Metal powder for additive manufacturing containing oxide nanoparticles and additive manufacturing body

Abstract

To provide a powder for metal laminate molding excellent in high temperature strength, and a laminate molded body excellent in high temperature strength produced using the powder for laminate molding.SOLUTION: In an alloy powder material for laminate molding, the Ni-base alloy powder to which oxide nanoparticles of Y2O3 are adhered, the surface of which is not subjected to surface treatment with an organic substance, is an alloy powder material to which oxide nanoparticles are added by 0.1-1.50 mass%, and the area ratio of the oxide nanoparticle agglomerated portion adhered to the surface of the alloy powder material is 0.1-10%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a metal powder for additive manufacturing that is mixed with particles made of oxides with nanometer-sized particles (hereinafter referred to as oxide nanoparticles), and to an additively manufactured object manufactured using this powder. [Background technology]

[0002] A method for manufacturing three-dimensional objects by irradiating powder material with a laser or electron beam (hereafter referred to as additive laser sintering) is known. A light beam is irradiated onto a powder layer made of metal powder to form a sintered layer, and methods for manufacturing metal powders for metal laser sintering have been proposed. Metal laser sintering is used to obtain three-dimensional objects by stacking the sintered layers. Representative metal laser sintering methods include the powder bed method (powder bed fusion method) and the metal deposition method (directed energy deposition method).

[0003] In the powder bed method, the irradiated areas of the spread powder are melted and solidified by irradiation with a laser beam or electron beam. This melting and solidification causes the powder particles to bond together. Irradiation is selectively applied to parts of the metal powder, and the unirradiated areas do not melt, forming a bonded layer only in the irradiated areas.

[0004] New metal powder is then laid on top of the bonded layer, and the powder is irradiated with a laser or electron beam. The irradiation melts and solidifies the metal particles, forming a new bonded layer. The new bonded layer also bonds with the existing bonded layer.

[0005] As the melting and solidification processes are repeated, the bonding layers gradually grow. This growth results in a three-dimensional object. Using this additive manufacturing method, it is easy to create objects with complex shapes.

[0006] Furthermore, as an additive manufacturing method using a metal deposition method (directed energy deposition method), for example, a method for manufacturing a powder in which an "iron-based powder" and "one or more types of powder selected from the group consisting of nickel, nickel-based alloys, copper, copper-based alloys, and graphite" are mixed as metal powder for metal laser sintering, in which a light beam is irradiated onto a powder layer made of metal powder to form a sintered layer and obtain a three-dimensional shaped object, has been proposed (see Patent Document 1).

[0007] In metal additive manufacturing, powder flowability is important for spreading the powder with high packing ability. The most well-known method for improving powder flowability is to increase the powder's circularity.

[0008] In addition, a method has been proposed in which oxide nanoparticles that have not been surface-treated with organic substances are mixed with metal particles of an Fe-based alloy to improve fluidity, thereby reducing the adhesive force between the metal powder particles (see Patent Document 2). However, because the oxide nanoparticles used are not surface-treated with organic substances, they tend to aggregate more easily than surface-treated nanoparticles, so an additional classification process using a jet mill is required to obtain a powder material that does not contain areas where the nanoparticles have aggregated (called nanoparticle aggregates).

[0009] Regarding high-temperature strength, a method that does not involve additive manufacturing is known in which metal raw materials are mixed with oxide nanoparticles, mechanically alloyed, and the resulting powder material is solidified and molded using HIP to form a material with excellent high-temperature strength by dispersing fine oxides in the metal structure (see Non-Patent Document 1). Mechanically alloyed powders with dispersed oxides are actually commercially available, such as MA6000 and MA754 for Ni-based alloys and MA956 for Fe-based alloys. However, mechanically alloyed powders have low sphericity and are not necessarily suitable for flowability and packing. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-81840 [Patent Document 2] Patent Publication No. 2021-75784 [Non-Patent Document 1] Yoshiya Kaieda, "Development Trends of Ceramic Dispersion Strengthened (ODS) Heat-Resistant Alloys," Turbo Machinery, Vol. 13 (1985) No. 4 Summary of the Invention [Problem to be solved by the invention]

[0011] In order to produce an additive manufacturing body with excellent high-temperature strength using metal powders, it is preferable to use metal powders with a high packing density, but it is difficult to obtain the desired sphericity using conventional mechanical alloying. Furthermore, in mechanical alloying, the particles are repeatedly rolled and folded, and pressed together and crushed, so oxides are not necessarily dispersed on the surface.

