Heat-resistant alloy

Abstract

To provide a heat-resistant alloy capable of improving alloy performance.SOLUTION: Provided is heat-resistant alloy in which the content of Ni is 58.0 mass% or more, the content of Cr is 20.0 mass% or more and 23.0 mass% or less, the content of Mo is 8.0 mass% or more and 10.0 mass% or less, the content of Nb is 3.15 mass% or more and 4.15 mass% or less, and the content of O is 0.002 mass% or more and 0.1 mass% or less, where the alloy contains Y, the ratio between the content of O in terms of mass and the content of Y in terms of mass is 0.5 or more and 100 or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a heat-resistant alloy. [Background technology]

[0002] Heat-resistant alloys are used in aircraft engines and the like. Additive manufacturing is known as a method for forming heat-resistant alloy compacts (e.g., Patent Document 1). It is known that ceramic particles containing Y (yttrium) or the like are dispersed within and at the grain boundaries of an alloy having columnar crystals (e.g., Patent Document 2). It is known that Y is added to a Ni (nickel)-based alloy (e.g., Non-Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-83959 [Patent Document 2] Japanese Patent Application Laid-Open No. 2019-60006 [Non-patent literature]

[0004] [Non-Patent Document 1] Journal of the Japan Institute of Metals, Vol. 70, No. 4 (2006), pp. 380-383. [Non-patent document 2] Materials Science and Engineering A 551 (2012), pp.236-240 Summary of the Invention [Problem to be solved by the invention]

[0005] For example, alloy compacts formed using additive manufacturing methods contain a large amount of O (oxygen). Alloys containing a large amount of oxygen can deteriorate their performance. Patent Document 2 and Non-Patent Documents 1 and 2 describe the addition of Y to alloys, but do not describe the relationship with O.

[0006] The present invention has been made in view of the above-mentioned problems, and has as its object to improve the performance of an alloy by specifying the ratio of oxygen to yttrium. [Means for solving the problem]

[0007] The present invention is a heat-resistant alloy having a Ni content of 58.0 mass% or more, a Cr content of 20.0 mass% or more and 23.0 mass% or less, a Mo content of 8.0 mass% or more and 10.0 mass% or less, a Nb content of 3.15 mass% or more and 4.15 mass% or less, and an O content of 0.002 mass% or more and 0.1 mass% or less, and containing Y, wherein the ratio of the Y content, in mass equivalent, to the O content, in mass equivalent, is 0.5 or more and 100 or less.

[0008] In the above configuration, the Fe content may be 5.0 mass% or less, the Al content may be 0.4 mass% or less, the Ti content may be 0.4 mass% or less, the Mn content may be 0.5 mass% or less, the C content may be 0.1 mass% or less, the Si content may be 0.5 mass% or less, the Co content may be 1.0 mass% or less, and the S content may be 0.015 mass% or less, with the remainder being Ni.

[0009] The present invention is a heat-resistant alloy having a Ni content of 41.0% by mass or more and 54.0% by mass or less, a Cr content of 20.5% by mass or more and 23.0% by mass or less, a Mo content of 8.0% by mass or more and 10.0% by mass or less, an Fe content of 17.0% by mass or more and 20.0% by mass or less, a W content of 0.2% by mass or more and 1.0% by mass or less, a Co content of 0.5% by mass or more and 2.5% by mass or less, and an O content of 0.002% by mass or more and 0.1% by mass or less, and containing Y, wherein the ratio of the Y content, in mass equivalent, to the O content, in mass equivalent, is 0.5 or more and 100 or less.

[0010] In the above configuration, the Al content may be 0.5 mass% or less, the Ti content may be 0.15 mass% or less, the C content may be 0.1 mass% or less, the Si content may be 1.0 mass% or less, and the remainder may be Ni. [Effects of the Invention]

[0011] According to the present invention, the performance of the alloy can be improved. [Brief explanation of the drawings]

[0012] [Figure 1] Figures 1(a) to 1(f) are scanning electron microscope images of STA-treated samples of the molded bodies obtained in Example 1 and Comparative Example 1, with Figures 1(a) to 1(c) being images of the molded body of Example 1 and Figures 1(d) to 1(f) being images of the molded body of Comparative Example 1. [Figure 2] FIG. 2 is a magnified image of Y2O3 particles in a sample obtained by slowly cooling the compact obtained in Example 1 from 1180°C to 1040°C at a rate of 50°C / h, observed with a transmission electron microscope. [Figure 3] 3(a) and 3(b) are graphs showing the creep characteristics and oxidation characteristics of the compacts obtained in Example 1 and Comparative Example 1, respectively. [Figure 4] 4(a) and 4(b) are scanning electron microscope images of the HIP sintered compacts obtained in Example 2 and Comparative Example 2, respectively. [Figure 5] FIG. 5 is a graph showing the creep properties of the HIP sintered compacts obtained in Example 2 and Comparative Example 2. [Figure 6] FIG. 6 shows the Ellingham diagrams of each oxide. [Figure 7] FIG. 7(a) is a graph showing the creep properties of the orthogonal direction samples in Example 3, and FIG. 7(b) is a graph showing the creep life and creep ductility as a function of the Y content. [Figure 8] FIG. 8(a) is a graph showing creep properties of the stacking direction DA (direct aging treatment) sample in Example 3, and FIG. 8(b) is a graph showing creep life and creep ductility as a function of Y content. [Figure 9] FIG. 9 is a diagram showing a stress-strain curve of the HIP sintered compact in Example 3. [Figure 10] FIG. 10(a) is a graph showing creep properties in Example 4 and Comparative Example 4, and FIG. 10(b) is a graph showing stress-strain curves. [Figure 11] 11(a) and 11(b) are diagrams showing creep properties in the orthogonal direction and lamination direction after molding for Example 5 and Comparative Example 5. FIG. [Figure 12] 12(a) and 12(b) are diagrams showing creep properties in the orthogonal direction and lamination direction after solution treatment (ST) for Example 5 and Comparative Example 5. FIG. [Figure 13] FIG. 13 is a diagram showing elemental mapping of the spark plasma sintered (SPS) compact in Example 6 using FE-EPMA. [Figure 14] FIG. 14 is a diagram showing elemental mapping of the SPS molded body in Comparative Example 6 using FE-EPMA. [Figure 15] FIG. 15 is a diagram showing an example of a method for producing a heat-resistant alloy formed body. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described in further detail. The heat-resistant alloy material of this embodiment is a heat-resistant alloy material that can be additively manufactured using a laser or an electron beam, and is characterized by containing a main component metal and Y. Hereinafter, the embodiment will be described in detail.

