Metal powder for directive energy deposition method, and method for manufacturing the same

Abstract

To provide a method for manufacturing composite metal powder for a directive energy accumulation method and composite metal powder for a directive energy deposition method, which enable high strength / high moldability.SOLUTION: Fine particles becoming a coagulated heterogeneous nucleus site are added into metal powder used in a directive energy deposition method, the number of nucleation sites in a molten pool formed by directive energy increases, and a molding structure is equiaxed crystallized, refined and homogenized. Simultaneously, laser absorption capability is enhanced by laser irregular reflection, due to fine particles obtained by depositing hetero solidification nucleus particles having laser absorption capability higher than that of metal, to the metal surface, melting capability by a laser beam of the metal powder is enhanced, and high strength and high moldability can be achieved at the same time. In addition, flowability of metal powder is enhanced by fine particles deposited to the surface of the metal powder, and high moldability and high strength can be achieved through stable meal powder supply. The heterogeneous nuclear particles have a melting point higher than that of base material metal, and have a parameter M represented by a predetermined expression of 12×10-3 or less.SELECTED DRAWING: Figure 14

Description

Technical Field

[0001] The present invention relates to composite metal powders for a directed energy deposition method capable of high strength and high formability, and methods for manufacturing the same.

Background Art

[0002] Metal additive manufacturing (metal laminated manufacturing), also called 3D printing, has attracted attention in recent years as a processing method capable of producing complex shapes that could not be manufactured by subtractive manufacturing such as machining and electrical discharge machining, or deformation processing such as plastic processing and casting. Fundamental research and practical application research are being actively conducted. Additive manufacturing can be classified into seven shaping methods: material extrusion method, vat photopolymerization method, sheet lamination method, binder jetting method, material jetting method, powder bed fusion method, and directed energy deposition method. Among these, the powder bed fusion method and the directed energy deposition method can directly shape metal products.

[0003] Figure 1 is a schematic diagram of the powder bed fusion method using a laser beam as a heat source. Currently, it is the most common metal laminated manufacturing method, and a fiber laser with an output of about 400 W to 1 kW is often used as the laser. The laser beam 1 is scanned by a galvanometer scanner 2 to melt and solidify the area to be shaped.

[0004] After one layer of shaping is completed, the shaping table 3 is lowered, the powder supply tank 4 is raised, and the powder is supplied by a recoater 5. The particle size of the metal powder used for shaping is about 10 to 40 μm, and finer powder is used compared to the powder bed fusion method using an electron beam as a heat source. Reducing the size of the metal powder used can reduce the layer thickness and the surface roughness of the shaped body.

[0005] In contrast, in the directed energy deposition method, while supplying a metal material, a concentrated heat source by directed energy is irradiated onto a base material, and the metal material is directly melted and deposited into a minute molten pool formed in the base material, and the metal is laminated by its solidification. Here, the molten pool is also called a melt pool, which refers to a liquid pool of molten metal formed on the base material side directly under the heat source during welding, and the minute molten region formed on the base material during metal additive manufacturing or shaping is also called this. The molten droplets transferred from the molten base material and the metal material to be deposited are mixed to form molten metal.

[0006] The shaping material is supplied by feeding metal powder or wire to the part where addition is desired. At the same time, by irradiating a high-energy beam, both the base material and the added metal material are melted, and the materials are deposited. If the material supply device and the beam source are relatively moved with respect to the base material, and the deposition position is continuously moved along the shape of the shaped object, a three-dimensional shaped object can be obtained.

[0007] In the directed energy deposition method, there are several techniques depending on the combination of the heat source and the material form. The main types used for the heat source are mainly three types: laser, electron beam, and arc, and the material forms used are powder and wire. A schematic diagram of the directed energy deposition method when the heat source is a laser and the material form is powder is shown in FIG. 2. The heat source laser 6 is irradiated onto the base material 7 to form a molten pool (melt pool) in the base material. The metal powder is injected into the molten pool by a material supply device 9 capable of supplying the metal powder 8, and the molten metal is deposited on the base material. By relatively moving the material supply device and the beam source with respect to the shaping platform 10 on which the base material is installed, a three-dimensional part is shaped. In this layer-by-layer shaping by the directed energy deposition method, it is only necessary to supply the material to the necessary parts, the layer thickness is large, the shaping speed is also fast, and it is suitable for shaping large members.

[0008] In the powder bed fusion method and the directed energy deposition method, a product is obtained by melting and solidifying metal in a minute region. In these processes, since melting and solidification occur under a large temperature gradient, columnar crystals that grow in the shaping direction are formed by epitaxial growth. Here, epitaxial growth refers to a growth mode in which when crystal growth occurs on a crystal serving as a base material, the crystals are arranged aligned with the crystal plane of the underlying base material. Fig. 3 shows a schematic diagram of the formation of a solidification structure under a temperature gradient. When epitaxial growth occurs in the solidification phase 11 in the solid phase 12 and the liquid phase 13, the crystal phase grows while inheriting the crystal orientation of the solid phase. As a result, elongated columnar crystals having a texture in the solidification progress direction are shown. Here, the texture refers to a state in which crystal grains constituting the material are preferentially arranged in a specific direction. Furthermore, in metal additive manufacturing, since each layer is repeatedly exposed to high temperatures when being shaped, growth of solid crystals is caused. As a result, most of the structures obtained by metal additive manufacturing exhibit columnar crystals and a texture. This becomes a hindrance when used as a structural member (Patent Document 1).

