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

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

Technical Field

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

Background Art

[0002] Metal powders are important basic materials as raw materials for powder compaction molding, powder metallurgy, metal injection molding (MIM), etc. in the field of shaped materials. These shaped material technologies using metal powders are suitable for various industrial products because of their excellent strength and mass productivity. In recent years, they are also used as raw materials for additive manufacturing methods (hereinafter referred to as metal additive manufacturing or simply additive manufacturing). The metal additive manufacturing method enables the production of shaped materials without a mold, and its importance is increasing.

[0003] Moreover, recently, from the perspective of environmental protection, the importance of conserving and effectively using metal resources has been increasing. For example, Patent Document 1 discloses a material powder for metal additive manufacturing and a method for manufacturing the same that can suppress a decrease in fluidity even when recycled. The material powder for metal additive manufacturing is manufactured so as to have a particle size distribution corresponding to a fluidity of a predetermined reference value or more based on the particle size distribution of virgin material, which is an unused material powder, and the fluidity of recycled material after recycling the virgin material a predetermined number of times in a metal additive manufacturing apparatus. It is also disclosed that silica particles may be added to the virgin material.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] However, even with the material powder for metal additive manufacturing described in Patent Document 1, repeated reuse leads to poor moldability and increased likelihood of metal spatter during manufacturing. As a result, there is a problem that defects such as voids are more likely to occur in the additively manufactured product. [Overview of the project] [Problems that the invention aims to solve]

[0006] Therefore, the object of the present invention is to provide a reusable alloy powder for additive manufacturing and a method for manufacturing additively manufactured products that enables stable manufacturing and suppresses defects even when additive manufacturing alloy powder is reused. [Means for solving the problem]

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

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

[0009] Preferably, the alloy powder contains more than 0.030% and less than 0.106% by mass of oxygen, and the oxide film has a maximum thickness of 1 nm or more and 100 nm or less. Furthermore, the alloy powder preferably contains 0.031% or more and less than 0.106% by mass of oxygen.

[0010] It is preferable that the outermost surface of the oxide film is an oxide mainly composed of Ni.

[0011] Preferably, the mixture contains Cr: 14.5-24.0% and Mo: 12.0-23.0% by mass, with the remainder being Ni and unavoidable impurities.

[0012] Preferably, the alloy powder is an Fe-based alloy, has an oxide film on its surface, 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] Preferably, the alloy powder contains more than 0.020% and less than 0.106% by mass of oxygen, and the oxide film has a maximum thickness of 1 nm or more and 150 nm or less.

[0014] Preferably, the material contains Ni: 14% to 22%, Ti: 0.1% to 5.0%, Al: 1% or less, and Si: 1% or less by mass, with the remainder being Fe and unavoidable impurities.

[0015] Preferably, the oxide film near the outermost surface contains at least one of the elements other than oxygen, with Ni, Ti, Si, or Al being the most abundant element.

[0016] Preferably, the alloy powder has a ratio of 90% integration frequency to 10% integration frequency in the integration distribution curve, which shows the relationship between particle size and volume integration from the small particle size side, determined by laser diffraction, that is between 3.0 and 10.0.

[0017] A method for manufacturing additively manufactured products, characterized by using an alloy powder containing any of the above-mentioned reuse alloy powders for additive manufacturing as a raw material powder, and performing additive manufacturing using this raw material powder.

[0018] Preferably, the raw material powder includes a reuse alloy powder for additive manufacturing having an oxide film comprising an oxide in which the most abundant element among the elements other than oxygen is either Ni or Fe, and an alloy powder for additive manufacturing having an oxide film comprising an oxide in which the most abundant element among the elements other than oxygen is an element other than Ni or Fe.

[0019] According to the present invention, it is possible to provide a reusable alloy powder for additive manufacturing that enables stable shaping even with raw material powder that has been repeatedly reused, and can suppress defects, and a method for manufacturing an additive manufactured product.