[0014] <Main metal component> Examples of the main component metal include metal elements such as Ni, Ti (titanium), Al (aluminum), Fe (iron), Cr (chromium), Co (cobalt), Nb (niobium), Cu (copper), Mn (manganese), Mo (molybdenum), Ta (tantalum), W (tungsten), Re (rhenium), Ru (ruthenium), Hf (hafnium), and Zr (zirconium), as well as metal oxides such as NiO, TiO, Al2O3, and Cr2O3. These may be used alone or in combination of two or more. In this embodiment, Ni, Ti, and Al, as well as their oxides (NiO, TiO, and Al2O3), and mixtures thereof, are particularly preferred as the main component metal.

[0015] In a compact made using the heat-resistant alloy material of this embodiment, these main component metals, particularly metal oxides, are preferably contained in the compact as an oxidation-resistant film or an oxide dispersion strengthened phase. The amount of each component in the main component metal can be determined arbitrarily depending on the composition. For example, when Ni is the main component, it is preferable to incorporate Ni at 40% by mass or more of the entire alloy material. Furthermore, when Al and Ti are the main components without Ni, it is preferable to incorporate Al and Ti at a total content of 50% by mass or more, or even 90% by mass or more, and both at 5% by mass or more of the entire heat-resistant alloy material.

[0016] Each component used as the main component metal is preferably used in particulate form (i.e., powder). There are no particular restrictions on the average particle size, and the component can be used with any desired particle size. (Method for measuring average particle size) The average particle size can be determined by visually measuring particle sizes observed under a transmission electron microscope and averaging them. Alternatively, the average can be determined by measuring the particle distribution density using a backscattered electron image obtained under a scanning electron microscope.

[0017] <Y(イットリウム)> Y having a purity of 99.9% or higher can be preferably used, and any commercially available metal Y can be used as an additive element without particular restrictions as long as it satisfies this purity. Furthermore, Y is preferably combined with O to form YO particles, with an average particle size of preferably 10 to 200 nm, more preferably 50 to 150 nm. The average particle size in this case can be determined in the same manner as described above.

[0018] Metal-based additive manufacturing involves placing metal powder on a flat surface and irradiating it with a laser only in the necessary areas, causing it to melt and solidify. This process carries the risk of residual oxygen on the powder surface dissolving and remaining in the molded product, degrading the properties of the sintered material. Oxygen also bonds with aluminum, a strengthening element, to form alumina, consuming the aluminum and reducing the high-temperature strength and oxidation resistance of the alloy. Yttrium (Y) bonds more readily with oxygen than aluminum, forming a stable oxide (YO). Therefore, in laser-based additive manufacturing, where oxygen contamination is unavoidable, including Y as an essential component can improve the heat resistance and oxidation resistance of the resulting molded product.

[0019] Additionally, Y2O3 (yttria), an oxide of Y, contributes to high-temperature strengthening as an oxide. However, the mechanical alloying method using yttria particles (a method of creating an alloy by mechanically mixing in a solid state) is extremely costly and unable to form materials with complex shapes, so it has only been applicable to very limited applications. However, with selective laser melting, the presence of dissolved oxygen makes it possible to form materials with complex shapes in which yttria particles, a compound of Y, are uniformly and finely dispersed at the density described below.

[0020] Furthermore, in casting methods other than additive manufacturing using alloy powders that involve special melting and refining processes (including forging after casting), the oxygen content is low at 20 ppm or less, so when Y is added, it does not bond with oxygen but bonds with other alloying elements to form harmful TCP (Topologically Close Packed) phases (see Non-Patent Document 1). Even in polycrystalline alloys, Y hardly bonds with oxygen, but segregates and bonds mainly with alloying elements to form harmful compounds, and the formation is uneven, with no Y oxides being formed throughout the entire compact (Non-Patent Document 2). However, by forming a compact using an additive manufacturing method using a laser from an alloy powder material to which Y has been added in advance, as in this embodiment, it is possible to uniformly generate fine Y oxides.