[0009] Also, when a laser is used as a heat source for directed energy, the laser absorption ability of the metal also becomes a major problem. Fig. 4 shows the wavelength dependence of the laser absorption ability of steel 14, iron 15, molybdenum 16, copper 17, gold 18, silver 19, and aluminum 20 (Non-Patent Document 1). Here, the wavelengths of the carbon dioxide laser 21 and the fiber laser / YAG laser 22 are indicated by dotted lines. It can be seen that all metals show a strong wavelength dependence in laser absorption ability, and most of them are reflected by lasers with longer wavelengths. Therefore, even when trying to melt the metal by irradiating it with a laser, there is a problem that most of it is reflected and the energy available for melting is very small.

[0010] Metal powders used in metal additive processing require properties such as powder shape, internal condition, fluidity, homogeneity, and low oxygen content in order to increase the precision and density of the molded object and to mold it stably. Gas atomization, centrifugal atomization (disk atomization), and plasma atomization are mainly used to manufacture metal powders used in metal additive processing, but in recent years, the use of inexpensive water atomization and high-quality metal powders produced by the plasma rotating electrode method have also been developed.

[0011] The principle of the gas atomization method is shown in Figure 5. In this method, molten metal or alloy 23 is made to flow out of an orifice 25 at the bottom of a melting crucible 24 to form a thin stream, and high-velocity gas 26 is blown onto the molten metal to disperse it, rapidly cooling and solidifying it to produce metal powder 27. The cooling rate is about 10 3 The cooling rate is about 10 °C / sec, and the metal powder obtained is spherical due to surface tension, and has high fluidity. It is also possible to produce clean metal powder with low oxygen content. However, tiny particles called satellites adhere to the powder surface, which reduces fluidity. Powdering can also be done with a water jet; this method is called water atomization, and the cooling rate is 10 4 ~10 5 The process is fast, at ℃ / second. Solidification ends at the moment of atomization, so the powder becomes irregularly shaped. By adjusting the water pressure and spray angle, it is possible to control the powder particle size and shape.

[0012] As shown in Fig. 6, the method of continuously dropping molten metal 28 onto a rapidly rotating disk 29, and scattering the resulting molten film 30 into droplets by centrifugal force to obtain spherical metal powder 31, is called the centrifugal atomization method (disk atomization method). With this method, spherical particles with a uniform particle size and no voids can be produced by controlling the molten metal temperature and disk rotation speed. As the powder is pulverized by centrifugal force, the powder is close to a perfect sphere and there is almost no adhesion of satellites.

[0013] However, these metal powder manufacturing technologies were developed mainly with powder bed fusion in mind, and it is difficult to say that they have the performance required for directed energy deposition. For example, in order to obtain a powder bed in powder bed fusion, the fluidity of the metal powder in recoating is important, but the fluidity required at this time is different from the fluidity required in directed energy deposition, in which metal powder sprayed from an orifice is used for modeling. In powder bed fusion, process control is performed by changing the scanning speed of the heat source beam, which is one of the modeling conditions, but if the scanning speed is changed in directed energy deposition, the amount of metal powder sprayed at that position also changes, which affects the shape of the model. Therefore, in directed energy deposition, it is essential to control the structure of the material without relying on process control, and metal powder that can achieve this is required.

[0014] Furthermore, as mentioned above, in normal metal additive processing, columnar crystals elongated in the stacking direction are formed by epitaxial growth, and exhibit texture. Here, the preferred growth direction of the metal is determined by the crystal structure of the solidified phase. In the case of metals with bcc and fcc crystal structures, the rate-limiting factor for the formation of solid phase crystals is the growth of the dense faces {110} and {111}, respectively, and therefore the rate-limiting factor for the formation of solid phase crystals is the growth of the dense faces {110} and {111}, respectively, surrounded by them. <100> As a result, in metal additive processing, the lamination direction is also <100> This results in an anisotropic texture in the mechanical properties, etc. (Non-Patent Document 2). [Prior art documents] [Non-patent literature]

