WO2023140326A1 - Method of forming single-crystal or directionally solidified three-dimensional formed objects - Google Patents

Abstract

The present invention is a method of manufacturing a single-crystal or directionally solidified three-dimensional formed object utilizing a metal-powder additive-forming device (100). The method includes the metal-powder additive-forming device (100): forming a thin layer (260) of powder material containing metal particles (140); selectively irradiating the thin layer (260) with a laser beam (112) so that the metal particles (140) contained in the powder material yield a planar molten-pool form, and by crystal growth accompanying solidification, forming a single-crystal or directionally solidified formed-object layer; and repeating the forming of the thin layer (260) and the forming of the formed-object layer in that order multiple times, to additively-grow the single-crystal or directionally solidified formed-object layers.

Description

Single crystal or unidirectionally solidified three-dimensional object molding method

The present invention relates to a method of forming a three-dimensional object of a single crystal alloy or a directionally solidified alloy suitable for use in aircraft engine turbine blades and the like.
This application claims priority based on Japanese Patent Application No. 2022-007463 filed in Japan on January 20, 2022, the content of which is incorporated herein.

Ni-based superalloys are used as heat resistant materials for aircraft engine turbines. Ni-based superalloys are used under conditions of high temperature and high stress, but the grain boundaries formed during manufacturing are weak parts that hinder durability, and fractures occur starting at the grain boundaries, reducing fatigue life and creep life.
A single crystal eliminates the grain boundaries and improves the strength. This single crystal is produced by casting, in which molten metal is poured into a mold and unidirectionally solidified (see Patent Document 1). Here, single crystals can be obtained because they solidify through passages that select only the growing grains in one direction, called the “selector” of the mold.
However, the manufacturing of turbine blades using a mold having a "selector" has the problem that it is manufactured in a large vacuum chamber, the manufacturing process is complicated, the productivity is not high, and the cost is high. Ni-based single-crystal superalloy parts manufactured by such a complicated and large-scale process are expensive, and the development of techniques for repairing these single-crystal parts by maintenance after being mounted on an actual machine is also progressing (see Patent Document 2). However, there is a problem that this repair technique is not a technique for manufacturing single crystal alloy parts.

　In recent years, the technology of 3D additive manufacturing, which can manufacture parts with complex shapes, has progressed, and the technology to shape Ni-based superalloy members by 3D additive manufacturing has been developed. Here, a technique has been reported in which a powder is laid on a seed crystal or a base material prepared in advance with a uniform crystal orientation, and the powder is melted on the seed base material by beam irradiation to cause crystal growth, thereby obtaining a material having the same single crystal or crystal as the base material (see Patent Documents 3 to 5 and Non-Patent Document 1). However, in this case, it is necessary to prepare seed crystals that are expensive and laborious to prepare in a separate process.

A technology for producing single crystals by 3D additive manufacturing without using seed crystals has recently been reported. This is an electron beam method in which an electron beam is irradiated onto a powder bed in a vacuum to melt and solidify the powder (see Non-Patent Documents 2 and 3). With this technology, it has become possible to form a single crystal without using a seed crystal in 3D additive manufacturing, but electron beam modeling equipment requires an expensive vacuum chamber, and the penetration rate of the equipment is low, and the size of the modeled body is also determined by the chamber size.

On the other hand, in 3D additive manufacturing, it is a device that irradiates a laser beam at a lower cost and is simpler. The selective laser melting method, in which a powder bed is melted and solidified to form a shape, has hitherto been unable to produce a single crystal.

Japanese Patent Laid-Open No. 7-247802 (A) Japanese Patent Application Laid-Open No. 2004-183652 (A) Japanese Patent Application Laid-Open No. 2015-189618 (A) Japanese Patent Application Laid-Open No. 2017-66023 (A) EP-A-2565294 (A)

The objective of the present invention is to realize the production of single crystals of Ni-based superalloys by controlling the crystal growth direction after laser irradiation without using seed crystals, using a selective laser melting method that allows the use of equipment at a lower cost than the electron beam method in 3D additive manufacturing.