[0021] <Mixing ratio> The blending ratio of the main component metal and Y is preferably such that, in the compact obtained, the blending ratio of Y is 2 atoms of Y for every 3 atoms of oxygen mixed in as Y2O3 oxide. Specifically, it is preferably adjusted to 0.005 mass% or more and less than 1.0 mass% of the total alloy material, and more preferably 0.01 to 0.5 mass%.

[0022] In addition, in the case of a Ti alloy or a TiAl alloy in which the main component metals are Ti and Al, the Y content is preferably adjusted to be 0.01 mass% or more and less than 1.0 mass% of the entire alloy material, more preferably 0.05 to 0.7 mass%, and most preferably 0.1 to 0.5 mass%.

[0023] Below the lower limit, sufficient performance improvement is not achieved, while adding more than 0.5% by mass results in deterioration of the final molded product. Therefore, it is preferable to keep the amount within the above range. The reason for this difference in effect depending on the amount added is that in the case of additive manufacturing, it is difficult to suppress trace amounts of oxygen even when manufacturing in a vacuum, and unnecessary oxides are formed during additive manufacturing, reducing heat resistance and oxidation resistance. However, by adding Y in the above-mentioned amount, Y2O3 is formed more quickly than oxides of other metal elements, reducing the amount of dissolved oxygen in Ti alloys and TiAl alloys, stabilizing the structure and preventing embrittlement of the substrate, and reducing the amount and size of harmful δ (delta) phase in INCONEL® 718 alloy (hereinafter referred to as IN718), resulting in improved properties. Furthermore, even when taking the amount of oxygen into consideration, keeping the amount of Y added within the above-mentioned range prevents the added Y from forming compounds with alloying elements and effectively converts O to Y2O3.

[0024] <Other ingredients> In this embodiment, the heat-resistant alloy material can be appropriately mixed with additive elements that are typically used in this type of heat-resistant alloy material. Examples of the additive elements include C (carbon), Si (silicon), B (boron), Ta, Re, Ru, Hf, and Zr. In particular, Hf and Zr form oxides that are more stable than Al and Ti, and therefore have the same effect as Y.

[0025] <Method of manufacturing and using heat-resistant alloy material (molded body)> The heat-resistant alloy material of this embodiment can be used by mixing the above-mentioned main component metals with Y by a known method. Specifically, for example, a heat-resistant alloy powder (heat-resistant alloy material) can be obtained by a method such as atomization, in which a molten metal containing Y element is sprayed, and this powder can be used as a heat-resistant alloy material for forming various molded bodies. Note that the heat-resistant alloy material of the present invention is suitable for additive manufacturing, but it is not limited to use in methods other than additive manufacturing, and can also be applied to other methods such as hot isostatic pressing (HIP).

[0026] That is, the molded body of this embodiment is a molded body obtained by layered manufacturing using the powder of the heat-resistant alloy material of this embodiment described above with a laser or an electron beam. The laser is usually performed in a rare gas atmosphere such as Ar (argon), and the electron beam is usually performed in a vacuum.

[0027] The compact of this embodiment is formed using the above-mentioned heat-resistant alloy material, and is therefore composed of the above-mentioned main component metal, an oxide of the main component metal, and Y2O3, and the Y2O3 is generated uniformly throughout the compact and exists in a dispersed state. This component composition can be confirmed qualitatively as shown in the examples below, but cannot be accurately expressed quantitatively or by numerical value. Therefore, it is appropriate to express it methodically as described above.

[0028] In addition, in the compact of this embodiment, the Y2O3 particles and Y particles are 30 particles / μm 2 It is preferable that the particles are finely dispersed at a density of 1000 kJ / cm or more.

[0029] Here, the method for manufacturing the molded body of this embodiment will be described in detail. The method for manufacturing the molded body of this embodiment can be carried out by performing a layer formation process in which powder of the above-mentioned heat-resistant alloy material is uniformly dispersed and mixed, and then scattered to a predetermined thickness at a predetermined location on an additive manufacturing device to form a powder layer of the heat-resistant alloy material; an irradiation process in which a laser is irradiated at a predetermined location on the powder layer; a process in which the layer formation process and the irradiation process are repeated; and finally a removal process in which unnecessary powdered heat-resistant alloy material is removed.

[0030] The dispersion and mixing in the layer formation step can be performed using any method commonly used in mixing powders, without any particular restrictions. The additive manufacturing device is also not particularly limited, as long as it is capable of melting and solidifying powder by laser irradiation. Examples of the laser used include a high-power Yb fiber laser. The predetermined location depends on the device and refers to a location in the device that can be irradiated with laser. The predetermined thickness can be determined arbitrarily depending on the laser output, but a thickness of 20 to 50 μm is preferred from the viewpoint of melting and solidifying to a degree that achieves the desired effect.

[0031] The laser irradiation conditions in the above irradiation step are preferably an output of 100 to 400 W and a scanning speed of 1 to 7 m / sec. The above repeated steps are carried out until the molded body is completed. The preferred conditions for laser irradiation and lamination are as follows. Laser power: 200W~400W Laser irradiation diameter: 100 μm Irradiation speed:<7m / s Layer pitch: 20 μm Layer thickness: 40 μm The removal step can be carried out using any known method commonly used for removing powder, such as a sandblaster, without any particular limitations. [Example]

[0032] The present embodiment will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these.

