Composite powder having iron-based particles coated with a graphene material

Abstract

The present invention relates to graphene-coated iron-based particles and a method for producing the same. A composite powder is provided that is suitable for powder metallurgy and additive manufacturing processes and comprises particles of an iron-based material having a coating of a graphene-based material, the concentration of the graphene-based material being between 0.1 wt% and 1.0 wt%.

Description

Technical Field

[0001] The present invention relates to graphene-coated iron-based particles and a method for manufacturing the same, and more particularly to stainless steel particles and iron particles coated with graphene or graphene-based materials for optimizing particles for additive manufacturing processes.

Background Art

[0002] Additive manufacturing (AM), or 3D printing, is a manufacturing technology that enables the formation of complex 3D objects under computer control. It enables rapid prototyping and manufacturing of plastic and metal parts. Additive manufacturing is an umbrella term that includes several techniques, among others, such as selective laser sintering (SLS), selective laser melting (SLM), electron beam melting (EBM), fused deposition modeling (FDM), and stereolithography (SLA).

[0003] Metal powder-based technologies are dominant in the area of AM for manufacturing metal products. Final products with complex geometries and tailored properties such as strength and hardness can be manufactured by powder-based AM. Parts are manufactured by melting the metal powder layer by layer, and the melting is performed by heating with a laser or an electron beam. Typically, the layers are formed by a method generally called the powder bed method. In the powder bed method, the machine reads data from a 3D CAD model and lays down successive layers of powder metal. These layers are melted together using a computer-controlled electron beam or laser beam. In this way, the final part is constructed. The process is carried out under vacuum (electron beam) or in a controlled atmosphere (laser beam), which makes it suitable for manufacturing parts from reactive materials with a high affinity for oxygen, such as titanium and iron.

[0004] The distribution of the metal powder is extremely important in the manufacturing process. The metal powder is typically provided to the build platform or on top of the part being formed after the first layer via a nozzle. A precision rake is often used to flatten the supplied metal powder across the upper surface. Alternatively, the powder may be spread to form a powder bed. Maintaining a constant thickness and density (packing density) within a given tolerance across the bed is a major concern in all technologies that utilize metal powder. A number of physical and chemical properties, including particle size and shape, surface roughness, and surface chemistry such as the tendency to react with surrounding substances, affect how the metal powder "behaves" when forming a powder bed. These properties are often summarized in terms of density metrics such as packing density or tapping density, and metrics related to how the metal powder flows or "flowability". As the technology has evolved towards thinner layers to better control the build process and material properties, the need to control packing density and flowability has increased. Also, the melting techniques used in AM place different requirements on the starting powder and can be variously sensitive to flowability characteristics. For example, AM processes that utilize laser sintering / melting typically require smaller metal particle sizes than electron beam-based methods. Generally, the smaller the particle size, the more prominent the flowability issues become.

[0005] Packing and flowability are recognized as problem areas within the AM community. This problem has been addressed, for example, by controlling the environment (especially controlling moisture), introducing coatings to render the particles inert, and adding lubricants, such as graphite-containing lubricants, to the powder. However, alloys used to form the final product, such as stainless steel alloys, are often sensitive to impurities. For example, the carbon content can significantly affect the properties of stainless steel, and even minor variations can be problematic. For this reason, any additives or composites should not affect the properties of the final product, or, if they do, they should be controllable in a manner that is controllable, reproducible, and does not degrade.

[0006] Better control of filling and fluidity is also important for technologies other than AM, such as classical powder metallurgy PM, which includes the manufacture of so-called green bodies, as well as advanced sintering technologies such as hot isostatic pressing technology HIP and wet binder technique.

[0007] WO 2018 / 189146 discloses that the sliding contact is formed from a composite material of Ag and graphene oxide, and that an Ag+GO composite powder is formed as an intermediate product. A GO content of about 0.01 wt% was found to be suitable in order to significantly reduce the friction and sliding contact of the final product.

[0008] US Patent No. 10,150,874 discloses a coating of steel and / or zinc for corrosion inhibition, where the coating contains graphene. US Patent Application Publication No. 2011 / 0256014 discloses a graphene coating of "base metal powder". Graphene is inserted as a thin layer between metal particles. The graphene layer is formed via the reduction of graphene oxide.

