Method of producing nitrogen-coated metal particle

Abstract

To provide a nitrogen-coated metal particle having high fluidity as a raw material powder for powder metallurgy or a 3D printer.SOLUTION: A method of producing a nitrogen-coated metal particle includes a nitriding step of heating metal particles at 500°C or higher and a melting point or lower under nitrogen atmosphere, so that nitrogen-coated metal particles have a Carr fluidity index of 70 or higher. The method of producing a nitrogen-coated metal particle further includes a carbon coating step of contacting metal particles with a soluble carbon material.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing highly fluid nitrogen-coated metal particles.

Background Art

[0002] Metals and alloys are used in a wide range of fields. Also, metal particles and alloy particles in the form of powders are used in applications such as powder metallurgy, 3D printers, and welding.

[0003] In the case of, for example, plate-shaped metals that are not powders, for the purpose of improving the surface strength, corrosion resistance (e.g., acid resistance), and fluidity, ammonia treatment, nitriding treatment by solid solution of nitrogen, and (Patent Document 1 , Non-Patent Document 1), carbon coating by vapor deposition has been studied (Non-Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Non-Patent Documents

[0005]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] As described above, although metal particles are used in various applications, there is a problem of poor fluidity. For example, in powder metallurgy, fluidity is important in filling the mold, and in 3D printer applications, fluidity is also important for filling the mold and transferring through thin nozzles. Also, the residual nitrogen and carbon components are also problems.

[0007] As described above, nitriding treatment and carbon coating have been studied for steel and stainless steel that are not powders, but in the nitriding treatment method using a chemical agent for a fine structure such as powder, since the reactivity is too high, harmful gases are generated, etc., it has been difficult to perform good treatment. Also, when nitrogen is dissolved in molten metal, the process has been complicated. Furthermore, also in carbon coating, in the vapor phase method, it has been difficult to coat parts where particles contact each other, etc.

[0008] In view of the above situation, the present invention aims to provide a method for manufacturing nitrogen-coated metal particles that can exhibit high fluidity (affecting handling properties, etc.), high grain boundary bonding properties (affecting strength, hardness, etc.), and high grain boundary denseness (affecting filling properties, etc.) after sintering or heating, and is useful for powder metallurgy, 3D printers, welding applications, etc.

Means for Solving the Problems

[0009] The present inventor conducted various studies to achieve the above object and arrived at the present invention. That is, a method for manufacturing nitrogen-coated metal particles, including a nitriding step of heating metal particles at 500°C or higher and below the melting point in a nitrogen atmosphere, and characterized in that the Carr's flowability index of the nitrogen-coated metal particles is 70 or higher. Further, it is a method for manufacturing nitrogen-coated metal particles, characterized by including a carbon coating step of contacting with a soluble carbon material.

Effects of the Invention

[0010] By using the manufacturing method of the present invention, it becomes possible to provide nitrogen-coated metal particles with high fluidity.

Modes for Carrying Out the Invention

[0011] Hereinafter, the present invention will be described in detail. Note that combinations of two or more of the individual preferred forms of the present invention described below are also preferred forms of the present invention.

[0012] [Method for Producing Nitrogen-Coated Metal Particles] <Nitriding Step> The method for producing nitrogen-coated metal particles of the present invention includes a nitriding step of heating metal particles at a temperature of 500°C or higher and lower than the melting point in a nitrogen atmosphere. The nitriding step may be either before or after the carbon coating step described later.

[0013] The heating in the nitriding step of the present invention only needs to be 500°C or higher, more preferably 600°C or higher, and even more preferably 700°C or higher. The upper limit of the heating only needs to be lower than the melting point of the metal particles as the raw material, more preferably (melting point - 50)°C or lower, and even more preferably (melting point - 100)°C or lower.

[0014] The nitriding step of the present invention is preferably carried out in a nitrogen atmosphere, and it may be heated in a firing furnace replaced with nitrogen gas, etc., or it may be heated with a nitrogen gas flow like a tubular furnace or a rotary kiln.

[0015] The nitriding step of the present invention may heat the metal particles as the raw material in a stationary state, but for efficient nitriding, it is also preferable to heat the particles in a fluidized state. For example, it is preferable to form a fluidized bed by a nitrogen flow from the vertical downward direction of the particles or to provide a stirring device like a rotary kiln.