[0033] Example 1 Example 1 is an example of IN (INCONEL®) 718 alloy as a Ni-based alloy. A powder of a heat-resistant alloy material was prepared with the composition shown in Table 1 below. The powder was prepared by a conventional gas atomization method. The metal powder and other additives used were Y, Ni, Fe, Cr, Co, Al, Nb, Cu, Mn, Ti, Mo, C, and B. A compact was fabricated from heat-resistant alloy powder obtained by gas atomization. The compact was fabricated using an additive manufacturing device that irradiates the powder with a laser. The compact was a massive block with a thickness of 45 mm. Test pieces with parallel dimensions of 19.6 mm x 2.8 mm x 3.0 mm were cut out from the block, and then the compact underwent solution treatment and aging (STA). The treatment conditions were solution heat treatment at 980°C for 1 hour, air cooling followed by a first-stage aging heat treatment at 718°C for 8 hours, cooling in a heat treatment furnace followed by a second-stage aging heat treatment at 621°C for 10 hours, and then air cooling.

[0034] The cross section of the obtained compact was observed using a SEM (Scanning Electron Microscope) and a TEM (Transmission Electron Microscope), and the creep properties and oxidation properties were measured under the following conditions. Creep properties: A creep test was carried out at 650°C, applying a stress of 550 MPa to the specimen to examine the elongation over time. Oxidation characteristics: An oxidation test was carried out in air at a temperature of 800°C. The mass increase of the compact with respect to the oxidation time was measured using an electronic balance.

[0035] Comparative Example 1 A heat-resistant alloy material was prepared and a compact was produced in the same manner as in Example 1, except that Y was not added. The obtained compact was observed by SEM in the same manner as in Example 1, and the creep properties and oxidation properties were measured.

[0036] The elemental compositions of the heat-resistant alloy powders in Example 1 and Comparative Example 1 are shown in Table 1. [Table 1]

[0037] Figures 1(a) to 1(f) are SEM images of samples of the molded bodies in Example 1 and Comparative Example 1 after STA treatment. Figures 1(a) to 1(c) are SEM images of Example 1, with the magnification increasing from Figure 1(a) to Figure 1(c). Figures 1(d) to 1(f) are SEM images of Comparative Example 1, with the magnification increasing from Figure 1(d) to Figure 1(f). The magnifications of Figures 1(a) to 1(c) and Figures 1(d) to 1(f) are approximately the same.

[0038] FIG. 2 shows a TEM image of the compact in Example 1, taken after additive manufacturing and heat treatment in which the compact was gradually cooled from 1180°C to 1040°C at a cooling rate of 50°C / h (hours). FIG. 3(a) shows the creep characteristics of samples of the compacts in Example 1 and Comparative Example 1 after STA treatment, and FIG. 3(b) shows the oxidation characteristics. FIG. 3(a) shows strain versus time, and FIG. 3(b) shows mass gain versus time. In FIG. 3(b), the dots indicate measurement points, and the curve is an approximation curve.

[0039] (Discussion of Example 1) 1(a) to 1(f), it is clear that the compact of Example 1 formed using the heat-resistant alloy material of this embodiment has a reduced density and amount of the harmful δ phase, which is a factor in reducing strength, and does not produce oxides such as aluminum oxide, as in the compact of Comparative Example 1. It is also clear that the compact of Example 1 produces uniformly dispersed Y2O3, which improves various properties such as strength.

[0040] As shown in Figure 2, it can be seen that Y2O3 particles with clearly defined contours were formed by slow cooling heat treatment from 1180°C to 1040°C at 50°C / h. Furthermore, as shown in Figure 3(a), in Comparative Example 1, the rupture time, which indicates creep life, was 134 hours, and the strain at rupture, which indicates creep ductility, was 1.29%. In Example 1, the creep life was 396 hours, and the creep ductility was 5.76%. As shown in Figure 3(b), the mass increase due to oxidation was smaller in Example 1 than in Comparative Example 1. As described above, in Example 1, the creep life, creep ductility, and oxidation resistance were significantly improved compared to Comparative Example 1.

[0041] Example 2 Powders of heat-resistant alloy materials having the compositions shown in Table 1 obtained in Example 1 and Comparative Example 1 were vacuum-sealed in stainless steel capsules and subjected to hot isostatic pressing (HIP) sintering at a temperature of 1180°C and a pressure of 175 MPa for 4 hours to obtain compacts. SEM photographs of the obtained compacts were taken in the same manner as in Example 1, and creep properties were measured.

[0042] Figures 4(a) and 4(b) show SEM images of the compacts in Example 2 and Comparative Example 2, respectively. Figure 5 shows the creep properties of the compacts in Example 2 and Comparative Example 2. As shown in Figure 4(a), in Example 2, white Laves phases and carbides are observed at the prior particle interfaces, but Al2O3 is not. In contrast, as shown in Figure 4(b), in Comparative Example 2, white Laves phases and fine Al2O3 are observed along the prior particle interfaces. As shown in Figure 5, in Comparative Example 2, the creep life is 20.4 hours and the creep ductility is 0.13%. In Example 2, the creep life is 322.5 hours and the creep ductility is 0.68%. As can be seen, the creep properties of Example 2 are improved compared to Comparative Example 2.