[1] A method for manufacturing a single-crystal or directionally-solidified three-dimensional object according to the present invention is a method for manufacturing a single-crystal or directionally-solidified three-dimensional object using a metal powder additive manufacturing apparatus,
forming a thin layer of powder material comprising metal particles;
selectively irradiating the thin layer with a laser beam, the metal particles contained in the powder material obtain a planar molten pool shape, and crystal growth accompanying solidification forms a monocrystalline or unidirectionally solidified model layer;
Repeating the forming of the thin layer and the formation of the model layer in this order a plurality of times to grow the single crystal or directionally solidified model layer by lamination.

[2] In the manufacturing method [1] of a single crystal or directionally solidified three-dimensional object of the present invention, preferably, the laser beam is a beam having a uniform intensity distribution in the irradiation plane or a difference in intensity distribution in the irradiation plane is within 10% of the maximum intensity.
[3] In the method [1] or [2] of the single crystal or directionally solidified three-dimensional object of the present invention, the spot diameter of the laser beam is preferably 100 μm or more and 1000 μm or less. More preferably, it is 300 μm or more and 800 μm or less, and the optimum range is 500 μm or more and 700 μm or less.
[4] In the methods [1] to [3] of single crystal or directionally solidified three-dimensional objects of the present invention, preferably, the thin layer of the powder material has a thickness of 10 μm or more and 70 μm or less. More preferably, the thickness is 20 μm or more and 50 μm or less, and the optimum range is 30 μm or more and 40 μm or less.
[5] In the methods [1] to [3] of the single crystal or unidirectionally solidified three-dimensional object of the present invention, it is preferable that D(50) of the particle size distribution of the powder material is 10 μm or more and 110 μm or less. More preferably, it is 25 μm or more and 80 μm or less, and the optimum range is 30 μm or more and 40 μm or less.
[6] In the method [1] to [5] of the single crystal or unidirectionally solidified three-dimensional object of the present invention, the planar molten pool shape preferably has a depth of 5 μm or more and 200 μm or less and a width of 100 μm or more and 1000 μm or less. More preferably, the depth is 10 μm to 100 μm and the width is 100 μm to 700 μm, and the optimum range is 15 μm to 70 μm and the width is 100 μm to 500 μm.
[7] In the methods [1] to [6] of the single crystal or unidirectionally solidified three-dimensional object of the present invention, the aspect ratio of the planar molten pool shape (depth at the center of the molten pool/width of the molten pool) is preferably 0.01 or more and 0.23 or less. More preferably, it should be 0.1 or more and 0.2 or less.

[8] In the methods [1] to [7] of single-crystal or directionally solidified three-dimensional objects of the present invention, preferably, as the substrate on which the thin layer of the powder material containing the metal particles is formed, a substrate or a seed crystal having a desired crystal orientation or crystal structure may be installed.
[9] In the methods [1] to [8] of forming a single crystal or unidirectionally solidified three-dimensional object of the present invention, it is preferable that a substrate or seed crystal having a desired crystal orientation or crystal structure is not installed as the substrate on which the thin layer of the powder material containing the metal particles is formed.
[10] In the methods [1] to [9] of single-crystal or directionally solidified three-dimensional objects of the present invention, preferably, an electron beam may be used in place of the laser beam.
[11] In the method [1] to [10] of a single crystal or directionally solidified three-dimensional object of the present invention, the single crystal or directionally solidified three-dimensional object is preferably a turbine stator blade or a turbine rotor blade.
[12] In the method [1] to [11] for forming a single crystal or directionally solidified three-dimensional object of the present invention, preferably, the metal particles are made of a metal material having a composition used for any of nickel, nickel-based superalloys, titanium alloys including β-type titanium alloys, and aluminum alloys.

According to the single-crystal or directionally-solidified three-dimensional object manufacturing method of the present invention, a flat-top laser that can obtain a laser beam with a uniform intensity distribution in the irradiation surface is used. Therefore, a planar molten pool shape can be obtained for a thin layer of a powder material containing metal particles, and a single crystal or directionally solidified can be grown.
According to the single crystal or directionally solidified three-dimensional object shaping method of the present invention, it is possible to manufacture without using seed crystals, and there is no need to prepare expensive seed crystals produced in a separate process. Even when a seed crystal is used for production, the process conditions for growing a single crystal or unidirectional solidification are preferable, so a three-dimensionally shaped object with a clean crystal structure can be obtained.

