Method for manufacturing a metal additive structure made of Ni-based alloy, and the fabricated structure

Abstract

This invention provides a method for manufacturing additively fabricated metal products using Inconel® 718, a nickel-based alloy, in which the creep fracture strength meets the specified value. [Solution] A method for manufacturing a metal additive manufacturing product made of a Ni-based alloy, characterized by comprising: a homogenization step 1 in which a metal additive manufacturing product made of a Ni-based alloy consisting of 50-55 mass% Ni, 17-21 mass% Cr, 2.8-3.3 mass% Mo, a total of 4.75-5.5 mass% Nb and Ta, 0.65-1.15 mass% Ti, 0.2-0.8 mass% Al, with the remainder being Fe and unavoidable impurities is homogenized at a temperature of 1050°C to 1250°C; a solution treatment step 2 in which a solution treatment is performed after the homogenization step; and an aging step 3 in which an aging treatment is performed at a temperature of 650°C to 720°C after the solution treatment step.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a metal laminated object made of a Ni-based alloy and to the object.

Background Art

[0002] As an alloy having high strength at high temperatures, Inconel (registered trademark) 718, a Ni-based alloy, is known. This alloy is a precipitation-strengthened alloy, has high strength at temperatures up to about 700°C, and has various characteristics such as excellent corrosion resistance. As a result, it is used in a wide range of applications, including turbine disks of aircraft jet engines, rotating parts of rocket engines, and high-tensile bolts. As a method for manufacturing Inconel (registered trademark) 718, for example, Patent Document 1 discloses a solution treatment step of subjecting a Ni-based alloy in which Ni is 50 to 55% by weight, Cr is 17 to 21% by weight, Mo is 2.8 to 3.3% by weight, Nb is 4.75 to 5.5% by weight, Ti is 0.65 to 1.15% by weight, Al is 0.2 to 0.8% by weight, and the balance is substantially composed of Fe to solution treatment at 1010°C or higher and 1070°C or lower, and an aging step of performing aging treatment at 680°C or higher and 720°C or lower for 5 hours or longer and 20 hours or shorter after the solution treatment step.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Conventionally, metal materials including alloys have mainly used melted materials using molds. The above Patent Document 1 is also a technology premised on melted materials. In contrast, the use of additively manufactured metal objects has been increasing in recent years. Additive manufacturing involves joining materials layer by layer from a 3D data model without using molds, and then stacking them to create an object. Additive manufacturing offers the following advantages compared to conventional metal fabrication: • High degree of design freedom: Complex shapes, structures with internal cavities, lattice structures, thin-walled structures, etc., are possible. Multiple parts can sometimes be integrated into a single unit. • Design changes are easy. • No molds are required. • Because mold manufacturing time is eliminated, production time and lead time are significantly reduced. • Product-specific traceability is possible, etc.

[0005] When Inconel® 718, a nickel-based alloy, is used in metal additive manufacturing, its high-temperature strength, particularly its creep rupture strength, often falls short of the SAE AMS5663 forging standard for Inconel® 718. The object of the present invention is to provide a method for manufacturing a metal additively fabricated product using Inconel® 718, a Ni-based alloy, in which the creep fracture strength meets the specified value. [Means for solving the problem]

[0006] The present invention, completed with this objective in mind, is a method for manufacturing a metal additive manufacturing product made of a Ni-based alloy, characterized by comprising: a homogenization step of homogenizing a metal additive manufacturing product made of a Ni-based alloy consisting of 50-55 mass% Ni, 17-21 mass% Cr, 2.8-3.3 mass% Mo, a total of 4.75-5.5 mass% Nb and Ta, 0.65-1.15 mass% Ti, 0.2-0.8 mass% Al, with the remainder being Fe and unavoidable impurities, at a temperature of 1050°C to 1250°C; a solution treatment step of performing a solution treatment after the homogenization step; and an aging step of performing an aging treatment at a temperature of 650°C to 720°C after the solution treatment step. In this case, the homogenization process may be carried out at a temperature of 1050°C or higher and 1250°C or lower for 2 hours or more. Furthermore, the fabricated object is made by metal additive manufacturing of a Ni-based alloy consisting of 50-55 mass% Ni, 17-21 mass% Cr, 2.8-3.3 mass% Mo, a total of 4.75-5.5 mass% Nb and Ta, 0.65-1.15 mass% Ti, 0.2-0.8 mass% Al, with the remainder being Fe and unavoidable impurities, and exhibits results that conform to the following tests. "Test" A specimen with a standard smooth section and notch for stress fracture testing conforming to ASTM E292 is prepared from a formed Ni-based alloy. Maintained at 649°C ± 2°C, an initial axial stress of 689 MPa is applied to the specimen, followed by continued loading. The first fracture occurs in the smooth section of the specimen, and this fracture occurs at least 23 hours later. Furthermore, the molded object may be a stator vane. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a method for manufacturing a metal additively fabricated product using Inconel® 718, a Ni-based alloy, in which the creep fracture strength meets the standard value. [Brief explanation of the drawing]

