Powder for additive manufacturing

Abstract

A powder for additive manufacturing, comprising: copper-containing particles; and a coating layer covering at least a portion of the periphery of the copper-containing particles, wherein the coating layer comprises Y, and wherein the average coverage of the periphery by the coating layer is 5% or more.

Description

Powder for Additive Manufacturing

[0001] This specification discloses a powder used for additive manufacturing.

[0002] In metal additive manufacturing, which is one of the Additive Manufacturing (so-called AM) technologies, for example, based on the cross-sectional data of the object to be manufactured, a laser beam or an electron beam is irradiated onto thinly spread metal powder, and a layer is formed by partial melting, solidification or sintering thereof, and by repeating the deposition of metal powder thereon and irradiation with a laser beam or the like, a shaped object is manufactured by stacking layers.

[0003] In such additive manufacturing, to manufacture a shaped object made of copper or a copper alloy that is excellent in electrical conductivity and thermal conductivity, copper powder or a copper alloy powder is used as the metal powder. Examples of this type of technology include those described in Patent Documents 1 and 2.

[0004] In Patent Document 1, for the purpose of "providing a copper powder for a 3D printer that has a high absorption rate during laser irradiation and enables efficient heat input, and thus can be melt-bonded with a low-energy laser", "copper powder having an absorption rate of 18.9% to 65.0% with respect to light having a wavelength λ = 1060 nm and an index represented by the absorption rate / oxygen concentration with respect to light having a wavelength λ = 1060 nm of 3.0 or more" has been proposed.

[0005] Patent Document 2 describes "a metal powder for additive manufacturing, which contains at least one of chromium and silicon in an amount of 0.10% by mass or more and 1.00% by mass or less, the total amount of the chromium and the silicon being 1.00% by mass or less, and the balance being copper". According to Patent Document 2, such a "metal powder" provides "a shaped object made of a copper alloy that can achieve both mechanical strength and conductivity".

[0006] Japanese Unexamined Patent Application Publication No. 2018 - 178239, Japanese Unexamined Patent Application Publication No. 2016 - 211062

[0007] Incidentally, due to their high thermal conductivity, copper and copper alloys easily lose heat from laser beams. Therefore, forming copper powder and copper alloy powders with a laser beam takes time, and it can take a relatively long time to obtain the resulting object. Furthermore, objects formed with insufficient laser heating tend to have low density and low conductivity.

[0008] This specification provides a powder for additive manufacturing that can improve the formability of additive manufacturing.

[0009] The additive manufacturing powder described in this specification comprises copper-containing particles containing Cu and a coating layer that covers at least a portion of the area surrounding the copper-containing particles, wherein the coating layer contains Y, and the average coverage rate of the area surrounding the copper-containing particles by the coating layer is 5% or more.

[0010] The additive manufacturing powder described above can improve the build quality of additive manufacturing.

[0011] This is a schematic cross-sectional view showing the surface coating particles contained in the additive manufacturing powder of one embodiment. This is a graph showing the relationship between the average coating rate of the additive manufacturing powders of Examples 3 to 6 and the conductivity of the manufactured objects produced using them.

[0012] The embodiments of the additive manufacturing powder described above and their manufacturing methods will be explained in detail below with reference to the drawings. Reference numerals will be used as needed, but may be omitted when not necessary.

[0013] (Additive Manufacturing Powder) In one embodiment, the additive manufacturing powder includes surface-coated particles 3 in which at least a portion of the surrounding area of ​​copper-containing particles 1 containing Cu is coated with a coating layer 2, as schematically shown in Figure 1. The coating layer 2 may, in many cases, consist of a number of powders attached in layers around the copper-containing particles 1, as shown in Figure 1, but is not limited to this.

[0014] Copper-containing particles 1 are made of copper or a copper alloy containing Cu. In the case of copper-containing particles 1 made of copper, the Cu content of the additive manufacturing powder is, for example, 99.9% by mass or more. In the case of copper-containing particles 1 made of copper alloy, the additive manufacturing powder may contain, for example, 90% to 99.9% by mass of Cu, and one or more alloying elements selected from the group consisting of Al, Cr, Fe, Ni, Nb, P, Si, Ti, Zn, and Zr, or if multiple elements are included, their total content may be 0.1% to 10% by mass. The Cu and alloying element content of the additive manufacturing powder can be measured by inductively coupled plasma atomic emission spectrometry (ICP-OES).

