Ni-based alloy powder for additive manufacturing and method for manufacturing Ni-based alloy shaped objects

Abstract

A molding in which cracking does not occur can be obtained by this method for powder melt additive manufacturing using a Ni-based alloy powder for additive manufacturing comprising, in terms of mass%, 6-12% Cr, 1-4% Mo, 4-8% Al, 6-11% Co, 7-12% W, 1-5% Ta, 1.5-7% Fe, 0.1-0.25% C, no more than 0.5% Ti, no more than 0.2% Zr, no more than 0.1% B, no more than 0.5% Nb, and no more than 0.5% Hf, the remainder being Ni and unavoidable impurities.

Description

[Technical Field]

[0001] The present invention relates to Ni-based alloy powders for additive manufacturing and methods for producing Ni-based alloy shaped articles. [Background technology]

[0002] Additively manufactured parts used at high temperatures, such as aircraft gas turbines and turbines for automobile turbochargers, require Ni (nickel)-based alloys with excellent heat resistance and high-temperature oxidation resistance.

[0003] For example, Patent Document 1 discloses a composition of such a Ni-based alloy, containing Ni as the main component and the following amounts by mass: Fe (iron): 2 to 8, Al (aluminum): 6.1 to 6.8, Cr (chromium): 12.5 to 15, W (tungsten): 1.5 to 4.5, Ta (tantalum): 2.5 to 5.5, Hf (hafnium): 1.2 to 2, C (carbon): 0.03 to 0.13, B (boron): 0.005 to 0.02, Zr (zirconium): 0.005 to 0.02, and Si (silicon): 0.005 to 0.02. The invention described in Patent Document 1 is said to provide a nickel-based alloy with excellent thermal and mechanical strength, oxidation resistance, and workability. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2021-504564 Summary of the Invention [Problem to be solved by the invention]

[0005] The alloy disclosed in Patent Document 1 is used to obtain additively manufactured products with excellent high-temperature strength and oxidation resistance. However, products manufactured using additive manufacturing methods using Ni-based alloy compositions such as those disclosed in Patent Document 1 have the problem of being prone to solidification cracking, which is not taken into consideration. The occurrence of cracking leads to a decrease in high-temperature strength, creep properties, and oxidation resistance.

[0006] Therefore, the present invention aims to provide a method for manufacturing a Ni-based alloy shaped object that can suppress the occurrence of cracks during melting and solidification, and a Ni-based alloy powder for additive manufacturing that can be used to manufacture a Ni-based alloy shaped object. [Means for solving the problem]

[0007] The first invention is a Ni-based alloy powder for additive manufacturing containing, by mass%, at least the following additive elements: Cr: 6% to 12%, Mo: 1% to 4%, Al: 4% to 8%, Co (cobalt): 6% to 11%, W: 7% to 12%, Ta: 1% to 5%, Fe: 1.5% to 7%, and C: 0.1% to 0.25%, with the remainder being Ni and unavoidable impurities.

[0008] Furthermore, the Ni-based alloy powder for additive manufacturing preferably contains, as an additive element, B: more than 0% and 0.1% or less.

[0009] Furthermore, the Ni-based alloy powder for additive manufacturing preferably contains, as an additive element, at least one of Nb (niobium): more than 0% and 0.5% or less, and Hf: more than 0% and 0.5% or less.

[0010] Furthermore, the Ni-based alloy powder for additive manufacturing preferably contains, as additive elements, Ti (titanium): more than 0% and 0.5% or less, and Zr: more than 0% and 0.2% or less.

[0011] The B content is preferably 0.005% or more and 0.05% or less.

[0012] The Zr content is preferably 0.02% or more and 0.15% or less.

[0013] The second invention is a method for producing a Ni-based alloy shaped product, which comprises supplying a Ni-based alloy powder for additive manufacturing containing, by mass %, at least the following additive elements: Cr: 6% to 12%, Mo: 1% to 4%, Al: 4% to 8%, Co: 6% to 11%, W: 7% to 12%, Ta: 1% to 5%, Fe: 1.5% to 7%, and C: 0.1% to 0.25%, with the remainder being Ni and unavoidable impurities; selectively irradiating the supplied Ni-based alloy powder with laser light to melt and solidify it; and performing a powder fusion additive manufacturing process to obtain a Ni-based alloy shaped product, in which the steps of supplying the Ni-based alloy powder and melting and solidifying it are repeated.

[0014] Furthermore, the Ni-based alloy powder for additive manufacturing preferably contains, as an additive element, B: more than 0% and 0.1% or less.

[0015] Furthermore, the Ni-based alloy powder for additive manufacturing preferably contains, as an additive element, at least one of Nb (niobium): more than 0% and 0.5% or less, and Hf: more than 0% and 0.5% or less.

[0016] Furthermore, the Ni-based alloy powder for additive manufacturing preferably contains, as additive elements, Ti (titanium): more than 0% and 0.5% or less, and Zr: more than 0% and 0.2% or less.

[0017] Furthermore, it is preferable that the boundary width of the primary dendrite structure in the cross-sectional structure of the Ni-based alloy shaped article is 0.4 μm or less.

[0018] It is also preferable to have a heat treatment step of subjecting the Ni-based alloy shaped article to a heat treatment after the additive manufacturing step.

[0019] The heat treatment step preferably includes a solution heat treatment and an aging heat treatment.