[0009] WO 2019 / 054931 discloses a multilayer graphene material that can be provided on a substrate, such as a metal substrate. The multilayer graphene material includes layers of graphene-based materials, and between the graphene-based layers there is a third intermediate layer containing a salt having at least two cyclic, planar groups capable of forming π-π stacking interactions with the layers containing the graphene-based material.

[0010] In the prior art, there is still a need for composite metal powders having fluidity characteristics optimized for powder metallurgy and additive manufacturing.

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0011] The object of the present invention is to provide a composite powder suitable for additive manufacturing and powder metallurgy, in particular a composite powder containing particles having an iron-based core and a graphene-based coating.

Means for Solving the Problems

[0012] This is achieved by the composite powder defined in claim 1 and the method defined in claim 10. The composite powder according to the present invention is suitable for powder metallurgy processes and additive manufacturing processes, and includes particles of an iron-based material having a coating of a graphene-based material, and the concentration of the graphene-based material is between 0.1 wt% and 1.0 wt%.

[0013] According to an aspect of the present invention, the concentration of the graphene-based material is between 0.1 wt% and 0.95 wt%, and more preferably between 0.1 wt% and 0.5 wt%. According to one aspect of the present invention, the iron-based material of the particles includes pure iron having inevitable impurities.

[0014] According to one aspect of the present invention, the iron-based particle material of the particles is stainless steel having inevitable impurities. According to one aspect of the present invention, the particles of the iron-based material have a particle size distribution in which the majority of the particles are in the range of 1 to 500 μm, preferably in the range of 1 to 100 μm, and more preferably in the range of 1 to 50 μm.

[0015] According to one aspect of the present invention, the graphene-based material of the coating is graphene oxide (GO). According to one aspect of the present invention, the graphene-based material of the coating is reduced graphene oxide (rGO).

[0016] According to one aspect of the present invention, the graphene-based material of the coating is a mixture of graphene oxide (GO) and reduced graphene oxide (rGO). The method according to the present invention is - a step of preparing an iron-based metal powder having a known particle size distribution, and - A step of preparing a dispersed graphene-based material; - A step of diluting the graphene-based material while recording the concentration of the graphene-based material in the solution and adjusting the pH by adding a basic substance, wherein the pH is adjusted to 3 to 9; - A step of separating graphene aggregates of the graphene material by ultrasonic treatment or stirring; - A step of dispersing iron-based metal powder in deionized water or a water / alcohol mixture to produce a slurry having a predetermined weight ratio of iron-based metal to water; - A step of adding the graphene material dispersion to the iron-based metal powder slurry at intervals or at a predetermined rate and completely mixing for a predetermined time; - A step of drying the composite powder It includes, and adjusts the amount of the added graphene material dispersion so that the concentration of the graphene material in the dried composite powder is between 0.1 wt% and 1.0 wt%.

[0017] According to one aspect of the present invention, the amount of the added graphene material dispersion is selected so that the concentration of the graphene material is between 0.1 wt% and 0.95 wt%, preferably between 0.1 wt% and 0.5 wt%.

[0018] According to one aspect of the present invention, the particulate iron-based material contains pure iron, and in the step of dilution and pH adjustment, the pH is adjusted within 4 to 8, preferably within 5 to 7. According to one aspect of the present invention, the iron-based material is stainless steel, and in the step of dilution and pH adjustment, the pH is adjusted within 3 to 8, preferably within 4 to 7.

[0019] According to one aspect of the present invention, the graphene-based material is graphene oxide (GO). According to one aspect of the present invention, the graphene-based material is reduced graphene oxide (rGO), or a mixture of reduced graphene oxide and graphene oxide.

[0020] Thanks to the present invention, composite powders with improved fluidity and fractal surfaces are provided, greatly improving powder handling in AM and other PM-based technologies. One advantage is that the graphene material coating reduces the oxidation of Fe-based material particles.

[0021] In the following, the present invention will be described in more detail with reference to the accompanying drawings, regarding non-limiting embodiments of the present invention, through examples.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7a

Figure 7b

Figure 8

Embodiments for Carrying Out the Invention

[0023] The following terms are defined and used throughout the specification and claims. at% is the atomic percentage, which is the short form of the number of one type of atom with respect to the total number of atoms.

[0024] wt% is the weight percentage, which is the short form of the weight of one compound with respect to the total weight of all compounds in a mixture or composite. Graphene is a one - atom - thick planar sheet of carbon atoms arranged in a hexagonal lattice structure.