[0012] Therefore, the problem to be solved by the present invention is to provide a powder for metal additive manufacturing that has excellent high-temperature strength, and an additive manufacturing object that has excellent high-temperature strength and is produced using this powder for additive manufacturing. [Means for solving the problem]

[0013] Therefore, after extensive research, the inventors discovered that a Ni-based or Fe-based alloy powder material for metal additive manufacturing, in which oxide nanoparticles that have not been surface-treated with organic substances are attached to the surface of the alloy powder particles at an area ratio of 10% or less, for the purpose of particle dispersion strengthening (ODS), and that using this powder material to manufacture products using metal additive manufacturing, has excellent high-temperature strength.

[0014] The means for solving the problems of the present invention is an alloy powder material for additive manufacturing consisting of Ni-based alloy powder or Fe-based alloy powder to which oxide nanoparticles are attached that have not been surface-treated with an organic substance.

[0015] The area ratio of the oxide nanoparticles adhering to the surface of the alloy powder material is preferably 10% or less, more preferably 5% or less, and from the viewpoint of particle dispersion strengthening (ODS), preferably 0.1% or more.

[0016] The amount of the oxide nanoparticles added is preferably 0.1 to 1.5 mass % or less.

[0017] The primary particle diameter of the oxide nanoparticles is preferably within the range of 1 to 100 nm.

[0018] The oxide nanoparticles are preferably any one of Y2O3, ThO2, Al2O3, TiO2, and SiO2, more preferably Y2O3 or Al2O3, and even more preferably Y2O3.

[0019] The metal additive manufacturing body is produced by additive manufacturing using these alloy powder materials for additive manufacturing. [Effects of the Invention]

[0020] When additive manufacturing is performed using the alloy powder for additive manufacturing of the present invention, oxides are finely dispersed in the shaped body, resulting in a shaped body that exhibits excellent high-temperature strength.

[0021] As the amount of oxide nanoparticles added increases, oxide nanoparticle agglomerates tend to form on the surface of the mixed powder. Although the nanoparticle agglomerates diffuse throughout the melt pool during laser melting and are dispersed throughout, if the area ratio of the nanoparticle agglomerates becomes excessively large, some of the nanoparticle agglomerates will not disperse completely and will remain as μm-scale agglomerated oxides. This type of residual μm-scale oxide occurs when the area ratio of the nanoparticle agglomerates exceeds 10%.

[0022] If the area ratio of oxide nanoparticle agglomerates on the surface of the alloy powder for additive manufacturing is kept within 10%, as in the present invention, when the powder is melted during additive manufacturing, the agglomerates of oxide nanoparticles dissolve and disperse into fine oxide particles of tens to hundreds of nanometers, strengthening the additive manufacturing body through particle dispersion strengthening. On the other hand, if the area ratio exceeds 10%, the agglomerates of nanoparticles are not sufficiently dissolved during melting, and μm-scale oxide nanoparticle agglomerates tend to remain. These μm-scale oxides then become the starting points for fracture, reducing the strength of the body.

[0023] By attaching oxide nanoparticles to the surface of the metal powder, the oxide nanoparticles are positioned between the metal powder particles, which results in the metal powder particles no longer coming into direct contact with each other, reducing the adhesive force acting between these particles, thereby improving the fluidity of the alloy powder material. [Brief explanation of the drawings]

[0024] [Figure 1] 1 shows scanning electron microscope (SEM) images of nickel-based alloy powder materials with oxide nanoparticles of the present invention attached to their surfaces, where (a) shows the case where 0.01 mass% of Y2O3 is added, and (b) shows the case where 0.3 mass% of Y2O3 is added. DETAILED DESCRIPTION OF THE INVENTION

[0025] [Preparation of Atomaz powder as the base for the test material] As base powders for the examples and comparative examples of the present invention, powder materials with the component compositions shown in Table 1 below were prepared by gas atomization. Gas atomization was carried out by melting raw materials mixed to a predetermined ratio in an alumina crucible in a vacuum using high-frequency induction heating, dropping the molten alloy from a nozzle with a diameter of about 5 mm below the crucible, and spraying it with high-pressure argon or high-pressure nitrogen. The average particle size D of the obtained powder was 50 (μm) and sphericity. The average particle size here is the volume average.

[0026] Specifically, as a Ni-based alloy equivalent to Inconel 718, (No.A)Fe-52%Ni-20%Cr-0.05C-0.1Mn-0.2Si-3.0Mo-0.3Co-5.2Nb-0.5Al-0.9Ti-0.003B, (No.B)Fe-52%Ni-20%Cr-0.05C-0.1Mn-0.2Si-3.0Mo-0.3Co-5.2Nb-0.5Al-0.9Ti-0.003B, In addition, as an Fe-based alloy equivalent to SUS630, (No. C) Atomized powder with the composition Fe-16Cr-4Ni-4Cu-0.9Mn-0.4Nb-0.25Si-0.05C was prepared.

