Powder material for additive manufacturing and method for manufacturing a molded object using the powder material

Abstract

To provide a powder material for additive manufacturing the main components of which are tungsten carbide and cobalt that can form an additive manufacturing model with excellent mechanical strength.SOLUTION: A powder material for additive manufacturing disclosed herein includes a carbon additive containing tungsten carbide (WC), cobalt (Co), and carbon (C) as main constituent elements, where a value of carbon percentage content A (mass%) represented by the following equation: (mass of carbon originated from WC + mass of carbon originated from the carbon additive) / (mass of WC)×100; meets a condition of 6.4≤A≤7.2.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a powder material used in additive manufacturing, and to a method for manufacturing a molded object by additive manufacturing using the powder material. [Background technology]

[0002] Three-dimensional modeling technology, which creates a target object based on data on its three-dimensional shape (e.g., three-dimensional CAD data), is becoming increasingly popular. One such modeling technology is additive manufacturing, in which powder material is spread out in thin layers, then bonded or sintered into a shape corresponding to the cross section of the target object, and these thin layers are then stacked one on top of the other. Resin materials have traditionally been widely used as powder building materials for such additive manufacturing, but in recent years, development has been progressing on powder materials for additive manufacturing made from metals or ceramics that can be used in additive manufacturing methods such as powder bed fusion (PBF) and laser powder deposition (LMD) (see Patent Documents 1 to 4). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2015 / 194678 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-113952 [Patent Document 3] Japanese Patent Application Publication No. 2017-114716 [Patent Document 4] Japanese Patent Application Laid-Open No. 2017-115194 Summary of the Invention [Problem to be solved by the invention]

[0004] One of the development goals for powder materials for additive manufacturing (AM), which are inorganic materials such as metals and ceramics, is to develop powder materials that can produce objects with high mechanical strength and no cracks or chips. To meet this goal, development is underway on powder materials primarily composed of tungsten carbide (WC) and cobalt (Co). Tungsten carbide and cobalt are the raw materials for cemented carbide (WC-Co alloy), and are suitable for manufacturing high-hardness objects using AM. However, there is still room for improvement in the powder materials based on tungsten carbide and cobalt that have been developed so far in order to further improve the mechanical strength of additively manufactured products.

[0005] In view of these circumstances, the present invention aims to provide a powder material for additive manufacturing (hereinafter also referred to as "WC / Co-containing powder material") containing tungsten carbide and cobalt as its main components, which can form additively manufactured objects with superior mechanical strength. Another aim is to provide a method for manufacturing an additively manufactured object using such a powder material. [Means for solving the problem]

[0006] In order to achieve the above object, the present inventors conducted detailed studies on the alloy structure of additively manufactured products made from powder material containing tungsten carbide and cobalt as the main components. As a result, they discovered that, when the η phase is present in the manufactured product, the higher the proportion of η phase present, the lower the mechanical strength of the manufactured product. However, they discovered that intentionally increasing the carbon (C) content in the WC / Co-containing powder material used for additive manufacturing can suppress the formation of the brittle η phase and improve the mechanical strength of the manufactured product, which led to the completion of the present invention.

[0007] The powder material for additive manufacturing disclosed herein is a powder material for additive manufacturing that includes tungsten carbide (WC), cobalt (Co), and a carbon additive that includes carbon (C) as its main constituent elements. And the following formula: (mass of C from WC + mass of C from carbon additive) / (mass of WC) × 100; is the carbon content A (mass %), the WC / Co-containing powder material satisfies the condition that the carbon content A (mass %) is 6.4≦A≦7.2.

[0008] According to the technical knowledge acquired by the present inventors, when conventional powder additive manufacturing (AM) such as powder bed fusion (PBF) or laser powder deposition (LMD) is performed using WC / Co-containing powder materials, the amount of carbon present is reduced below the theoretical value due to the irradiation energy of the laser light or electron beam during the manufacturing process, which can make it easier for the η phase, a brittle layer, to form within the structure of the manufactured object. Furthermore, the present inventors have realized that by adding a predetermined amount of carbon-containing material (carbon additive) to the WC / Co-containing powder material in advance, the amount of carbon present during AM is not reduced, which results in the suppression of the formation of the η phase, a brittle layer, within the structure of the manufactured object, and the suppression of the decrease in mechanical strength due to the presence of the η phase in the manufactured object made from the WC / Co-containing powder material. Therefore, the WC / Co-containing powder material for additive manufacturing disclosed herein can prevent a decrease in the carbon component during additive manufacturing, suppress the formation of η phase within the structure of the molded object, and prevent a decrease in the mechanical strength of the molded object. Therefore, the technology disclosed herein makes it possible to manufacture an additively manufactured object made of a cemented carbide containing WC—Co as a constituent element, and having excellent mechanical properties.

