Methods for creating graphite and graphite fabricated objects

Abstract

To provide a method that enables the high-precision and low-cost production of graphite-containing articles by a powder bed melt bonding process.SOLUTION: A method for producing an article containing graphite includes a step of laying a powder and a step of solidifying the powder by irradiating the powder with laser light. The powder contains graphite powder and silicon carbide powder. In the step of solidifying the powder, the laser light is applied under the condition that allows the silicon carbide powder to decompose into carbon and silicon.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a technology for manufacturing articles mainly composed of graphite using a raw material powder containing graphite, using a powder bed fusion method. [Background technology]

[0002] Graphite possesses excellent properties such as heat resistance, heat dissipation, conductivity, and chemical resistance, and therefore structures containing graphite are used in a variety of fields.

[0003] Patent Document 1 discloses a method for obtaining a molded body by compression molding a graphite mixture containing rhombohedral graphite and, if necessary, additives and / or binders, followed by heat treatment in the absence of oxygen.

[0004] Patent Document 2 proposes a method for producing a graphite molded body by removing the solvent from a graphene oxide molded body obtained by molding a graphene oxide solvent dispersion, and then combining a step of reducing the molded body by electric heating with a step of pressurizing it. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 8-175870 [Patent Document 2] Japanese Patent Publication No. 2019-206447 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Methods such as those described in Patent Documents 1 and 2, which involve molding a raw material containing graphite to form a molded body, require the preparation of a mold first, which incurs time and cost, making them unsuitable for the production of prototypes or small quantities of diverse items.

[0007] In recent years, powder bed fusion (PBL), a type of additive manufacturing technology (so-called 3D printing), has been increasingly utilized in the manufacturing of goods. PBL is a method of creating objects by irradiating raw material powders such as metals and resins with a laser to melt them according to the shape data of the object to be manufactured. Because PBL offers a high degree of freedom in shape creation and allows for the creation of objects in a relatively short time, it is particularly suitable for the production of prototypes with complex shapes and for the manufacturing of small quantities of diverse items.

[0008] However, unlike metals and resins, graphite has a very high melting point of 3700-4000°C, making it difficult to fabricate objects by irradiating graphite powder with a laser to melt it. [Means for solving the problem]

[0009] The present invention relates to a method for manufacturing an article containing graphite, comprising the steps of laying down powder and solidifying the powder by irradiating it with laser light, wherein the powder contains graphite powder and silicon carbide powder, and in the step of solidifying the powder, the laser is irradiated under conditions in which the silicon carbide powder decomposes into carbon and silicon. [Effects of the Invention]

[0010] According to the present invention, it is possible to manufacture articles containing graphite with high precision and low cost by powder bed fusion bonding. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram of the apparatus according to the present invention. [Figure 2] (a) is a schematic diagram showing the order of laser irradiation in the present invention, and (b) is a schematic diagram showing the order of laser irradiation in the prior art. [Figure 3] (a) is a diagram showing the focus position of the laser beam, and (b) is a diagram showing the light intensity distribution at the focus and defocus positions of the laser beam. [Figure 4]This is a diagram showing the state of forming by irradiating laser light in a defocused state.

Embodiments for Carrying out the Invention

[0012] The powder bed fusion method is a method of forming by spreading raw material powder evenly to a predetermined thickness and repeatedly melting and then solidifying the powder in the order of milliseconds by scanning laser light according to slice data generated from the shape data of the formed model.

[0013] Since graphite has a very high melting point of 3700 to 4000 °C, it is difficult to form while melting graphite powder in the order of milliseconds by scanning laser light. Also, when resin is mixed with graphite powder and the melted resin is used as a binder for forming, removal (debinding) of the organic matter is required at the end, and the formed object shrinks due to debinding. A high level of proficiency is required for the operator to obtain a formed object with high accuracy.

[0014] As a result of intensive studies to solve such problems, a method for producing an article containing graphite by adding silicon carbide powder that functions as a binder to graphite powder has been found. Hereinafter, embodiments for carrying out the present invention will be described in detail.

[0015] Although silicon carbide has a higher resistivity than graphite, its heat resistance, thermal conductivity, linear expansion coefficient, etc. are equivalent to those of graphite, and it is a material with mechanical strength superior to graphite. The physical properties of the article obtained by the present invention deviate from those of pure graphite depending on the mixing ratio of graphite powder and silicon carbide powder, but by adjusting the mixing ratio according to the application, it is possible to satisfy the required physical properties.

