Ni-based alloy powder for additive manufacturing and method for manufacturing Ni-based alloy molded article

Abstract

By performing a powder melting additive manufacturing method using the Ni-based alloy powder for additive manufacturing, it is possible to obtain a molded article that does not generate cracks. The Ni-based alloy powder for additive manufacturing contains, in mass%, from 6% to 12% (inclusive) of Cr, from 1% to 4% (inclusive) of Mo, from 4% to 8% (inclusive) of Al, from 6% to 11% (inclusive) of Co, from 7% to 12% (inclusive) of W, from 1% to 5% (inclusive) of Ta, from 1.5% to 7% (inclusive) of Fe, from 0.1% to 0.25% (inclusive) of C, 0.5% or less of Ti, 0.2% or less of Zr, 0.1% or less of B, 0.5% or less of Nb, and 0.5% or less of Hf, with the balance being Ni and unavoidable impurities.

Description

Technical Field

[0001] This invention relates to Ni-based alloy powder for additive manufacturing and a method for manufacturing Ni-based alloy molded objects. Background Technology

[0002] For additive manufacturing components used at high temperatures, such as gas turbines for aircraft and turbines for automotive turbochargers, Ni-based alloys with excellent heat resistance and high-temperature oxidation resistance are required.

[0003] As such a Ni-based alloy, Patent Document 1 discloses, for example, the composition of a Ni-based alloy containing Ni as the main component, and the following components in mass percent: Fe (iron): 2-8, Al (aluminum): 6.1-6.8, Cr (chromium): 12.5-15, W (tungsten): 1.5-4.5, Ta (tantalum): 2.5-5.5, Hf (hafnium): 1.2-2, C (carbon): 0.03-0.13, B (boron): 0.005-0.02, Zr (zirconium): 0.005-0.02, and Si (silicon): 0.005-0.02. According to the invention described in Patent Document 1, a nickel-based alloy with excellent thermomechanical strength, oxidation resistance, and processability can be provided.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Publication No. 2021-504564 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] The alloy disclosed in Patent Document 1 yields additively manufactured articles with excellent strength and oxidation resistance at high temperatures. However, in articles shaped using additive manufacturing methods with Ni-based alloys as disclosed in Patent Document 1, there is a problem of easy formation of solidification cracks, which has not been considered. If cracks occur, there will be a decrease in high-temperature strength, a decrease in creep properties, and a decrease in oxidation resistance.

[0009] Therefore, the object of the present invention is to provide a method for manufacturing Ni-based alloy molded objects that can suppress the generation of cracks during melting and solidification, and Ni-based alloy powder for additive manufacturing of Ni-based alloy molded objects.

[0010] Solution for solving the problem

[0011] The first invention is a Ni-based alloy powder for additive manufacturing, wherein, as additive elements, it contains at least, by mass%, Cr: 6% and 12%, Mo: 1% and 4%, Al: 4% and 8%, Co (cobalt): 6% and 11%, W: 7% and 12%, Ta: 1% and 5%, Fe: 1.5% and 7%, C: 0.1% and 0.25%, with the balance being Ni and unavoidable impurities.

[0012] In addition, the aforementioned Ni-based alloy powder for additive manufacturing preferably contains B: more than 0% and less than 0.1% as an additive element.

[0013] In addition, the aforementioned Ni-based alloy powder for additive manufacturing preferably contains at least one of Nb (niobium): more than 0% and less than 0.5% and Hf: more than 0% and less than 0.5% as an additive element.

[0014] In addition, the aforementioned Ni-based alloy powder for additive manufacturing preferably contains Ti (titanium): more than 0% and less than 0.5% and Zr: more than 0% and less than 0.2% as additive elements.

[0015] In addition, the aforementioned B is preferably 0.005% or more and 0.05% or less.

[0016] In addition, the Zr content is preferably 0.02% or more and 0.15% or less.

[0017] The second invention is a method for manufacturing Ni-based alloy molded objects, which obtains Ni-based alloy molded objects by powder melting additive manufacturing. The powder melting additive manufacturing method repeatedly performs the following steps: supplying Ni-based alloy powder for additive manufacturing, selectively irradiating the supplied Ni-based alloy powder with a laser to melt and solidify it, and performing the supply and melting / solidification of Ni-based alloy powder. The Ni-based alloy powder for additive manufacturing contains, as additive elements, at least by mass% Cr: 6% or more and 12% or less, Mo: 1% or more and 4% or less, Al: 4% or more and 8% or less, Co: 6% or more and 11% or less, W: 7% or more and 12% or less, Ta: 1% or more and 5% or less, Fe: 1.5% or more and 7% or less, and C: 0.1% or more and 0.25% or less, with the balance being Ni and unavoidable impurities.

[0018] In addition, the aforementioned Ni-based alloy powder for additive manufacturing preferably contains B: more than 0% and less than 0.1% as an additive element.

[0019] In addition, the aforementioned Ni-based alloy powder for additive manufacturing preferably contains at least one of Nb (niobium): more than 0% and less than 0.5% and Hf: more than 0% and less than 0.5% as an additive element.

[0020] In addition, the aforementioned Ni-based alloy powder for additive manufacturing preferably contains Ti (titanium): more than 0% and less than 0.5% and Zr: more than 0% and less than 0.2% as additive elements.