[0009] A preferred embodiment of the powder material disclosed herein satisfies the condition that the value of the carbon content A satisfies 6.6≦A≦6.9. The powder material for additive manufacturing having such a configuration can more effectively suppress the formation of the η phase while maintaining better mechanical properties of the molded object.

[0010] In another preferred embodiment of the powder material disclosed herein, the carbon additive comprises at least one solid carbon material selected from the group consisting of graphite, carbon black, activated carbon, carbon fiber, and nanocarbon. According to the powder material for additive manufacturing having such a configuration, the carbon additive is made of a material made of solid carbon, so that it is possible to effectively replenish the carbon component.

[0011] In another preferred embodiment of the powder material disclosed herein, the carbon additive contains a carbide of at least one metal selected from the group consisting of titanium (Ti), vanadium (V), chromium (Cr), niobium (Nb), and molybdenum (Mo). According to the powder material for additive manufacturing having such a configuration, since it contains any of the above metal carbides as a carbon additive, it is possible to produce an object made of an alloy material that has excellent mechanical strength due to the presence of dissimilar metal elements other than WC and Co in addition to supplementing the carbon component.

[0012] In another preferred embodiment of the powder material disclosed herein, the powder material is composed of granulated and sintered particles in which the tungsten carbide, the cobalt, and the carbon additive are mixed. A powder material composed of granulated and sintered particles in which the above three types of components are mixed, for example, granulated and sintered particles (which can be considered secondary particles, the same applies below) in which particles made of tungsten carbide are mixed with particles made of cobalt and particles constituting the carbon additive, can effectively replenish the carbon component and more effectively suppress the formation of the η phase. Preferably, the average particle size of the granulated sintered particles is 10 μm or more and 30 μm or less, and the particles (primary particles) constituting the granulated sintered particles include particles made of tungsten carbide having an average particle size of less than 1 μm, particles made of cobalt having an average particle size of 2 μm or more and 10 μm or less, and particles constituting the carbon additive having an average particle size of 1 μm or more and 5 μm or less. Granulated and sintered particles having a particle size specified in this manner can more effectively suppress the formation of the η phase.

[0013] The present teachings also provide a method for manufacturing a molded object, characterized by performing additive manufacturing using any of the powder materials disclosed herein. As described above, the technology disclosed herein makes it possible to manufacture an additively manufactured object made of a cemented carbide containing WC—Co as a constituent element and having excellent mechanical properties. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a simplified diagram of a powder additive manufacturing apparatus according to an embodiment; [Figure 2] 1 is an XRD chart showing the relationship between the amount of carbon added and the degree of suppression of the formation of the η phase in a shaped article. [Figure 3] 1 is an optical microscope photograph showing a cross section of a cube-shaped object (sintered body) produced using a powder material according to an example. DETAILED DESCRIPTION OF THE INVENTION

[0015] Preferred embodiments of the present invention will be described below. Matters necessary for carrying out the present invention other than those specifically mentioned in this specification can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The present invention can be carried out based on the contents disclosed in this specification and the common general technical knowledge in the relevant field. In the specification, the expression "X to Y" indicating a numerical range means "at least X and at most Y" unless otherwise specified.

[0016] <Definition> As used herein, the term "powder material" refers to a powdered material used in additive manufacturing. The powder material disclosed herein is a WC / Co-containing powder material, i.e., a powder material for additive manufacturing whose main components are tungsten carbide and cobalt (i.e., a powder material for additive manufacturing whose largest components by mass of the entire powder material are WC and Co). As used herein, the term "primary particle" refers to the smallest unit of the morphological components constituting the powder material that can be identified as a granular material from its appearance. Therefore, when the WC / Co-containing powder material disclosed herein contains secondary particles (e.g., granulated particles), the particles constituting the secondary particles can be referred to as primary particles. Here, "secondary particles" refers to particulate matter (in the form of particles) in which primary particles are three-dimensionally bonded together and behave as a single particle. Granulated particles and granulated and sintered particles obtained by granulation are typical examples of "secondary particles" as used herein.