[0008] [Figure 1] This graph schematically illustrates the manufacturing method of Ni-based alloys. [Figure 2] This figure schematically shows the microstructure of the Ni-based alloy of this embodiment. [Figure 3] These are graphs and schematic diagrams showing the effect of heat treatment temperature on the crystal structure in the homogenization process of this embodiment. (a) is a graph showing the relationship between heat treatment time and crystal grain size when the heat treatment temperature is changed, (b) is a graph showing the relationship between heat treatment time and isotropy:crystal grain aspect ratio when the heat treatment temperature is changed, and (c) is a schematic diagram explaining the aspect ratio in the microstructure. [Figure 4] This is a schematic diagram showing the structure of a stator vane. [Figure 5]This diagram illustrates the test specimen prepared in the example. (a) is a schematic diagram showing the overall shape and dimensions of the test specimen, and (b) is a diagram showing the shape of the notch. [Modes for carrying out the invention]

[0009] The embodiments of the present invention will be described in detail below. The embodiments shown below are illustrative and do not limit the technical scope of the present invention to the following embodiments. In this disclosure, unless otherwise specified, the expressions "greater than or equal to XX and less than or equal to XX" or "XX to XX" refer to the numerical range including the stated upper and lower limits.

[0010] In the manufacturing method according to this embodiment, a metal additively fabricated object composed of a Ni-based alloy of a specific composition is used. The composition of the Ni-based alloy is 50-55 mass% Ni, 17-21 mass% Cr, 2.8-3.3 mass% Mo, 4.75-5.5 mass% Nb and Ta combined, 0.65-1.15 mass% Ti, 0.2-0.8 mass% Al, with the remainder being Fe and unavoidable impurities. This chemical composition corresponds to the composition range of a precipitation-hardening nickel-chromium-iron alloy called Inconel® 718. Figure 1 shows a schematic graph illustrating the manufacturing method of Ni-based alloys, such as those in this embodiment. In the conventional SAE AMS5663 forging standard for Inconel® 718, the manufacturing method from the raw Ni-based alloy involves the heat treatment shown by the solid line in Figure 1. Specifically, solution treatment step 2 is performed at 941°C to 1010°C for 1 hour, followed by cooling, and then aging treatment step 3, followed by cooling. In aging treatment step 3, for example, aging treatment was performed at 720°C for 8 hours, followed by aging treatment at 620°C for 8 hours. In the manufacturing method of a metal additive manufacturing product made of a Ni-based alloy according to this embodiment, first a homogenization treatment step 1, shown by the dotted line in Figure 1, is performed, followed by the conventional solution treatment step 2 and aging treatment step 3.

[0011] The manufacturing method according to this embodiment will be described with reference to FIG. 2 schematically showing the microstructure of a Ni-based alloy. Four circles in FIG. 2 are shown. The upper left circle schematically shows the microstructure of the Ni-based alloy in each state before heat treatment, the upper right circle after homogenization treatment, the lower left circle after solution treatment, and the lower right circle after aging treatment. These microstructures are usually observed by a scanning electron microscope (SEM), and more detailed structures are observed by a transmission electron microscope (TEM). The means for observing the microstructure is not limited to these, and other means may also be used. The upper left circle in FIG. 2 shows the state of the microstructure before heat treatment in this embodiment. It is a state diagram of the microstructure of a metal laminated structure made of a Ni-based alloy with the above-mentioned specific composition.

