Heat-resistant alloy, heat-resistant alloy powder for additive manufacturing, heat-resistant alloy additive manufactured object, and method for producing the same

Abstract

This heat-resistant alloy contains: at least one element from among Al, Ti, Ni, Cr, and Mo; O; and Y, the ratio of the Y content in terms of mass to the O content in terms of mass being 5-100 inclusive.　

Description

Technical Field

[0001] The present invention relates to a heat-resistant alloy, for additive manufacturing heat-resistant alloy powder, heat-resistant alloy additive manufacturing formed body and a method for manufacturing the same.

Background Art

[0002] Heat-resistant alloys are used in aircraft engines and the like. As a method for forming a formed body of a heat-resistant alloy, a laminated manufacturing method is known (for example, Patent Document 1). It is known to disperse ceramic particles having Y (yttrium) or the like in crystal grains and grain boundaries in an alloy having columnar crystals (for example, Patent Document 2). It is known to add Y to a Ni (nickel) - based alloy (for example, Non-Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0004]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] For example, a molded body of an alloy formed using a layered manufacturing method contains a large amount of O (oxygen). In an alloy containing a large amount of oxygen, the performance of the alloy may deteriorate. Patent Document 2, Non-Patent Documents 1 and 2 describe adding Y to the alloy, but do not describe the relationship with O.

[0006] The present invention has been made in view of the above problems, and an object thereof is to improve the performance of an alloy by specifying the ratio of oxygen to yttrium.

Means for Solving the Problems

[0007] The present invention is a heat-resistant alloy containing at least one element of Al, Ti, Ni, Cr, and Mo, O, and Y, and the ratio of the content of Y in terms of mass to the content of O in terms of mass is 0.5 or more and 100 or less.

[0008] In the above configuration, the content of Ni can be 40.0% by mass or more, and the content of O can be 0.002% by mass or more and 0.1% by mass or less.

[0009] In the above configuration, the content of Ni can be 50.0% by mass or more and 55.0% by mass or less, the content of Cr can be 17.0% by mass or more and 21.0% by mass or less, the content of Fe can be 11.0% by mass or more and 25.0% by mass or less, the content of Mo can be 2.8% by mass or more and 3.3% by mass or less, the content of Nb can be 4.75% by mass or more and 5.50% by mass or less, the content of Al can be 0.20% by mass or more and 0.80% by mass or less, the content of Ti can be 0.65% by mass or more and 1.15% by mass or less, and the content of O can be 0.002% by mass or more and 0.1% by mass or less.

[0010] In the above configuration, the content of Ni can be 58.0% by mass or more, the content of Cr can be 20.0% by mass or more and 23.0% by mass or less, the content of Mo can be 8.0% by mass or more and 10.0% by mass or less, the content of Nb can be 3.15% by mass or more and 4.15% by mass or less, and the content of O can be 0.002% by mass or more and 0.1% by mass or less.

[0011] In the above composition, the Ni content can be 41.0 mass% or more and 54.0 mass% or less, the Cr content can be 20.5 mass% or more and 23.0 mass% or less, the Mo content can be 8.0 mass% or more and 10.0 mass% or less, the Fe content can be 17.0 mass% or more and 20.0 mass% or less, the W content can be 0.2 mass% or more and 1.0 mass% or less, the Co content can be 0.5 mass% or more and 2.5 mass% or less, and the O content can be 0.002 mass% or more and 0.1 mass% or less.

[0012] In the above composition, the Ti content can be 50 mass% or more, or the Ti content can be 30 mass% or more and the Al content can be 3 mass% or more, and the O content can be 0.05 mass% or more and 1.0 mass% or less.

[0013] In the above composition, the Ti content can be 56.0 mass% or more and 64.0 mass% or less, the Al content can be 33.0 mass% or more and 35.0 mass% or less, the Cr content can be 2.2 mass% or more and 2.7 mass% or less, the Nb content can be 4.5 mass% or more and 5.1 mass% or less, and the O content can be 0.06 mass% or more and 1.0 mass% or less.

[0014] In the above composition, the ratio of the content of Y in terms of mass to the content of O in terms of mass can be 2.0 or more and 43 or less.

[0015] In the above composition, at least a part of Y can be contained as yttria.

[0016] The present invention is a heat-resistant alloy powder containing the above heat-resistant alloy.

[0017] The present invention is a heat-resistant alloy formed body containing the above heat-resistant alloy.

[0018] The present invention is a method for manufacturing a heat-resistant alloy formed body, including a step of forming a formed body by molding the above heat-resistant alloy powder.

Advantages of the Invention

[0019] According to the present invention, the performance of the alloy can be improved.