[0017] The term "bonding" as used herein refers to the direct or indirect joining of two or more primary particles, and includes, for example, bonding between primary particles due to a chemical reaction, bonding between primary particles attracting each other due to simple adsorption, bonding using the anchor effect of allowing an adhesive or the like to penetrate into the unevenness of the primary particle surface, bonding between primary particles using the effect of attraction due to static electricity, and bonding in which the surfaces of primary particles are melted and integrated together. In addition, in this specification, the term "raw material particles" refers to particles that constitute the powder in the raw material stage used to form the powder material disclosed herein. In this specification, unless otherwise specified, the "average particle size" of a powder material refers to the average particle size at 50% of the cumulative value in the volume-based particle size distribution measured by a particle size distribution measuring device based on the laser scattering and diffraction method (50% volume average particle size; D 50 ) means

[0018] <Powder material composition> As described above, the powder material disclosed herein is a WC / Co-containing powder material that includes tungsten carbide, cobalt, and a carbon additive that includes carbon as the predominant constituent element (i.e., a material in which carbon is the largest constituent element by mass). One suitable form of such powder material is, for example, one prepared by mixing WC particles, Co particles, and particles constituting a carbon additive as raw material particles, but is not limited to this form. For example, a high-carbon WC powder (HighC-WC powder) may be used, in which an excess amount of carbon is added to WC particles (powder) as raw material particles, resulting in the presence of an amount of C exceeding the stoichiometric composition ratio of WC. In one embodiment of the powder material disclosed herein, such HighC-WC powder can be said to be a component in which tungsten carbide and a carbon additive are combined.

[0019] As the WC powder (which may be a High C-WC powder) made from tungsten carbide raw material particles, various commercially available WC powder materials for forming cemented carbides can be used. Preferably, tungsten carbide raw material particles with an average particle size of less than 1 μm (e.g., 0.05 to 0.5 μm, particularly 0.1 to 0.3 μm) can be used. By using WC powder made from tungsten carbide raw material particles of such small size, it is possible to produce an additive manufacturing object made from a denser WC-Co alloy. Furthermore, as the Co powder made of cobalt raw material particles used in the production of the powder material disclosed herein, any conventional Co powder used in powder metallurgy or the production of cemented carbide materials can be used without particular limitation. Co powder with an average particle size of 1 μm or more (e.g., 2 μm or more) and 10 μm or less (e.g., 5 μm or less) can be preferably used.

[0020] The powder material disclosed herein is characterized in that a carbon additive containing carbon (C) as a main constituent element is added in a specified amount determined based on the above-mentioned carbon content A (mass %). Suitable carbon additives include carbon materials that are solid at room temperature (preferably particulate solid carbon materials). Examples of such solid carbon materials include graphite, carbon black (acetylene black, ketjen black, etc.), activated carbon, carbon fiber (PAN-based carbon fiber, pitch-based carbon fiber, graphite fiber, etc.), and nanocarbons (carbon nanotubes, fullerenes, graphene, diamond particles, etc.). These types of solid carbon materials can also be used as a carbon component source when producing the HighC-WC powder.

[0021] Alternatively, another suitable form of carbon additive is a carbide of a metal element that can form a hard alloy together with WC and Co. Such a metal carbide is a compound that can function as a carbon source when irradiated with energy from a laser beam, an electron beam, or the like during additive manufacturing together with WC and Co. Although not particularly limited, such a metal carbide can be a carbide of any of titanium (Ti), vanadium (V), chromium (Cr), niobium (Nb), and molybdenum (Mo). As the carbon additive made of the above-mentioned solid carbon material or metal carbide, a particulate carbon additive having an average particle size in the particle size range of about 0.5 μm or more (e.g., 1 μm or more) and 10 μm or less (e.g., 5 μm or less) can be particularly preferably used. Alternatively, as described below, optional components such as binders used to produce the powder material disclosed herein may also function as carbon additives. For example, the carbon component of an organic material that can be used as a binder and remains in the final powder material is taken into account as the mass of C derived from the carbon additive (binder, etc.) in determining the carbon content A.

[0022] The powder material disclosed herein is a powder material for additive manufacturing (WC / Co-containing powder material) primarily composed of tungsten carbide and cobalt, and the WC and Co contents (by mass) in the entire powder material are not particularly limited as long as a good WC-Co alloy can be formed. For example, WC is suitably 60 mass% or more of the entire powder material, preferably 70 mass% or more, and particularly preferably 75 mass% or more. On the other hand, the content of Co is suitably 10% by mass or more of the entire powder material, preferably 15% by mass or more, and particularly preferably 15% by mass or more. From the viewpoint of preventing the WC content from becoming too low, the content is suitably 40% by mass or less, preferably 30% by mass or less, and particularly preferably 25% by mass or less. For example, a powder material containing 80 to 85% by mass of WC and 15 to 20% by mass of Co is a particularly preferred embodiment, since a good WC-Co based cemented carbide can be obtained.

