch and a high-frequency coil • Supply rate of powder particles to the reaction vessel: 213.3 g / min • Power supplied to the DC plasma torch: 3 kW • Power supplied to the high-frequency coil: 17 kW • Pressure in the reaction vessel: 30 kPa (226 Torr) • Plasma gas: Ar • Flow rate of plasma gas: 100 slm • H ２ Gas supply volume: 1 slm

[0087] The pressure in the reaction vessel described above is the pressure range in which the plasma flame generated inside the pressure vessel becomes a flowing, viscous fluid. Furthermore, each of the above conditions is designed to set the temperature of the plasma flame to a temperature range in which the maximum temperature of the powder particles is above the melting point of the Fe-Ni-Co-Mo alloy particles, and the Fe-Ni-Co-Mo alloy particles do not evaporate.

[0088] The average particle size, sphericity, and oxygen concentration were measured or calculated for Fe-Ni-Co-Mo alloy particles before and after plasma treatment. The measurement and calculation methods were the same as those used in Example 1.

[0089] Table 6 shows the measured or calculated average particle size, sphericity, and oxygen concentration. Figure 17 is an SEM image of Fe-Ni-Co-Mo alloy particles after plasma treatment. As shown in Table 6 and Figure 17, the Fe-Ni-Co-Mo alloy particles after plasma treatment had higher sphericity than the Fe-Ni-Co-Mo alloy particles before plasma treatment. Also, as shown in Table 6, the oxygen concentration of the Fe-Ni-Co-Mo alloy particles after plasma treatment was significantly reduced compared to the Fe-Ni-Co-Mo alloy particles before plasma treatment. These results demonstrate that by treating Fe-Ni-Co-Mo alloy particles with the activation method of this disclosure, it is possible to achieve both the maintenance of spherical shape and the reduction of oxides, thereby increasing sphericity.

[0090] Although details are omitted here, we have confirmed that the sphericity of TiAl particles and Ti6Al4V particles can also be significantly improved.

[0091] 1. Activation device 2. Powder particles 10. DC plasma torch 11. Plasma flame 20. Powder supply unit 30. Reaction vessel 40. Cooling unit 50. Recovery unit 70. High-frequency coil

Claims

1. An activation method for activating powder particles containing a metal element, which are used as material for articles manufactured by a powder-based 3D printer using a laser or electron beam, comprising: a supply step of supplying the powder particles to a reaction vessel equipped with a plasma torch that generates a plasma flame by plasmaizing a working gas; and a plasma treatment step of processing the powder particles with the plasma flame while the pressure inside the reaction vessel is set to a pressure range in which the plasma flame becomes a flowing viscous fluid, and the temperature of the plasma flame is set to a temperature range in which the maximum temperature of the powder particles is above the melting point of the powder particles and the powder particles do not evaporate.

2. The activation method according to claim 1, further comprising a cooling step of cooling the powder particles after the plasma treatment step.

3. The activation method according to claim 1, wherein in the plasma treatment step, the pressure inside the reaction vessel is set to 0.1 to 400 Torr.

4. The activation method according to claim 1, wherein the power supplied to the plasma torch in the plasma processing step is 5 kW or more.

5. The activation method according to claim 1, wherein in the plasma processing step, the plasma flame sphericalizes the powder particles and simultaneously reduces the surface oxygen concentration of the powder particles by etching.

6. The activation method according to claim 1, wherein the powder particles contain Al as the metal element.

7. The activation method according to claim 1, wherein the powder particles are an alloy containing Al, Si, and Mg.

8. The activation method according to claim 1, wherein the powder particles are an alloy containing Al, Mg, Sc, and Zr.

9. The activation method according to claim 1, wherein the powder particles are Cu.

10. The activation method according to claim 1, wherein the powder particles are Cu1.5Cr0.5Zr.

11. The activation method according to claim 1, wherein the powder particles are an Fe-Ni-Co alloy.

12. The activation method according to claim 1, wherein the powder particles are an Fe-Ni-Co-Mo alloy.

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