[0020] In addition, it is preferable that the area ratio of carbides in the cross-sectional structure of the Ni-based alloy shaped article is 5% or more and 12% or less. [Effects of the Invention]

[0021] According to the present invention, it is possible to provide a method for manufacturing a Ni-based alloy shaped object that can suppress the occurrence of cracks during melting and solidification, and a Ni-based alloy powder for additive manufacturing that can be used to manufacture a Ni-based alloy shaped object. [Brief explanation of the drawings]

[0022] [Figure 1] 10 is a cross-sectional photograph of a molded object showing an example of a crack. [Figure 2] FIG. 1 is a schematic diagram of a powder bed fusion process. [Figure 3] This is a cross-sectional photograph of a primary dendrite in a molded object in which no cracks occurred. [Figure 4] This is a cross-sectional photograph of a secondary dendrite that occurred near a crack. [Figure 5] 1 is a STEM image of Example 2 after additive manufacturing. [Figure 6] 10 is a cross-sectional photograph of the object of Example 2 after the heat treatment step. [Figure 7] 1 is a photograph of gamma-prime precipitates in Example 1 after a heat treatment step. [Figure 8] 1 is a photograph of gamma-prime precipitates in Example 3 after a heat treatment step. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, an embodiment of the present invention will be described. Powder fusion additive manufacturing (hereinafter simply referred to as additive manufacturing) is an additive manufacturing method that applies heat source energy, such as a laser or electron beam, only to a very small, limited area of ​​a metal powder. The heat source energy is then transferred at high speed to melt and solidify the metal powder, instantly melting the fine metal powder and then solidifying it through heat dissipation. The solidification rate of molten metal powder is known to be extremely fast. As a result, some Ni-based alloy compositions have been subject to the issue of cracking during solidification during additive manufacturing. Figure 1 shows a cross-sectional photograph of a molded object showing an example of cracking. It can be seen that elongated cracks have formed in the molding direction. The mechanism behind this is that during solidification, the phase transformation occurs: from a high temperature where the entire material is liquid, to a coexistence of liquid and solid phases as the temperature decreases, and then to a pure solid phase as the temperature decreases further. However, in additive manufacturing, the extremely fast cooling rate causes low-melting-point segregation at the grain boundaries, which then shrinks during cooling, resulting in cracks at the grain boundaries. As a result, as shown in Figure 1, cracks propagate in the stacking direction, which is the direction of cooling. Based on the above, the following describes an embodiment of the present invention, in which a new composition of a Ni-based alloy that does not crack when manufactured using additive manufacturing methods, and a method for manufacturing a molded object using additive manufacturing methods using a powder material made of that composition.

[0024] An embodiment of the present invention will be described below. First, a Ni-based alloy powder for additive manufacturing (hereinafter simply referred to as Ni-based alloy powder) will be described, followed by a Ni-based alloy shaped object produced by additive manufacturing using this Ni-based alloy powder and a method for producing the same. However, the present invention is not limited to the embodiment described here, and appropriate combinations and improvements are possible without departing from the technical spirit of the invention.

[0025] [Ni-based alloy powder] The Ni-based alloy powder according to a first embodiment of the present invention contains, by mass, 6% to 12% Cr, 1% to 4% Mo, 4% to 8% Al, 6% to 11% Co, 7% to 12% W, 1% to 5% Ta, 1.5% to 7% Fe, and 0.1% to 0.25% C, with the remainder being Ni and unavoidable impurities. Hereinafter, Cr, Mo, Al, Co, W, Ta, Fe, and C are referred to as essential additive elements. It is also preferable to add one or more of the following: B (greater than 0% to 0.1%), Nb (greater than 0% to 0.5%), Hf (greater than 0% to 0.5%), Ti (greater than 0% to 0.5%), and Zr (greater than 0% to 0.2%). Hereinafter, B, Nb, Hf, Ti, and Zr are referred to as optional additive elements. This Ni-based alloy powder is used for additive manufacturing, as described below.

[0026] <Alloy composition> The reasons for limiting each compositional component in the Ni-based alloy powder of this embodiment will be explained below. First, the essential additive elements will be explained, followed by the optional additive elements. In the following explanation, % indicates mass %. Furthermore, in this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limit values. Furthermore, the upper limit value and the lower limit value can be combined arbitrarily.

[0027] (Essential addition element) (Cr: 6% or more and 12% or less) Cr is effective in improving oxidation resistance and is an important main component for obtaining good oxidation resistance at high temperatures. 6% or more is necessary to improve oxidation resistance through the Cr oxide film. On the other hand, if more than 12% is added, the amount of other alloying elements must be reduced, resulting in a decrease in high-temperature strength and high-temperature creep properties. The preferred range is 7 to 11%, and the more preferred range is 8 to 9%.

[0028] (Mo: 1% or more and 4% or less) Molybdenum (Mo) content must be 1% or more to improve high-temperature strength and high-temperature creep properties through solid solution strengthening (the interaction between solid solution in the crystal and dislocations prevents dislocation movement, resulting in strengthening, mainly tensile strength improvement), and to improve oxidation resistance. However, excessive addition of Mo requires the addition of less of other alloying elements, so the content is set to 4% or less. The content is preferably 1.5 to 3.5% or less, and more preferably 2 to 3%.

[0029] (Al: 4% or more and 8% or less) Al combines with Ni after the aging heat treatment described below to form gamma-prime precipitates. The formation of gamma-prime precipitates improves high-temperature strength and high-temperature creep properties. For this reason, 4% or more is required. Excessive addition of Al generates brittle compounds of NiAl2, so the content is set to 8% or less. The preferred range is 5 to 7%, and the more preferred range is 5.5 to 6.5%.