[0023] The amount of carbon additive added to the powder material disclosed herein is determined by the following formula: (mass of C from WC + mass of C from carbon additive) / (mass of WC) × 100; The carbon content A (mass %) is specified to be within a predetermined range. The carbon content A is preferably 6.4% by mass or more, and particularly preferably 6.6% by mass or more. Also, A is preferably 7.2% by mass or less, and particularly preferably 6.9% by mass or less. If the carbon content A is lower than 6.4% by mass, the deficiency of C may not be compensated for, and the effect of inhibiting the formation of the η phase may decrease, which is undesirable. On the other hand, if the carbon content A is higher than 7.2% by mass, the amount of C present may become excessive, which may be detrimental to the formation of a WC-Co based cemented carbide, which is undesirable.

[0024] The powder material disclosed herein may contain other optional components as long as the carbon content A can be set within a predetermined range and a good WC-Co alloy can be formed. Examples include binders, dispersants, surfactants, inorganic pigments, organic pigments, and the like, which do not function as carbon additives during additive manufacturing (those that can function as carbon additives are included in the category of carbon additives in this technology).

[0025] <Preparation of powder materials> The powder material disclosed herein can be prepared by mixing, for example, raw material particles made of tungsten carbide (WC), raw material particles made of cobalt (Co), and raw material particles constituting a carbon additive containing carbon (C) as the main constituent element (when using High C-WC powder, raw material particles constituting the carbon additive may not be required independently), together with other optional components. A material made of such a mixed powder is a typical example of the WC / Co-containing powder material disclosed herein.

[0026] However, a more suitable powder material is one composed of granulated and sintered particles containing a mixture of the above components. Typically, the powder material is made by mixing and granulating raw material particles (primary particles) of the components, and then sintering the resulting primary particles to form granulated and sintered particles, which are then three-dimensionally bonded together with gaps between them, forming secondary particles. Hereinafter, an example of a granulation and sintering method for producing such granulated and sintered particles will be described, but the present invention is not limited to this method.

[0027] <Production of Granulated Sintered Particles> The granulation sintering method is a technique in which raw material particles are granulated into the form of secondary particles and then sintered to bond (sinter) the raw material particles together. In such a granulation sintering method, granulation can be carried out using a granulation method such as dry granulation or wet granulation. Examples of granulation methods include tumbling granulation, fluidized bed granulation, stirring frame granulation, crushing granulation, melt granulation, spray granulation, and microemulsion granulation. Among these, spray granulation is a preferred granulation method.

[0028] Using the spray granulation method, powder materials can be produced, for example, by the following procedure. First, raw material particles corresponding to the tungsten carbide, cobalt, and carbon additive are prepared, and their surfaces are stabilized as needed with a protective agent or the like. The stabilized raw material particles are then dispersed in an appropriate solvent, along with optional spacer particles made of an organic material such as a binder, to prepare a spray solution. Dispersion of the raw material particles in the solvent can be carried out using, for example, a mixer or disperser such as a homogenizer or blade stirrer. Finally, droplets are formed from the spray solution using an ultrasonic atomizer or the like, and the droplets are then entrained in an airflow and passed through a spray-drying device (spray dryer) to form granulated particles. The resulting granulated particles are introduced into a predetermined sintering furnace and sintered to obtain a powder material consisting of granulated and sintered particles in the form of secondary particles in which primary particles are bonded together with gaps. Note that the primary particles may have substantially the same size and shape as the raw material particles, or the raw material particles may have grown and bonded together by sintering.

[0029] In the above manufacturing process, when the droplets are dried, the raw material particles and the binder are in a uniformly mixed state, and the raw material particles are bound by the binder to form mixed particles. When spacer particles are used, the raw material particles and the spacer particles are in a uniformly mixed state and bound by the binder to form mixed particles. When these mixed particles are fired, the binder (and the spacer particles) disappear (burn out), and the raw material particles are sintered, forming secondary particles in which primary particles are bound together with gaps between them. During sintering, some of the raw material particles may become liquid and contribute to bonding with other particles, depending on their composition and size. As a result, the average particle size of the primary particles may be larger than that of the raw material particles of the starting material. The average particle size of the secondary particles and primary particles, as well as the size and proportion of the gaps formed between the primary particles, can be designed according to the desired shape of the secondary particles.

[0030] In the above-mentioned manufacturing process, the concentration of raw material particles in the spray liquid is preferably adjusted to 10 to 40% by mass. Examples of binders to be added include carboxymethyl cellulose (CMC) and polyvinylpyrrolidone (PVP). The amount of binder added is preferably adjusted to 0.05 to 10% by mass (e.g., 1 to 5% by mass) relative to the mass of the raw material particles. The firing environment is not particularly limited, but may be in air, vacuum, or an inert gas atmosphere, and sintering is preferably performed at a temperature of 600°C to 1600°C. In particular, when spacer particles, binders, etc. made of organic materials are used, sintering may be performed in an oxygen-containing atmosphere in order to remove the organic materials from the granulated particles. If necessary, the produced secondary particles may be crushed and classified.