Brief Description of the Drawings

[0020] [Fig. 1] FIGS. 1(a) to 1(f) are scanning electron microscope images of STA-treated samples of the formed bodies obtained in Example 1 and Comparative Example 1, FIGS. 1(a) to 1(c) are images of the formed body of Example 1, and FIGS. 1(d) to 1(f) are images of the formed body of Comparative Example 1. [Fig. 2] FIG. 2 is an image obtained by magnifying and observing Y2O3 particles in a sample obtained by subjecting the formed body obtained in Example 1 to slow cooling heat treatment at 50 ° C. / h from 1180 ° C. to 1040 ° C. with a transmission electron microscope. [Fig. 3] FIGS. 3(a) and 3(b) are graphs showing the creep characteristics and oxidation characteristics of the formed bodies obtained in Example 1 and Comparative Example 1, respectively. [Fig. 4] FIGS. 4(a) and 4(b) are scanning electron microscope images of HIP sintered compacts obtained in Example 2 and Comparative Example 2, respectively. [Fig. 5] FIG. 5 is a graph showing the creep characteristics of the HIP sintered compacts obtained in Example 2 and Comparative Example 2. [Fig. 6] FIG. 6 is a diagram showing the Ellingham diagram of each oxide. [Fig. 7] FIG. 7(a) is a diagram showing the creep characteristics of an orthogonal direction sample in Example 3, and FIG. 7(b) is a diagram showing the creep life and creep ductility with respect to the Y content. [Fig. 8] FIG. 8(a) is a diagram showing the creep characteristics of a laminated direction DA (direct aging treatment) sample in Example 3, and FIG. 8(b) is a diagram showing the creep life and creep ductility with respect to the Y content. [Fig. 9] FIG. 9 is a diagram showing the stress-strain curve of the HIP sintered compact in Example 3. [Fig. 10]Fig. 10(a) is a diagram showing the creep characteristics in Example 4 and Comparative Example 4, and Fig. 10(b) is a diagram showing the stress-strain curve. [Fig. 11] Figs. 11(a) and 11(b) are diagrams showing the creep characteristics in the orthogonal direction and the lamination direction after molding in Example 5 and Comparative Example 5. [Fig. 12] Figs. 12(a) and 12(b) are diagrams showing the creep characteristics in the orthogonal direction and the lamination direction after solution treatment (ST) in Example 5 and Comparative Example 5. [Fig. 13] Fig. 13 is a diagram showing the elemental mapping using FE-EPMA of the discharge plasma sintering (SPS) compact in Example 6. [Fig. 14] Fig. 14 is a diagram showing the elemental mapping using FE-EPMA of the SPS compact in Comparative Example 6. [Fig. 15] Fig. 15 is a diagram showing an example of the manufacturing method of the heat-resistant alloy compact.

Embodiments for Carrying Out the Invention

[0021] Hereinafter, embodiments of the present invention will be described in more detail. The heat-resistant alloy material of this embodiment is a heat-resistant alloy material capable of being laminated and formed by a laser or an electron beam, and is characterized by containing a main component metal and Y. This will be described in detail below.

[0022] <Main component metal> Examples of the above main component metals 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), Zr (zirconium), etc., and metal oxides such as NiO, TiO, Al2O3, Cr2O3, etc. When used, they can be used alone or as a mixture of two or more. In this embodiment, in particular, the above main component metals can preferably be Ni, Ti, Al and their oxides (NiO, TiO, Al2O3) and mixtures thereof.

[0023] In the molded body made of the heat-resistant alloy material of this embodiment, these main component metals, especially metal oxides, are preferably contained in the molded body as an oxidation-resistant film or an oxide dispersion strengthening phase. The blending amount of each component in the main component metal is arbitrary depending on the composition. For example, when Ni is the main component, it is preferably blended so that Ni is contained in the entire alloy material at 40% by mass or more. When Al and Ti are the main components without using Ni, it is preferably blended so that the total of Al and Ti is contained in the entire heat-resistant alloy material at 50% by mass or more, further 90% by mass or more, and both are contained at 5% by mass or more.

[0024] In addition, each component used as the above main component metal is preferably used in a particulate form (i.e., powder). Its average particle size is not particularly limited and can be used with a desired particle size. (Measurement method of average particle size) The above average particle size can be obtained by visually measuring the particle size confirmed by a transmission electron microscope and taking the average. Also, the distribution density of the particles can be measured with a scanning electron microscope reflection electron image to obtain the average.

[0025] <Y (yttrium)> As Y, those with a purity of 99.9% or more can preferably be used, and as long as they satisfy this purity, commercially available metal Y can be used as an additive element without particular limitation. Further, Y preferably combines with O to form Y2O3 particles, and its average particle size is preferably 10 to 200 nm, more preferably 50 to 150 nm. Further, the average particle size at this time can be determined in the same manner as the above method.

[0026] The laminated manufacturing method using metal is a method of placing metal powder on a plane, performing laser irradiation only on necessary portions thereof, and melting and solidifying it to perform shaping. At this time, there is a risk that the remaining oxygen on the powder surface will dissolve and remain in the shaped article as it is, deteriorating the properties of the sintered material. Further, oxygen also has a problem of combining with Al, which is a strengthening element, to form alumina, consuming Al, and deteriorating the high-temperature strength and oxidation resistance of the alloy. In this regard, Y (yttrium) binds to oxygen more weakly than Al and forms a stable oxide (Y2O3). Therefore, in the laminated manufacturing method using a laser in which oxygen contamination is inevitable, by containing Y as an essential component, the heat resistance and oxidation resistance of the obtained molded body can be improved.

[0027] Further, Y2O3 (yttria), which is an oxide of Y, contributes to high-temperature strengthening as an oxide. However, the mechanical alloying method (a method of mechanically mixing in a solid state to produce an alloy) using yttria particles is extremely costly and impossible to mold materials with complex shapes, and is applicable only to extremely limited uses. However, in the selective laser melting method, due to the presence of dissolved oxygen, yttria particles, which are compounds of Y, can be used to mold complex-shaped materials in which they are uniformly and finely dispersed at the density described below.