[0030] (Co: 6% or more and 11% or less) Co is required to be 6% or more to improve high-temperature strength and high-temperature creep properties through solid solution strengthening. If added excessively, it will be difficult to increase the amount of other added elements, so the content is set to 11% or less. The preferred range is 7 to 10%, and the more preferred range is 8 to 9%.

[0031] (W: 7% or more and 12% or less) W needs to be 7% or more to improve high-temperature strength and high-temperature creep properties through solid solution strengthening and carbide formation. Adding too much W makes it difficult to increase the amount of other additive elements and forms an embrittlement phase, so the content is set to 12% or less. It is preferably 8 to 11%, and more preferably 7 to 10%.

[0032] (Ta: 1% or more and 5% or less) Ta combines with Ni after the aging heat treatment described below to form gamma-prime precipitates. The formation of gamma-prime precipitates improves high-temperature strength and high-temperature creep properties. For this reason, 1% or more is required. Since excessive addition makes it difficult to increase the amount of other added elements, the content is set to 5% or less. The preferred range is 1.2 to 4%, and the more preferred range is 1.3 to 3%.

[0033] (Fe: 1.5% or more and 7% or less) The addition of Fe is effective in preventing cracking. Because Fe reduces high-temperature strength and high-temperature creep properties, it is generally not added to Ni-based alloys, which have excellent high-temperature properties. However, in the present invention, it has been demonstrated that Fe is effective in preventing cracking. Furthermore, it has been demonstrated that a small amount of Fe reduces high-temperature properties only slightly. Therefore, 1.5% or more is necessary to prevent cracking. However, excessive addition significantly reduces high-temperature strength and high-temperature creep properties, so it must be 7% or less. The Fe content is preferably 2 to 6%, and more preferably 2.5 to 5.0%.

[0034] (C: 0.1% or more and 0.25% or less) It was revealed that in Ni-based alloys, the more C added, the more effective it is in preventing cracking, and that forming carbides at grain boundaries can improve high-temperature creep properties, and forming them within grains is also effective in improving high-temperature strength. The carbides that form at grain boundaries and within grains are all composite carbides of W, Mo, and Ta. The amount of C added is The content is set to 0.1% or more to prevent this and to contribute to improving high-temperature strength and high-temperature creep properties. However, if added in excess, the amount of carbides increases too much, resulting in a decrease in toughness and a decrease in high-temperature fatigue strength, so the content is set to 0.25% or less. The content is preferably 0.12 to 0.22%, and more preferably 0.15 to 0.2%.

[0035] (Optional addition element) (B: More than 0% and less than 0.1%) B forms compounds with Cr and Mo at grain boundaries, suppressing grain boundary sliding and improving high-temperature creep properties. However, excessive B addition can actually degrade high-temperature creep properties, so even if added, it must be added in small amounts. Therefore, B is an optional element, and when added, it is set to more than 0% but not more than 0.1%. The preferred range is 0.005 to 0.05%. Adding 0.005% or more of B compounds precipitates uniformly and throughout the grain boundaries, improving high-temperature creep properties. Setting the B content to 0.05% or less prevents degradation of high-temperature creep properties due to excessive addition, even if the B concentration becomes uneven. The preferred range is 0.01 to 0.04%. Since B is unlikely to increase the likelihood of cracking even when added, it is recommended that B be added preferentially among optional elements.

[0036] (Nb: more than 0% and less than 0.5%) Nb is an element that improves high-temperature strength and high-temperature creep properties through solid solution strengthening. However, the addition of Nb makes cracks more likely to occur, so even if added, it must be kept to a small amount. Therefore, Nb is an optional element, and if added, it is limited to more than 0% but not more than 0.5%. The preferred range is 0.05% or more and 0.2% or less.

[0037] (Hf: more than 0% and less than 0.5%) Hf is an element that improves high-temperature creep properties by segregating at grain boundaries when molten metal powder solidifies. However, adding Hf makes cracks more likely to occur, so even if added, it must be small. Therefore, Hf is an optional element, and if added, its content is set to more than 0% but not more than 0.5%. Preferably, it is set to 0.05% or more but not more than 0.2%.

[0038] (Zr: more than 0% and less than 0.2%) Zr is an element that improves high-temperature creep properties by forming carbides at grain boundaries and suppressing grain boundary sliding after the aging heat treatment described below. However, adding excessive Zr can actually reduce creep properties and increase the likelihood of cracking, so even if added, it must be added in small amounts. Therefore, Zr is an optional element, and when added, it is set to more than 0% and 0.2% or less. A preferable range is 0.02 to 0.15%. Adding 0.02% or more disperses and precipitates Zr carbides uniformly and throughout the grain boundaries, improving high-temperature creep properties, while adding 0.15% or less prevents cracking even when forming complex shapes. A more preferable range is 0.05 to 0.13%.

[0039] (Ti: more than 0% and less than 0.5%), Ti is an element that improves high-temperature strength and high-temperature creep properties by forming gamma-prime precipitates, which are compounds with Ni, after the aging heat treatment described below. However, the addition of Ti makes cracks more likely to occur, so even if Ti is added, it must be kept to a small amount. Therefore, Ti is an optional element, and if added, its content is set to more than 0% but not more than 0.5%. Preferably, it is 0.05% or more but not more than 0.2%. More preferably, it is 0.05% or more but not more than 0.1%.