[0025] A graphene - based material is a layered material that contains at least 30 at% of carbon and has properties generally attributed to graphene - class materials. The graphene - based material can be any type of graphene, such as single - layer graphene, few - layer graphene, multi - layer graphene, graphene oxide (GO), reduced graphene oxide (rGO), and graphene nanoplatelets (GNP).

[0026] Iron-based powder materials are materials in which iron is the main constituent, such as, but not limited to, pure iron and stainless steel. The stainless steel may be, for example, austenitic steel grade 316 or the equivalent. Typical particle sizes of powder materials suitable for AM and PM depend on the AM / PM method used and are in the range of 1 - 500 μm. For AM methods utilizing laser melting / sintering, particle sizes in the range of 1 - 100 μm are most suitable, and the same applies to conventional PM. An extensive review is "Powders for powder bed fusion: a review", Silvia Vock et al., Progress in Additive Manufacturing https: / / doi.org / 10.1007 / s40964-019-00078-6, which is incorporated herein by reference. Iron-based powder materials, which are starting materials for the method according to the present invention, are commercially available in a wide range of compositions, particle size distributions and qualities. The starting materials can be produced, for example, by gas atomization or water atomization methods.

[0027] Flowability or powder flowability is defined as the ease with which a powder flows under a specific set of conditions. Some of these conditions include the pressure on the powder, the humidity of the air around the powder, and the device through or from which the powder flows. Flowability can be measured using revolution powder analysis (RPA), which gives a set of parameters characterizing the flow properties of the powder material analyzed. The properties include the angle of repose [°], fracture energy [KJ / Kg], energy of repose [KJ / Kg] and surface fractal.

[0028] Energy of repose [kJ / kg] - The energy released by the repose. Calculation: Energy level of the powder after repose, minus, energy level of the powder before repose. RPA reports the average energy of repose for all powder repose.

[0029] Destruction energy [kJ / kg] - Calculation: The maximum energy level of the sample powder before the onset of avalanche, minus, the lowest possible energy level for the powder (with a flat and uniform surface). It is based on the volume and mass of the powder. This value represents the amount of energy required to initiate each avalanche.

[0030] Avalanche angle [°] - The powder angle at the maximum powder before the powder starts to avalanche. The measured value is the average value for the total avalanche angle. It is calculated from the center point on the powder edge to its apex. This angle is the average angle required to initiate and maintain the powder flow.

[0031] Surface fractal - The surface fractal is the fractal dimension of the surface of the powder and gives an indication of how rough the surface is. The measurement is taken after each avalanche and determines how the powder reorganizes itself. If the powder forms a smooth and uniform surface, the surface fractal is approximately 2. A rough and jagged surface gives a surface fractal greater than 5. For applications that require a uniform distribution of the powder, such as AM, the closer the surface fractal is to 2, the better the powder will function.

[0032] A method for producing a metal powder suitable for AM, including iron-based particles, is described with reference to FIG. 1 and includes the following main steps. - The step of preparing an iron-based metal powder having a known particle size distribution (not shown).

[0033] - The step of preparing a dispersed graphene-based material (not shown). - (a) Diluting and pH-adjusting the graphene-based material with distilled water or other diluents, and adding a basic substance, such as NaOH (aqueous solution), until the pH reaches a predetermined range to adjust the pH. The concentration of the graphene-based material in the solution is recorded to enable control of the final ratio between the graphene material and the iron-based material.

[0034] - (b) Separating the graphene aggregates of the graphene material, for example, by ultrasonic treatment or large-scale stirring. - (c)Dispersing the iron-based metal powder in deionized water or other liquid to create a slurry having a predetermined weight ratio of iron-based metal to water.

[0035] - (d)Adding the graphene material dispersion to the iron-based metal powder dispersion at intervals or at a predetermined gentle rate selected to be effective for mixing. The graphene material is completely mixed with the iron-based metal powder for at least 2 hours. The amount of the added graphene material dispersion is adjusted so that the concentration of the graphene material is between 0.1 wt% and 1.3 wt% in the final dried composite powder.

[0036] - (e)Drying the composite powder. This method is carried out before the drying step, - (e2)Filtering the composite powder - (e3)Further, washing the filter cake (filtered composite powder) with a solvent to remove any impurities such as free graphene or salts One or both of these steps may optionally be included.

[0037] The filtering step should be regarded as a non-limiting example. As will be recognized by those skilled in the art, filtration or separation can be carried out in various ways using different known filtration or sieving techniques.