[0012] Metal additive manufacturing is to create a shape by melting and solidifying the necessary parts layer by layer of metal powder as a raw material based on a three-dimensional data model of the target shaped material without using a mold, and stacking the layers. A metal additive manufactured object refers to an object such as a metal part manufactured by metal additive manufacturing. The main methods for manufacturing a metal additive manufactured object are as follows. · A method of melting, solidifying, and stacking raw metal powder with a laser or an electron beam. · A method of spreading metal powder with a uniform thickness, printing each layer with a binder, stacking them, and passing through a sintering process after stacking. · A method of melting and stacking a raw material obtained by kneading metal powder and a plastic resin while extruding the plastic resin, and passing through a sintering process after stacking. In the present invention, the method using the laser or electron beam described first is preferred. In this embodiment, the raw metal powder has the same composition as the target Ni-based alloy, with Ni being 50 to 55% by mass, Cr being 17 to 21% by mass, Mo being 2.8 to 3.3% by mass, the total of Nb and Ta being 4.75 to 5.5% by mass, Ti being 0.65 to 1.15% by mass, Al being 0.2 to 0.8% by mass, and the balance being Fe and unavoidable impurities. This metal powder is melted and solidified layer by layer with a laser or an electron beam, and the layers are stacked to obtain a desired metal additive manufactured object.

[0013] A schematic diagram of the microstructure of the obtained metal laminated structure is shown by the circle in the upper left of FIG. 2 as described above. In the microstructure, 11 is a crystal grain, and 12 is a grain boundary showing the boundary between crystals. In the microstructure after metal laminated manufacturing, the crystal grains 11 extend in the layer direction during metal laminated manufacturing and gather in a slightly elongated shape to form a structure. The black dots in the crystal grains 11 are minute crystals of the δ phase precipitated in the crystal grains 11. In the microstructure, the black lines between the crystals are the grain boundaries 12 which are the boundaries of the crystals. In this microstructure, there are black dots at the grain boundaries 12, and these black dots are minute crystals precipitated on the grain boundaries 12.

[0014] Next, homogenization treatment is performed. This is a heat treatment that has not been performed in the conventional Inconel (registered trademark) 718 as described above. Homogenization treatment is a heat treatment in which a Ni-based alloy is heated and held at a relatively high temperature and then cooled in order to eliminate the non-uniformity of the structure generated by metal laminated manufacturing. It is also called diffusion annealing. By homogenization treatment, the separation of elements in the alloy is eliminated, the anisotropy of the crystal structure is eliminated, the structure is isotropized, and the crystals grow in this process. In the present embodiment, it has been observed that Nb segregated in the crystals diffuses in the structure and the whole structure is homogenized. Note that due to the growth of the crystal grains 11, the particle structure becomes rough, and there is a tendency that the strength such as the tensile strength is likely to decrease. Therefore, it is necessary to carefully select the conditions such as the temperature and time of the homogenization treatment.

[0015] Figure 3 shows a graph illustrating the effect of heat treatment temperature on the crystal structure in the homogenization process of this embodiment. Figure 3(a) is a graph showing the relationship between heat treatment time and crystal grain size when the heat treatment temperature is changed, and Figure 3(b) shows the relationship between heat treatment time and isotropy:crystal grain aspect ratio when the heat treatment temperature is changed. In Figure 3, the same Ni-based alloy raw material powder as in Example 1 described later was used, and test specimens suitable for the study were prepared by the same metal additive manufacturing operation as in Example 1, and observed using SEM. The aspect ratio of the crystal grains was determined by selecting the two longest straight lines perpendicular to each crystal grain 11 at a 90-degree angle, as shown in the schematic diagram of the microstructure in Figure 3(c), and the average value for 50 crystals was calculated for each. As can be seen from the graph in Figure 3(a), when homogenization treatment was performed at temperatures of 1100°C, 1140°C, and 1200°C, the grain size after treatment was largest at 1200°C, approximately 120 μm at 1200°C, and approximately 80 μm at 1100°C and 1140°C. Furthermore, the aspect ratio indicating isotropy was approximately 2.0 at all three temperatures after heat treatment times of 1 to 4 hours, indicating that the effect is nearly saturated. Based on these considerations, it has been determined that in homogenization step 1, the heat treatment temperature is preferably 1050°C to 1250°C, particularly preferably 1100°C to 1240°C, and even more preferably 1130°C to 1210°C. Furthermore, the heat treatment time in homogenization step 1 is preferably 1 hour or more, particularly preferably 3 hours or more, and even more preferably 4 hours or more. Since the effect of heat treatment saturates after 4 hours or more, there is no upper limit to the heat treatment time, but since heat treatment for longer than necessary is not efficient, for example, 6 hours or less, and even more preferably 5 hours or less, is preferable. After homogenization treatment step 1, the microstructure of the Ni-based alloy, as shown in the circle in the upper right of Figure 2, shows that the crystal grains 11 are closer to circles, the aspect ratio is smaller, and the isotropy is improved compared to before the homogenization treatment. In addition, the δ phase crystals that had precipitated within the crystal grains 11 have disappeared, and the crystals that had precipitated at the grain boundaries 12 have also disappeared. After homogenization treatment, the Ni-based alloy is cooled to near room temperature.