[0015] [Non-Patent Document 1] E. Schubert et al.: LIA Proc.ICALEO'98 Vol. 85 (1998) G111 [Non-Patent Document 2] Koji Hagiwara et al.: Materia Vol. 57 No. 4 (2018) 145 [Non-Patent Document 3] Masaharu Kato: Iron and Steel, Vol. 78, No. 2 (1992), 209 [Non-Patent Document 4] X. Lu et al.: Addit.Manuf. Vol. 26 (2019), 166 [Non-Patent Document 5] Y. Watanabe et al.: Mater. Trans. Vol. 64, No. 6 (2023), 1083 [Patent Document 1] Yoshimi Watanabe, Sanshu Chiba, Hisashi Sato, Masashi Sato, Hiroyuki Kanno, Zen Nakano, Naoko Sato: Application filed November 2017, Patent No. 6997984 Summary of the Invention [Problem to be solved by the invention]

[0016] The present invention relates to a technology for metal additive processing by directed energy deposition using metal powder as a material. By adding fine particles that become heterogeneous nucleation sites for solidification to the metal powder used in the directed energy deposition method, the number of nucleation sites in the molten pool formed by the directed energy increases, making it possible to achieve equiaxed crystallization, fineness, and homogenization of the molded structure. At the same time, heterogeneous solidification nucleation particles with higher laser absorption than metal are attached to the metal surface to increase the laser absorption ability, and the fine particles attached to the metal powder surface cause diffuse reflection of the laser to increase the laser absorption ability, thereby increasing the melting ability of the metal powder by laser, thereby providing a metal powder suitable for directed energy deposition that can simultaneously achieve high strength and high formability. In addition, a composite metal powder suitable for directed energy deposition that can achieve high formability and high strength through stable metal powder supply by attaching fine particles to the metal powder surface to increase the fluidity of the metal powder is provided. [Means for solving the problem]

[0017] The metal powder according to one embodiment of the present invention is used for metal additive processing. The metal powder according to the present invention includes a metal powder and a heterogeneous core particle. The heterogeneous core particle has a melting point higher than that of the base alloy, and the parameter M (Non-Patent Document 3) expressed by the formula (1) is 12×10 -3 The following is the result.

number

Equation

Equation

[0018] In the metal powder of the present invention, the volume ratio of the heterogeneous nuclei particles to the metal powder may be 20% or less.

[0019] Also, the metal powder may be a titanium alloy, an aluminum alloy, a steel material including stainless steel, a copper alloy, a nickel alloy, or a single metal thereof.

[0020] Also, the heterogeneous nuclei particles may be one or more compound particles selected from TiC, TiB 2 , Al 3 Ti, and a third element Me added to form a crystal structure of L1 2 phase (Al 1-x Me x ) 3 Ti, SrО.

[0021] Also, the heterogeneous nuclei particles may particularly preferably be TiC particles.

[0022] Another aspect of the present invention, a method for producing a composite metal powder containing heterogeneous core particles, is a technique of attaching heterogeneous core particles to the surface of a metal powder by mechanical mixing of a mixed powder composed of the metal powder and the heterogeneous core particles.

Advantages of the Invention

[0023] If metal additive processing is performed by the directed energy deposition method using the metal powder of the present invention, stable material injection can be ensured with the improvement of fluidity, and it becomes possible to melt the metal powder even with a small laser output with the improvement of the laser absorption ability. Since solidification occurs due to the heterogeneous nuclei, equiaxed crystallization, refinement, and homogenization of crystal grains can be achieved, and the strength of the shaped material can be increased. Further, by using this metal powder, it becomes possible to control the structure while keeping the process parameters in shaping fixed, and a shaped material with equiaxed crystallization, refinement, and homogenization of crystal grains can be obtained. Even in products with complex shapes that are difficult to control by process parameters, it becomes possible to manufacture high-strength shaped bodies.

Brief Description of the Drawings

[0024]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Embodiments for Carrying Out the Invention

[0025] Hereinafter, embodiments of the present invention will be described. The metal powder of the present invention can be applied, for example, to titanium and titanium alloys, aluminum and aluminum alloys, steel materials including stainless steel, copper and copper alloys, nickel and nickel alloys, etc., and heterogeneous nucleation particles adhere to the powder surfaces of these alloys. The heterogeneous nucleation particles have a melting point higher than that of the base alloy, and the parameter M represented by the aforementioned formula (1) is 12×10 -3 as follows.

[0026] In the present invention, based on the heterogeneous nucleation theory, a composite metal powder suitable for the directed energy deposition method is provided, in which heterogeneous nucleation particles having a melting point higher than that of the material alloy of the metal powder used and having good atomic arrangement consistency with respect to the phase that becomes the primary crystal of the metal powder are premixed.

[0027] When this metal powder is used as a material for the directed energy deposition method, the fluidity is enhanced due to the presence of the added heterogeneous nucleation particles, enabling a stable supply of the material. Further, by dispersing fine heterogeneous nucleation particles with a high laser absorption ability on the surface as compared with the metal powder, the laser absorption ability is enhanced and at the same time the laser diffuse reflection is promoted, and as a result, it becomes possible to melt the metal powder with a small laser output. In addition, the heterogeneous nucleation particles supplied into the melt pool will act as nuclei for crystal growth. When the wettability with respect to the molten alloy is good, by optimizing the size and distribution of the heterogeneous nucleation particles, uniform solidification in various locations is promoted as compared with the case of forming using conventional metal powder under the same conditions. Thereby, it is possible to manufacture a shaped material with few internal defects and suppress the development of columnar crystals extending in the forming direction and a non-uniform internal structure.