[0027] [Table 1]

[0028] [Mixing metal powder and oxide nanoparticles] The oxide nanoparticles used were Y2O3 nanoparticles (average particle size 29 nm) from CIK Nanotech Co., Ltd. To produce alloy powder with oxide nanoparticles attached to its surface, they were mechanically mixed using a V-type mixer. Powders can also be mixed using a tumbler mixer, ball mixer, or other tool to the extent that they adhere to the surface of the metal powder. They can also be mixed by hand in a container.

[0029] [Removal of unattached oxide nanoparticles] Even after these mixing steps, oxide nanoparticles may remain that are not attached to the metal powder particles. These oxide nanoparticles range in size from a few microns to a few hundred microns. Therefore, these unattached oxide nanoparticles were removed by sieving. This removal process allows for the production of a more suitable mixed powder material.

[0030] [Fabrication of tensile and rupture test specimens using metal additive manufacturing] Using the powder with nanoparticles attached to the surface after the above treatment, tensile test pieces and rupture test pieces were prepared by the following two methods. (i) Test specimens were fabricated by metal additive manufacturing using the laser powder sintering additive manufacturing (SLM) method using a mixed powder of Ni-based alloy (31.2 μm) No. A in Table 1 and Fe-based alloy (31.2 μm) No. C in Table 1. (ii) Test specimens were fabricated by metal additive manufacturing using the binder jet method using mixed powder of Ni-based alloy (8.3 μm) No. B in Table 1. It should be noted that the additive manufacturing method using the powder of the present invention is not limited to these techniques, and additive manufacturing can also be performed using electron beam powder sintering additive manufacturing (EBM) or laser deposition. However, in this example, we will evaluate test pieces prepared using the two methods described above.

[0031] [Metal powder morphology] Alloy powder size: 2μm≦D 50 ≦150μm If the size of the alloy powder is less than 2 μm, excessive pulverization will cause a significant decrease in the flowability of the powder. On the other hand, if the size of the alloy powder is more than 150 μm, the powder packing rate will decrease and the density of the molded body will decrease. Therefore, the size of the alloy powder should be 2 μm≦D 50 ≦150 μm.

[0032] The preferred particle size range varies depending on the additive manufacturing method, as follows: By adjusting the size of the alloy powder according to these methods, it is possible to obtain an appropriate layered object. Selective Laser Sintering (SLM): 10≦D 50 ≦45μm Laser deposition method, electron beam method: 45≦D 50 ≦150μm Binder jet method: 2≦D 50 ≦25μm

[0033] [Oxide nanoparticle morphology] Size of oxide nanoparticles: preferably 1 to 100 nm in primary particle diameter The oxide nanoparticles preferably have a primary particle diameter of 1 to 100 nm. Since the smaller the particle diameter, the greater the effect of particle dispersion strengthening (ODS) during additive manufacturing, the size of the oxide nanoparticles is more preferably 1 to 50 nm, and even more preferably 1 to 30 nm. The primary particle diameter of the mixed powder to which the oxide nanoparticles have been attached is the same as the primary particle diameter of the oxide nanoparticles before mixing, and the primary particle diameter can be determined based on specific surface area measurement by gas adsorption method.

[0034] Nanoparticle addition amount: 0.1 to 1.5% The amount of nanoparticles added to the alloy powder of the present invention can be 0.1 to 1.5% by mass. If it is less than 0.1%, the effect of particle dispersion strengthening (ODS) cannot be fully obtained. If it is 1.5% or more, oxide agglomerates are likely to occur, resulting in a decrease in strength. The amount of nanoparticles added is preferably 0.2 to 1.5%, and more preferably 0.25 to 1.0%.

[0035] Nanoparticle shape and manufacturing method: Methods for producing oxide nanoparticles that have not been surface-treated with organic substances include flame spray pyrolysis (FSP) and physical vapor synthesis (FSP). Because the use of oxide nanoparticles with high sphericity is effective in preventing excessive aggregation of oxide nanoparticles, oxide nanoparticle powders obtained by physical vapor synthesis have higher sphericity than those obtained by FSP, making it easier to obtain desirable powders.