[0015] At least a portion of the area surrounding the copper-containing particle 1 is covered with a coating layer 2 containing the element Y (yttrium). This makes it more difficult for the coating layer to dissipate heat from the laser during additive manufacturing, thereby improving the buildability. Furthermore, the coating layer 2 surrounding the copper-containing particle 1 is expected to promote the absorption of the laser beam into the copper-containing particle 1, making it easier for the copper-containing particle 1 to melt or sinter. As a result, it is possible to improve the buildability in terms of at least one of the following: an improvement in the build speed during additive manufacturing, and an improvement in the density and conductivity of the resulting manufactured object.

[0016] The presence of Y in coating layer 2 can be confirmed by wavelength-dispersive X-ray spectroscopy (WDS) or energy-dispersive X-ray spectroscopy (EDS).

[0017] Here, the average coverage rate of the surface of the copper-containing particles 1 by the coating layer 2 is set to 5% or more. If the average coverage rate is less than 5%, only a small portion of the copper-containing particles 1 is covered by the coating layer 2, and the copper-containing particles 1 are too exposed, so the above-mentioned effect of improving moldability cannot be fully obtained. On the other hand, if the average coverage rate is 5% or more, even if the surface-covered particles 3 are not mostly covered by the coating layer 2, it has been found that the laser beam is more likely to hit the coating layer 2 during additive manufacturing due to multiple reflections from the surface of the copper-containing particles 1, and the effect of improving moldability due to the provision of the coating layer 2 tends to be obtained. On the other hand, if the average coverage rate is too high, it may be difficult to spread the additive manufacturing powder as intended during manufacturing. For this reason, the average coverage rate is preferably 20% to 80%, more preferably 20% to 60%, and more preferably 40% to 60%.

[0018] The average coverage rate described above can be calculated by applying image processing to images acquired by wavelength-dispersive X-ray spectroscopy (WDS). More specifically, for each of the five surface-coated particles 3 randomly selected from the image acquired by wavelength-dispersive X-ray spectroscopy, the area inside a square with the center of the surface-coated particle 3 (or the center of the smallest inclusion circle surrounding it if the surface-coated particle 3 is not circular) as the center and the radius of the surface-coated particle 3 (or the radius of its smallest inclusion circle if the surface-coated particle 3 is not circular) as the side length is divided into 200 x 200 areas. Based on whether or not Y is detected in the divided area, the area is divided into areas where Y is detected and areas where Y is not detected. Next, the area of ​​the area where Y is detected is divided by the area of ​​the square described above and expressed as a percentage to obtain the coverage rate. The average value of the coverage rates of the five surface-coated particles 3 is then taken as the average coverage rate. For image acquisition, for example, an X-ray analyzer attached to the FE-EPMA (JXA-8500F, manufactured by JEOL Ltd.) was used, with an acceleration voltage of 15 kV and an acceleration current of 2.0 × 10⁻¹⁴. -8A. By performing a measurement with a measurement time of 10 msec, one integration cycle, a magnification of 5000x, and a region division of 200x200, a mapping image can be obtained. Note that any measurement method that can identify the position of elements, such as energy-dispersive X-ray spectroscopy (EDS), can be used for mapping, and in any device, the coverage can be calculated by dividing the area into parts that exceed the detection limit of Y and parts that do not.

[0019] Of the five surface coating particles 3 described above, the smallest coating rate ("minimum coating rate") is preferably 1% or more, and more preferably 5% or more. If the minimum coating rate is too small, the laser may not hit the surface coating particles. Also, of the five surface coating particles 3, the largest coating rate ("maximum coating rate") is preferably 90% or less, more preferably 80% or less, and more preferably 70% or less. If the maximum coating rate is too large, there is a concern that the surface coating particles will aggregate, resulting in poor melting.

[0020] The coating layer 2 may contain Y in any form, but it is preferable that it contains Y as an oxide, that is, yttrium oxide. In this case, Y does not easily dissolve in the copper in the crystal and does not easily reduce conductivity. Furthermore, it is preferable that the yttrium oxide in the coating layer 2 contains Y2O3. This reduces the density of the coating layer, making it easier to flow out during fabrication and easier to remove. The presence of yttrium oxide and Y2O3 in the coating layer 2 can be confirmed by X-ray photoelectron spectroscopy (XPS).

[0021] The average particle size D50 of the additive manufacturing powder is preferably 10 μm to 150 μm. By not making the average particle size D50 too small, the powder is less likely to scatter during manufacturing, making it easier to handle. In addition, the required fluidity is achieved, allowing the powder to be spread in the intended location and improving the build quality. By keeping the average particle size D50 at a certain size, the energy required to melt or sinter the additive manufacturing powder with a laser beam can be kept low, and the accuracy of the manufacturing can be improved.

