JP7336944B2 - Molded object manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing a modeled object.

Additive manufacturing techniques create objects based on numerical representations of three-dimensional shapes (typically 3D CAD data) by depositing materials. Typically, powder materials (additive manufacturing materials) are bonded or sintered as thin layers having a shape corresponding to the cross section of the object to be shaped, and the thin layers are sequentially stacked to obtain the desired three-dimensional shape. to shape. In this additive manufacturing, in recent years, there has been a demand for improvement in the additive manufacturing technology, which uses a cemented carbide powder material such as a WC base and directly forms a cemented carbide member without the need for a mold (for example, Patent Document 1-4).

WO2015/194678 JP 2017-113952 A JP 2017-114716 A JP 2017-115194 A

In the layered manufacturing method, there is a demand for a technique for manufacturing a dense and hard modeled object.

Here, the present inventors describe the additive manufacturing method for producing a three-dimensional modeled object by irradiating a laser beam or an electron beam, the composition and modeling process of the powder material for additive manufacturing, and the physical properties of the modeled product. We examined the relationship between As a result, the present inventors have found that by specifying the components of the powder material for lamination molding and the molding process under specific conditions, it is possible to manufacture a dense and highly rigid molded object.
SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for manufacturing a three-dimensional shaped object that is dense and has high hardness.

A method for manufacturing a model according to an aspect of the present invention includes a step of forming a three-dimensional model by irradiating a laser beam or an electron beam using a powder material for layered manufacturing containing tungsten carbide and cobalt. , heat-treating the shaped object in a reduced-pressure atmosphere; and subjecting the heat-treated shaped object to hot isostatic pressing.
A modeled object according to one aspect of the present invention is a powder material for additive manufacturing, which is used for producing a three-dimensional modeled object by irradiating it with a laser beam or an electron beam, and comprises tungsten carbide and cobalt. , titanium carbide, and the content of titanium carbide is 1% by mass or more and 20% by mass or less.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the molded object which can shape a three-dimensional-shaped molded object densely and with high hardness can be provided.

FIG. 1 is a schematic diagram showing a configuration example of a layered modeling apparatus for executing a method for manufacturing a modeled article according to an embodiment of the present invention. FIG. 2 is an SEM image showing an enlarged cross section of the three-dimensional structure (Comparative Example 2) after heat treatment. FIG. 3 is an SEM image showing an enlarged cross section of the three-dimensional structure (Example 1) after HIP. FIG. 4 is an SEM image showing an enlarged cross section of the three-dimensional structure (Example 2) after HIP.

<Definition>
As used herein, the term “powder material” refers to a powdered material used for additive manufacturing. A powder material may be referred to as a building material. The powder material is typically composed of an aggregate of secondary particles, which will be described later, but needless to say, primary particles, which will be described later, are allowed to mix. As used herein, the term “primary particles” means the smallest unit that can be identified as a particulate matter from its appearance, among the morphological constituent elements that constitute the powder material. In particular, it refers to one particle (one particulate matter) that constitutes a secondary particle to be described later.

As used herein, the term “secondary particles” refers to particulate matter (particles in the form of particles) in which primary particles are three-dimensionally combined and act like one grain. The term “bonding” as used herein refers to the direct or indirect bonding of two or more primary particles. It includes bonding where particles are attracted to each other, bonding between primary particles utilizing the effect of electrostatic attraction, and bonding where the surfaces of primary particles are melted and integrated.

As used herein, the term "raw material particles" refers to particles that constitute a raw material powder for forming a powder material. Secondary particles can be produced by three-dimensionally bonding raw material particles by an appropriate method. Particles constituting the secondary particles thus produced are called primary particles. The primary particles may have substantially the same form as the raw material particles, or may have a form different from the raw material particles such that two or more raw material particles react or integrate to such an extent that they cannot be morphologically distinguished. There may be. Further, the primary particles may have the same composition as the raw material particles, or may have a composition different from that of the raw material particles by, for example, reacting two or more kinds of raw material particles.