[0028] In addition, in a casting method (including a forging method in which forging is performed after casting) that has undergone a special melting and refining process other than the additive manufacturing method using alloy powder, since the oxygen content is as low as 20 ppm or less, when Y is added, Y does not combine with oxygen but combines with other alloy elements to form a harmful TCP (Topologically Close Packed) phase (see Non-Patent Document 1). Also, in a polycrystalline alloy, Y hardly combines with oxygen, segregates, and mainly combines with alloy elements to form harmful compounds, and the generation is non-uniform and Y oxides are not generated throughout the molded body (Non-Patent Document 2). However, by using an alloy powder material with Y as an additive element in advance as in this embodiment to form a molded body by an additive manufacturing method using a laser, Y oxides can be uniformly and finely generated.

[0029] <Mixing ratio> The mixing ratio of the above main component metal and Y is preferably adjusted so that in the molded body obtained with the mixing ratio of Y, Y is 2 atoms with respect to 3 atoms of mixed oxygen as Y2O3 oxide. Specifically, it is preferably adjusted to be 0.005 mass% or more and less than 1.0 mass% in the entire alloy material, and more preferably 0.01 to 0.5 mass%.

[0030] In addition, when the main component metals are Ti and Al, in the case of a Ti alloy and a TiAl alloy, the mixing ratio of Y is preferably adjusted to be 0.01 mass% or more and less than 1.0 mass% in the entire alloy material, more preferably 0.05 to 0.7 mass%, and most preferably 0.1 to 0.5 mass%.

[0031] If the amount is less than the lower limit, sufficient improvement in performance cannot be obtained. If the amount added is 0.5% by mass or more, deterioration will be observed in the finally obtained molded article. Therefore, it is preferable to set the amount within the above range. The reason why the effects obtained vary depending on the addition amount is that in the case of laminated manufacturing, it is difficult to suppress a small amount of oxygen even when manufacturing in a vacuum, and unnecessary oxides are generated during laminated manufacturing, reducing heat resistance and oxidation resistance. However, by containing Y in the above addition amount, Y2O3 is generated earlier than the oxides of other metal elements. In Ti alloys and TiAl alloys, the amount of dissolved oxygen is reduced, the structure is stabilized, and embrittlement of the base material is prevented. In INCONEL (registered trademark) 718 alloy (hereinafter referred to as IN718), the amount and size of the harmful δ (delta) phase are reduced, and as a result, each property can be enhanced. Also, considering the amount of oxygen, by setting the addition amount of Y within the above range, the added Y can be suppressed from forming alloys and compounds with alloying elements, and O can be effectively converted into Y2O3.

[0032] <Other components> In addition, in the present embodiment, additive elements that are usually used in this type of heat-resistant alloy material can be appropriately mixed and used in the heat-resistant alloy material. Examples of the above additive elements include C (carbon), Si (silicon), B (boron), Ta, Re, Ru, Hf, Zr, and the like. In particular, Hf and Zr form oxides that are more stable than Al and Ti, and thus have the same effect as Y.

[0033] <Method for manufacturing and using heat-resistant alloy material (molded article)> The heat-resistant alloy material of the present embodiment can be mixed with the above main component metal and Y by a known method and used. Specifically, for example, a method such as an atomizing method of spraying a molten metal added with Y element can be used to obtain a powder of a heat-resistant alloy (heat-resistant alloy material), and this powder can be used as a heat-resistant alloy material for forming various molded articles. Note that the heat-resistant alloy material of the present invention can be suitably used in the laminated manufacturing method, and is not limited to being used only in the laminated manufacturing method, and can also be applied to other methods such as the hot isostatic pressing (HIP) method.

[0034] That is, the molded body of the present embodiment is a molded body obtained by performing additive manufacturing using a laser or an electron beam with the powder of the heat-resistant alloy material of the present embodiment described above. The laser is usually performed in an inert gas atmosphere such as Ar (argon), and the electron beam is usually performed in a vacuum.

[0035] Since the molded body of the present embodiment is formed using the above heat-resistant alloy material, it is composed of the above main component metal, the oxide of the main component metal, and Y2O3, and Y2O3 is uniformly generated and dispersed throughout the molded body. Although such a component configuration can be qualitatively confirmed as shown in the examples described later, it cannot be accurately shown by quantifying it numerically. Therefore, it is reasonable to express it methodologically as described above.

[0036] Also, in the molded body of the present embodiment, it is preferable that Y2O3 particles and Y particles are finely dispersed at a density of 30 particles / μm 2 or more.

[0037] Here, the manufacturing method of the molded body of the present embodiment will be described in detail. The manufacturing method of the molded body of the present embodiment is to uniformly disperse and mix the powder of the heat-resistant alloy material, and then spray it to a predetermined thickness at a predetermined position of a laminating apparatus to form a powder layer of the heat-resistant alloy material, an irradiation step of irradiating a laser at a predetermined position of the powder layer, a step of repeating the layer formation step and the irradiation step, and finally removing unnecessary powder-like heat-resistant alloy material. It can be implemented by performing a removal step.

