Alloy material, alloy product using the same, and mechanical device having the same

Abstract

Provided are an alloy material capable of suppressing the coarse growth and agglomeration of undesirable intermetallic compound phases, an alloy product using the alloy material, and a mechanical device having the alloy product. The alloy material of the present invention contains each of Co, Cr, Fe, and Ni in a range of 5 atomic % to 40 atomic %, Mo in a range of greater than 0 atomic % to less than 8 atomic %, Ti in a range of greater than 1 atomic % to less than 8 atomic %, and at least one of Ta and Nb in a range of greater than 0 atomic % to less than 4 atomic %, with the total amount of Ti and at least one of Ta and Nb being 3 atomic % to 8 atomic %, with the remainder being unavoidable impurities. In an alloy product using the alloy material, the combined occupancy of precipitates of η phase and Laves phase with a size of 1 μm or greater is suppressed to less than 5 area %.

Description

Technical Field

[0001] The present invention relates to a technology for alloys having excellent corrosion resistance and mechanical properties, and in particular to an alloy material called a high-entropy alloy, an alloy product using the alloy material, and a mechanical device having the alloy product. Background Art

[0002] In recent years, high-entropy alloys (HEAs) / multiple primary element alloys (MPEAs) have been proposed as a new technological concept that differs significantly from conventional alloys (e.g., alloys with trace amounts of multiple secondary elements added to one to three primary elements). HEAs / MPEAs are alloys composed of at least four primary metal elements (each comprising less than half, for example, 5 to 35 atomic percent) and are known to exhibit the following characteristics.

[0003] For example, there are: (a) stabilization of the mixing state due to the increase in the mixing entropy term in the Gibbs free energy formula in the negative direction, (b) diffusion delay due to the complex microstructure, (c) improvement in mechanical properties due to high lattice strain caused by the size difference of the constituent atoms, (d) improvement in corrosion resistance due to the combined effect (also called cocktail effect) caused by the coexistence of multiple elements, etc.

[0004] For example, patent document 1 (WO2017 / 138191A1) discloses an alloy component, which is an alloy component using a high entropy alloy, containing Co (cobalt), Ni (nickel), Cr (chromium), Fe (iron), and Ti (titanium) in a range of more than 5 atomic % and less than 35 atomic %, and containing Mo (molybdenum) in a range of more than 0 atomic % and less than 8 atomic %, and the remainder is composed of unavoidable impurities, and extremely small particles with an average particle size of less than 40 nm are dispersed and precipitated in the parent phase grains.

[0005] According to Patent Document 1, a high-entropy alloy having high mechanical strength and high corrosion resistance is used to provide an alloy member having excellent homogeneity of alloy composition and microstructure and excellent shape controllability.

[0006] In addition, patent document 2 (WO2019 / 088157A1) discloses an alloy material, which contains Co, Cr, Fe, Ni, and Ti in a range of more than 5 atomic % and less than 35 atomic %, Mo in a range of more than 0 atomic % and less than 8 atomic %, and an element with an atomic radius larger than the atomic radius of the above-mentioned Co, Cr, Fe, and Ni in a range of more than 0 atomic % and less than 4 atomic %, and the remainder is composed of unavoidable impurities.

[0007] In Patent Document 2, based on the chemical composition of Patent Document 1, by adding one or more of Ta, Nb, Hf, Zr and Y as elements with a larger atomic radius, an alloy material showing higher mechanical properties and / or higher corrosion resistance can be provided.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: International Publication No. 2017 / 138191

[0011] Patent Document 2: International Publication No. 2019 / 088157 Summary of the Invention

[0012] Problems to be solved by the invention

[0013] The alloy materials described in Patent Documents 1 and 2 have extremely small particles dispersed and precipitated within the parent phase grains, and exhibit excellent mechanical properties and corrosion resistance that are equal to or better than those of other Ni-based alloys and stainless steels. However, if coarse grains of undesirable intermetallic compound phases (e.g., η phase (Ni3Ti phase) and Laves phase (Fe2Ti phase)) grow or aggregate, the mechanical properties of the alloy materials (e.g., tensile strength and ductility) are significantly reduced.

[0014] The present inventors investigated various applications based on the alloy materials described in Patent Documents 1 and 2. They discovered that controlling precipitates becomes more difficult as the volume of the alloy product increases. After extensive investigation and research into the primary cause, they concluded that this phenomenon is caused by the increased heat capacity of the alloy product, making it difficult to control the cooling rate during the pseudo-solution heat treatment step.

[0015] From the perspective of the reliability and manufacturing yield of the alloy product, it is preferred that the alloy product exhibit the expected properties with good reproducibility without being affected by its volume and heat capacity (hereinafter referred to as volume / heat capacity). Therefore, it is expected that the coarse grain growth and cohesion precipitation of the undesirable intermetallic compound phase can be controlled and suppressed.

[0016] Therefore, the object of the present invention is to provide an alloy material that can suppress the coarse grain growth and agglomeration precipitation of undesirable intermetallic compound phases (such as η phase (Ni3Ti-based phase), Laves phase (Fe2Ti-based phase), etc.), an alloy product using the alloy material, and a mechanical device having the alloy product.

[0017] Methods for solving problems

[0018] (I) One embodiment of the present invention provides an alloy material characterized in that it contains each of Co, Cr, Fe, and Ni in a range of 5 atomic % or more and 40 atomic % or less, contains Mo in an amount greater than 0 atomic % and less than 8 atomic %, contains Ti in an amount greater than 1 atomic % and less than 8 atomic % and contains at least one of Ta and Nb in an amount greater than 0 atomic % and less than 4 atomic %, wherein the total of the Ti and at least one of the Ta and Nb is 3 atomic % or more and 8 atomic % or less, and the remainder is composed of unavoidable impurities.

[0019] The present invention can add the following improvements and modifications to the above-mentioned alloy material (I).

[0020] (i) Contains 2 atomic % or more and less than 5 atomic % of the above-mentioned Ti.