Brief Description of the Drawings

[0020] [Figure 1] An optical microscope image of the reusable Ni-based alloy powder. [Figure 2] STEM image and elemental mapping diagram of the reusable alloy powder P1 of Example 1. [Figure 3] STEM image and elemental mapping diagram of the reusable alloy powder P2 of Example 1. [Figure 4] STEM image and elemental mapping diagram of the reusable alloy powder P3 of Example 1. [Figure 5] STEM image and elemental mapping diagram of the reusable alloy powder P4 of Example 2. [Figure 6] STEM image and elemental mapping diagram of the reusable alloy powder P4 of Example 2. [Figure 7] A diagram for estimating the change in the number of reuses and the amount of oxygen of the reusable Ni-based alloy powder. [Figure 8] STEM image and elemental mapping diagram of the reusable alloy powder P13 of Example 4. [Figure 9] STEM image and elemental mapping diagram of the reusable alloy powder P13 of Example 4. [Figure 10] STEM image and elemental mapping diagram of the reusable alloy powder P13 of Example 4. [Figure 11] A schematic diagram of an additive manufacturing apparatus known as the powder bed fusion method is shown. [Figure 12] A schematic diagram of an additive manufacturing apparatus known as the directed energy deposition method is shown.

Modes for Carrying Out the Invention

[0021] The following describes in detail embodiments of the manufacturing method for reused alloy powder for additive manufacturing and additively manufactured products. First, the manufacturing method for reused alloy powder for additive manufacturing will be described, followed by the manufacturing method for additively manufactured products. In the description, "reusable alloy powder for additive manufacturing" may be referred to as "reusable alloy powder" or simply "alloy powder." Also, unused alloy powder that has never been used in additive manufacturing may be referred to as "raw material powder" or "new product." In this specification, the numerical range indicated by "~" includes the preceding and following numbers, both of which are "greater than or equal to" and "less than or equal to." When "greater than" or "less than" is added to a number, that number is not included. In the figures, identical or similar parts are denoted by the same reference numeral, and their descriptions are not repeated.

[0022] <Alloy powder> The reused alloy powder of this embodiment is made by reusing raw material powders such as Ni-based alloys and Fe-based alloys used in additive manufacturing, and these alloy powders have an oxide film on their surface. Furthermore, the alloy powder itself contains more than 0.015% by mass and less than 0.106% by mass of oxygen, preferably in the range of more than 0.020% by mass and less than 0.106% by mass, and more preferably more than 0.030% by mass at the lower limit. Moreover, the maximum thickness of the oxide film is 200 nm or less (however, there is no case of 0 nm), preferably 100 nm or less, and even more preferably 1 nm to 150 nm. If the alloy powder has such an oxygen content and oxide film thickness, it can be repeatedly reused for additive manufacturing.

[0023] [Alloy composition] The alloy powder in the embodiments of this application can be a powdered alloy known as a heat-resistant alloy, a corrosion-resistant alloy, or a wear-resistant alloy. More preferably, it is a Ni-based alloy or an Fe-based alloy.

[0024] Ni-based alloys refer to alloys that primarily consist of nickel, with additive elements such as chromium (Cr) and molybdenum (Mo). Examples of commercially available alloys include M252, Waspaloy, Rene41, Udimat520, Inconel718, Inconel725, Inconel713, Inconel738, MM246, MM247, Rene80, GMR235, Inconel625, Nimonic263, Hastelloy B, C, and X grades, as well as Hicoroy11 and MAT21. However, these are merely examples and not exhaustive. (Note that 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 Ni-Cr-Mo, and its composition is preferably such that, in mass%, Cr and Mo, which are second only to the main component Ni, are Cr: 10.0-30.0% and Mo: 5.0-30.0%, more preferably Cr: 10.0-25.0% and Mo: 8.0-25.0%, and particularly preferably Cr: 14.5-24.0% and Mo: 12.0-23.0%.

[0026] Furthermore, Fe-based alloys refer to alloys that primarily consist of Fe, with additive elements such as Ni, Cr, and Co. For example, commonly used materials in additive manufacturing include 18Ni maraging steel of grades 200, 250, 300, and 350, as well as stainless steels such as SUS304, SUS316, SUS630, SUS310S, SUH660, SCH13, and SCH22.

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

[0028] Furthermore, the amount of Si is preferably 1% or less by mass, more preferably less than 1%, and even more preferably 0.5% or less. Similarly, the amount of Al is preferably 1% or less by mass, more preferably less than 1%, even more preferably 0.5% or less, and even more preferably 0.25% or less. It may also contain Mo or Ti, and if it is Mo, it is preferably 5% or less by mass, more preferably 0.5% to 5.0%, and even more preferably 1.5% to 2.5%. If it is Ti, it is preferably 5% or less by mass, more preferably 0.5% to 5.0%, and even more preferably 1.5% to 2.5%.