[0022] The average particle size D50 mentioned above refers to the particle size at which the cumulative frequency of the additive manufacturing powder reaches 50% in the particle size histogram (particle size distribution graph) obtained by measuring the particle size of the additive manufacturing powder using a laser diffraction / scattering particle size distribution analyzer, and is measured according to JIS Z8825 (2013). More specifically, for measuring the average particle size D50, the Microtrac-Bell MT3300EXII can be used, with pure water as the solvent and a refractive index of 1.33.

[0023] In typical laser-based additive manufacturing, a fiber laser with a wavelength of approximately 1060 nm is used. Therefore, the laser absorption rate of the additive manufacturing powder is calculated by measuring the reflectance at a wavelength of 1060 nm using the following equipment and conditions. The laser absorption rate of the additive manufacturing powder is preferably 15% or higher, and more preferably 25% or higher. Manufacturer: Shimadzu Corporation Equipment name: Spectrophotometer (MPC-3100, using powder holder) Measurement wavelength: 300-1500 mm Slit width: 20 nm Reference: BaSO4 Measured physical property: Reflectance / Absorptance (%) = 1 - (Reflectance (%))

[0024] For additive manufacturing, the powder preferably has a fluidity of 25 s / 50 g or less, and more preferably 20 s / 50 g or less, as measured by whole flow measurement. This makes it easier to spread the additive manufacturing powder as intended during additive manufacturing. If the coverage rate, such as the average coverage rate, is made too high, the fluidity tends to decrease slightly. From the viewpoint of increasing fluidity, it is desirable not to make the coverage rate unnecessarily high.

[0025] To measure the fluidity described above, the measurement is performed according to JIS Z2502, the method for measuring the fluidity of metal powders. This method involves placing 50 g of additive manufacturing powder into a funnel and measuring the time it takes for all of the powder to fall through a 2.5 mm diameter hole. A smaller value indicates better fluidity.

[0026] (Manufacturing Method) To manufacture the additive manufacturing powder described above, for example, copper powder or copper alloy powder is prepared first. Copper powder or copper alloy powder can be obtained from a supplier or other pre-made product, or it may be manufactured by atomization or other various methods.

[0027] Copper powder mainly contains copper-containing particles that contain Cu, and it is preferable that the Cu content is 99.9% by mass or more (purity of 3N or more). Copper alloy powder mainly contains copper-containing particles that contain copper alloy. As for copper alloy powder, the Cu content is 80% by mass or more, more preferably 85% by mass or more, more preferably 90% by mass or more, and more preferably 99% by mass or more, and in addition to Cu, it may contain one or more alloying elements selected from the group consisting of Al, Cr, Fe, Ti, Ni, Nb, P, Si, Zn, and Zr.

[0028] The copper powder or copper alloy powder is preferably prepared with an average particle size D50 of 10 μm to 150 μm, after adjusting the particle size by sieving or other means as necessary. This average particle size D50 is the same as the average particle size D50 described above for additive manufacturing powders and can be measured by the same method.

[0029] By mixing the above-mentioned copper powder or copper alloy powder with a coating powder, the coating powder adheres to the surface of the copper-containing particles, thereby producing a powder for additive manufacturing.

[0030] The coating powder to be mixed with copper-containing particles of copper powder or copper alloy powder is preferably a fine-particle powder. The average particle size D50 of the coating powder is preferably 10 μm or less. This average particle size D50 is the same as the average particle size D50 mentioned above.

[0031] However, fine coating powders, such as those with an average particle size D50 of 10 μm or less, may aggregate. If there is a lot of aggregation in the coating powder, the aggregation can be easily resolved by mixing it with copper powder or copper alloy powder and then sieving it together with the copper powder or copper alloy powder.

[0032] Regarding the mixing method, any method can be used, such as mixing in a ball mill. For example, copper powder or copper alloy powder, coating powder such as Y2O3 powder, and pure water are put into a ball mill and rotated at 20 rpm or more for about 10 to 180 minutes. This results in a powder for additive manufacturing containing surface coating particles 3 as shown in Figure 1. The coating rate, such as the average coating rate mentioned above, has a corresponding relationship to (weight of coating powder) / (weight of copper powder or copper alloy powder), and the coating rate can be increased by increasing the weight of the coating powder. To obtain a powder for additive manufacturing with a desired coating rate, it is desirable to appropriately adjust the amount of coating powder put in, the rotation speed of the ball mill, the mixing time, etc.

[0033] As described above, it is possible to manufacture additive manufacturing powder containing copper-containing particles and coating powder.

[0034] Next, we prototyped the additive manufacturing powder described above and confirmed its effects, which are explained below. However, this explanation is merely illustrative and not intended to be limiting.