[0021] In addition, it is preferable that the boundary width of the primary dendrite structure in the cross-sectional microstructure of the aforementioned Ni-based alloy molded object is less than 0.4 μm.

[0022] In addition, it is preferable to have a heat treatment process after the aforementioned additive manufacturing process, in which the aforementioned Ni-based alloy molded object is subjected to heat treatment.

[0023] In addition, the aforementioned heat treatment process preferably includes solution heat treatment and aging heat treatment.

[0024] Furthermore, in the cross-sectional microstructure of the aforementioned Ni-based alloy molded object, the area ratio of carbides is preferably 5% or more and 12% or less.

[0025] The effects of the invention

[0026] According to the present invention, a method for manufacturing Ni-based alloy molded objects capable of suppressing the generation of cracks during melting and solidification, and Ni-based alloy powder for additive manufacturing of Ni-based alloy molded objects are provided. Attached Figure Description

[0027] Figure 1 This is a cross-sectional photograph of an example of a shape showing a crack.

[0028] Figure 2 This is a schematic diagram of the powder bed melting method.

[0029] Figure 3 This is a cross-sectional photograph of a primary dendrite in a sculpted object that has not yet developed cracks.

[0030] Figure 4 This is a cross-sectional photograph of secondary dendrites that formed near the crack.

[0031] Figure 5 These are STEM images of Example 2 after additive manufacturing.

[0032] Figure 6 This is a cross-sectional photograph of the object from Example 2 after the heat treatment process.

[0033] Figure 7 This is a photograph of the γ′ precipitate in Example 1 after the heat treatment process.

[0034] Figure 8 This is a photograph of the γ′ precipitate in Example 3 after the heat treatment process. Detailed Implementation

[0035] The embodiments of the present invention will be described below.

[0036] Powder melting additive manufacturing (hereinafter referred to as additive manufacturing) involves supplying heat energy, such as laser or electron beam, to a tiny, extremely limited area of ​​a metal powder. This heat energy travels at high speed, causing the metal powder to melt and solidify. The additive manufacturing method involves instantaneously melting the fine metal powder and then releasing heat to solidify it. It is known that the solidification rate of the molten metal powder is extremely fast. Therefore, in some Ni-based alloy compositions, if used for molding, there is a problem of cracking during solidification in additive manufacturing. A cross-sectional photograph of a molded object showing an example of cracking is shown below. Figure 1 It can be seen that elongated cracks 20 were generated in the shaping direction. As a mechanism, the phase transformation during solidification begins at high temperatures when the entire phase is liquid. If the temperature decreases, the liquid and solid phases coexist; if the temperature decreases further, it becomes solely solid. However, in additive manufacturing, the cooling rate is very fast, resulting in low-melting-point segregation at grain boundaries. Cracks then form at these grain boundaries due to shrinkage during cooling. Therefore, as... Figure 1 As shown, the cracks propagate in the direction of cooling, i.e., the stacking direction. Based on the above, the following discloses a new composition of a Ni-based alloy that does not produce cracks even when shaped using additive manufacturing, and a method for manufacturing a shaped object based on additive manufacturing using a powder material composed of this composition.

[0037] The following describes one embodiment of the present invention. First, Ni-based alloy powder for additive manufacturing (hereinafter referred to as Ni-based alloy powder) will be described, followed by a description of a Ni-based alloy model manufactured using the Ni-based alloy powder by additive manufacturing and a method thereof. However, the present invention is not limited to the embodiments listed herein, and appropriate combinations and modifications can be made without departing from the technical concept of the present invention.

[0038] [Ni-based alloy powder]

[0039] The Ni-based alloy powder according to the first embodiment of the present invention is characterized in that, by mass%, it contains Cr: 6% or more and 12% or less, Mo: 1% or more and 4% or less, Al: 4% or more and 8% or less, Co: 6% or more and 11% or less, W: 7% or more and 12% or less, Ta: 1% or more and 5% or less, Fe: 1.5% or more and 7% or less, and C: 0.1% or more and 0.25% or less, with the balance being Ni and unavoidable impurities. Hereinafter, Cr, Mo, Al, Co, W, Ta, Fe, and C are referred to as essential additive elements. Furthermore, it is preferable to add one or more of the following: B: more than 0% and 0.1% or less, Nb: more than 0% and 0.5% or less, Hf: more than 0% and 0.5% or less, Ti: more than 0% and 0.5% or less, and Zr: more than 0% and 0.2% or less. 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 later.

[0040] <Alloy Composition>

[0041] The reasons for limiting the components in the Ni-based alloy powder of this embodiment will be explained below. First, the elements that must be added will be explained, followed by the elements that can be added arbitrarily. It should be noted that in the following description, % represents mass%. In addition, the numerical range indicated by "~" in this specification refers to the range including the values ​​before and after "~" as the lower limit and the upper limit. Furthermore, the upper limit and the lower limit can be combined arbitrarily.

[0042] (Elements must be added)

[0043] (Cr: 6% or more but less than 12%)

[0044] Cr is effective in improving oxidation resistance and is an important main component for obtaining good oxidation resistance at high temperatures. To improve oxidation resistance through Cr oxide coating, a content of 6% or more is required. On the other hand, if more than 12% is added, the amount of other alloying elements needs to be reduced, thus resulting in a decrease in high-temperature strength and high-temperature creep properties. Preferably, it is 7-11%. More preferably, it is 8-9%.