[0021] (ii) Contains 25 atomic % or more and 38 atomic % or less of the above-mentioned Co, 16 atomic % or more and 23 atomic % or less of the above-mentioned Cr, 12 atomic % or more and 20 atomic % or less of the above-mentioned Fe, 17 atomic % or more and 28 atomic % or less of the above-mentioned Ni, and 1 atomic % or more and 7 atomic % or less of the above-mentioned Mo.

[0022] (II) Another embodiment of the present invention provides an alloy product using the above-mentioned alloy material, characterized in that when a secondary electron image of a cross section of the above-mentioned alloy product is observed using a scanning electron microscope, the total occupancy rate of precipitates of η phase and Laves phase with a size of 1 μm or more is less than 5 area%.

[0023] The present invention can add the following improvements and modifications to the above-mentioned alloy product (II).

[0024] (iii) Very small particles having an average particle size of 130 nm or less are dispersed and precipitated in the matrix grains of the alloy product.

[0025] (III) Another embodiment of the present invention is a mechanical device including the alloy product described above.

[0026] Effects of the Invention

[0027] According to the present invention, it is possible to provide an alloy material capable of suppressing the coarse grain growth and agglomeration precipitation of a predetermined intermetallic compound phase, an alloy product using the alloy material, and a mechanical device having the alloy product. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a secondary electron image taken by a scanning electron microscope (SEM) showing an example of the cross-sectional microstructure of the alloy product of the present invention.

[0029] Figure 2 This is a schematic diagram showing a power transmission device as an example of a mechanical device including the alloy product of the present invention.

[0030] Figure 3 This is a process diagram showing an example of a method for producing an alloy product of the present invention.

[0031] Figure 4A This is a SEM secondary electron image showing the cross-sectional microstructure of a sample of alloy product P3 using alloy material A3.

[0032] Figure 4B This is a SEM secondary electron image showing the cross-sectional microstructure of a sample of an alloy product P2 using alloy material A2.

[0033] Figure 5 This is a SEM secondary electron image of a sample of the alloy product P1 observed at a high magnification.

[0034] Figure 6A This is a SEM secondary electron image showing the cross-sectional microstructure of a sample of alloy product P7 using alloy material A7.

[0035] Figure 6B This is a SEM secondary electron image showing the cross-sectional microstructure of a sample of an alloy product P8 using the alloy material A8.

[0036] Figure 6C This is a SEM secondary electron image showing the cross-sectional microstructure of a sample of an alloy product P11 using the alloy material A11.

[0037] Figure 7 (a) A dark field image of the matrix phase grains and (b) an electron diffraction pattern of the matrix phase grains obtained by scanning transmission electron microscopy.

[0038] Figure 8 This is an image showing the element distribution of extremely small particles in the parent phase grains obtained by energy dispersive X-ray analysis. DETAILED DESCRIPTION

[0039] (Basic idea of ​​the present invention)

[0040] As described above, the alloy materials described in Patent Documents 1 and 2 show a tendency to make it difficult to control precipitates as the volume of the alloy product to be produced increases. Various investigations and studies have been conducted on the main cause of this phenomenon, and it is believed that this phenomenon is caused by the increased heat capacity of the alloy product, which makes it difficult to control the cooling rate during the pseudo-solution heat treatment process.

[0041] From the perspective of the reliability and manufacturing yield of alloy products, it is preferred that the alloy products exhibit the expected properties with good reproducibility without being affected by their volume / heat capacity. Therefore, it is desirable to produce an alloy material that can suppress the coarse grain growth (e.g., precipitates with a size of 1 μm or more) and the cohesive precipitation of undesirable intermetallic compound phases.

[0042] Therefore, in order to meet the above requirements, the present inventors conducted intensive research on the component balance in the alloy (particularly the balance of components closely related to the formation of undesirable intermetallic compound phases such as η phase (Ni3Ti-based phase) and Laves phase (Fe2Ti-based phase)). As a result, they discovered that by incorporating at least one of Ta and Nb (hereinafter sometimes referred to as Ta and / or Nb) and further controlling the total content of Ti and Ta and / or Nb, the coarse grain growth and aggregation precipitation of η phase and Laves phase can be suppressed. The present invention was completed based on this finding.

[0043] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments listed here, and can be appropriately combined with or improved based on known technologies within the scope of the technical concept of the invention.

[0044] [Chemical composition of alloy materials]

[0045] The alloy material of the present invention contains, among the total specified elements, each of Co, Cr, Fe, and Ni in a range of 5 atomic % or more and 40 atomic % or less, Mo in a range of more than 0 atomic % and less than 8 atomic %, Ti in a range of more than 1 atomic % and less than 8 atomic %, and at least one of Ta and Nb in a range of more than 0 atomic % and less than 4 atomic %, wherein the total of the above-mentioned Ti and at least one of the above-mentioned Ta and Nb is 3 atomic % or more and 8 atomic % or less, and the remainder is composed of unavoidable impurities.

[0046] Co, Cr, Fe, and Ni are believed to be the main constituent elements of the parent phase grains of alloy materials or alloy products, contributing to improvements in mechanical strength and corrosion resistance due to solid solution strengthening and the cocktail effect. Furthermore, by including these elements in equimolar amounts, the configuration entropy increases, facilitating the stabilization of the face-centered cubic (fcc) solid solution structure.

[0047] Below, the content of these component elements in the alloy material is described in more detail. It should be noted that the upper limit and lower limit of the following component elements can be combined arbitrarily. In addition, preferred range, more preferred range and further preferred range can also be appropriately combined.

[0048] The Co content is preferably 20 atomic % or more and 40 atomic % or less, more preferably 25 atomic % or more and 38 atomic % or less, further preferably 30 atomic % or more and 37 atomic % or less, and even more preferably 32 atomic % or more and 36 atomic % or less.

[0049] The Cr content is preferably 10 atomic % or more and 25 atomic % or less, more preferably 16 atomic % or more and 23 atomic % or less, and still more preferably 18 atomic % or more and 21 atomic % or less.

[0050] The Fe content is preferably 10 atomic % or more and 25 atomic % or less, more preferably 12 atomic % or more and 20 atomic % or less, and still more preferably 14 atomic % or more and 17 atomic % or less.