As used herein, "additive manufacturing" broadly encompasses various manufacturing methods that use powder materials in additive manufacturing techniques. Additive manufacturing may also be referred to as powder additive manufacturing. Examples of methods for bonding powder materials in layered manufacturing include a laser powder build-up method (laser metal deposition method; LMD), a selective laser melting method (selective laser melting method; SLM), and an electron beam melting method. (Electronic Beam Melting Method; EBM) and other beam irradiation methods.
In this specification, "X to Y" indicating a range means "X or more and Y or less".
In addition, the present invention is not limited only to the following embodiments. Also, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may differ from the actual ratios.

<Powder material>
(composition)
The powder material according to the embodiment of the present invention (hereinafter referred to as the present embodiment) has, as raw material particles,
(1) cobalt (Co);
(2) titanium carbide (TiC);
(3) tungsten carbide (WC);
including.
The raw material particles (1) to (3) above are combined by sintering to form a granulated sintered powder. It can also be understood that the powder material according to the present embodiment has the raw material particles of (1) to (3) as primary particles, and the granulated sintered powder forms the body of secondary particles. The raw material particles of (1) to (3) constitute the secondary particles in a generally uniformly mixed and dispersed state. Needless to say, in such a powder material, it is permissible (for example, 10% by mass or less) to contain the raw material particles of the above (1) to (3) in the form of primary particles.

In the powder material according to the present embodiment, the cobalt content is, for example, preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. In addition, in the powder material according to the present embodiment, the content of cobalt is, for example, preferably 50% by mass or less, more preferably 35% by mass or less, and even more preferably 25% by mass or less. If the cobalt content is within the above numerical range, WC and Co can be combined to form a WC—Co-based cemented carbide when lamination molding is performed using a laser beam or an electron beam. can.

In the powder material according to the present embodiment, the content of titanium carbide is, for example, preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more. In addition, in the powder material according to the present embodiment, the content of titanium carbide is, for example, preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less. .

If the content of titanium carbide is within the above numerical range, carbon (C) is supplied from titanium carbide to tungsten carbide (WC) when lamination manufacturing is performed using a laser beam or an electron beam. In additive manufacturing using a laser beam or an electron beam, the powder material is heated to a high temperature in a short time compared to ordinary powder metallurgy. Insufficient state (that is, W-rich state) is likely to occur. However, titanium carbide supplies C to tungsten carbide so as to compensate for this volatilized C. As a result, formation of η phase (brittle phase) can be suppressed in the WC—Co based cemented carbide.

Further, titanium carbide contained in the powder material reacts with tungsten carbide to become tungsten titanium carbide (WTiC). TiC does not remain in the WC—Co based cemented carbide after molding (or, if it does, the amount is very small). A WC—Co based cemented carbide can further increase its hardness by containing WTiC.

In the powder material according to the present embodiment, the content of tungsten carbide is, for example, preferably 75% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more. Moreover, in the powder material according to the present embodiment, it is more preferable that the content of tungsten carbide is, for example, 94% by mass or less. If the content of tungsten carbide is within the above numerical range, WC and Co combine to form a WC—Co-based cemented carbide when lamination molding is performed using a laser beam or an electron beam. can be done.

(granulated sintered powder)
The powder material according to the present embodiment may be configured as an aggregate of granulated sintered powder having the form of secondary particles as described above. The term “granulated sintered powder” refers to a particulate matter (particle body) in which primary particles are sintered and act like a single grain. “Sintered” refers to a state in which primary particles are directly bonded to each other. Therefore, sintering may be either solid phase sintering or liquid phase sintering. Also, sintering as used herein may include so-called fusion bonding and fusion bonding.