[0016] Silicon carbide is a sublimable substance that vaporizes at 3500 °C. However, in the temperature range of 2800 °C or higher and less than 3500 °C, it decomposes into carbon and silicon, and at least a part of the thermally decomposed silicon exists in a molten state. Therefore, if a mixed powder of graphite powder and silicon carbide powder is irradiated with a laser under the condition that the temperature at which silicon carbide decomposes into carbon and silicon, that is, 2800 °C or higher and less than 3500 °C, it becomes possible to solidify the graphite powder using the molten silicon as a binder. At less than 2800 °C, silicon carbide does not thermally decompose, so no molten silicon is produced. At 3500 °C or higher, silicon carbide sublimates, making shaping difficult.

[0017] Although the decomposition point and sublimation point of silicon carbide powder vary somewhat depending on the purity of the silicon carbide powder and the types of impurities, if the temperature of the silicon carbide powder is raised to a range of 2800 °C or higher and less than 3500 °C, silicon carbide can be thermally decomposed to produce a molten silicon. The molten silicon penetrates between the graphite powders and solidifies after the laser light passes through. As a result, the graphite powder solidifies and shaping becomes possible.

[0018] If the binder is silicon, there is no need for subsequent debinding like an organic binder, and it becomes possible to maintain the accuracy during shaping. If the temperature of silicon carbide is raised to a range of 2800 °C or higher and less than 3500 °C, silicon carbide can be decomposed to produce a molten silicon. However, it is more preferable to raise the temperature to 2900 °C or higher and 3400 °C or lower. In this temperature range, it becomes possible to stably produce a molten silicon.

[0019] The raw material powder used in the present invention is a mixed powder of graphite powder and silicon carbide powder. Depending on the application, to obtain physical properties close to those of an article made of graphite alone (graphite article), the total of the graphite powder and the silicon carbide powder is preferably 90 mol% or more, more preferably 95 mol% or more, and even more preferably 98 mol% or more of the total powder.

[0020] Furthermore, the higher the proportion of graphite powder, the closer the physical properties of the resulting molded object can be to those of graphite. However, if the proportion of silicon carbide powder, which functions as a binder, is too low, molding becomes difficult. Therefore, the raw material powder needs to contain 20 mol% or more of silicon carbide powder. Also, when considering use in the same applications as graphite articles, it is preferable that the silicon carbide powder contained in the raw material powder be 50 mol% or less. Therefore, the silicon carbide powder contained in the powder is preferably 20 mol% to 50 mol%, and more preferably 25 mol% to 40 mol%.

[0021] If the raw material powder contains a resin with a low melting point, it may boil or vaporize upon laser irradiation, causing the surrounding powder to scatter. Therefore, the amount of resin contained in the powder is preferably less than 0.2 mol%, preferably 0.1 mol% or less, and more preferably 0.05 mol% or less.

[0022] The particle size of the particles contained in the raw material powder is preferably between 0.5 μm and 200 μm, and more preferably between 1 μm and 70 μm. If the particles contained in the raw material powder are within this range, suitable particle fluidity for laying the powder during molding is obtained, and it becomes possible to mold fine shapes.

[0023] In powder bed fusion fusion, the temperature of the laser irradiation area is generally adjusted by the laser irradiation intensity (laser power), laser scanning speed, laser scanning interval, and powder thickness. In addition, by dispersing the laser beam, reducing the temperature gradient within the laser irradiation spot, and controlling the auxiliary heating temperature of the powder and the fabricated object, it becomes possible to raise the temperature of the silicon carbide in the laser irradiation area to a more appropriate temperature range. As a result, it becomes possible to control the thermal decomposition of silicon carbide to a stable state and produce a silicon melt.

[0024] The following describes the general configuration of the 3D printing apparatus and the 3D printing process, followed by a description of a method for manufacturing articles containing graphite using graphite powder.

[0025] Figure 1 shows a schematic configuration of a molding apparatus 100 used in powder bed fusion fusion. The molding apparatus 100 is equipped with a chamber 101 having a gas inlet 113 and an exhaust port 114. The atmosphere inside can be controlled by introducing gas from the gas inlet 113 and exhausting it from the exhaust port 114. The exhaust port 114 may be connected to a pressure adjustment mechanism such as a butterfly valve to adjust the pressure, or it may be connected to a configuration that can adjust the atmosphere inside the chamber due to gas supply and the resulting pressure rise (generally called blow displacement). Note that Figure 1 is just one example of a molding apparatus and is not limited to it; it can be modified as appropriate.

[0026] The chamber 101 contains a molding container 120 for creating three-dimensional objects and a powder container 122 for containing raw material powder (hereinafter sometimes simply referred to as powder) 106. The molding container 120 is equipped with a heating function, allowing for the heating of the powder inside the container and the molded object.