[0029] (Inevitable impurities) As an unavoidable impurity, carbon (C) forms carbides with chromium (Cr) near grain boundaries, increasing the deterioration of corrosion resistance. Therefore, its content was kept below 0.05%. In addition, sulfur (S) and phosphorus (P) segregate at grain boundaries and cause high-temperature cracking, so their content must be suppressed to below 0.01%. Furthermore, it is preferable to have low content of these unavoidable impurities, and it may even be 0%.

[0030] [Oxygen content of alloy powder and oxide film thickness] In additive manufacturing, raw material powder (alloy powder) from areas not irradiated by the laser is repeatedly reused. However, with each re-use, the amount of oxygen increases due to oxidation of the powder surface. On the other hand, when the raw material powder melts during additive manufacturing, metal spatter is generated, which can lead to defects such as shape defects in the additively manufactured product or residual metal spatter inside the product. It has been found that this spatter is caused by the expansion and bursting of oxygen contained in the powder, and that the oxide film on the powder surface also plays a role.

[0031] Furthermore, when metal powder is irradiated with a laser beam, multiple reflections occur in the oxide film, which increases the laser absorption rate. This increases the amount of heat input, which in turn increases the amount of alloy powder melted, resulting in a larger melt pool. As a result, residual stress due to thermal shrinkage during the solidification process may exceed tensile stress, potentially making the material more prone to cracking.

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

[0033] By maintaining these oxygen content and film thickness ranges, metal spatter caused by oxygen expansion and rupture during the melting of the alloy powder can be suppressed, thereby reducing defects in additively manufactured products through stable molding. The oxygen content in the powder can be measured using inert gas fusion infrared absorption spectroscopy.

[0034] [Oxide film (substance)] It is preferable that the outermost surface of the aforementioned oxide film contains the elements that mainly constitute the alloy powder. For example, in the case of a Ni-based alloy, it is preferable that it contains an oxide mainly composed of Ni. Since oxides mainly composed of Ni have a relatively low melting point, they evaporate first when irradiated with a laser beam, making sputtering less likely. This is also considered not to adversely affect the melting and solidification process. In this specification, the "mainly constituting elements" refer to the element that is most abundant among the elements other than oxygen.

[0035] Furthermore, the alloy powder may contain a mixture of alloy powders having an oxide film mainly composed of Ni oxide and alloy powders having an oxide film mainly composed of metal elements other than Ni. For example, in the case of Ni-Cr-Mo alloy powder, the oxide mainly composed of minor components (optional additives) such as Ta and Cr may be present. The presence of an oxide film mainly composed of Ta and Cr may occur in newly manufactured alloy powders, as well as in alloy powders that have been used in molding once, where sputter has adhered to the surface, resulting in an oxide film with more Ta and Cr oxides than unused alloy powder.

[0036] Figure 1 shows the results of reusing Ni-Cr-Mo alloy powder, but the alloy powder may also contain the alloy powders shown within the dashed box in the figure. Cross-sectional observation of each alloy powder revealed that some had an oxide film mainly composed of Ni, and others had an oxide film mainly composed of Ta, Cr, etc. Thus, powders with oxide films mainly composed of different elements may be included, and even if such powders are mixed, it is thought that the moldability will not be significantly affected as long as the amount of oxygen in the powder is within the preferred range described above.

[0037] Furthermore, even in the case of alloy powders mainly composed of Fe, such as Fe-based alloy powders, a mixture of alloy powders having an oxide film mainly composed of Fe oxides and alloy powders having an oxide film mainly composed of metal elements other than Fe may be present. For example, in the case of Fe-Ni alloy powders, the oxide mainly composed of at least one of Ni, Ti, Si, or Al may be present. An oxide film mainly composed of at least one of Ni, Ti, Si, or Al may be present in new (unused) alloy powders, as well as in alloy powders that have been used in molding once, where sputter has adhered to the surface, resulting in an oxide film where at least one of Ni, Ti, Si, or Al is more abundant than in unused alloy powders. This is because Si, Ti, Al, etc., are easily oxidized elements, and when oxidized, stable oxides such as SiO2, TiO2, or Al2O3 are formed.