In the powder material according to the present embodiment, for example, in secondary particles (particle aggregates) having the form of granular particles, fine particle-coated particles in which fine particles are bonded around core particles, etc., individual primary particles are sintered. It may be realized by being firmly integrated by bonding. A laser beam, an electron beam, an arc, or the like is used as an energy source in layered manufacturing. When a powder material is irradiated with laser light, an electron beam, or the like, high energy may be released to cause an impact on the powder material. Due to this impact, simple granule particles may collapse or primary particles may scatter. In order to avoid this situation, the granule particles are formed as so-called granulated sintered powder in which individual primary particles are combined by sintering. This granulated sintered powder is preferable because the powder material is less likely to collapse and scatter even when irradiated with a laser beam or the like having a higher intensity as an energy source. This is preferable because it can lead to an increase in the modeling speed (for example, the laser scanning speed can be increased, or there is no need to reduce the laser scanning speed) without impairing the modeling accuracy and quality of the modeled object.

(granule strength)
The strength of granule particles in the granulated sintered powder (hereinafter referred to as granule strength) can be specified to exceed 1 MPa. As a result, it is possible to suitably prevent the granulated sintered powder from collapsing or scattering due to energy for modeling. As a result, the supply of the material powder to the modeling area is stabilized, so that it is possible to form a uniform, high-quality object, which is preferable. The granular strength of the granulated sintered powder is preferably 1 kg/mm ² or more, more preferably 5 kg/mm ² or more, and 10 kg/mm ² or more (for example, 20 kg/mm ² or more). is more preferred. However, if the granule strength is too high, it will be difficult to sufficiently melt the powder material, which is undesirable. In addition, granulated sintered powder with too strong granule strength is sintered until it has a structure similar to that of single particles that are not granulated, and the properties are similar to spherical particles. put away. From this point of view, the granule strength should be less than 1000 kg/mm ² . Granule strength is preferably 500 kg/mm ² or less, more preferably 250 kg/mm ² or less, and even more preferably 100 kg/mm ² or less (for example, 80 kg/mm ² or less).

In the powder material (eg, granulated sintered powder) according to the present embodiment, the raw material particles (typically primary particles) of (1) to (3) are three-dimensionally bonded to each other. It constitutes granulated sintered powder. This structure has the advantage that the powder material easily receives energy from an energy source (heat source) and is easily melted. As a result, for example, it is possible to obtain a highly dense and highly rigid molded article, which is similar to a sintered body (bulk body) manufactured using a mold.

In particular, the powder material according to the present embodiment contains not only tungsten carbide, but also cobalt, which has a lower melting point than tungsten carbide. Also, the plurality of primary particles that constitute the powder material are three-dimensionally bonded. As a result, cobalt melts first in the powder material, and the cobalt melt can spread over the surface of the tungsten carbide. Alternatively, tungsten carbide can be incorporated in a dispersed state within a matrix of molten tungsten carbide. This promotes melting of the tungsten carbide, making it possible to obtain a dense model. Alternatively, it is possible to obtain a dense shaped article in the form of a phase of tungsten carbide dispersed in a phase of cobalt.

(Average particle size)
The average particle size of the powder material (for example, granulated sintered powder) according to the present embodiment is not particularly limited, and can be set to a size suitable for the standard of the additive manufacturing apparatus to be used. For example, the average particle size of the powder material can be of a size suitable for feeding the powder material in additive manufacturing. The upper limit of the average particle size of the powder material is typically less than or equal to 200 μm, although it may be greater, for example, greater than 200 μm. The upper limit of the average particle size of the powder material is preferably 150 µm or less, more preferably 100 µm or less, and even more preferably 40 µm or less. As the powder material has a smaller average particle size, the packing of the powder material can improve, for example, in the build area. As a result, it is possible to suitably increase the density of the three-dimensional modeled object. In addition, it is possible to reduce the surface roughness (Ra) of the three-dimensional modeled object and to improve the dimensional accuracy.

Moreover, the lower limit of the average particle size of the powder material is not particularly limited as long as it does not affect the fluidity of the powder material. However, in consideration of handling when forming the powder material and fluidity of the powder material, the lower limit of the average particle size can be 1 μm or more, preferably 5 μm or more, and more preferably 10 μm or more. As the average particle size of the powder material increases, the fluidity of the powder material improves. As a result, it is possible to satisfactorily supply the powder material to the modeling apparatus, and the three-dimensional model to be produced has a good finish, which is preferable.

