Material for additive manufacturing and method for manufacturing an additively manufactured object using the same

Abstract

To provide a material for the additive manufacturing and a manufacturing method for an additive manufacturing model using it that can prevent a defect such as an internal vacancy and a coarse heterogeneous structure from being formed at the time of the additive manufacturing to enhance energy efficiency.SOLUTION: A material for the additive manufacturing 10 is used for the additive manufacturing of a three-dimensional structure. The material for the additive manufacturing 10 includes a parent metal (SUS316 L particle 8) and heterogeneity nuclear particles (SrO particles 9). The parent metal is stainless steel. The heterogeneity nuclear particle has a malting-point higher than that of the parent metal, and the parameter M represented by a prescribed equation is less than or equal to 12×10-3.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a material for additive manufacturing and a method for manufacturing an additive manufactured object using the same. [Background technology]

[0002] In recent years, a new processing method called additive manufacturing (AM) has been attracting attention. This is a method for creating three-dimensional structures based on digital data generated by computer-aided design (CAD), and in Japan it is known as additive manufacturing, 3D additive manufacturing, or 3D printer technology (hereinafter referred to as "3D additive manufacturing" or simply "additive manufacturing").

[0003] In Japan, resin-based 3D additive manufacturing was one of the first to be put into practical use, and is used for rapid prototyping of exhibits and prototypes. Resin-based 3D additive manufacturing uses photocurable resins or thermoreversible resins, i.e., chemical reactions, to create the product. While this has the advantage of fast manufacturing speed, it also has the disadvantage of poor strength and durability. Therefore, when manufacturing higher-end products that require high strength and durability, metal 3D additive manufacturing technology is required.

[0004] Metal 3D additive manufacturing technologies can be broadly divided into powder bed fusion and directed energy deposition. Powder bed fusion is a method in which metal powder spread evenly on a stage is irradiated with a laser or electron beam according to slice data from 3D CAD data, melting and solidifying the metal powder locally and selectively, and this process is repeated to create a 3D structure. On the other hand, directed energy deposition, like the above, uses a laser or electron beam as a heat source, but supplies metal powder directly to the irradiation position. In other words, it is a 3D additive manufacturing method similar to laser cladding (build-up welding). [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Toshihiko Koseki: Weld Metal Solidification and Control of Solidification Structure, Journal of the Japan Welding Society, 70 (2001) [Non-patent document 2] Masaharu Kato: Materia, 56 (2017) [Non-patent document 3] Y.Ji, M.Zhang, H.Ren:Metals 8(2018) [Non-patent document 4] Yoshikuni Nakao, Kazutoshi Nishimoto, and Wenping Zhang: Journal of the Japan Welding Society, 7 (1989) [Non-Patent Document 5] A.Simchi, H.Pohl:Mater.Sci.Eng.,A 359(2003) [Non-patent document 6] JMGregg,HKDHBhadeshia:Acta Mater.45(1997) Summary of the Invention [Problem to be solved by the invention]

[0006] As mentioned above, demand for 3D additive manufacturing technology for metals is expected to continue to expand in the future. Among metals, stainless steel is particularly widely used due to its excellent corrosion resistance, and its application to 3D additive manufacturing is highly anticipated. However, because 3D additive manufacturing of metals requires the elemental processes of melting and solidification, which are unique to metals, it is prone to the formation of internal voids due to unmelted powder and volumetric shrinkage during cooling. Furthermore, this method poses potential problems, such as the formation of a coarse, non-uniform structure (columnar structure) similar to that of a cast structure, which reduces strength and also leads to anisotropy in mechanical properties.

[0007] The present invention provides a material for additive manufacturing that can suppress the formation of defects such as internal voids and large, non-uniform structures during additive manufacturing, thereby improving energy efficiency, and a method for manufacturing an additive manufactured object using the same. [Means for solving the problem]

[0008] The additive manufacturing material according to one aspect of the present invention is used for additive manufacturing of a three-dimensional structure. The additive manufacturing material includes a base metal and heterogeneous core particles. The base metal is stainless steel. The heterogeneous core particles have a higher melting point than the base metal, and the parameter M expressed by formula (1) is 12 × 10 -3 The following is the result.