[0040] Among the optional elements, B is an optional element, but its addition does not promote cracking, and a small amount can improve creep properties. Nb and Hf are also optional elements, but a small amount prevents cracking and improves creep properties. Similarly, a small amount of Zr and Ti does not cause cracking, and creep properties can be improved by aging heat treatment.

[0041] (unavoidable impurities) Furthermore, the remainder contains inevitable impurities. Inevitable impurities refer to trace elements mixed in the raw materials and trace amounts of impurities that are technically difficult to remove due to reactions with various members contacted during the manufacturing process. Among these impurities, the impurities that should be particularly restricted are P, S, O, N, etc. It is preferable that P is 0.01% or less, S is 0.01% or less, O is 0.1% or less, and N is 0.1% or less. Of course, it is more preferable that the content of these inevitable impurities is less, and it is even better if it is 0%.

[0042] Furthermore, the remainder may further contain trace elements with a deoxidizing effect such as Mn and Si. It is preferable that each of these trace elements is 1.0% or less. More preferably, it is 0.5% or less. The composition of the alloy powder can be analyzed using, for example, high-frequency inductively coupled plasma (ICP) optical emission spectrometry.

[0043] <Particle size distribution of Ni-based alloy powder> Regarding the particle size distribution of the Ni-based alloy powder of this embodiment, if the particle size is too small, the fluidity will deteriorate. Conversely, if the particle size is too large, the accuracy of the shaped product will deteriorate and the defect rate will also increase. Therefore, in the cumulative distribution curve representing the relationship between the particle size obtained by the laser diffraction method and the volume integration from each particle size, it is preferable that the particle size D50 (average particle size) corresponding to a cumulative frequency of 50% is 10 μm or more and 100 μm or less. More preferably, it is 20 μm or more and 50 μm or less. As a method for manufacturing such Ni-based alloy powder, a gas atomization method, a water atomization method, a disk atomization method, etc. can be used, but it is preferable to produce it by the gas atomization method which is easy to obtain spherical powder and has a low manufacturing cost.

[0044] [Manufacturing method of additive manufactured object] A second embodiment of the present invention relates to a method for producing a Ni-based alloy shaped product, which is characterized by supplying a Ni-based alloy powder for additive manufacturing containing, by mass %, at least the following additive elements: Cr: 6% to 12%, Mo: 1% to 4%, Al: 4% to 8%, Co: 6% to 11%, W: 7% to 12%, Ta: 1% to 5%, Fe: 1.5% to 7%, and C: 0.1% to 0.25%, with the remainder being Ni and unavoidable impurities; selectively irradiating the supplied Ni-based alloy powder with heat source energy to partially melt and solidify the Ni-based alloy powder; and performing a powder melting additive manufacturing process in which the supplying and melting and solidifying steps are repeated to obtain a Ni-based alloy shaped product. The Ni-based alloy powder for additive manufacturing preferably contains one or more of B: more than 0% and not more than 0.1%, Nb: more than 0% and not more than 0.5%, Hf: more than 0% and not more than 0.5%, Ti: more than 0% and not more than 0.5%, and Zr: more than 0% and not more than 0.2%. Laser light is preferably used as the heat source energy.

[0045] An embodiment of a method for manufacturing a Ni-based alloy shaped product using the Ni-based alloy powder described above will be described. The method for manufacturing a Ni-based alloy shaped product according to this embodiment is an additive manufacturing method that involves supplying the Ni-based alloy powder described above, selectively irradiating the supplied Ni-based alloy powder with laser light to partially melt and solidify the powder, and then repeating the steps of supplying the Ni-based alloy powder and melting and solidifying the powder. Generally, additive manufacturing methods using metal powder as a raw material are called Powder Bed Fusion (PBE). Fusion (PBF) and Directed Energy Deposition (DED) The method for producing a Ni-based alloy shaped article according to this embodiment can be broadly divided into two types: Deposition (DED) and Plasma Deposition (PDE). Either method can be applied.

[0046] Figure 2 shows a schematic diagram of the powder bed fusion method as an example of this embodiment. Powder 1 in a powder supply container 9 is pushed up by raising the powder supply stage 2, and is supplied onto a modeling box 10 by moving a recoater 3 in the X direction. Any remaining powder 1 goes into a powder recovery box 11. Next, the laser beam 5 emitted from a laser oscillator 4 is irradiated at a predetermined irradiation area 7, and the irradiation position is controlled (scanned) by a galvanometer scanner 6, thereby melting and solidifying the powder 1. Next, the modeling stage 8 is lowered. This process is repeated to create a three-dimensional model.

[0047] By subjecting the Ni-based alloy shaped object produced in this way immediately after additive manufacturing to a heat treatment process consisting of solution heat treatment and aging heat treatment, it is possible to further improve its high-temperature strength.

[0048] Solution heat treatment is typically performed to homogenize the composition, and in the case of the Ni-based alloy shaped product of this embodiment, to eliminate the boundaries 23 of the primary dendrite structure that solidification segregation occurs. If the solution heat treatment temperature is too low, the diffusion rate is slow and the boundaries 23 of the primary dendrite structure do not disappear, while if the temperature is too high, the Ni-based alloy shaped product melts. Therefore, the heat treatment temperature is preferably 1160°C or higher and 1300°C or lower. Furthermore, if the solution heat treatment time is too short, the boundaries 23 of the primary dendrite structure do not disappear, while if it is too long, the crystal grains become coarse and the high-temperature strength decreases. Therefore, the heat treatment time is preferably 1 hour or higher and 20 hours or lower. In summary, the solution heat treatment in this embodiment can be described as a process in which the Ni-based alloy shaped product after additive manufacturing is held in a furnace set at a heat treatment temperature of 1160°C or higher and 1300°C or lower for a heat treatment time of 1 hour or higher and 20 hours or lower, followed by rapid cooling. In this case, it is preferable to use a vacuum or nitrogen atmosphere during the solution heat treatment and rapid cooling, as this can prevent oxidation of the Ni-based alloy shaped article.