[0035] A pure copper powder with an average particle size D50 of approximately 30 μm to 45 μm was prepared. The copper content of this pure copper powder was 99.9% by mass.

[0036] In Comparative Example 1, the above copper powder was used as is for additive manufacturing. In Examples 1 to 6, the above copper powder was mixed with Y2O3 powder (coating powder) for 30 minutes using a ball mill to produce additive manufacturing powder in which a coating layer containing Y2O3 was formed around the copper-containing particles by the adhesion of the Y2O3 powder. In Examples 1 to 6, the amount of Y2O3 powder added to the ball mill was varied, thereby obtaining additive manufacturing powders with different coating rates, as shown in Table 1. The additive manufacturing powders of Examples 1 to 6 were confirmed by the analysis described above to have a coating layer containing Y2O3 formed around the copper-containing particles.

[0037] For the additive manufacturing powders obtained in Comparative Example 1 and Examples 1 to 6, the average particle size D50, laser absorptivity, minimum coverage, average coverage, maximum coverage, and fluidity were measured according to the methods described above. For the coverage measurement, as previously mentioned, wavelength-dispersive X-ray spectroscopy (WDS) was used to observe and acquire an image, and five particles (N=5) were randomly selected from the particles in the image. The results are shown in Table 1.

[0038] Furthermore, using each additive manufacturing powder, 10 mm cube-shaped objects were fabricated by additive manufacturing in a 3D printer, and the density and conductivity of these objects were evaluated. The 3D printer was set to an output of 500W and 380W. The printing speed during additive manufacturing was calculated by dividing the printing output by the input energy density.

[0039] The density of the fabricated object described above was determined by measuring the ratio of the area occupied by voids relative to the image observed with an optical microscope. The relative density was calculated using the formula: Relative density = ((Area of ​​fabricated object - Area of ​​voids) / Area of ​​fabricated object) × 100 (%). The conductivity of the fabricated object was calculated by passing eddy currents through the object and measuring the current value of the eddy currents. These results are also shown in Table 1.

[0040]

[0041] As shown in Table 1, the additive manufacturing powders used in Examples 1 to 6, which formed a coating layer with a predetermined coverage ratio, resulted in faster manufacturing speeds and produced objects with high density and conductivity during additive manufacturing. In particular, Examples 1, 2, 5, and 6 achieved a density of 99% or higher and a conductivity of 95% IACS or higher. These results suggest that the additive manufacturing powders described above have the potential to improve the buildability of objects produced by additive manufacturing.

[0042] Also, the relationship between the average coating rate of the powder for laminated modeling in Examples 3 to 6 with a modeling output of 380 W and the conductivity of the modeled object produced using the same is shown graphically in FIG. 2. From FIG. 2, it can be seen that as the average coating rate of the powder for laminated modeling increases, the conductivity of the modeled object increases. While a general copper alloy (CuCrZr) is about 90% IACS, from the perspective of obtaining a sufficiently high conductivity, it can be said that it is desirable to set the average coating rate of the powder for laminated modeling to 5% or more.

[0043] (Possibility of contribution to SDGs) According to the above-described embodiment, since the moldability of the modeled object by laminated modeling can be improved, there is a possibility of contributing to the advancement of the laminated modeling technology. Therefore, this embodiment may contribute to Goal 9 of the Sustainable Development Goals (SDGs) led by the United Nations, which aims to "build resilient infrastructure, promote inclusive and sustainable industrialization, and foster innovation."

[0044] 1 Copper-containing particles 2 Coating layer 3 Surface-coated particles

Claims

1. A powder for additive manufacturing, comprising copper-containing particles containing Cu and a coating layer that covers at least a portion of the area surrounding the copper-containing particles, wherein the coating layer contains Y, and the average coverage rate of the area surrounding the copper-containing particles by the coating layer is 5% or more.

2. The additive manufacturing powder according to claim 1, wherein the average coverage rate is 20% to 80%.

3. The additive manufacturing powder according to claim 1 or 2, wherein the minimum coverage rate around the copper-containing particles by the coating layer is 1% or more.

4. The additive manufacturing powder according to claim 1 or 2, wherein the maximum coverage rate around the copper-containing particles by the coating layer is 90% or less.

5. The additive manufacturing powder according to claim 1 or 2, wherein the coating layer contains yttrium oxide.

6. The additive manufacturing powder according to claim 5, wherein the yttrium oxide comprises Y2O3.

7. The additive manufacturing powder according to claim 1 or 2, wherein the average particle size D50 is 10 μm to 150 μm.

8. The additive manufacturing powder according to claim 1 or 2, wherein the fluidity measured by whole flow measurement is 25 s / 50 g or less.

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