[0027] The bottoms of the build container 120 and the powder container 122 can be adjusted vertically by the lifting mechanism 109. The bottom of the build container 120 also functions as a build stage 108 on which a base plate 121 can be installed.

[0028] The raw material powder contained in the powder container 122 is transported to the molding container 120 by the powder spreading mechanism 107 and laid on the base plate 121 installed on the molding stage 108 to a predetermined thickness. The direction and amount of movement of the lifting mechanism 109 are controlled by the control unit 115 according to the thickness of the raw material powder laid on the base plate 121. Since the raw material powder is generally laid on the base plate 121 to a thickness of 10 μm to 50 μm, it is desirable that the height resolution of the lifting mechanism 109 be 1 μm or less.

[0029] The powder spreading mechanism 107 has at least one of a squeegee and a roller to transport the raw material powder 106 from the powder container 122 to the molding container 120 and to spread the raw material powder 106 to a set thickness. To increase the density of the molded object, it is preferable to have both a squeegee and a roller, and to adjust the thickness of the powder with the squeegee and then pressurize with the roller to increase the density of the powder.

[0030] The molding apparatus 100 further includes a laser light source 102 for melting the laid raw material powder, scanning mirrors 103A and 103B for scanning the laser beam 112 in two axes, and an optical system 104 for focusing the laser beam 112 onto the irradiation area. Since the laser beam 112 is irradiated from outside the chamber 101, the chamber 101 is provided with an introduction window 105 for introducing the laser beam 112 into the interior. Various parameters related to the laser beam 112 are controlled by the control unit 115. The position of the molding container 120 and the optical system 104 should be adjusted in advance so that the beam diameter of the laser beam is a desired value on the surface of the laid raw material powder 106. The beam diameter on the surface of the laid raw material powder 106 affects the molding accuracy, so it is preferably 30 μm to 100 μm, and more preferably 30 μm to 50 μm.

[0031] Galvano mirrors can be suitably used as scanning mirrors 103A and 103B. Since galvano mirrors operate at high speed while reflecting laser light, it is desirable that they be made of a lightweight material with a low coefficient of thermal expansion.

[0032] A versatile YAG laser is often used as the laser light source 102, but a CO2 laser or semiconductor laser may also be used. The driving method may be pulsed or continuous irradiation. For the laser light 112, light with a wavelength corresponding to the absorption wavelength of the raw material powder 106 should be selected. It is preferable to use light with a wavelength in which the raw material powder 106 has an absorption rate of 50% or more, and more preferable to use light with a wavelength in which the absorption rate is 80% or more.

[0033] Next, I will explain the molding process.

[0034] First, the base plate 121 is placed on the build stage 108, and the inside of the chamber 101 is replaced with an inert gas such as nitrogen or argon. Once the replacement is complete, the raw material powder 106 is laid on the build surface of the base plate 121 by the powder spreading mechanism 107. The thickness of the laid raw material powder 106 is determined based on the slice pitch, i.e., the layer pitch, of the slice data generated from the shape data of the three-dimensional model to be built.

[0035] A laser beam 112 is scanned over the raw material powder 106 according to the slice data, and the laser beam is irradiated onto a predetermined area of ​​the raw material powder. In the area irradiated with the laser beam 112, the raw material powder 106 solidifies and becomes a solidified area 110, while the area not irradiated with the laser beam 112 remains as an unsolidified area 111.

[0036] Once the laser beam irradiation for one layer of slice data is complete, the lifting mechanism 109 lowers the molding stage 108 and raises the bottom of the powder container 122 according to the layer pitch. Then, the powder spreading mechanism 107 transports the raw material powder 106 from the powder container 122 to the molding container 120, laying new raw material powder on the molding surface consisting of a solidified section (molded object) 110 and an unsolidified section 111, and irradiating it with the laser beam 112 while scanning. Hereinafter, the solidified section 110 corresponding to one layer of slice data will be called a solidified layer, and the solidified section 110 will be referred to as the solidified section when the solidified layers are stacked and integrated.

[0037] The base plate 121 is made of a meltable material such as stainless steel. When the raw material powder initially laid on the base plate 121 is melted and solidified, part of its surface melts along with the raw material powder, integrating the first solidified layer with the base plate 121, and fixing the molded object to the base plate so that its position does not shift during the molding process.

[0038] When irradiating the raw material powder laid on the solidification section 110 with laser light, it is preferable to scan under conditions that cause the surface of the solidification section 110 to remelt and then solidify together with the raw material powder. At the boundary between the newly formed solidified layer and the solidification section 110, the materials mix and solidify, becoming one. Therefore, the position of the solidification section 110 on the base plate 121 can be fixed so as not to shift during the molding process. After the molding is complete, the base plate 121 is mechanically separated from the molded object.