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[0009] In the material for additive manufacturing, the volume ratio of the heterogeneous core particles to the base metal may be 1.0% or less.

[0010] The base metal may also be an austenitic stainless steel.

[0011] The base metal may also be SUS316L.

[0012] The heterogeneous core particles may be particles of one or more compounds selected from SrO, YN, CaO, VN, MgO, TiN, and TiB.

[0013] The heterogeneous core particles may also be SrO particles.

[0014] Another aspect of the present invention is a method for manufacturing an additively shaped object, which uses the additively shaped material described above. The method for manufacturing an additively shaped object involves melting and solidifying a base metal in the additively shaped material, and repeating this process to perform additive manufacturing. [Effects of the Invention]

[0015] The additive manufacturing material of the present invention can suppress the formation of defects such as internal voids and coarse, non-uniform structures during additive manufacturing, thereby improving energy efficiency. Furthermore, by using this additive manufacturing material, an additive manufacturing object can be obtained in which the formation of defects such as internal voids and coarse, non-uniform structures is suppressed, enabling additive manufacturing with high energy efficiency. [Brief explanation of the drawings]

[0016] [Figure 1] 1A to 1C are diagrams showing the procedure for manufacturing an additive manufacturing object using an additive manufacturing material by powder bed fusion. [Figure 2] (Fe-18 mass% Cr-2.5 mass% Mo)-Ni pseudobinary phase diagram. [Figure 3] This is a scanning electron microscope (SEM) photograph of a material for additive manufacturing. [Figure 4] FIG. 1 is a diagram showing an outline of laser drawing conditions during additive manufacturing (the arrows in the diagram indicate the direction of laser scanning). [Figure 5] 1 is a graph showing the relative density of additive-manufactured bodies (material without additives, material with SrO added) versus the energy density during additive manufacturing. [Figure 6] FIG. 10 is a diagram showing the distribution of defects in the additive-free material and the SrO-added material. [Figure 7] 1 is a graph showing the Vickers hardness of additive-manufactured bodies (material without additives, material with SrO added) versus the energy density during additive manufacturing. [Figure 8] FIG. 1 shows the internal structure of the layered manufactured body (material without additives, material with SrO added). DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, an embodiment of the present invention will be described. The additive manufacturing material of the present invention is used, for example, in additive manufacturing of a three-dimensional structure by additive manufacturing, and includes a base metal and heterogeneous core particles. The base metal is stainless steel. The heterogeneous core particles have a higher melting point than the base metal, and the parameter M expressed by the formula (1) described below is 12 × 10 -3 The following is the result.

[0018] The present invention relates to a new additive manufacturing material based on heterogeneous nucleation theory, which has a higher melting point than the base metal and is pre-mixed with heterogeneous nuclei particles whose atomic arrangement is well-matched with the phase that becomes the primary crystal of the base metal.

[0019] When this additive manufacturing material is irradiated with a high-energy beam such as a laser or electron beam to selectively melt the base metal, the base metal melts, and the heterogeneous nucleus particles act as nuclei for crystal growth as it solidifies during the subsequent cooling process. Furthermore, if the heterogeneous nucleus particles have good wettability with the molten base metal, optimizing their size and distribution can expand the molten region under the same manufacturing conditions, promoting uniform solidification in various locations.

[0020] This makes it possible to manufacture high-density additively manufactured bodies with few internal voids, and suppress the development of coarse and uneven internal structures. It is also thought that the heterogeneous nucleus particles act as an obstacle (pinning effect) to grain growth due to repeated heat input, and it is expected that the fine structure will be maintained even after manufacturing.

[0021] Microstructural control based on heterogeneous nucleation theory is also used in welding engineering and casting engineering (Non-Patent Document 1). However, the present invention differs from the techniques used in welding engineering and casting engineering. In welding engineering, the main target metal is steel material, and a large amount of oxide is formed in the weld by using oxide flux or wire containing oxide, or oxygen gas as a shielding gas, and this forms a nucleation site, resulting in a fine microstructure. On the other hand, in casting engineering, microstructural refinement is achieved by adding heterogeneous nucleation particles to the molten metal. Therefore, both methods require a secondary process to be inserted during the process, which differs from the method of the present invention.