[0031] The strength of the granulated and sintered particles that make up the powder material produced in this way (hereinafter referred to as "granule strength") is 1 kgf / mm 2 It is preferable that the resistance is 5 kgf / mm or more. 2 More preferably, it is 10 kgf / mm or more. 2or more (e.g., 20 kgf / mm 2 It is particularly preferable that the above conditions are satisfied. This makes it possible to effectively prevent the granulated and sintered powder from collapsing or scattering due to the energy required for manufacturing. As a result, the supply of powder material to the manufacturing area is stabilized, making it possible to manufacture a high-quality object without unevenness. On the other hand, if the granule strength is too high, it is difficult to melt the powder material sufficiently, which is undesirable. From this point of view, the granule strength is set to 500 kgf / mm 2 Less than 300kgf / mm is appropriate. 2 It is preferable that the resistance is 200 kgf / mm or less. 2 More preferably, it is 100 kgf / mm or less. 2 Less than (for example, 50 kgf / mm 2 It is particularly preferred that

[0032] <Additive Manufacturing> The powder material (WC / Co-containing powder material) disclosed herein can be used in the same additive manufacturing method as that used to manufacture additively manufactured objects made of conventional WC-Co alloys. Typical examples of such additive manufacturing methods include laser powder deposition (also known as laser metal deposition; LMD) and powder bed fusion (PBF). Powder bed fusion (PBF) encompasses selective laser melting (SLM), which uses a laser as the irradiation energy, and electron beam melting (EBM), which uses an electron beam as the irradiation energy.

[0033] Laser powder cladding is a technology that provides powder material to a desired part of a structure, and then irradiates it with laser light to melt and solidify the powder material, thereby cladding the part (i.e., manufacturing a shaped object). For example, when physical deterioration such as wear occurs in a structure, this method can be used to provide the material that makes up the structure or reinforcing material as powder to the deteriorated part, and then melt and solidify the powder material to cladding the deteriorated part. Powder bed fusion is a method of forming three-dimensional structures by scanning a laser or electron beam onto a powder layer made of deposited powder material based on slice data created from a design drawing, and melting and solidifying the powder layer into the desired shape, repeating this process for each cross section (each slice data).

[0034] An example of a method for manufacturing a molded object by powder additive manufacturing using the powder material disclosed herein will be described with reference to FIG. Fig. 1 is a simplified diagram of an additive manufacturing device for powder additive manufacturing. As shown in this diagram, the additive manufacturing device is roughly configured to include an additive manufacturing area 10, which is the space where additive manufacturing takes place, a stock 12 for storing powder material, a wiper 11 for assisting in the supply of powder material to the additive manufacturing area 10, and a solidification means 13 for solidifying the powder material (a laser oscillator such as a carbon dioxide laser or a YAG laser, or an energy irradiation means such as a beam irradiator). The stacking area 10 typically has a surrounding periphery of a build space below the build surface, and is equipped with a lifting table 14 that can rise and fall within this build space. This lifting table 14 can be lowered in increments of a predetermined thickness Δt1, and the desired object is built on this lifting table 14. The stock 12 is arranged near the stacking area 10, and is equipped, for example, with a bottom plate (lifting table) that can be raised and lowered by a cylinder or the like within a storage space that is surrounded by the periphery. By raising the bottom plate, a predetermined amount of powder material can be supplied (extruded) onto the build surface.

[0035] In this additive manufacturing apparatus, the powder material layer 20 having the predetermined thickness Δt1 can be prepared by supplying the powder material layer 20 to the deposition area 10 while the lift table 14 is lowered by a predetermined thickness Δt1 from the building surface. At this time, by scanning the wiper 11 across the building surface, the powder material extruded from the stock 12 is supplied onto the deposition area 10 and the surface of the powder material is flattened to form a homogeneous powder material layer 20. Then, for example, by irradiating the formed first powder material layer 20 with energy such as laser light or electron beam via the solidification means 13 only in a solidified region corresponding to the slice data for the first layer, the powder material is melted or sintered into a desired cross-sectional shape, thereby forming the first solidified powder layer 21.