[0038] According to an embodiment of the present invention, the graphene material is graphene oxide (GO) in the form of a high-concentration (about 2.5 wt%) graphene oxide paste or solution. The iron-based material is pure iron or stainless steel having a particle size distribution in the range of 1 to 100 μm, for example, austenitic steel grade 316 or an equivalent steel. According to the embodiment, this method includes the following steps.

[0039] (A)Diluting and pH-adjusting the graphene oxide paste. 1.Transfer an amount of GO paste specified by the effective mass to a container. 2.Add DI water.

[0040] 3. Check the pH of the diluted GO solution. Note: The initial pH of the solution is often approximately pH 2. 4. Adjust the pH of the solution to a pH within the range of 5 - 8 by adding 1M NaOH solution (pH 14) or its equivalent. Complete the adjustment to the desired pH by adding 0.1M NaOH solution or its equivalent. For stainless steel materials, a pH in the range of 3 - 8 is preferred. For pure iron materials, a pH in the range of 4 - 8 is preferred because oxidation increases at lower pH.

[0041] 5. Weigh the mass of the solution and calculate the final concentration. (B) Separating graphene aggregates by sonicating the GO solution for at least 1 hour.

[0042] (C - D) Coating metal particles. 1. Weigh the desired amount of metal powder. 2. Calculate the amount of GO solution required to coat the particles based on the desired concentration.

[0043] 3. Transfer the GO solution to a suitable container and add deionized water (DI) in a 1:1 ratio. 4. Sonicate the solution at room temperature for 1 hour.

[0044] 5. Transfer the metal powder to a rotary mixing device such as a rotary evaporator and add DI water until the powder is completely covered. 6. Mix the metal powder in the rotary mixing device at 90 r.p.m. for 15 minutes.

[0045] 7. Add the prepared GO solution into the rotary mixing device. 8. Mix the powder with the GO solution in the rotary mixing device at 90 r.p.m. for 2 hours.

[0046] 9. To dry the solvent, start the vacuum pump, cooler, and warm water bath of the rotary evaporator. Alternatively, transfer the mixture to another rotary drying container. a. Temperature of the water bath: 88 °C b. Speed: 90 r.p.m c. Vacuum degree: 200 mbar to 100 mbar d. Temperature of the cooler: 3 °C to 10 °C 10. Once the powder is completely dry, turn off the rotary evaporator and remove the material from the container / balloon.

[0047] 11. Grind the material into fine powder without agglomeration. 12. In a vacuum furnace, dry the powder at 88 °C for 24 to 35 hours in high vacuum. Embodiments of this method may include one or a combination of the following steps, performed before the drying step (step 9): - Filter the coated powder to remove most of the water in a Buchner funnel using suction - Wash the filter cake in the Buchner funnel with DI water (or ethanol) to remove free graphene and / or salts - Place the filtered powder in a furnace at 60 °C for at least 12 hours (or place the powder in a flask and continue with step 9), then continue with step 11 may optionally be included.

[0048] In the above example, water is used as the process liquid. Other water-miscible solvents, such as alcohols like ethanol or mixtures of alcohols, can also be used. Mixtures of water and one or more alcohols, such as water / ethanol mixtures, are also embodiments of this method.

[0049] In embodiments using GO, the experimental parameters, detailed times, pressures, solvents, and temperatures provided should be regarded as guidelines. The exact parameters will depend on the individual choices or preferences regarding the equipment used, the amount of materials used, and the processing time related to, for example, temperature. However, from these indicative parameters, those skilled in the art will be able to make the necessary adjustments for a particular apparatus and other conditions.

[0050] As described in steps (a) of the general method and steps 3 - 4 of the above embodiments, pH control and adjustment are one way to control coating formation. At lower pH (1 - 2), there is an attractive electrostatic force between GO and Fe particles, but there is insufficient repulsive force between GO sheets, resulting in aggregates that are not favorable when attempting to achieve a uniform coating. Mostly, instead, mixing occurs. At low pH (1 - 2), there is also intense oxidation of Fe particles. As the pH increases (3 - 4), GO aggregate formation becomes less, and corrosion of Fe particles that is acceptable for some applications occurs. At a certain point, (during the processing step / time) there is little oxidation and few aggregates, but there is still an electrostatic attraction between the GO sheets and Fe particles. This exists in the pH range of 5 - 9 (10).