<Manufacturing method>
(Method for producing powder material)
As long as the powder material in the present embodiment contains the raw material particles of (1) to (3) above, the production method is not particularly limited. For example, as a preferred example, a case of producing a powder material by a granulation sintering method will be described below. However, the method of manufacturing the powder material disclosed herein is not limited to this.

The granulation sintering method is a method of sintering the individual raw material particles by granulating the powder containing the raw material particles of the above (1) to (3) into secondary particles and then firing the secondary particles. For granulation, various known granulation methods can be used as appropriate. For example, as a granulation method, a granulation method such as dry granulation or wet granulation can be used. Specific examples include tumbling granulation, fluid bed granulation, frame granulation, crushing granulation, melt granulation, spray granulation, and microemulsion granulation. A particularly suitable granulation method is the spray granulation method.

According to the spray granulation method, for example, a modeling material can be produced by the following procedure. That is, first, a powder (hereinafter also referred to as mixed powder) is prepared by blending the raw material particles of (1) to (3) at a predetermined mass ratio. If necessary, the surface is stabilized with a protective agent or the like. Then, the stabilized compounded powder is dispersed in an appropriate solvent together with, for example, a binder and optionally spacer particles made of an organic material or the like, to prepare a spray liquid. The dispersion of the raw material particles in the solvent can be carried out using, for example, a homogenizer, a mixer such as a blade stirrer, a disperser, or the like. As a result, the raw material particles (1) to (3) above are sprayed into an air stream using a spray granulator and dried. As a result, secondary particles in which the raw material particles of (1) to (3) are three-dimensionally bound by the binder can be obtained.

Next, the granulated secondary particles are fired to sinter the raw material particles (1) to (3) contained in the secondary particles. As a result, the raw material particles can be strongly bonded (sintered) to each other. In this granulation and sintering method, for example, granulated particles produced by the above granulation method are subjected to a sintering treatment. At this time, the granulated raw material particles are sintered at their mutual contact points, and are sintered while generally maintaining the granulated shape. The binder disappears during sintering. In systems using spacer particles, the spacer particles also disappear upon firing. This makes it possible to obtain a powder material composed of particles in the form of secondary particles in which the primary particles are sintered. In this powder material, the primary particles may have substantially the same size and shape as the raw material particles, or the raw material particles may be grown and combined by firing.

In the above manufacturing process, in the state of the granulated particles, the raw material particles and the binder are in a uniform mixed state, and the raw material particles are bound by the binder to form the mixed particles. In a system using spacer particles, raw material particles and spacer particles are uniformly mixed and bound together by a binder to form mixed particles. By firing the mixed particles, the binder (and spacer particles) disappears (burns out), and the raw material particles are sintered to form secondary particles in which the primary particles are bonded. It is formed.

During sintering, depending on the composition and size of the raw material particles, some of them may become liquid phase and contribute to bonding with other particles. Therefore, the average particle size of the primary particles may be larger than that of the raw material particles of the starting material. The size and ratio of the average particle sizes of these secondary particles and primary particles can be appropriately designed according to the desired form of the secondary particles.

In the manufacturing process described above, the concentration of the raw material particles in the spray liquid to be adjusted is preferably 10 to 40% by mass. Binders to be added include, for example, carboxymethyl cellulose, polyvinyl picolidone, polyvinyl picolidone and the like. The binder to be added is preferably adjusted at a ratio of 0.05 to 10% by mass with respect to the mass of the raw material particles. The sintering environment is not particularly limited, but it may be in the air, in a vacuum, or in an inert gas atmosphere, and sintering is preferably performed at a temperature of 600° C. or higher and 1600° C. or lower. In particular, when using spacer particles, a binder, etc., made of an organic material or the like, sintering may be performed in an atmosphere in which oxygen is present for the purpose of removing the organic material in the granulated particles. If necessary, the produced secondary particles may be pulverized and classified.

