Metal powder for additive manufacturing and additively manufactured body

Abstract

To form a stable powder bed for obtaining an additively manufactured body having a relative density of 99% or higher.SOLUTION: This invention relates to a metal powder for additive manufacturing, used for forming an additively manufactured body by an additive manufacturing method, wherein a -63 μm + 45 μm sieve particle size (by mass) is 9% or more, and a particle diameter D5 is 9 μm or more. An additively manufactured body is formed using the metal powder for additive manufacturing and an additive manufacturing apparatus, wherein a relative density of the additively manufactured body is 99.0% or more.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a metal powder for additive manufacturing and an additive manufactured object.

Background Art

[0002] In the above technical field, Patent Document 1 discloses that when a powder bed is formed using a metal powder having characteristics defined by an average particle diameter D50 and TD (tap density) and additive manufacturing is performed, an additive manufactured object having a relative density of 95% or more can be obtained.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, at a relative density of 95%, open pores are generated, and when handling fluids as an application of the additive manufactured object, errors such as leakage can be considered. Therefore, in order to obtain a high-density additive manufactured object having a relative density of 99% or more, it is necessary to form a more stable powder bed. An object of the present invention is to provide a technique for solving the above problems.

Means for Solving the Problems

[0005] To achieve the above object, the metal powder for additive manufacturing according to the present invention is a metal powder for additive manufacturing used for manufacturing an additive manufactured object by an additive manufacturing method, having a -63μm + 45μm sieve particle size (mass%) of 9% or more and a particle diameter D5 of 9μm or more.

[0006] To achieve the above object, the additive manufactured object according to the present invention is A laminated formed body formed by a laminating forming apparatus using the above-described metal powder for laminated forming, The relative density of the laminated formed body is 99.0% or more.

Advantages of the Invention

[0007] According to the present invention, a stable powder bed for obtaining a high-density laminated formed body with a relative density of 99% or more can be formed.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be exemplarily described in detail with reference to the drawings. However, the components described in the following embodiments are merely examples, and are not intended to limit the technical scope of the present invention thereto.

[0010] The copper alloy powder (alloy powder mainly composed of copper) as the metal powder for laminated forming in this embodiment will be described. Before that, first, the current situation of the copper alloy powder for laminated forming will be described.

[0011] <Current Situation of Metal Powder for Laminated Forming> Patent Document 1 discloses that when a powder bed is formed with a metal powder having characteristics defined by an average particle diameter D50 and TD (tap density) and laminated manufacturing is performed, a laminated compact having a relative density of 95% or more can be obtained.

[0012] However, the average particle diameter D50 represents the median value in the particle size distribution of the powder. Therefore, as shown in the particle size distribution 110 of FIG. 1, even for powders having the same value of the average particle diameter D50, a broad powder diameter distribution 111 with a large amount of fine powder and coarse powder, a sharp powder diameter distribution 112 with almost no fine powder or coarse powder, etc. are assumed. Therefore, since the amounts of fine powder and coarse powder cannot be clearly known from the value of the average particle diameter D50, the powder bed may not be stable even when the average particle diameter D50 is adjusted, and when the relative density of the laminated compact is less than 99%, particularly when handling fluids, problems such as leakage may occur.

[0013] The powder diameter distributions 113 and 114 in FIG. 1 show powder diameter distributions intermediate between the broad powder diameter distribution 111 and the sharp powder diameter distribution 112, and it is considered that there exists a powder diameter distribution in which the powder bed is stably generated and the relative density of the laminated compact is stable at 99% or more.

[0014] <Metal Powder for Laminated Manufacturing of the Present Embodiment> The inventors of the present invention focused on the particle diameter D5 (μm) representing the size of fine particles that inhibit the powder bed and the -63μm + 45μm sieve particle size (mass%) indicating the amount of coarse powder for improving fluidity and the density of the powder bed to form a stable powder bed, as characteristics defining a powder diameter distribution in which the powder bed is stably generated and the relative density of the laminated compact is stable at 99% or more. Here, the particle diameter D5 is a value obtained by the laser diffraction method, and the 63 - 45μm sieve particle size is a value obtained by the sieving test method defined in JIS Z8815:1994.