[0038] In the above layer formation process, the dispersion mixing can be carried out using the methods used in ordinary powder mixing without any particular limitation. Further, the additive manufacturing apparatus may be any apparatus that can melt and solidify the powder by laser irradiation without any particular limitation. Examples of the laser to be used include high-power Yb fiber lasers. The above-mentioned predetermined location depends on the apparatus and means the location where laser irradiation is possible in the apparatus used. Also, the predetermined thickness is arbitrary depending on the output of the laser, but it is preferably 20 to 50 μm from the viewpoint of achieving the desired effect of melting and solidifying.

[0039] In the above irradiation process, the laser irradiation conditions are preferably such that the output is 100 to 400 W and the scanning speed is 1 to 7 m / s. The above repeating process is to be carried out until the molded body is completed. The preferable conditions for laser irradiation and lamination are as follows. Laser output: 200 W to 400 W Laser irradiation diameter: 100 μm Irradiation speed: <7 m / s Lamination pitch: 20 μm Lamination thickness: 40 μm The above removal process can be carried out using the methods used in the removal of usually known powders, such as a sandblaster, etc., without any particular limitation.

Examples

[0040] Hereinafter, the present embodiment will be specifically described by way of examples and comparative examples, but the present invention is not limited thereto.

[0041] 〔Example 1〕 Example 1 is an example of IN (INCONEL (registered trademark)) 718 alloy as a Ni-based alloy. Powders of a heat-resistant alloy material were prepared with the compositions shown in Table 1 below. Note that the powders were prepared using the ordinary gas atomization method. The metal powders and other additives used were Y, Ni, Fe, Cr, Co, Al, Nb, Cu, Mn, Ti, Mo, C, and B. A compact body was fabricated from a heat-resistant alloy powder obtained by the gas atomization method. The compact body was fabricated using a laminated manufacturing apparatus that irradiates the powder with a laser. The thickness of the compact body is a 45-mm massive block. After cutting out a test piece with parallel part dimensions of 19.6 mm × 2.8 mm × 3.0 mm from the block, solution treatment and aging (STA) were performed on the compact body. The treatment conditions were solution heat treatment at 980°C for 1 hour, followed by air cooling, first-stage aging heat treatment at 718°C for 8 hours after air cooling, second-stage aging heat treatment at 621°C for 10 hours after cooling in a heat treatment furnace, and then air cooling.

[0042] For the obtained compact body, the cross section was observed using SEM (Scanning Electron Microscope) and TEM (Transmission Electron Microscope). Also, the creep characteristics and oxidation characteristics were measured under the conditions shown below. Creep characteristics: A creep test was conducted in which a stress of 550 MPa was applied at a temperature of 650°C, and the elongation with respect to time was examined. Oxidation characteristics: An oxidation test was conducted at a temperature of 800°C in the atmosphere. The mass increase of the compact body with respect to the oxidation time was measured using an electronic balance.

[0043] [Comparative Example 1] A heat-resistant alloy material was adjusted and a compact body was fabricated in the same manner as in Example 1 except that Y was not added. For the obtained compact body, SEM observation was performed in the same manner as in Example 1, and the creep characteristics and oxidation characteristics were measured.

[0044] The elemental compositions of the heat-resistant alloy powders in Example 1 and Comparative Example 1 are shown in Table 1. [Table 1]

[0045] Figs. 1(a) to 1(f) are diagrams showing SEM observation images of the samples after STA treatment of the molded bodies in Example 1 and Comparative Example 1. Figs. 1(a) to 1(c) are SEM images of Example 1, and the magnification increases as going from Fig. 1(a) to Fig. 1(c). Figs. 1(d) to 1(f) are SEM images of Comparative Example 1, and the magnification increases as going from Fig. 1(d) to Fig. 1(f). The magnifications of Figs. 1(a) to 1(c) and Figs. 1(d) to 1(f) are approximately the same, respectively.

[0046] Fig. 2 shows a TEM observation image of the molded body in Example 1, which is a TEM image after heat treatment of cooling the molded body from 1180 °C to 1040 °C at a cooling rate of 50 °C / h (hour) after laminated manufacturing. Fig. 3(a) is a diagram showing the creep characteristics of the samples after STA treatment of the molded bodies in Example 1 and Comparative Example 1, and Fig. 3(b) is a diagram showing the oxidation characteristics. Fig. 3(a) shows the strain with respect to time, and Fig. 3(b) shows the mass gain with respect to time. In Fig. 3(b), the dots are the measurement points and the curve is an approximate curve.

[0047] (Discussion of Example 1) As is clear from the results shown in Figs. 1(a) to 1(f), in the molded body of Example 1 formed using the heat-resistant alloy material of the present embodiment, the density and amount of the harmful phase δ phase, which is a factor reducing the strength, are decreased, and it can be seen that oxides such as aluminum oxides are not generated as in the molded body of Comparative Example 1. Further, it can be seen that Y2O3, which improves various properties such as strength, is generated in a state of being uniformly dispersed in the molded body of Example 1.

[0048] As shown in Fig. 2, it can be seen that Y2O3 particles with distinct contours are formed by slow cooling heat treatment at 50 °C / h from 1180 °C to 1040 °C. Also, as shown in Fig. 3(a), in Comparative Example 1, the rupture time indicating creep life is 134 hours, and the strain at the rupture point indicating creep ductility is 1.29%. In Example 1, the creep life is 396 hours, and the creep ductility is 5.76%. As shown in Fig. 3(b), the mass increase due to oxidation is smaller in Example 1 than in Comparative Example 1. As described above, in Example 1, the creep life, creep ductility, and oxidation resistance are significantly improved compared to Comparative Example 1.

