Ni-based alloy additive manufacturing

Abstract

To provide a metal lamination-shaped article of Ni-based alloy which exhibits high hardness in a short heat treatment time.SOLUTION: Provided is lamination-shaped bodies made of Ni-based alloy in which αCr phase, γ phase and / or γ' phase are precipitated in a layered state, and which do not include granular precipitates having a grain diameter of 400nm or more in an equivalent circle diameter. Further, prior γ grain diameter of the lamination-shaped bodies is 100 μm or less, the shaped bodies have hardness of 50.0HRC or more, hardness of 513HV or more, and contain Cr: 30.0 to 45.0%, Al: 2.5 to 5.0%. Furthermore, the bodies contain C: 0.2% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an additively shaped object made of a Ni-based alloy, which is manufactured by a three-dimensional additive manufacturing method. [Background technology]

[0002] Conventionally, NiCrAl alloys have been used as Ni-based alloys exhibiting wear resistance and corrosion resistance in engine parts, etc. For example, there is a Ni-based high-strength heat-resistant alloy having an alloy composition containing, by mass%, 0.1% or less of C, 2.0% or less of Si, 2.0% or less of Mn, 30 to 45% of Cr, and 3.1 to 5% of Al, with the remainder consisting of unavoidable impurities and Ni, and strengthened by the complex precipitation of γ' and α phases (see Patent Document 1). This alloy material is an attempt to obtain hardness by precipitating lamellae of the α-Cr phase and the γ' phase.

[0003] In recent years, NiCrAl alloys have also been applied to metal additive manufacturing. For example, Ni-based alloy products have been produced using Ni-based alloy powder containing 0.3-1.0% C, 36.0-50.0% Cr, 3.0-7.0% Al, and the remainder being Ni and unavoidable impurities (see Patent Document 2). This alloy is an attempt to obtain hardness by adding C to NiCrAl alloy to form carbides. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-69557 [Patent Document 2] Japanese Patent Publication No. 2021-188069 [Non-Patent Document 1] Electric Steelmaking Vol. 77 No. 2 p. 134 Fig. 1(a) Summary of the Invention [Problem to be solved by the invention]

[0005] Although the NiCrAl alloys in these documents aim for hardness and corrosion resistance, it takes time for the lamellar structure to precipitate. For example, Patent Document 2 requires an aging time of about 16 to 20 hours. Therefore, there is a manufacturing difficulty in that the heat treatment is time-consuming and costly.

[0006] Therefore, the problem that the present invention aims to solve is to provide a metal additive manufacturing product made of a Ni-based alloy such as a NiCrAl alloy that exhibits high hardness with a short heat treatment time. [Means for solving the problem]

[0007] After extensive research, the inventors have invented a Ni-based alloy additive manufacturing product in which NiCrAl alloy powder is subjected to metal additive manufacturing and then directly aged without solution treatment, resulting in a lamellar structure of γ phase or γ' phase and αCr phase that does not contain granular precipitates with a particle size of 400 nm or more.

[0008] That is, the first means for solving the problems of the present invention is: The αCr phase and the γ and / or γ' phases are precipitated in layers, And it does not contain granular precipitates with a circle equivalent diameter of 400 nm or more. It is an additive manufacturing body made of a Ni-based alloy.

[0009] The second means is an additive manufacturing body made of a Ni-based alloy according to the first means, in which the prior γ grain size is 100 μm or less.

[0010] The third means is an additive manufacturing product made of the Ni-based alloy according to the first or second means, which has a Rockwell hardness of 50.0 HRC or more.

[0011] The fourth means is an additive manufacturing product made of a Ni-based alloy according to any one of the first to third means, having a Vickers hardness of 513 HV or more.

[0012] The fifth means is an additive manufacturing body made of a Ni-based alloy according to any one of the first to fourth means, which contains, in mass %, 30.0 to 45.0% Cr, 2.5 to 5.0% Al, and 0 to 0.2% C, with the remainder being Ni and unavoidable impurities. [Effects of the Invention]

[0013] According to the above method, it is possible to obtain additively manufactured NiCrAl alloys with high hardness, with a Rockwell hardness of 50.0 HRC or more and a Vickers hardness of 513 HV or more, by omitting the solution treatment and carrying out a short aging heat treatment of less than 10 hours, thereby achieving a product that has high hardness but requires low energy costs for production.