(Method for manufacturing three-dimensional model)
The powder material obtained as described above can be applied to various layered manufacturing (for example, LMD, SLM, EBM, etc.). As an example of a method for manufacturing a three-dimensional model, powder layered manufacturing will be described using a selective laser melting method (SLM) as an example. The manufacturing method of the three-dimensional structure disclosed here includes the following steps.
(A) A step of supplying a powder material (e.g., granulated sintered powder) to the stacking area of the layered manufacturing apparatus (B) Flattening the supplied powder material with a wiper or the like so as to deposit it uniformly and thinly on the stacking area Step (C): A step of solidifying the powder material by providing a means for bonding and sintering the powder material to the formed thin layer of the powder material (for example, by irradiating a laser beam). (D) A step of supplying a new powder material on top of the solidified powder material and stacking it by repeating the steps (B) to (D) after the step (A) to obtain a three-dimensional model (E ) A step of heat-treating the obtained three-dimensional model in a reduced-pressure atmosphere. The “solidification” of the step (D) includes directly bonding the secondary particles constituting the powder material by melting and solidification to fix the shape to a predetermined cross-sectional shape.

Laser Metal Deposition (LMD) is a technology that provides a powder material to the desired part of a structure, melts and solidifies the powder material by irradiating it with a laser beam, and builds up the part. is. By using this technology, for example, when physical deterioration such as wear occurs in a structure, a material that constitutes the structure or a reinforcing material is supplied as a powder material to the deteriorated part, and the powder By melting and solidifying the material, it is possible to build up the deteriorated portion.

Selective Laser Melting (SLM) is an operation to melt and solidify a powder layer into a desired shape by scanning a powder layer on which powder materials are deposited based on slice data created from a design drawing. This is a technique for forming a three-dimensional structure by repeatedly layering each cross section (slice data). In addition, the electrified beam melting method (EBM) is based on slice data created from 3D CAD data. It is a technology to form a structure that is flexible. Both techniques include a step of supplying a powder material, which is the raw material of the structure, to a predetermined modeling position.

FIG. 1 is a schematic diagram showing a configuration example of a layered modeling apparatus 100 for executing a method for manufacturing a modeled article according to an embodiment of the present invention. As shown in FIG. 1 , the layered manufacturing apparatus 100 includes a modeling area 10 that is a space in which layered modeling is performed, a stock 12 that stores powder materials, and a wiper that assists the supply of powder materials to the modeling area 10 . 11 and solidifying means (energy supplying means such as a laser oscillator) 13 for solidifying the powder material.

The modeling area 10 has a modeling space surrounded by an outer periphery below a modeling surface, and includes an elevating table 14 that can be raised and lowered in the modeling space. The elevating table 14 can be moved downward by a predetermined thickness Δt1, and a desired modeled object is formed on the elevating table 14.例文帳に追加The stock 12 is arranged beside the modeling area 10, and includes, for example, a bottom plate (elevating table) that can be raised and lowered by a cylinder or the like in a storage space whose outer periphery is surrounded. The stock 12 supplies (extrudes) a predetermined amount of powder material to the modeling surface by raising the bottom plate.

The layered manufacturing apparatus 100 can perform the above steps (A) to (D). For example, the layered manufacturing apparatus 100 prepares a layer of the powder material 20 having a predetermined thickness Δt1 by supplying the powder material 20 to the modeling area 10 with the elevation table 14 lowered from the modeling surface by a predetermined thickness Δt1.
Next, the layered manufacturing apparatus 100 scans the molding surface with the wiper 11 to supply the powder material extruded from the stock 12 onto the molding area 10 and flatten the upper surface of the powder material to form a homogeneous powder. A layer of material 20 is formed.
Next, the layered manufacturing apparatus 100 applies energy via the solidification means 13 only to the solidified region corresponding to the slice data of the first layer of the formed powder material 20 of the first layer. , the powder material is melted or sintered into a desired cross-sectional shape to form the first solidified powder layer 21 .