[0049] Aging heat treatment is performed after solution heat treatment to precipitate fine gamma-prime precipitates of NiAl or NiTa, called γ'. As described above, aging heat treatment improves high-temperature strength by intragranular precipitation of gamma-prime precipitates. If the aging heat treatment temperature is too low and the time is too short, the aging heat treatment is insufficient and high-temperature strength is not improved. On the other hand, if the aging heat treatment temperature is too high and the time is too long, overaging occurs, resulting in coarsening of the gamma-prime precipitates and a decrease in high-temperature strength. Therefore, the aging heat treatment temperature is preferably 840°C to 1100°C, and the heat treatment time is preferably 5 hours to 30 hours. In summary, the aging heat treatment in this embodiment can be described as a process in which a Ni-based alloy shaped product after solution heat treatment is held in a furnace set at a heat treatment temperature of 840°C to 1100°C for a heat treatment time of 5 hours to 30 hours, and then removed from the furnace and cooled. In this case, it is preferable to use a vacuum or nitrogen atmosphere during the solution heat treatment and rapid cooling, as this can prevent oxidation of the Ni-based alloy shaped article.

[0050] [Ni-based alloy shaped object] The Ni-based alloy shaped product obtained by the above-described method for manufacturing a Ni-based alloy shaped product contains, by mass, at least the following additive elements: Cr: 6% to 12%, Mo: 1% to 4%, Al: 4% to 8%, Co: 6% to 11%, W: 7% to 12%, Ta: 1% to 5%, Fe: 1.5% to 7%, and C: 0.1% to 0.25%, with the balance being Ni and unavoidable impurities. The Ni-based alloy powder for additive manufacturing preferably contains one or more of: B: >0% to 0.1%, Nb: >0% to 0.5%, Hf: >0% to 0.5%, Ti: >0% to 0.5%, and Zr: >0% to 0.2%. The chemical composition and content of the Ni-based alloy shaped product are the same as those of the Ni-based alloy powder, and therefore are not described here.

[0051] <Structure of Ni-based alloy molded object after additive manufacturing> The Ni-based alloy shaped product of this embodiment has a dendritic structure as shown in FIG. 3 . Here, the boundary width between the primary dendritic structures 21 is preferably 0.4 μm or less. As described above, in shaped products manufactured by conventional additive manufacturing methods using Ni-based alloy powder, solidification segregation occurs at grain boundaries during rapid solidification in the additive manufacturing process, resulting in tensile stress and cracking. Cracking is particularly prevalent in Ni-based alloy shaped products with alloy compositions that form gamma-prime precipitates. The Ni-based alloy shaped product of this embodiment can narrow the boundary width 23 between the primary dendritic structures 21 and prevent cracking by appropriately selecting the composition of the Ni-based alloy powder used as the raw material, as described above. It is more preferable that the Ni-based alloy shaped product does not have a secondary dendritic structure. This reduces segregation at the grain boundaries (boundaries 23), thereby preventing cracking of the shaped product.

[0052] <Structure of Ni-based alloy molded product after heat treatment> The Ni-based alloy shaped object of this embodiment may be subjected to a heat treatment process consisting of the solution heat treatment and the aging heat treatment described above. Among the heat treatment processes, the structure of the Ni-based alloy shaped object subjected to the solution heat treatment is such that the primary dendrite structure 21 disappears and becomes a structure of crystal grains 30 and carbides 32 as shown in FIG. 6. At this time, it is preferable that carbides are formed inside the crystal grains 30 and at the grain boundaries of the crystal grains 30, respectively. The carbide 31 formed inside the crystal grains 30 improves the high-temperature strength by preventing the movement of dislocations (precipitation strengthening). In addition, the carbide 32 formed at the grain boundary 24 suppresses grain boundary sliding, so the high-temperature creep characteristics are improved. As the ratio of carbide formation, if the ratio of carbide decreases, the high-temperature strength and high-temperature creep characteristics decrease, so it is preferably 5% or more, and if the ratio of carbide is too large, embrittlement occurs, so it is preferably 12% or less. More preferably, it is 7% or more and 10% or less, and even more preferably, it is 8% or more and 9% or less. Such a carbide formation ratio can be measured by calculating the area ratio in the cross-sectional structure image. Further, the structure of the Ni-based alloy shaped object subjected to the aging heat treatment after the solution heat treatment is such that gamma prime precipitates are formed in the crystal grains 30. The gamma prime precipitate is an intermetallic compound composed of Ni and Al or Ta, and is represented as Ni3Al or Ni3Ta. Further, when the Ni-based alloy shaped object contains Ti which is an optional additive element, Ni3Ti may be formed as the gamma prime precipitate. By forming such gamma prime precipitates, the high-temperature mechanical properties and creep characteristics are improved.