[0014] Because it does not contain granular precipitates with a particle size of 400 nm or more, it is possible to obtain additively manufactured NiCrAl alloys with high hardness, with a Rockwell hardness of 59.5 HRC or more and a Vickers hardness of 700 HV or more, without significantly impairing mechanical properties such as toughness. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is an SEM image of an additive manufacturing product made of the Ni-based alloy of the present invention, which was held at 700°C for 4 hours and then air-cooled. [Figure 2] FIG. 2 is an SEM image of the microstructure of an additive manufacturing product made of the Ni-based alloy of the present invention, which was held at 500°C for 8 hours and then air-cooled. [Figure 3] Figure 3 shows an SEM image of an additively manufactured Ni-based alloy of the present invention that was solution-treated by holding it at 1150°C for 30 minutes and then water-cooling, and then held it at 500°C for 2 hours and then air-cooled. The arrows indicate the direction of lamellar growth and show how the growth of the lamellar structure is stopped by granular precipitates. DETAILED DESCRIPTION OF THE INVENTION

[0016] Before describing the embodiments of the present invention, we will explain the reasons for specifying the components to be added to Ni, the reasons for specifying that αCr and γ and / or γ' precipitate in layers, and the reasons for specifying that particulate precipitates with a particle size of 400 nm or more are not included. Note that % in the components refers to mass %. The remaining components are Ni and unavoidable impurities.

[0017] [component] The Ni-based alloy used in the present invention contains the following elements, with the balance consisting of Ni and unavoidable impurities. The types of added elements, their component ranges, and the reasons for their limitations are as follows: The percentages of the components are mass%.

[0018] First, the main constituent Ni and the essential additives Cr and Al will be explained. The present invention is based on Ni, since Ni is an ingredient that can provide a material with excellent corrosion resistance, strength, and toughness.

[0019] Cr: 30.0~45.0% Cr is a necessary element for lamellar formation. When a Ni-based alloy containing a certain amount of Cr is aged, the αCr phase and the γ and / or γ' phases precipitate in layers, contributing to high strength and hardness. Furthermore, Cr forms a protective film on the material surface in various corrosive environments, significantly contributing to improved high-temperature corrosion resistance.

[0020] If the Cr content is too low, the lamellar structure cannot be stably formed throughout the entire structure by aging treatment, resulting in a decrease in hardness. Therefore, the Cr content must be 30.0% or more. The Cr content is preferably 33.0% or more, and more preferably 36.0% or more.

[0021] On the other hand, if the Cr content is excessive, the Ni content will be relatively low, resulting in an insufficient amount of γ' phase precipitation. Therefore, the Cr content must be 45.0% or less. The Cr content is preferably 42.0% or less, and more preferably 40.0% or less.

[0022] Al: 2.5 to 5.0% Al is a forming element necessary for lamella formation. Furthermore, Al forms Ni3Al (γ' phase) by aging. In NiCrAl alloys, lamellar structures are formed by the precipitation of the αCr phase and the γ phase and / or γ' phase in layers, resulting in high hardness. Furthermore, Al contributes to improving high-temperature corrosion resistance and oxidation resistance. To achieve these effects, Al must be 2.5% or more. The Al content is preferably 3.0% or more, and more preferably 3.5% or more.

[0023] On the other hand, if Al is excessive, solidification cracking is likely to occur during metal additive manufacturing. Therefore, Al must be 5.0% or less. Al is preferably 4.5% or less, and more preferably 4.0% or less.

[0024] C: 0 to 0.2% In addition to these constituent elements, the Ni-based alloy according to the present invention may contain C as an additional component, but the content may be 0% or less, and should be 0.2% or less. C is a component that forms carbides and contributes to increasing the hardness of the material, but excessive C can lead to deterioration of the toughness of the material due to the formation of coarse carbides. Therefore, even when C is contained as an impurity, the C content must be 0.2% or less. C is preferably 0.1% or less, and more preferably 0.03% or less.

[0025] The αCr phase and the γ phase and / or the γ' phase are precipitated in layers, and no granular precipitates with a circle equivalent diameter of 400 nm or more are contained. High hardness is achieved by the growth of the αCr and γ phases, or the αCr and γ' phases, or the αCr and γ and γ' phases into a layered lamellar structure. The finer the lamellar spacing, the higher the hardness, which is desirable. Since the growth of lamellar structures is inhibited when they come into contact with coarse granular precipitates, it is useful for the granular precipitates not to be coarse, and it is desirable that they do not contain precipitates with an equivalent circle diameter of 400 nm or more. Since granular precipitates grow during solution treatment, this material has excellent aging hardness even without solution treatment.

