Re-used alloy powder for deposition modeling and method for producing deposition model

Abstract

[Problem] The present invention addresses the problem of providing a re-used alloy powder for deposition modeling and a method for producing a deposition model, wherein stable modeling is possible and defects can be suppressed even in cases where an alloy powder for deposition modeling is re-used. [Solution] The present invention provides a re-used alloy powder for deposition modeling, the re-used alloy powder being characterized in that: the surface of the alloy powder is provided with an oxide film; the alloy powder contains, in mass%, more than 0.15% but less than 0.106% of oxygen; and the oxide film has a maximum thickness of 200 nm or less (excluding 0).

Description

Reusable alloy powder for additive manufacturing and manufacturing method for additive manufactured products

[0001] The present invention relates to alloy powder, and more particularly to the reuse of alloy powder for additive manufacturing.

[0002] Metal powders are important basic materials in the field of forming materials, such as those used in powder compaction, powder metallurgy, and metal injection molding (MIM). These forming techniques using metal powders are suitable for various industrial products due to their excellent strength and mass productivity. In recent years, metal powders have also been used as raw materials for additive manufacturing (hereinafter referred to as metal additive manufacturing or simply additive manufacturing), which has made it possible to manufacture forming materials without molds, and their importance is increasing.

[0003] Furthermore, in recent years, the conservation and effective use of metal resources has become increasingly important from the perspective of environmental conservation. For example, Patent Document 1 discloses a material powder for metal additive manufacturing (MMA) that can suppress a decrease in fluidity even when recycled, and a method for manufacturing the same, in which the material powder for MMA is manufactured to have a particle size distribution corresponding to a fluidity equal to or greater than a predetermined reference value, based on the particle size distribution of a virgin material, which is unused material powder, and the fluidity of a recycled material after recycling the virgin material a predetermined number of times in a MMA device, and that silica particles may be added to the virgin material.

[0004] JP 2021-25062 A

[0005] However, even the material powder for metal additive manufacturing described in Patent Document 1 deteriorates in formability when reused repeatedly, and metal droplets known as sputtering are likely to occur during manufacturing, resulting in the problem of defects such as voids being more likely to occur in the additively manufactured product.

[0006] Based on the above, the object of the present invention is to provide a reused alloy powder for additive manufacturing that enables stable manufacturing and suppresses defects even when the alloy powder for additive manufacturing is reused, and a method for manufacturing additive manufactured products.

[0007] The present invention provides a reusable alloy powder for additive manufacturing, characterized in that the alloy powder has an oxide film on the surface thereof, the alloy powder contains, by mass%, more than 0.015% but less than 0.106% oxygen, and the oxide film has a maximum thickness of 200 nm or less (excluding 0).

[0008] It is preferable that the alloy powder is a Ni-based alloy, the alloy powder contains, by mass%, more than 0.015% and less than 0.106% oxygen, and the oxide film has a maximum thickness of 100 nm or less (excluding 0).

[0009] It is preferable that the alloy powder contains, by mass %, more than 0.030% and less than 0.106% oxygen, and that the oxide film has a maximum thickness of 1 nm or more and 100 nm or less.

[0010] The oxide film preferably has a portion near its outermost surface that is an oxide mainly containing Ni.

[0011] It is preferable that the alloy contains, in mass %, 14.5 to 24.0% Cr, 12.0 to 23.0% Mo, and the balance being Ni and inevitable impurities.

[0012] It is preferable that the alloy powder is an Fe-based alloy and has an oxide film on the surface of the alloy powder, the alloy powder contains more than 0.015% and less than 0.106% oxygen by mass, and the oxide film has a maximum thickness of 200 nm or less (excluding 0).

[0013] It is preferable that the alloy powder contains, by mass %, more than 0.020% and less than 0.106% oxygen, and that the oxide film has a maximum thickness of 1 nm or more and 150 nm or less.

[0014] It preferably contains, in mass %, Ni: 14% to 22%, Ti: 0.1% to 5.0%, Al: 1% or less, Si: 1% or less, with the balance being Fe and inevitable impurities.

[0015] The oxide film near the outermost surface is preferably an oxide containing at least one of Ni, Ti, Si and Al as the most abundant element among elements other than oxygen.

[0016] It is preferable that the alloy powder has a ratio of an integrated frequency of 90% to an integrated frequency of 10% by volume in an integrated distribution curve showing the relationship between particle diameter and volume integration from the small particle diameter side, determined by a laser diffraction method, of 3.0 or more and 10.0 or less.

[0017] A method for manufacturing an additive manufacturing product, characterized in that an alloy powder containing any one of the above-mentioned reuse alloy powders for additive manufacturing is used as a raw material powder, and additive manufacturing is performed using this raw material powder.

[0018] It is preferable that the raw material powder includes a reused alloy powder for additive manufacturing having an oxide film with an oxide containing one of Ni or Fe as the most abundant element among the elements contained other than oxygen, and an alloy powder for additive manufacturing having an oxide film with an oxide containing an element other than Ni or Fe as the most abundant element among the elements contained other than oxygen.

[0019] According to the present invention, it is possible to provide a reused alloy powder for additive manufacturing and a method for manufacturing additive manufactured products that can enable stable manufacturing even with repeatedly reused raw material powder and suppress defects.