[0022] As an index for selecting and evaluating heterogeneous nucleus particles that exhibit the above-mentioned effects of the present invention, there is a parameter M (Non-Patent Document 2) that is approximately proportional to elastic strain. Parameter M is calculated using the following formula (1), and the smaller this value, the smaller the energy required for nucleation, and therefore it is considered that the particle acts as an effective heterogeneous nucleus.

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[0023] Also, ε x and ε y is calculated using the following formulas (2) and (3).

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[0024] The parameter M can be considered for all crystal orientation relationships, not just low-index planes and orientations. Furthermore, since the parameter M is approximately proportional to the elastic strain energy due to the misfit strain introduced at the interface between different phases, it is a parameter with physical meaning.

[0025] In the present invention, heterogeneous nucleus particles that become effective heterogeneous solidification nuclei for the base metal are selected based on two elements, namely, the melting point and the parameter M, which is an evaluation parameter for the consistency of the atomic arrangement, and are mixed with the base metal to provide a material for additive manufacturing. In this case, a material that has a high melting point and a parameter M of 12 × 10 is selected. -3 The following material is selected as the heterogeneous nucleus:

[0026] There are countless possible crystal orientation relationships at the interface between the base metal and the heterogeneous nucleus, but in the present invention, for example, low-index planes are considered, and the one with the smallest value can be used as the parameter M of that material relative to the base metal.

[0027] The use of such additive manufacturing materials makes it possible to manufacture high-quality additive manufactured objects with fine structures, suppressing the formation of defects such as internal voids and large, uneven structures. It also enables additive manufacturing using a lower-energy heat source, achieving high energy efficiency and energy savings in the additive manufacturing process.

[0028] In the additive manufacturing material, the volume ratio of the heterogeneous nucleus particles to the base metal is preferably 1.0% or less. That is, when the base metal is taken as 100% by volume, the heterogeneous nucleus particles are preferably 1.0% or less by volume. In this case, the heterogeneous nucleus particles effectively act as nuclei for crystal growth of the molten base metal. The volume ratio of the heterogeneous nucleus particles to the base metal can be, for example, 0.1% or more in order to fully exert the above-mentioned effects of the heterogeneous nucleus particles.

[0029] Although it is not desirable to impair the alloy composition in metals, the addition of very small amounts of heterogeneous nucleus particles to the base metal results in very little change in composition. Conversely, the added heterogeneous nucleus particles are expected to pin grain growth that accompanies the inevitable heating that occurs during subsequent additive manufacturing, even after solidification, and prevent grain coarsening. They can also be expected to act as a strengthening phase that prevents dislocation movement.

[0030] The base metal may be in any form, for example, powder, a sheet having a certain shape, or the like. Accordingly, the additive manufacturing material may also be in any form as long as it can be used for additive manufacturing. For example, it may be a powdered additive manufacturing material having a powdered base metal and heterogeneous core particles, or a sheet-like additive manufacturing material in which heterogeneous core particles are dispersed in a sheet-like base metal.

[0031] Examples of stainless steel that can be used as the material for the base metal include austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, precipitation hardening stainless steel, etc. Among these, austenitic stainless steel is preferred because it is particularly excellent in corrosion resistance, workability, etc., is nonmagnetic, is not brittle at low temperatures, exhibits significant work hardening at room temperature, can obtain significantly high strength through working, and has a wide range of applications, including household goods, construction, automobile parts, the chemical industry, the food industry, the synthetic fiber industry, nuclear power generation, LNG plants, etc., and plays an important industrial role.

[0032] Examples of austenitic stainless steels that can be used include SUS316L, SUS304, and SUS310S. SUS316L is preferred because it combines particularly good mechanical properties, corrosion resistance, and weldability, making it an important material for use in chemical equipment, heat exchangers, marine structures, and the like. Examples of ferritic stainless steels that can be used include SUS430 and SUS410L. Examples of martensitic stainless steels that can be used include SUS440C, SUS403, and SUS420. Examples of precipitation hardening stainless steels that can be used include SUS630 and SUS631.

[0033] As the base metal, basically one of the above-mentioned stainless steels such as austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, and precipitation hardening stainless steel can be used, but a material that is a mixture of multiple types of stainless steel can also be used.