[0053] <High-temperature strength and creep characteristics of Ni-based alloy shaped object> Ni-based alloys in which gamma-prime precipitates are formed by heat treatment are known to have good high-temperature mechanical properties and creep properties, and have been manufactured by casting, forging, and rolling. However, when an alloy with such a composition is manufactured by an additive manufacturing method, there is a problem that cracks occur due to rapid solidification. By performing additive manufacturing using the powder of the composition of the present invention, even a Ni-based alloy composition in which gamma-prime precipitates are formed after heat treatment can be obtained without cracks, and a shaped body having good high-temperature mechanical properties and creep properties can be obtained. Due to multiple factors such as intragranular precipitation strengthening by gamma-prime precipitates such as Ni3Al and Ni3Ta, intragranular solid solution strengthening by Mo, Co, and W, grain boundary strengthening by B and Zr, grain boundary strengthening by carbide 31, and intragranular precipitation strengthening by carbide 32, the Ni-based alloy shaped body of the present embodiment has excellent high-temperature mechanical properties and creep properties.

Example

[0054] <Composition of Ni-based alloy powder and crack evaluation of shaped body> First, the composition of the metal powder used for shaping is shown in Table 1. Examples 1 to 6 and Comparative Examples 1 to 3 are set from these compositions. Next, using seven types of metal powders with an average particle size (D50) of 25 μm produced by the gas atomization method, by the laser powder bed fusion method (Laser Powder Bed Fusion: LPBF), with a laser diameter of 75 μm, a stacking thickness of 30 μm per layer of metal powder, a scan interval of 0.05 mm fixed, and a laser output of 160 to 200 W and a scan speed of 800 to 1400 mm / s, a cubic shaped body (sample) of 10 mm × 10 mm × 10 mm was produced. In addition, for each shaped body, in order to confirm whether there are cracks in the shaped body, the cross section was mirror-polished and evaluated with a microscope. Table 1 shows all shaping conditions, that is, a combination of three conditions of laser output of 160, 180, and 200 W and four conditions of scan speed of 800, 1000, 1200, and 1400 mm / s For samples that were shaped under a total of 12 conditions of combination and did not crack in all the shaped objects, "no crack" was described on the right side of the table. For samples that cracked under any one of the conditions, "crack" was described on the right side of the table. As a result of cross-sectional observation, cracks occurred in the shaped objects of Comparative Examples 1 to 3, and no cracks occurred in the shaped objects of Examples 1 to 6. Although the C addition amount is set to 0.1 mass% or more in all compositions to suppress cracking, in addition to that, in Examples 1 to 6, it is considered that no cracks occurred because the addition amount of Fe was as much as 2 mass% or more. On the other hand, as the cause of cracking in Comparative Examples 1 to 3, it is considered that in Comparative Examples 1 to 2, more than 0.5 mass% of Ti was added, and in Comparative Example 3, although no Ti was added, the addition amount of Fe was less than 1.0 mass% and insufficient. From this, it was confirmed that an addition amount of C of 0.1 mass% or more, an addition amount of Ti of 0.5 mass% or less, and an addition of at least 1.5 mass% or more of Fe are effective in preventing cracking. Also, in all of Examples 1 to 6, the same amount of B as in the comparative examples was added, but none of them cracked. Therefore, it is considered that the addition of B is less likely to be involved in cracking and is less likely to promote the occurrence of cracking. It is considered that no cracks occurred because the addition amount of Fe was as much as 2 mass% or more. On the other hand, as the cause of cracking in Comparative Examples 1 to 3, it is considered that in Comparative Examples 1 to 2, more than 0.5 mass% of Ti was added, and in Comparative Example 3, although no Ti was added, the addition amount of Fe was less than 1.0 mass% and insufficient. From this, it was confirmed that an addition amount of C of 0.1 mass% or more, an addition amount of Ti of 0.5 mass% or less, and an addition of at least 1.5 mass% or more of Fe are effective in preventing cracking. Also, in all of Examples 1 to 6, the same amount of B as in the comparative examples was added, but none of them cracked. Therefore, it is considered that the addition of B is less likely to be involved in cracking and is less likely to promote the occurrence of cracking. It is considered that the addition of B is less likely to be involved in cracking and is less likely to promote the occurrence of cracking.

[0055]

Table 1

[0056] <Observation of the microstructure of Ni-based alloy shaped objects> Figure 3 shows a 10,000x scanning electron microscope (SEM) micrograph of the structure of Example 2 in a cross section perpendicular to the stacking direction. As with the aforementioned confirmation using the microscope, no cracks are observed in the molded object of Example 2. In addition, in Figure 3, the primary dendrite structure 21 has grown in the stacking direction and has a shape elongated in the stacking direction with a width of about 0.5 to 2 μm. No secondary dendrite structure 22, as shown in Figure 4 described below, is formed at the boundaries 23 between the primary dendrite structures 21, and the width of the boundaries 23 is very narrow, at 0.1 to 0.4 μm. It is therefore believed that no cracks were generated. For this reason, it is preferable to set the width of the boundaries 23 to 0.4 μm or less. It was confirmed that in all of Examples 1 to 6 in which no cracking occurred, no secondary dendritic structures 22 were formed and the width of the boundaries 23 was narrow. Therefore, it was found that by appropriately selecting the composition of the Ni-based alloy powder used as the raw material, it is possible to control the width of the boundaries 23 between the primary dendritic structures 21 to be narrow, thereby preventing cracking.