[0016] Next, solution treatment step 2 is performed. This treatment was also applied to conventional Inconel® 718. Solution treatment is a heat treatment process that homogenizes the internal structure of a nickel-based alloy by uniformly heating a homogenized nickel-based alloy to a high temperature that results in a solid solution state, and then cooling it. This process eliminates abnormal crystal structures within the alloy, improving the functionality of the alloy material. In this embodiment, the δ phase is precipitated at the grain boundaries 12 during the solution treatment step 2. The precipitation of the δ phase on the microstructure can be detected by SEM observation and component analysis. The δ phase precipitates at the grain boundary 12, which can fix the grain boundary 12 through a peening effect. However, in the next aging treatment step 3, the strengthening phases γ′ and γ″ are precipitated at the grain boundary 12 to strengthen the Ni-based alloy. Since the δ, γ′, and γ″ phases have the same composition, if the amount of δ phase precipitated is excessive, the strengthening phase component will be consumed. Also, the δ phase precipitates at the grain boundary 12 first, and then precipitates within the crystal grains 11. Therefore, the solution treatment time is selected to allow the δ phase to precipitate at the grain boundaries 12 but not within the crystal grains 11.

[0017] Based on these conditions, the solution treatment is preferably performed at a temperature of 935°C to 1010°C, and more preferably at 935°C to 965°C. Furthermore, the solution treatment time is preferably 2 hours to 6 hours. Generally, in the final metal additively manufactured product, the strength of the product often differs between the direction perpendicular to the additive manufacturing process (abbreviated as "V direction") and the direction of the additive manufacturing process (abbreviated as "H direction"). In the present invention, as shown in the examples, the results of the creep rupture test in the V direction and the H direction of the test piece differ. In this embodiment, the conditions under which the creep rupture test results in the V direction and the H direction are satisfactory are that the combination of homogenization treatment and solution treatment is preferably such that the homogenization treatment is performed at 1050°C to 1250°C for 3 to 5 hours, and the solution treatment is performed at 935°C to 965°C for 2 to 5 hours, particularly 3 to 4 hours. Furthermore, in the V-direction, where the strength of the test specimen tends to be weaker, a combination of homogenization treatment and solution treatment is preferable to ensure that both creep rupture tests and high-temperature tensile tests are performed under the same conditions. Specifically, the homogenization treatment should be performed at 1050°C to 1250°C for 1 to 2 hours, and the solution treatment should be performed at 935°C to 965°C for 2 to 4 hours. After solution treatment, the Ni-based alloy is cooled to near room temperature. After solution treatment step 2, the microstructure of the Ni-based alloy, as shown in the circle in the lower left of Figure 2, shows that the shape of the crystal grains 11 remains almost unchanged compared to after homogenization treatment, and δ-phase crystals have precipitated at the grain boundaries 12.

[0018] Next, aging treatment process 3 is performed. This treatment is also the same treatment that was applied to conventional Inconel® 718. The Ni-based alloy after aging treatment will have a hardness of 350 HV or higher. Aging treatment is a process in which a Ni-based alloy that has undergone solution treatment is heated to precipitate a strengthening phase and improve its strength. The alloy in this embodiment is a precipitation-hardening alloy, and aging treatment can precipitate the strengthening phases γ′ and γ″ within the crystal grains 11 in the Ni-based alloy, thereby improving its strength. Both the γ′ and γ″ phases have a face-centered cubic structure, while the stable phase δ has a body-centered cubic structure. As aging treatment progresses, the strength of the Ni-based alloy improves, but there is also the side effect of increased "notch susceptibility." "Notch susceptibility," as described in the examples, refers to the tendency for the initial fracture to occur at the notch rather than at the smooth part of the specimen when a notched test piece is prepared from a Ni-based alloy and stress is applied to the piece and it is pulled. For Inconel® 718, creep rupture tests require that the initial fracture point be on a smooth surface when tension is applied at high temperatures. Excessive heating during aging treatment can cause brittleness in the alloy material, increasing the tendency for fracture at notches.