[0034] The heterogeneous core particles have a melting point higher than that of the base metal (stainless steel) and a parameter M of 12 × 10 -3 The following materials can be used. Examples of such materials include particles of one or more compounds selected from SrO, YN, CaO, VN, MgO, TiN, and TiB, each having a NaCl crystal structure. Among these, SrO particles are preferred because they have an extremely small parameter M and are highly compatible with the matrix metal.

[0035] For example, when the base metal is an austenitic stainless steel SUS316L, a martensitic stainless steel SUS440C, or a precipitation hardened stainless steel SUS630, one or more compound particles selected from SrO, YN, and CaO can be used as the heterogeneous nucleus particles. Also, when the base metal is a ferritic stainless steel SUS430, one or more compound particles selected from VN, MgO, TiN, and TiB can be used as the heterogeneous nucleus particles.

[0036] As described above, the heterogeneous core particles can be composed of one or more materials. Furthermore, in order to fully exert the effects of the heterogeneous core particles, the heterogeneous core particles are preferably mixed so as to be uniformly distributed in the base metal. Furthermore, when the base metal is in powder form, the heterogeneous core particles preferably have a particle size that is finer than or similar to that of the base metal.

[0037] The additive manufacturing material may contain materials other than the base metal and heterogeneous core particles, such as rare earth elements such as Ce and La, which are used to refine the grain size of cast steel (Non-Patent Document 3), to the extent that the effects of the present invention described above can be fully achieved.

[0038] The manufacturing method of an additive manufacturing object using the additive manufacturing material described above involves melting and solidifying the base metal of the additive manufacturing material, and repeating this process to create an additive manufacturing object. The additive manufacturing method can use a general metal three-dimensional additive manufacturing technique, such as powder bed fusion or directed energy deposition.

[0039] As an example, an additive manufacturing method using powder bed fusion will be explained with reference to Figure 1. First, the powder supply tank 1 is filled with additive manufacturing material 2. Then, the base plate 3 is lowered by the layer pitch, and conversely, the powder supply tank 1 is raised by the layer pitch (Figure 1(a)). Next, a roller called a recoater 4 spreads the powdered base metal over the base plate 3, forming a uniform powder surface (Figure 1(b)).

[0040] Thereafter, a laser 6 is irradiated from a laser source 5 above the base plate 3 based on a pre-created modeling program, causing the base metal in the additive manufacturing material 2 to melt and solidify, thereby forming one layer (Fig. 1(c)). By repeating this modeling process and stacking the layers, an additive manufactured object 7 is obtained (Fig. 1(d)).

[0041] (Example) The present invention will now be described with reference to examples. In this study, the base metal for the additive manufacturing material was SUS316L powder, an austenitic stainless steel. SUS316L, the base metal selected, is an important alloy used in the nuclear industry for nuclear materials such as the lining of reactor pressure vessels and piping, as well as for materials used in corrosive environments.

[0042] SUS316L has a chemical composition of Fe-(17-19) mass% Cr-(13-15) mass% Ni-(2.25-3) mass% Mo. According to the (Fe-18 mass% Cr-2.5 mass% Mo)-Ni pseudobinary phase diagram created using TCFE7 in the integrated thermodynamic calculation software Thermo-Calc, as shown in Figure 2, SUS316L crystallizes as the α phase as the primary crystal. However, because cooling from the liquid phase during additive manufacturing is extremely rapid, most of the structure crystallizes as the primary γ phase (Non-Patent Document 4), and ultimately the structure becomes almost entirely composed of the γ phase. The α phase of SUS316L has a body-centered cubic (bcc) crystal structure, while the γ phase has a face-centered cubic (fcc) crystal structure.

[0043] Therefore, when SUS316L is selected as the base metal, a foreign material having a higher melting point than SUS316L and a high atomic arrangement matching with the primary γ phase of SUS316L can be selected as the heterogeneous core material.

[0044] Next, heterogeneous core particles that constitute the additive manufacturing material are selected. Table 1 shows the melting points, crystal structures, and lattice constants of various compounds (TiNb, Nb, SrO, YN, CaO) containing SUS316L as a constituent element, as well as the parameter M calculated using the above-mentioned formulas (1), (2), and (3). Note that the parameter M was calculated assuming an orientation relationship between the low-index planes in the primary γ phase and heterogeneous solidification nuclei of SUS316L.