[0039] In this way, by performing the process of laying raw material powder on the molding surface and the process of irradiating it with laser light 112 while scanning multiple times, it is possible to manufacture a three-dimensional object (molded object, solidified part) in which the solidified layer is integrated.

[0040] As mentioned above, silicon carbide is a sublimable material, so if the area irradiated with laser light contains parts that are heated to a temperature of 3500°C or higher, it will rapidly vaporize and scatter the surrounding powder, making fabrication difficult. Therefore, in this invention, in addition to the laser power, laser scanning speed, laser scanning interval, and powder thickness, as described above, more stable fabrication is possible by controlling the dispersion of laser light irradiation, reduction of the temperature gradient within the irradiation spot, and auxiliary heating temperature.

[0041] There are two methods for controlling laser power: controlling the in-plane power density and controlling the spatial power density. In-plane power density is the irradiation intensity of laser light per unit area, and its unit is J / mm². 2 It is expressed as follows: Spatial power density is the irradiation intensity of laser light per unit volume, and is expressed in J / mm². 3 This is expressed as follows. When forming a molded object by controlling the thickness of the raw material powder, such as in powder bed fusion, it is appropriate to consider the spatial power density. Spatial power density J V It can be expressed by the following equation. J V =W / (P×V×D)

[0042] Here, W is the laser power, P is the irradiation pitch (scanning interval) of the laser beam, V is the scanning speed of the laser beam, and D is the thickness of the raw material powder. In general shaping, the laser power W is 10 W or more and 1000 W or less, the irradiation pitch P of the laser beam is 5 μm or more and 500 μm or less, the scanning speed of the laser beam is 10 mm / sec or more and 10000 mm / sec or less, and the thickness D of the raw material powder is 5 μm or more and 500 μm or less. Controlling the parameters of W, P, V, and D based on the above ranges as a guide, J V is 10 J / mm 3 or more and 100 J / mm 3 or less. It may be controlled so that it becomes. The lower limit of 10 J / mm 3 is the energy required to melt the powder to such an extent that the silicon carbide powder can be solidified, and the upper limit of 100 J / mm 3 is a region where silicon carbide vaporizes and shaping becomes impossible.

[0043] In addition to controlling the spatial power density J of the laser beam, by adjusting the irradiation method of the laser beam, the focal position, etc., it is possible to reduce the temperature unevenness due to the irradiation of the laser beam and stably perform shaping while decomposing silicon carbide to generate a melt of silicon. V

[0044] As shown in Fig. 2(b), when the laser beam is continuously scanned in one stroke according to the shape of the irradiation region, irradiation heat accumulates in a portion where a large number of turning points of the scanning are close to each other (the region surrounded by the dotted line in the figure), and the temperature locally rises. As a result, scattering of the raw material powder due to vaporization of silicon carbide occurs in the portion where a large number of turning points of the scanning are close to each other, resulting in variations in the composition of the shaped object or the generation of voids.

[0045] However, if the laser beam is irradiated dispersedly, the number of turns of the adjacent scans can be reduced to suppress local temperature rise and reduce temperature unevenness within the shaping surface. Specifically, as shown in Fig. 2(a), it is advisable to divide the irradiation region into a plurality of regions and perform discrete irradiation. An example of the irradiation order is described in each region. The size of each region is such that one side is 1 mm or more and 5 mm or less, and the area is 1 mm 2More than 25mm 2 The following rectangle is preferred. However, the shape of the irradiation area does not necessarily have to be rectangular, and the area can be 1 mm². 2 More than 25mm 2 The shapes may be polygons, circles, or combinations thereof, but it is preferable to be able to fill the plane with one or a few types of shapes. The size of each rectangular area is preferably 5 mm x 5 mm or less, and more preferably 2 mm x 2 mm or less.

[0046] Furthermore, it is preferable to reduce the temperature gradient within the laser beam irradiation spot. Specifically, it is preferable to irradiate the powder with laser light in a defocused state. The focused and defocused states will be explained using the conceptual diagram in Figure 3. The focused state refers to a state in which the laser beam is focused on the surface of the laid powder, while the defocused state refers to a state in which the laser beam is not focused on the surface of the laid powder. Specifically, the defocused state refers to a state in which the focal position determined by the focusing optical system of the device being used is shifted from the surface of the laid powder.