[0016] The nitriding step of the present invention only needs to be in a nitrogen atmosphere. From the viewpoint of suppressing the oxidation of metal particles, the oxygen concentration is preferably 5% by volume or less. More preferably 3% by volume or less, even more preferably 1% by volume or less, and most preferably 0.1% by volume or less.

[0017] <Carbon Coating Step> The method for manufacturing the nitrogen-coated metal particles of the present invention may further include a carbon coating step of bringing the metal particles into contact with a soluble carbon material. Bringing into contact includes, for example, (1) mixing the soluble carbon material and the metal particles in a solvent. At this time, the soluble carbon material may be added to the solvent first, the metal particles may be added first, or they may be added simultaneously. Also, bringing into contact includes (2) firing the metal particles and the soluble carbon material raw material in a mixed state to generate the soluble carbon material in the mixed state, and then a solvent may be added. In both (1) and (2), the soluble carbon material can uniformly cover the metal surface. The solvent is not particularly limited, and it may be a solvent in which the soluble carbon material is soluble, insoluble, or only dispersible. However, from the viewpoint of most effectively exhibiting the effects of the present invention, it is preferable to use a solvent in which the above-mentioned soluble carbon material is soluble.

[0018] The carbon coating step of the present invention may be carried out at room temperature or heated in a solvent. The heating temperature is not particularly limited, but it is preferably 200°C or lower. It is possible to adjust with the boiling point of the selected solvent as the maximum temperature.

[0019] In the carbon coating step of the present invention, from the viewpoint of enhancing the dispersibility of the metal particles in the mixing of the metal particles and the soluble carbon material in a solvent, a dispersion treatment may be used. Examples of the dispersion treatment include shear treatments such as a mixer and a homogenizer, and ultrasonic treatment.

[0020] In the carbon coating step of the present invention, after mixing the metal particles and the soluble carbon material, it is also preferable to add a solvent and remove the solution in which the soluble carbon material has dissolved. Or it is also preferable to remove the solution in which the already existing soluble carbon material has dissolved. That is, it is also preferable to dissolve and wash the soluble carbon material not involved in the carbon coating with a solvent. Furthermore, it is also preferable to repeatedly remove the excess solution and add the solvent for purification. For this purification step, centrifugation, filtration, decantation, etc. can be used. The solvent for the purification step may be the same as the solvent used in the contact step or a different solvent. In addition, in the purification step, by adjusting the amounts of the soluble carbon material and metal particles to be brought into contact, it is possible to uniformly coat them even without purification. That is, the purification step may or may not be performed.

[0021] The carbon coating step of the present invention may further include a heat firing step. After forming the carbon coating layer, by heat firing, the bond between the metal particles and the carbon coating layer can be made stronger, and the carbonization of the carbon coating layer can also proceed further. The temperature of the heat firing step is preferably 300°C to 1000°C, more preferably 500 to 900°C, and most preferably 600 to 800°C. At the above temperature, the carbonization can proceed well and the bond can be strengthened. From the viewpoint of avoiding combustion of the carbon coating layer, the atmosphere of the heat firing step is preferably a vacuum or an inert gas atmosphere. The heat firing step may be before, after, or simultaneous with the nitriding step. From the viewpoint of process simplicity, the heat firing step is preferably performed simultaneously with the nitriding step.

[0022] [Nitrogen-coated metal particles] The nitrogen-coated metal particles obtained by the production method of the present invention preferably have a nitrogen content of 0.1% or more by an inert gas melting method. Thereby, particles with good fluidity are obtained. From the viewpoint of fluidity, it is preferably 0.2% or more, more preferably 0.3% or more, and most preferably 0.5% or more. The upper limit is not particularly limited, but from the viewpoint of not reducing the original metal component ratio, it is 5% or less, more preferably 3% or less, and even more preferably 2% or less. When the metal particles as raw materials contain a nitrogen component, the difference is the value of the nitrogen content in the present invention.