1 is an overall functional block diagram showing an example of a metal powder 3D printer used for selective laser melting; FIG. 4 is a flow chart illustrating an example of the operation of a metal powder 3D printer; FIG. 2 is an explanatory diagram of the vertical in-plane intensity distribution in the apparatus of FIG. 1, showing a flat top type showing one embodiment of the present invention, and showing a perspective view. FIG. 1 is an explanatory diagram of the vertical in-plane intensity distribution in the apparatus of FIG. 1, showing a flat top type showing one embodiment of the present invention, and showing the distribution from the upper surface side. It is an explanatory view of the vertical in-plane intensity distribution in the conventional apparatus, showing a Gaussian type, and showing a perspective view. It is an explanatory diagram of the vertical in-plane intensity distribution in the conventional apparatus, showing a Gaussian type, and showing the distribution from the upper surface side. FIG. 4 is an explanatory diagram of a molten pool shape by a flat-top type laser showing an embodiment of the present invention; FIG. 5 is an explanatory diagram of a molten pool shape obtained by a conventional Gaussian laser as a comparative example. 1 is a perspective view of a shaped sample shape showing an embodiment of the present invention; FIG. It is an image obtained by EBSD analysis of pure Ni samples of an example (FT3, directionally solidified alloy) of the present invention and comparative examples (FT1, FT2) shaped by a flat-top laser (upper: surface perpendicular to the beam direction, lower: surface parallel to the beam direction). FIG. 4 is an explanatory diagram of the crystal orientation distribution of Comparative Example FT1; It is explanatory drawing of the crystal orientation distribution of comparative example FT2. FIG. 4 is an explanatory diagram of the crystal orientation distribution of Example FT3; It is an image (upper: surface perpendicular to the beam direction, lower: surface parallel to the beam direction) obtained by EBSD analysis of pure Ni samples of an example (FT6, single crystal alloy) and comparative examples (FT2, FT7) of the present invention fabricated by a flat-top laser. It is explanatory drawing of the crystal orientation distribution of comparative example FT2. It is explanatory drawing of the crystal orientation distribution of Example FT6. It is explanatory drawing of the crystal orientation distribution of comparative example FT7. It is an image obtained by EBSD analysis of pure Ni samples of comparative examples (FT2, FT4 and FT5) formed by a flat-top laser (upper: plane perpendicular to the beam direction, lower: plane parallel to the beam direction). It is explanatory drawing of the crystal orientation distribution of comparative example FT2. It is explanatory drawing of the crystal orientation distribution of comparative example FT4. It is explanatory drawing of the crystal orientation distribution of comparative example FT5. It is an image obtained by EBSD analysis of pure Ni samples of comparative examples (G1, G2 and G8) shaped by a Gaussian laser (upper: surface perpendicular to the beam direction, lower: surface parallel to the beam direction). FIG. 4 is an explanatory diagram of the crystal orientation distribution of Comparative Example G1; FIG. 10 is an explanatory diagram of the crystal orientation distribution of Comparative Example G2; FIG. 10 is an explanatory diagram of the crystal orientation distribution of Comparative Example G8; It is explanatory drawing of the molten pool shape by the flat top type laser of a comparative example (condition: FT2, FT4, FT5). FIG. 4 is an explanatory diagram of a molten pool shape obtained by a flat-top type laser in one example of the present invention (condition: FT3, directionally solidified alloy). FIG. 4 is an explanatory diagram of a molten pool shape obtained by a flat-top type laser according to an example of the present invention (conditions: FT6, single crystal alloy). FIG. 10 is an explanatory diagram of a molten pool shape obtained by a Gaussian laser in a comparative example (condition: G1). FIG. 10 is an explanatory diagram of a molten pool shape obtained by a Gaussian laser in a comparative example (condition: G2). FIG. 10 is an explanatory diagram of a molten pool shape by a Gaussian laser in a comparative example (condition: G8).