[0028] As an index for selecting and evaluating heterogeneous nucleation particles that exhibit the effects of the present invention described above, there is a parameter M that is approximately proportional to the elastic strain. The parameter M is calculated by the following formula (1), and the smaller this value, the smaller the energy required for nucleation, and thus it is regarded as acting as an effective heterogeneous nucleus.

Equation

[0029] Also, ε x and ε y are calculated by the following formulas (2) and (3).

Equation

Equation

[0030] Parameter M can be considered for all crystal orientation relationships, not just low-index planes and orientations. Also, since parameter M is approximately proportional to the elastic strain energy due to the misfit strain introduced at the heterointerface, it is a parameter with physical meaning.

[0031] In the present invention, based on two types of elements, namely the melting point and the atomic arrangement matching evaluation parameter represented by parameter M, a heterogeneous nucleation particle that serves as an effective heterogeneous solidification nucleus for the base metal is selected, and a composite metal powder for the directed energy deposition method in which this is mixed with metal powder is provided. At this time, a substance having a high melting point with respect to the primary crystal of the powder alloy and having a parameter M at the solidification temperature of 12×10 -3 as follows is selected as the heterogeneous nucleus.

[0032] Although there are innumerable possible crystal orientation relationships at the interface between the solidifying metal / alloy and the heterogeneous nucleus, in the present invention, for example, among these, low-index planes are considered, and the one with the minimum value can be used as the parameter M of that substance with respect to the solidifying metal / solidifying alloy.

[0033] In the composite metal powder, the volume fraction of the heterogeneous nucleation particles with respect to the base alloy is preferably 20% or less, and more preferably 10% or less. The manufacturing process of the metal powder may be in any form. For example, it may be the gas atomization method or the centrifugal atomization method (disk atomization method). Therefore, as long as it is a fluid metal powder, the manufacturing method of the metal powder may be in any form.

[0034] As the heterogeneous nucleation particles, those having a melting point higher than that of the metal powder and having a parameter M of 12×10 -3The following substances can be used. Such substances include, for example, TiC and TiB for aluminum and aluminum alloys. 2 , Al 3 Ti and a third element Me are added to transform the crystal structure into L1 2 phase (Al 1-x Me x ) 3 One or more kinds of compound particles selected from Ti can be used. Among these, TiC particles are preferable because the parameter M is small and the compatibility with the matrix metal is high.

[0035] As described above, the heterogeneous nucleation particles can be composed of one or more substances. Further, in order to sufficiently exhibit the effects of the heterogeneous nucleation particles, it is preferable that the heterogeneous nucleation particles are manufactured so as to be uniformly distributed on the surface of the metal powder in the process of manufacturing the composite metal powder.

[0036] The shaping method using the above-described composite metal powder can be used not only for the ordinary directional energy deposition method but also for the multi-beam type directional energy deposition method having a plurality of lasers or electron beams. Further, any method can be used as long as the material is a powdery metal and the shaping method involves additive processing with melting and solidification on the base material. Thus, any method can be used as long as it is a method of melting, solidifying, and adding the powder regardless of the presence or absence of the formation of a melt pool.

[0037] (Example 1) Hereinafter, the present invention will be described by way of examples. Here, a Ti-6Al-4V alloy is used as the metal powder. The selected Ti-6Al-4V alloy for the metal powder is a titanium alloy that combines the characteristics of the α-phase with a hexagonal close-packed (hcp) structure and the β-phase with a body-centered cubic (bcc) structure in a well-balanced manner. It has excellent mechanical properties, corrosion resistance, and biocompatibility, and due to its strength, it is widely used in the aircraft and aerospace industries and is also widely used as a medical metal. The reason for selecting the Ti-6Al-4V alloy is that it is a titanium alloy that is widely used, accounting for about 70% of titanium alloys, and at the same time, it is an alloy known as a difficult-to-machine material. As long as it is within the scope of the present invention, there is no problem using any alloy.

[0038] Using the integrated thermodynamics calculation software Thermo-Calc and the TCFE7 database, the temperature dependence of the phase composition of the Ti-6Al-4V alloy is shown in Fig. 7. As shown in the figure, in the solidification process, at about 1650 °C, first, the β-phase 33 crystallizes as the primary crystal from the liquid phase 32. After that, below about 950 °C, a phase transformation occurs, and the α-phase 34 begins to precipitate in the β-phase, and finally, at room temperature, a two-phase state of the α-phase and the remaining β-phase coexists.