[0038] [Particle size] Additive manufacturing is a method of forming objects by repeatedly melting and solidifying individual powders. However, if the particle size of the alloy powder is less than 5 μm, it becomes difficult to obtain the volume required for one melting and solidification cycle, making it difficult to obtain a sound additively manufactured product. On the other hand, if the particle size of the alloy powder exceeds 250 μm, the volume required for one melting and solidification cycle is too large, making it difficult to obtain a sound additively manufactured product. Therefore, the particle size of the alloy powder is preferably between 5 and 250 μm, and more preferably between 10 μm and 150 μm. Powder obtained by the gas atomization method, which yields a spherical shape, is 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] To give examples by additive manufacturing method, 10 μm to 50 μm is more preferable for selective laser melting (SLM), and 45 μm to 105 μm is more preferable for electron beam melting (EBM).

[0040] Furthermore, for the laser beam powder deposition (LMD) method, a thickness of 30 μm to 250 μm is recommended.

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

[0042] If the D90 / D10 ratio is 10.0 or less, the proportion of large particles will not be too high, making it easier to suppress defects caused by insufficient powder melting during laser irradiation. Furthermore, if the D90 / D10 ratio is 3.0 or higher, the friction between the particles constituting the powder will not become too large, preventing a decrease in fluidity, suppressing powder packing defects, and thus reducing internal defects in the resulting additively fabricated body.

[0043] <Method for manufacturing additively manufactured products> Next, a method for manufacturing additively manufactured products according to the present invention will be described with reference to Figures 11 and 12. The embodiment of the method for manufacturing additively manufactured products is characterized by using alloy powder containing the above-mentioned reuse alloy powder for additive manufacturing as a raw material powder, and performing additive manufacturing using this raw material powder. That is, the raw material powder only needs to contain at least the reuse alloy powder of the present invention that has been used repeatedly. It is also possible to use only the alloy powder of the present invention, but it is preferable to use it in mixture with new raw material powder. Furthermore, it is also possible to periodically add the reuse alloy powder of the present invention that has been used repeatedly.

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

[0045] Furthermore, while Ni-based alloy powders and Fe-based alloy powders for additive manufacturing include at least reused products, Ni-based alloy powders having an oxide film mainly composed of elements other than Ni may be reused products or new alloy powders, as described above. Similarly, Fe-based alloy powders having an oxide film mainly composed of elements other than Fe may be reused products or new alloy powders, as described above.

[0046] As a method of additive manufacturing, for example, by supplying the Ni-based corrosion-resistant alloy powder for additive manufacturing of the present invention to a powder bed fusion (PBF) additive manufacturing apparatus as shown in Figure 11, and irradiating the area where the powder is laid with high energy such as a laser or electron beam, the alloy powder is selectively melted and bonded, thereby enabling the additive manufacturing of additively manufactured parts of the desired shape.

[0047] Furthermore, in addition to those shown in Figure 11, depending on the shape of the additively manufactured product, it is also possible to use additive manufacturing equipment such as the Directed Energy Deposition (DED) type shown in Figure 12, and there are no particular restrictions on the type of additive manufacturing equipment.

[0048] [Applications / Products] The alloy powders described above can be suitably used in metal additive manufacturing such as additive manufacturing, powder compaction, powder metallurgy, and metal injection molding, but their applications and manufactured products are not particularly limited.

[0049] The additively manufactured products using the alloy powder of the present invention are expected to have applications in a wide range of fields, including chemical plants, pharmaceutical manufacturing equipment, and the oil and gas sectors. For example, it is possible to provide semiconductor manufacturing equipment components that have excellent corrosion resistance and extremely few defects. [Examples]

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

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

[0052] [Table 1]

[0053] Next, to simulate obtaining 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 powders P1 (300°C x 100 minutes), P2 (400°C x 100 minutes), and P3 (500°C x 100 minutes) were obtained. Subsequently, the oxygen content and elemental analysis of the alloy powders, as well as the oxide film thickness, were measured. The measurement methods are as follows.

[0054] (Oxygen content of the powder) The oxygen content in the powder was determined using the inert gas fusion-infrared absorption method. Two measurements were taken, and the average value was calculated.

[0055] (Thickness of oxide film) Furthermore, the thickness of the oxide 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). For elemental analysis of the oxide film, energy dispersive X-ray spectroscopy (EDX) can be used to analyze the elements of an arbitrary cross-section of the alloy powder, for example. The sample for observation can be prepared by cutting the powder using a focused ion beam (FIB) microsampling device and obtaining the cross-sectional surface.