[0026] Prior γ grain size is 100 μm or less Conventionally, the prior γ grain size was approximately 400 μm (see Non-Patent Document 1), but products manufactured by metal additive manufacturing are suitable for obtaining a fine prior γ grain size, and the prior γ grain size can be set to 100 μm or less. A fine prior γ grain size of 100 μm or less can shorten the time until the precipitation of a lamellar structure is completed. Therefore, it is desirable that the prior γ grain size of the manufactured product before aging heat treatment be 100 μm or less.

[0027] [Powder] The Ni-based alloy powder used in additive manufacturing is preferably a gas-atomized powder, since it is desirable that it be nearly spherical, have excellent fluidity, and be able to be filled without gaps.The average particle size of the Ni-based alloy powder is preferably 10 to 100 μm on a volume average basis.

[0028] [molding] One method for producing shaped objects is the rapid melting and solidification process, which involves melting and solidifying a metal powder. Specific examples of this process include three-dimensional additive manufacturing, thermal spraying, laser coating, and cladding. The Ni-based alloy powder of the present invention is particularly suitable for powder bed fusion-based three-dimensional additive manufacturing, which allows for the formation of large-sized, high-density objects.

[0029] For example, a 3D printer can be used as a three-dimensional additive manufacturing method. In the powder bed fusion method (powder bed method) among additive manufacturing methods, a laser beam or an electron beam is irradiated onto a spread Ni-based alloy powder of the present invention.

[0030] The particles are rapidly heated and melted by the irradiation. The melted particles then rapidly solidify. This melting and solidification process bonds the particles together. The irradiation is selectively performed on a portion of the spread Ni-based alloy powder. The portion of the spread powder that is not irradiated does not melt. A bonding layer is formed only in the irradiated portion.

[0031] A thin layer of Ni-based alloy powder is spread on top of the bonding layer. A laser beam or electron beam is irradiated onto a portion of this Ni-based alloy powder. The irradiation causes the particles to rapidly melt. The molten particles then rapidly solidify. This melting and solidification process bonds the particles in the powder together, forming a new bonding layer. The new bonding layer also bonds with the existing bonding layer. Repeated bonding by irradiation gradually grows the aggregate of bonding layers. This growth results in a three-dimensional object. This additive manufacturing method makes it easy to obtain objects with complex shapes.

[0032] [Heat treatment] When using Ni-based alloy powder for additive manufacturing, rather than using the unheat-treated product as is, the unheat-treated product is subjected to an aging heat treatment process to obtain a product with the desired characteristics of the present invention.

[0033] When NiCrAl alloys are used in conventional processes such as forging, they are generally solution-treated at temperatures of 1100°C or higher. However, when manufacturing objects using metal additive manufacturing, as in the present invention, we have found that excellent mechanical properties can be achieved by directly performing aging treatment without solution treatment.

[0034] Regarding the aging heat treatment temperature, by performing the heat treatment at 600°C or less, the lamellar spacing between the αCr phase and the γ or γ' phase becomes finer, and a highly hard molded product can be obtained. The aging temperature is preferably 600°C or less, more preferably 585°C or less, even more preferably 540°C or less, and most preferably 500°C or less.

[0035] The energy cost can be reduced by shortening the aging heat treatment time, which is preferably 10 hours or less, more preferably 8 hours or less, even more preferably 4 hours or less, and most preferably 2 hours or less.

[0036] [Lamellar morphology] Aging a Ni-based alloy shaped body precipitates a lamellar structure of the αCr phase and the γ phase (and / or the γ' phase). Figure 1 shows an SEM image of an additively molded product of the Ni-based alloy of the present invention, which was held at 700°C for 4 hours and then air-cooled. It can be seen that lamellae on the scale of several tens of nanometers were formed at 700°C. Figure 2 shows an SEM image of the microstructure of an additively molded product of the Ni-based alloy of the present invention, which was held at 500°C for 8 hours and then air-cooled. It can be seen that when aged at 500°C, the lamellar spacing is smaller and the structure is very fine compared to when aged at 700°C.

[0037] Since the finer the lamellar spacing, the higher the hardness, it is preferable to perform aging at a low temperature to precipitate fine lamellae.

[0038] [Area ratio of granular precipitates] Figure 3 shows an SEM image of an additively manufactured Ni-based alloy of the present invention, which was solution-treated by holding it at 1150°C for 30 minutes and then water-cooling, followed by holding it at 500°C for 2 hours and then air-cooling. It can be seen that the solution treatment resulted in the formation of coarse granular precipitates with a grain size of 400 nm or more. EDS analysis revealed that the granular precipitates were rich in Cr, suggesting that they were the α-Cr phase. The lamellae grow in the direction indicated by the arrows in the image, but it can be seen that lamellar growth is inhibited where the coarse granular precipitates come into contact with the tips of the grown lamellae.