[0015] The powder size distributions 111 to 114 of powders having the same average particle size D50 value were plotted on a graph 120 with the horizontal axis representing the particle size D5 (μm) of the fine particles and the vertical axis representing the amount of coarse powder (-63 μm + 45 μm sieve size (mass%)) for forming a stable powder bed. Based on the results of the examples and comparative examples, a particle size threshold 121 (particle size D5 is 9 μm) and a sieve size threshold 122 (-63 μm + 45 μm sieve size (mass%) is 9%) were obtained to separate the powder size distribution 113 in which the powder bed is stably generated and the relative density of the laminated compact is stable at 99% or more from the other powder size distributions 111, 112, and 114.

[0016] Powders with a particle size D5 smaller than 9 μm and a -63 μm + 45 μm sieve size (mass%) of 9% or more have a broad particle size distribution like the powder size distribution 111. Therefore, segregation occurs during storage of the metal powder for laminated manufacturing in the laminated manufacturing apparatus, and a stable powder bed cannot be formed until the laminated manufacturing is completed.

[0017] Powders with a particle size D5 of 9 μm or more and a -63 μm + 45 μm sieve size (mass%) of less than 9% are powders with a sharp particle size distribution and good fluidity like the powder size distribution 112. However, due to the overly uniform particle size, the density of the powder bed decreases, leading to a decrease in relative density. In addition, powders produced by an atomization method or the like require sieving in a very narrow particle size range, resulting in poor productivity.

[0018] Powders with a particle size D5 smaller than 9 μm and a -63 μm + 45 μm sieve size (mass%) of less than 9% are powders with a certain balance in particle size distribution like the powder size distribution 114. However, the fluidity is impaired due to the overall pulverization of the powder, and a powder bed cannot be formed in the first place.

[0019] By using a metal powder with a particle size distribution of the powder size distribution 113 in which the -63 μm + 45 μm sieve size (mass%) is 9% or more and the particle size D5 (volume distribution) by the laser diffraction method is 9 μm or more, a laminated compact with high density (relative density of 99% or more) can be stably obtained.

[0020] [First Embodiment] As the metal powder for laminated forming of the first embodiment, copper powder and copper alloy powder (alloy powder mainly composed of copper) will be described.

[0021] The copper powder of this embodiment contains copper and inevitable impurities. Examples of inevitable impurities include elements P and Al at 0.01 mass% or less.

[0022] In addition, the copper alloy powder of this embodiment contains an additive element M (at least one element of elements Mg, Al, Si, P, Cr, Fe, Ni, Zn, Zr, Ag, and Sn) in the range of 0.01 mass% or more and 32.0 mass% or less, and the balance is copper and inevitable impurities.

[0023] The additive element M is added to improve the characteristics of the copper alloy powder (such as fluidity), the characteristics during laminated forming (such as laser reflectivity and laser absorptivity), and the characteristics of the laminated formed body (mechanical characteristics: strength, wear resistance, toughness, etc., physical characteristics: conductivity, heat resistance, etc.). However, in this embodiment, conditions for specifying a copper alloy powder in which a powder bed is stably generated and the relative density of the laminated formed body is stabilized at 99% or more have been found.

[0024] Each element of the additive element M is added in the following ranges such that the total amount of the additive element M falls within the range of 0.01 mass% or more and 32.0 mass% or less. For example, Al is in the range of 0.01 mass% or more and 3.92 mass% or less, Si is in the range of 0.03 mass% or more and 0.97 mass% or less, P is in the range of 0.01 mass% or more and 0.14 mass% or less, Cr is in the range of 0.01 mass% or more and 1.33 mass% or less, Fe is in the range of 0.01 mass% or more and 0.29 mass% or less, Ni is in the range of 0.06 mass% or more and 4.08 mass% or less, Zr is in the range of 0.04 mass% or more and 0.31 mass% or less, Sn is in the range of 0.24 mass% or more and 5.09 mass% or less, and so on.

[0025] <Manufacturing Method of Copper Alloy Powder> The manufacturing method of the copper alloy powder for laminated manufacturing is not particularly limited, but a method in which powder particles are rapidly solidified from a molten state, such as the gas atomization method, water atomization method, centrifugal atomization method, plasma atomization method, plasma rotating electrode method, etc., is preferable. From the viewpoint of mass productivity, the gas atomization method is particularly preferable. The manufactured powder can be classified under predetermined classification conditions by a known classification method and adjusted to a copper alloy powder for laminated manufacturing with an appropriate particle size. As a classification device for performing classification, an air classifier can be preferably used. Further, mechanical milling or the like may be performed on the copper alloy powder. For example, the ball mill method, bead mill method, planetary ball mill method, attritor method, vibration ball mill method, etc. are used.