[0045] (Mo: 1% or more but less than 4%)

[0046] To improve high-temperature strength and high-temperature creep properties, as well as oxidation resistance, through solid solution strengthening (strengthening by hindering dislocation movement through the interaction of solid solution with dislocations in the crystal, mainly resulting in improved tensile strength), Mo needs to be at least 1%. On the other hand, if it is added in excess, the amount of other alloying elements needs to be reduced, so it is set to 4% or less. Preferably, it is 1.5 to 3.5% or less. More preferably, it is 2 to 3%.

[0047] (Al: 4% or more but less than 8%)

[0048] Al combines with Ni after the aging heat treatment described later to form γ′ precipitates. The formation of γ′ precipitates improves high-temperature strength and high-temperature creep properties. Therefore, a content of 4% or more is required. Excessive addition will generate brittle NiAl2 compounds, so the content is set to 8% or less. Preferably, it is 5-7%. More preferably, it is 5.5-6.5%.

[0049] (Co: 6% or more but less than 11%)

[0050] To improve high-temperature strength and high-temperature creep properties through solid solution strengthening, Co needs to be at least 6%. If added in excess, it becomes impossible to add other elements; therefore, it is set to 11% or less. Preferably, it is 7-10%. More preferably, it is 8-9%.

[0051] (W: 7% or higher but less than 12%)

[0052] To improve high-temperature strength and high-temperature creep properties through solid solution strengthening and carbide formation, W needs to be 7% or more. If added in excess, it will prevent the addition of other elements and the formation of an embrittled phase; therefore, it is set to 12% or less. Preferably, it is 8-11%. More preferably, it is 7-10%.

[0053] (Ta: 1% or more but less than 5%)

[0054] Ta combines with Ni after the aging heat treatment described later to form γ′ precipitates. The formation of γ′ precipitates improves high-temperature strength and high-temperature creep properties. Therefore, a content of 1% or more is required. If an excessive amount is added, it is impossible to increase the addition of other elements; therefore, it is set to 5% or less. Preferably, it is 1.2 to 4%. More preferably, it is 1.3 to 3%.

[0055] (Fe: 1.5% or more and 7% or less)

[0056] The addition of Fe is effective in preventing cracking. It is known that Fe reduces high-temperature strength and high-temperature creep properties, and is therefore generally not added to Ni-based alloys, which have excellent high-temperature properties. However, in this invention, it is effective in preventing cracking. Furthermore, it is also known that a small amount results in a smaller reduction in high-temperature properties. Therefore, to prevent cracking, 1.5% or more is required. However, if excessive amounts are added, high-temperature strength and high-temperature creep properties will decrease significantly, so 7% or less is required. Preferably, it is 2 to 6%. More preferably, it is 2.5 to 5.0%.

[0057] (C: 0.1% or more and 0.25% or less)

[0058] In Ni-based alloys, it has been established that the higher the amount of carbon added, the more effective it is in preventing cracks. Furthermore, by forming carbides at grain boundaries, it improves high-temperature creep characteristics, and by forming carbides within the grains, it effectively improves high-temperature strength. The carbides formed at grain boundaries and within the grains are composite carbides of W, Mo, and Ta. To help prevent cracks and improve high-temperature strength and creep characteristics, the amount of carbon added is set to 0.1% or more. However, if added excessively, the amount of carbides will increase excessively, resulting in a decrease in toughness and a decrease in high-temperature fatigue strength; therefore, it is set to 0.25% or less. Preferably, it is 0.12 to 0.22%. More preferably, it is 0.15 to 0.2%.

[0059] (Add any elements)

[0060] (B: More than 0% and less than 0.1%)

[0061] Boron (B) forms compounds with Cr and Mo at grain boundaries, inhibiting grain boundary sliding and improving high-temperature creep properties. However, excessive addition of B can actually reduce high-temperature creep properties, so it must be added in small amounts. Therefore, B is added as an optional additive element, and the content is set to more than 0% and less than 0.1%. Preferably, it is 0.005% to 0.05%. By adding more than 0.005%, the B compound precipitates uniformly and throughout the grain boundaries, improving high-temperature creep properties. By setting it to less than 0.05%, even if uneven B concentration occurs, the reduction in high-temperature creep caused by excessive addition can be prevented. More preferably, it is 0.01% to 0.04%. It should be noted that even with the addition of B, the possibility of crack formation is low, so it can be preferentially added among optional additive elements.

[0062] (Nb: above 0% and below 0.5%)

[0063] Nitrogen oxides (Nb) are elements that improve high-temperature strength and high-temperature creep properties through solid solution strengthening. However, the addition of Nb can easily cause cracks, so even when added, it needs to be in small amounts. Therefore, Nb can be added arbitrarily, and when added, it is set to more than 0% and less than 0.5%. Preferably, it is more than 0.05% and less than 0.2%.

[0064] (Hf: above 0% and below 0.5%)

[0065] Hf is an element that improves high-temperature creep properties by causing grain boundary segregation during the solidification of molten metal powder. However, the addition of Hf can easily cause cracks, so even if added, it needs to be in small amounts. Therefore, Hf is an arbitrary additive element, and when added, it is set to more than 0% and less than 0.5%. Preferably, it is more than 0.05% and less than 0.2%.