[0045] [Table 1]

[0046] Here, an example will be given to explain evaluation using the parameter M. For example, when SrO, which has a face-centered cubic (fcc) crystal structure as a heterogeneous nucleus, is considered in relation to the primary gamma phase of SUS316L, which has a face-centered cubic (fcc) lattice, and it is assumed that the lattice constant of the gamma phase of SUS316L is the same as that of the Fe-C gamma phase, the respective lattice constants are 0.3640 nm for the gamma phase of SUS316L and 0.5160 nm for SrO.

[0047] Considering that the interface between the γ phase of SUS316L and SrO during solidification is parallel to each other in the (100) plane, and that the

[0011] direction of the γ phase of SUS316L is parallel to the

[0001] direction of SrO, ε can be calculated from the above equations (1), (2), and (3). x and ε y are both 1.165 x 10 -3 This results in a parameter M of 0.003×10 -3 This becomes:

[0048] As shown in Table 1, SrO, YN, and CaO, which have a crystal structure of NaCl, have higher melting points than SUS316L, and the parameter M is 12 × 10 -3 It is believed that SrO acts effectively as a heterogeneous nucleus because it has the following properties: Among them, SrO was selected as the heterogeneous nucleus material in this example because it has a higher melting point than SUS316L and a smaller parameter M.

[0049] Next, a material for additive manufacturing is prepared. First, SUS316L powder, which is the base metal, and SrO particles selected as heterogeneous core particles are prepared.

[0050] The SUS316L powder selected had a particle size of 25 to 53 μm. The SUS316L powder is a gas atomized powder with spherical particles. Gas atomized powder is produced by the gas atomization method, where molten metal is made to flow down from above and then pulverized by spraying high-pressure gas onto it. The SrO particles selected had a particle size of 2 to 30 μm. The SrO particles are polygonal particles that tend to agglomerate.

[0051] The SrO particles were then placed in a 1000 mL container together with the SUS316L powder and mixed for one hour using a turbulator mixer powder mixer until uniform. While typical mixers are designed to combine two-dimensional motion on one axis or three-dimensional motion on multiple axes, the turbulator mixer performs shaking through three-dimensional motion and alternating acceleration and deceleration, making it possible to uniformly mix even materials with large differences in specific gravity. The amount of SrO particles added to the SUS316L powder was 0.3 vol% (volume %). In other words, the volume ratio of SrO particles to the SUS316L powder was 0.3 vol% (vol %). This resulted in the production of a material for additive manufacturing.

[0052] Figure 3 shows a scanning electron microscope (SEM) image of an additive manufacturing material made by mixing 0.3 vol% SrO particles with SUS316L powder. From this image, it is possible to observe additive manufacturing material 10, in which SrO particles 9, which are heterogeneous nuclei, are attached to the surface of spherical SUS316L particles 8, which are the base metal.

[0053] Next, an additive manufacturing object is produced using the additive manufacturing material and evaluated. Here, as an example of the present invention, a metal powder in which SrO particles are added to SUS316L powder (hereinafter referred to as "SrO-added powder") is prepared, and as a comparative example, a metal powder consisting of only SUS316L powder without the addition of SrO particles (hereinafter referred to as "additive-free powder") is prepared.

[0054] Then, using the powder bed fusion method shown in Figure 1, we fabricated an additive-manufactured object using SrO-added powder (hereinafter referred to as "SrO-added material") and an additive-free powder (hereinafter referred to as "additive-free material"), and performed various evaluations to demonstrate the usefulness of additive manufacturing materials with heterogeneous solidification nuclei added.

[0055] Table 2 shows the additive manufacturing conditions. Additive manufacturing was performed by fixing the laser power, scanning pitch, defocus position, and layer pitch, and varying the scanning speed. Figure 4 shows the imaging conditions for laser scanning. After metal powder was spread on a SUS316L plate set as a base plate, laser scanning was performed (the arrow in the figure indicates the laser scanning direction 11). Additive manufacturing was then performed until an additive manufacturing object measuring 5 mm in length, 5 mm in width, and 5 mm in height was obtained.

