LAMINATION-SHAPED ARTICLE MADE OF Ni-BASED ALLOY

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 a laminated object made of a Ni-based alloy formed by a three-dimensional laminated manufacturing method.

Background Art

[0002] Conventionally, as a Ni-based alloy exhibiting wear resistance and corrosion resistance, a NiCrAl alloy has been used for engine parts and the like. For example, an alloy composition containing, by mass%, C: 0.1% or less, Si: 2.0% or less, Mn: 2.0% or less, Cr: 30 to 45%, and Al: 3.1 to 5%, with the balance being inevitable impurities and Ni, and being strengthened by the composite precipitation of γ' phase and α phase, can be mentioned (see Patent Document 1). This alloy material is an attempt to obtain hardness by precipitating lamellae of α-Cr phase and γ' phase.

[0003] In recent years, NiCrAl alloys have also come to be applied to metal laminated manufacturing. For example, Ni-based alloy products using Ni-based alloy powder containing C: 0.3 to 1.0%, Cr: 36.0 to 50.0%, Al: 3.0 to 7.0%, with the balance being Ni and inevitable impurities, can be mentioned (see Patent Document 2). This alloy is an attempt to obtain hardness by forming carbides by adding C to the NiCrAl alloy.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Although the NiCrAl alloys in these documents are aimed at hardness and corrosion resistance, it takes time for the precipitation of the lamellar structure. For example, in Patent Document 2, an aging time of about 16 to 20 hours is required. Therefore, there are manufacturing difficulties such as high time costs for heat treatment.

[0006] Therefore, the problem to be solved by the present invention is to provide a metal laminated structure 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] As a result of intensive studies, the inventors have reached the invention of a Ni-based alloy laminated structure in which NiCrAl alloy powder is additively manufactured, directly aged without solutionizing, and a lamellar structure of a γ-phase or γ'-phase and an αCr phase that does not contain granular precipitates with a particle size of 400 nm or more is obtained.

[0008] That is, the first means for solving the problem of the present invention is an αCr phase and a γ-phase and / or γ'-phase are precipitated in layers, and it does not contain granular precipitates with a particle size of 400 nm or more in terms of the equivalent circle diameter, and is a laminated structure made of a Ni-based alloy.

[0009] The second means is a laminated structure made of the Ni-based alloy described in the first means, in which the old γ particle size is 100 μm or less.

[0010] The third means is a laminated structure made of the Ni-based alloy described in the first or second means, in which the Rockwell hardness is 50.0 HRC or more.

[0011] The fourth means is a laminated structure made of the Ni-based alloy described in any one of the first to third means, in which the Vickers hardness is 513 HV or more.

[0012] The fifth means is a laminated structure made of a Ni-based alloy according to any one of the first to fourth means, which contains, by mass%, Cr: 30.0 to 45.0% and Al: 2.5 to 5.0%, and further C: 0 to 0.2%, with the balance being Ni and unavoidable impurities.

Advantages of the Invention

[0013] According to the above means, a laminated structure of a NiCrAl alloy with a high hardness, such as a Rockwell hardness of 50.0 HRC or more and a Vickers hardness of 513 HV or more, can be obtained by an aging heat treatment in a short time within 10 hours, omitting the solution treatment. Also, it has high hardness while having a low energy cost in manufacturing.

[0014] Since it does not contain particulate precipitates with a particle size of 400 nm or more, a laminated structure of a NiCrAl alloy with a high hardness, such as a Rockwell hardness of 59.5 HRC or more and a Vickers hardness of 700 HV or more, can be obtained without significantly deteriorating mechanical properties such as toughness.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0016] Prior to the description of the embodiments in which the present invention can be implemented, the reasons for defining "each component added to Ni" in the present invention, "αCr, and γ and / or γ' being precipitated in layers", and "not containing granular precipitates having a particle size of 400 nm or more" will be described. In addition, % in the components represents mass%. The balance of the components is Ni and inevitable impurities.