[0023] The nitrogen-coated metal particles obtained by the production method of the present invention preferably have a carbon content of 0.01% by mass or more as determined by the combustion-infrared absorption method. This results in particles with good fluidity. From the perspective of fluidity, it is more preferably 0.02% or more. The upper limit is not particularly limited, but from the perspective of not reducing the original metal component ratio, it is 5% or less, more preferably 3% or less, and even more preferably 1% or less. When the raw material metal particles contain a carbon component, the difference is the value of the carbon content of the present invention.

[0024] The nitrogen-coated metal particles obtained by the production method of the present invention preferably have a peak in the G band (around 1580 cm−1 derived from the benzene hexagonal network structure) in Raman spectroscopic analysis. Further, it preferably has a peak in the D band (around 1350 cm−1 derived from defects and functional groups). By having these peaks, it can be characterized as having a skeleton as a carbon material, and it can be seen that a carbon coating layer with good fluidity, bonding property, and denseness is formed. -1 near) and preferably further has a peak in the D band (near 1350 cm -1 −1 derived from defects and functional groups). By having these peaks, it can be characterized as having a skeleton as a carbon material, and it can be seen that a carbon coating layer with good fluidity, bonding property, and denseness is formed.

[0025] The nitrogen-coated metal particles obtained by the production method of the present invention have a Carr's fluidity index of 70 or more as determined by analysis using a Hosokawa Micron powder tester (PT-X). Carr's fluidity index is the sum of the indexes given to four items: the angle of repose of the powder, the spatula angle (average angle before and after impact), compressibility, and uniformity. More preferably, Carr's fluidity index is 80 or more, and even more preferably Carr's fluidity index is 90 or more. Generally, a fluidity index of 70 or more is considered good, 80 or more is better, and 90 or more is the best. That is, it can be said that the Carr's fluidity index of the nitrogen-coated metal particles being 70 or more has good properties for handling as a powder.

[0026] The nitrogen-coated metal particles obtained by the production method of the present invention preferably have an angle of repose of 40° or less, and more preferably 35° or less. This results in particles with high fluidity.

[0027] The nitrogen-coated metal particles obtained by the production method of the present invention preferably have a spatula angle (before impact) of 50° or less, more preferably 40° or less. Also, the spatula angle (after impact) is preferably 30° or less, more preferably 25° or less. Thereby, particles with high fluidity are obtained.

[0028] The nitrogen-coated metal particles obtained by the production method of the present invention preferably have a proportion of the number of particles consisting only of carbon of 1% or less when observing the particles with an electron microscope or an optical microscope. More preferably, it is 0.5% or less, still more preferably 0.1% or less. Thereby, high-quality carbon-coated metal particles are obtained. The identification of nitrogen-coated metal particles and particles consisting only of carbon can be identified by EDS mapping analysis in an electron microscope. The metal components contained in the core particles are detected from the nitrogen-coated metal particles (for example, 50% or more), but in the particles consisting only of carbon, most of the components are carbon elements (for example, 50% or more). In an optical microscope, it can be identified by whether the particles have a metallic luster or not. In an optical microscope, the nitrogen-coated metal particles have a metallic luster, while the particles consisting only of carbon are black. Note that the particles consisting only of carbon refer to, for example, particles of 100 nm or more.

[0029] The nitrogen-coated metal particles obtained by the production method of the present invention preferably have a ratio of the total peak area derived from carbon-oxygen bonds (such as C-O bonds and C=O bonds) to the total binding peak area of 10% or more when analyzed by O1s XPS. Thereby, it has a bond between carbon, oxygen, and metal, and high-quality carbon-coated metal particles are obtained. More preferably, it is 15% or more, still more preferably 20% or more, particularly preferably 25% or more, and most preferably 30% or more.

[0030] The shape of the nitrogen-coated metal particles obtained by the production method of the present invention is not particularly limited, but from the viewpoint of fluidity, it is preferably spherical or rounded. Among these, spherical is particularly preferable.

[0031] The nitrogen-coated metal particles obtained by the production method of the present invention preferably contain particles with a particle size of 1 μm or more and 100 μm or less in the particle size measurement by optical microscope or scanning electron microscope observation. By including particles in this range, the fluidity becomes higher.

[0032] The nitrogen-coated metal particles obtained by the production method of the present invention preferably have a volume average particle size D50 of 10 μm or more and 100 μm or less. By being in this range, the fluidity is further excellent.