[0056] The oxygen content and oxide film thickness of alloy powders P1 to P3 were measured. P1 had an oxygen content of 0.031% and a maximum oxide film thickness of 4 nm. P2 had an oxygen content of 0.047% and a maximum oxide film thickness of 7 nm. P3 had an oxygen content of 0.106% and a maximum oxide film thickness of 18 nm. Note that the oxygen content (%) in the powder is expressed as mass percent.

[0057] As described above, the oxygen content in each of the alloy powders P1 to P3 was measured using the inert gas melting-infrared absorption method, and the average value was taken from two measurements. The maximum thickness of the oxide film was taken from the area with the greatest oxide film thickness observed using a scanning transmission electron microscope (JEOL, model: JEM-ARM200F). Even with the same powder, thicknesses of 20 nm or more may be observed in some observation areas, but the maximum is considered to be 100 nm or less. Since the oxide film is generally uniform, it is sufficient to observe it in a specific field of view / range. Alloy powders P1 to P3 simulate the oxygen content and oxide film thickness in a reused state, but in reality, it is desirable to collect data on the number of reuses of the alloy powder, the oxygen content, and the number of reuses and oxide film thickness in order to determine the number of times it can be reused in advance.

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

[0059] Figures 2(a), 3(a), and 4(a) show STEM (observation) images of the powder cross-section for each of P1 to P3. In the figures, 10 is the powder itself, 14 is the oxide film, and 16 is the carbon protective film applied to avoid surface contamination and oxidation during the preparation of the observation sample. Figures 2(b), 3(b), and 4(b) show the elemental analysis results. The STEM images are cross-sectional observation images obtained by cutting powder particles 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] Furthermore, elemental analysis was performed and evaluated using an energy-dispersive X-ray spectroscopy (EDX) system equipped on a scanning transmission electron microscope. The measurement conditions for elemental analysis were as follows: acceleration voltage: 200kV, STEM mode: 5C, quantitative analysis: 30Lsec, elemental map: 256×256, 0.01msec / Pix, line analysis: 256Pix, 1.0msec / Pix. The scanning direction for sampling was from the powder 10 side toward the oxide film 14 in the direction of the arrow 12 in the figure.

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

[0062] Next, additive manufacturing was performed using only raw material powders P1 to P3 with a PBF (Powder-Based Fabrication) type additive manufacturing system (Mlab cusing 200R) using the SLM (Scaling-Luminous Manufacturing) method to produce additively manufactured parts (10mm x 10mm x 10mm blocks) F1 to F3. The layering conditions were: layer thickness: 0.04mm, laser output: 200W, scanning speed: 800mm / s, and scanning pitch: 0.11mm. Subsequently, the defect rate of the additively manufactured parts was measured. The energy density (E) was set to 56.8 J / mm3. The energy density (E) is calculated by dividing the output (P) by the scanning speed (v), scanning pitch (a), and layer thickness (d) (E = P / vad).

[0063] (Defect rate) The defect rate is defined as the area ratio of defects obtained by image processing of cross-sectional photographs (1.58 mm x 1.25 mm) of the additively manufactured product. To measure the defect rate, a microscope (Keyence VHX-6000) was used. A threshold was set using the microscope's area ratio derivation function, the image was binarized, and the area ratio of the defects that appeared in black was determined. The average of the area ratios of five locations was then 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 produced using these powders. As shown in Table 2, it was confirmed that additively manufactured products with defect rates of 0.1% or less (F1: 0.03%, F2: 0.06%) can be produced using F1, which has an oxygen content (mass%) of 0.031%, and F2, which has an oxygen content (mass%) of 0.047%.

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

[0066] [Table 2]

[0067] From the above, we confirmed that alloy powders with an oxygen content of more than 0.015% and 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 additively manufactured products F1 to F3, including tensile strength, elongation, and Vickers hardness. The corrosion resistance of F3 (boiling 10% sulfuric acid and boiling 2% hydrochloric acid) was measured. As a reference example, Table 3 also shows the mechanical properties of an additively manufactured product using the new raw material powder, designated as F0, including tensile strength, elongation, and Vickers hardness. As shown in Table 3, the mechanical properties of additively manufactured products F1 to F3 using the alloy powder of the present invention are excellent, and the corrosion resistance is also excellent, as shown in the results for F3, confirming that it is equivalent to that of additively manufactured product F0 using the new raw material powder. [Table 3]

[0068] (Example 2) Alloy powder P4 was prepared by mixing alloy powder with a maximum oxide film thickness of 60 nm and alloy powder with a maximum oxide film thickness of 50 nm. The oxygen content in alloy powder P4 was 0.033 mass%. The alloy composition and powder particle size were the same as those of P1 to P3 above. The maximum oxide film thickness is the maximum thickness of the oxide film observed over a 140 nm circumferential distance in the observation area.