[0020] 1 is an optical microscope image of a reused Ni-based alloy powder. FIG. 2 is a STEM image and elemental mapping diagram of reused alloy powder P1 of this Example 1. FIG. 3 is a STEM image and elemental mapping diagram of reused alloy powder P2 of this Example 1. FIG. 4 is a STEM image and elemental mapping diagram of reused alloy powder P3 of this Example 1. FIG. 5 is a STEM image and elemental mapping diagram of reused alloy powder P4 of this Example 2. FIG. 6 is a diagram estimating the change in oxygen content versus the number of times the reused Ni-based alloy powder has been reused. FIG. 7 is a STEM image and elemental mapping diagram of reused alloy powder P13 of this Example 4. FIG. 8 is a STEM image and elemental mapping diagram of reused alloy powder P13 of this Example 4. FIG. 9 is a STEM image and elemental mapping diagram of reused alloy powder P13 of this Example 4. FIG. 10 is a schematic diagram of an additive manufacturing apparatus known as a powder bed fusion method. 1 shows a schematic diagram of an additive manufacturing apparatus known as a directed energy deposition method.

[0021] Hereinafter, embodiments of the reused alloy powder for additive manufacturing and the manufacturing method for additive manufactured products will be described in detail. First, the reused alloy powder for additive manufacturing will be described, followed by the manufacturing method for additive manufactured products. In the description, "reused alloy powder for additive manufacturing" may be referred to as "reused alloy powder" or simply as "alloy powder." Furthermore, unused alloy powder that has never been additively manufactured may be referred to as "raw material powder" or "new product." In this specification, a numerical range beginning with "to" is defined as a range that includes the preceding and following numerical values, with "greater than" and "less than" being used. Furthermore, when a numerical value is followed by "greater than" or "less than," the value is not included. In the drawings, the same or similar parts are designated by the same reference numerals, and their description will not be repeated.

[0022] <Alloy Powder> The reused alloy powder of this embodiment is a recycled raw material powder, such as a Ni-based alloy or an Fe-based alloy, used in additive manufacturing. The alloy powder has an oxide film on its surface. The alloy powder itself contains more than 0.015% by mass but less than 0.106% by mass of oxygen, preferably more than 0.020% by mass but less than 0.106% by mass, with the lower limit being more than 0.030% by mass. The oxide film has a maximum thickness of 200 nm or less (however, it does not have a thickness of 0 nm), preferably 100 nm or less, and more preferably 1 nm to 150 nm. Alloy powders with the appropriate oxygen content and oxide film thickness can be repeatedly reused for additive manufacturing.

[0023] [Alloy Composition] The alloy powder used in the present embodiment may be a powder of an alloy known as a heat-resistant alloy, a corrosion-resistant alloy, or a wear-resistant alloy, and more preferably a Ni-based alloy or an Fe-based alloy.

[0024] The Ni-based alloy refers to an alloy that is primarily composed of Ni and contains additional elements such as Cr and Mo. For example, commercially available alloys include M252, Waspaloy, Rene 41, Udimat 520, Inconel 718, Inconel 725, Inconel 713, Inconel 738, MM246, MM247, Rene 80, GMR 235, Inconel 625, Nimonic 263, Hastelloy B, C, and X materials, Hicoroy 11, and MAT 21. However, these are merely examples and are not limited to these. (Waspaloy is a registered trademark of United Technologies, Rene is a registered trademark of GE, Udimat is a registered trademark of Special Metals, Inconel and Nimonic are registered trademarks of Huntington Alloys, Hastelloy is a registered trademark of Haynes International, and MAT21 is a registered trademark of Hitachi Metals.)

[0025] The Ni-based alloy is preferably a Ni-Cr-Mo alloy, and its composition, in mass %, of Cr and Mo following Ni as the main component, is preferably Cr: 10.0 to 30.0%, Mo: 5.0 to 30.0%, more preferably Cr: 10.0% to 25.0%, Mo: 8.0 to 25.0%, and particularly preferably Cr: 14.5 to 24.0%, Mo: 12.0 to 23.0%.

[0026] An Fe-based alloy refers to an alloy that is primarily composed of Fe and contains additional elements such as Ni, Cr, and Co. For example, materials commonly used in additive manufacturing include 18Ni maraging steels of grades 200, 250, 300, and 350, and stainless steels such as SUS304, SUS316, SUS630, SUS310S, SUH660, SCH13, and SCH22.

[0027] The Fe-based alloy used in the present application is preferably an Fe—Ni alloy, and its composition is such that, after the main component Fe, Ni is preferably 14.0 to 22.0% by mass, more preferably 16.0 to 20.0%, and particularly preferably 17.0 to 19.0% by mass. Examples of such an Fe—Ni alloy include the aforementioned maraging steel and heat-resistant stainless steel containing a large amount of Ni.

[0028] Furthermore, the Si content, in mass %, is preferably 1% or less, more preferably less than 1%, and even more preferably 0.5% or less. The Al content, in mass %, is preferably 1% or less, more preferably less than 1%, even more preferably 0.5% or less, and even more preferably 0.25% or less. Mo, Ti, etc. may also be contained, and in mass %, Mo is preferably 5% or less, more preferably 0.5% to 5.0%, and even more preferably 1.5% to 2.5%. In mass %, Ti is preferably 5% or less, more preferably 0.5 to 5.0%, and even more preferably 1.5% to 2.5%.