[0026] <Method for manufacturing a laminated structure> For the production of a copper alloy laminated structure, various known metal laminated manufacturing techniques can be used. For example, in the powder bed melting method, metal powder is leveled on a forming stage with a blade or roller and spread to form a powder layer, and the production of a laminated structure is carried out while repeating the process of irradiating a laser or electron beam at a predetermined position of the formed powder layer to sinter and melt the metal powder. In the forming process of metal laminated manufacturing, it is necessary to control a very large number of process parameters in order to obtain a high-quality laminated structure. In the laser powder bed melting method, there are a large number of scanning conditions such as laser output and laser scanning speed. Therefore, when setting the optimal scanning conditions, the main parameters are adjusted using the energy density, which is an index summarizing the main parameters. The energy density E [J / mm 3 is determined by E = P / (v × s × t), where P [W] is the output of the laser, v [mm / s] is the laser scanning speed, s [mm] is the laser scanning pitch, and t [mm] is the thickness of the powder layer. In the laser powder bed melting method, the energy density is preferably 150 J / mm 3 or more and 450 J / mm 3 or less. When the energy density is less than 150 J / mm 3 , unmelted or poor fusion occurs in the powder layer, and defects such as voids occur in the laminated structure. When the energy density is 450 J / mm 3If it exceeds this value, sputtering occurs and the surface of the powder layer becomes unstable, resulting in defects such as voids in the laminated body. In the electron beam powder bed melting method, when an electron beam is irradiated onto the powder layer, if a negative charge accumulates in the powder layer and charge-up occurs, a smoke phenomenon where the powder flutters upward in a misty state is caused, leading to poor melting. Therefore, a preliminary process of preheating the powder layer to perform pre-sintering is required to prevent charge-up. However, if the preheating temperature is too high, sintering progresses and necking is caused, making it difficult to remove the powder remaining inside the laminated body after shaping. For this reason, in the copper alloy powder for laminated manufacturing, it is preferable to set the preheating temperature to 400 to 800 °C. Here, although the metal laminated manufacturing technology by the powder bed melting method is exemplified, the general laminated manufacturing method for manufacturing a laminated body using the copper alloy powder for laminated manufacturing of the present invention is not limited to this. For example, a laminated manufacturing method by the directed energy deposition method may be adopted.

[0027] <Method for measuring relative density> As a method for measuring relative density, there are (1) a method of manufacturing a laminated body using a 3D powder laminated manufacturing machine and calculating the relative density (%) as the cross-sectional area ratio obtained by subtracting the porosity of the cross-section of the laminated body from 100, and (2) a method of manufacturing a laminated body using a 3D powder laminated manufacturing machine, measuring the density of the manufactured laminated body by the Archimedes method, and calculating the relative density (%) with the theoretical density (the density of the melted material having the same composition as the laminated body) as 100%. In this embodiment, the method (1) was adopted.

[0028] According to this embodiment, the copper powder or copper alloy powder for laminated manufacturing is (1) The amount of coarse powder for forming a high-density and stable powder bed without reducing the apparent density as a powder characteristic is defined by the "-63 μm + 45 μm sieve particle size (mass%)" obtained by the "JIS Z8815:1994 Sieving test method", (2) By defining the particle diameter of the fine powder that affects fluidity by "D5 (μm)" defined by the laser diffraction method, A powder bed for obtaining a laminated compact with a high relative density (99% or more) could be stably formed.

[0029] [Second Embodiment] As the metal powder for additive manufacturing of the second embodiment, a nickel alloy powder (an alloy powder having an element with nickel as the main component) will be described.

[0030] The nickel alloy powder of this embodiment contains 50.88 mass% of additive element N (at least one element among the elements Al, Si, Ti, Cr, Mn, Fe, Co, Nb, and Mo), and the balance is nickel and unavoidable impurities.