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

[0070] Furthermore, the elemental analysis results using EDX are shown for each analysis position (61-64) shown in Figure 6(a). As shown in Table 5, it was confirmed that an oxide mainly composed of Ni was formed near the surface of the powder. In the figure, 50 and 60 are the powder body, 56 and 66 are the oxide film, 57 and 67 are the carbon protective film, and 55 and 65 are the scanning direction.

[0071] [Table 4]

[0072] [Table 5]

[0073] A layered fabricated product F4 was obtained by layering alloy powder P4 under the same conditions as in Example 1. As with P1 and P2, layering was performed without any problems. Furthermore, the defect rate of the obtained layered fabricated product F4 was 0.06%, confirming that defects can be suppressed. From the above, it was found that if the oxygen content in the powder is between 0.015% and less than 0.106%, and the maximum thickness of the oxide film is within the range of 200 nm or less (excluding 0), it does not significantly affect the formability, and the defect rate of the resulting additively manufactured products can also be suppressed. In addition, if the oxygen content in the powder and the thickness of the oxide film are within the above range, even if the alloy powder contains a mixture of alloy powders having an oxide film mainly composed of oxides such as Ta and Cr as shown in Figure 5, and alloy powders having an oxide film mainly composed of oxides such as Ni as shown in Figure 6, it does not significantly affect the formability, and the defect rate of the resulting additively manufactured products can also be suppressed.

[0074] (Example 3) Additively fabricated parts were manufactured using the SLM method with the additive manufacturing apparatus described above. The raw material powder prepared in Table 1 was reused repeatedly, for a total of 69 times. During this time, when the powder decreased, new powder was added 5 times. Measurements similar to those in Example 1 were performed on this reused Ni-based alloy powder. As a result, the oxygen content was 0.033 mass%, which corresponds to the oxygen content of the simulated alloy powder P1, which was 0.031 mass%. The maximum thickness of the oxide film ranged from 1 nm to 60 nm.

[0075] Furthermore, while the particle sizes of the new raw material powders were 18.4 μm for D10, 33.2 μm for D50, and 56.8 μm for D90, the particle sizes of the powder after 69 reuses were 20.5 μm for D10, 39.8 μm for D50, and 72.2 μm for D90. In other words, the particle size of the powder tended 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. We believe that maintaining a D90 / D10 range of 3.0 to 10.0 allowed us to maintain the fluidity of the alloy powder and suppress powder packing defects, thereby enabling the successful completion of additive manufacturing. In addition, as described later, we believe that suppressing insufficient melting of the alloy powder also helped to suppress the defect rate of the additively manufactured body.

[0076] Furthermore, the defect rate of the additively manufactured parts was 0.06%, which is below the acceptable range of 0.2%. In addition, the mechanical properties and corrosion resistance of the additively manufactured parts were measured, but no significant differences were found. Based on these findings, it was concluded that approximately 70 reuses are acceptable.

[0077] Therefore, we estimated the relationship between the number of reuses and the amount of oxygen. 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, we obtain the relationship between the number of reuses and the amount of oxygen shown in Figure 7. That is, even if it is reused 100 times, for example, the amount of oxygen is predicted to be around 0.04 mass%. In reality, new powder is added during the repetition process, so the increase in the amount of oxygen is expected to be further suppressed. In any case, as mentioned above, it is desirable to collect data on the number of reuses and the amount of oxygen of unused alloy powder, as well as the number of reuses and the oxide film thickness, in order to determine and understand in advance how many times it can be reused.

[0078] (Example 4) Next, we will describe an example using Fe-based alloy powder. For the Fe-based alloy powder, we used an Fe-Ni alloy, a type of maraging steel. The Fe-Ni alloy contained, by mass%, Ni: 14% to 22%, Ti: 0.1% to 5.0%, Al: 1% or less, and Si: 1% or less. We prepared raw material powder (new product) that had not undergone any additive manufacturing (P10), and alloy powders containing raw material powder and reused alloy powder (P11 to P13).