[0051] Increasing the pH also creates a more negatively charged population on the basal plane of the GO sheets, which would be favorable for achieving a good coating. However, if the pH is too high, the net surface charge of the Fe particles also becomes negative, creating an electrostatic repulsion between the GO sheets and Fe particles. This is clearly seen at pH values above 10, but there is a risk of affecting the coating quality from pH values above 7. When the iron - based material has good corrosion resistance independently, for example, grades of stainless steel such as grade 316, a lower pH can be selected without the risk of surface oxidation of the particles. The effect of pH is summarized in Table 1.

[0052]

Table 1

[0053] According to one embodiment of the present invention, the pH is adjusted within 3 to 9, preferably within 3 to 7. According to one embodiment of the present invention, the pH is adjusted within 5 to 8.

[0054] According to one embodiment, the iron-based material is pure iron, and the pH is adjusted within 4 to 8, preferably within 5 to 7. According to one embodiment, the iron-based material is stainless steel, and the pH is adjusted within 3 to 8, preferably within 4 to 7.

[0055] Figure 3 is the diffraction pattern of various powders with and without GO coating, derived from various pH values used. Here, slight oxidation of iron at pH 3 can be observed (the magnetite Fe3O4 peak is seen), which is still acceptable for some applications. For other pH values, this oxidation is not seen. Even for pre-coated powders, there are no peaks in the region where GO aggregates appear in the diffraction pattern. This indicates that there is no free and aggregated GO around the particles (at low values). This is also confirmed by SEM with little observable aggregation of free GO.

[0056] In one embodiment of the present invention, the graphene material is reduced graphene oxide (rGO), partially reduced graphene oxide, or a mixture of graphene oxide and reduced graphene oxide.

[0057] It should be noted that graphene oxide can be affected by the method. For example, when the starting material is graphene oxide (GO), a certain step, especially the final drying step, may induce the reduction of graphene oxide, so that the final composite powder may also contain reduced graphene oxide (rGO). The reduction mechanism of GO and methods to control them are well known to those skilled in the art.

[0058] According to one embodiment, the metal particles are pure iron. The method according to the present invention produces a composite powder containing Fe-based metal particles with a graphene coating. This method enables fine-tuning of the degree of coating and optimization of the fluidity of the composite powder by varying the concentration of the graphene material in the process, thereby also varying the concentration in the final composite powder.

[0059] Figure 2 schematically shows a) two uncoated iron-based particles 20 of a metal powder according to the prior art, and b) two iron-based particles 21 coated with a graphene material 22 forming a composite powder according to the present invention. The metal-metal contact of the metal powder of the prior art usually results in considerably higher friction than the graphene-graphene contact of the composite powder according to the present invention. This is illustrated by the enlarged cross-sectional view of Figure 2. Even in the situation of particles only partially covered by the graphene material, the metal-graphene contact will still exhibit considerably lower friction than the metal-metal contact.

[0060] The SEM images of Figures 4a - c show stainless steel particles with a coating of graphene oxide of the composite powder. Figure 4a shows stainless steel particles with a coating of graphene oxide of the composite powder with a graphene oxide content of 0.2 wt%, verifying that the method according to the present invention can produce coated iron-based metal particles. This is verified by morphology inspection and EDS analysis.

[0061] The SEM image of Figure 4b shows a composite powder with a graphene oxide content of 0.5 wt%, explaining that the composite powder is well-dispersed. This is verified by morphology inspection and EDS analysis.

[0062] Increasing the concentration of the graphene material to 1.3 wt% or more will cause some aggregation of the particles in the composite powder, as explained by the SEM image of Figure 4c.

[0063] The SEM images of Figs. 5a and 5b show pure iron particles of the composite powder having a coating of graphene oxide with a graphene oxide content of 0.1 wt%. Figs. 6a - d are SEM images of composite powders containing pure iron and metal particles with graphene oxide contents of a) 0.05 wt%, b) 0.1 wt%, c) 0.2 wt% and d) 0.5 wt%. Similar to the composite powder containing stainless steel particles, when the graphene oxide concentration (0.05 wt% and 0.1 wt%) is lower, the particle surface is partially covered with graphene oxide. A graphene oxide concentration of 0.2 wt% results in a particle surface completely covered with graphene oxide. Further increasing the graphene oxide concentration (0.5 wt%) results in the aggregation of excess graphene sheets separated from the completely covered iron particles.