[0039] Therefore, when the Ti-6Al-4V alloy is selected as the metal powder, substances with a melting point higher than 1650 °C, which is the melting point of the Ti-6Al-4V alloy, and high atomic arrangement consistency with the primary crystal β-phase of the Ti-6Al-4V alloy at 1650 °C can be selected as the heterogeneous nucleating substances.

[0040] Next, the heterogeneous nucleating particles constituting the composite metal powder are selected. Table 1 shows the crystal structures, melting points, lattice parameters at room temperature, and values of parameter M for Ti-6Al-4V at room temperature for several compounds (TiFe, TiNi, TiCo, TiZn, TiC, TiN, and TiB).

[0041]

Table 1

[0042] Here, an example will be given to explain the evaluation by parameter M. For example, when considering TiZn having a CsCl structure as a heterogeneous nucleus with respect to the primary β-phase of Ti-6Al-4V having a bcc structure, considering that the interface between the primary β-phase of Ti-6Al-4V and TiZn during solidification is parallel to the respective (001) planes, and the

[0100] direction of the β-phase is parallel to the

[0100] direction of TiC, from the above equations (1), (2) and (3), ε x and ε y both become 2.78×10 -2 . As a result, the value of parameter M at room temperature becomes 2.1×10 -3 .

[0043] When considering TiC having an NaCl structure as a heterogeneous nucleus, in the crystallographic orientation relationship where the interface between the primary β-phase of Ti-6Al-4V and TiC during solidification is parallel to the respective (001) planes, and the

[0100] direction of the β-phase is parallel to the

[0100] direction of TiC, the value of parameter M at room temperature is 303×10 -3 . However, in the crystal orientation relationship where the interface between the primary β-phase of Ti-6Al-4V and TiC is parallel to the respective (001) planes, and the

[0110] direction of the β-phase is parallel to the

[0100] direction of TiC, the value of parameter M at room temperature is 8.3×10 -3 , and it is considered that solidification occurs in this crystallographic orientation relationship with a small parameter M.

[0044] From Table 1, the value of parameter M of TiZn with respect to Ti-6Al-4V is 2.1×10 -3 , and it is considered to effectively act as a heterogeneous solidification nucleus. However, the melting point of TiZn is lower than that of Ti-6Al-4V, and there is a concern that it will decompose early during the additive manufacturing process. In contrast, the melting point of TiC is 3067 °C, and it is expected that it will not decompose even by heating by laser irradiation during the additive manufacturing process. Furthermore, the value of parameter M of TiC is also relatively small at 8.3×10 -3 , and it is expected to act as a heterogeneous solidification nucleus with respect to Ti-6Al-4V.

[0045] The value of parameter M at room temperature for the primary β phase of TiC in Ti-6Al-4V is 8.3×10 -3 However, the temperature dependence of the thermal expansion of Ti-6Al-4V is 8.78×10 ―6 at 20°C, 10×10 ―6 at 205°C, 11.2×10 ―6 at 500°C, 12.3×10 ―6 at 995°C, 12.4×10 ―6 at 1100°C, 12.42×10 ―6 at 1600°C, 12.5×10 ―6 (Non-Patent Document 4). Since the linear expansion coefficient of TiC is 7.76×10 -6 , the lattice constant at 660°C can be obtained, and thus the value of parameter M at 660°C, 7.89×10 -3 is obtained.

[0046] Using these values, the temperature dependence of the lattice parameters of the TiC phase 35 and the β phase 36 of Ti-6Al-4V, and the values of parameter M 37 at each temperature obtained therefrom are shown in Fig. 8. As shown in this figure, TiC having a NaCl crystal structure has a higher melting point than Ti-6Al-4V, and the parameter M at 1650°C is 12×10 -3 or less, so it is considered to effectively act as a heterogeneous nucleus. Therefore, TiC was selected as the heterogeneous nucleating substance in this example.

[0047] Next, a composite metal powder is prepared. First, Ti-6Al-4V powder, which is a metal powder, and TiC particles selected as heterogeneous nucleating particles are prepared. As the Ti-6Al-4V powder, which is a metal powder, the one produced by gas atomization was selected. The particle size is 45 μm or less, and it is a spherical powder close to a true sphere. As the TiC particles, those with a particle size of 2 to 5 μm were selected. The TiC particles are polygonal particles.

[0048] Then, mechanical mixing was carried out for 60 minutes using a turbular shaker mixer powder mixing device to produce a composite metal powder in which TiC particles were dispersed on the surface of Ti-6Al-4V powder. While general mixers are designed with a combination of one-axis two-dimensional motion or multi-axis three-dimensional motion, the turbular shaker mixer performs shaking by accelerating and decelerating that occur alternately with three-dimensional motion, and has the characteristic that even those with a large specific gravity difference can be uniformly mixed. The composite metal powder was produced so that TiC, which is a heterogeneous nucleating particle, has a volume fraction of 1. Figure 9 shows a scanning electron microscope photograph of the produced composite metal powder. It can be seen that TiC particles 39 are uniformly dispersed on the surface of Ti-6Al-4V powder 38.