The present invention will be described below with reference to the drawings.
For example, SLM280 manufactured by SLM Solution Co., Ltd. located in Lubeck, Federal Republic of Germany can be used as the metal powder additive manufacturing apparatus used in the present invention.
[Overview of Laser Metal Powder Additive Manufacturing Equipment]
FIG. 1 is an overall functional block diagram showing an embodiment of a metal powder 3D printer used for selective laser melting. With reference to FIG. 1, the lamination-molding apparatus 100 is a laser lamination-molding apparatus, for example. The layered manufacturing apparatus 100 includes a laser device 110 , a galvanomirror 120 , a control device 130 and a chamber 200 .

The laser device 110 emits laser light. Laser device 110 is, for example, a fiber laser, a CO ₂ laser, or the like. Laser device 110 may be provided with a lens system (not shown). The lens system receives laser light from laser device 110 and focuses the laser light to form laser 112 . The galvanomirror 120 performs irradiation operation of the laser 112 . That is, the galvanomirror 120 adjusts the position where the laser 112 is irradiated.

The chamber 200 includes a layer forming chamber 210, a modeling table 230, a powder supply chamber 220, and a recoater 250. In order to prevent the metal powder particles 140 from being oxidized during the irradiation operation of the laser 112, the inside of the chamber 200 is kept filled with an inert gas (argon, nitrogen, etc.) or kept in a vacuum state.

The layer forming chamber 210 has a housing shape with an opening at the upper end. The modeling table 230 is housed in the layer forming chamber 210 and supported so as to be able to move up and down in the vertical direction (Z direction). The modeling table 230 is moved up and down by a motor (not shown).

The powder supply chamber 220 is arranged next to the layer formation chamber 210 . The powder supply chamber 220 has a housing-like shape, and includes a vertically movable piston 240 therein. Metal powder particles 140 are layered on the piston 240 . The metal powder particles 140 are the raw material for the modeled object. A layer of the metal powder particles 140 is discharged from the upper opening of the layer forming chamber 210 by raising the piston 240 . The metal powder particles 140 are, for example, metal powders of nickel-based superalloys, cobalt-based superalloys, and iron-based superalloys having high heat resistance. Instead of the metal powder particles 140, ceramics such as Al ₂ O ₃ may be used together with the metal powder particles 140, or inorganic powder particles such as ceramic particles may be used alone.

The recoater 250 is arranged near the upper opening of the powder supply chamber 220 . The recoater 250 is moved in a specific direction (horizontal direction) by a motor (not shown) and reciprocates between the powder supply chamber 220 and the layer forming chamber 210 . In FIG. 1, the recoater 250 reciprocates in the X direction.
By moving in the X direction, the recoater 250 horizontally moves the layer of the metal powder particles 140 discharged from the powder supply chamber 220 and supplies the layer to the layer forming chamber 210 . A metal powder layer 260 made of the metal powder particles 140 is formed on the modeling table 230 by the metal powder particles 140 deposited on the modeling table 230 in the layer forming chamber 210 . By moving the recoater 250 in the X direction, the metal powder particles 140 move in the horizontal direction, and the surface of the metal powder layer 260 is flattened.

The control device 130 includes a central processing unit (CPU) (not shown), a memory, and a storage device such as a hard disk drive (HDD). The storage device stores well-known CAD (Computer Aided Design) applications and CAM (Computer Aided Manufacturing) applications. The control device 130 uses a CAD application to create three-dimensional shape data of a modeled object to be manufactured.

The control device 130 further uses the CAM application to create processing condition data based on the three-dimensional data. In the layered manufacturing method, a plurality of modeled object parts formed by the laser 112 are layered to form a modeled object. The processing condition data includes processing conditions for forming each modeled object portion. In other words, the processing condition data is created for each molded object portion. The control device 130 controls the laser device 110, the lens system and the galvanomirror 120 based on the processing condition data to adjust the output of the laser 112, scanning speed, scanning interval and irradiation position.