[0064] The flowability characteristics were measured using rotational powder analysis (RPA), and the parameters of angle of repose [°], fracture energy [KJ / kg], energy of repose [KJ / kg] and surface fractal are shown in Table 2a (stainless steel) and Table 2b (pure iron) for the stainless steel samples, and are explained for the reference sample (uncoated) and the samples (increasing concentration) from left to right as angle of repose, fracture energy, energy of repose in the graphs of Fig. 7a (stainless steel) and 7b (pure iron), and surface fractal is explained in the graphs of Fig. 8a (stainless steel) and 8b (pure iron).

[0065]

Table 2

[0066]

Table 3

[0067] As is evident from the flowability measurements, a significant reduction in the parameters related to flowability and surface fractal is also evident for pure Fe particles. The composite powder according to the present invention includes particles having a core of an iron-based material with a coating of a graphene-based material, and the concentration of the graphene-based material is in the range of 0.1 wt% to 1.0 wt%, preferably between 0.1 wt% and 0.5 wt%, and even more preferably between 0.1 wt% and 0.3 wt%. As will be apparent to those skilled in the art, depending on the parameters of the iron-based particles, such as the particle size distribution of the iron-based particles, the optimal concentration range can be adjusted, which can explain that the surface area is on a different scale from the mass of the particles. With the information that there is an optimal range, the basic geometric relationships, and the data presented herein, such adjustments will not be an undue burden for those skilled in the art. The method described above represents a preferred method for manufacturing the composite powder according to the present invention.

[0068] Comparing the flowability data (Tables 1a and 1b / Figures 7-8) and SEM images, it can be noticed that the positive effect on flowability occurs not at the concentration of the graphene material that results in completely coated metal particles, but rather starts, for example, at 0.1 wt%. The positive flowability effect appears to fully develop at approximately 0.2 wt% that results in completely coated metal particles. As understood by those skilled in the art, the terms used to describe the degree of coating of the metal particles should be interpreted in a statistical sense. The composite powder includes, for all concentrations, a mixture of completely coated particles and partially coated particles, and "completely coated metal particles" and "partially coated metal particles" are descriptions of representative composite particles for different concentrations.

[0069] According to one embodiment, the graphene-based material of the coating includes graphene oxide. As a result of the manufacturing method or further treatment, the graphene oxide may be at least partially reduced, so that the coating includes a mixture of graphene oxide (GO) and reduced graphene oxide (rGO).

[0070] According to one embodiment of the present invention, the iron-based core of the composite powder has a particle size distribution in the range of 1 to 100 μm, i.e., a particle size range known to be suitable for laser sintering / melting and conventional PM. According to one embodiment, the iron-based core of the composite powder has a particle size distribution in the range of 1 to 100 μm.

[0071] Both the iron-based material and the graphene-based material may contain inevitable impurities associated with their respective materials. Details of the experiment Effect of pH: To investigate the effect of pH in the coating process, a series of experiments in the pH range of 1 to 13 were conducted. Solutions with pH values from 1 to 13 were prepared by adding NaOH to samples with pH above 6 or HCl to samples with pH below 6 to deionized water. The pH of each sample was controlled using a calibrated VWR pHenomenal 1100H pH meter. For the pH 6 sample, only deionized water was used because deionized water is weakly acidic due to the dissolution of atmospheric carbon dioxide (CO2). The salt concentration in each sample was varied because the salt concentration was not intentionally increased further to avoid changing the surface charge of graphene oxide (GO). For each sample, 0.010 g of GO was diluted in 8 ml of a solution with the desired pH and sonicated for over 1 hour. Then, 1 g of Fe powder was added, followed by mixing for 1 minute. Visual inspections of the samples were performed before adding Fe, 1 minute after mixing, and 1 hour after mixing. In addition to this, after 1 minute, 1 hour, and 20 hours of mixing, some powder was taken out and left at room temperature to dry. Pure Fe powder was also mixed at pH 3, 5, or 8 for 4 hours to analyze the effect of corrosion.