[0051] The Ni content is preferably 15 atomic % or more and 30 atomic % or less, more preferably 17 atomic % or more and 28 atomic % or less, and even more preferably 21 atomic % or more and 26 atomic % or less.

[0052] The Mo content is preferably greater than 0 atomic % and less than 8 atomic %, more preferably greater than 1 atomic % and less than 7 atomic %, and even more preferably greater than 2 atomic % and less than 5 atomic %. Mo is believed to contribute to improved corrosion resistance together with Cr. However, if the Mo content is 0 atomic %, no effect of improving corrosion resistance is achieved. If the Mo content exceeds 8 atomic %, the formation of brittle intermetallic compounds such as σ phase (tetragonal system), μ phase (rhombohedral system), and Laves phase (face-centered cubic system or hexagonal system) is promoted.

[0053] The Ti content is preferably 1 atomic % or more and less than 8 atomic %, more preferably 2 atomic % or more and less than 7 atomic %, and further preferably 2 atomic % or more and less than 5 atomic %. It is believed that Ti is a component that constitutes extremely small particles dispersed and precipitated in the parent phase grains, and contributes to improving the mechanical strength of the alloy material. When the Ti content is less than 1 atomic %, the effect of improving the mechanical strength is not obtained. When it is 8 atomic % or more, it is easy to induce coarse grain growth and cohesion precipitation of undesirable intermetallic compound phases.

[0054] The content of Ta and / or Nb (at least one of Ta and Nb) is preferably greater than 0 atomic % and less than 4 atomic %, more preferably greater than 0.5 atomic % and less than 3 atomic %, and even more preferably greater than 1 atomic % and less than 2.5 atomic %. By adding at least one of Ta and Nb, which have large atomic sizes, the mechanical properties of the alloy can be further improved through solid solution strengthening. Furthermore, the passive film of the alloy is strengthened, thereby improving pitting corrosion resistance. When the content of Ta and / or Nb is 0 atomic %, no effect of improving mechanical properties or pitting corrosion resistance is achieved. When the content of Ta and / or Nb exceeds 4 atomic %, the precipitation of undesirable intermetallic compounds is promoted.

[0055] In the alloy material of the present invention, Ta and / or Nb are appropriately contained to suppress the Ti content compared to conventional alloy materials. The total content of Ti, Ta and / or Nb in the prescribed element as a whole is preferably 3 atomic % or more and 8 atomic % or less, more preferably 4 atomic % or more and less than 8 atomic %, and further preferably 4.5 atomic % or more and 7.5 atomic % or less. If the total content of Ti, Ta and / or Nb is less than 3 atomic %, the contribution of strengthening and solid solution strengthening brought about by extremely small particles becomes small, and therefore the improvement effect of mechanical properties cannot be obtained. If it exceeds 8 atomic %, the coarse grain growth and cohesion precipitation of undesirable intermetallic compound phases are promoted.

[0056] By controlling the composition of each component within the above range, it is possible to suppress the undesirable coarse grain growth and aggregation of the intermetallic compound phase. In other words, if each component deviates from its own preferred composition range, it is difficult to achieve the desired properties.

[0057] Inevitable impurities are components that are difficult to completely remove but are preferably reduced as much as possible. Examples include Si (silicon), P (phosphorus), S (sulfur), N (nitrogen), and O (oxygen). The total content of inevitable impurities is preferably 1% by mass or less. In other words, the total content of intentionally included components is preferably 99% by mass or more of the total alloy mass.

[0058] Regarding the content of inevitable impurities, for example, Si is preferably 0.2 mass% or less, more preferably 0.1 mass% or less, and even more preferably 0.05 mass% or less. P is preferably 0.1 mass% or less, more preferably 0.05 mass% or less, and even more preferably 0.02 mass% or less. S is preferably 0.1 mass% or less, more preferably 0.05 mass% or less, and even more preferably 0.02 mass% or less. N is preferably 0.1 mass% or less, more preferably 0.05 mass% or less, and even more preferably 0.02 mass% or less. O is preferably 0.2 mass% or less, more preferably 0.1 mass% or less, and even more preferably 0.05 mass% or less.

[0059] [Alloy products using alloy materials]

[0060] (Microstructure)

[0061] An alloy product using the alloy material of the present invention has a fine structure in which matrix phase grains and extremely small particles of an L12 type ordered phase are dispersed and precipitated in the matrix phase grains.

[0062] The parent phase grains are preferably equiaxed crystals with an average grain size of less than 300 μm, and their crystal structure is face-centered cubic (FCC). When the average grain size is less than 300 μm, mechanical properties and corrosion resistance are improved. The average grain size of the parent phase grains is preferably less than 200 μm, more preferably less than 150 μm. It should be noted that, in the present invention, the crystal structure of the parent phase grains may include simple cubic crystals (SC). In addition, in the present invention, the average grain size of the parent phase grains is set to, and the image observed by the microstructure is subjected to image analysis to obtain the diameter of the equivalent area circle of each parent phase grain, and the value obtained by averaging them. The image analysis software is not particularly limited, and any software can be used.

[0063] The average particle size of the dispersed and precipitated extremely small particles is 130 nm or less, preferably 10 nm or more and 130 nm or less, and more preferably 20 nm or more and 100 nm or less. When the average particle size of the extremely small particles is 10 nm or more and 130 nm or less, the mechanical properties are improved. It should be noted that in the present invention, the average particle size of the extremely small particles is the value obtained by performing image analysis on the image of the microstructure observation, determining the maximum length of each extremely small particle, and averaging these values.

[0064] Furthermore, in this alloy product, the coarse grain growth and aggregation precipitation of the η phase (Ni3Ti-based phase) and the Laves phase (Fe2Ti-based phase) are suppressed. Specifically, when a secondary electron image (e.g., 400μm×300μm) of a cross-section of the alloy product is observed using a scanning electron microscope (SEM), the occupancy rate of precipitates (coarse precipitates) of the η phase and / or Laves phase with a size of 1μm or larger is 5 area% or less. This occupancy rate is more preferably 2 area% or less, and even more preferably 1 area% or less.