[0033] The nitrogen-coated metal particles obtained by the production method of the present invention preferably do not show a peak in the G band in Raman spectroscopic analysis after sintering or heat-melting and solidifying. This is because, as described above, it is preferable that no carbon component remains after sintering or heat-melting and solidifying (for example, after welding). The nitrogen-coated metal particles of the present invention preferably further have a carbon coating layer for improving fluidity, but the carbon coating layer itself disappears when exposed to high temperatures such as heat-melting. That is, the carbon coating layer contributes to improving fluidity and bonding properties, but has no influence on the structure after heating (melting, sintering, etc.).

[0034] The nitrogen-coated metal particles obtained by the production method of the present invention preferably have a Carr's fluidity index 5 or more higher than that of the raw material metal particles or the particles obtained by removing the nitrogen coating layer and the carbon coating layer from the nitrogen-coated metal particles. That is, it is preferable that the Carr's fluidity index is 5 or more higher due to the effects of the nitrogen coating layer and the carbon coating layer. More preferably 6 or more, still more preferably 7 or more, and particularly preferably 7.5 or more. Since the fluidity of the nitrogen-coated metal particles greatly depends on the original raw material particles, it is important that the relative value (relative value to the core particles) is good in order to represent the effects of the nitrogen coating layer and the carbon coating layer together with the absolute value as described above.

[0035] [Metal particles] Examples of the types of metal particles that are raw materials for the production method of the present invention include metal particles composed of one element or alloy particles composed of two or more elements, and may also be a mixture of two or more metal particles or alloy particles. As the element of the metal particles composed of one element, those that are stable in air are preferable, and Mg, Al, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, La, W, Ir, Pt, Au, Pb, and Bi are preferable. Examples of the alloy particles composed of two or more elements include stainless steel (including Fe and Cr and containing one or more elements such as C, Si, Al, Mn, Ni, Co, Mo, V, and W), nickel alloy (including Ni and containing one or more elements such as B, C, Si, Al, Cu, Cr, Fe, Mo, Nb, and W), aluminum alloy (including Al and containing one or more elements such as Cu, Mn, Ti, Si, Mg, Zn, and Ni), magnesium alloy (including Mg and containing one or more elements such as Al and Zn), cobalt alloy (including Co and containing one or more elements such as C, Cr, Al, Ni, Mo, W, and Y), and titanium alloy (including Ti and containing one or more elements such as Al, Cr, V, Sn, Zr, Mo, and Nb). The above elements may contain non-metals, and for example, B, C, Si, etc. are preferable. Among these, steel particles, stainless steel particles, aluminum alloy particles, and titanium alloy particles are particularly preferable.

[0036] As the metal particles that are raw materials for the production method of the present invention, it is preferable that their constituent elements do not contain nitrogen and carbon. Although nitrogen and carbon may be contained as impurities, in order to exhibit the effects of the present invention, it is preferable that nitrogen and carbon are 0.1% or less. More preferably, it is 0.05% or less, and most preferably, it is 0.01% or less.

[0037] As the metal particles that are raw materials for the production method of the present invention, the metal particles may have a layer of different components on the surface (for example, a core-shell structure). Among them, it is preferable that the shell layer contains a metal component. Thereby, since the metal layer (in some cases, a metal oxide layer such as a passive film) is exposed on the surface, carbon coating can be performed well.

[0038] The metal particles, which are the raw materials of the production method of the present invention, are preferably metal particles that form a passive state. Thereby, the interaction with the nitrogen coating layer and the carbon coating layer becomes stronger.

[0039] The shape of the metal particles, which are the raw materials of the production method of the present invention, is not particularly limited, but from the viewpoint of fluidity, it is preferably spherical or rounded. Among these, spherical is particularly preferred.

[0040] The melting point of the metal particles, which are the raw materials of the production method of the present invention, is preferably 600 °C or higher. By having a high melting point, it becomes possible to perform the nitriding process well. More preferably, it is 700 °C or higher, and even more preferably 800 °C or higher.