[0029] (Inevitable Impurities) As an inevitable impurity, C forms carbides with Cr near the grain boundaries, which increases the deterioration of corrosion resistance. Therefore, the content is set to less than 0.05%. Furthermore, S and P segregate at the grain boundaries and cause hot cracking, so they must be kept to less than 0.01%. Furthermore, the content of these inevitable impurities is preferably low, and may be 0%.

[0030] [Oxygen content of alloy powder and oxide film thickness] In additive manufacturing, raw material powder (alloy powder) in areas not irradiated with laser is repeatedly reused. However, the amount of oxygen increases with each repetition due to oxidation of the powder surface. Meanwhile, if metal spatter occurs when the raw material powder melts during additive manufacturing, defects such as poor shape or residual metal spatter in the additively manufactured product are likely to occur. It has been discovered that the cause of this spatter is the expansion and explosion of oxygen contained in the powder, and that the oxide film on the powder surface also plays a role.

[0031] In addition, when the metal powder is irradiated with a laser beam, multiple reflections occur in the oxide film, which increases the laser absorption rate, and the amount of melted alloy powder increases due to the increased heat input, resulting in a larger melt pool. As a result, the residual stress caused by thermal contraction during the solidification process may exceed the tensile stress, making it more likely to crack.

[0032] Therefore, it can be said that there is a limit to the reusability of raw material powders. In view of this, the alloy powder according to the present invention contains, by mass, more than 0.015% but less than 0.106% oxygen, and the oxide film has a maximum thickness (maximum thickness) of 200 nm or less. Furthermore, it is preferable to limit the oxygen content to more than 0.020% but less than 0.106%, and the oxide film to a maximum thickness of 1 nm to 150 nm. More preferably, the oxygen content is more than 0.030% but less than 0.106%, and the oxide film to a maximum thickness of 1 nm to 100 nm. In the case of Fe-based alloy powders, the thickness is preferably 20 nm to 200 nm, more preferably 50 nm to 200 nm, and even more preferably 60 nm to 150 nm.

[0033] By setting the oxygen content and film thickness within these ranges, it is possible to suppress metal spatter caused by oxygen expansion and explosion when the alloy powder melts, and to suppress defects in the additively manufactured product through stable manufacturing. The oxygen content in the powder can be measured using inert gas fusion infrared absorption spectroscopy.

[0034] [Oxide Film (Substance)] The oxide film preferably contains an element that mainly constitutes the alloy powder near the outermost surface. For example, in the case of a Ni-based alloy, it is preferable to have an oxide mainly composed of Ni. Since an oxide mainly composed of Ni has a relatively low melting point, it evaporates first when irradiated with a laser beam, making it less likely to cause sputtering. This is also thought to prevent adverse effects on the melting and solidification process. In this specification, the term "mainly constituting element" refers to the element that is most abundant among the elements contained other than oxygen.

[0035] Furthermore, among the metal elements constituting the alloy powder, alloy powders having an oxide film mainly made up of oxides of Ni and alloy powders having an oxide film mainly made up of oxides of metal elements other than Ni may be mixed. For example, in the case of Ni-Cr-Mo alloy powder, the oxide mainly made up of metal elements other than Ni may be an oxide mainly made up of Ta, Cr, or the like, which are minor components (optional added elements). The oxide film mainly made up of Ta, Cr, or the like may be present in the case of a new alloy powder, or in the case of an alloy powder that has been used once for molding and has an oxide film formed of more oxides mainly made up of Ta, Cr, or the like than in unused alloy powder, due to sputtering adhering to the surface of the alloy powder.

[0036] 1 shows the state of Ni-Cr-Mo alloy powder when it is reused, but it may also contain alloy powders such as those shown in the dashed frame in the figure. Cross-sectional observation of each alloy powder revealed that some alloy powders had oxide films containing oxides primarily of Ni, while others had oxides primarily of Ta, Cr, etc. Thus, powders containing oxide films primarily composed of different elements may be included, and even if they are mixed, it is believed that this will not significantly affect the formability as long as the oxygen content in the powder is within the preferred range described above.

[0037] Furthermore, even in the case of an alloy powder mainly composed of Fe, such as an Fe-based alloy powder, alloy powder having an oxide film mainly composed of an oxide of Fe and alloy powder having an oxide film mainly composed of an oxide of a metal element other than Fe may be mixed. For example, in the case of an Fe-Ni alloy powder, the oxide mainly composed of a metal element other than Fe may be an oxide mainly composed of at least one of Ni, Ti, Si, or Al. The oxide film mainly composed of at least one of Ni, Ti, Si, or Al may be present in the case of a new (unused) alloy powder, or in the case of an alloy powder that has been used once for molding, whereby sputtering adheres to the surface of the alloy powder, resulting in a larger oxide film mainly composed of at least one of Ni, Ti, Si, or Al than in the case of an unused alloy powder. This is because Si, Ti, Al, and the like are elements that are easily oxidized, and are oxidized to form SiO ２ , TiO２ or Al ２ O ３ Stable oxides such as