[0031] Additive element N is added to improve the characteristics of the nickel alloy powder, the characteristics during additive manufacturing, and the characteristics of the laminated compact (mechanical characteristics, physical characteristics). However, in this embodiment, conditions for specifying a nickel alloy powder in which a powder bed is stably generated and the relative density of the laminated compact is stabilized at 99% or more have been found. Therefore, the range of the addition amount of each element of additive element N is not limited and can be appropriately selected.

[0032] The method for manufacturing the nickel alloy powder, the method for manufacturing the laminated compact using the nickel alloy powder, and the method for measuring the relative density are the same as those of the copper alloy powder in the first embodiment, and thus duplicate explanations are omitted.

[0033] According to this embodiment, the nickel alloy powder for additive manufacturing is (1) The amount of coarse powder for forming a high-density and stable powder bed without reducing the apparent density as a powder characteristic is defined by the "-63 μm + 45 μm sieve particle size (mass%)" obtained by the "Sieving Test Method of JIS Z8815:1994", (2) By defining the particle diameter of fine powder that affects fluidity by "D5 (μm)" defined by the laser diffraction method, A powder bed for obtaining a laminated compact with a high relative density (99% or more) could be stably formed.

[0034] [Other Embodiments] The definition of the metal powder for additive manufacturing or the alloy powder for additive manufacturing that forms a stable powder bed to obtain a high-density laminated structure body with a relative density of 99% or more, where the -63 μm + 45 μm sieve particle size (mass%) is 9% or more and the particle size D5 (μm) is 9 μm or more, is not limited to copper, nickel, and their alloys as shown in the above first and second embodiments. The definition that the -63 μm + 45 μm sieve particle size (mass%) is 9% or more and the particle size D5 (μm) is 9 μm or more is a perfunctory definition that does not depend on the type of metal or the type of its alloy.

Examples

[0035] Hereinafter, experiments were conducted on metals containing only inevitable impurities or alloys with different main component elements regarding the relationship between the -63 μm + 45 μm sieve particle size (mass%) and the particle size D5 (μm), the quality and stability of the formation of the powder bed, and the stable height of the relative density of the laminated structure body in various combinations of metals and elements. The experimental results are shown in [Table 1A] to [Table 2B]. Here, Examples 101 to 122 and Comparative Examples 101 to 111 are the experimental results of copper powder or copper alloy powder, and Example 201 is the experimental result of nickel alloy powder.

[0036]

Table 1A

Table 1B

Table 2A

Table 2B

[0037] The quality of the powder bed shown in [Table 1A] to [Table 2B] (○: good, △: unstable, X: unacceptable) is evaluated by forming a powder bed using a metal powder for additive manufacturing or an alloy powder for additive manufacturing, as shown in Fig. 2. In Example 110 (201 in Fig. 2), a uniform powder bed is formed (○). In Comparative Example 104 (202 in Fig. 2), powder lumps partially occur and the powder bed is unstable (△). In Comparative Example 109 (203 in Fig. 2), the powder bed cannot be formed completely and additive manufacturing is impossible (X). The thick frame in [Table 2B] shows the sieve particle size (-63 μm + 45 μm, mass %) or particle diameter D5 (μm) outside the specified range.

[0038] The relative density of the additive manufactured object shown in [Table 1A] to [Table 2B] was determined by a method in which an additive manufactured body was produced using a 3D powder additive manufacturing machine, and the relative density (%) was calculated as the cross-sectional area ratio obtained by subtracting the porosity of the cross-section of the additive manufactured body from 100.

[0039] As shown in [Table 1A] to [Table 2B], in [Table 1A] and [Table 1B] (Examples 101 to 122, 201), for metals containing only inevitable impurities or alloys with different main component elements, in various combinations of metals and elements, since the sieve particle size (-63 μm + 45 μm, mass %) is 9% or more and the particle diameter D5 is 9 μm or more, a high-density and stable powder bed is formed, and an additive manufactured body with a relative density of 99% or more is stably manufactured.

[0040] On the other hand, in [Table 2A] and [Table 2B], for metals containing only inevitable impurities or alloys with different main component elements, in various combinations of metals and elements, since the sieve particle size (-63 μm + 45 μm, mass %) is less than 9% and / or the particle diameter D5 is less than 9 μm, a mottled and unstable powder bed is formed, showing metal powders and alloy powders for which an additive manufactured body with a relative density of 99% or more could not be manufactured.