[Details of manufacturing process]
FIG. 2 is a flow chart explaining an example of the operation of the metal powder 3D printer. In the metal powder additive manufacturing apparatus, the object to be molded is manufactured in the following steps according to the flow chart shown in FIG.
As a preparatory step for the metal powder additive manufacturing apparatus, a vacuum pump is used to evacuate the chamber 200 . After the chamber 200 is evacuated, inert gas (argon, nitrogen, etc.) is supplied into the chamber 200 . It should be noted that the inside of the chamber 200 may be replaced while flowing an inert gas without drawing a vacuum, and the modeling table 230 in the layer forming chamber 210 may be preheated.

Next, a metal powder layer 260, which is a thin layer of powder material containing metal particles, is formed (S100).
The metal particles may be a metal material having a composition used for any of nickel, nickel-based superalloys, titanium alloys, including beta-titanium alloys, or aluminum alloys. The content of metal particles contained in the powder material may be 70% by mass or more, 90% by mass or more, or 100% by mass.
Next, the thin layer is selectively irradiated with laser light (for example, flat top laser light). The metal particles contained in the powder material heated by the irradiation of the laser light are sintered or melt-bonded. As a result, a model layer made of sintered or melt-bonded metal particles is formed (S110). The step of forming the thin layer and the step of forming the modeled object layer are repeated in this order multiple times to stack the modeled object layer (S120).
The number of repetitions may be, for example, 2 or more, 2 to 30,000, 10 to 5,000, or 100 to 1,500.
To selectively irradiate a laser beam means to irradiate a laser beam only to a cross-sectional area of a three-dimensional molded object in the spread metal powder layer. That is, it means irradiating a predetermined region (region intended to form a three-dimensional object) of the metal powder layer with a laser beam.
In this way, the desired shape of the three-dimensional object is obtained (S140).

3A and 3B are explanatory diagrams of the vertical in-plane intensity distribution in the apparatus of FIG. 1, showing a flat top type showing an embodiment of the present invention. FIG. 3A is a perspective view showing the temperature distribution, and FIG. 3B shows the temperature distribution from the top side. The flat-top type has a truncated cone shape with a generally flat top surface, and the laser beam is not perfectly focused, but is generally evenly converged within the range of the top surface of the truncated cone. The hatch width h (μm) corresponds to the spacing of the laser scans, while the truncated cone top represents the spread of the laser light in the aperture area and has a diameter of, for example, 500 μm to 700 μm. The frustoconical top may have a diameter of 30 μm to 3 mm, and may have a diameter of 200 μm to 1 mm.
A homogenizer is used in the flat-top laser beam so that the beam has a uniform intensity distribution in the irradiation surface. The accuracy of the homogenizer is such that the difference in intensity distribution within the irradiation surface is preferably within 10% of the maximum intensity, more preferably within 1%. Types of homogenizers include fly-eye type, DOE (diffractive optical element) type, light pipe type, and fiber type. The wavelengths of laser light are, for example, 795 nm, 808 nm, 915 nm, 940 nm and 980 nm. The focal length depends on the beam size, but is for example 50 mm to 3000 mm. There are various beam shapes such as square, circle, hexagon, and rectangle. The beam size has a minimum diameter of Φ0.1 mm and a maximum diameter of Φ1 mm, for example. The laser light output is, for example, about 10 kW and can be adjusted.

3C to 3D are explanatory diagrams of the vertical in-plane intensity distribution in the conventional apparatus, showing a Gaussian type. FIG. 3C is a perspective view, and FIG. 3D shows the distribution from the top side. The Gaussian type has a bell-shaped temperature distribution shape, which is similar to a laser beam condensed at one point with some degree of aberration. The hatch width h (μm) corresponds to the spacing of the laser scans, while the truncated cone top represents the spread of the laser light in the aperture area and has a diameter of, for example, 80 μm to 100 μm.

The energy density of flat-top laser light may be 0.1 J/mm ³ to 5000 J/mm ³ , 1 J/mm ³ to 400 J/mm ³ , or 10 J/mm ³ to 100 J/mm ³ .