[0038] [Particle size] The additive manufacturing method is a manufacturing method in which individual powders are repeatedly melted and solidified to create a shape. However, if the particle size of the alloy powder is less than 5 μm, it is difficult to obtain the volume required for one melt-solidification cycle, making it difficult to obtain a sound additive manufactured product. On the other hand, if the particle size of the alloy powder is greater than 250 μm, the volume required for one melt-solidification cycle is too large, making it difficult to obtain a sound additive manufactured product. Therefore, the particle size of the alloy powder is preferably 5 to 250 μm. More preferably, it is 10 μm to 150 μm. Powders obtained by gas atomization, which produces spherical shapes, are preferred. The particle size of the powder can be measured by measuring the particle size distribution using, for example, a laser diffraction particle size distribution analyzer.

[0039] For example, by additive manufacturing method, a thickness of 10 μm to 50 μm is more preferable for selective laser melting (SLM) method, and a thickness of 45 μm to 105 μm is more preferable for electron beam melting (EBM) method.

[0040] In addition, in the case of the laser metal deposition (LMD) method, it is preferable to set the thickness to 30 μm to 250 μm.

[0041] In addition, in an integrated distribution curve showing the relationship between particle diameter and volume integration from the small particle diameter side, obtained by laser diffraction, when an integrated frequency of 10% by volume is represented as D10, an integrated frequency of 50% by volume as D50, and an integrated frequency of 90% by volume as D90, the ratio of the integrated frequency of 90% by volume to the integrated frequency of 10% by volume (D90 / D10) is preferably 3.0 to 10.0, more preferably 3.0 to 8.0, more preferably 3.0 to 5.0, and even more preferably 3.1 to 3.6.

[0042] If D90 / D10 is 10.0 or less, the proportion of large particles will not be too high, making it easier to suppress defects due to insufficient melting of the powder during laser irradiation. Also, if D90 / D10 is 3.0 or more, friction between the particles constituting the powder will not be too high, preventing a decrease in fluidity, suppressing poor powder spreading, and is expected to suppress internal defects in the resulting layered object.

[0043] <Method for manufacturing an additively manufactured product> Next, a method for manufacturing an additively manufactured product according to the present invention will be described with reference to Figures 11 and 12. An embodiment of the method for manufacturing an additively manufactured product is characterized in that alloy powder containing the above-mentioned reused alloy powder for additive manufacturing is used as raw material powder, and additive manufacturing is performed using this raw material powder. In other words, it is sufficient that the raw material powder contains at least the reused alloy powder of the present invention that has been reused. It is possible to use the alloy powder of the present invention alone, but it is preferable to use it mixed with new raw material powder. It is also possible to periodically add the reused alloy powder of the present invention.

[0044] The raw material powder may also be a mixture of, for example, a Ni-based alloy powder for additive manufacturing having an oxide film mainly made of an oxide of Ni and a Ni-based alloy powder for additive manufacturing having an oxide film mainly made of an oxide of an element other than Ni. Alternatively, the raw material powder may be a mixture of an Fe-based alloy powder for additive manufacturing having an oxide film mainly made of an oxide of Fe and a Fe-based alloy powder for additive manufacturing having an oxide film mainly made of an oxide of an element other than Fe.

[0045] The Ni-based alloy powders and Fe-based alloy powders for additive manufacturing include at least reused products, but the Ni-based alloy powder having an oxide film mainly made up of oxides of elements other than Ni may be reused products as described above, or may be new alloy powders. Similarly, the Fe-based alloy powder having an oxide film mainly made up of oxides of elements other than Fe may be reused products as described above, or may be new alloy powders.

[0046] As a method of additive manufacturing, for example, the Ni-based corrosion-resistant alloy powder for additive manufacturing of the present invention is supplied to a powder bed fusion (PBF) type additive manufacturing device shown in FIG. 11 , and high energy such as a laser or electron beam is irradiated onto the area where the powder is laid, thereby selectively fusing and bonding the alloy powder, thereby additively manufacturing an additive manufactured product of a desired shape.

[0047] Furthermore, in addition to the one shown in FIG. 11 , depending on the shape of the additive manufacturing product, a Directed Energy Deposition (DED) type additive manufacturing device shown in FIG. 12 can also be used, and there are no particular restrictions on the type of additive manufacturing device.

[0048] [Uses and Products] The alloy powder described above can be suitably used in metal additive manufacturing such as additive manufacturing, powder compaction, powder metallurgy, metal injection molding, and the like, but there are no particular limitations on the uses and products.

[0049] Additive manufacturing products using the alloy powder of the present invention are expected to be applied in a wide range of fields, such as chemical plants, pharmaceutical manufacturing facilities, and the oil and gas industry. For example, it is possible to provide semiconductor manufacturing equipment components with excellent corrosion resistance and extremely few defects.

[0050] The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0051] Example 1 As the Ni-based alloy powder, a Ni-Cr-Mo alloy (Ni-19Cr-18Mo-2Ta) was prepared as shown in Table 1. The particle size of the alloy powder was set to 10 μm to 53 μm.