[0056] [Table 2]

[0057] In addition, based on the above additive manufacturing conditions, the introduced energy per unit volume by laser irradiation (energy density (J / mm 3 )) was calculated using the following formula (4).

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[0058] Energy density: 79.4J / mm 3 (Scan speed: 600 mm / s) and energy density: 119.0 J / mm 3 Under the additive manufacturing conditions of (scan speed: 400 mm / s), each additive manufactured body (material without additives, material with SrO addition) will be produced and evaluated for relative density, defect distribution, Vickers hardness, and crystal grain refinement.

[0059] Figure 5 shows the results of evaluating the relative density of an AM object using the Archimedes method. The horizontal axis of the figure represents the energy density calculated using equation (4) above. The Archimedes method is a relatively simple method for measuring relative density using water and a scale, and calculates the relative density by measuring the buoyancy caused by the density difference between the water and the object.

[0060] The figure shows that the SrO-added material has a higher relative density than the additive-free material. Furthermore, while the relative density increases with increasing energy density, the increase in relative density due to the addition of SrO particles is greater at lower energy densities. These results demonstrate that the use of the additive manufacturing material of the present invention makes it possible to produce additively manufactured objects with higher relative densities. Furthermore, additive manufacturing using a laser with a lower energy density is possible, which contributes to improving the energy efficiency and saving of processes in 3D additive manufacturing technology.

[0061] Figure 6(a) and (b) show the energy density: 79.4 J / mm 3 The figure shows the results of measuring the defect distribution of an additive manufacturing object made using an X-ray computed tomography (X-ray CT) scanner (scan speed: 600 mm / s). X-ray CT is a method of non-destructively evaluating materials by passing X-rays through a stage that is rotated 360° and collecting the images with a detector to construct a three-dimensional image. The figure shows that the SrO-added material has fewer internal defects than the additive-free material. These results demonstrate that additive manufacturing using the additive manufacturing material of the present invention can produce denser additive manufacturing objects.

[0062] Figure 7 is a graph showing measurements of Vickers hardness with the top surface of the additive manufacturing object (the surface parallel to the layering surface) as the observation surface. The Vickers hardness test is a type of mechanical property evaluation method that evaluates the hardness of a material from the indentation depth when a diamond indenter is pressed into the surface of a sample with a specified load. The figure shows that the SrO-added material exhibits a Vickers hardness that is higher or equal to that of the additive-free material. These results demonstrate that additive manufacturing using the additive manufacturing material of the present invention can produce additive manufacturing objects with higher strength.

[0063] Figure 8(a) and (b) show the energy density: 79.4 J / mm 3 This figure shows the results of an EBSD observation of the internal structure of the layer surface of an additive manufacturing object (scan speed: 600 mm / s). EBSD is a method of indexing the reflected diffraction pattern obtained from the sample surface using an SEM to measure the crystal orientation at the point where the EBSD pattern originates and determine the crystal system. It can be seen from the figure that the SrO-added material has finer crystal grains than the additive-free material (fcc grain boundaries 12 are shown in the figure). These results demonstrate that additive manufacturing using the additive manufacturing material of the present invention can produce additive manufacturing objects with a finer structure.

[0064] Furthermore, as described above, the SrO-added material of the present invention has fewer internal voids and a finer structure than the additive-free material of the comparative example. Therefore, the SrO-added material is expected to have improved tensile properties (tensile strength, elongation) and impact properties compared to the additive-free material. Tensile tests and Charpy tests are generally used to evaluate tensile properties and impact properties, respectively.

[0065] A tensile test is a test method defined by JIS standards in which a tension force is applied to a test specimen until it breaks, and the yield point, tensile strength, elongation, etc. of the test specimen are evaluated. A fine structure with a higher number of grain boundaries that can hinder the movement of dislocations in the metal structure that cause deformation when tension is applied improves the yield point and tensile strength, and also improves elongation by promoting uniform deformation. Therefore, it is believed that an additive manufacturing object made using the additive manufacturing material of the present invention will exhibit excellent tensile properties.

[0066] The Charpy test is a test method in which a test piece with a notch (cut) specified by JIS standards is broken by swinging a hammer down on it to measure the energy absorbed. If the test piece contains a large number of voids, the absorbed energy is small and the piece is prone to breakage. Therefore, it is believed that an additive manufacturing object made using the additive manufacturing material of the present invention absorbs a large amount of energy and has high toughness.