Next, the layered manufacturing apparatus 100 lowers the elevating table 14 by a predetermined thickness Δt1, supplies the powder material again, and smoothes it with the wiper 11 to form the powder material 20 of the second layer. Then, the layered manufacturing apparatus 100 applies a heat source through the solidification means 13 only to the solidified region corresponding to the slice data of the powder material 20 of the second layer to solidify the powder material, thereby solidifying the powder material of the second layer. A layer 21 is formed. At this time, the solidified powder layer 21 of the second layer and the solidified powder layer 21 of the first layer, which is the lower layer, are integrated to form a laminate up to the second layer.

Subsequently, the layered manufacturing apparatus 100 lowers the elevating table 14 by a predetermined thickness Δt1 to form a new layer of the powder material 20, applies a heat source through the solidification means 13, and forms a solidified powder layer 21 at a desired location. . The layered manufacturing apparatus 100 can manufacture a target three-dimensional model by repeating this process.
As a means for solidifying the powder material, a method of applying heat with a laser beam or an electron beam to melt and solidify (including sintering) the powder material is selected. For example, a carbon dioxide laser or a YAG laser can be preferably used.

In the method for manufacturing a three-dimensional structure according to the present embodiment, after the step (D), the process proceeds to the step (E). In the above step (E), heat treatment is applied to the three-dimensional modeled object. The temperature of the heat treatment (E) is, for example, 1200° C. or higher and 1500° C. or lower. The pressure of the heat treatment (E) is, for example, 1 Pa or more and 100 Pa or less. The three-dimensional structure is sintered and densified by the heat treatment (E).

Next, proceed to the step (F) above. The above (F) hot isostatic pressing (HIP) is a technique for pressurizing an object at high temperature and high pressure. In this embodiment, the object is a three-dimensional structure after undergoing the heat treatment of (E). For example, the three-dimensional structure after heat treatment is air-cooled to a temperature close to room temperature, and then subjected to HIP.

The HIP heating temperature is, for example, 1200° C. or higher and 1400° C. or lower, preferably 1300° C. or higher and 1400° C. or lower. The HIP pressure is sufficiently higher than the heat treatment pressure (E), and is, for example, 50 MPa or more and 180 MPa or less. The HIP processing time is, for example, 1 hour or more and 5 hours or less. HIP is performed, for example, in a state in which the three-dimensional structure is placed in an inert gas atmosphere such as argon (Ar).

In the three-dimensional structure after the heat treatment of (E), micropores remain in the WC—Co-based cemented carbide, and the strength tends to decrease. In this embodiment, micropores are reduced by performing HIP after the heat treatment (E). As a result, the three-dimensional structure is further densified and its strength is increased.

<Effects of Embodiment>
As described above, in the method for manufacturing a modeled object according to the embodiment of the present invention, a powder material for layered manufacturing containing tungsten carbide and cobalt is used to irradiate a laser beam or an electron beam to form a three-dimensional shape. The method includes a step of forming an object, a step of heat-treating the shaped object in a reduced-pressure atmosphere, and a step of subjecting the heat-treated shaped object to hot isostatic pressing. According to this, the three-dimensional structure sintered and densified by heat treatment is further densified by HIP to reduce micropores. As a result, it is possible to manufacture a three-dimensional modeled object that is dense and has high hardness. The reduced-pressure atmosphere is a pressure lower than the atmospheric pressure, and means, for example, a vacuum or a pressure close to a vacuum.