[0039] Coarse granular precipitates inhibit the growth of lamellae and increase the time required for the precipitation reaction to be completed (for lamellae to precipitate over the entire surface), resulting in increased energy costs for heat treatment. Therefore, it is preferable to prevent the precipitation of coarse granular precipitates. The occurrence of coarse granular precipitates can be avoided by avoiding solution treatment and long aging.

[0040] [Prior γ grain size] Since lamellae in NiCrAl alloys precipitate in a cellular form from grain boundaries, the finer the structure, the faster the completion of the precipitation reaction, which is preferable. It is preferably 100 μm or less, more preferably 90 μm or less, even more preferably 80 μm or less, and most preferably 70 μm or less.

[0041] [Hardness] NiCrAl alloys are used in bearing parts and engine parts, so high hardness is desirable. Therefore, the Rockwell hardness of the layered object of the present invention is preferably 50.0 HRC or more, more preferably 60.0 HRC or more, even more preferably 61.0 HRC or more, and most preferably 62.0 HRC or more. Furthermore, the Vickers hardness of the layered object of the present invention is preferably 513 HV or more, more preferably 700 HV or more, even more preferably 750 HV or more, and most preferably 790 HV or more.

[0042] [Powder] Table 1 shows the chemical composition of the powder used in the examples. The Ni-based alloy powder used in the additive manufacturing was produced by vacuum melting inert gas atomization and then classified using a -63 μm sieve. In the examples, argon was used as the inert gas. Note that the components C, Si, Mn, Fe, Co, Mo, P, S, O, and N in Table 1 are unavoidable impurities.

[0043] [Table 1]

[0044] The additively manufactured object made of a Ni-based alloy according to the present invention is produced by a process involving rapid melting, rapid cooling, and solidification using a Ni-based alloy powder containing Cr and Al. The material of this additively manufactured object is a Ni-based alloy containing Cr and Al. Aging the manufactured object results in a lamellar structure in which the α-Cr phase and the γ and / or γ' phases are arranged in layers.

[0045] [molding] Using these Ni-based alloy powders as raw materials, additive manufacturing was carried out using a 3D additive manufacturing device (EOS-M290) to create 10 x 10 x 10 mm rectangular parallelepipeds as test pieces for hardness and structure investigations. The manufacturing conditions were based on the device's standard parameters HX (layer thickness 40 μm), but with the output changed to 200 W, scanning speed 1200 mm / s, and hatch width 0.05 mm.

[0046] [Heat treatment] Table 2 shows the heat treatment conditions for Examples 1 to 6, and Table 3 shows the heat treatment conditions for Comparative Examples 1 to 15. The solution treatment and aging were carried out under the following conditions. Solution treatment: After holding in the air at the temperature shown in Table 3 for 30 minutes, the specimens were water-cooled. Note that, in the examples shown in Table 2, no solution treatment was performed. Aging treatment: After being held in the air at the temperatures and times shown in Tables 2 and 3, the specimens were air-cooled.

[0047] [Structural observation: Determination of area ratio of granular precipitates] The heat-treated shaped body (10 × 10 × 10 mm) was cut along a plane parallel to the lamination direction, mechanically polished, and ion-milled. The center of the polished sample was observed using a field emission scanning electron microscope (FE-SEM). Observations were performed at a magnification of 10,000x, and images were taken of the areas shown in Figures 1 to 3. Image analysis was performed to determine the area ratio of granular precipitates with a diameter of 400 nm or more. Note that the diameter here refers to the circle-equivalent diameter calculated by area conversion using image analysis.

[0048] [Structural observation: determination of prior γ grain size] The embedded specimens, prepared using the same procedure as for FE-SEM, were polished with colloidal silica and then measured by electron backscatter diffraction (EBSD). The prior γ grain size was determined from the crystal orientation map obtained by EBSD. Note that a boundary with a misorientation of 15° or more was defined as a grain boundary.

[0049] [Table 2] *In the table, the symbol "-" in the solution treatment temperature and solution treatment time columns indicates that solution treatment was not performed.

[0050] [Table 3]

[0051] [Rockwell hardness measurement] The hardness of the heat-treated test piece was measured using a Rockwell hardness tester on the surface perpendicular to the lamination direction.

[0052] [Vickers hardness measurement] The heat-treated test pieces were embedded in resin, and the surfaces of the test pieces were polished. The hardness was measured using a micro-Vickers hardness tester. A load of 1.96 N was applied.