[0057] FIG. 4 shows a 5000x SEM micrograph of the cross section of Comparative Example 1 perpendicular to the stacking direction. In Comparative Example 1, a crack 20 has occurred vertically through the center of the image in FIG. 4, as confirmed by visual inspection. This indicates that the crack 20 also forms in the stacking direction. Similarly to Example 2, Comparative Example 1 also showed primary dendritic structures 21 with a width of 0.5 to 2 μm growing in the stacking direction. However, secondary dendritic structures 22 were formed at the boundaries 23 between the primary dendritic structures 21 around the cracks 20, resulting in a width of approximately 0.5 to 2 μm, which was wider than that of Example 2. The formation of such secondary dendritic structures 22 is believed to be the cause of the cracks.

[0058] In addition, in order to examine the distribution of elements in Example 2, cross-section observation was carried out using a scanning transmission electron microscope (STEM). Figure 5 shows a cross-section photograph of Example 2 taken by STEM at 25,000 magnifications. Figure 5(a) shows a backscattered electron image, and Figures 5(b) to (l) show the electron distributions of the elements contained in Example 2. The following shows mapping images of the elements Ni, Cr, Al, Mo, Fe, Co, W, Ta, Zr, C, and B. From Figure 5(a), a cross section perpendicular to the stacking direction is observed. Because of this, polygonal primary dendrite structures 21 were observed. Furthermore, in Figures 5(c), (e), (h), (i), and (j), which show the distribution of Cr, Mo, W, Ta, and Zr, the boundaries 23 are closer to white than the primary dendrite structures 21. This indicates that Cr, Mo, W, Ta, and Zr segregate at the boundaries 23 between the primary dendrite structures 21. Because this segregation reduces the mechanical properties, heat treatment is required to eliminate the segregation.

[0059] <Structure of heat-treated Ni-based alloy molded product> The heat treatment process consisting of solution heat treatment and aging heat treatment was performed using Examples 1, 2, and 3. As mentioned above, the solution heat treatment was performed to homogenize the composition and eliminate the boundaries 23 of the solidification segregated primary dendritic structure. The aging heat treatment was performed to precipitate fine gamma-prime precipitates of Ni3Al or Ni3Ta. The solution heat treatment was performed by holding the sample at 1220°C in a vacuum for 10 hours and then quenching in a high-pressure nitrogen atmosphere at 0.5 MPa. The aging heat treatment was then performed by heating the sample to 870°C in a vacuum, holding the sample for 16 hours, and then quenching in a high-pressure nitrogen atmosphere at 0.5 MPa. These solution heat treatments and aging heat treatments can improve high-temperature strength and creep properties.

[0060] FIG. 6 shows a 3000x SEM cross-sectional photograph of Example 2 after the heat treatment process described above. The structure shows crystal grains 30 growing in the stacking direction, and two types of carbides were generated by the heat treatment: carbides 31 (hereinafter simply referred to as carbides 31) precipitated at the grain boundaries of crystal grains 30, and carbides 32 (hereinafter simply referred to as carbides 32) precipitated within crystal grains 30. Analysis using energy dispersive X-ray analysis with a scanning electron microscope revealed that the carbides 31 and 32 were composite carbides containing W or Mo, with the same composition. Furthermore, the cross-sectional photograph was binarized to determine the proportion of the area occupied by the regions of carbides 31 and 32 in the image, which was 8.8%. Similarly, the proportions of carbides 31 and 32 were 8.7% for Example 1, 7.6% for Example 3, and 6.2% for Example 4. In all Examples, the carbide proportion was within the range of 5 to 12%.

[0061] 7 shows a 19,000x SEM photograph of gamma prime precipitates in the heat-treated product of Example 1. The figure shows carbides 31 and 0.1 μm precipitates in the crystal grains. It was confirmed that granular gamma prime precipitates 33 of about 1000 nm had been formed. FIG. 8 shows a cross-sectional photograph of Example 3, which had been subjected to the heat treatment process, taken by an SEM at 30,000 magnifications. In this case, phosphoric acid electrolytic etching was performed on Example 3. Because phosphoric acid electrolytic etching was performed, carbides 31 were not observed, but cubic shapes of 0.1 to 0.2 μm in size were observed. The formation of gamma-prime precipitates 33 was confirmed. Analysis using energy dispersive X-ray analysis with a scanning electron microscope revealed that the gamma-prime precipitates 33 are precipitates containing Ni, Ta, and Al, and are thought to be Ni3Al or Ni3Ta. These precipitates precipitate during aging heat treatment, and because they are hard and ductile, they are effective in improving high-temperature strength and creep properties.

[0062] <Mechanical properties of heat-treated Ni-based alloy molded products> High-temperature tensile tests and creep tests were conducted on Examples 1 to 4, which had undergone the heat treatment process described above. The high-temperature tensile tests and creep tests were conducted in accordance with ASTM-E8 / E8M and ASTM-E139, respectively. Table 2 shows the results of the high-temperature tensile tests. All Examples achieved good tensile strengths of 1300 MPa or more at room temperature, 1000 MPa or more at 700°C, 900 MPa or more at 800°C, 600 MPa or more at 900°C, and 300 MPa or more at 1000°C. The elongation at room temperature was 15% or more, and the elongation at 700°C or higher was 20% or more, and the reduction of area was also good, being 20% ​​or more. Table 3 also shows the results of evaluating the creep properties of Example 1. A creep test was conducted at a test temperature of 800°C and a creep load of 350 MPa, confirming that a good rupture time of 1380 hours was achieved. Furthermore, the time to rupture was 302 hours at a test temperature of 900°C and a creep load of 200 MPa, and 268 hours at a test temperature of 980°C and a creep load of 100 MPa, both of which were satisfactory times to rupture.