[0041] Figure 3 is a graph plotting the quality of powder bed formation in [Table 1A] to [Table 2B] with the particle diameter D5 on the horizontal axis and the -63μm + 45μm sieve particle size (mass%) on the vertical axis. As shown in Figure 3, powder groups 311 to 314 for the quality of powder bed formation exist with a threshold as a boundary, similar to Figure 1. Figure 4 is a powder diameter distribution with the particle diameter D5 on the horizontal axis corresponding to the powder groups 311 to 314 in Figure 3.

[0042] In Figure 4, for powders with a particle diameter D5 smaller than 9μm and a -63μm + 45μm sieve particle size (mass%) of 9% or more, the particle size distribution is broad like the powder diameter distribution 311. Therefore, segregation occurs during the storage of the metal powder for additive manufacturing in the additive manufacturing apparatus, and a stable powder bed cannot be formed until the additive manufacturing is completed.

[0043] In Figure 4, for powders with a particle diameter D5 of 9μm or more and a -63μm + 45μm sieve particle size (mass%) less than 9%, the particle size distribution is sharp like the powder diameter distribution 312 and has good fluidity. However, due to the overly uniform particle size, the density of the powder bed decreases, leading to a decrease in relative density. Also, powders produced by methods such as the atomization method require sieving in a very narrow particle size range, resulting in poor productivity.

[0044] In Figure 4, for powders with a particle diameter D5 smaller than 9μm and a -63μm + 45μm sieve particle size (mass%) less than 9%, the particle size distribution is a powder with a certain balance like the powder diameter distribution 314. However, the fluidity is impaired due to the overall pulverization of the powder, and a powder bed cannot be formed in the first place.

[0045] Thus, by using a metal powder with a -63μm + 45μm sieve particle size (mass%) of 9% or more and a particle diameter D5 (volume distribution) by the laser diffraction method of 9μm or more, and with a particle size distribution like the powder diameter distribution 313 in Figure 4, a high-density (relative density of 99% or more) additive manufactured body can be stably obtained.

Example

[0046] Using the copper alloy powders of Example 110 and Comparative Example 102 above, cylinders with a maximum thickness of 2 mm and a minimum thickness of 1 mm were fabricated, and leak checks were performed using compressed air at 0.2 MPa. The results of the leak checks using compressed air at 0.2 MPa are shown in Fig. 5.

[0047] As shown in Fig. 5, a cylinder 501 with a maximum thickness of 2 mm and a minimum thickness of 1 mm was fabricated. Compressed air at 0.2 MPa was applied to this cylinder 501, and it was confirmed whether there was air leakage in water. There was no air leakage in the cylinder 502 fabricated by additive manufacturing using the copper alloy powder of Example 110. On the other hand, air leakage occurred in the cylinder 503 fabricated by additive manufacturing using the copper alloy powder of Comparative Example 102. Since the relative density of the cylinder 503 was in the 98% range and open pores were generated, it is considered that air leakage occurred.

Claims

1. A metal powder for additive manufacturing used to manufacture an additive manufacturing body by an additive manufacturing method, A metal powder for additive manufacturing, having a -63 μm + 45 μm sieve particle size (mass%) of 9% or more and a particle diameter D5 of 9 μm or more.

2. The -63 μm + 45 μm sieve particle size (mass%) is a value obtained by a sieving test method defined in JIS Z8815:1994, and the particle diameter D5 is a value obtained by a laser diffraction method. The metal powder for additive manufacturing according to claim 1.

3. The metal powder for additive manufacturing is a copper alloy powder, 3. The metal powder for additive manufacturing according to claim 2, containing 0.01% by mass or more and 32.0% by mass or less of an additive element M (at least one of the elements Mg, Al, Si, P, Cr, Fe, Ni, Zn, Zr, Ag, and Sn), with the remainder being copper and unavoidable impurities.

4. A layered object manufactured by an additive manufacturing apparatus using the metal powder for additive manufacturing according to any one of claims 1 to 3, The layered object has a relative density of 99.0% or more.

5. The layered object according to claim 4 , wherein the relative density is a cross-sectional area ratio obtained by subtracting the porosity of the cross section of the layered object from 100.

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