[0052]

[0053] Next, to simulate the alloy powder of the present invention, an oxidation treatment was performed by holding the powder in an atmospheric furnace heated to 300°C to 500°C for 100 minutes. Specifically, alloy powder P1 was obtained at 300°C for 100 minutes, alloy powder P2 at 400°C for 100 minutes, and alloy powder P3 at 500°C for 100 minutes. Subsequently, the amount of oxygen in the alloy powder was analyzed, elemental analysis was performed, and the oxide film thickness was measured. The measurement methods are as follows.

[0054] (Oxygen content of powder) The oxygen content of the powder was measured using an inert gas fusion-infrared absorption method, where the measurement was carried out twice and the average value was calculated.

[0055] (Thickness of oxide film) The thickness of the oxide film (or film) formed on the surface of the alloy powder can be measured by observing an arbitrary cross section of the alloy powder using a scanning transmission electron microscope (STEM). As an elemental analysis method for the oxide film, elemental analysis can be performed on, for example, an arbitrary cross section of the alloy powder using energy dispersive X-ray spectroscopy (EDX). Note that the observation sample can be obtained by cutting the powder using a focused ion beam (FIB) microsampling device.

[0056] The oxygen content and oxide film thickness of alloy powders P1 to P3 were measured. The oxygen content of P1 was 0.031%, and the maximum oxide film thickness was 4 nm. The oxygen content of P2 was 0.047%, and the maximum oxide film thickness was 7 nm. The oxygen content of P3 was 0.106%, and the maximum oxide film thickness was 18 nm. The oxygen content (%) in the powder is mass %.

[0057] As described above, the oxygen content in each of the alloy powders P1 to P3 was measured using the inert gas fusion-infrared absorption method, and the average value was calculated from two measurements. The maximum oxide film thickness was measured using a scanning transmission electron microscope (JEOL, model: JEM-ARM200F) at the location where the oxide film was thickest. Even for the same powder, thicknesses of 20 nm or more can be observed depending on the observation area, but the maximum thickness is estimated to be 100 nm or less. Because the oxide film is generally uniform, it is sufficient to observe it within a specific field of view and range. Although alloy powders P1 to P3 simulate the oxygen content and oxide film thickness in a reused state, it is desirable to actually obtain data on the number of times the alloy powder can be reused, the oxygen content, and the number of times it can be reused and the oxide film thickness in advance.

[0058] Next, FIG. 2 shows an STEM image and elemental analysis results of alloy powder P1, FIG. 3 shows an STEM image and elemental analysis results of alloy powder P2, and FIG. 4 shows an STEM image and elemental analysis results of alloy powder P3.

[0059] For each of P1 to P3, STEM (observation) images of the powder cross section are shown in Figures 2(a), 3(a), and 4(a). In the figures, 10 denotes the powder itself, 14 denotes an oxide film, and 16 denotes a carbon protective film applied to prevent surface contamination and oxidation during the preparation of the observation sample. The elemental analysis results are shown in Figures 2(b), 3(b), and 4(b). The STEM images are cross-sectional observation images of powder particles cut using a focused ion beam (FIB) microsampling device (FIB, manufactured by Hitachi High-Tech Corporation, model: FB-2100; microsampling is a registered trademark of Hitachi High-Tech Corporation).

[0060] Elemental analysis was performed using an energy dispersive X-ray spectroscopy (EDX) system equipped with a scanning transmission electron microscope. The measurement conditions for elemental analysis were: acceleration voltage: 200 kV, STEM mode: 5C, quantitative analysis: 30 Lsec, element map: 256 x 256, 0.01 msec / Pix, line analysis: 256 Pix, 1.0 msec / Pix. The scanning direction for sampling was from the powder 10 side toward the oxide film 14, as indicated by the arrow 12 in the figure.

[0061] As shown in Figures 2 and 3, for P1 and P2, a Ni peak is observed outside of the Ta and Cr peaks. That is, it was confirmed that an oxide mainly composed of Ni was formed near the outermost surface of the powder. For P3, Ta and Cr also appear on the outside, but a Ni peak is observed further out. From this, it was confirmed that an oxide mainly composed of Ni was also formed near the outermost surface of P3.

[0062] Next, using only the raw material powders P1 to P3, additive manufacturing was performed using the SLM method with a PBF additive manufacturing device (Mlab cusing 200R), and additive manufactured products (10 mm x 10 mm x 10 mm blocks) F1 to F3 were produced. The additive manufacturing conditions were: layer thickness: 0.04 mm; laser output: 200 W; scanning speed: 800 mm / s; scanning pitch: 0.11 mm. The defect rate of the additive manufactured products was then measured. The energy density (E): was 56.8 J / mm3. The energy density (E) is calculated by dividing the power (P) by the scanning speed (v), scanning pitch (a), and layer thickness (d) (E = P / vad).

[0063] (Defect Rate) The defect rate is the area ratio of defects determined by image processing of a cross-sectional photograph (1.58 mm × 1.25 mm) of an additively manufactured product. The defect rate was measured using a microscope (Keyence VHX-6000), with a threshold value determined using the microscope's area ratio derivation function to digitize the image, the area ratio of defects appearing as black was determined, and the average of the area ratios of five locations was taken.