[0053] The obtained results were evaluated for the characteristics of the examples and comparative examples according to the following criteria. Aging time: If the aging time was within 10 hours, it was considered to be good and marked as "good," and if the aging time was over 10 hours, it was considered to be inferior and marked as "NG (not good)." Rockwell hardness: If it was 59.5 HRC or higher, it was rated as A, as it was considered to have excellent hardness; if it was between 50.0 and 59.5 HRC, it was rated as B, as it was considered to have fair hardness; if it was less than 50.0 HRC, it was rated as C, as it was considered to have poor hardness and was unacceptable. Vickers hardness: If it was 700HV or more, it was rated as A, which means it had excellent hardness; if it was 513HV to less than 700HV, it was rated as B, which means it was acceptable; if it was less than 513HV, it was rated as C, which means it was poor in hardness and unacceptable. The results are shown in Tables 4 and 5.

[0054] [Table 4]

[0055] [Table 5]

[0056] As shown in Examples 1 to 6, when aging treatment was performed at low temperatures such as 500°C and 585°C, coarse granular precipitates were not generated, and it was confirmed that high hardness of Rockwell hardness of 59.5 HRC or more and Vickers hardness of 700 HV or more could be achieved.

[0057] It is now possible to obtain a high hardness product in a shorter time than the 16 hours required for the conventional products disclosed in Patent Documents 1 and 2, and this makes it possible to significantly reduce the energy costs involved in production.

[0058] The closest example to the present invention is "Ni-38Cr-3.8Al-0.1C, aged at 600°C for 16 hours (Comparative Example 2)," as described in Patent Document 2. However, Cr carbides are contained in the structure, and the hardness after aging is only 680 HV. The examples of the present invention do not contain coarse granular precipitates, have higher hardness, and have a short aging time, which is also excellent in terms of energy cost.

[0059] Even if the hardness appears to be the same, materials containing coarse granular precipitates generally have poor toughness, resulting in completely different mechanical properties. The present invention does not contain coarse granular precipitates, resulting in excellent mechanical properties including toughness. On the other hand, for example, Non-Patent Document 1 is a wrought material, and therefore coarse granular precipitates are formed by solution treatment, resulting in inferior mechanical properties compared to the present invention.

[0060] Comparative Example 1 in Tables 3 and 5 meets the hardness standards, but is inferior in terms of energy cost due to long-term aging. In addition, the long-term aging causes the formation of granular precipitates with a particle size of 400 nm or more. In Comparative Examples 2 to 5, aging treatment at 700°C resulted in the formation of granular precipitates with a particle size of 400 nm or more, and Cr was consumed by the granular precipitates, resulting in a decrease in the strengthening of the lamellar structure and a decrease in hardness. In Comparative Examples 6 to 15, the solution treatment resulted in the formation of granular precipitates with a particle size of 400 nm or more, which resulted in a decrease in hardness, or a decrease in the lamellar precipitation rate, which resulted in a longer time for precipitation to be completed than in the case of direct aging, making them inferior in terms of energy cost.

[0061] As can be seen from Table 3, the prior γ grain size decreases due to solution treatment. This is because fine new crystal grains are generated from the grain boundaries during solution treatment.

[0062] The prior γ grain size in the present invention is 100 μm or less, which is smaller than the prior γ grain size (approximately 400 μm) of the ingot material described in Non-Patent Document 1. The fine prior γ grain size specific to metal additive manufacturing in the present invention is thought to be effective in shortening the time required to complete precipitation of a lamellar structure. [Industrial Applicability]

[0063] The additive manufacturing products using the Ni-based alloy according to the present invention can be used for engine parts, bearing parts, molds, medical wires, etc.

Claims

1. An additively manufactured body made of a Ni-based alloy containing, by mass%, 30.0 to 45.0% Cr, 2.5 to 5.0% Al, and 0 to 0.2% C, with the remainder being Ni and unavoidable impurities, in which an αCr phase and a γ phase and / or a γ' phase are precipitated in layers, and which does not contain granular precipitates with a particle size of 400 nm or more in equivalent circle diameter.

2. 2. The layered manufactured product made of a Ni-based alloy according to claim 1, wherein the prior γ grain size is 100 μm or less.

3. 2. An additive manufacturing product made of the Ni-based alloy according to claim 1, having a Rockwell hardness of 50.0 HRC or more.

4. 2. An additive manufacturing product made of the Ni-based alloy according to claim 1, having a Vickers hardness of 513 HV or more.

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