[0047] The light intensity distribution at the focus position of laser beam 112 (section A-A' in Figure 3(a)) is a steep Gaussian distribution, as shown in the upper part of Figure 3(b). On the other hand, the intensity distribution at the defocus position of laser beam 112 (near the section B-B' in Figure 3(a)) is a gentler intensity distribution compared to the focus position, as shown in the lower part of Figure 3(b).

[0048] In particular, at the focus position, the difference in light intensity between the center and periphery of the irradiation spot becomes large. Therefore, when focused laser light is irradiated onto the raw material powder, a large temperature gradient is created within the irradiation spot, potentially leading to localized heating exceeding 3500°C. However, by irradiating the molding powder with laser light in a defocused state, it is possible to reduce the temperature gradient within the laser light irradiation spot.

[0049] While defocusing was described as a method to reduce the temperature gradient within the laser beam irradiation spot, this method is not the only option. For example, a method using a beam shaping element to create a top-hat shaped light intensity distribution and irradiating the fabrication powder with it is also preferable.

[0050] Figure 4 shows the process of creating an object by irradiating raw material powder 117 laid on the build surface 116 with laser light 112 in a defocused state. The raw material powder 117 refers to the powder laid to form one solidification layer. In Figure 4, the focus position F is shifted upward (away from the base plate 121) from the surface of the raw material powder 117 laid on the build surface 116.

[0051] Two methods for defocusing are possible: shifting the focus position F of the laser beam 112 above or below the surface of the raw material powder 117 laid on the build surface 116. However, if the focus position F is shifted below the surface of the raw material powder 117, there is a risk that the solidified area or raw material powder below the build surface 116 may boil or sublimate, causing voids in the solidified area, or that the non-build area may solidify, forming a solidified area that is not based on the slice data.

[0052] Therefore, when irradiating the raw material powder 117 with laser light 112 in a defocused state, the optical system is adjusted so that the focus position F of the laser light 112 is shifted above the surface of the raw material powder 117 laid on the molding surface, as shown in Figure 4. If the distance S between the focus position F and the surface of the raw material powder 117 (defocus amount) is too small, the temperature gradient within the irradiation area cannot be reduced, and the molten powder is prone to bumping. Also, if the defocus amount S is too large, the powder will not melt, and molding will not be possible. Therefore, the defocus amount S needs to be set within an appropriate range. Depending on the optical system of the molding device used, when using a YAG laser, the defocus amount S is preferably greater than 0 mm and 15 mm or less, and more preferably between 5 mm and 10 mm.

[0053] To form a single solidified section 110 (molded object) by stacking multiple solidified layers, it is necessary to improve the adhesion between the previously formed solidified layer and the next solidified layer to be formed. To improve adhesion, it is effective to allow the silicon molten by thermal decomposition to permeate to the interface with the previously formed solidified layer, and this can be achieved by adjusting the thickness of the powder laid. Although it may depend on the molding conditions, experiments have shown that the thickness of the raw material powder laid per molding while maintaining sufficient adhesion between solidified layers is preferably 5 μm to 200 μm. Considering the time required for molding and the molding accuracy, 10 μm to 100 μm is more preferable.

[0054] The base plate 121 is often made of a metal material with a relatively low melting point, such as aluminum or stainless steel. This is because, when creating the first solidification layer, a portion of the base plate 121 is melted to integrate the solidification layer and the base plate 121, thereby fixing the solidified portion 110 to the base plate 121. Because these metal materials have high thermal conductivity, the heat generated when heated by laser irradiation easily diffuses into the surroundings, and the heat from the powder escapes to the base plate 121, preventing it from melting sufficiently, which can make it difficult to fix the solidified portion 110 to the base plate 121. As the molding progresses and the solidified portion 110 rises, the diffusion of heat to the base plate decreases, but the molded object becomes embedded in the powder bed with high thermal conductivity, so heat escapes through the surrounding powder, and the powder tends not to heat up sufficiently when irradiated with laser light.

[0055] To improve this condition, it is preferable to provide a heating mechanism in the molding container 120 to preheat the powder in the base plate 121, the solidified part (molded object) 110, and the unsolidified part 111. The heating mechanism should preferably be capable of heating the powder in the solidified part (molded object) 110 and the unsolidified part 111 to a temperature of 30°C to 100°C. For example, a heater can be installed around the molding container 120, or a laser can be provided for preheating in addition to the laser used to melt the powder. If the preheating temperature is below 30°C, the heat will diffuse during laser irradiation and the raw material powder may not dissolve sufficiently, creating a gap between the base plate 121 and the solidified part 110, or between the solidified part 110 and the solidified layer, which may cause delamination. If the preheating temperature exceeds 100°C, the raw material powder tends to aggregate.