[0017] [Components] The Ni-based alloy used in the present invention contains the following elements, and the balance consists of Ni and inevitable impurities. The types of additive elements, their component ranges, and the reasons for their limitation are as follows. Here, % of the components is by mass.

[0018] First, Ni, which is the main constituent, and Cr and Al, which are essential additives to Ni, will be described. Since Ni is a component capable of obtaining a material excellent in corrosion resistance and strength and toughness, the present invention is based on Ni.

[0019] Cr: 30.0 to 45.0% Cr is a forming element necessary for lamella formation. When a Ni-based alloy containing a predetermined amount of Cr is age-hardened, an αCr phase, and a γ phase and / or a γ' phase are precipitated in layers, contributing to high strength and high hardness. Further, Cr forms a protective film on the material surface in various corrosion environments, greatly contributing to the improvement of high-temperature corrosion resistance.

[0020] When the amount of Cr is too small, it becomes impossible to stably form a lamellar structure in the entire region of the structure by age-hardening, and the hardness decreases. Therefore, the amount of Cr needs to be 30.0% or more. The amount of Cr is preferably 33.0% or more, more preferably 36.0% or more.

[0021] On the other hand, when the amount of Cr becomes excessive, the amount of Ni relatively decreases, and the amount of precipitation of the γ' phase becomes insufficient. Therefore, the amount of Cr needs to be 45.0% or less. The amount of Cr is preferably 42.0% or less, more preferably 40.0% or less.

[0022] Al: 2.5 - 5.0% Al is a forming element necessary for lamella formation. Also, Al forms Ni3Al (γ' phase) upon aging. In NiCrAl alloys, the αCr phase, and the γ phase and / or γ' phase precipitate in layers, thereby forming a lamellar structure and achieving high hardness. Further, Al also contributes to the improvement of high-temperature corrosion resistance and oxidation resistance. To obtain such effects, Al needs to be 2.5% or more. Al is preferably 3.0% or more, more preferably 3.5% or more.

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

[0024] C: 0 - 0.2% The Ni-based alloy according to the present invention may contain C as an additional component in addition to these constituent elements, but it may also be 0%, and is 0.2% or less. C is a component that forms carbides and contributes to the hardening of the material. However, when C is excessive, coarse carbides cause deterioration of the toughness of the material. Therefore, even when C is contained as an impurity, the content of C needs to be 0.2% or less. C is preferably 0.1% or less, more preferably 0.03% or less.

[0025] The αCr phase, and the γ phase and / or γ' phase precipitate in layers, and no granular precipitate having a particle size of 400 nm or more in terms of equivalent circle diameter is contained, The αCr phase and the γ phase, or the αCr phase and the γ' phase, or the αCr phase and the γ and γ' phases grow into a layered lamellar structure, thereby obtaining high hardness. And it is desirable that the lamellar spacing is finer for higher hardness. The growth of the lamellar structure is inhibited when it comes into contact with coarse granular precipitates. Therefore, it is useful that the size of the granular precipitates is not coarse, and it is desirable that the precipitates do not contain those with an equivalent circle diameter of 400 nm or more. Since the granular precipitates grow through solution treatment, it is excellent in age hardening without solution treatment.

[0026] The prior γ grain size is 100 μm or less The conventional prior γ grain size was about 400 μm (see Non-Patent Document 1), but the shaped article by metal additive manufacturing is suitable for obtaining a fine prior γ grain size, and the prior γ grain size can be made 100 μm or less. When the prior γ grain size is fine, i.e., 100 μm or less, the time until the precipitation of the lamellar structure is completed can be shortened. Therefore, it is desirable that the prior γ grain size of the shaped article before age heat treatment is 100 μm or less.

[0027] [Powder] The Ni-based alloy powder used for additive manufacturing is preferably gas atomized powder because it is desirable that it is close to spherical shape, has excellent fluidity, and can be filled without gaps. The average particle diameter of the Ni-based alloy powder is desirably 10 to 100 μm in volume average.