[0036] Types of oxide nanoparticles: Examples of oxide nanoparticles that can be used in the present invention include Y2O3, ThO2, Al2O3, TiO2, and SiO2. Any oxide nanoparticles that can exist stably in a matrix even at high temperatures are suitable, and are not limited to these exemplified oxides. Of these, Y2O3 and Al2O3 are preferred because they can exist stably in a matrix even at high temperatures. YO3 is even more preferred. In the examples, Y2O3 is used as a representative example of oxide nanoparticles.

[0037] [Area ratio of oxide nanoparticle agglomerates] In the present invention, the area ratio of the agglomerated portions of the oxide nanoparticles adhering to the surface of the alloy powder is 10% or less. If the area ratio of nanoparticle agglomerates is 10% or less, when the powder is melted during additive manufacturing, the nanoparticle oxide agglomerates dissolve and disperse as fine oxides measuring tens to hundreds of micrometers, and the additive manufacturing object is strengthened by ODS. On the other hand, if the content is 10% or more, the nanoparticles do not disaggregate sufficiently during melting, leaving behind micrometer-scale oxides that can become the starting point for fracture and reduce the strength of the molded object.

[0038] To improve fluidity, a nanoparticle addition amount of 0.01% or more but less than 0.1% is sufficient, but to achieve particle dispersion strengthening (ODS), it is necessary to add 0.1% or more oxide nanoparticles. If the amount of nanoparticles added is increased to 0.1% or more, agglomerations of 1 μm or more will inevitably occur.

[0039] [Heat treatment of the formed object] The test pieces after molding were subjected to the following heat treatment. (Ni-based alloy) Solution treatment: After holding at 980°C for 1 hour, the material was air-cooled. Aging treatment: After holding at 720°C for 8 hours, the specimen was furnace cooled to 620°C (in 2 hours), held at 620°C for 8 hours, and then air cooled. (Fe-based alloy) Solution treatment: After holding at 1040°C for 1 hour, the material was water-cooled. Aging treatment: After holding at 480°C for 2 hours, the specimen was air-cooled.

[0040] [Evaluation of the area ratio of nanoparticle agglomerates] Thirty particles of the alloy powder material with oxide nanoparticles attached are observed using a scanning electron microscope (SEM). Next, energy dispersive X-ray analysis (EDS) is used to identify whether it is a metal or an oxide. The portion where the particle diameter converted from the area exceeds 1 μm is defined as an oxide nanoparticle agglomeration portion, and the area ratio of the nanoparticle agglomeration portion is calculated by the following formula. Area ratio of oxide nanoparticle agglomerates = (total area of ​​oxide nanoparticle agglomerates observed in one alloy powder particle) / (area of ​​one powder particle) Here, only the area of ​​one powder particle that is visible in the SEM image is counted (the overlapping and invisible areas are not counted). This calculation is then carried out for 30 powder particles, and the average value is taken as the area ratio of the oxide nanoparticle agglomerates.

[0041] [D 50 Measurement method] Average particle diameter D 50 In the measurement, the total volume of the powder is taken as 100% and a cumulative curve is obtained. The particle diameter at the point on this curve where the cumulative volume is 50% is D 50 Particle diameter D 50 is measured by the laser diffraction scattering method. A suitable device for this measurement is the Microtrac MT3000 laser diffraction and scattering particle size distribution analyzer from Nikkiso Co., Ltd. Powder is poured into the cell of this device together with pure water, and the particle size is detected based on the light scattering information of the particles.

[0042] [Hausner ratio] The Hausner ratio is an index defined as tap density / apparent density. The lower the Hausner ratio, the better the powder's flowability. The tap density is calculated by measuring approximately 50 g of powder in a volume of 100 cm. 3The powder was packed into a cylinder, dropped from a height of 10 mm, and tapped 200 times to evaluate the packing density.

[0043] [High temperature tensile strength] Using alloy powder material, type 6 test specimens (φ6 × GL30 mm) were fabricated using additive manufacturing (SLM or binder jetting) according to Table A-3 of the Japanese Industrial Standards (JIS) G0567 (2020). Using these test specimens, the maximum tensile stress σ applied during the tensile test was calculated as the tensile strength (σ = measurement load F / cross-sectional area S). The tensile test was conducted at 649°C.

[0044] [Rupture Test] Creep rupture test specimens with a parallel portion having a diameter of 6 mm were prepared under the following conditions: A rupture test (fracture test) was conducted under the following conditions. ·Ni-based alloy: 649℃, 690MPa ·Fe-based alloy: 482℃, 665MPa

[0045] As shown in Tables 2 and 3, mixed powder materials, Examples 1 to 5, Reference Examples 6 to 7, and Comparative Examples 1 to 7, were prepared by varying the amount of oxide nanoparticles added to Ni-based alloys No. A and No. B, and Fe-based alloy No. C listed in Table 1, and these were subjected to additive manufacturing. The properties of each were evaluated using the method described above. The results are shown in Tables 2 and 3. The combinations of powders used in Table 1 are indicated by D in Table 2. 50 As shown in the table, Ni-based alloy No. B in Table 1 is used in Example No. 2 in Table 2 and Comparative Example No. 2 in Table 3. The oxide nanoparticles used in the examples and comparative examples were all Y2O3.