[0043] In Comparative Example 1, the long and thin bright areas in Figures 1(d) to 1(f) are the δ phase (Ni3Nb). The dark, dotted areas are Al2O3. The reaction formula for the formation of the δ phase and Al2O3 phase in the IN718 alloy is thought to be as follows: Ni3(Al,Ti)+O→Ni+Al2O3+TiO (Reaction 1) 3Ni+Nb→Ni3Nb(δ phase) (Reaction formula 2)

[0044] In Example 1, as shown in Figures 1(a) to 1(c), the bright δ phase is hardly observed. Elemental mapping by FE-EPMA (Field Emission Electron Probe Microanalysis) has revealed that the gray region in Figure 1(c) mainly contains Y and O. This suggests that the gray region is the YO phase.

[0045] The reason why the creep properties and oxidation resistance of Example 1 were improved is thought to be that the reaction of Reaction Formula 1 was suppressed because Example 1 contained Y, and instead Y was oxidized to produce Y2O3.

[0046] FIG. 6 shows the Ellingham diagrams of each oxide, plotting the standard Gibbs free energy of formation versus temperature. As shown in FIG. 6, the standard Gibbs free energy of formation of the oxides of Ca, Hf, and Y, CaO, HfO, and YO, is lower than that of the oxides of Ni, Cr, Al, and Ti, NiO, Cr2O3, Al2O3, and TiO. In particular, YO has the lowest standard Gibbs free energy of formation. Therefore, the O contained in the alloy is primarily used to oxidize Y, but not Ni, Cr, Ti, and Al. This is thought to have suppressed the formation of the harmful δ phase in Example 1, resulting in improved creep properties and oxidation resistance.

[0047] Example 3 To investigate the appropriate Y content relative to the O content in the IN718 alloy, IN718 alloys with different Y contents were produced. The method for producing the compacts was the same as in Example 1, where a compact was formed using additive manufacturing and then subjected to STA processing. The additive manufacturing device used was an M280 manufactured by EOS (Electro Optical Systems). Table 2 shows the elemental compositions of the alloy powders in Samples A to E. Sample A corresponds to Comparative Example 1, Sample C corresponds to Example 1, and Samples B, D, and E correspond to Example 3. Sample B' is a compact produced using Sample B. Min and Max are the minimum and maximum values, respectively, of the alloy composition specifications. Bal. stands for balance and indicates the remainder. The same applies to the tables showing the elemental compositions of the following Examples. The Fe content was converted from the content of the other elements. [Table 2]

[0048] Y / O indicates the ratio of the mass-equivalent yttrium content to the mass-equivalent oxygen content. The theoretical value of Y / O in Y2O3 is 3.9. When Y / O is the theoretical value of 3.9, and all Y becomes Y2O3, most of the O in the alloy is consumed by Y2O3. In sample A of comparative example 1, Y / O is 0. In sample B of example 3, Y / O is 5.2, which is almost the theoretical value. In sample C of example 1, Y / O is 10.0, which is about three times the theoretical value, and in sample D of example 3, Y / O is 45.7, which is about ten times the theoretical value. In sample E of example 3, although the Y content is high, the O content is also high, so Y / O is 40.8, which is about ten times the theoretical value.

[0049] Comparing Sample B and Sample B', the powder and the compact have almost the same content of each element, including O. This suggests that the content of each element in the powder is almost the same as the content of each element in the compact.

[0050] For each sample, samples were prepared to measure creep properties in the stacking direction and in the direction perpendicular to the stacking direction in the additive manufacturing process. Samples in which the creep direction (the direction in which stress is applied) was the stacking direction were called stacking direction samples, and samples in which the creep direction was perpendicular to the stacking direction were called orthogonal direction samples.

[0051] In Figures 7(a) to 8(b), the creep properties of each sample were measured at a temperature of 650°C and a stress of 550 MPa. Figure 7(a) shows the creep properties of the stacking direction sample in Example 3, and Figure 7(b) shows the creep life and creep ductility (strain at fracture point) as a function of Y content. As shown in Figures 7(a) and 7(b), the creep life increases with increasing Y content. Sample C, which contains 0.07 mass% Y, has the greatest creep ductility.

[0052] Fig. 8(a) shows the creep properties of the orthogonal direction samples in Example 3, and Fig. 8(b) shows the creep life and creep ductility (strain at fracture point) as a function of Y content. As shown in Fig. 8(a) and Fig. 8(b), except for the creep life in the stacking direction, the creep life and creep ductility are greatest for sample C with a Y content of 0.07 mass%.

[0053] As described above, except for the creep life in the lamination direction, sample C with a Y / O ratio of 10 has the longest creep life and creep ductility. The creep life and creep ductility of sample B with a Y / O ratio of 5.2 are not as high as those of sample C, but are higher than those of sample A in Comparative Example 1. The creep life and creep ductility in the orthogonal direction and the creep ductility in the lamination direction of sample D with a Y / O ratio of 45.7 are lower than those of sample C, but higher than those of sample A. Sample E has a higher Y content than sample D, but its Y / O is similar to that of sample D. The creep life and creep ductility of sample E are not significantly different from those of sample D. Thus, it is thought that Y / O has a greater effect on creep properties than Y content.

[0054] Using powders from samples A and C, compacts were produced by the HIP method. The production conditions were a temperature of 1180°C and a pressure of 175 MPa applied for 4 hours. The compacts produced by the HIP method were then subjected to STA treatment. The stress-strain curves of the samples produced by the HIP method and those after the STA treatment were measured at 650°C.