[0056] The resulting molded object contains, in addition to graphite, silicon and carbon produced by thermal decomposition. However, when the molded object is heat-treated, the carbon and silicon in the object react to form silicon carbide, which improves the physical properties of the object. Although the melting point of silicon is 1414°C, it is known that when silicon and carbon are brought into close proximity and heat-treated at 1300°C, a reaction occurs and they are transformed into silicon carbide. Since silicon carbide decomposes at temperatures above 2800°C, the heat treatment temperature after molding is preferably between 1300°C and 2800°C, and more preferably between 1500°C and 2500°C.

[0057] The fabricated objects produced using the method described above exhibit a characteristic structure. When the fabricated objects, or objects that have undergone heat treatment after fabrication, are evaluated by Raman spectroscopy from the surface of the last fabricated side in the depth direction, more silicon carbide is detected in a region corresponding to the thickness of one solidified layer, closer to the base plate 121. Furthermore, a structure is observed in which regions where the ratio of silicon carbide to graphite changes in one direction appear periodically, depending on the thickness of the laid powder (thickness of the solidified layer) and the number of layers. From this, it is inferred that when the mixed powder is irradiated with a laser under appropriate conditions, the silicon carbide on the surface side is thermally decomposed into silicon and carbon, the molten silicon seeps into the laid powder due to gravity, reacts with graphite to change into silicon carbide, solidifies and binds the surrounding powder together, and so on.

[0058] The molded object produced by the procedure described above contains voids within it, depending on the packing density of the laid powder. Even with the densest possible powder packing, only about 70% packing density can be achieved, and powder scattering during molding cannot be eliminated, so the void ratio of the molded object is about 40-50%. Therefore, it is preferable to impregnate the molded object to improve its density, and thus its mechanical strength. By performing pitch impregnation, the voids can be converted into graphite, thus bringing the properties of the final product closer to those of graphite.

[0059] Pitch impregnation involves first immersing the object in pitch and applying pressure to allow the pitch to penetrate the object. During the impregnation process, degassing the object in a vacuum or heating it to a temperature above the pitch's softening point can facilitate the pitch's penetration. After the pitch-impregnated object is fired at 700°C to 1000°C to carbonize the pitch, the pitch impregnation and firing process is repeated multiple times as needed. Depending on the desired properties of the object, the voids within the object are reduced with carbonaceous material, and then the object is heated to 2700°C to convert the carbonaceous material into graphite. This graphitization of the carbonaceous material develops a crystalline structure, resulting in the acquisition of graphite-specific physical properties. The resulting object then exhibits a higher proportion of graphite, closer to the properties of graphite. [Examples]

[0060] Examples of the present invention will now be described. However, the type of powder, composition, particle size, shape, laser power, etc., described below should be appropriately changed depending on the configuration of the apparatus to which the invention is applied and various conditions, and this is not intended to limit the invention to the scope of disclosure herein.

[0061] <Example 1> As raw material powders, graphite powder with an average particle size of 30 μm (manufactured by Ito Graphite Industry Co., Ltd., product name SG-BL30, 99.0 at% graphite) and silicon carbide powder with an average particle size of 14.7 μm (manufactured by Taiheiyo Random Co., Ltd., product name NC#800, 98.7 at% silicon carbide) were used. A stainless steel base plate 121 was installed on stage 108.

[0062] After mixing graphite powder and silicon carbide powder in a 50 mol:50 mol ratio, the mixture was left to stand in a chamber, and after vacuuming, N2 gas was introduced multiple times to replace the chamber with an inert atmosphere. Argon gas may be used instead of N2 gas. The heater of the build container 120 was set to 40°C, and the mixed powder and base plate 121 were preheated. The height of the stage 108 was adjusted, and the mixed powder from the powder container 122 was supplied onto the stage 108 by the powder spreading mechanism 107, and spread on the base plate 121 to a thickness of 50 μm.

[0063] Next, the powder was irradiated with laser light to perform the fabrication process. The defocus amount S of laser beam 112 was adjusted to 7 mm by moving the stage up and down. An Nd:YAG laser with a wavelength of 1060 nm was used as the laser light source. The laser power was set to 100 W, the pitch to 40 μm, and the scanning speed to 2000 mm / sec. The spatial laser power density at this time was 25 J / mm². 3 This is the calculated result. After the first layer of laser light irradiation is complete, the process of laying the powder and irradiating it with laser light is repeated multiple times using the same procedure until the object reaches the desired height.