[0065] It should be noted that the "size" in the phrase "size 1 μm or larger" refers to the maximum length of the precipitate as determined by image analysis of microstructure observation images. Furthermore, the aforementioned η phase and Laves phase include not only phases composed of Ni3Ti and Fe2Ti, but also structures in which the Ni, Fe, and Ti components that constitute these phases are partially substituted.

[0066] Figure 1 This is a SEM secondary electron image showing an example of the cross-sectional microstructure of an alloy product of the present invention (alloy product P1 described later). Figure 1 As shown in FIG. 1 , in the alloy product of the present invention, the coarse grain growth and aggregation precipitation of the η phase and the Laves phase are suppressed. Specifically, Figure 1 The occupancy rate of coarse precipitates of the η phase and / or Laves phase was measured by image analysis and found to be 0.3 area %, which was very small.

[0067] It is believed that the alloy product of the present invention mainly comprises face-centered cubic crystals in which the parent phase grains are a type of closest-packed structure, extremely small particles are dispersed and precipitated in the parent phase grains, and coarse precipitates of η phase and Laves phase are suppressed, thereby achieving both good corrosion resistance and good mechanical properties.

[0068] The alloy products of the present invention can improve corrosion resistance and mechanical properties, making them suitable for use as components requiring high mechanical properties in harsh environments. Examples of such components include turbine components such as turbine blades, boiler components, engine components, nozzle components, housings, piping, structural materials for equipment such as valves and pumps, structural materials for generators, structural materials for nuclear reactors, structural materials for aerospace applications, components for hydraulic equipment, and mechanical components for various devices such as bearings, pistons, gears, and rotating shafts.

[0069] [Mechanical device with alloy components]

[0070] The mechanical device of the present invention can improve high mechanical properties under harsh environments, and is therefore preferably used in turbines, boilers, engines, nozzles, equipment, generators, nuclear reactors, aerospace equipment, hydraulic equipment, and various other equipment. For example, Figure 2 This is a schematic diagram showing an example of a power transmission device. By combining alloy products (a first gear, a first rotating shaft, a second gear, and a second rotating shaft), a power transmission device with excellent corrosion resistance and durability can be obtained.

[0071] The manufacturing method of each of the first gear, the first rotating shaft, the second gear, and the second rotating shaft is not particularly limited, but from the perspective of mass production, for example, a casting-forging method, a powder metallurgy method, an additive manufacturing method, etc. can be appropriately utilized. Figure 2 , a gear mechanism based on spur gears is shown, but the power transmission device of the present invention is not limited to spur gears, and may also be other gears (such as internal gears, helical gears, spiral gears, bevel gears, etc.).

[0072] [Method for producing alloy products]

[0073] Figure 3 FIG. 1 is a process diagram showing an example of a method for manufacturing an alloy product of the present invention. Figure 3 As shown, the method for producing the alloy product of the present invention generally comprises at least an alloy material preparation step S1 and a forming step S2, and further comprises a pseudo-solution heat treatment step S3 or a sintering step S4 depending on the forming process. Each step will be described in more detail below.

[0074] (Alloy material production process)

[0075] First, an alloy material preparation step S1 is performed to prepare an alloy material that will serve as the basis for the alloy product. The detailed steps of the alloy material preparation step S1 are not particularly limited as long as an alloy material capable of forming the desired alloy product can be obtained. For example, the steps include a raw material mixing and melting step S1a in which raw materials are mixed and melted to form a melt having a desired alloy composition, and an alloy solidification step S1b in which the melt is solidified to obtain the alloy material.

[0076] The raw material mixing and melting step S1a is not particularly limited as long as it is a step of mixing and melting raw material metals to obtain a melt. For example, to further reduce the content of impurities in the alloy (refining the alloy), it may be a step including the following steps: a melting step of mixing and temporarily melting the raw material metals to obtain a melt; an alloy ingot forming step of temporarily solidifying the melt to form an alloy ingot for remelting; and a remelting step of remelting the alloy ingot for remelting to obtain a purified melt. The remelting method is not particularly limited as long as it can improve the cleanliness of the alloy. For example, vacuum arc remelting (VAR) is preferably used.

[0077] The alloy solidification step S1b is not particularly limited as long as it can produce an alloy material in a form (e.g., alloy block (ingot), alloy powder, etc.) suitable for use in the next forming step S2. For example, a casting method or an atomization method can be appropriately utilized. When an ingot is prepared by casting, the alloy material of the present invention can suppress the growth and coarse-grained precipitation of η phase and Laves phase. Therefore, it has the advantage of suppressing undesirable solidification cracking caused by coarse precipitates even in ingots with large volume and heat capacity.

[0078] On the other hand, when the alloy powder is prepared by atomization in the alloy solidification step S1b, from the perspective of the fluidity and filling properties of the alloy powder when the alloy powder is formed (e.g., powder metallurgy process, additive manufacturing process) in the subsequent forming process step S2, the average particle size of the alloy powder is preferably 5 μm or more and 200 μm or less, more preferably 10 μm or more and 100 μm or less, and even more preferably 10 μm or more and 50 μm or less. It should be noted that in the present invention, the average particle size of the alloy powder is a volume-based weighted average particle size measured using a laser diffraction particle size distribution measuring device.

[0079] When the average particle size of the alloy powder is 5 μm or greater, the fluidity of the alloy powder is maintained during the molding process S2, minimizing the impact on the shape accuracy of the molded product. Furthermore, when the average particle size of the alloy powder is 200 μm or less, the filling properties of the alloy powder are maintained during the molding process S2. A deterioration in filling properties can cause internal voids and surface roughness in the molded product.

[0080] Based on the above, a powder classification step can be further performed to classify the average particle size of the alloy powder into a range of 5 μm to 200 μm. The powder classification step is not a necessary step, but is preferably performed from the perspective of improving the usability of the alloy powder. It should be noted that if the particle size distribution of the alloy powder is measured and the result is confirmed to be within the desired range, this step can also be considered to have been performed.

[0081] (Molding process)

[0082] Next, a forming step S2 is performed to form a molded body of a desired shape using the alloy material obtained in the alloy material production step S1. The forming method is not particularly limited as long as a molded body of the desired shape can be formed. For example, when the alloy material is an ingot, shearing, plastic working (forging, drawing, rolling, etc.), and mechanical working (punching, cutting, etc.) can be appropriately utilized.