[0055] Fig. 9 is a diagram showing a stress-strain curve in Example 3. The tensile strain rate was 4.25 × 10 -4 seconds -1 In Figure 9, "as-HIP" refers to the sample immediately after HIP production, and "STA" refers to the sample after STA treatment. As shown in Figure 9, in the as-HIP process, sample C has lower proof stress but higher ductility than sample A. In the STA process, the ductility of both samples A and C decreases. Sample C has a high fracture stress and high ductility. Thus, sample C with a Y / O ratio of 10 has higher ductility than sample A of Comparative Example 1.

[0056] FE-EPMA elemental mapping of samples B and D, which were produced by additive manufacturing, showed that regions containing Al and O were observed in sample B, suggesting the presence of Al2O3. Regions containing Nb and Y were observed in sample D, suggesting the presence of a compound of Nb and Y. Thus, in sample B, where the Y / O ratio is the theoretical value, oxygen is present that bonds with Al, and it is thought that a δ phase also exists. In sample D, where the Y / O ratio is 10 times the theoretical value, there is an excess of Y, which is thought to react with Nb.

[0057] In sample C, where the Y / O ratio is 10, approximately three times the theoretical value, almost no Al2O3 is formed and the size and amount of the δ phase are reduced, which is thought to be why the creep properties are improved the most.

[0058] Example 4 Example 4 is an example of IN625 (INCONEL (registered trademark) 625 alloy (hereinafter referred to as IN625)). Alloy powder was produced using the atomization method, and a compact was produced using the additive manufacturing method. The additive manufacturing device used was an EOS M280. STA processing was then performed. The STA conditions were heat treatment for 1 hour at 1120°C (sample for creep property measurement in Figure 10(a)) or 980°C (sample for stress-strain curve measurement in Figure 10(b)), followed by air cooling and then treatment at 718°C for 8 hours, cooling in a heat treatment furnace followed by heat treatment at 621°C for 10 hours, followed by air cooling.

[0059] Table 3 shows the elemental composition of the alloy powder. In Example 4, Y / O is 2.53. In Comparative Example 4, Y is not contained. [Table 3]

[0060] The creep properties in the lamination direction were measured for Example 4 and Comparative Example 4. The measurement conditions were a temperature of 650°C and a stress of 550 MPa. Stress-strain curves were also measured. The measurement temperature was 650°C.

[0061] FIG. 10(a) shows the creep properties of Example 4 and Comparative Example 4, and FIG. 10(b) shows the stress-strain curve. As shown in FIG. 10(a), Example 4 has greater creep life and creep ductility than Comparative Example 4. As shown in FIG. 10(b), Example 4 has lower yield strength than Comparative Example 4, but improved ductility. The lower yield strength in Example 4 is thought to be due to a decrease in the size and amount of the δ phase. As described above, Example 4 has improved creep properties and ductility compared to Comparative Example 4.

[0062] Example 5 Example 5 is an example of HASTELLOY (registered trademark) X, a Ni-based alloy containing Cr and Mo. Alloy powder was produced using an atomization method, and a compact was produced using an additive manufacturing method. The additive manufacturing device used was an M290 manufactured by EOS. The heat treatment was a solution treatment (ST) at a temperature of 1177°C for 2 hours.

[0063] Table 4 shows the elemental composition of the alloy powder. In Example 5, Y / O is 3.9. In Comparative Example 5, Y is not contained. The Ni content was calculated from the contents of other elements. [Table 4]

[0064] The creep properties of the samples of Example 5 and Comparative Example 5 after molding and after ST treatment were measured. The measurement conditions were a temperature of 900°C and a stress of 80 MPa. Element mapping of the molded sample of Example 5 using EDS (Energy Dispersive X-ray Spectroscopy) revealed regions where Y and O were unevenly distributed. This indicated the presence of a YO phase.

[0065] Figures 11(a) and 11(b) are graphs showing creep properties in the stacking direction and perpendicular direction, respectively, after molding for Example 5 and Comparative Example 5. Figures 12(a) and 12(b) are graphs showing creep properties in the stacking direction and perpendicular direction, respectively, after ST treatment for Example 5 and Comparative Example 5.

[0066] 11(a) to 12(b), both after compact production and after ST treatment, Example 5 has a longer creep life and greater creep ductility in both the stacking direction and the perpendicular direction than Comparative Example 5. Thus, Example 5 has improved creep properties compared to Comparative Example 5. Even in solid-solution strengthened alloys that do not contain Nb, Al, or Ti, as in Example 5, the addition of Y improves creep properties.

[0067] Example 6 Example 6 is an example of a TiAl alloy using TiAl4822 alloy. An atomization method was used to prepare alloy powder, and a compact was produced using the spark plasma sintering (SPS) method. The SPS method sinters a workpiece in a vacuum by mechanical pressure and pulse current heating. Heat treatment was then performed under the following conditions: the pressure in the SPS method was 50 MPa, and the temperature was held at 1075°C for 10 minutes. The heat treatment involved a homogenization heat treatment in a vacuum at 1205°C for 5 hours, followed by furnace cooling.