[0036] Next, the lift table 14 is lowered by a predetermined thickness Δt1, and powder material is again supplied. The powder material is then smoothed out with the wiper 11 to form a second powder material layer 20. Energy is then irradiated via the solidification means 13 only to solidified regions of the powder material layer 20 that correspond to the slice data for the second layer, solidifying the powder material and forming a second solidified powder layer 21. At this time, the second solidified powder layer 21 and the underlying first solidified powder layer 21 are integrated to form a stack up to the second layer. Subsequently, the lift table 14 is lowered by a predetermined thickness Δt1 to form a new powder material layer 20, and energy is irradiated via the solidification means 13 to form the solidified powder layer 21 only in the required locations. By repeating this process, the additive manufacturing device can manufacture a desired three-dimensional object based on slice data created from a previously prepared design drawing (3D CAD data). As described above, the powder material disclosed herein suppresses the formation of the η phase (Co3W3C) through the additive manufacturing process described above, making it possible to produce three-dimensional cemented carbide objects primarily composed of WC-Co that are highly hard and have little cracking or chipping.

[0037] Examples relating to the powder material and the production of a shaped object disclosed herein will be described below, but it is not intended that the present technology be limited to those shown in the following examples.

[0038] <Test example> The raw material powder has an average particle diameter (D 50 ) is approximately 0.2 μm, and the average particle diameter (D 50 Cobalt (Co) powder with a particle size of approximately 5 μm was prepared. The powder material was blended so that 17 mass% of the total powder material was Co powder, 1 mass% was binder (CMC), and the remainder was WC powder. The resulting blended powder was wet mixed and then granulated using a spray dryer. The resulting granulated particles were sintered to produce a powder material consisting of granulated and sintered particles (secondary particles). This powder material was designated Sample A in this test example. As mentioned above, Sample A did not contain any carbon additive. Next, graphite particles (D 50 : approx. 4 μm), vanadium carbide (VC) particles (D 50 One or two of the above powder materials (approximately 4 μm) were appropriately combined and mixed in six different ratios to prepare powder materials consisting of six types of granulated and sintered particles with different carbon contents. These were classified in descending order of carbon content as follows: Sample A, Sample B, Sample C, Sample D, Sample E, Sample F, and Sample G (A <B<C<D<E<F<G)とした。

[0039] Next, the powder materials of Samples A to G were each tested, and simple cube-shaped additive manufacturing objects were fabricated using a commercially available additive manufacturing device (product name: ProX DMP200, manufactured by 3D System). In other words, a cube-shaped object was fabricated by irradiating a laser beam onto a flatly laid powder material, melting it layer by layer, and repeating this process. In this test example, the output was 300 W, the scanning speed was 300 mm / s, the pitch width was 0.1 mm, and the thickness of each layer was 30 μm. After the additive manufacturing, the resulting molded object was subjected to a firing treatment (heat treatment) in a reduced pressure atmosphere (10 Pa) at 1380°C for 2 hours (continuously).

[0040] Next, XRD (X-ray diffraction) measurements were performed on the sintered bodies of the obtained shaped articles. The intensities of the peak (40.1°) representing Co3W3C (η phase) from the XRD chart were compared between samples A to G. The results are shown in Figure 2. As is clear from a comparison of the heights of the peaks around 40.1° (i.e., peaks indicating the η phase) for each sample shown in the figure, the formation of the η phase was clearly observed in the structures of the molded objects made from samples A, B, C, and D, which are powder materials with relatively low carbon contents. On the other hand, no peaks indicating the formation of the η phase were observed in the structures of the molded objects made from samples E, F, and G, which are powder materials with relatively high carbon contents. These results indicate that the addition of a predetermined amount of carbon additive can suppress the formation of the η phase, which is a brittle layer, in the structure of a shaped product made of a WC-Co alloy.

[0041] <Production example> (Sample 1) The raw material powder has an average particle diameter (D 50 ) is approximately 0.2 μm, and the average particle diameter (D 50 ) of about 5 μm and cobalt (Co) powder with an average particle diameter (D 50 Graphite (C) powder with a particle size of approximately 4 μm was prepared. CMC was prepared as a binder. The powder material was mixed so that 17% by mass of the total powder material was Co powder, 1% by mass of CMC, 0.56% by mass of graphite powder, and the remainder was WC powder. The resulting mixed powder was wet mixed and then granulated using a spray dryer. The resulting granulated particles were sintered to produce a powder material consisting of granulated and sintered particles (secondary particles). This powder material was designated Sample 1 according to this production example.