[0083] On the other hand, when the alloy material is an alloy powder, a powder metallurgy process or an additive manufacturing process can be appropriately utilized. The powder metallurgy process or the additive manufacturing process is not particularly limited, and conventional processes can be appropriately utilized.

[0084] Additive manufacturing (AM) is a process that layers alloy powders into a desired shape. It allows for the production of near-net-shape alloy products through localized melting and rapid solidification without sintering. This allows for the direct manufacture of complex three-dimensional components with mechanical properties comparable to or better than those of forged materials. Examples of AM methods include selective laser melting (SLM), electron beam melting (EBM), and directed energy deposition (DED).

[0085] The additive manufacturing process in the SLM method is briefly described. This additive manufacturing process forms a compact by repeatedly performing an alloy powder bed preparation step, in which alloy powder is spread throughout the bed to prepare a predetermined thickness, and a laser melting and solidification step, in which a predetermined area of ​​the alloy powder bed is irradiated with a laser to cause localized melting and rapid solidification of the alloy powder in that area.

[0086] More specifically, in order to maximize the density and shape accuracy of the formed body, for example, the thickness h of the alloy powder bed is set to a range of 0.02 mm to 0.2 mm, the laser output P is set to a range of 50 W to 1000 W, the laser scanning speed S is set to a range of 50 mm / s to 10000 mm / s, and the laser scanning interval L is set to a range of 0.05 mm to 0.2 mm. The volume energy density E of local melting represented by "E = P / (h × S × L)" is preferably controlled to 20 J / mm 3 Above and 200J / mm 3 The following range is more preferably controlled at 40J / mm 3 Above and 150J / mm 3 Within the following range.

[0087] The molded body formed by the SLM method is buried in the alloy powder bed. Therefore, the stacked molding process can also include a removal step for removing the molded body from the alloy powder bed after the laser melting and solidification step. The method for removing the molded body is not particularly limited, and conventional methods can be used. It should be noted that in the EBM method, sandblasting using alloy powder can be preferably used as the removal step. Sandblasting using alloy powder has the advantage of being able to be reused as alloy powder by crushing it together with the removed alloy powder bed.

[0088] Furthermore, when the alloy material is alloy powder, in order to improve the shape accuracy of the molded product, the molded body produced by a laminate molding process, a powder metallurgy process, etc. may be further subjected to cutting, plastic working, machining, etc.

[0089] (Pseudo-solution heat treatment process)

[0090] The pseudo-solution heat treatment step S3 is a heat treatment step performed on a molded body formed from an ingot or produced through an additive manufacturing process. It is performed to homogenize any segregants and composition distribution that may remain in the molded body. It should be noted that, for the alloy material of the present invention, there is currently no established academic understanding, such as a phase equilibrium diagram, and it is impossible to accurately define the temperature at which segregants are completely dissolved. Therefore, the heat treatment in this step is referred to as pseudo-solution treatment.

[0091] The temperature of the main heat treatment is preferably in the range of 1000°C or more and 1250°C or less, more preferably 1050°C or more and 1200°C or less, and further preferably 1100°C or more and 1180°C or less. If the temperature of the main heat treatment is 1000°C or more, sufficient homogenization can be performed. In addition, if the temperature of the main heat treatment is 1250°C or less, the parent phase grains will not be excessively coarsened, and the corrosion resistance and mechanical properties will be improved. The heat treatment atmosphere is not particularly limited and may be in the air or in a non-oxidizing atmosphere (an atmosphere in which oxygen is substantially absent, such as in a vacuum, in high-purity argon, or in high-purity nitrogen).

[0092] In addition, the holding time in the heat treatment can be suitably set in the range of more than 0.1 hour and below 100 hours as long as the volume / heat capacity and the temperature of the heat treated body are considered. In the alloy material of the present invention and the alloy product, the coarse precipitate of η phase, Laves phase is suppressed. Therefore, even if the cooling rate after the high temperature is maintained is slower than the cooling rate of the alloy material in the past, the fine structure of nano-level extremely small particles dispersed in the parent phase grains can be obtained. Therefore, cooling method can be freely selected, and the management of cooling rate becomes easy. For example, nitrogen cooling after water cooling, air cooling or vacuum can be carried out.

[0093] Furthermore, even when uniform cooling is required, such as when the alloy product is large, a uniform internal structure without defects or central precipitates can be easily obtained, and mechanical properties can be maintained. It should be noted that from the perspective of controlling the average particle size of extremely small particles, it is preferable to quickly pass through the temperature range where the intermetallic compound phase easily grows (e.g., the temperature range of 900 to 800°C) within the possible range.

[0094] (Sintering process)

[0095] The sintering step S4 is a heat treatment step performed on the molded body formed by the powder metallurgy process. The heat treatment method is not particularly limited, and conventional methods can be appropriately utilized. For example, the forming process S2 and the sintering step S4 can be performed completely independently (only forming is performed in the forming process S2, and only sintering is performed in the sintering process S4), or the forming process S2 and the sintering step S4 can be performed integrally as in hot isostatic pressing (HIP).

[0096] The sintering temperature is not particularly limited, and for example, the same temperature range as that of the pseudo-solution treatment step S3 can be used. Specifically, the sintering temperature is preferably in the range of 1000°C to 1250°C, more preferably 1050°C to 1200°C, and even more preferably 1100°C to 1180°C.

[0097] (Finishing process)

[0098] Figure 3 Although not shown in the figures, the alloy product obtained through the pseudo-solution heat treatment step S3 and the sintering step S4 may be further subjected to a surface finishing step as needed.

[0099] Example

[0100] Hereinafter, the present invention will be described in detail based on Examples and Comparative Examples, but the present invention is not limited to these experimental examples.