[0066] (Zr: greater than 0% and less than 0.2%)

[0067] Zr is an element that, after the aging heat treatment described later, forms carbides at grain boundaries, inhibiting grain boundary slip and thereby improving high-temperature creep properties. However, excessive addition of Zr can actually reduce creep properties or increase the likelihood of cracking; therefore, even when added, it should be in small amounts. Thus, Zr is an optional additive element, and when added, it is set to more than 0% and less than 0.2%. Preferably, it is 0.02% to 0.15%. By adding more than 0.02%, Zr carbides are uniformly and comprehensively dispersed and precipitated at grain boundaries, improving high-temperature creep properties. By setting it to less than 0.15%, even complex shapes can be prevented from cracking. More preferably, it is 0.05% to 0.13%.

[0068] (Ti: above 0% and below 0.5%)

[0069] Ti is an element that, after the aging heat treatment described later, forms a γ′ precipitate as a compound with Ni, thereby improving high-temperature strength and high-temperature creep properties. However, the addition of Ti easily causes cracking, so even if added, it needs to be in small amounts. Therefore, Ti is an arbitrary added element, and when added, it is set to more than 0% and less than 0.5%. Preferably, it is 0.05% or more and less than 0.2%. More preferably, it is 0.05% or more and less than 0.1%.

[0070] Among the arbitrarily added elements, B is an arbitrary addition element, but its addition will not promote crack formation; in small amounts, it can improve creep properties. Similarly, Nb and Hf are arbitrarily added elements, but in small amounts, they will not cause cracks and can improve creep properties. The same applies to Zr and Ti; in small amounts, they will not cause cracks, but their creep properties can be improved by implementing aging heat treatment.

[0071] (Unavoidable impurities)

[0072] Furthermore, the remaining amount contains unavoidable impurities. Unavoidable impurities refer to trace amounts of impurities that are technically difficult to remove due to trace elements mixed in with the raw materials, reactions with various components during the manufacturing process, etc. Among these impurities, impurities such as P, S, O, and N should be particularly limited. P is preferably 0.01% or less, S is preferably 0.01% or less, O is preferably 0.1% or less, and N is preferably 0.1% or less. Of course, the lower the content of these unavoidable impurities, the better; 0% is even more desirable.

[0073] Furthermore, the balance may also contain trace elements such as Mn and Si, which have deoxidizing effects. These trace elements are preferably 1.0% or less, and more preferably 0.5% or less. It should be noted that the composition of the alloy powder can be analyzed, for example, using high-frequency inductively coupled plasma (ICP) emission spectrometry.

[0074] <Particle size distribution of Ni-based alloy powder>

[0075] Regarding the particle size distribution of the Ni-based alloy powder in this embodiment, if the particle size is too small, the flowability deteriorates; conversely, if the particle size is too large, the precision of the molded object deteriorates, and the defect rate increases. Therefore, in the cumulative distribution curve showing the relationship between the particle size determined by laser diffraction and the volume accumulation based on each particle size, the particle size D50 (average particle size) corresponding to 50% of the cumulative frequency is preferably 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, gas atomization, water atomization, disk atomization, etc., can be used, but gas atomization, which easily produces spherical powder and has low manufacturing costs, is preferred.

[0076] [Manufacturing Method of Additively Manufactured Products]

[0077] The method for manufacturing Ni-based alloy molded objects according to the second embodiment of the present invention is characterized in that Ni-based alloy molded objects are obtained by powder melting additive manufacturing, wherein the powder melting additive manufacturing method repeatedly performs the following steps: supplying Ni-based alloy powder for additive manufacturing, selectively irradiating the supplied Ni-based alloy powder with heat source energy to partially melt and solidify the Ni-based alloy powder, and performing supply and melting and solidification, wherein the Ni-based alloy powder for additive manufacturing contains, as additive elements, at least by mass% Cr: 6% or more and 12% or less, Mo: 1% or more and 4% or less, Al: 4% or more and 8% or less, Co: 6% or more and 11% or less, W: 7% or more and 12% or less, Ta: 1% or more and 5% or less, Fe: 1.5% or more and 7% or less, C: 0.1% or more and 0.25% or less, with the balance being Ni and unavoidable impurities. Furthermore, the Ni-based alloy powder for additive manufacturing preferably contains one or more of the following: B: more than 0% and less than 0.1%; Nb: more than 0% and less than 0.5%; Hf: more than 0% and less than 0.5%; Ti: more than 0% and less than 0.5%; and Zr: more than 0% and less than 0.2%. Additionally, a laser is preferably used as the heat source.

[0078] An embodiment of the method for manufacturing Ni-based alloy molded objects using the Ni-based alloy powder described above will be described. The method for manufacturing Ni-based alloy molded objects in this embodiment is based on an additive manufacturing method that repeatedly performs the following steps: supplying the Ni-based alloy powder described above, selectively irradiating the supplied Ni-based alloy powder with a laser to partially melt and solidify it, and performing the supply and melting / solidification of Ni-based alloy powder.

[0079] Generally speaking, additive manufacturing methods using metal powder as raw material can be broadly divided into powder bed fusion (PBF) and directed energy deposition (DED). However, in the manufacturing method of Ni-based alloy molded objects in this embodiment, either method can be applied.