[0063] [Table 2]

[0064] [Table 3] [Explanation of symbols]

[0065] 1: Powder, 2: Powder supply stage, 3: Recoater, 4: Laser oscillator, 5: Laser light, 6: Galvano scanner, 7: Irradiation area, 8: Build stage, 9: Powder supply container, 10: Build box, 11: Powder collection box, 20: Crack, 21: Primary dendritic structure, 22: Secondary dendritic structure, 23: Boundary of primary dendritic structure, 24: Grain boundary, 30: Grain, 31: Carbide precipitated at grain boundary, 32: Carbide precipitated within grain, 33: Gamma prime precipitate

Claims

1. As an added element, in mass %, Cr: 6% or more and 11% or less, Mo: 1% or more and 3% or less, Al: 4% or more and 7% or less, Co: 6% or more and 11% or less, W: 7% or more and 10% or less, Ta: 1% or more and 3% or less, Fe: 1.5% or more and 5% or less, C: 0.1% or more and 0.25% or less, The balance of the Ni-based alloy powder for additive manufacturing is Ni and unavoidable impurities.

2. As an additive element, in mass %, Cr: 6% or more and 11% or less, Mo: 1% or more and 3% or less, Al: 4% or more and 7% or less, Co: 6% or more and 11% or less, W: 7% or more and 10% or less, Ta: 1% or more and 3% or less, Fe: 1.5% or more and 5% or less, C: 0.1% or more and 0.25% or less, B: More than 0% and 0.1% or less, The balance of the Ni-based alloy powder for additive manufacturing is Ni and unavoidable impurities.

3. The additive elements are, in mass %, Nb: more than 0% and less than 0.5%, Hf: more than 0% and less than 0.5% The Ni-based alloy powder for additive manufacturing according to claim 1 or 2, characterized in that it contains at least one of the following:

4. The additive elements are, in mass %, Ti: more than 0% and less than 0.5%, Zr: more than 0% and less than 0.2%, The Ni-based alloy powder for additive manufacturing according to claim 1 or 2, characterized in that it contains at least one of the following:

5. In mass%, The B content is 0.005% or more and 0.05% or less, The Ni-based alloy powder for additive manufacturing according to claim 2, characterized in that

6. In mass%, Zr: 0.02% or more and 0.15% or less 5. The Ni-based alloy powder for additive manufacturing according to claim 4, comprising:

7. As an added element, in mass %, Cr: 6% or more and 11% or less, Mo: 1% or more and 3% or less, Al: 4% or more and 7% or less, Co: 6% or more and 11% or less, W: 7% or more and 10% or less, Ta: 1% or more and 3% or less, Fe: 1.5% or more and 5% or less, C: 0.1% or more and 0.25% or less, Supplying a Ni-based alloy powder for additive manufacturing, the balance being Ni and unavoidable impurities; A method for manufacturing a Ni-based alloy object, in which the supplied Ni-based alloy powder for additive manufacturing is selectively irradiated with laser light to melt and solidify it, and a powder fusion additive manufacturing method is performed in which the process of supplying the Ni-based alloy powder for additive manufacturing and melting and solidifying it is repeated to obtain a Ni-based alloy object.

8. As an additive element, in mass %, Cr: 6% or more and 11% or less, Mo: 1% or more and 3% or less, Al: 4% or more and 7% or less, Co: 6% or more and 11% or less, W: 7% or more and 10% or less, Ta: 1% or more and 3% or less, Fe: 1.5% or more and 5% or less, C: 0.1% or more and 0.25% or less, B: More than 0% and 0.1% or less, Supplying a Ni-based alloy powder for additive manufacturing, the balance of which is Ni and unavoidable impurities; A method for manufacturing a Ni-based alloy object, in which the supplied Ni-based alloy powder for additive manufacturing is selectively irradiated with laser light to melt and solidify it, and a powder fusion additive manufacturing method is performed in which the process of supplying the Ni-based alloy powder for additive manufacturing and melting and solidifying it is repeated to obtain a Ni-based alloy object.

9. The Ni-based alloy powder for additive manufacturing contains, as an additive element, in mass %: Nb: more than 0% and less than 0.5%, Hf: more than 0% and less than 0.5% 9. The method for producing a Ni-based alloy shaped article according to claim 7 or 8, characterized in that the Ni-based alloy shaped article contains at least one of the following:

10. The Ni-based alloy powder for additive manufacturing contains, as an additive element, in mass %: Ti: more than 0% and less than 0.5%, Zr: more than 0% and less than 0.2% 9. The method for producing a Ni-based alloy shaped article according to claim 7 or 8, characterized in that the Ni-based alloy shaped article contains at least one of the following:

11. 9. The method for producing a Ni-based alloy shaped article according to claim 7 or 8, wherein the boundary width of the primary dendrite structure in the cross-sectional structure of the Ni-based alloy shaped article is 0.4 μm or less.

12. The method for producing a Ni-based alloy shaped article according to claim 7 or 8, further comprising a heat treatment step of subjecting the Ni-based alloy shaped article obtained by the powder fusion additive manufacturing method to a heat treatment.

13. The method for producing a Ni-based alloy shaped article according to claim 12, wherein the heat treatment step includes a solution heat treatment and an aging heat treatment.

14. 9. The method for producing a Ni-based alloy shaped article according to claim 7 or 8, wherein an area ratio of carbides in a cross-sectional structure of the Ni-based alloy shaped article is 5% or more and 12% or less.

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