[0019] In aging treatment step 3, the aging treatment temperature is preferably 650°C to 720°C, and more preferably 680°C to 720°C. At temperatures above 680°C, the hardness of the Ni-based alloy quickly reaches the standard value of 350HV, but as mentioned above, excessive heat treatment is undesirable. Therefore, the heat treatment time is preferably 2 hours or more, and although there is no theoretical upper limit, in practice, a time of 25 hours or less is adopted. The heat treatment for aging can be carried out at a single temperature, but as shown in Figure 1, it is also possible to change the temperature during the process.

[0020] After aging treatment, the Ni-based alloy is cooled to near room temperature. The aging treatment yields the metal additive manufactured product of this embodiment. After aging treatment step 3, the microstructure of the Ni-based alloy, as shown in the circle in the lower right of Figure 2, shows that the shape of the crystal grains 11 remains almost unchanged compared to after solution treatment, and crystals of the γ′ phase and γ″ phase precipitate within the crystal grains 11, as indicated by the black dots.

[0021] The metal additively manufactured product of this embodiment has high high-temperature strength and excellent corrosion resistance, processability, and other properties. As shown in the example, the metal additively manufactured product of this embodiment satisfies all three conditions of the creep fracture test standard values, or at least two conditions. When two conditions are met, it is particularly preferable that the fracture of the test piece occurs on a smooth surface and that the fracture time is at least 23 hours. In addition, as shown in the reference example, it may also satisfy at least some of the high-temperature tensile test standard values ​​specified in SAE AMS5663. The metal additive manufactured product of this embodiment can be used in the following applications where conventional Inconel® 718 has been used: Turbine discs for aircraft jet engines, rotating and fixed components for gas turbines and rocket engines, high-tensile bolts, springs, fasteners, components for nuclear reactors and spacecraft, high-temperature tools for extrusion or shearing (such as copper), pump shafts used in offshore and marine engineering, high-stress wellhead equipment, oil well equipment, alloys for well drilling equipment for sour oil and sour gas (including hydrogen sulfide, carbon dioxide, and chloride), etc. A major feature of the metal additive manufacturing process in this embodiment is that it can produce complex structures with protrusions such as fins and wings as a single piece without using connecting parts such as bolts and nuts. For example, it is possible to manufacture a stator vane 20, as shown in Figure 4, using the Ni-based alloy of this embodiment.

[0022] The present invention is not limited to the embodiments described above, and other embodiments are possible as long as they are within the spirit of the present invention.

[0023] [Examples] The embodiments of the invention will be described in detail below with reference to examples, but the embodiments of the invention are not limited to these examples. In the following description, unless otherwise specified, "%" refers to mass.

[0024] (Examples 1-3) <Preparation of test specimens> A Ni-based alloy powder with the following chemical composition was prepared. "Powder composition" • Ni: 53.02% •Cr: 18.6% •Mo: 2.97% • Nb+Ta: 5.07% Ti: 0.87% Al: 0.61% • C: 0.04% · Mn: 0.01% • Si: 0.04% P: 0.005% · B: 0.001% ·O :0.006% N: 0.002% • Fe: Remaining Using this powder as a raw material, test specimens were fabricated using the EOS M290 3D additive manufacturing system (manufactured by EOS Corporation). The fabrication method was Powder Bed Fusion-Laser Beam (PBF-LB), and the standard fabrication conditions of the system were adopted. The prepared specimen is a stress fracture test specimen conforming to ASTM E292, and is a standard notched specimen. The overall shape and dimensions of the specimen are shown in Figure 5(a), and the shape of the notch A in Figure 5(b). Two types of test specimens were prepared for each example: one with the vertical direction of three-dimensional additive manufacturing (abbreviated as "V direction") as the length direction, and another with the layering direction of three-dimensional additive manufacturing (abbreviated as "H direction") as the length direction. Therefore, two notched test specimens were prepared for each example, one with the length direction as the V direction and one as the length direction as the H direction.

[0025] <Heat treatment> Each prepared test specimen was subjected to homogenization treatment under the conditions shown in Table 1. The cooling method during this treatment was furnace cooling. Following the homogenization treatment, a solution treatment was performed under the conditions shown in Table 1. The cooling method during this treatment was furnace cooling. Furthermore, after the solution treatment, an aging treatment was performed under the conditions shown in Table 1. The cooling method during this treatment was furnace cooling.