[0049] 〔Example 2〕 The powders of the heat-resistant alloy materials with 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 respectively to obtain compacts. For the obtained compacts, SEM photographs were taken in the same manner as in Example 1, and the creep characteristics were measured.

[0050] Figs. 4(a) and 4(b) are diagrams showing SEM images of the compacts in Example 2 and Comparative Example 2 respectively. Fig. 5 is a diagram showing the creep characteristics of the compacts in Example 2 and Comparative Example 2. As shown in Fig. 4(a), in Example 2, white Laves phase and carbides are observed at the old particle interface, but Al2O3 is not observed. In contrast, as shown in Fig. 4(b), in Comparative Example 2, white Laves phase and fine Al2O3 are observed along the old particle interface. As shown in Fig. 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%. Thus, it can be seen that the creep characteristics are improved in Example 2 compared to Comparative Example 2.

[0051] In Comparative Example 1, the elongated bright regions in FIGS. 1(d) to 1(f) are the δ phase (Ni3Nb). The dark dot-like regions are Al2O3. The reaction equations for the formation of the δ phase and the Al2O3 phase in the IN718 alloy are considered as follows. Ni3(Al,Ti) + O → Ni + Al2O3 + TiO (Reaction Equation 1) 3Ni + Nb → Ni3Nb (δ phase) (Reaction Equation 2)

[0052] In Example 1, as shown in FIGS. 1(a) to 1(c), almost no bright δ phase is observed. In the gray region in FIG. 1(c), it is found by elemental mapping of FE-EPMA (Field Emission Electron Probe Micro Analysis) that mainly Y and O are present. Thus, the gray region is considered to be the Y2O3 phase.

[0053] The reason for the improved creep properties and oxidation resistance in Example 1 is considered to be that in Example 1, since Y is contained, the reaction of Reaction Equation 1 is suppressed, and instead Y is oxidized to produce Y2O3.

[0054] FIG. 6 is a diagram showing the Ellingham diagrams of various oxides, and is a diagram showing the standard Gibbs free energy of formation with respect to temperature. As shown in FIG. 6, the standard Gibbs free energies of formation of the oxides CaO, HfO2, and Y2O3 of Ca, Hf, and Y are lower than those of the oxides NiO, Cr2O3, Al2O3, and TiO of Ni, Cr, Al, and Ti. In particular, the standard Gibbs free energy of formation of Y2O3 is the lowest. For this reason, the O contained in the alloy is mainly used for the oxidation of Y and not for the oxidation of Ni, Cr, Ti, and Al. Thus, in Example 1, it is considered that the formation of the harmful δ phase is suppressed, and the creep properties and oxidation resistance are improved.

[0055] [Example 3] In IN718 alloy, IN718 alloys with different Y contents were prepared to investigate the appropriate Y content with respect to the O content. The method for fabricating the formed body was the same as in Example 1. The laminated manufacturing method was used to form the formed body, and then STA treatment was performed. EOS (Electro Optical Systems) M280 was used as the laminated manufacturing apparatus. Table 2 is a table showing the elemental compositions of the alloy powders in Samples A to E. Sample A is Comparative Example 1, Sample C is Example 1, and Samples B, D, and E are Example 3. Sample B' is a formed body formed using Sample B. Min and Max are the minimum and maximum values of the alloy composition standards, respectively. Bal. is Balance, indicating the remainder. The tables showing the elemental compositions of the following examples are the same. The Fe content was converted from the contents of other elements.

Table 2

[0056] Y / O represents the ratio of the content of yttrium in terms of mass to the content of oxygen in terms of mass. 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, almost all of the O in the alloy is consumed in 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. 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 large, the O content is also large, so Y / O is 40.8, which is about ten times the theoretical value.

[0057] When comparing Sample B and Sample B', the contents of each element including O are almost the same in the powder and the formed body. Thus, it is considered that the content of each element in the powder is almost the same as the content of each element in the formed body.

[0058] For each sample, samples were prepared to measure the creep characteristics in the lamination direction of the additive manufacturing method and in the direction orthogonal to the lamination direction. A sample with the creep direction (the direction in which stress is applied) being the lamination direction is defined as the lamination direction sample, and a sample with the creep direction being the direction orthogonal to the lamination direction is defined as the orthogonal direction sample.

[0059] In Figs. 7(a) to 8(b), For each sample, the creep characteristics were measured with a stress of 550 MPa applied at a temperature of 650 °C. Fig. 7(a) is a diagram showing the creep characteristics of the lamination direction sample in Example 3, and Fig. 7(b) is a diagram showing the creep life and creep ductility (strain at the breaking point) with respect to the Y content. As shown in Fig. 7(a) and Fig. 7(b), as the Y content increases, the creep life becomes longer. The creep ductility is the largest for sample C with a Y content of 0.07 mass% .

[0060] Fig. 8(a) is a diagram showing the creep characteristics of the orthogonal direction sample in Example 3, and Fig. 8(b) is a diagram showing the creep life and creep ductility (strain at the breaking point) with respect to the Y content. As shown in Fig. 8(a) and Fig. 8(b), except for the creep life in the lamination direction, the creep life and creep ductility are the largest for sample C with a Y content of 0.07 mass%.