[0049] Using this composite metal powder to which TiC, which is this heterogeneous nucleating particle, was added and Ti-6Al-4V powder to which TiC was not added, a metal additive manufacturing apparatus by the directed energy deposition method manufactured by Mitsubishi Heavy Industries Machine Tool Co., Ltd. (currently Nidec Machine Tool Co., Ltd.) shown in Figure 10 was used to conduct a laminated manufacturing experiment. This apparatus has the characteristic that various metal materials can be laminated at high speed by adopting a method of continuously supplying metal powder to the laser melting point at a pinpoint by nozzle. A laser beam is in the center of the double nozzle, and metal powder passes around it and melting action (solidifying immediately afterwards) occurs at the focal point, and lamination proceeds by nozzle scanning (movement). It enables high-speed manufacturing more than 10 times faster than the normal powder bed fusion method, and can also suppress waste of metal powder. Additional manufacturing on the surface of parts such as for repair purposes, multi-layer manufacturing of different metal powders, and manufacturing of large parts are possible. The laser is equipped with a 2kW fiber laser.

[0050] The shaping conditions were as follows: the rotational speed of the disk of the powder feeder was 0.5 rpm, the flow rate of the carrier gas was 4 liters per minute, the flow rate of the outer shield gas was 20 liters per minute, and the flow rate of the inner shield gas was 15 liters per minute. A laser with a spot diameter of 0.2 mm was used, and the laser output was varied to 200 W, 400 W, 600 W, and 800 W, and the scanning speed was varied to 800 mm per minute, 1200 mm per minute, and 1600 mm per minute for shaping. However, for the purpose of investigating the relationship between the laser output and the density of the shaped body, shaping with a laser output of up to 1000 W was carried out only for shaping using Ti-6Al-4V powder without TiC added under the condition of a scanning speed of 3000 mm per minute. The base plate is a Ti-6Al-4V plate material and has dimensions of 70 mm × 70 mm × 5.4 mm. The scanning area was 10 mm × 10 mm, and lamination of 10 layers was carried out under the conditions of a hatch pitch of 1 mm and a Z pitch of 0.5 mm. Here, the shaped bodies were shaped with a distance of 5 mm between each shaped body. Fig. 11 shows the dimensions of the shaped body, the coordinate axes, and the laser scanning direction 40.

[0051] Fig. 12(a) shows an external photograph of a shaped body using Ti-6Al-4V powder without TiC added, and Fig. 12(b) shows an external photograph of a shaped body using Ti-6Al-4V powder with 1 volume fraction of TiC added. Fig. 12(c) shows the laser output and the scanning speed when shaping these. As shown in the figure, it can be seen that shaping is possible for any powder and any condition.

[0052] Fig. 13 shows the relationship between the laser output and the density of the shaped body measured by the Archimedes method for a shaped body using Ti-6Al-4V powder without TiC added. However, it shows shaping 41 under the condition of a scanning speed of 800 mm per minute, shaping 42 under the condition of 1200 mm per minute, shaping 43 under the condition of 1600 mm per minute, and shaping 44 under the condition of 3000 mm per minute. It can be seen that as the laser output increases, the density of the shaped body increases. However, it can be seen that when the laser output is 800 W or more, it shows a constant value, and the density of the shaped body does not increase even if more energy is introduced.

[0053] Next, the influence of TiC addition on the density of the formed body using Ti-6Al-4V powder is shown in Fig. 14. The density was measured by the Archimedes method. On the left side of the data formed under each condition is the formed body 45 using Ti-6Al-4V powder without TiC addition, and on the right side of the data is the result of the formed body 46 using Ti-6Al-4V powder with 1 volume fraction of TiC added. It can be seen that the density of the formed body increases as the input energy increases. In the samples formed under any conditions, the density of the formed body is formed by the addition of TiC heterogeneous nucleation particles. Also in the directed energy deposition method, it was found that the formability is improved by the addition of heterogeneous nucleation particles.

[0054] To confirm this phenomenon, the defect distribution of the formed body was measured using an X-ray computed tomography device (X-ray CT). Here, X-ray CT is a kind of method for non-destructively evaluating materials by constructing a three-dimensional image by transmitting X-rays while rotating the stage 360° and collecting it with a detector.

[0055] Fig. 15(a) shows the X-ray CT image of the sample formed without adding TiC to Ti-6Al-4V powder under the conditions of a laser output of 200 W and a scanning speed of 800 mm per minute, and Fig. 15(b) shows the X-ray CT image of the sample formed by adding 1 volume fraction of TiC to Ti-6Al-4V powder under the conditions of a laser output of 200 W and a scanning speed of 800 mm per minute. Both figures are the results observed from the y-z plane. In addition, the result of the sample formed without adding TiC to Ti-6Al-4V powder under the conditions of a laser output of 200 W and a scanning speed of 800 mm per minute observed from the x-z plane is shown in Fig. 15(a'), and the result of the sample formed by adding 1 volume fraction of TiC to Ti-6Al-4V powder under the conditions of a laser output of 200 W and a scanning speed of 800 mm per minute observed from the x-z plane is shown in Fig. 15(b'). From the figure, it was found that the defects are formed along the y direction, which is the laser scanning direction. Furthermore, it can be seen that the internal defects are reduced in the TiC additive compared to the non-additive. This result shows that a denser formed body can be obtained by performing additive processing by the directed energy deposition method using the composite metal powder of the present invention.