[0080] Figure 2 A schematic diagram of the powder bed melting method, as an example of this embodiment, is shown. Powder 1 in the powder supply container 9 is pushed upwards by raising the powder supply stage 2, and supplied to the molding box 10 by moving the coater 3 in the X direction. The remaining powder 1 enters the powder recovery box 11. Next, the irradiation position of the laser 5 oscillating from the laser oscillator 4 is controlled (scanned) by the electro-detector scanner 6, thereby melting and solidifying the powder 1 in the designated irradiation area 7. Then, the molding stage 8 is lowered. This process is repeated to create a three-dimensional model.

[0081] By subjecting the Ni-based alloy model made in this way to a heat treatment process consisting of solution heat treatment and aging heat treatment, the high-temperature strength can be further improved.

[0082] Solution heat treatment is typically performed not only to achieve uniform composition but also to eliminate the boundaries 23 of the primary dendrites that have segregated during solidification in the Ni-based alloy molded article of this embodiment. If the solution heat treatment temperature is too low, the diffusion rate is slow, and therefore the boundaries 23 of the primary dendrites do not disappear. If it is too high, the Ni-based alloy molded article will melt. Therefore, the heat treatment temperature is preferably 1160°C or higher and 1300°C or lower. In addition, if the solution heat treatment time is too short, the boundaries 23 of the primary dendrites will not disappear. If it is too long, the grains will coarsen and the high-temperature strength will decrease. Therefore, the heat treatment time is preferably 1 hour or more and 20 hours or less. In summary, the solution heat treatment in this embodiment can be described as a process in which the additively manufactured Ni-based alloy molded article is held in a furnace with a heat treatment temperature set at 1160°C or higher and 1300°C or lower for a heat treatment time of 1 hour or more and 20 hours or less, and then removed from the furnace and rapidly cooled. At this point, by setting the atmosphere during solution heat treatment and rapid cooling to a vacuum or nitrogen atmosphere, oxidation of the Ni-based alloy molded object can be prevented, and therefore this is preferred.

[0083] Furthermore, to induce the precipitation of fine γ′ precipitates, known as γ′ Ni3Al or Ni3Ta, aging heat treatment is performed after solution heat treatment. As described above, aging heat treatment causes the γ′ precipitates to precipitate within the grains, thereby improving high-temperature strength. If the aging heat treatment temperature is too low or the time is too short, the aging heat treatment will be insufficient, and the high-temperature strength will not improve. Conversely, if the aging heat treatment temperature is too high or the time is too long, it will result in over-aging, coarsening of the γ′ precipitates, and a decrease in high-temperature strength. Therefore, the heat treatment temperature in the aging heat treatment is preferably 840°C or higher and 1100°C or lower, and the heat treatment time is preferably 5 hours or higher and 30 hours or lower. In summary, the aging heat treatment in this embodiment can be described as a process in which a Ni-based alloy molded object after solution heat treatment is held in a furnace with a heat treatment temperature set at 840°C or higher and 1100°C or lower for a heat treatment time of 5 hours or higher and 30 hours or lower, and then removed from the furnace and cooled. At this point, by setting the atmosphere during solution heat treatment and rapid cooling to a vacuum or nitrogen atmosphere, oxidation of the Ni-based alloy molded object can be prevented, and therefore this is preferred.

[0084] [Ni-based alloy sculptures]

[0085] For the Ni-based alloy molded articles obtained by the aforementioned method for manufacturing Ni-based alloy molded articles, the additive elements, by mass%, contain at least the following: Cr: 6% or more and 12% or less; Mo: 1% or more and 4% or less; Al: 4% or more and 8% or less; Co: 6% or more and 11% or less; W: 7% or more and 12% or less; Ta: 1% or more and 5% or less; Fe: 1.5% or more and 7% or less; C: 0.1% or more and 0.25% or less, with the balance being Ni and unavoidable impurities. Furthermore, the Ni-based alloy powder for additive manufacturing preferably contains one or more of the following: B: more than 0% and 0.1% or less; Nb: more than 0% and 0.5% or less; Hf: more than 0% and 0.5% or less; Ti: more than 0% and 0.5% or less; Zr: more than 0% and 0.2% or less.

[0086] It should be noted that the chemical composition and content of Ni-based alloy molded objects are the same as those of Ni-based alloy powder, so the description is omitted.

[0087] <Microstructure of Ni-based alloy models after additive manufacturing>

[0088] The Ni-based alloy model of this embodiment has Figure 3Such a dendritic structure. At this time, the boundary width between the primary dendrites 21 is preferably 0.4 μm or less. As described above, in the molded articles manufactured by the additive manufacturing method using conventional Ni-based alloy powder, solidification segregation occurs at the grain boundaries during rapid solidification in the additive manufacturing process, thereby generating tensile stress and cracks. In particular, cracks are significantly generated in Ni-based alloy molded articles composed of alloys that form γ′ precipitates. By appropriately selecting the composition of the Ni-based alloy powder used as raw material as described above, the Ni-based alloy molded article of this embodiment can reduce the width of the boundary 23 between the primary dendrites 21 and prevent cracks. It is more preferable that there is no secondary dendrite structure. As a result, segregation at the grain boundaries (boundaries 23) is reduced, and cracks in the molded article can be prevented.