[0101] [Experiment 1]

[0102] (Production of Alloy Materials A1 to A6)

[0103] First, raw material metals were mixed according to the names of alloy materials A1 to A6 shown in Table 1 below, and mixed raw materials for producing alloy materials A1 to A6 were prepared. Next, an automatic arc melting furnace (manufactured by Daya Vacuum Co., Ltd.) was used to melt the mixed raw materials on a water-cooled copper hearth in a reduced-pressure Ar atmosphere. This melt was then solidified to produce alloy ingots (approximately 34 mm in diameter and approximately 50 g in mass). Furthermore, in order to homogenize the alloy ingots, the alloy ingots were each inverted and remelted six times, thereby producing alloy materials A1 to A6 (alloy material production process).

[0104] [Table 1]

[0105] Table 1 Nominal alloy composition of alloy materials A1 to A6 (unit: atomic %)

[0106] Alloy materials Co Cr Fe Ni Mo Ti Ta Nb Ti+Ta+Nb A1 34.4 19.7 14.5 23.5 2.4 4.5 1.0 - 5.5 A2 32.6 19.7 14.5 23.5 2.4 6.7 0.5 0.1 7.3 A3 31.0 19.7 14.5 23.5 2.4 8.9 - - 8.9 A4 26.5 17.8 17.8 26.7 1.8 8.9 0.5 - 9.4 A5 26.5 17.7 17.7 26.5 1.8 8.8 1.0 - 9.8 A6 26.3 17.6 17.6 26.4 1.8 8.8 1.5 - 10.3

[0107] -: Indicates that it is not intentionally contained

[0108] As shown in Table 1, alloy materials A1 to A2 are alloy materials of the present invention (Examples), and alloy materials A3 to A6 are alloy materials that deviate from the provisions of the present invention (Comparative Examples).

[0109] [Experiment 2]

[0110] (Production of Alloy Products P1 to P6)

[0111] Next, each of the alloy materials A1 to A6 was subjected to machining to form a molded body (diameter 20 mm×height 10 mm) (molding process).

[0112] Next, the formed bodies made of alloy materials A1 to A6 were subjected to pseudo-solution heat treatment (pseudo-solution heat treatment step) by holding them at 1120°C for 1 hour in vacuum and then cooling them. Cooling after high-temperature holding was performed by introducing and circulating nitrogen gas into the furnace.

[0113] Furthermore, to further clarify the effects of the present invention (suppression of coarse precipitates of η phase and Laves phase), the molded body subjected to pseudo-solution heat treatment was subjected to aging heat treatment at 650°C for 24 hours in the atmosphere. By the above operation, samples of alloy products P1 to P6 were prepared.

[0114] [Experiment 3]

[0115] (Testing and Evaluation of Alloy Products P1 to P6)

[0116] (Microstructure Observation)

[0117] First, X-ray diffraction (XRD) measurements were performed on samples of alloy products P1 to P6 to identify the crystal structure of the matrix grains and the precipitated phases. The results showed that the matrix grains in alloy products P1 to P6 all had a predominantly fcc structure. However, since XRD measurements cannot completely distinguish between face-centered cubic (fcc) and simple cubic (sc) crystals, it cannot be concluded that sc is not present.

[0118] Regarding precipitated phases, η phase and / or Laves phase were detected in samples of alloy products P3 to P6, which served as comparative examples. On the other hand, neither η phase nor Laves phase was detected in samples of alloy products P1 to P2, which served as examples. This result suggests that even if some precipitated phases were present in samples of alloy products P1 to P2, the size of these precipitates was very small.

[0119] Next, samples of alloy products P1 to P6 were cut, and the cross section of one cut piece was mirror-polished and electrolytically etched (10% by mass oxalic acid aqueous solution, electric field conditions of 3 V × 0.2 A). This treated cross section was observed under SEM (observation area = 400 μm × 300 μm), and the occupancy rate of precipitates (coarse precipitates) with a size of 1 μm or more of η phase and / or Laves phase was measured by image analysis. A coarse precipitate occupancy rate exceeding 5 area% was evaluated as "unacceptable", a rate of 5 area% or less was evaluated as "acceptable", and a rate of 2 area% or less was evaluated as "excellent".

[0120] Figure 4A This is a SEM secondary electron image showing the cross-sectional microstructure of a sample of an alloy product P3 using alloy material A3 (comparative example). Figure 4BThis is a SEM secondary electron image showing the cross-sectional microstructure of a sample of an alloy product P2 using alloy material A2 (Example). Figure 1 This is a SEM secondary electron image of a sample of alloy product P1 using alloy material A1 (Example).

[0121] like Figure 4A As shown, coarse precipitates of η phase and / or Laves phase were clearly observed in the sample of alloy product P3, which serves as a comparative example. The occupancy rate of these coarse precipitates was measured to be 21.3% by area. Although not shown in the figure, coarse precipitates of η phase and / or Laves phase were also clearly observed in the samples of alloy products P4 to P6, which serve as comparative examples, similarly to the sample of alloy product P3.

[0122] In contrast, Figure 4B 、 Figure 1 As shown, the samples of alloy products P2 and P1, which are examples, showed a low amount of coarse precipitates, and the growth and aggregation of coarse grains of the η phase and Laves phase were suppressed. The percentage of coarse precipitates in the samples of alloy products P2 and P1 was measured to be 2.4 area% and 0.3 area%, respectively.

[0123] The measurement results of the occupancy of coarse precipitates of the η phase and / or Laves phase are summarized in the following Table 2. Based on the results of microstructure observation, the alloy samples of Examples are expected to exhibit higher ductility and toughness than the samples of Comparative Examples.

[0124] Furthermore, samples of the alloy products P1 to P6 were observed at high magnification (approximately 10,000 to 50,000 times). Figure 5 This is a SEM secondary electron image of the sample of alloy product P1 observed at 20,000 times. Figure 5 In this experiment, the average particle size of the extremely small particles was calculated by analyzing the SEM secondary electron image (observation area = 3μm×3μm) and taking the average value of the major axis (maximum length) of each extremely small particle.

[0125] Regarding the average particle size of the extremely small particles, those exceeding 130 nm were evaluated as "unacceptable," those 130 nm or less were evaluated as "acceptable," and those 100 nm or less were evaluated as "excellent." The measurement and evaluation results of the average particle size of the extremely small particles are summarized in Table 2. As can be seen from the results in Table 2, samples P1 to P2, which are examples of alloy products, were evaluated as "excellent," while samples P3 to P6, which are comparative examples of alloy products, were evaluated as "unacceptable." This suggests that the samples of the alloy products of the examples suppressed the coarsening of the extremely small particles dispersed and precipitated within the parent phase grains.