[0056] The influence of TiC addition on the microstructure of a formed body using Ti-6Al-4V powder is shown in Fig. 16. The microstructure was formed under the conditions of a laser power of 200 W and a scanning speed of 1600 mm per minute. Fig. 16(a) shows the microstructure of a sample formed without adding TiC to the Ti-6Al-4V powder, and Fig. 16(b) shows the microstructure of a sample formed by adding 1 volume fraction of TiC to the Ti-6Al-4V powder. These were observed by an optical microscope from the x-z plane. Discontinuous beads 47 and unmelted metal powder 48 between them are observed. The addition of TiC heterogeneous nucleation particles reduces the amount of unmelted powder, and as a result, the bead spacing in the forming direction is narrowed. At the same time, it can be seen that the width of each bead has also become longer. As a result, the amount of internal defects has decreased, and an improvement in the density of the formed body has been achieved. Thus, the internal defects generated in the formed body are reduced by the addition of heterogeneous nucleation particles, and it has been discovered that the formability is improved by the addition of heterogeneous nucleation particles even in the directed energy deposition method.

[0057] (Example 2) Here, an example using pure aluminum as the metal powder and TiC having an NaCl structure as the heterogeneous nucleus is shown. Considering that the lattice constant of the α-Al phase is 0.40496 nm, the lattice constant of TiC is 0.4329 nm, the interface between the α-Al phase and TiC during solidification is parallel to their respective (100) planes, and the

[0011] direction of the α-Al phase and the

[0011] direction of TiC are parallel, the value of parameter M at room temperature is 12.5×10 -3 becomes. Furthermore, the temperature dependence of the aluminum lattice is [Number] is obtained by, and since the linear expansion coefficient of TiC is 7.76×10 -6 , the lattice constant at 660 °C can be obtained, and thereby, the value of parameter M at 660 °C, 7.89×10 -3 is obtained (Non-Patent Document 5).

[0058] TiC with a crystal structure having an NaCl structure has a melting point higher than that of aluminum, and the parameter M at 660 °C is 12×10 -3 Since it shows the following, it is considered to effectively act as a heterogeneous nucleus. Therefore, in this example, TiC with a particle size of 2 to 5 μm was selected as the heterogeneous nucleus material. Also, as the aluminum powder, a powder with a particle size of 63 μm or less produced by disk atomization was selected. Then, a composite metal powder was produced by mixing for 60 minutes using a turbular shaker mixer powder mixing device. When the angle of repose of the produced composite metal powder and the aluminum powder produced by disk atomization was measured, they were 39.5 degrees and 48.5 degrees, respectively. Here, the angle of repose is the maximum inclination angle at which powder can be piled up without collapsing, and in the case of a powder with high fluidity, the angle of repose becomes smaller. Therefore, by attaching minute heterogeneous nucleus particles to the surface of the metal powder, improvement in fluidity was achieved.

[0059] Using a metal additive manufacturing apparatus by the directed energy deposition method manufactured by Muraya Machinery Works, a laminated manufacturing experiment was conducted. This apparatus is also called a multi-beam type laser coating apparatus. The feature of the apparatus is that powder can be supplied from the center of the manufacturing nozzle, and six far-infrared lasers (wavelength: 975 nm) with an output of up to 50 W can be irradiated from around it. As a result, the appearance of a melt pool generated during manufacturing by a general directed energy deposition method can be suppressed as much as possible, and instead, manufacturing can be performed by hitting the formed body with metal powder in a remelting state.

[0060] Using this apparatus, shaping was performed under the conditions of a laser output of 270 W, two drawing numbers, two lamination numbers, a bead length of 15 mm, a lamination pitch of 0.20 mm, and a feed pitch of 0.20 mm. Figure 17(a) shows the structure of a sample shaped without adding TiC to pure aluminum powder, and Figure 17(b) shows the structure of a sample shaped by adding 0.3 volume fraction of TiC to pure aluminum powder. It can be seen that a pure aluminum shaped body 50 is continuously formed on a pure aluminum base plate 49. Also, as can be seen from the figure, continuous shaping without unevenness became possible by adding TiC. Thus, it has been discovered that the addition of heterogeneous nucleation particles in metal addition by the directed energy deposition method is effective for different material systems even when using different types of directed energy deposition apparatuses.