[0061] As described above, except for the creep life in the lamination direction, the creep life and creep ductility of sample C with Y / O of 10 are the largest. The creep life and creep ductility of sample B with Y / O of 5.2 are not as large as those of sample C, but are larger 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 Y / O of 45.7 are smaller than those of sample C but larger than those of sample A. Sample E has a larger Y content than sample D, but the Y / O is about the same as 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 considered that Y / O affects the creep characteristics rather than the Y content.

[0062] Using the powders of Sample A and C, compacts were fabricated by the HIP method. The fabrication conditions were a pressure of 175 MPa applied for 4 hours at a temperature of 1180°C. The compacts fabricated using the HIP method were subjected to STA treatment. For the samples after fabrication by the HIP method and after STA treatment, stress-strain curves were measured at 650°C.

[0063] Figure 9 is a diagram showing the stress-strain curves in Example 3. The test was conducted at a tensile strain rate of 4.25×10 -4 seconds -1 In Figure 9, as-HIP is the sample immediately after fabrication by HIP, and STA is the sample after STA treatment. As shown in Figure 9, in as-HIP, although the endurance of Sample C is lower than that of Sample A, its ductility is greater. In the STA treatment, the ductility of both Sample A and C decreases. Sample C has a high breaking stress and large ductility. Thus, Sample C with Y / O of 10 has greater ductility than Sample A of Comparative Example 1.

[0064] As a result of the elemental mapping of FE-EPMA of Samples B and D fabricated by the laminated manufacturing method, in Sample B, regions where Al and O are present were observed, and it is considered that Al2O3 is present. In Sample D, regions where Nb and Y are present were observed, and it is considered that a compound of Nb and Y is present. Thus, in Sample B with Y / O being the theoretical value, oxygen that binds to Al is present, and it is considered that the δ phase is also present. In Sample D with Y / O being 10 times the theoretical value, it is considered that Y becomes excessive and reacts with Nb.

[0065] In Sample C with Y / O of 10 and approximately 3 times the theoretical value, almost no Al2O3 is formed, and the size and amount of the δ phase decrease. Therefore, it is considered that the creep characteristics are most improved.

[0066] 〔Example 4〕 Example 4 is an example of IN625 (INCONEL (registered trademark) 625 alloy (hereinafter IN625)). Alloy powder was produced using the atomization method, and a molded body was produced using the additive manufacturing method. M280 manufactured by EOS was used as the additive manufacturing apparatus. Thereafter, STA treatment was performed. The STA conditions were heat treatment at 1120 °C (sample for creep characteristics in Fig. 10(a)) or 980 °C (sample for stress-strain curve in Fig. 10(b)) for 1 hour, treatment at 718 °C for 8 hours after air cooling, heat treatment at 621 °C for 10 hours after cooling in a heat treatment furnace, and then air cooling.

[0067] Table 3 is a table showing the elemental composition in the alloy powder. In Example 4, Y / O is 2.53. Comparative Example 4 does not contain Y.

Table 3

[0068] For Example 4 and Comparative Example 4, the creep characteristics in the stacking direction were measured. The measurement conditions were a temperature of 650 °C and a stress of 550 MPa. Also, the stress-strain curve was measured. The measurement temperature was 650 °C.

[0069] Fig. 10(a) is a diagram showing the creep characteristics in Example 4 and Comparative Example 4, and Fig. 10(b) is a diagram showing the stress-strain curve. As shown in Fig. 10(a), Example 4 has a greater creep life and creep ductility than Comparative Example 4. As shown in Fig. 10(b), although the yield strength of Example 4 is lower than that of Comparative Example 4, the ductility is improved. It is considered that the decrease in the yield strength in Example 4 is due to the decrease in the size and amount of the δ phase. As described above, Example 4 has improved creep characteristics and improved ductility compared to Comparative Example 4.

[0070] 〔Example 5〕 Example 5 is an example of the Ni-based alloy HASTELLOY (registered trademark) X containing Cr and Mo. Alloy powder was produced using the atomization method, and a formed body was produced using the additive manufacturing method. M290 manufactured by EOS was used as the additive manufacturing apparatus. As heat treatment, solution treatment (ST) at a temperature of 1177°C for 2 hours was performed.

[0071] Table 4 is a table showing the elemental composition in the alloy powder. In Example 5, Y / O is 3.9. Comparative Example 5 does not contain Y. The Ni content was converted from the contents of other elements.

Table 4

[0072] For Example 5 and Comparative Example 5, the creep properties of the samples after forming and after ST treatment were measured. The measurement conditions were a temperature of 900°C and a stress of 80 MPa. When elemental mapping was performed on the as-formed sample of Example 5 using the EDS (Energy Dispersive X-ray Spectroscopy) method, regions where Y and O were unevenly distributed were observed. From this, it was found that the Y2O3 phase was present.

[0073] Figures 11(a) and 11(b) are diagrams showing the creep properties in the stacking direction and the orthogonal direction after forming for Example 5 and Comparative Example 5, respectively. Figures 12(a) and 12(b) are diagrams showing the creep properties in the stacking direction and the orthogonal direction after ST treatment for Example 5 and Comparative Example 5, respectively.