A flat molten pool shape can be obtained by heating the thin layer under appropriate conditions. The molten pool is a region formed in the heated portion of the thin layer as a result of the thin layer being heated, melted, and solidified by the laser beam.
The weld pool can be identified by analyzing a cross-section of the sample, for example with EBSD. The molten pool can be distinguished from the non-melted pool by the difference in crystal structure.

The aspect ratio of the weld pool shape can be obtained from the weld pool center depth/weld pool width.
Among the molten pool shapes, a flat molten pool shape means, for example, one having an aspect ratio of 0.23 or less. Although not particularly limited, the aspect ratio may be 0.01 or more.

FIG. 4A is an explanatory diagram of the molten pool shape by a flat-top laser, showing one embodiment of the present invention. In this embodiment, a plate made of pure Ni is melted instead of metal powder particles, and the laser output is 900 W and the scanning speed is 500 mm/s. The plate material, which is a pure Ni sample, was melted with a width of 341.49 μm and an average penetration depth of 30.5 μm.

FIG. 4B is an explanatory diagram of a molten pool shape by a conventional Gaussian laser as a comparative example. In this comparative example, a plate made of pure Ni is melted instead of metal powder particles, and the laser output is 200 W and the scanning speed is 600 mm/s. The pure Ni sample plate material was melted with a width of 122.78 μm and a maximum penetration depth of 91.73 μm.
Generally speaking, conventionally used lasers have a laser spot diameter of about 80 μm and have a Gaussian intensity distribution in the vertical plane. In this case, the shape of the molten pool also becomes Gaussian, and the crystal growth direction during solidification deviates greatly from the beam irradiation direction. In that case, solidification fronts of growing crystals collide and form grain boundaries at their interfaces. Also, dislocations introduced by thermal strain during thermal contraction promote the formation of grain boundaries.
Ni-based superalloys are used under conditions of high temperature and high stress, but the grain boundaries formed during manufacturing are weak parts that hinder durability, and fractures occur starting at the grain boundaries, reducing fatigue life and creep life.

FIG. 5 is a perspective view of a modeled sample shape showing an embodiment of the present invention, showing a perspective view of a cylindrical body and its coordinate system. The shape of the modeled sample is a cylindrical body with a height H of 30 mm and a diameter D of 12 mm. The coordinate system of the modeled sample is a three-dimensional coordinate system, which is an XYZ orthogonal coordinate system.
A pure Ni sample was used as the material to be shaped. The powder grain size of the pure Ni sample is D(10) of 24.6 μm, D(50) of 35.1 μm, and D(90) of 51.8 μm. The thickness of the powder layer laid in each layer during molding is 30 μm.

Table 1 shows the laser output P (W), scanning speed v (mm/s), and hatch width h (μm) as powder molding parameters of the flat top type laser.

6A to 6D are explanatory diagrams of the crystal orientation distribution of the entire pure Ni sample formed by melting and solidifying the powder bed with a flat-top laser showing one embodiment of the present invention, FT3 is a directionally solidified alloy, and FT1 and 2 are comparative examples. Here, the crystal orientation distribution is determined, for example, by EBSD (electron back scattering diffraction) analysis. EBSD analysis is to measure the orientation of a minute region based on the Kikuchi line diffraction pattern obtained by electron beam backscattering in a scanning electron microscope (SEM). The laser output is 600 W and the energy density is 61.16 J/mm ³ in FT3, 400 W and 40.77 J/mm ³ in FT1, and 500 W and 50.96 J/mm ³ in FT2.

In the figure, FT3 has an irregular grain boundary shape such as a circular cross section with an average grain size of 50 to 200 μm or an oval cross section on a plane perpendicular to the beam direction, and an average length of 1000 μm or more on a plane parallel to the beam direction. In addition, in the crystal orientation distribution map with (001), (101), and (111) vertices, there are many crystal grains close to the (101) orientation. Here, the size of a dot indicates the ratio of crystal grains of that orientation.
On the other hand, in the crystal orientation distribution map with vertexes (001), (101), and (111), on the plane perpendicular to the beam direction, the 001 orientation is dominant in FT1, and the 101 orientation is dominant in FT2, but large points and small points are distributed, indicating a polycrystalline state.