[0042] (Samples 2-7) The raw material powder has an average particle diameter (D 50The powder material of Sample 2 was produced by the same process as Sample 1, except that vanadium carbide (VC) powder having a particle size of approximately 4 μm was further prepared, and the powder material was mixed so that 17 mass% of the total powder material was Co powder, 1 mass% was CMC, 1 mass% was VC, 0.28 mass% was graphite powder, and the remainder was WC powder. In addition, the powder material of Sample 3 was manufactured by the same process as Sample 1, except that the powder material was formulated so that 17 mass% of the total powder material was Co powder, 1 mass% was CMC, 0.84 mass% was graphite powder, and the remainder was WC powder. In addition, the powder material of Sample 4 was produced by the same process as Sample 1, except that the powder material was formulated so that 17 mass% of the total powder material was Co powder, 1 mass% was CMC, 3 mass% was VC, 0.14 mass% was graphite powder, and the remainder was WC powder. In addition, the powder material of Sample 5 was produced by the same process as Sample 1, except that the powder material was mixed so that 17 mass% of the total powder material was Co powder, 1 mass% was CMC, 0.28 mass% was graphite powder, and the remainder was WC powder. In addition, the powder material of Sample 6 was produced by the same process as Sample 1, except that the powder material was mixed so that 17 mass% of the total powder material was Co powder, 1 mass% was CMC, 0.14 mass% was graphite powder, and the remainder was WC powder. In addition, the powder material of Sample 7 was manufactured by the same process as Sample 1, except that 17 mass % of the total powder material was Co powder, 1 mass % was CMC, and the remainder was WC powder. In other words, no substance equivalent to a carbon additive was added to the powder material of Sample 7.

[0043] The volumetric particle size distribution of the powder materials (granulated and sintered particles) of Samples 1 to 7 was measured using a commercially available particle size distribution measuring device based on the laser diffraction and scattering method. 10 ,D 50 ,D 90 and D 97 The values ​​shown were: The average particle diameter (D50 ) was in the range of 15-20 μm, and most of the particles were in the range of 8-40 μm.

[0044] The powder materials (granulated sintered particles) of Samples 1 to 7 were quantitatively analyzed for W, Co, V, and unavoidable impurities (here, Fe and Zr) using a commercially available wavelength dispersive X-ray fluorescence analyzer (XRF-1800: product of Shimadzu Corporation) based on the X-ray fluorescence analysis method. The total C amount was measured using a commercially available carbon / sulfur analyzer (EMIA, manufactured by Horiba, Ltd.). The amount of C derived from WC was stoichiometrically calculated from the quantitative value of W, and the amount of C derived from the WC was subtracted from the total C amount to obtain the amount of C derived from the carbon additive. The content (mass%) of each element thus obtained is shown in the corresponding column in Table 1. The carbon content A (mass%) of each sample is also shown in the corresponding column in Table 1 based on the above-mentioned calculation formula.

[0045] The granule strength of the powder materials (granulated sintered particles) of Samples 1 to 7 was measured using an electromagnetic force loading compression tester. Specifically, 10 or more granulated sintered particles constituting the powder material of each sample were randomly sampled, and the arithmetic mean value of the breaking strength measured using a commercially available micro-compression tester (MCT-500: product of Shimadzu Corporation) was used to calculate the granule strength (kgf / mm 2 ) for the granulated and sintered particles. When the critical load obtained in the compression test is L [N] and the average particle diameter is d [mm], the breaking strength σ [MPa] of the granulated and sintered particles can be calculated using the formula: σ = 2.8 × L / π / d2. The granule strength (kgf / mm 2 ) are shown in the corresponding columns in Table 1.

[0046] Next, the powder materials of Samples 1 to 7 were each tested, and simple cube-shaped additive models were fabricated using a commercially available additive manufacturing device (product name: ProX DMP200, manufactured by 3D Systems). That is, as in the test example, a laser beam was irradiated onto a flatly laid powder material, melting it layer by layer, and this process was repeated to fabricate cube-shaped models. In this test example, the output was 300 W, the scanning speed was 300 mm / s, the pitch width was 0.1 mm, and the thickness of each layer was 30 μm. After the additive manufacturing, the resulting molded object was subjected to a firing treatment (heat treatment) in a reduced pressure atmosphere (10 Pa) at 1380°C for 2 hours (continuously).