[0064] Table 2 shows the oxygen content of each alloy powder P1 to P3, the maximum thickness of the oxide film observed in the observation field, and the defect rate of additively manufactured products F1 to F3 manufactured using these powders. As shown in Table 2, it was confirmed that additively manufactured products with a defect rate of 0.1% or less (F1: 0.03%, F2: 0.06%) could be produced using powders F1 with an oxygen content (mass%) of 0.031% and F2 with an oxygen content (mass%) of 0.047%.

[0065] On the other hand, the defect rate of F3, which had a maximum oxide film thickness of 18 nm but an oxygen content (mass%) of 0.106% in the powder, was 0.2%. Although a defect rate of 0.2% is practical, minute inclusions were observed, and it was predicted that the defect rate would further increase if P3 were further stacked and reused. For these reasons, the defect rate was set at less than 0.2%, and the upper limit of the oxygen content was set at 0.106%. Furthermore, since the thickness of the oxide film in Experiment 2 described below was 60 nm, and since the oxide film is thought to have less of an effect on the defect rate and inclusions than the oxygen content in the powder, it is preferable to set the upper limit at 100 nm.

[0066]

[0067] From the above, we confirmed that alloy powders with an oxygen content of more than 0.015% but less than 0.106% and a maximum oxide film thickness of 200 nm or less (excluding 0) can reduce the defect rate of additively manufactured products, enable stable manufacturing, and suppress defects. Table 3 shows the mechanical properties of tensile strength, elongation, and Vickers hardness for additively manufactured products F1 to F3. The corrosion resistance of F3 was measured (boiling 10% sulfuric acid and boiling 2% hydrochloric acid). Table 3 also shows the mechanical properties of an additively manufactured product using the novel raw material powder, designated F0, as a reference example. As shown in Table 3, the additively manufactured products F1 to F3 using the alloy powder of the present invention have excellent mechanical properties, and their corrosion resistance is also excellent, as shown in the results for F3, and is equivalent to that of additively manufactured product F0 using the novel raw material powder.

[0068] Example 2 Alloy powder P4 was prepared, which contained a mixture of alloy powders each having an oxide film with a maximum thickness of 60 nm and alloy powders each having an oxide film with a maximum thickness of 50 nm. The oxygen content of alloy powder P4 was 0.033 mass%. The alloy composition and powder particle size were the same as those of alloy powders P1 to P3. The maximum oxide film thickness was measured in the observation area over a 140 nm circumferential direction of the oxide film.

[0069] It was confirmed that P4 contained a mixture of alloy powder having an oxide film mainly composed of oxides of Ta, Cr, etc., as shown in FIG. 5(b), and alloy powder having an oxide film mainly composed of oxides of Ni, as shown in FIG. 6(b). Both of these mixed alloy powders were reused. The results of elemental analysis using EDX for each analysis position (51-54) shown in FIG. 5(a) are also shown. As shown in Table 4, it was confirmed that oxides mainly composed of Ta, Cr, etc. were formed near the powder surface.

[0070] The results of elemental analysis using EDX are also shown for each analysis position (61 to 64) shown in Figure 6(a). As shown in Table 5, it was confirmed that oxides mainly consisting of Ni were formed near the powder surface. In the figure, 50 and 60 represent the powder itself, 56 and 66 represent oxide films, 57 and 67 represent carbon protective films, and 55 and 65 represent the scanning direction.

[0071]

[0072]

[0073] Using alloy powder P4, additive manufacturing was performed under the same conditions as in Example 1 to obtain additively manufactured product F4. As with P1 and P2, additive manufacturing was also successful. Furthermore, the defect rate of the resulting additively manufactured product F4 was 0.06%, confirming that defects could be suppressed. From the above, it was found that as long as the oxygen content in the powder was greater than 0.015% and less than 0.106%, and the maximum oxide film thickness was within the range of 200 nm or less (excluding 0), the moldability was not significantly affected and the defect rate of the resulting additively manufactured product could be suppressed. In addition, as long as the oxygen content and oxide film thickness in the powder were within the above-mentioned ranges, even when the alloy powder contained a mixture of alloy powder having an oxide film primarily composed of oxides of Ta, Cr, etc., as shown in FIG. 5, and alloy powder having an oxide film primarily composed of oxides of Ni, as shown in FIG. 6, the mixture did not significantly affect the moldability and the defect rate of the resulting additively manufactured product could be suppressed.

[0074] (Example 3) An additive manufacturing product was manufactured by the SLM method using the additive manufacturing device described above. The raw material powder prepared in Table 1 was repeatedly used and reused a total of 69 times. During this time, new powder was added five times as the powder decreased. Measurements similar to those in Example 1 were carried out on this reused Ni-based alloy powder. The result was that the oxygen content was 0.033% by mass. This corresponds to the oxygen content of the simulated alloy powder P1, which was 0.031% by mass. The maximum thickness of the oxide film was 1 nm to 60 nm.