[0061] Also, in the above-described embodiments, TiC particles were used as the heterogeneous nucleation particles, but it is considered that the same results can be obtained if particles with a parameter M of 12×10 -3 or less are used. Further, although Ti-6Al-4V alloy and pure aluminum were used as the metal powders, for example, even when other titanium alloys or aluminum alloys are used, the same heterogeneous nucleation particles can be used and the same results are considered to be obtained. Also, in addition to titanium and titanium alloys, and aluminum and aluminum alloys, steel materials including stainless steel, copper and copper alloys, nickel and nickel alloys, etc. can also be used as the metal powders.

[0062] The present invention is not limited to the above-described embodiments (examples) at all, and it goes without saying that the present invention can be implemented in various modes without departing from the scope of the present invention. For example, the function possessed by one component in the above-described embodiment may be distributed as a plurality of components, or the functions possessed by a plurality of components may be integrated into one component. Also, a part of the configuration of the above-described embodiment may be omitted. Further, at least a part of the configuration of the above-described embodiment may be added to, replaced with, etc. the configuration of other above-described embodiments. Note that all modes included in the technical idea specified from the language described in the claims are embodiments of the present invention.

Explanation of Reference Numerals

[0063] 1... Laser beam, 2... Galvanometer scanner, 3... Forming table, 4... Powder supply tank, 5... Recoater, 6... Heat source laser, 7... Substrate, 8... Metal powder, 9... Material supply device, 10... Forming platform, 11... Solidification phase, 12... Solid phase, 13... Liquid phase, 14... Steel, 15... Iron, 16... Molybdenum, 17... Copper, 18... Gold, 19... Silver, 20... Aluminum, 21... Wavelength of carbon dioxide laser, 22... Wavelength of fiber laser / YAG laser, 23... Molten metal, 24... Melting crucible, 25... Orifice, 26... High-speed gas, 27... Metal powder, 28... Molten metal, 29... High-speed rotating disk, 30... Molten film, 31... Spherical metal powder, 32... Liquid phase, 33... β phase, 34... α phase, 35... Lattice number of TiC phase, 36... Lattice number of β phase of Ti-6Al-4V, 37... Value of parameter M, 38... Ti-6Al-4V powder, 39... TiC particles, 40... Laser scanning direction, 41... Scanning speed of 800 mm per minute, 42... Scanning speed of 1200 mm per minute, 43... Scanning speed of 1600 mm per minute, 44... Scanning speed of 3000 mm per minute, 45... Formed body using Ti-6Al-4V powder without added TiC, 46... Formed body using Ti-6Al-4V powder with 1 volume fraction of added TiC, 47... Bead, 48... Unmelted Ti-6Al-4V powder, 49... Pure aluminum base plate, 50... Pure aluminum formed body

Claims

1. A composite metal powder, wherein at least one or more heterogeneous nucleating particles are attached to the surface of the metal powder, and the metal powder is spherical.

2. The composite metal powder according to Claim 1, wherein the metal powder is spherical particles produced by a gas atomization method or a disk atomization method.

3. The composite metal powder according to Claim 2, wherein the spherical particles are titanium and titanium alloys, aluminum and aluminum alloys, steel materials including stainless steel, copper and copper alloys, nickel and nickel alloys produced by a gas atomization method or a disk atomization method.

4. The composite metal powder according to Claim 3, wherein the composite metal powder is used for additive processing by a directed energy deposition method.

5. Composite metal powder for a directed energy deposition method, characterized in that at least one or more heterogeneous nucleation particles are attached to the surface of the metal powder, and the metal powder is spherical particles produced by a gas atomization method or a disk atomization method, wherein the heterogeneous nucleation particles have a melting point higher than that of the metal powder, and the parameter M represented by the formula (1) is 12×10 －３ or less. 【Number 1】 (where ε ｘ and ε ｙ are the principal strains along the principal axes x and y orthogonal to each of the lattices of the heterogeneous nuclear phase and the lattice of the solidified phase, respectively, and ε ｘ and ε ｙ are calculated by the following formulas (2) and (3).) 【Number 2】 【Number 3】 (where x ｉ , y ｉ and x ｊ , y ｊ are the principal strain directions of substance i and substance j, respectively, and a ｉ and a ｊ are the lattice constants of substance i and substance j, respectively.)

6. The heterogeneous core particles are TiC, TiB ２ , Al ３ Ti, a third element Me is added to crystallize the crystal structure into L1 ２ transformed (Al １－ｘ Me ｘ ), ３ a composite metal powder which is one or more compound particles selected from Ti, SrO

7. The composite metal powder according to Claim 6, wherein the heterogeneous nucleating particles are TiC particles.

8. A method for producing a composite metal powder according to any one of Claims 1 to 7, characterized in that the metal powder and the heterogeneous nuclei are compounded by mechanical mixing.

9. The method for producing a composite metal powder according to Claim 8, wherein the mechanical mixing is performed using a turbular shaker mixer.

Images