[0064] The stainless steel used in base plate 121 has relatively high thermal conductivity, which can cause the heat generated by the laser beam to dissipate, resulting in poor adhesion between the printed object and the base plate. In such cases, in addition to preheating, the spatial laser power density when printing the first 1-3 layers should be set to 50 J / mm². 3 It's good to raise it up to this point.

[0065] The laser light was applied in a dispersed manner. Specifically, the irradiation area was a square with sides of 1 mm, and the distance between the centers of adjacent squares was set to 0.8 mm, overlapping adjacent irradiation areas by 0.1 mm each. Of the two solidified layers formed consecutively, the second solidified layer was formed while translating the irradiation area of ​​the first solidified layer in a constant direction by 0.25 mm increments within the build plane, and rotating its angle within the build plane by 18°. Through these measures, temperature homogeneity within the build plane could be ensured, and a relatively strong object could be obtained.

[0066] If the irradiation area is not translated or rotated within the build surface, the printed object is formed by stacking solidified layers of 1mm squares, resulting in a state where square prisms are lined up and tightly pressed together. Such printed objects tend to have weak bonding forces between the square prisms, making them prone to breakage.

[0067] After the laser irradiation process was complete, the printed object was immersed in pitch, pressure was applied to allow the pitch to penetrate, and then the pitch-impregnated object was fired at 1000°C. This process was repeated 2-3 times to reduce the porosity. Subsequently, the object was heated by electric current to 3000°C, converting the carbonaceous material in the impregnated pitch into graphite. The resulting object had a porosity of approximately 50% before pitch impregnation, but after pitch impregnation, the voids were filled with graphite, resulting in a final composition of approximately 75 mol% graphite and 25 mol% silicon carbide.

[0068] Microscopic examination of the tissue revealed that the obtained material contained virtually no voids.

[0069] Furthermore, the bending strength and resistivity of the obtained materials were evaluated. The evaluation of each material property was performed using the following method.

[0070] (Bending strength) The bending strength was evaluated by a three-point bending test. Five test specimens were prepared using the method described above. For each specimen, the maximum load at failure was P [N], the distance between external supports was L [mm], the width of the specimen was w [mm], and the thickness of the specimen was t [mm]. 3×P×L / (2×w×t) (Formula 1) The bending strength was calculated using the following methods, and the average of these values ​​was used as the bending strength.

[0071] (Electrical resistivity) The electrical resistivity of the test specimens prepared using the method described above was measured using the four-terminal method while a constant current was supplied from a current source.

[0072] The evaluation results confirmed that the resulting material had a bending strength of 54.3 MPa and an electrical resistivity of 13.3 μΩ·m, exhibiting properties similar to conventional graphite.

[0073] <Example 2> In Example 2, the object was fabricated in the same manner as in Example 1, except that the composition of the silicon carbide powder used as a binder was changed during graphite fabrication.

[0074] As raw material powders, graphite powder with an average particle size of 30.0 μm (manufactured by Ito Graphite Industry Co., Ltd., product name SG-BL30, 99.0 at% graphite) and SiC powder with an average particle size of 14.7 μm (manufactured by Taiheiyo Random Co., Ltd., product name NC#800) were used. The graphite powder composition was 80 mol.% and the silicon carbide composition was 20 mol.% and mixed in a ball mill. Laser irradiation was performed under the same conditions as in Example 1. As a result, a fabricated object was obtained that showed slight pattern distortion at the corners.

[0075] From these results, it is considered preferable that the silicon carbide, which functions as a binder, be contained in the raw material powder at a concentration of 20 mol% or more. The composition after pitch impregnation was 90 mol% graphite and 10 mol% silicon carbide. When the bending strength and electrical resistivity were evaluated in the same manner as in Example 1, the bending strength was 45.1 MPa and the electrical resistivity was 11.9 μΩ·m, obtaining physical properties that were even closer to the characteristics of graphite than in Example 1.

[0076] <Comparative Example 1> As a comparative example, fabrication was performed using only graphite powder.

[0077] As the raw material powder, graphite powder with an average particle size of 30.0 μm (manufactured by Ito Graphite Industry Co., Ltd., product name SG-BL30, 99.0 at% graphite) was used.

[0078] When the raw material powder was irradiated with laser light under the same conditions as in Example 1 to perform fabrication, the graphite powder scattered in the laser irradiation area, making it impossible to stack the fabricated object on the base plate. This is thought to be because the difference between the melting point and boiling point of graphite is narrow, preventing it from melting and solidifying with laser irradiation. [Explanation of Symbols]

[0079] 100 Modeling equipment 102 Energy beam source 106 Raw material powder 107 Powder spreading mechanism 108 stages 110 Sculptures 111 Powder bed 112 Energy Beam

Claims

1. A method for manufacturing an article mainly composed of graphite, The process of laying down the powder, A step of irradiating the powder with laser light to solidify the powder, It has, The aforementioned powder contains graphite powder and silicon carbide powder. A method for manufacturing an article, characterized in that, in the step of solidifying the powder, the laser light is irradiated under conditions in which the silicon carbide powder decomposes into carbon and silicon.