[0075] Furthermore, the D10 of the new raw material powder was 18.4 μm, the D50 was 33.2 μm, and the D90 was 56.8 μm, while the D10 of the powder after 69 reuses was 20.5 μm, the D50 was 39.8 μm, and the D90 was 72.2 μm. That is, the particle size of the powder tends to increase with reuse. For example, when comparing the ratio of D90 to D10 (D90 / D10), it was 3.06 for the raw material powder and 3.5 for the powder reused 69 times. By keeping the D90 / D10 in the range of 3.0 to 10.0, it is believed that the fluidity of the alloy powder was maintained and poor powder spreading was suppressed, thereby enabling the additive manufacturing to be completed. Furthermore, as described below, it is believed that the defect rate of the additive manufacturing body was also reduced by suppressing insufficient melting of the alloy powder.

[0076] The defect rate of the AM products was 0.06%, which was below the acceptable range of 0.2%. Furthermore, the mechanical properties and corrosion resistance of the AM products were also measured, but no significant differences were found. Based on the above, it was found that there would be no problem with reusing the products approximately 70 times.

[0077] Therefore, the relationship between the number of reuses and the amount of oxygen was estimated. First, the oxygen content of the new alloy powder was 0.015 mass%. Assuming that this increases linearly and combining this with the above results, the relationship between the number of reuses and the amount of oxygen shown in Figure 7 is obtained. That is, even if the powder is reused 100 times, the amount of oxygen is predicted to be about 0.04 mass%. In reality, new powder is added during the repetition, so it is thought that the increase in the amount of oxygen can be further suppressed. In any case, as mentioned above, it is desirable to obtain data on the number of reuses and oxygen content of unused alloy powder, as well as the number of reuses and oxide film thickness, and to determine and grasp in advance the number of times the powder can be reused.

[0078] Example 4 Next, an example using an Fe-based alloy powder will be described. The Fe-based alloy powder used was an Fe—Ni alloy, which is a type of maraging steel. The Fe—Ni alloy contained, in mass%, 14% to 22% Ni, 0.1% to 5.0% Ti, 1% or less Al, and 1% or less Si. P10 was a raw material powder (new product) that had never been subjected to additive manufacturing, and P11 to P13 were alloy powders containing the raw material powder and reused alloy powder.

[0079] Table 6 shows the alloy compositions and oxygen content of P10 to P13. As shown in Table 6, the oxygen content (mass%) in the powder was 0.022% for P10, 0.028% for P11, 0.034% for P12, and 0.042% for P13. The oxygen content in the alloy powder was measured using the inert gas fusion-infrared absorption method, as described above. Note that Ni was measured using the volumetric method, Co and Al using atomic absorption spectrometry, and Si, Mo, and Ti using absorptiometry. The average value of two measurements was used. The oxide film thickness of the powder was 1 nm to 10 nm for P10, and 1 nm to 200 nm for P11 to P13. Furthermore, elemental analysis of the oxide films of P11 and P13 confirmed the presence of a mixture of alloy powders with oxide films mainly composed of Fe and alloy powders with oxide films mainly composed of Si. The maximum thickness of the oxide film is the maximum thickness of the oxide film when the oxide film is observed in the circumferential direction of 260 nm in the observation area.

[0080] Furthermore, P12 contains alloy powders as shown in Figures 8, 9, and 10, which are believed to include reused powders. Table 7 shows the results of elemental analysis using EDX for each analysis position (71-74) shown in Figure 8. As shown in Table 7, it was confirmed that oxides mainly composed of Ti were formed near the powder surface. Table 8 shows the results of elemental analysis using EDX for each analysis position (81-84) shown in Figure 9. As shown in Table 8, it was confirmed that oxides mainly composed of Si or Fe were formed near the powder surface.

[0081] Table 9 shows the results of elemental analysis using EDX for each analysis position (91-94) shown in Figure 10. As shown in Table 9, it was confirmed that an oxide mainly composed of Fe was formed near the powder surface. From the above, it was confirmed that P12 contains a mixture of alloy powder having an oxide film mainly composed of Ti oxide, alloy powder having an oxide film mainly composed of Si oxide, and alloy powder having an oxide film mainly composed of Fe oxide. In the figure, 70, 80, and 90 represent the powder itself, 76, 86, and 96 represent oxide films, 77, 87, and 97 represent carbon protective films, and 75, 85, and 95 represent the scanning direction.

[0082] Table 10 shows the measurement results for D10, D50, and D90 for each of P10 to P12, as well as the ratio of D90 to D10 (D90 / D10). As shown in Table 10, the ratio of D90 to D10 (D90 / D10) was 3.08 for P10, 3.29 for P11, and 3.3 for P12. Since D90 / D10 was in the range of 3.0 to 10.0, it is believed that the fluidity of the alloy powder was maintained, which prevented powder laying defects and allowed the additive manufacturing to be completed without any problems. In addition, as described below, it is believed that the defect rate of the additive manufacturing body was also reduced by preventing insufficient melting of the alloy powder. In addition, D10, D50, and D90 are D10, D50, and D90, respectively, where D10 is an integrated frequency of 10% by volume, D50 is an integrated frequency of 50% by volume, and D90 is an integrated frequency of 90% by volume in an integrated distribution curve showing the relationship between particle diameter and volume integration from the small particle diameter side, which is determined by a laser diffraction method.