[0028] [Shaping] As a method for producing a shaped article, there is a rapid melting and rapid solidification process which is a process of melting and solidifying metal powder. Specific examples of this process include three-dimensional additive manufacturing method, thermal spraying method, laser coating method, and build-up welding method. In particular, the Ni-based alloy powder of the present invention is suitable for the powder bed fusion bonding type three-dimensional additive manufacturing method, and a large-sized shaped article can be formed at high density.

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

[0030] Upon irradiation, the particles are rapidly heated and melted. The melted particles then rapidly solidify. Due to this melting and solidification, the particles bond to each other. The irradiation is selectively performed on a part of the spread Ni-based alloy powder. Among the spread powder, the part that is not irradiated does not melt. A bonding layer will be formed only in the part that has been irradiated.

[0031] On top of the bonding layer, Ni-based alloy powder is further thinly spread. A part of this Ni-based alloy powder is irradiated with a laser beam or an electron beam. Upon irradiation, the particles rapidly melt. The melted particles then rapidly solidify. Due to this melting and solidification, the particles in the powder bond to each other, and a new bonding layer is formed. The new bonding layer also bonds to the existing bonding layer. By repeating the bonding by irradiation, an aggregate of bonding layers gradually grows. Due to this growth, a shaped object having a three-dimensional shape is obtained. By this additive manufacturing method, a shaped object with a complex shape can be easily obtained.

[0032] [Heat treatment] For the additive manufactured object using Ni-based alloy powder, instead of using the as-formed non-heat-treated shaped object as it is, by going through the process of performing aging heat treatment on the non-heat-treated shaped object, a shaped object with the desired characteristics of the present invention can be obtained.

[0033] When NiCrAl alloy is used in conventional processes such as forging, it is generally solution-treated at a temperature of 1100°C or higher. However, it has been found that when manufacturing a shaped object by metal additive manufacturing as in the present invention, excellent mechanical properties can also be exhibited by omitting the solution treatment and directly performing aging treatment.

[0034] Regarding the aging heat treatment temperature, by performing heat treatment at 600°C or lower, the interlamellar spacing between the αCr phase and the γ phase or γ' phase becomes finer, and a shaped object with high hardness can be obtained. The aging temperature is preferably 600°C or lower, more preferably 585°C or lower, still more preferably 540°C or lower, and most preferably 500°C or lower.

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

[0036] [Morphology of lamellae] By aging the shaped body of the Ni-based alloy, a lamellar structure of the αCr phase and the γ phase (and / or γ' phase) precipitates. Fig. 1 shows the SEM image of the laminated shaped body of the Ni-based alloy of the present invention air-cooled after holding at 700°C for 4 hours. It can be seen that lamellae on the order of several tens of nm are formed at 700°C. Fig. 2 shows the SEM image of the microstructure of the laminated shaped body of the Ni-based alloy of the present invention air-cooled after holding at 500°C for 8 hours. When aging at 500°C, it can be seen that the lamellar spacing is finer and the structure is very fine compared to the case of aging at 700°C.

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

[0038] [Area ratio of granular precipitates] Fig. 3 shows the SEM image of the laminated shaped body of the Ni-based alloy of the present invention after solution treatment by holding at 1150°C for 30 minutes and then water-cooling, and then air-cooling after holding at 500°C for 2 hours. It can be seen that coarse granular precipitates with a particle size of 400 nm or more are generated by performing the solution treatment. As a result of EDS analysis, since the granular precipitates are Cr-rich, they are presumed to be the α-Cr phase. Although the lamellae grow in the direction indicated by the arrow in the figure, it can be seen that the growth of the lamellae is inhibited at the location where the tip of the coarse granular precipitate contacts the grown lamellae.

[0039] Coarse granular precipitates inhibit the growth of lamellae and increase the time required for the precipitation reaction to be completed (lamellae precipitate over the entire surface), resulting in an additional energy cost for the heat treatment. Therefore, it is preferable that no coarse granular precipitates precipitate. Generation of coarse granular precipitates can be avoided by avoiding solution treatment and long-term aging.