[0041] The production method of the metal particles, which are the raw materials of the production method of the present invention, is not particularly limited, but from the viewpoint of fluidity, those produced by the atomization method are preferred. Among these, particularly the water atomization method and the gas atomization method are preferred. In the production method of the present invention, even metal particles produced by the water atomization method or the gas atomization method can be imparted with better fluidity and high quality due to the effects of the nitrogen coating layer and the carbon coating layer.

[0042] [Carbon Coating Layer] The average thickness of the carbon coating layer obtained by the production method of the present invention is preferably 10 nm or less. This can be evaluated by randomly observing 10 particles with a transmission electron microscope. More preferably, it is 7 nm or less, and most preferably 5 nm or less.

[0043] The carbon coating layer obtained by the production method of the present invention has a peak in Raman spectroscopy at the G band (around 1580 cm -1 near) derived from the benzene hexagonal network structure. Furthermore, it preferably has a peak at the D band (around 1350 cm -1 near) derived from defects and functional groups. Furthermore, the G' band (around 2700 cm -1It is preferable to have peaks in the vicinity). By having these peaks, it can be characterized as having a skeleton as a carbon material, and it can be said that it is a good carbon coating layer.

[0044] The carbon coating layer obtained by the production method of the present invention preferably has a coating rate of 80% or more with respect to the particles. Thereby, a high-quality carbon coating layer is obtained. The coating rate can be evaluated by the ratio at which the G-band peak is observed when 100 points on the particles are randomly analyzed in Raman spectroscopic analysis. More preferably, it is 90% or more, and most preferably 95% or more.

[0045] [Soluble carbon material] The soluble carbon material used in the present invention is soluble in a solvent. General carbon materials (graphite, activated carbon, carbon black, graphene, carbon nanotubes, etc.) are insoluble in solvents. Some of them can be dispersed, but essentially, being soluble in a solvent means dissolving in the solvent, and for example, it also passes through a membrane filter (for example, pore sizes of 0.1 or 0.45 μm). On the other hand, general carbon materials cannot pass through. That is, the determination of solubility is as follows: after mixing the carbon material to 0.01% by mass with respect to the solvent, ultrasonic treatment is performed for 1 hour, and when the obtained liquid is passed through a GL chromatodisk (model 13P, pore size 0.45 μm) manufactured by GL Sciences Inc., the case where the carbon material passes through the filter paper is considered to be soluble in that solvent. Since the carbon material to be coated is soluble in the solvent, it is possible to coat in a state where the particles are sufficiently dispersed in the liquid phase, and since the carbon component is dissolved (present in the order of angstroms to nanosizes), it is possible to thinly and uniformly coat the particles. Also, being soluble facilitates the removal of excess carbon components.

[0046] The solvent in which the soluble carbon material used in the present invention is soluble is not particularly limited, and examples thereof include nitrogen-containing solvents such as N,N-dimethylformamide and N-methylpyrrolidone, ketone solvents such as acetone, ester solvents such as ethyl acetate, alcohol solvents such as ethanol and 2-propanol, halogen solvents such as chloroform, and water. The solvent may be a single type or a mixed solvent of two or more types. Among these, it is particularly preferable that the material is soluble in N,N-dimethylformamide.

[0047] In the Raman spectroscopic analysis, the soluble carbon material used in the present invention preferably has a peak at the G band, and more preferably has a peak at the D band. More preferably, it has a peak at the G' band (around 2700 cm -1 nearby). By having these peaks, it can be characterized as having a skeleton as a carbon material, and good carbon coating becomes possible.

[0048] Examples of the soluble carbon material used in the present invention include polyhydric phenols such as phloroglucinol and hexahydroxytriphenylene (compounds having two or more phenolic hydroxyl groups in the structure) and polyphenols such as catechin as precursor compounds, and those that release water molecules during carbonization and polymerize and carbonize are preferred. The soluble carbon material can be obtained by firing the precursor compound at a low temperature of 300°C or lower. This firing temperature is preferably 200°C or higher and 300°C or lower. Also, the atmosphere during this firing is not particularly limited, and it can be suitably used under any of atmospheric, vacuum, and inert gas atmospheres.