[0072] GO was diluted in deionized water and NaOH solution to produce three dispersions with equal GO concentrations at pH 3.0, 5.4, and 8.0. Subsequently, the dispersions were sonicated for 60 minutes to dissolve all visible precipitates. Metal powder (5 g) and 10 g of deionized water were added to a beaker to create a slurry. The sonicated GO dispersion was slowly added to the metal powder slurry under stirring, and then further mixed in a rotary evaporator (Buchi R-300) at 90 rpm (300 mbar pressure) for 2.5 hours. The composite powder was filtered, rinsed with deionized water, and dried at 50 °C. Composition of stainless steel: The stainless steel is austenitic stainless steel with a composition of C 0.03%, Cr 17.0%, Ni 12.0%, Mo 2.5%, Si 0.7%, Mn 1.5%, S 0.03%, P 0.04%, and the balance Fe. Particle size distribution of metal particles: Table 2 shows the typical particle size distribution of stainless steel particles.

[0073]

Table 4

[0074] The pure iron particles contain Alfa Aesar 99.5% Iron and have a particle size distribution of approximately 10 μm. Field tests were carried out using composite powders containing iron-based materials, and objects were manufactured using AM (SLM) and sintering. The composite powder was handled well in the AM device, and the adjustment of printing parameters was considered not a problem for a skilled operator. The manufactured objects have the expected material properties compared to the objects manufactured from the uncoated starting powder material. This specification includes the disclosure of the following invention. [Item 1] A composite powder suitable for powder metallurgy processes and additive manufacturing processes, comprising particles having a core of an iron-based material and a coating of a graphene-based material, wherein the concentration of the graphene-based material is between 0.1 wt% and 1.0 wt%. [Item 2] The composite powder according to Item 1, wherein the concentration of the graphene-based material is between 0.1 wt% and 0.95 wt%, more preferably between 0.1 wt% and 0.5 wt%. [Item 3] The composite powder according to Item 1, wherein the iron-based material of the particles is pure iron. [Item 4] The composite powder according to Item 1, wherein the iron-based particle material of the particles is stainless steel. [Item 5] The composite powder according to any one of Items 1 to 4, wherein the core of the iron-based material has a particle size distribution in which the majority of the particles are in the range of 1 to 100 μm. [Item 6] The composite powder according to Item 5, wherein the core of the iron-based material has a particle size distribution in which the majority of the particles are in the range of 1 to 50 μm. [Item 7] The composite powder according to any one of Items 1 to 6, wherein the graphene-based material of the coating is graphene oxide (GO). [Item 8] The composite powder according to any one of Items 1 to 6, wherein the graphene-based material of the coating is reduced graphene oxide (rGO). [Item 9] The composite powder according to any one of Items 1 to 6, wherein the graphene-based material of the coating is a mixture of graphene oxide (GO) and reduced graphene oxide (rGO). [Item 10] A method for producing a composite powder suitable for powder metallurgy processes and additive manufacturing processes, wherein the composite powder comprises particles of an iron-based material having a coating of a graphene-based material, the method comprising: - preparing an iron-based metal powder having a known particle size distribution; - preparing a dispersed graphene-based material; - diluting the graphene-based material while recording the concentration of the graphene-based material in the solution and adjusting the pH by adding a basic substance, wherein the pH is adjusted to 3 to 9; - separating the graphene aggregates of the graphene material by ultrasonic treatment or stirring; - dispersing the iron-based metal powder in deionized water to produce a slurry having a predetermined weight ratio of iron-based metal to water. - Adding a graphene material dispersion to an iron-based metal powder slurry at intervals or at a predetermined rate, and completely mixing for a predetermined time; - Drying the composite powder; The method includes adjusting the amount of the added graphene material dispersion so that the concentration of the graphene material in the dried composite powder is between 0.1 wt% and 1.0 wt%. Method. [Item 11] The method according to item 10, wherein the amount of the added graphene material dispersion is selected so that the concentration of the graphene material is between 0.1 wt% and 0.95 wt%. [Item 12] The method according to item 11, wherein the amount of the added graphene material dispersion is selected so that the concentration of the graphene material is between 0.1 wt% and 0.5 wt%. [Item 13] The method according to any one of items 10 to 12, wherein the iron-based material of the particles contains pure iron, and in the steps of dilution and pH adjustment, the pH is adjusted within 4 to 8, preferably within 5 to 7. [Item 14] The method according to any one of items 10 to 12, wherein the iron-based material is stainless steel, and in the steps of dilution and pH adjustment, the pH is adjusted within 3 to 8, preferably within 4 to 7. [Item 15] The method according to any one of items 10 to 12, wherein the iron-based material of the particles contains pure iron. [Item 16] The method according to any one of items 10 to 12, wherein the iron-based particle material of the particles is stainless steel. [Item 17] The method according to any one of items 10 to 16, wherein the graphene-based material contains graphene oxide (GO). [Item 18] The method according to any one of items 10 to 17, wherein the graphene-based material contains reduced graphene oxide (rGO).