The powder material according to the embodiment of the present invention is a powder material for additive manufacturing, which is used for producing a three-dimensional shaped object by irradiating a laser beam or an electron beam, and is composed of tungsten carbide and cobalt. , titanium carbide, and the content of titanium carbide is 1% by mass or more and 20% by mass or less. According to this, titanium carbide (TiC) reacts with tungsten carbide (WC) to become tungsten titanium carbide (WTiC) when lamination manufacturing is performed using a laser beam or an electron beam. Since WTiC is part of the composition of the WC—Co based cemented carbide, it is possible to obtain a WC—Co based cemented carbide with higher hardness. Also, carbon (C) is supplied from the titanium carbide to the tungsten carbide when lamination manufacturing is performed using a laser beam or an electron beam. This makes it possible to obtain a WC—Co-based cemented carbide in which the formation of η phase (brittle phase) is suppressed.

In addition, in this embodiment, the powder material may not contain titanium carbide. In the method for manufacturing a modeled object according to the present embodiment, even if the powder material does not contain titanium carbide, the HIP described in (F) is performed after the heat treatment (E) described above, so that a dense and hard 3 modeled product can be obtained. Dimensional shaped objects can be manufactured.

The present invention will be described in more detail using the following examples and comparative examples. However, the technical scope of the present invention is not limited only to the following examples.
<Example 1>
(Method for producing powder material)
As raw material powders, tungsten carbide (WC) powder with an average particle size of 0.76 μm, cobalt (Co) powder with an average particle size of 1.30 μm, and titanium carbide (TiC) powder with an average particle size of 0.6 μm. prepared.
Each of the prepared raw material powders was blended at the ratio shown in Table 1 below to obtain a blended powder (in the form of primary particles). The resulting compounded powder was wet mixed and then granulated with a spray dryer. The obtained granulated powder was sintered to prepare a granulated sintered powder (in the form of secondary particles). The obtained granulated sintered powder was classified with a sieve having an opening of 25 μm. The average particle size, bulk density and granule strength of each granule obtained after classification were measured. Table 1 shows the average particle size, bulk density, granule strength, and chemical components of each granule after classification.

The "average particle size" of the primary particles includes the particle size at 50% of the integrated value in the volume-based particle size distribution measured by a particle size distribution measuring device based on the laser diffraction/scattering method (50% volume average particle size; D50 )It was adopted. For powders (tungsten carbide powders) with an average particle size of less than 1 μm, the value calculated as the diameter of spherical particles (equivalent sphere diameter) calculated from the specific surface area was adopted. The average particle diameter (Dave) of the primary particles can be obtained based on the formula: Dave=6/(ρSm), where Sm is the specific surface area of the raw material powder and ρ is the density. The specific surface area can be a value calculated by the BET method from the amount of adsorbed gas such as _N measured by a continuous flow method using a specific surface area measuring device (FlowSorb II 2300 manufactured by Micromeritics Inc.), for example. can. This specific surface area can be measured in accordance with "Method for measuring specific surface area of powder (solid) by gas adsorption" defined in JIS Z8830:2013 (ISO9277:2010).

The "average particle size" of the secondary particles includes the particle size at 50% of the integrated value in the volume-based particle size distribution measured by a particle size distribution measuring device based on the laser diffraction/scattering method (50% volume average particle size; D50 )It was adopted.
As the bulk density, a value measured according to the metal powder-apparent density measurement method specified in JIS Z2504:2012 was adopted. Specifically, the bulk density was calculated by measuring the mass of the powder when the powder naturally flowed out from the orifice with a diameter of 2.5 mm filled a container of a predetermined capacity in a state of natural filling. For the measurement of bulk density, a value measured using a JIS umbrella specific gravity meter for metal powder (manufactured by Tsutsui Rikagaku Kikai Co., Ltd.) was employed.

As the granule strength, the value of the breaking strength of granule particles measured using an electromagnetic force loading type compression tester was adopted. Specifically, for any 10 or more granulated sintered powders constituting the powder material, the arithmetic mean value of the breaking strength measured using a microcompression tester (manufactured by Shimadzu Corporation, MCT-500) , was taken as the granule strength. Regarding the granulated sintered powder, 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 sintered powder is It is calculated by the formula: σ=2.8×L/π/d2.