[0126] (Vickers hardness test)

[0127] The room temperature Vickers hardness (HV) of the other cut pieces of the alloy samples P1 to P6 was measured as an indicator of mechanical strength. A micro Vickers hardness tester (MMT-X series, manufactured by Matsuzawa Co., Ltd.) was used to measure 10 points (load: 200 gf, hold time: 15 seconds). The average of the 8 Vickers hardness values, excluding the maximum and minimum values, was used as the Vickers hardness of the sample.

[0128] Vickers hardness was evaluated as "pass" if HV 450 or higher, and "fail" if HV 450 or lower. All samples of alloy products P1 to P6 were evaluated as passing. The results of the Vickers hardness measurements are summarized in Table 2. In other words, the alloy samples of the examples were found to have mechanical strength comparable to that of the comparative examples.

[0129] (Pitting test)

[0130] As a corrosion resistance test, a pitting test was conducted. In addition, samples of alloy products P1 to P6 were made and polarization test pieces (length 15mm × width 15mm × thickness 2mm) were collected for pitting test. The pitting test was conducted on each polarization test piece in accordance with JIS G0577. Specifically, in the "test area: 1cm 2 The anodic polarization curve of the polarization test piece was measured under the following conditions: a gap anti-corrosion electrode was installed on the polarization test piece, a reference electrode was a saturated silver-silver chloride electrode, a test solution was a 3.5 mass% sodium chloride aqueous solution after argon degassing, a test temperature was 80°C, and a potential sweep rate was 20 mV / min. The anodic polarization curve of the polarization test piece was obtained with a current density of 100 μA / cm 2 Corresponding pitting generation potential (unit: Vvs.Ag / AgCl).

[0131] In the pitting corrosion test, a value less than 0.50V was evaluated as "failed," a value greater than 0.50V was evaluated as "passed," and a value greater than 1.00V was evaluated as "excellent." The pitting corrosion test results are summarized in Table 2. Alloy products P2 to P6 were evaluated as passing, while alloy product P1 was evaluated as excellent. In other words, the alloy products of the examples exhibited corrosion resistance comparable to or better than that of the comparative examples.

[0132] [Table 2]

[0133] Table 2 Test and evaluation results of alloy products P1 to P6

[0134]

[0135] [Experiment 4]

[0136] (Production of alloy materials A7 to A11)

[0137] Alloy materials A7 to A11 having the nominal compositions shown in Table 3 were prepared in the same manner as in Experiment 1. Alloy materials A7 to A11 are all alloy materials (Examples) of the present invention.

[0138] [Table 3]

[0139] Table 3 Nominal alloy composition of alloy materials A7 to A11 (unit: atomic %)

[0140] Alloy materials Co Cr Fe Ni Mo Ti Ta Nb Ti+Ta+Nb A7 33.4 19.7 14.5 23.5 2.4 5.5 1.0 - 6.5 A8 35.4 19.7 14.5 23.5 2.4 3.5 1.0 - 4.5 A9 33.9 19.7 14.5 23.5 2.4 4.5 1.5 - 6.0 A10 34.9 19.7 14.5 23.5 2.4 4.5 0.5 - 5.0 A11 33.9 19.7 14.5 23.5 2.4 4.5 1.0 0.5 5.5

[0141] -: Indicates that it is not intentionally contained

[0142] [Experiment 5]

[0143] (Production of Alloy Products P7 to P11)

[0144] Alloy materials A7 to A11 were formed into molded bodies in the same manner as in Experiment 2. Each molded body was subjected to a pseudo-solution heat treatment in which the molded body was held at 1120°C in a vacuum for 1 hour and then cooled. Cooling after the high-temperature holding was performed by introducing and circulating nitrogen gas into the furnace.

[0145] Next, the molded bodies that had undergone pseudo-solution heat treatment were subjected to aging heat treatment. Alloy products P7, P9, and P11 were subjected to aging heat treatment at 650°C in air for 8 hours. Furthermore, alloy products P8 and P10 were subjected to aging heat treatment at 700°C in air for 8 hours. Through the above operations, samples of alloy products P7 to P11 were produced.

[0146] [Experiment 6]

[0147] (Testing and Evaluation of Alloy Products P7 to P11)

[0148] Microstructure observation and Vickers hardness measurement and evaluation of alloy products P7 to P11 were performed in the same manner as in Experiment 3. The measurement and evaluation results are shown in Table 4.

[0149] in addition, Figure 6A This is a SEM secondary electron image showing the cross-sectional microstructure of a sample of alloy product P7 using alloy material A7. Figure 6B This is a SEM secondary electron image showing the cross-sectional microstructure of a sample of alloy product P8 using alloy material A8. Figure 6C This is a SEM secondary electron image showing the cross-sectional microstructure of a sample of an alloy product P11 using the alloy material A11.

[0150] [Table 4]

[0151] Table 4 Test and evaluation results of alloy products P7 to P11

[0152]

[0153] like Figures 6A to 6C As shown in Table 4, it was confirmed that the samples of the alloy products P7 to P11 and the sample of the alloy product P2 as an example (refer to Figure 4B Compared to the alloys shown in Table 2, the amount of precipitates is lower, and the growth and aggregation of coarse η-phase and Laves-phase grains are suppressed. Furthermore, the percentage of coarse precipitates in alloys P7 to P11 is all rated "Excellent," and the average particle size of the ultra-fine particles is also all rated "Excellent." The Vickers hardness of alloys P7 to P11 is also all rated HV450 or higher, a "Pass" rating.

[0154] Although not shown in the figure, coarse precipitates of η phase and / or Laves phase were clearly observed in samples of alloy products P9 and P10, similar to samples of alloy products P8 and P11. While pitting corrosion testing was not performed in this experiment, the results of the coarse precipitate occupancy rate indicate that all alloy products P7 to P11 were rated "Excellent."