2. A method for manufacturing an article containing graphite, The process of laying down the powder, A step of irradiating the powder with laser light to solidify the powder, It has, The aforementioned powder contains graphite powder and silicon carbide powder. The silicon carbide powder contained in the aforementioned powder is 50 mol% or less. A method for manufacturing an article, characterized in that, in the step of solidifying the powder, the laser light is irradiated under conditions in which the silicon carbide powder decomposes into carbon and silicon.

3. A method for manufacturing an article containing graphite, The process of laying down the powder, A step of irradiating the powder with laser light to solidify the powder, It has, The aforementioned powder contains graphite powder and silicon carbide powder. A method for manufacturing an article, characterized in that, in the step of solidifying the powder, the laser light is irradiated under conditions that the temperature of the part irradiated with the laser light is 2800°C or more and less than 3500°C.

4. A method for manufacturing an article according to any one of claims 1 to 3, characterized in that, in the step of solidifying the powder, the region to be solidified is divided into multiple sections and irradiated discretely with a laser.

5. The area of ​​the aforementioned region is 1 mm ２ 25mm or more ２ The method for manufacturing an article according to the following feature (4).

6. A method for manufacturing an article according to any one of claims 1 to 5, characterized in that the focus position of the laser beam is above the surface of the laid powder.

7. The method for manufacturing an article according to claim 6, characterized in that the distance between the focus position of the laser beam and the surface of the laid powder is greater than 0 mm and less than 10 mm.

8. The aforementioned laser light has a spatial power density of 10 J / mm². ３ 100J / mm or more ３ A method for manufacturing an article according to any one of claims 1 to 7, characterized by irradiating in the following manner.

9. A method for manufacturing an article according to any one of claims 1 to 8, characterized in that, while performing the steps of laying the powder and solidifying the powder, the temperature of the base plate on which the powder is laid and the powder itself are heated to 30°C or more and 100°C or less.

10. A method for producing an article according to any one of claims 1 to 9, characterized in that the silicon carbide powder contained in the powder is 20 mol% or more and less than 50 mol%.

11. A method for producing an article according to any one of claims 1 to 10, characterized in that the average particle size of the powder is 0.5 μm or more and 200 μm or less.

12. The process involves laying the aforementioned powder and solidifying the aforementioned powder to obtain a molded object, then impregnating the object with pitch and firing it to make it carbonaceous, The process of heating the carbonaceous material to convert it into graphite, A method for manufacturing an article according to any one of claims 1 to 11, further comprising:

13. The method for manufacturing an article according to claim 1 or 2, characterized in that, in the step of solidifying the powder, the laser light is irradiated under conditions such that the temperature of the part irradiated with the laser light is 2800°C or more and less than 3500°C.

14. Powder used in powder bed fusion bonding, It contains graphite powder and silicon carbide powder. The powder is characterized in that the total amount of graphite powder and silicon carbide powder contained in the powder is 90 mol% or more of the powder, and the silicon carbide powder is 20 mol% or more but less than 50 mol%.

15. The powder according to claim 14, characterized in that the total amount of the graphite powder and the silicon carbide powder contained in the powder is 95 mol% or more.

16. The powder according to claim 14, characterized in that the total amount of graphite powder and silicon carbide powder contained in the powder is 98 mol% or more.

17. The powder according to any one of claims 14 to 16, characterized in that the silicon carbide powder contained in the powder is 25 mol% or more and 40 mol%.

18. The powder according to any one of claims 14 to 17, characterized in that the average particle size is 0.5 μm or more and 200 μm or less.

19. The powder according to any one of claims 14 to 18, characterized in that the resin contained in the powder is less than 0.2 mol%.

20. Articles whose main component is graphite, An article characterized by comprising a plurality of graphite particles and silicon which functions as a binder for the plurality of graphite particles.

21. Articles whose main component is graphite, An article characterized by comprising a plurality of graphite particles and silicon carbide which functions as a binder for the plurality of graphite particles.

22. The article according to claim 20 or 21, characterized in that the particle size of the plurality of graphite particles is 0.5 μm or more and 200 μm or less.

23. The article according to claim 20 or 21, characterized in that the silicon carbide content is 50 mol% or less.

Images