[0074] As shown in Figures 11(a) to 12(b), in both the as-formed state and after ST treatment, in both the stacking direction and the orthogonal direction, Example 5 has a longer creep life and greater creep ductility than Comparative Example 5. Thus, the creep properties of Example 5 are improved compared to Comparative Example 5. Even in a solid-solution strengthened alloy that does not contain Nb, Al, and Ti, such as Example 5, adding Y improves the creep properties.

[0075] [Example 6] Example 6 is an example of a TiAl4822 alloy as a TiAl alloy. Alloy powder was produced using the atomization method, and a compact was produced using the Spark Plasma Sintering (SPS) method. The SPS method is a method of sintering a workpiece in a vacuum by mechanical pressure and pulsed electric current heating. Then, heat treatment was performed. Each condition is as follows. The applied pressure in the SPS method was 50 MPa, and the temperature was maintained at 1075 °C for 10 minutes. As the heat treatment, homogenization heat treatment was performed in which the temperature was 1205 °C in a vacuum for 5 hours and then furnace cooling was carried out.

[0076] Table 5 is a table showing the elemental composition in the alloy powder. In Example 6, Y / O is 2.63. In Comparative Example 6, Y is not contained. The Ti content was converted from the contents of other elements.

Table 5

[0077] For Example 6 and Comparative Example 6, elemental mapping was performed using FE-EPMA. Fig. 13 is a diagram showing elemental mapping using FE-EPMA in Example 6, and Fig. 14 is a diagram showing elemental mapping using FE-EPMA in Comparative Example 6. COMPO is a SEM backscattered electron composition image. As shown in Fig. 14, in Comparative Example 6, a coarse white phase is observed in the SEM image. This phase contains a large amount of Ti and O and is a segregation phase of Ti and O. As shown in Fig. 13, in Example 6, no segregation phase of Ti and O was observed. Thus, by adding Y to the TiAl alloy, the segregation of Ti and O is suppressed and the tissue stability is improved.

[0078] [Summary of Examples] When manufacturing alloys using the casting and forging (C&W: Cast & Wrought) method, the casting method, and the forging method, the oxygen concentration can be reduced. However, it is difficult to manufacture molded bodies with complex shapes using these methods. Additive manufacturing methods such as the SLM (Selective Laser Melting) method using a laser beam and the EBM (Electron Beam Melting) method using an electron beam, the HIP (Hot Isostatic Pressing) method, the PBF (Powder Bed fusion) method, and the DED (Direct Energy Deposition) method are used to form alloy molded bodies. This makes it possible to manufacture molded bodies with complex shapes. These methods form molded bodies from alloy powders. Since alloy powders have a large surface area, oxygen is easily incorporated into the alloy. As a result, the molded bodies formed from alloy powders also contain a large amount of oxygen.

[0079] Molded bodies other than those formed from heat-resistant alloy powders may also contain a large amount of oxygen. The performance of such heat-resistant alloy molded bodies, such as creep characteristics, deteriorates. As in Comparative Examples 1 to 6, heat-resistant alloys containing at least one element of Al, Ti, Ni, Cr, and Mo form harmful phases due to the oxidation of these elements, resulting in deterioration of the alloy performance. Therefore, as shown in FIG. 6, Y, which has a lower standard Gibbs free energy of oxide formation than Al, Ti, Ni, Cr, and Mo, is added to the alloy. The ratio Y / O of the content of Y in mass conversion to the content of O in mass conversion in the stoichiometric composition ratio of yttria (Y2O3) is 3.9. Therefore, Y / O is set to 0.5 or more and 100 or less. Oxidation of at least one of Al, Ti, Ni, Cr, and Mo can be suppressed. Thus, the performance of heat-resistant alloys, such as creep characteristics, can be improved.

[0080] 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.

[0081] In Ni-based alloys such as those of Examples 1 to 4, the Ni content is 40.0 mass% or more, for example 50.0 mass% or more. In Ni-based alloys, the O content in alloys produced by casting forging methods, casting methods, and forging methods is, for example, 5 ppm to 20 ppm. In contrast, the O content in alloy powders and compacts formed from alloy powders is, for example, 50 ppm to 200 ppm. When the O content in the alloy is 0.002 mass% (20 ppm) or more, deterioration of performance due to oxides occurs as compared with alloys produced by casting forging methods, casting methods, and forging methods. Therefore, it is preferable to add Y. When the O content in the alloy is 0.005 mass% (50 ppm) or more, the performance of the alloy deteriorates more. 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 0.1 mass% (1000 ppm) or less, and more preferably 0.05 mass% (500 ppm) or less.

[0082] In the case of Ni-based alloys, when the content of at least one element of Al, Ti, Cr, and Mo is 0.01 mass% or more, at least one element of Al, Ti, Cr, and Mo oxidizes and the performance of the alloy deteriorates. Therefore, it is preferable to add Y. When the content of at least one element of Al, Ti, Cr, and Mo is 0.1 mass% or more, at least one element of Al, Ti, Cr, and Mo oxidizes and the performance of the alloy deteriorates more. Therefore, it is preferable to add Y.