[0068] Table 5 shows the elemental composition of the alloy powder. In Example 6, Y / O is 2.63. In Comparative Example 6, Y is not contained. The content of Ti was calculated from the contents of other elements. [Table 5]

[0069] Elemental mapping was performed using FE-EPMA for Example 6 and Comparative Example 6. FIG. 13 shows elemental mapping using FE-EPMA for Example 6, and FIG. 14 shows elemental mapping using FE-EPMA for Comparative Example 6. COMPO is an SEM backscattered electron composition image. As shown in FIG. 14, a coarse white phase is observed in the SEM image of Comparative Example 6. This phase contains a large amount of Ti and O and is a segregated phase of Ti and O. As shown in FIG. 13, no segregated phase of Ti and O was observed in Example 6. Thus, adding Y to the TiAl alloy suppresses the segregation of Ti and O, improving structural stability.

[0070] Summary of Examples The oxygen concentration can be reduced by producing alloys using the cast and wrought (C&W) method, casting method, and forging method. However, these methods make it difficult to produce compacts with complex shapes. Alloy compacts can be formed using additive manufacturing methods such as selective laser melting (SLM) using laser light and electron beam melting (EBM) using electron beams, hot isostatic pressing (HIP), powder bed fusion (PBF), and directed energy deposition (DED). These methods allow for the production of compacts with complex shapes. These methods form compacts from alloy powder. Because alloy powder has a large surface area, oxygen is easily incorporated into the alloy. As a result, compacts formed from alloy powder also contain a large amount of oxygen.

[0071] Compacts other than those made from heat-resistant alloy powders may also contain large amounts of oxygen. Such heat-resistant alloy compacts suffer from poor performance, such as poor creep properties. Heat-resistant alloys containing at least one of Al, Ti, Ni, Cr, and Mo, as in Comparative Examples 1 to 6, suffer from the formation of harmful phases due to oxidation of these elements, resulting in poor performance. Therefore, as shown in Figure 6, Y, whose standard Gibbs free energy of oxide formation is lower than that of Al, Ti, Ni, Cr, and Mo, is added to the alloy. The stoichiometric composition of yttria (YO), Y / O, is the ratio of the mass-equivalent Y content to the mass-equivalent O content, is 3.9. Therefore, Y / O is set to 0.5 or more and 100 or less. This suppresses oxidation of at least one of Al, Ti, Ni, Cr, and Mo. This improves the creep properties and other performance of the heat-resistant alloy.

[0072] From the viewpoint of suppressing harmful phases, Y / O is preferably 1.0 or more, more preferably 2.6 or more, and even more preferably 3.9 or more. Also, from the viewpoint of suppressing excess Y, Y / O is preferably 71 or less, more preferably 40 or less, and even more preferably 10 or less.

[0073] In the Ni-based alloys of Examples 1 to 4, the Ni content is 40.0% by mass or more, for example, 50.0% by mass or more. The O content in Ni-based alloys produced by the casting and forging methods is, for example, 5 ppm to 20 ppm. In contrast, the O content in alloy powders and compacts formed from the alloy powders is, for example, 50 ppm to 200 ppm. When the O content in the alloy is 0.002% by mass (20 ppm) or more, performance degradation due to oxides occurs compared to alloys produced by the casting and forging methods. Therefore, it is preferable to add Y. When the O content in the alloy is 0.005% by mass (50 ppm) or more, the performance of the alloy is further degraded. Therefore, it is preferable to add Y to the alloy. To prevent deterioration of the alloy's performance, the O content in the alloy is preferably 0.1% by mass (1000 ppm) or less, more preferably 0.05% by mass (500 ppm) or less.

[0074] In the case of Ni-based alloys, when the content of at least one of Al, Ti, Cr, and Mo is 0.01% by mass or more, at least one of Al, Ti, Cr, and Mo is oxidized, deteriorating the performance of the alloy. Therefore, it is preferable to add Y. When the content of at least one of Al, Ti, Cr, and Mo is 0.1% by mass or more, at least one of Al, Ti, Cr, and Mo is oxidized, further deteriorating the performance of the alloy. Therefore, it is preferable to add Y.

[0075] When Ni-based alloys, such as IN718 and IN625, contain Al, Ti, and Nb, the δ phase forms, degrading the alloy's performance. Therefore, it is preferable to add Y when the content of at least one of Al and Ti in the alloy is 0.01% by mass or more and 1.0% by mass or less, and the content of Nb is 1.0% by mass or more and 10.0% by mass or less. It is more preferable to add Y when the content of at least one of Al and Ti is 0.05% by mass or more, or 0.1% by mass or more. It is more preferable to add Y when the content of Nb is 2.0% by mass or more.

[0076] In IN718 alloy, the contents of the main elements are as shown in Table 2. The Ni content is 50.0 mass% or more and 55.0 mass% or less, The Cr content is 17.0 mass% or more and 21.0 mass% or less, The Fe content is 11.0 mass% or more and 25.0 mass% or less, The Mo content is 2.8 mass% or more and 3.3 mass% or less. The Nb content is 4.75 mass% or more and 5.50 mass% or less, The Al content is 0.20 mass% or more and 0.80 mass% or less, The Ti content is 0.65 mass % or more and 1.15 mass % or less.

[0077] In IN625 alloy, the contents of the main elements are as shown in Table 3. Ni content is 58.0 mass% or more, The Cr content is 20.0 mass% or more and 23.0 mass% or less, The Mo content is 8.0 mass% or more and 10.0 mass% or less, The Nb content is 3.15 mass % or more and 4.15 mass % or less.