[0049] From the viewpoint of suppressing adverse effects on metal particles, it is preferable that the soluble carbon material and its precursor of the present invention do not contain halogen, nitrogen, or sulfur elements. These impurity elements can be evaluated by XPS analysis. The content of each of the halogen, nitrogen, and sulfur elements is 1000 ppm or less, more preferably 500 ppm or less, and even more preferably 100 ppm or less.

Examples

[0050] Examples are given below to explain the present invention in more detail, but the present invention is not limited only to these examples. Unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass".

[0051] [Raman spectroscopy measurement] Microscopic laser Raman spectroscopic analysis was performed using the following apparatus and conditions. NRS-3100 manufactured by JASCO Corporation, excitation wavelength 532 nm, number of accumulations 128 times

[0052] [TG-DSC measurement] Simultaneous differential thermal-thermogravimetric measurement (TG-DSC) was performed using the following apparatus and conditions. Manufactured by Netzsch, STA 449 F5 Jupiter, using an alumina pan, argon, under an air atmosphere, analyzed from 50 to 1500 °C or from 50 to 700 °C at a heating rate of 10 K / min

[0053] [Evaluation of car flowability index] The evaluation of the car flowability index was performed using the following apparatus and conditions. Analysis of the flowability of the powder (by analysis of the angle of repose, spatula angle (average angle before and after impact), compressibility, and homogeneity) using a powder property evaluation apparatus (PT-X manufactured by Hosokawa Micron)

[0054] [Measurement of nitrogen content] The measurement of the nitrogen content in the nitrogen-coated metal particles by the inert gas fusion method was performed using the following apparatus and conditions. Oxygen / nitrogen analyzer: LECO, ONH836 Carrier gas: helium, detection method: thermal conductivity

[0055] [Measurement of carbon content] The measurement of the carbon content in the nitrogen-coated metal particles by the combustion-infrared absorption method was performed using the following apparatus and conditions. Carbon / sulfur analyzer: LECO, CS844 Carrier gas: oxygen, detection method: infrared

[0056] [Preparation of Soluble Carbon Material (S1)] Phloroglucinol was calcined at 300 °C for 1 hour using a tube furnace in an air atmosphere to synthesize a soluble carbon material (S1). The G, D, and G’ bands of the soluble carbon material (S1) were confirmed by Raman spectroscopic analysis. It was also soluble in N,N-dimethylformamide. By XPS analysis, no elements other than C and O were identified (excluding H element which could not be analyzed at 100 ppm or less).

[0057] [Example 1] Stainless steel particles (1) (SUS316L, volume average particle diameter 30 μm) synthesized by the gas atomization method were heated at 800 °C for 3 hours using a tube furnace in a nitrogen (4N) atmosphere (1 L / min flow rate) to obtain nitrogen-coated metal particles (1A). The nitrogen content of the obtained nitrogen-coated metal particles (1A) was 0.8%.

[0058] [Example 2] AlSi10Mg alloy particles (2) (volume average particle diameter 30 μm) synthesized by the gas atomization method were heated at 800 °C for 3 hours using a tube furnace in a nitrogen (4N) atmosphere (1 L / min flow rate) to obtain nitrogen-coated metal particles (2A). The nitrogen content of the obtained nitrogen-coated metal particles (2A) was 0.8%.

[0059] [Example 3] Ti6Al4V alloy particles (3) (volume average particle diameter 30 μm) synthesized by the gas atomization method were heated at 800 °C for 3 hours using a tube furnace in a nitrogen (4N) atmosphere (1 L / min flow rate) to obtain nitrogen-coated metal particles (3A). The nitrogen content of the obtained nitrogen-coated metal particles (3A) was 0.8%.

[0060] [Example 4] 100 parts by mass of stainless steel particles (1) (SUS316L, average particle diameter 30 μm) synthesized by the gas atomization method were suspended in N,N-dimethylformamide, and 1 part by mass of a soluble carbon material (S1) dissolved in N,N-dimethylformamide was added thereto and contact-mixed. After stirring for 30 minutes, carbon-coated metal particles (1B) before the heat baking step were obtained by filtration and washing with N,N-dimethylformamide. The obtained carbon-coated metal particles (1B) were heat-baked (nitriding step) at 800 °C for 2 hours in a nitrogen atmosphere to obtain nitrogen-coated metal particles (1C). The carbon content of the obtained nitrogen-coated metal particles (1C) was 0.02%. The presence of G and D band peaks was confirmed by Raman spectroscopic analysis of the obtained nitrogen-coated metal particles (1C). It was confirmed by optical microscope observation that the particles included particles having a particle diameter of 1 μm or more and 100 μm or less. Further, it was confirmed from Raman spectroscopic analysis of the melt solidified product obtained by TG-DSC that the G and D bands had disappeared.