[0046] [Table 2]

[0047] [Table 3]

[0048] As shown in FIG. 1, it was confirmed that nanoparticle agglomerations occurred in the sample to which 0.3 mass % of Y2O3 nanoparticles was added.

[0049] Furthermore, the additively manufactured bodies made from the Ni-based alloy powders of the Examples all had higher tensile strength and were less likely to break than the additively manufactured bodies made from the Ni-based alloy powders of the Comparative Examples, and exhibited excellent high-temperature strength. The additively manufactured bodies made from the Ni-based alloy powders of the Examples all had higher tensile strength and were less likely to break than the additively manufactured bodies made from the Ni-based alloy powders of the Comparative Examples, and exhibited excellent high-temperature strength. The additively manufactured bodies made from the Fe-based alloy powders of the Reference Examples all had higher tensile strength and were less likely to break than the additively manufactured bodies made from the Fe-based alloy powders of the Comparative Examples, and exhibited excellent high-temperature strength.

[0050] Furthermore, the examples also showed a low Hausner ratio and excellent fluidity, confirming that they are suitable as alloy powder materials for additive manufacturing.

[0051] Comparative Ni-based alloy No. 2 and comparative Fe-based alloy No. 6 both had poor fluidity and did not flow, making it impossible to measure the apparent density and evaluate the Hausner ratio. Thus, although these alloys were previously unsuitable as alloy powder materials for additive manufacturing, the addition of oxide nanoparticles as in the present invention ensured their suitability for additive manufacturing and also provided excellent high-temperature strength. [Industrial Applicability]

[0052] The alloy powder material of the present invention is suitable as a metal powder for additive manufacturing using metal deposition methods, powder bed methods, electron beam methods, and binder jet methods. The additively manufactured body is also suitable for heat-resistant parts.

Claims

1. The powder surface is not treated with organic substances. 2 O 3 The Ni-based alloy powder to which oxide nanoparticles are attached is an alloy powder material to which 0.1 to 1.50 mass % of oxide nanoparticles are added, and the area ratio of the oxide nanoparticle agglomerates attached to the surface of the alloy powder material is 0.1 to 10%.

2. An Ni-based alloy powder having oxide nanoparticles of Y 2 O 3 attached to the powder surface that has not been surface treated with an organic substance is an alloy powder material to which oxide nanoparticles have been added in an amount of 0.15 to 1.43 mass%, and the area ratio of the oxide nanoparticle agglomerates attached to the surface of the alloy powder material is 0.9 to 4.8%, an alloy powder material for additive manufacturing.

3. The alloy powder material for additive manufacturing according to claim 1 or 2, characterized in that the oxide nanoparticles have a primary particle diameter in the range of 1 to 100 nm.

4. The alloy powder material for additive manufacturing according to any one of claims 1 to 3, characterized in that it is oxide nanoparticles produced by physical vapor synthesis.

5. A metal additive manufacturing body manufactured by additive manufacturing using the alloy powder material for additive manufacturing according to any one of claims 1 to 4.

6. Ni-based alloy powder produced by physical vapor phase synthesis without surface treatment using organic substances. 2 O 3 The method for producing an alloy powder material for additive manufacturing includes adding 0.1 to 1.50 mass % of oxide nanoparticles of the above-mentioned formula (1) and mixing them to adhere the oxide nanoparticles to the Ni-based alloy powder, and then removing the unadhered oxide nanoparticles by classification, thereby producing an alloy powder material for additive manufacturing in which the area ratio of oxide nanoparticle agglomerates adhering to the surface of the alloy powder material is 0.1 to 10%.

7. A method for producing an alloy powder material for additive manufacturing, which comprises adding 0.15 to 1.45 mass% of oxide nanoparticles of Y2O3 that have not been surface treated with organic substances and that are produced by physical vapor synthesis to Ni-based alloy powder, mixing the powder to cause the oxide nanoparticles to adhere to the Ni-based alloy powder, and removing the unadhered oxide nanoparticles by classification, thereby producing an alloy powder material for additive manufacturing in which the area ratio of oxide nanoparticle agglomerates adhering to the surface of the alloy powder material is 0.9% to 4.8%.

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