[0026] <Creep rupture test> After heat treatment, the test specimens were maintained at 649°C ± 2°C. An initial stress of 689 MPa was applied axially, and then the same stress was continued until the specimen fractured. Table 1 shows the fracture location of the test specimen, the number of hours stress was applied until fracture, and the elongation percentage of the test specimen after fracture relative to the start of the test (%). The "smooth section" at the fracture location refers to section B in Figure 5(a). The fracture location of the test specimen is usually either the smooth section B or the notched section A. Furthermore, the standard value for creep rupture testing in AMS5663 must satisfy all three of the following conditions. • Fracture location of the test specimen: Smooth section (not notch A) • Time until breakage: 23 hours or more • Elongation of the test specimen at fracture: 4% or more

[0027] [Table 1]

[0028] The overall results in Table 1 were determined according to the following criteria. A: It satisfies all three conditions for the creep rupture test. B: Two of the three conditions for the creep rupture test are met (pass). C: One of the three conditions for the creep rupture test is met, or none of the conditions are met (fail).

[0029] (Comparative example) Using the same powder as in Examples 1-3 as the raw material, test specimens with two notches in the V-direction and H-direction were prepared under the same molding conditions as in Examples 1-3. The following heat treatments, as specified in SAE AMS5663, the forging standard for Inconel® 718, were sequentially applied to the two test specimens created. Solution treatment: 1 hour at 941°C • Aging treatment: 8 hours at 720°C, followed by 8 hours at 620°C. After each heat treatment, the respective processes were cooled by furnace cooling. Creep rupture tests were performed on heat-treated specimens in the same manner as in Examples 1-3. The results, along with the overall results, are shown in Table 2. The criteria for the overall results are the same as in Table 1.

[0030] [Table 2]

[0031] (Reference example) <Preparation of test specimens> Except for using specimens that conform to ASTM E8 / E81, two specimens were prepared in the same manner as in Example 1, with the longitudinal direction being the V direction and the longitudinal direction being the H direction. <Heat treatment> These test specimens were subjected to the same heat treatment as in Example 1. <High-temperature tensile test> For heat-treated specimens, tensile tests were conducted at a high temperature of 649°C ± 3°C as specified in ASTM E21 for metallic materials, to determine elongation at fracture and area reduction. The results are shown in Table 3. Elongation at break is the elongation of the specimen in the longitudinal direction when it breaks during a tensile test, expressed as a percentage of its length before the test. Area reduction is the reduction in the cross-sectional area of ​​the specimen when it breaks during a tensile test, expressed as a percentage of its cross-sectional area before the test. Furthermore, the high-temperature tensile specifications for AMS5663 are an elongation of 12% or more at break and an area reduction of 15% or more. The results shown in Table 3 all satisfy the specifications for elongation and area reduction for AMS5663.

[0032] [Table 3] [Explanation of Symbols]

[0033] 1…Homogenization process, 2…Solution treatment process, 3…Aging process, 11…Crystal grain, 12…Crystal grain boundary, 20…Stator vane, A…Notch in the test specimen, B…Smooth part of the test specimen

Claims

1. For metal additive manufacturing products composed of a Ni-based alloy consisting of 50-55 mass% Ni, 17-21 mass% Cr, 2.8-3.3 mass% Mo, 4.75-5.5 mass% total of Nb and Ta, 0.65-1.15 mass% Ti, 0.2-0.8 mass% Al, with the remainder being Fe and unavoidable impurities, A homogenization process in which homogenization is performed at a temperature of 1050°C or higher and 1250°C or lower, A solution treatment step is performed after the homogenization treatment step, After the solution treatment step, there is an aging step in which the material is aged at a temperature of 650°C to 720°C. A method for manufacturing a metal additive structure made of a Ni-based alloy, characterized by having the following:

2. The method for manufacturing a metal additively manufactured product according to claim 1, wherein the homogenization process is performed at a temperature of 1050°C or higher and 1250°C or lower for 2 hours or more.

3. A Ni-based alloy, comprising 50-55 mass% Ni, 17-21 mass% Cr, 2.8-3.3 mass% Mo, 4.75-5.5 mass% Nb and Ta combined, 0.65-1.15 mass% Ti, 0.2-0.8 mass% Al, with the remainder being Fe and unavoidable impurities, is formed by metal additive manufacturing. A model that demonstrates results that meet the requirements for the following test. "test" A specimen with a standard smooth section and notch for stress fracture testing conforming to ASTM E292 is prepared from a formed Ni-based alloy. Maintained at 649°C ± 2°C, an initial axial stress of 689 MPa is applied to the specimen, followed by continued loading. The first fracture occurs in the smooth section of the specimen, at least 23 hours later.

4. The molded object according to claim 3, wherein the molded object is a stator vane.

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