[0083] When Ni-based alloys contain Al, Ti, and Nb as in IN718 and IN625, a δ phase is formed and the performance of the alloy deteriorates. Therefore, it is preferable to add Y when the content of at least one of the elements Al and Ti in the alloy is 0.01 mass% or more and 1.0 mass% or less, and the Nb content is 1.0 mass% or more and 10.0 mass% or less. It is more preferable to add Y when the content of at least one of the elements Al and Ti is 0.05 mass% or more, or 0.1 mass% or more. It is more preferable to add Y when the Nb content is 2.0 mass% or more.

[0084] In the IN718 alloy, the contents of the main elements are as shown in Table 2: The content of Ni is 50.0 mass% or more and 55.0 mass% or less. The content of Cr is 17.0 mass% or more and 21.0 mass% or less. The content of Fe is 11.0 mass% or more and 25.0 mass% or less. The content of Mo is 2.8 mass% or more and 3.3 mass% or less. The content of Nb is 4.75 mass% or more and 5.50 mass% or less. The content of Al is 0.20 mass% or more and 0.80 mass% or less. The content of Ti is 0.65 mass% or more and 1.15 mass% or less.

[0085] In the IN625 alloy, the contents of the main elements are as shown in Table 3: 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.

[0086] When the content of at least one of Cr and Mo in the Ni-based alloy is 1 mass% or more, as in the HASTELLOY® X alloy in Example 5, it is preferable to add Y. The content of at least one of the elements Cr and Mo is more preferably 5 mass% or more.

[0087] In the HASTELLOY® X alloy, the contents of the main elements are as shown in Table 4: The content of Ni is 41.0 mass% or more and 54.0 mass% or less. The content of Cr is 20.5 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 Fe is 17.0 mass% or more and 20.0 mass% or less. The content of W 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.

[0088] In the Ti-based alloy, the Ti content is 50 mass% or more, for example 60 mass% or more. In the TiAl alloy, the Ti content is 30 mass% or more, for example 50 mass% or more. The Al content is 3 mass% or more, for example 10 mass% or more, for example 30 mass% or more. In the Ti-based alloy and the TiAl alloy, the O content in the alloy produced by the casting forging method, the casting method, and the forging method is, for example, 250 ppm to 500 ppm. On the other hand, the O content in the alloy powder and the molded body formed from the alloy powder is, for example, 700 ppm to 1100 ppm. When the O content in the alloy is 0.05 mass% (500 ppm) or more, the performance deterioration due to oxides occurs compared to the alloy produced by the casting forging method, the casting method, and the forging method. Therefore, it is preferable to add Y. When the O content in the alloy is 0.07 mass% (700 ppm) or more, the performance of the alloy deteriorates more. 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.

[0089] In the 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, and is.

[0090] Also, Y may be added to the Ti64 alloy. In the Ti64 alloy, the contents of the main elements are, The Ti content is bal, 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 content of V is 3.5% by mass or more and 4.5% by mass or less, and is as follows.

[0091] FIG. 15 is a diagram showing an example of a method for manufacturing a heat-resistant alloy formed body. As shown in FIG. 15, first, alloy powder is produced (step S10). The alloy powder is produced, for example, using an atomization method. Next, an alloy formed body is produced by forming the alloy powder (step S12). For the production of the alloy formed body, for example, a layered manufacturing method, a hot forging method, a powder bed fusion bonding method, and a directed energy deposition method can be used. Next, the formed body is heat-treated (step S14). As the heat treatment, for example, solution aging treatment (STA) and direct aging treatment (DA: Direct Aging) can be used.

[0092] The heat-resistant alloy may be the heat-resistant alloy powder produced in step S10, or the heat-resistant alloy formed body produced in steps S12 and S14.

[0093] As described above, since the heat-resistant alloy of the present embodiment has improved high-temperature strength characteristics and oxidation resistance, it is useful in fields such as aircraft engines, rocket engines, industrial gas turbines, and automobile engines.

[0094] 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 changes are possible within the scope of the gist of the present invention described in the claims.

Claims

1. 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, The Cu content is 0.3 mass% or less, The Mn content is 0.35 mass% or less, The C content is 0.08 mass% or less, The Si content is 0.35 mass% or less, and The O content is greater than 0.002 mass% and 0.1 mass% or less, The balance is Fe, contains Y, at least a part of Y is contained as yttria, A heat-resistant alloy in which the ratio of the mass-converted content of Y to the mass-converted content of O is greater than 3.9, which is the theoretical value of the ratio in the yttria, and 40 or less.

2. The heat-resistant alloy according to claim 1, wherein the O content is 0.005 mass% or more and 0.02 mass% or less.

3. The heat-resistant alloy according to claim 1 or 2, wherein the Y content is 0.026 mass% or more and less than 0.5 mass%.

4. The heat-resistant alloy according to any one of claims 1 to 3, wherein the ratio of the mass-converted content of Y to the mass-converted content of O is 5.2 or more and 40 or less.

5. A heat-resistant alloy powder for additive manufacturing, comprising the heat-resistant alloy according to any one of claims 1 to 4.

6. A heat-resistant alloy laminated formed body made of the heat-resistant alloy according to any one of claims 1 to 4.

7. A step of forming a heat-resistant alloy powder made of the heat-resistant alloy according to any one of claims 1 to 4 using a molten metal added with metal Y, A step of forming a formed body by molding the heat-resistant alloy powder, and a method for manufacturing a heat-resistant alloy laminated formed body including the steps.

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