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

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

[0081] Furthermore, Table 9 shows the elemental analysis results 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 powders having an oxide film mainly composed of Ti, alloy powders having an oxide film mainly composed of Si, and alloy powders having an oxide film mainly composed of Fe. In the figure, 70, 80, and 90 are the powder body, 76, 86, and 96 are the oxide film, 77, 87, and 97 are the carbon protective film, and 75, 85, and 95 are the scanning directions. [Table 6] [Table 7] [Table 8] [Table 9]

[0082] Table 10 shows the measurement results for D10, D50, and D90 for 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 is in the range of 3.0 to 10.0, we believe that the fluidity of the alloy powder was maintained, which suppressed powder packing defects and allowed the additive manufacturing to be completed without problems. Furthermore, as will be described later, we believe that the defect rate of the additively manufactured body was also suppressed by suppressing insufficient melting of the alloy powder. Furthermore, D10, D50, and D90 are calculated using laser diffraction and represent the integration distribution curve showing the relationship between particle size and volume integration from the small particle size side. D10 represents an integration frequency of 10 volume%, D50 represents an integration frequency of 50 volume%, and D90 represents an integration frequency of 90 volume%. [Table 10]

[0083] Next, additively manufactured parts were fabricated using each of the P11-P13 alloy powders. A 250 x 250 x 36 mm base plate (made of S50C) was placed on the build platform, and additively manufactured parts (rectangular prism shapes of 57 mm x 12 mm x 12 mm height, 40 mm x 10 mm x 10 mm height, and 10 mm x 10 mm x 10 mm height) were fabricated on the base plate. The additively manufactured part using P11 was designated F11, the part using P12 was designated F12, and the part using P13 was designated F13. The fabrication conditions were: power output (P): 250W, 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 calculated by dividing the output (P) by the scanning speed (v), scanning pitch (a), and stack thickness (d) (E = P / vad).

[0084] The defect rates of additively manufactured parts (10mm x 10mm x 10mm) F11 to F13 were measured. As a result, the defect rates were approximately 0.13% for F11, approximately 0.16% for F12, and approximately 0.15% for F13, with all defect rates below 0.2%. In this example, the defect rate is defined as the area ratio of defects obtained by image processing of cross-sectional photographs (1.58mm x 1.25mm) of the additively manufactured parts. The defect rate was measured using a microscope (Keyence VHX-6000). A threshold was set using the microscope's area ratio derivation function, and the image was binarized to obtain the area ratio of the defects that appeared in black. The average of the area ratios of five locations was then taken. [Table 11]

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

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

[0087] The embodiments and examples described above are provided 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 parts of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add configurations from other embodiments to the configuration of one embodiment. In other words, the present invention allows for the deletion, replacement, or addition of parts of the configurations of the embodiments and examples specified herein. [Explanation of Symbols]

[0088] 10: Powder 12: Scanning direction 14: Oxide film (substance) 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 (substance) 57, 67, 77, 87, 97:C (carbon) protective film

Claims

1. The alloy powder has an oxide film on its surface, The aforementioned alloy powder is It is a Ni-based alloy, In mass percent, the oxygen content is 0.031% or more and less than 0.106%. The oxide film has a maximum thickness of 1 nm or more and 100 nm or less. The outermost surface of the oxide film is an oxide mainly composed of Ni. A reusable alloy powder for additive manufacturing characterized by the following features.

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

3. The reuse alloy powder for additive manufacturing according to claim 1 or 2, characterized in that the oxide film has a maximum thickness of 60 nm or less.

4. The reuse alloy powder for additive manufacturing according to any one of claims 1 to 3, characterized in that the vicinity of the outermost surface of the oxide film is an oxide in which the most abundant element among the elements other than oxygen is at least one of Ni, Ti, Si, or Al.

5. A method for manufacturing an additively manufactured product, characterized by using a powder containing the reuse alloy powder for additive manufacturing described in any one of claims 1 to 4 as a raw material powder, and performing additive manufacturing using the powder.

6. The aforementioned powder is It contains alloy powder with a maximum oxide film thickness of 60 nm and alloy powder with a maximum oxide film thickness of 50 nm. The method for manufacturing an additively manufactured product according to feature 5.

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