[0089] <Microstructure of Ni-based alloy molded objects after heat treatment>

[0090] The Ni-based alloy molded object of this embodiment can undergo the aforementioned heat treatment process consisting of solution heat treatment and aging heat treatment. In the heat treatment process, the microstructure of the Ni-based alloy molded object that has undergone solution heat treatment is as follows: Figure 6 As shown, the primary dendrite structure 21 disappears, resulting in a structure of grains 30 and carbides 32. At this time, it is preferable that carbides are formed both inside the grains 30 and at the grain boundaries of the grains 30. The carbides 31 formed inside the grains 30 improve high-temperature strength (precipitation strengthening) by hindering dislocation movement. Furthermore, the carbides 32 formed at the grain boundaries 24 suppress grain boundary slip, thus improving high-temperature creep characteristics. Regarding the proportion of carbides formed, a decrease in the proportion of carbides will result in a reduction in high-temperature strength and high-temperature creep characteristics; therefore, 5% or more is preferred. If the proportion of carbides is too large, embrittlement will occur; therefore, 12% or less is preferred. More preferably, 7% or more and 10% or less is preferred, and even more preferably, 8% or more and 9% or less is preferred. Such a carbide formation proportion can be determined by calculating the area ratio in the cross-sectional microstructure image. Additionally, in the Ni-based alloy molded object that has undergone aging heat treatment after solution heat treatment, γ′ precipitates are formed in the grains 30. γ′ precipitates are intermetallic compounds composed of Ni and Al or Ta, denoted as Ni3Al or Ni3Ta. Additionally, Ni3Ti can also form as γ′ precipitates when Ti is present as an arbitrary additive element in a Ni-based alloy. The formation of such γ′ precipitates improves high-temperature mechanical properties and creep characteristics.

[0091] <High-temperature strength and creep characteristics of Ni-based alloy molded objects>

[0092] Ni-based alloys with γ′ precipitates formed through heat treatment are known to possess excellent high-temperature mechanical properties and creep characteristics, and have been manufactured to date using casting, forging, and rolling. However, when such alloys are manufactured using additive manufacturing methods, cracking due to rapid solidification occurs. By using the powder of the composition of this invention for additive manufacturing, even Ni-based alloy compositions with γ′ precipitates formed after heat treatment do not develop cracks, and molded articles with excellent high-temperature mechanical properties and creep characteristics can be obtained. Due to multiple factors such as intragranular precipitation strengthening caused by γ′ precipitates like Ni3Al and Ni3Ta, intragranular solid solution strengthening caused by Mo, Co, and W, grain boundary strengthening caused by B and Zr, grain boundary strengthening caused by carbide 31, and intragranular precipitation strengthening caused by carbide 32, the Ni-based alloy molded articles of this embodiment exhibit excellent high-temperature mechanical properties and creep characteristics.

[0093] Example

[0094] <Composition of Ni-based alloy powder and crack evaluation of molded bodies>

[0095] First, the composition of the metal powder used for modeling is shown in Table 1. These compositions are used as Examples 1-6 and Comparative Examples 1-3. Next, using metal powders with an average particle size (D50) of 25 μm prepared by gas atomization, cubic models (samples) of 10 mm × 10 mm × 10 mm were fabricated using laser powder bed fusion (LPBF). The laser diameter was fixed at 75 μm, the layer thickness of each metal powder layer was 30 μm, the scanning interval was 0.05 mm, and the laser output power was 160-200 W, with a scanning speed of 800-1400 mm / s. In addition, for each model, the cross-section was mirror-polished and evaluated under a microscope to check for cracks. In Table 1, samples that did not develop cracks in any of the 12 molded products under all molding conditions (i.e., laser output power of 160, 180, and 200 W, and scanning speed of 800, 1000, 1200, and 1400 mm / s) are listed as "crack-free" on the right side of the table. Samples that developed cracks under any of the conditions are listed as "cracked" on the right side of the table. Cross-sectional observation showed that cracks occurred in the molded products of Comparative Examples 1-3, but no cracks occurred in the molded products of Examples 1-6. To suppress cracking, the amount of C added was set to 0.1% by mass or more in all components; however, it is believed that in Examples 1-6, since the amount of Fe added was as high as 2% by mass or more, no cracks occurred. On the other hand, the reason for the cracks in Comparative Examples 1-3 is believed to be that more than 0.5% by mass of Ti was added in Comparative Examples 1-2, while in Comparative Example 3, although no Ti was added, the amount of Fe added was less than 1.0% by mass, which was insufficient. Therefore, it was confirmed that adding 0.1% by mass or more of C, 0.5% by mass or less of Ti, and at least 1.5% by mass of Fe is effective in preventing cracks. Furthermore, in all Examples 1 to 6, although the same amount of B as in the Comparative Examples was added, no cracks appeared. Therefore, it is believed that the addition of B is unlikely to cause cracks and does not promote crack formation.

[0096] [Table 1]

[0097]

[0098] In the table, "-" indicates no content.

[0099] <Microstructure observation of Ni-based alloy molded objects>

[0100] Figure 3This is a 10,000x magnified tissue photograph of a section perpendicular to the stacking direction, obtained using a scanning electron microscope (SEM) in Example 2. Similar to the confirmation using the aforementioned microscope, no cracks were observed in the specimen of Example 2. Furthermore, in Figure 3 In this process, primary dendrites 21 grow along the stacking direction, forming elongated shapes with a width of approximately 0.5–2 μm along the stacking direction. The boundaries 23 between the primary dendrites 21 are not visible (as described later). Figure 4 The secondary dendrite structure 22 shown has a very narrow boundary 23 with a width of 0.1 to 0.4 μm. Therefore, it is considered that no cracks are formed. Thus, the width of the boundary 23 is preferably 0.4 μm or less. In Examples 1 to 6 where no cracks were formed, the secondary dendrite structure 22 was not formed, confirming the narrow width of the boundary 23. Therefore, it can be seen that by appropriately selecting the composition of the Ni-based alloy powder used as raw material, cracks can be prevented by narrowing the width of the boundaries 23 between the primary dendrite structures 21.