[0155] [Experiment 7]

[0156] (Production of Alloy Material A12)

[0157] The raw metals were mixed according to the composition shown in Table 5, melted in a high-frequency melting furnace to form a melt (raw material mixing and melting process), and then alloy powder was formed from the melt using a gas atomization method (alloy solidification process). Next, the obtained alloy powder was classified using a sieve and screened to a particle size of 20 to 45 μm to produce alloy material A12. The particle size distribution of alloy material A12 was measured using a laser diffraction particle size distribution analyzer, and the average particle size was approximately 30 μm. As shown in Table 5, alloy material A12 is an alloy material (Example) of the present invention.

[0158] [Table 5]

[0159] Table 5 Nominal alloy composition of alloy material A12 (unit: atomic %)

[0160] Alloy materials Co Cr Fe Ni Mo Ti Ta Nb Ti+Ta+Nb A12 34.4 19.7 14.5 23.5 4.5 2.4 1.0 - 3.4

[0161] -: Indicates that it is not intentionally contained

[0162] [Experiment 8]

[0163] (Production of Alloy Product P12)

[0164] A laminated molding apparatus (EOSINT M280, manufactured by Electro-Optical Systems GmbH, Germany) was used to form a molded body (a prismatic material with a length of 25 mm, a width of 25 mm, and a height of 70 mm (the height direction is the lamination direction)) made of the alloy material A12 by SLM according to the aforementioned process. The laminated molding conditions were as follows: the thickness h of the alloy powder bed was set to 0.04 mm, and the volume energy density E was set to 40 to 100 J / mm. 3 The laser output P, ​​laser scanning speed S, and laser scanning interval L are controlled in this way.

[0165] After the removal process, the formed body was subjected to a pseudo-solution heat treatment, where it was held in the atmosphere at 1120°C for 3 hours and then cooled. Furthermore, an aging heat treatment was performed, where it was held in the atmosphere at 700°C for 8 hours and then cooled. Air cooling (with an average cooling rate of approximately 10°C / s at 900-800°C) was used as the cooling method. Through the above operations, an alloy product P12 was produced, which was composed of the alloy material A12 using the stacking molding method.

[0166] [Experiment 10]

[0167] (Testing and Evaluation of Alloy Product P12)

[0168] As in Experiment 3, alloy product P12 was subjected to microstructural observation and Vickers hardness measurement and evaluation using the following methods. Furthermore, a room temperature tensile test according to ASTM E8 was performed to measure the 0.2% yield strength, tensile strength, and elongation at break. The measurement and evaluation results are shown in Table 6.

[0169] [Table 6]

[0170] Table 6 Test and evaluation results of alloy product P12

[0171]

[0172] As shown in Table 6, the percentage of coarse precipitates was a very low 0.03 area%, which, along with the average particle size of the extremely small particles, was rated "Excellent." The Vickers hardness was also HV450 or higher, which was rated "Pass." Furthermore, tensile test results confirmed a sufficiently high 0.2% yield strength and tensile strength, while also exhibiting a surprising elongation at break.

[0173] (Observation and analysis of extremely small particles)

[0174] High-magnification observation and analysis of extremely small particles in the matrix grains of the alloy product P12 were performed using a scanning transmission electron microscope-energy dispersive X-ray analyzer (STEM-EDX, manufactured by JEOL Ltd., model JEM-ARM200F).

[0175] First, one side of a sample of the alloy product FA1 was mirror-polished. Using a focused ion beam (FIB) processing system (manufactured by Hitachi High-Technologies Corporation, Model FB-2100), a test piece approximately 100 nm thick was cut from the polished surface using microsampling. The resulting test piece was then observed and analyzed at high magnification.

[0176] Figure 7 The dark field image (DFI) (a) and electron diffraction pattern (b) of the matrix phase grains obtained by STEM observation are shown. Figure 8 This is an image showing the element distribution of extremely small particles in the parent phase grains obtained by EDX.

[0177] according to Figure 7 The dark field image of (a) shows that there are extremely small particles with a particle size of about 10 to 20 nm dispersed and precipitated. Figure 7 The electron diffraction pattern (b) shows the pattern from the face-centered cubic (fcc) phase and the pattern from the γ' phase. Figure 8 The element distribution images confirm that within the parent phase grains, the concentrations of Ni and Ti are higher in the microparticles than elsewhere. Based on these observations and analysis, it is believed that the microparticles are the γ' phase observed in the electron diffraction pattern.

[0178] The above-described embodiments and experimental examples are provided to facilitate understanding of the present invention, and the present invention is not limited to the specific configurations described. For example, a portion of the configurations in the embodiments may be replaced with configurations that are common knowledge among those skilled in the art, or a configuration that is common knowledge among those skilled in the art may be added to the configurations in the embodiments. That is, within the scope of the present invention, portions of the configurations in the embodiments and experimental examples of this specification may be deleted, replaced with other configurations, or added to without departing from the technical spirit of the invention.

Claims

1. An alloy material, characterized in that: Containing 25 atomic % or more and 38 atomic % or less of Co, Containing 16 atomic % or more and 23 atomic % or less of Cr, Containing 12 atomic % or more and 20 atomic % or less of Fe, Containing 17 atomic % or more and 28 atomic % or less of Ni, Contains 1 atomic % or more and 7 atomic % or less of Mo, Containing 2 atomic % or more and less than 5 atomic % of Ti, Contains at least one of Ta and Nb in an amount greater than 0 atomic % and less than 4 atomic %, and the total amount of the Ti and at least one of the Ta and Nb is 3 atomic % or more and 8 atomic % or less, The remainder consists of unavoidable impurities.

2. An alloy product using the alloy material according to claim 1, characterized in that: When a secondary electron image of a cross section of the alloy product was observed using a scanning electron microscope, the total occupancy rate of precipitates of the η phase and the Laves phase having a size of 1 μm or more was 5 area % or less.

3. The alloy product according to claim 2, characterized in that In the matrix grains of the alloy product, extremely small particles having an average particle size of 130 nm or less are dispersed and precipitated.

4. A mechanical device, characterized in that: A product made of an alloy according to claim 2 or 3.

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