[0078] It is preferable to add Y when the content of at least one of Cr and Mo in the Ni-based alloy is 1% by mass or more, such as in the HASTELLOY® X alloy in Example 5. The content of at least one of Cr and Mo is more preferably 5% by mass or more.

[0079] In HASTELLOY® X alloy, the contents of the major elements are as shown in Table 4. The Ni content is 41.0 mass% or more and 54.0 mass% or less, The Cr content is 20.5 mass% or more and 23.0 mass% or less, The Mo content is 8.0 mass% or more and 10.0 mass% or less, The Fe content is 17.0 mass% or more and 20.0 mass% or less, The W content is 0.2 mass% or more and 1.0 mass% or less, The Co content is 0.5 mass % or more and 2.5 mass % or less.

[0080] In Ti-based alloys, the Ti content is 50% by mass or more, for example, 60% by mass or more. In TiAl alloys, the Ti content is 30% by mass or more, for example, 50% by mass or more. The Al content is 3% by mass or more, for example, 10% by mass or more, for example, 30% by mass or more. In Ti-based alloys and TiAl alloys, the O content in alloys produced by the casting forging method, casting method, and forging method is, for example, 250 ppm to 500 ppm. In contrast, the O content in alloy powders and compacts formed from the alloy powders is, for example, 700 ppm to 1100 ppm. If the O content in the alloy is 0.05% by mass (500 ppm) or more, performance degradation due to oxides occurs compared to alloys produced by the casting forging method, casting method, and forging method. Therefore, it is preferable to add Y. If the O content in the alloy is 0.07% by mass (700 ppm) or more, the performance of the alloy is further deteriorated. Therefore, it is preferable to add Y to the alloy. In order not to deteriorate the performance of the alloy, the O content in the alloy is preferably 1.0 mass % (10000 ppm) or less, and more preferably 0.2 mass % (2000 ppm) or less.

[0081] In TiAl4822 alloy, the contents of the main elements are as shown in Table 5. The Ti content is 56.0 mass% or more and 64.0 mass% or less, The Al content is 33.0 mass% or more and 35.0 mass% or less, The Cr content is 2.2 mass% or more and 2.7 mass% or less. The Nb content is 4.5 mass% or more and 5.1 mass% or less, is.

[0082] Y may also be added to Ti64 alloy. In Ti64 alloy, the contents of the main elements are: The Ti content is bal, and is 88.0 mass% or more and 91.0 mass% or less. The Al content is 5.5 mass% or more and 6.75 mass% or less, The V content is 3.5 mass% or more and 4.5 mass% or less, is.

[0083] FIG. 15 is a diagram showing an example of a method for manufacturing a heat-resistant alloy compact. As shown in FIG. 15, first, an alloy powder is prepared (step S10). The alloy powder is prepared, for example, by atomization. Next, the alloy powder is compacted to prepare an alloy compact (step S12). To prepare the alloy compact, for example, additive manufacturing, hot isostatic pressing, powder bed fusion, and directed energy deposition can be used. Next, the compact is heat-treated (step S14). For example, solution aging (STA) and direct aging (DA) can be used as the heat treatment.

[0084] The heat-resistant alloy may be the heat-resistant alloy powder produced in step S10, or may be the heat-resistant alloy compact produced in steps S12 and S14.

[0085] As described above, the heat-resistant alloy of this embodiment has improved high-temperature strength characteristics and oxidation resistance, and is therefore useful in fields such as aircraft engines, rocket engines, industrial gas turbines, and automobile engines.

[0086] Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as set forth in the claims.

Claims

1. The Ni content is 58.0 mass% or more, The Cr content is 20.0 mass% or more and 23.0 mass% or less, The Mo content is 8.0 mass% or more and 10.0 mass% or less, The Nb content is 3.15% by mass or more and 4.15% by mass or less, and The content of O is 0.002% by mass or more and 0.1% by mass or less, A heat-resistant alloy containing Y, wherein the ratio of the content of Y, converted into mass, to the content of O, converted into mass, is 0.5 or more and 100 or less.

2. The Fe content is 5.0 mass% or less, The content of Al is 0.4 mass% or less, The content of Ti is 0.4 mass% or less, The Mn content is 0.5 mass% or less, The C content is 0.1 mass% or less, The Si content is 0.5 mass% or less, The Co content is 1.0 mass% or less, and The S content is 0.015 mass% or less, 2. The heat-resistant alloy according to claim 1, wherein the balance is Ni.

3. The Ni content is 41.0 mass% or more and 54.0 mass% or less, The Cr content is 20.5 mass% or more and 23.0 mass% or less, The Mo content is 8.0 mass% or more and 10.0 mass% or less, The Fe content is 17.0 mass% or more and 20.0 mass% or less, The W content is 0.2 mass% or more and 1.0 mass% or less, The Co content is 0.5 mass% or more and 2.5 mass% or less, and The content of O is 0.002% by mass or more and 0.1% by mass or less, A heat-resistant alloy containing Y, wherein the ratio of the content of Y, converted into mass, to the content of O, converted into mass, is 0.5 or more and 100 or less.

4. The content of Al is 0.5 mass% or less, The content of Ti is 0.15 mass% or less, The content of C is 0.1% by mass or less, and The Si content is 1.0 mass% or less, 4. The heat-resistant alloy according to claim 3, wherein the balance is Ni.

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