[0040] [Old γ particle size] Since the lamellae of the NiCrAl alloy precipitate in a cell shape from the grain boundaries, the finer the microstructure, the faster the precipitation reaction is completed, which is preferable. It is preferably 100 μm or less, more preferably 90 μm or less, still more preferably 80 μm or less, and most preferably 70 μm or less.

[0041] [Hardness] Since the NiCrAl alloy is used for bearing parts and engine parts, it is desirable to have high hardness. Therefore, the Rockwell hardness of the laminated object of the present invention is preferably 50.0 HRC or more, more preferably 60.0 HRC or more, still more preferably 61.0 HRC or more, and most preferably 62.0 HRC or more. Also, the Vickers hardness of the laminated object of the present invention is preferably 513 HV or more, more preferably 700 HV or more, still 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 for laminated manufacturing was produced by the vacuum melting inert gas atomization method and then classified with a -63 μm sieve. Argon was used as the inert gas in the examples. Note that the components of C, Si, Mn, Fe, Co, Mo, P, S, O, and N in Table 1 are inevitable impurities.

[0043]

Table 1

[0044] Now, the laminated structure made of the Ni-based alloy according to the present invention is produced by a process involving rapid melting and rapid solidification using Ni-based alloy powder containing Cr and Al as the material. The material of this laminated structure is a Ni-based alloy containing Cr and Al. By subjecting the shaped article to aging heat treatment, a lamellar structure in which the αCr phase and the γ phase and / or γ' phase are arranged in layers can be obtained.

[0045] [Shaping] Using these Ni-based alloy powders as raw materials, a three-dimensional laminated shaping method using a three-dimensional laminated shaping apparatus (EOS-M290) was carried out to shape a rectangular parallelepiped of 10×10×10 mm, which was used as a test piece for hardness and microstructure investigation. The shaping conditions were based on the device standard parameters HX (lamination thickness 40 μm), and those with the output changed to 200 W, the scanning speed changed to 1200 mm / s, and the hatch width changed to 0.05 mm were used.

[0046] [Heat Treatment] Table 2 shows the heat treatment conditions of Examples 1 to 6, and Table 3 shows the heat treatment conditions of Comparative Examples 1 to 15. Solution treatment and aging were carried out under the following conditions. · Solution treatment: It was held at the temperature shown in Table 3 for 30 minutes in an air atmosphere and then water-cooled. In the examples, no solution treatment was carried out as shown in Table 2. · Aging treatment: It was held at the temperatures and times shown in Tables 2 and 3 respectively in an air atmosphere and then air-cooled.

[0047] [Microstructure Observation: Determination of the Area Ratio of Granular Precipitates] After cutting the heat-treated shaped body (10×10×10 mm) with a plane parallel to the lamination direction, it was mechanically polished and ion milled, and the central part of the polished sample was observed with a FE-SEM (field emission scanning electron microscope). Observation was carried out at a magnification of 10,000 times, and from the images taken in the areas shown in Figures 1 to 3, the area ratio of granular precipitates with a particle size of 400 nm or more was determined by image analysis. Here, the particle size refers to the equivalent circle diameter obtained by area conversion by image analysis.

[0048] [Microstructure Observation: Determination of the Grain Size of the Old γ Phase] The samples before the embedded aging heat treatment prepared by the same procedure as FE-SEM were polished by colloidal silica polishing and then subjected to EBSD (electron backscatter diffraction) measurement. The prior γ grain size was determined from the crystal orientation map obtained by EBSD measurement. The boundary with an orientation difference of 15° or more was defined as the grain boundary.

[0049] [Table 2] ※ In the table, the symbol "-" in the columns of solutionizing temperature and solutionizing time indicates that solutionizing was not carried out.