[0083] Next, additive manufacturing products were produced using each of the alloy powders P11 to P13. A 250 x 250 x 36 mm base plate (made of S50C) was placed on the building platform, and additive manufacturing products (57 mm x 12 mm x 12 mm high, 40 mm x 10 mm x 10 mm high, and 10 mm x 10 mm x 10 mm high rectangular pillar shapes) were manufactured on the base plate. The additive manufacturing product using P11 was designated F11, the additive manufacturing product using P12 was designated F12, and the additive manufacturing product using P13 was designated F13. The manufacturing conditions were: power (P): 250 W, scanning speed (v): 600 mm / s, scanning pitch (a): 0.09 mm, layer thickness (d): 0.05 mm, and energy density (E): 92.6 J / mm3. The energy density (E) is the power (P) divided by the scanning speed (v), the scanning pitch (a), and the layer thickness (d) (E=P / vad).

[0084] The defect rate of the additively manufactured products (10 mm x 10 mm x 10 mm) F11 to F13 was measured. The results were approximately 0.13% for F11, approximately 0.16% for F12, and approximately 0.15% for F13, resulting in a defect rate of 0.2% or less for all of F11 to F13. The defect rate in this example refers to the defect area ratio determined by image processing of cross-sectional photographs (1.58 mm x 1.25 mm) of the additively manufactured products. The defect rate was measured using a microscope (Keyence VHX-6000), where a threshold was set using the microscope's area ratio derivation function to digitize the image, determine the area ratio of defects appearing in black, and then take the average of the area ratios of five locations.

[0085] From the above, it was confirmed that alloy powders with an oxygen content of more than 0.015% by mass but less than 0.0106% by mass and an oxide film thickness of 1 nm or more and 200 nm or less can reduce the defect rate of additively manufactured products, enable stable manufacturing, and suppress defects. The additively manufactured products F11 to F13 were evaluated for 0.2% yield strength, tensile strength, elongation, reduction of area, and Charpy impact value. Table 12 shows the results for 0.2% yield strength, tensile strength, elongation, reduction of area, and Charpy impact value for additively manufactured products F11 to F13. As shown in Table 12, it was confirmed that the mechanical properties of additively manufactured products F11 to F13 were equivalent to those of additively manufactured product F10, which was manufactured using raw material powder.

[0086] From the results of Example 4, it was found that even in Fe-based alloy powders, as long as the oxygen content in the powder is more than 0.015% and less than 0.106% and the maximum oxide film thickness is 200 nm or less (excluding 0), the formability is not significantly affected and the defect rate of the resulting additive manufactured product can be reduced. In addition, it was confirmed that, even in the case where the alloy powder contains a mixture of alloy powders having an oxide film mainly composed of an oxide of at least one of Ni, Ti, Si, and Al and alloy powders having an oxide film mainly composed of an oxide of Fe, the formability is not significantly affected and the defect rate of the resulting additive manufactured product can be reduced as long as the oxygen content in the powder is more than 0.015% and less than 0.106% and the maximum oxide film thickness is 200 nm or less (excluding 0), the alloy powders do not significantly affect the formability and the defect rate of the resulting additive manufactured product can be reduced.

[0087] The above-described embodiments and examples have been described to aid in understanding the present invention, and the present invention is not limited to the specific configurations described. For example, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. In other words, it is possible to delete part of the configuration of the embodiments and examples in this specification, replace it with another configuration, or add another configuration.

[0088] 10: Powder 12: Scanning direction 14: Oxide film (material) 16: C (carbon) protective film 50, 60, 70, 80, 90: Powder 51, 61, 71, 81, 91: Analysis position 52, 62, 72, 82, 92: Analysis position 53, 63, 73, 83, 93: Analysis position 54, 64, 74, 84, 94: Analysis position 55, 65: Scanning direction 56, 66, 76, 86, 96: Oxide film (material) 57, 67, 77, 87, 97: C (carbon) protective film

Claims

1. The alloy powder has an oxide film on its surface. The alloy powder is It is a Ni-based alloy, In mass percent, Contains 0.031% or more and less than 0.106% oxygen, and The reuse alloy powder for additive manufacturing is characterized in that the oxide film has a maximum thickness of 200 nm or less (excluding 0).

2. The alloy powder comprises: In mass percent, Cr: 14.5% or more and 24.0% or less, Mo: 12.0% or more and 23.0% or less The reuse alloy powder for additive manufacturing according to claim 1 .

3. The reused alloy powder for additive manufacturing as described in claim 1, characterized in that the oxide film has a maximum thickness of 100 nm or less (excluding 0).

4. The reuse alloy powder for additive manufacturing according to any one of claims 1 to 3, characterized in that the oxide film in the vicinity of its outermost surface is an oxide mainly composed of Ni.

5. A reused alloy powder for additive manufacturing as described in any one of claims 1 to 4, characterized in that the oxide film near the outermost surface is an oxide containing at least one of Ni, Ti, Si or Al as the most abundant element other than oxygen.

6. A method for manufacturing an additive manufacturing product, characterized in that a powder containing the reuse alloy powder for additive manufacturing described in any one of claims 1 to 5 is used as a raw material powder, and additive manufacturing is performed using the powder.

7. The powder, The alloy powder includes an alloy powder having an oxide film with a maximum thickness of 60 nm and an alloy powder having an oxide film with a maximum thickness of 50 nm. The method for producing an additive manufacturing product according to claim 6 .