7A to 7D are explanatory diagrams of the crystal orientation distribution of the entire pure Ni sample shaped by a flat-top laser showing one embodiment of the present invention, FT6 is a single crystal alloy, and FT2 and 7 are comparative examples. The scanning speed is 143 mm/s and the energy density is 43.07 J/mm ³ in FT6, 150 mm/s, 50.96 J/mm ³ in FT2, and 143 mm/s, 36.04 J/mm ³ in FT7.
In the figure, FT6 is a single crystal with no black solid line indicating large-angle grain boundaries. In addition, in the crystal orientation distribution map with (001), (101), and (111) vertices, it shows that there is one crystal grain in which the (001) orientation is dominant.
Although the (001) orientation is dominant in FT7, many large points and small points are seen in the crystal orientation distribution map with vertices (001), (101), and (111), indicating a polycrystalline state. FT2 is the same as FT2 in FIG. 6A.

8A to 8D are explanatory diagrams of the crystal orientation distribution of the entire pure Ni sample shaped by a flat-top type laser showing one example of the present invention, and FT2, 4, and 5 are comparative examples. The hatch width is 100 μm and the energy density is 50.96 J/mm ³ in FT2, 140 μm and 33.98 J/mm ³ in FT4, and 200 μm and 25.48 J/mm ³ in FT5.
In the crystal orientation distribution map with (001), (101), and (111) vertices, many large points and small points are seen in a wide range, indicating a polycrystalline state.

Table 2 shows laser output P (W), scanning speed v (mm/s), and hatch width h (μm) as shaping parameters of a conventional Gaussian laser.

9A to 9D are explanatory diagrams of the crystal orientation distribution of the entire pure Ni sample formed by melting and solidifying the powder bed with a Gaussian laser showing a comparative example of the present invention, and G1, 2, and 8 are comparative examples.
In the figure, unmelted black regions can be seen, and crystal grains of various orientations are present. In the crystal orientation distribution map with vertices at (001), (101), and (111), large points and small points are distributed over a wide range, indicating a polycrystalline state.

FIGS. 10A to 10F are explanatory diagrams of the shapes of molten pools in which pure Ni plate material is melted instead of metal powder particles. A cross section of the sample was analyzed by EBSD and the resulting image is shown. The boundary defined by a series of white dots inside the sample indicates the boundary between the molten pool and the non-melted pool. The area where the central depth of the molten pool and the width of the molten pool are indicated is the molten pool. Under the conditions of the single crystal alloy of FT6 melted by the flat-top type laser in FIG. Under the conditions of the unidirectionally solidified FT3 alloy melted by the flat-top type laser in FIG. In FT2, FT4, and FT5 of comparative examples, the central depth of the molten pool is 24.5 μm, the width is 386.2 μm, and the aspect ratio is 0.06. G1 melted by the Gaussian laser of the comparative example has a central depth of the molten pool of 24.5 μm, a width of 69.9 μm, and an aspect ratio of 0.35; G2 has a central depth of the molten pool of 37.0 μm, a width of 80.9 μm, and an aspect ratio of 0.46; All of G1, G2 and G8 had an aspect of 0.24 or more.

Table 3 shows the large-angle grain boundary length of each pure Ni sample measured by a flat-top laser showing an example of the present invention. The molding conditions for each pure Ni sample FT1 to FT7 are the same as in Table 1.
In the directionally solidified alloy of FT3, the large angle grain boundary length is 5 cm/mm ² . In the FT6 single crystal alloy, the large-angle grain boundary length is 0 cm/mm ² . FT1, 2, 4, 5, and 7, which are comparative examples, are polycrystalline alloys, and the large-angle grain boundary length is in the range of 1 to 5 cm/mm ² .

Table 4 shows the large-angle grain boundary length of a pure Ni sample by a conventional Gaussian laser as a comparative example. The molding conditions for each of the pure Ni samples G1 to G7 are the same as in Table 2. In conventional Gaussian lasers, as comparative examples, all of them are polycrystalline alloys, and the large-angle grain boundary length is in the range of 6 to 27 cm/mm ² .