[0067] As described above, the additive manufacturing material of the present invention is a base metal to which heterogeneous nucleus particles have been added. These particles act as nuclei for crystal growth when the base metal is melted by a high-energy beam and subsequently solidifies. Meanwhile, the heterogeneous nucleus particles can also act as nuclei for crystal growth during phase transformation in the solid phase if they are well matched at the interface with the product phase (Non-Patent Document 6).

[0068] In the above-described examples, SrO particles were used as heterogeneous nuclei particles. However, as shown in Table 2, the parameter M was 12×10 -3 It is believed that similar results can be obtained even when YN particles or CaO particles are used as described below. Furthermore, although austenitic stainless steel was used as the base metal, it is believed that similar heterogeneous core particles (SrO particles, YN particles, CaO particles) can be used even when, for example, martensitic stainless steel or precipitation hardened stainless steel is used, and similar results can be obtained.

[0069] Ferritic stainless steel may also be used as the base metal. Table 3 shows the melting points, crystal structures, and lattice constants of various compounds (VN, MgO, TiN, TiB, and TiC) containing the ferritic stainless steel SUS430 as a constituent element, as well as the parameter M calculated using the above-mentioned formulas (1), (2), and (3). Note that the parameter M was calculated assuming an orientation relationship between the primary α phase of SUS430 and the low-index plane in the heterogeneous solidification nuclei.

[0070] [Table 3]

[0071] As shown in Table 3, VN, MgO, TiN, and TiB have a NaCl crystal structure, a higher melting point than SUS430, and a parameter M of 12 × 10 -3 It is believed that the heterogeneous nuclei function effectively because of the following: By using such heterogeneous nuclei particles, it is believed that the same results as those in the above-mentioned examples can be obtained.

[0072] The present invention is not limited to the above-described embodiments (examples), and may be embodied in various forms without departing from the scope of the present invention. For example, the function of one component in the above-described embodiments may be distributed among multiple components, or the functions of multiple components may be integrated into one component. Also, part of the configuration of the above-described embodiments may be omitted. Furthermore, at least part of the configuration of the above-described embodiments may be added to or substituted for the configuration of another of the above-described embodiments. Note that all aspects included in the technical idea specified by the wording of the claims are embodiments of the present invention. [Explanation of symbols]

[0073] 1...Powder supply tank, 2...Additive manufacturing material, 3...Base plate, 4...Recoater, 5...Laser source, 6...Laser, 7...Additive manufacturing object, 8...SUS316L particles, 9...SrO particles, 10...Additive manufacturing material, 11...Laser scanning direction, 12...fcc grain boundary

Claims

1. A material for additive manufacturing used in additive manufacturing of a three-dimensional structure, The alloy includes a base metal and heterogeneous core particles, the base metal is an austenitic stainless steel, The heterogeneous core particles are SrO particles, have a melting point higher than that of the base metal, and have a parameter M expressed by formula (1) of 12×10 －３ 1. A material for additive manufacturing, comprising: [Equation 1] (In the formula, ε ｘ and ε ｙ are the principal axis strains along the principal axes x and y, which are perpendicular to each other in the lattice of the heterogeneous core phase and the lattice of the solidified phase at the interface between the heterogeneous core phase and the solidified phase, respectively, and ε ｘ and ε ｙ is calculated using the following formulas (2) and (3): [Equation 2] [Equation 3] (In the formula, x i , y i and x ｊ , y ｊ are the principal axial strain directions of material i and material j, respectively, and a ｉ and a ｊ are the lattice constants of material i and material j, respectively. Material i is the heterogeneous core particle in the heterogeneous core phase, and material j is the base metal in the solidified phase.

2. The material for additive manufacturing according to claim 1 , wherein a volume ratio of the heterogeneous core particles to the base metal is 1.0% or less.

3. The additive manufacturing material according to claim 1 or 2, wherein the base metal is SUS316L.

4. A method for manufacturing an additive manufacturing object using the additive manufacturing material according to any one of claims 1 to 3, A method for manufacturing an additively manufactured object, which involves melting and solidifying the base metal in the additively manufactured material, and repeating this process to manufacture the additively manufactured object.

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