Claims

1. A composite powder suitable for powder metallurgy processes and additive manufacturing processes, comprising particles having a core of an iron-based material and a coating of a graphene-based material, wherein the concentration of the graphene-based material is between 0.2 wt% and 1.0 wt%, the core is completely covered by the graphene-based material, and the graphene-based material is monolayer graphene, few-layer graphene, multilayer graphene, graphene oxide (GO), reduced graphene oxide (rGO), partially reduced graphene oxide, a mixture of graphene oxide and reduced graphene oxide, or graphene nanoplatelet (GNP), characterized in that it is a composite powder.

2. The composite powder according to claim 1, wherein the concentration of the graphene-based material is between 0.2 wt% and 0.95 wt%.

3. The composite powder according to claim 1, wherein the concentration of the graphene-based material is between 0.2 wt% and 0.5 wt%.

4. The composite powder according to claim 1, wherein the iron-based material of the particles is pure iron.

5. The composite powder according to claim 1, wherein the iron-based particle material of the particles is stainless steel.

6. The composite powder according to any one of claims 1 to 5, wherein the core of the iron-based material has a particle size distribution in which the majority of the particles are in the range of 1 to 100 μm.

7. The composite powder according to claim 6, wherein the core of the iron-based material has a particle size distribution in which the majority of the particles are in the range of 1 to 50 μm.

8. The composite powder according to any one of claims 1 to 7, wherein the graphene-based material of the coating is graphene oxide (GO).

9. The composite powder according to any one of claims 1 to 7, wherein the graphene-based material of the coating is reduced graphene oxide (rGO).

10. The composite powder according to any one of claims 1 to 7, wherein the graphene-based material of the coating is a mixture of graphene oxide (GO) and reduced graphene oxide (rGO).

11. A method for manufacturing a composite powder suitable for powder metallurgy processes and additive manufacturing processes, wherein the composite powder comprises particles of an iron-based material having a coating of a graphene-based material, and the method comprises: - a step of preparing an iron-based metal powder having a known particle size distribution; - a step of preparing a dispersed graphene-based material; - A step of diluting the graphene-based material while recording the concentration of the graphene-based material in the solution and adjusting the pH by adding a basic substance, wherein the pH is adjusted to 3 to 9; - A step of separating the graphene aggregates of the graphene material by ultrasonic treatment or stirring; - A step of dispersing the iron-based metal powder in deionized water to produce a slurry having a predetermined weight ratio of the iron-based metal to water; - A step of adding the graphene material dispersion to the iron-based metal powder slurry at intervals or at a predetermined rate and mixing completely for a predetermined time; - A step of drying the composite powder including adjusting the amount of the added graphene material dispersion so that the concentration of the graphene material in the dried composite powder is between 0.1 wt% and 1.0 wt%, and the graphene-based material is monolayer graphene, few-layer graphene, multilayer graphene, graphene oxide (GO), reduced graphene oxide (rGO), partially reduced graphene oxide, a mixture of graphene oxide and reduced graphene oxide, or graphene nanoplatelet (GNP), Method.

12. The method according to claim 11, wherein the amount of the added graphene material dispersion is selected such that the concentration of the graphene material is between 0.1 wt% and 0.95 wt%.

13. The method according to claim 12, wherein the amount of the added graphene material dispersion is selected such that the concentration of the graphene material is between 0.1 wt% and 0.5 wt%.

14. The method according to any one of claims 11 to 13, wherein the particulate iron-based material contains pure iron and the pH is adjusted to within 4 to 8 in the step of dilution and pH adjustment.

15. The method according to any one of claims 11 to 13, wherein the iron-based material is stainless steel and the pH is adjusted to within 3 to 8 in the step of dilution and pH adjustment.

16. The method according to any one of claims 11 to 13, wherein the particulate iron-based material contains pure iron.

17. The method according to any one of claims 11 to 13, wherein the particulate iron-based particle material is stainless steel.

18. The method according to any one of claims 11 to 17, wherein the graphene-based material contains graphene oxide (GO).

19. The method according to any one of claims 11 to 18, wherein the graphene-based material contains reduced graphene oxide (rGO).

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