[0101] in addition, Figure 4 This image shows a 5000x SEM photograph of the tissue in Comparative Example 1, perpendicular to the stacking direction. In Comparative Example 1, as visually confirmed, the cross-section is longitudinally... Figure 4 Crack 20 is generated in the center of the image. This indicates that crack 20 also forms in the stacking direction. Furthermore, in Comparative Example 1, similar to Example 2, it can be confirmed that primary dendrites 21 with a width of 0.5~2 μm grow in the stacking direction. However, since secondary dendrites 22 form at the boundaries 23 of the primary dendrites 21 around crack 20, the width of the boundaries 23 is approximately 0.5~2 μm, which is wider than in Example 2. It is believed that the formation of such secondary dendrites 22 is the cause of the crack.

[0102] In addition, cross-sectional observations were performed using a scanning transmission electron microscope (STEM) to investigate the distribution of elements in Example 2. Figure 5 This shows a cross-sectional photograph obtained using STEM at 25,000x magnification in Example 2. Figure 5 (a) shows a reflected electron image. Figure 5 Images (b) to (l) show mapping images of Ni, Cr, Al, Mo, Fe, Co, W, Ta, Zr, C, and B, which are elements contained in Example 2. Figure 5 In (a), a polygonal primary dendritic structure 21 is observed by examining a cross-section perpendicular to the stacking direction. Furthermore, in the diagram representing the distribution of Cr, Mo, W, Ta, and Zr... Figure 5In (c), (e), (h), (i), and (j), boundary 23 is closer to white than the primary dendrite 21. This indicates that Cr, Mo, W, Ta, and Zr segregate at the boundaries 23 of the primary dendrites 21. This segregation reduces mechanical properties, therefore heat treatment is required to eliminate it.

[0103] <Microstructure of Ni-based alloy molded objects after heat treatment>

[0104] Examples 1, 2, and 3 were used to implement a heat treatment process consisting of solution heat treatment and aging heat treatment. It should be noted that, as described above, solution heat treatment is performed to achieve a homogenized composition, eliminating the boundaries 23 of the primary dendrites that segregate during solidification. Aging heat treatment is performed to precipitate fine γ′ precipitates of Ni3Al or Ni3Ta. Solution heat treatment involves holding the solution at 1220°C in a vacuum for 10 hours, followed by rapid cooling in a high-pressure nitrogen atmosphere at 0.5 MPa. Subsequently, aging heat treatment involves heating to 870°C in a vacuum and holding for 16 hours, followed by rapid cooling in a high-pressure nitrogen atmosphere at 0.5 MPa. This solution heat treatment and aging heat treatment improve high-temperature strength and creep properties.

[0105] Figure 6 This image shows a 3000x cross-sectional photograph obtained using SEM of Example 2, which underwent the aforementioned heat treatment process. The grains 30 formed a structure grown in the stacking direction. Two types of carbides were generated through heat treatment: carbides 31 precipitated at the grain boundaries of the grains 30 (hereinafter simply referred to as carbides 31) and carbides 32 precipitated within the grains 30 (hereinafter simply referred to as carbides 32). Analysis using energy-dispersive X-ray diffraction (EDXD) with a scanning electron microscope revealed that the carbides were composites containing W or Mo, and that carbides 31 and 32 had the same composition. Furthermore, the cross-sectional photograph was binarized to determine the proportion of the area occupied by carbides 31 and 32 within the image area, which was 8.8%. Similarly, the proportion of carbides 31 and 32 was 8.7% in Example 1, 7.6% in Example 3, and 6.2% in Example 4. The carbide proportion in any of the examples was in the range of 5% to 12%.

[0106] exist Figure 7 The image shown is a 19,000x SEM image of the γ′ precipitates in the model of Example 1, which underwent a heat treatment process. Figure 7 It can be confirmed that granular γ′ precipitates 33 with a diameter of approximately 0.1 μm were formed in carbide 31 and the grains. Furthermore, Figure 8The image shows a 30,000x cross-sectional photograph obtained using SEM of Example 3, which underwent a heat treatment process. Phosphoric acid electrolytic etching was performed during cross-sectional observation in Example 3. Due to the phosphoric acid electrolytic etching, carbides 31 were not observed, but the formation of cubic γ′ precipitates 33 with a size of 0.1–0.2 μm was confirmed. Analysis using energy-dispersive X-ray diffraction (EDXD) with scanning electron microscopy revealed that γ′ precipitates 33 are precipitates containing Ni, Ta, and Al, and are considered to be Ni3Al or Ni3Ta. These precipitates, formed during aging heat treatment, are hard and ductile, and therefore effective in improving high-temperature strength and creep properties.