In the above embodiment, the case where the substrate or seed crystal having the desired crystal orientation and crystal structure is not installed is shown, but the present invention is not limited to this, and the substrate or seed crystal having the desired crystal orientation and crystal structure may be installed.
In the above embodiment, the metal particles are pure nickel samples, but the present invention is not limited to this, and may be nickel-based superalloys, titanium alloys including β-type titanium alloys, or aluminum alloys.

According to the manufacturing method of the single crystal or unidirectionally solidified three-dimensional object of the present invention, since it is manufactured using a metal powder additive manufacturing apparatus, it is possible to manufacture a Ni-based single crystal superalloy model at a low cost. There is a possibility that the use of Ni-based single crystal superalloys will spread not only to aircraft but also to other applications such as automobiles.

REFERENCE SIGNS LIST 10 pure Ni sample 100 layered manufacturing device 110 laser device 112 laser 120 galvanomirror 130 control device 140 metal powder particles 200 chamber 210 layer forming chamber 220 powder supply chamber 230 molding table 250 recoater 260 metal powder layer

Claims (12)

1. A method for manufacturing a single crystal or directionally solidified three-dimensional object using a metal powder additive manufacturing apparatus,
   forming a thin layer of powder material comprising metal particles;
   selectively irradiating the thin layer with a laser beam, the metal particles contained in the powder material obtain a planar molten pool shape, and crystal growth accompanying solidification forms a monocrystalline or unidirectionally solidified model layer;
   Repeating the steps of forming the thin layer and forming the model layer in this order a plurality of times to grow the single crystal or directionally solidified model layer by stacking;
   A method for forming a single crystal or unidirectionally solidified three-dimensional object comprising:
2. The method of manufacturing a single crystal or directionally solidified three-dimensional object according to claim 1, wherein the laser beam has a uniform intensity distribution within the irradiation surface or a difference in intensity distribution within the irradiation surface within 10% of the maximum intensity.
3. The method for forming a single-crystal or directionally solidified three-dimensional object according to claim 1 or 2, wherein the spot diameter of the laser beam is 100 µm or more and 1000 µm or less.
4. The method for forming a single crystal or directionally solidified three-dimensional object according to any one of claims 1 to 3, wherein the thin layer of the powder material has a thickness of 10 µm or more and 70 µm or less.
5. The single-crystal or directionally solidified three-dimensional object modeling method according to any one of claims 1 to 4, wherein D(50) of the particle size distribution of the powder material is 10 µm or more and 110 µm or less.
6. 6. The method for forming a single-crystal or unidirectionally solidified three-dimensional object according to any one of claims 1 to 5, wherein the planar molten pool shape has a depth of 10 µm or more and 100 µm or less and a width of 80 µm or more and 400 µm or less.
7. The method for forming a single-crystal or unidirectionally solidified three-dimensional object according to any one of claims 1 to 6, wherein the planar molten pool has an aspect ratio (depth at the center of the molten pool/width of the molten pool) of 0.01 or more and 0.23 or less.
8. The method for forming a single crystal or directionally solidified three-dimensional object according to any one of claims 1 to 7, wherein a base material or a seed crystal having a desired crystal orientation and crystal structure is provided as the base material on which the thin layer of the powder material containing the metal particles is formed.
9. The method for forming a single crystal or directionally solidified three-dimensional object according to any one of claims 1 to 7, wherein a substrate having a desired crystal orientation and crystal structure or a seed crystal is not installed as a substrate on which the thin layer of the powder material containing the metal particles is formed.
10. The method for forming a single crystal or directionally solidified three-dimensional object according to any one of claims 1 to 9, wherein an electron beam is used instead of the laser beam.
11. The method for forming a single-crystal or directionally-solidified three-dimensional object according to any one of claims 1 to 10, wherein the single-crystal or directionally-solidified three-dimensional object is a turbine stator blade or a turbine rotor blade.
12. The method for forming a single crystal or directionally solidified three-dimensional object according to any one of claims 1 to 11, wherein the metal particles are made of a metal material having a composition used in any one of nickel, a nickel-based superalloy, a titanium alloy containing β-type titanium, or an aluminum alloy.

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