[0061] [Example 5] 100 parts by mass of AlSi10Mg alloy particles (2) (average particle diameter 30 μm) synthesized by the gas atomization method were suspended in N,N-dimethylformamide, and 1 part by mass of a soluble carbon material (1S) dissolved in N,N-dimethylformamide was added thereto and contact-mixed. After stirring for 30 minutes, carbon-coated metal particles (2B) before the heat baking step were obtained by filtration and washing with N,N-dimethylformamide. The obtained carbon-coated metal particles (2B) were heat-baked (nitriding step) at 800 °C for 2 hours in a nitrogen atmosphere to obtain nitrogen-coated metal particles (2C). The carbon content of the obtained nitrogen-coated metal particles (2C) was 0.02%. The presence of G and D band peaks was confirmed by Raman spectroscopic analysis of the obtained nitrogen-coated metal particles (2C). It was confirmed by optical microscope observation that the particles included particles having a particle diameter of 1 μm or more and 100 μm or less. Further, it was confirmed from Raman spectroscopic analysis of the melt solidified product obtained by TG-DSC that the G and D bands had disappeared.

[0062] [Example 6] 100 parts by mass of Ti6Al4V alloy particles (3) (average particle diameter: 30 μm) synthesized by the gas atomization method were suspended in N,N-dimethylformamide, and 1 part by mass of a soluble carbon material (1S) dissolved in N,N-dimethylformamide was added thereto, followed by contact mixing. After stirring for 30 minutes, carbon-coated metal particles (3B) before the heat baking step were obtained by filtration and washing with N,N-dimethylformamide. The obtained carbon-coated metal particles (3B) were heat baked at 800°C for 2 hours in a nitrogen atmosphere (nitriding step) to obtain nitrogen-coated metal particles (3C). The carbon content of the obtained nitrogen-coated metal particles (3C) was 0.02%. The presence of G and D band peaks was confirmed by Raman spectroscopic analysis of the obtained nitrogen-coated metal particles (3C). It was confirmed by optical microscope observation that particles having a particle diameter of 1 μm or more and 100 μm or less were included. Further, it was confirmed from Raman spectroscopic analysis of the melt solidified product obtained by TG-DSC that the G and D bands had disappeared.

[0063] [Comparative Examples 1 to 3] The raw material metal particles used in Examples 1 to 3 were used as they were. For all three types of metal particles, G and D bands could not be confirmed by Raman spectroscopic analysis. The nitrogen content and the carbon content were each less than 0.01%.

[0064] The fluidity evaluation results and analysis results of the Examples and Comparative Examples were summarized in Table 1. From the above results, by performing nitrogen and carbon coating of the present invention, metal particles with high fluidity were obtained.

[0065]

Table 1

[0066] By using the nitrogen- and carbon-coated metal particles of the present invention, good fluidity is exhibited, and they can be used as particles with high handleability, transferability, and fillability, and can be used in powder metallurgy, sintering, 3D printers, welding applications, and the like.

Claims

1. A method for producing nitrogen-coated metal particles, comprising: a nitriding step of heating metal particles at a temperature of 500°C or higher and lower than the melting point in a nitrogen atmosphere; The method for producing nitrogen-coated metal particles, characterized in that the Carr's flowability index of the nitrogen-coated metal particles is 70 or higher.

2. The method for producing nitrogen-coated metal particles according to claim 1, further comprising a carbon coating step of contacting with a soluble carbon material.

3. The method for producing nitrogen-coated metal particles according to claim 2, characterized in that the carbon content by combustion-infrared absorption method is 0.01% by mass or more.

4. The method for producing nitrogen-coated metal particles according to any one of claims 1 to 3, characterized in that the nitrogen content is 0.1% by mass or more by inert gas melting method.

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