[0107] <Mechanical properties of Ni-based alloy molded objects after heat treatment>

[0108] High-temperature tensile tests and creep tests were conducted on Examples 1-4, which underwent the aforementioned heat treatment process. The high-temperature tensile tests and creep tests were performed according to ASTM-E8 / E8M and ASTM-E139, respectively. Table 2 shows the results of the high-temperature tensile tests. All examples obtained good tensile strengths of ≥1300 MPa at room temperature, ≥1000 MPa at 700°C, ≥900 MPa at 800°C, ≥600 MPa at 900°C, and ≥300 MPa at 1000°C. The elongation at room temperature was ≥15%, and the elongation at test temperatures above 700°C was ≥20%, with a reduction of area also ≥20%, which is considered good. Furthermore, the results of evaluating creep characteristics in Example 1 are shown in Table 3. A creep test was conducted at a test temperature of 800°C and a creep load of 350 MPa, confirming a good fracture time of 1380 hours. Furthermore, the fracture time was 302 hours at a test temperature of 900℃ and a creep load of 200MPa, and 268 hours at a test temperature of 980℃ and a creep load of 100MPa, both of which are good fracture times.

[0109] [Table 2]

[0110]

[0111] [Table 3]

[0112]

[0113] Explanation of reference numerals in the attached figures

[0114] 1: Powder; 2: Powder supply stage; 3: Coating device; 4: Laser oscillator; 5: Laser; 6: Electro-detector; 7: Irradiation area; 8: Molding stage; 9: Powder supply container; 10: Molding box; 11: Powder recovery box; 20: Crack; 21: Primary dendrite structure; 22: Secondary dendrite structure; 23: Boundary of primary dendrite structure; 24: Grain boundary; 30: Grain; 31: Carbide precipitated at grain boundary; 32: Carbide precipitated within grain; 33: γ′ precipitate.

Claims

1. A Ni-based alloy powder for additive manufacturing, wherein, As an added element, it contains at least [amount]% by mass. Cr: 6% or more but less than 12% Mo: 1% or more but less than 4% A1: 4% or higher but less than 8% Co: 6% or more but less than 11% W: 7% or higher but less than 12% Ta: 1% or more but less than 5% Fe: 1.5% or more and less than 7% C: Above 0.1% and below 0.25%, The balance is Ni and unavoidable impurities.

2. The Ni-based alloy powder for additive manufacturing according to claim 1, characterized in that, As the added element, it contains, by mass% B: More than 0% and less than 0.1%.

3. The Ni-based alloy powder for additive manufacturing according to claim 1, characterized in that, As the added element, it contains, by mass% Nb: Above 0% and below 0.5% Hf: at least one of the following: more than 0% and less than 0.5%.

4. The Ni-based alloy powder for additive manufacturing according to claim 1, characterized in that, As the added element, it contains, by mass% Ti: Above 0% and below 0.5% Zr: at least one of the following: more than 0% and less than 0.2%.

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

6. The Ni-based alloy powder for additive manufacturing according to claim 1, characterized in that, Contains, by mass% Zr content above 0.02% and below 0.15%.

7. A method for manufacturing a Ni-based alloy model, wherein the Ni-based alloy model is obtained by powder melting additive manufacturing, wherein the powder melting additive manufacturing method repeatedly performs the following steps: Supply of Ni-based alloy powder for additive manufacturing The supplied Ni-based alloy powder for additive manufacturing is selectively irradiated with a laser to melt and solidify it; this process of supplying and melting / solidifying the Ni-based alloy powder for additive manufacturing is performed. The Ni-based alloy powder for additive manufacturing contains, as an additive element, at least as a percentage by mass: Cr: 6% or more but less than 12% Mo: 1% or more but less than 4% A1: 4% or higher but less than 8% Co: 6% or more but less than 11% W: 7% or higher but less than 12% Ta: 1% or more but less than 5% Fe: 1.5% or more and less than 7% C: Above 0.1% and below 0.25%, The balance is Ni and unavoidable impurities.

8. The method for manufacturing Ni-based alloy molded objects according to claim 7, characterized in that, As an additive element, the Ni-based alloy powder for additive manufacturing contains, by mass%, B: More than 0% and less than 0.1%.

9. The method for manufacturing Ni-based alloy molded objects according to claim 7, characterized in that, As an additive element, the Ni-based alloy powder for additive manufacturing contains, by mass%, Nb: Above 0% and below 0.5% Hf: at least one of the following: more than 0% and less than 0.5%.

10. The method for manufacturing Ni-based alloy molded objects according to claim 7, characterized in that, As an additive element, the Ni-based alloy powder for additive manufacturing contains, by mass%, Ti: Above 0% and below 0.5% Zr: at least one of the following: more than 0% and less than 0.2%.

11. The method for manufacturing Ni-based alloy molded objects according to claim 7, characterized in that, The boundary width of the primary dendrites in the cross-sectional microstructure of the Ni-based alloy model is less than 0.4 μm.

12. The method for manufacturing Ni-based alloy molded objects according to claim 7, characterized in that, It has a heat treatment process for heat-treating the Ni-based alloy model obtained by the powder melt additive manufacturing method.

13. The method for manufacturing Ni-based alloy molded objects according to claim 12, characterized in that, The heat treatment process includes solution heat treatment and aging heat treatment.

14. The method for manufacturing Ni-based alloy molded objects according to claim 7, characterized in that, In the cross-sectional microstructure of the Ni-based alloy model, the area ratio of carbides is more than 5% and less than 12%.

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