[0047] Next, XRD (X-ray diffraction) measurements were performed on the sintered bodies of the resulting shaped products. In this XRD measurement, the intensity of the peak (40.1°) representing Co3W3C (η phase) and the peak (35.6°) representing WC were detected, and the presence or absence and degree of η phase formation in the sintered bodies of each sample was evaluated from the ratio of these peaks (Co3W3C / WC). The results are shown in the corresponding columns in Table 1. In the "Presence of η Phase" column of Table 1, those with an XRD measurement peak ratio (%) of 0% are entered as "absent" because no η phase was observed, and those with an XRD measurement peak ratio (%) of less than 1% but not 0 are entered as "almost absent" because although the presence of η phase was observed, its presence was at an extremely small level. On the other hand, for specimens with an XRD measurement peak ratio (%) of 1% or more but less than 3%, the presence of the η phase was slightly observed, but the proportion of the η phase was so small that it did not substantially affect the mechanical strength, and therefore it was recorded as "slightly present." For specimens with an XRD measurement peak ratio (%) of 3% or more, the presence of the η phase was observed, but the proportion of the η phase was so small that it could substantially affect the mechanical strength compared to specimens without the η phase, and therefore it was recorded as "present."

[0048] The cube-shaped shaped product (sintered product) of Sample 1 was cut in a direction perpendicular to the stacking direction, and the cross sections were observed under an optical microscope. Figure 3 is a micrograph showing the cut surface of the shaped product (sintered product) of Sample 1.

[0049] [Table 1]

[0050] As is clear from Table 1 and Figure 3 showing the results of this manufacturing example, in the shaped objects (sintered bodies) manufactured by additive manufacturing using the powder materials of Samples 1 to 6, in which a carbon additive was added to the WC / Co-containing powder material so that the C content exceeded the stoichiometric ratio of WC, specifically, the carbon additive (here, graphite, VC, CMC) was added so that the carbon content A (mass%) satisfied the condition of 6.4≦A≦7.2, no η phase was formed in the WC-Co alloy structure, or if it was formed, it was only to a very small extent. As a result, it was possible to manufacture shaped objects consisting of a dense WC-Co alloy structure without any cracks or chips, as shown in Figure 3. In the molded object produced from the powder material of Sample 7, in which the carbon content A was almost the stoichiometric composition ratio of WC, a relatively large amount of η phase was formed in the structure, and no improvement in mechanical strength was observed. Although detailed data are not shown, the mechanical properties (hardness, etc.) of the shaped articles (sintered bodies) produced from the powder material of Samples 1, 2, and 5, in which a carbon additive such as graphite was added so that the carbon content A (mass%) satisfied the condition of 6.6≦A≦6.9, were superior to the mechanical properties of the shaped articles (sintered bodies) produced from the powder material of the other samples. This indicates that by adding a more suitable amount of carbon additive (in other words, a more suitable amount of C), the formation of the η phase in the WC-Co alloy structure can be effectively suppressed without including an excessive amount of C in the alloy structure. [Explanation of symbols]

[0051] 10 Stacking Area 11 wiper 12 Stock 13 Solidification means 14 Lift table 20 Powder material layer 21 Powder solidification layer

Claims

1. A powder material for additive manufacturing, comprising: As primary particles, tungsten carbide (WC) particles; Cobalt (Co) particles; Particles constituting a carbon additive material containing carbon (C) as a main constituent element; Including, The primary particles are three-dimensionally bonded together with gaps therebetween, Granule strength is 5 kgf / mm ２ Over 500 kgf / mm ２ It is composed of granulated and sintered particles that are less than where the following formula: (mass of C derived from WC + mass of C derived from carbon additive) / (mass of WC) × 100; The powder material satisfies the condition that the carbon content A (mass%) represented by the formula (1) satisfies the condition of 6.4≦A≦7.

2.

2. The powder material according to claim 1, wherein the carbon content A (mass%) satisfies the condition 6.6≦A≦6.

9.

3. 3. The powder material according to claim 1, wherein the carbon additive comprises at least one solid carbon material selected from the group consisting of graphite, carbon black, activated carbon, carbon fiber, and nanocarbon.

4. The powder material according to any one of claims 1 to 3, wherein the carbon additive comprises a carbide of at least one metal selected from the group consisting of titanium (Ti), vanadium (V), chromium (Cr), niobium (Nb), and molybdenum (Mo).

5. The powder material according to any one of claims 1 to 4, wherein the powder material is composed of the granulated and sintered particles in which the tungsten carbide particles, the cobalt particles, and particles constituting the carbon additive are mixed.

6. the average particle size of the granulated and sintered particles is 10 μm or more and 30 μm or less, Here, the particles constituting the granulated and sintered particles are: Particles made of tungsten carbide having an average particle size of less than 1 μm; particles made of cobalt having an average particle size of 2 μm or more and 10 μm or less; Particles constituting the carbon additive material have an average particle diameter of 1 μm or more and 5 μm or less; The powder material according to any one of claims 1 to 5, comprising:

7. A method for manufacturing a shaped object, comprising layer-by-layer manufacturing using the powder material according to any one of claims 1 to 6.

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