[0050] [Table 3]

[0051] [Rockwell hardness measurement] The hardness was measured with a Rockwell hardness tester on the surface perpendicular to the lamination direction of the test piece after heat treatment.

[0052] [Vickers hardness measurement] The test piece after heat treatment was embedded in resin and the surface of the test piece was polished. Furthermore, the hardness was measured using a micro-Vickers hardness tester. The load was 1.96 N.

[0053] For the obtained results, the characteristics of the examples and comparative examples were evaluated according to the following criteria. · Aging time: If the aging time is within 10 hours, it is denoted as good, and if the aging time exceeds 10 hours, it is denoted as NG (not good) as inferior. · Rockwell hardness: If it is 59.5 HRC or more, it is evaluated as A as excellent in hardness, if it is less than 50.0 - 59.5 HRC, it is evaluated as B as acceptable, and those less than 50.0 HRC are evaluated as C as inferior in hardness. · Vickers hardness: If it is 700 HV or more, it is evaluated as A as excellent in hardness, if it is less than 513 - 700 HV, it is evaluated as B as acceptable, and those less than 513 HV are regarded as C as inferior in hardness. 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 is performed at low temperatures such as 500°C and 585°C, no coarse granular precipitates are generated, so it was confirmed that high hardness with a Rockwell hardness of 59.5 HRC or more and a Vickers hardness of 700 HV or more can be achieved.

[0057] It is possible to obtain a high-hardness material in a time shorter than 16 h as in the materials of Conventional Patent Documents 1 and 2, and it is possible to greatly reduce the energy cost in manufacturing.

[0058] As the example closest to the present invention, Patent Document 2 describes "Ni-38Cr-3.8Al-0.1C, aged at 600°C for 16 h (Comparative Example 2)", but the structure contains Cr carbides, and the hardness after aging remains at 680 HV. The examples of the present invention do not contain coarse granular precipitates, have higher hardness, shorter aging time, and are excellent in terms of energy cost.

[0059] Note that even if the hardness appears to be the same at first glance, those containing coarse granular precipitates generally have deteriorated toughness, so other mechanical properties will be completely different. Since the present invention does not contain coarse granular precipitates, it has excellent results in mechanical properties including toughness. On the other hand, for example, Non-Patent Document 1 is a melted material, and coarse granular precipitates are generated by solution treatment, so it is inferior in mechanical properties compared to the present invention.

[0060] Comparative Example 1 in Table 3 and Table 5 meets the hardness standard, but is inferior in terms of energy cost due to long-term aging. Also, due to long-term aging, granular precipitates with a particle size of 400 nm or more have occurred. In Comparative Examples 2 to 5, granular precipitates with a particle size of 400 nm or more have occurred due to aging treatment at 700°C. Since Cr has been consumed by the granular precipitates, the amount of strengthening of the lamellar structure has decreased and the hardness has decreased. In Comparative Examples 6 to 15, granular precipitates with a particle size of 400 nm or more have occurred due to solution treatment, resulting in a decrease in hardness, or the precipitation completion time takes longer than in the case of direct aging due to a decrease in the lamellar precipitation rate, which is 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 crystal grains are newly generated from the grain boundaries during solution treatment.

[0062] The prior γ grain size in the present invention is all 100 μm or less, which is smaller than the prior γ grain size (about 400 μm) of the ingot material described in Non-Patent Document 1. The fine prior γ grain size peculiar to metal additive manufacturing in the present invention is considered to be effective in accelerating the precipitation completion time of the lamellar structure.

Industrial Applicability

[0063] The additive manufactured object using the Ni-based alloy according to the present invention can be used for engine parts, bearing parts, molds, medical wires, and the like.

Claims

1. The αCr phase and the γ phase and / or the γ' phase are precipitated in layers, And it does not contain particulate precipitates with a circle equivalent diameter of 400 nm or more. An additive manufacturing body made of a Ni-based alloy.

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.

5. A bearing part, which is an additively formed body made of a Ni-based alloy according to any one of claims 1 to 4.

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