(Method of forming a three-dimensional object)
Using the above powder material, a laser beam is applied to the powder material laid flat by a layered modeling device (product name: ProX DMP200, manufactured by 3D System) to melt it layer by layer, and this process is repeated to create a three-dimensional manufactured a molding. At this time, the output was 300 W, the scanning speed was 300 mm/s, the pitch width was 0.1 mm, and the lamination thickness was 30 μm. After modeling, the relative density (%), Rockwell hardness (HRA), and transverse rupture strength (MPa) of the three-dimensional model were measured. This measured value is referred to as Comparative Example 1. Note that the relative density is an index indicating the state between the densest state and the more sparse state. Transverse rupture strength is a physical property value indicating strength against bending. Bending strength may also be referred to as bending strength.

Next, heat treatment was applied to the three-dimensional structure. The heat treatment conditions are a reduced pressure atmosphere (10 Pa), a heating temperature of 1500° C., and a heating time of 2 hours (continuous). After the heat treatment, the relative density (%), Rockwell hardness (HRA), and transverse rupture strength (MPa) of the three-dimensional structure were measured. This measured value is referred to as Comparative Example 2.
Next, hot isostatic pressing (HIP) was applied to the three-dimensional structure after the heat treatment. The HIP conditions are a pressurized argon (Ar) gas atmosphere (100 MPa), a heating temperature of 1380° C., and a heating time of 4 hours (continuous). After HIP, the relative density (%), Rockwell hardness (HRA), and transverse rupture strength (MPa) of the three-dimensional structure were measured. This measured value was used as the evaluation result of Example 1.
(evaluation)
Table 2 shows the evaluation results of Example 1 and Comparative Examples 1 and 2.

As shown in Table 2, it was confirmed that the Rockwell hardness decreased when the three-dimensional modeled product was heat-treated. Moreover, it was confirmed that the Rockwell hardness increased when the three-dimensional structure after heat treatment was subjected to HIP. It was confirmed that the three-dimensional modeled article after HIP (Example 1) has a higher Rockwell hardness than those after modeled and after heat treatment.
FIG. 2 is an SEM (Scanning Electron Microscope) image showing an enlarged cross section of the three-dimensional structure (Comparative Example 2) after heat treatment. FIG. 3 is an SEM image showing an enlarged cross section of the three-dimensional structure (Example 1) after HIP.

In FIGS. 2 and 3, white portions are tungsten carbide (WC) and black portions are cobalt (Co). The gray areas are tungsten titanium carbide (WTiC). As can be seen by comparing FIGS. 2 and 3, tungsten carbide exists in fibrous form in the three-dimensional model after heat treatment, whereas tungsten carbide exists in granular form in the three-dimensional model after HIP. are doing. Tungsten-titanium carbide is uniformly distributed in the three-dimensional model after HIP, and the overall hardness is high.

<Example 2>
(Method for producing powder material)
As raw material powders, tungsten carbide (WC) powder with an average particle size of 0.76 μm and cobalt (Co) powder with an average particle size of 6.72 μm were prepared. In Example 2, the only difference from Example 1 is that the powder material does not contain titanium carbide (TiC). The prepared raw material powders were blended at a ratio of 17% by mass of cobalt and 83% by mass of tungsten carbide to obtain blended powders (in the form of primary particles).
The subsequent steps are the same as in the first embodiment. That is, the obtained compounded powder was wet-mixed and then granulated with a spray dryer. The obtained granulated powder was sintered to prepare a granulated sintered powder (in the form of secondary particles). The obtained granulated sintered powder was classified with a sieve having an opening of 25 μm.

(Method of forming a three-dimensional object)
Using the above powder material, the powder material laid flat was irradiated with a laser beam by a lamination molding apparatus to melt layer by layer, and this process was repeated to manufacture a three-dimensional model. At this time, the output was 300 W, the scanning speed was 300 mm/s, the pitch width was 0.1 mm, and the lamination thickness was 30 μm. After modeling, the relative density (%), Rockwell hardness (HRA), and transverse rupture strength (MPa) of the three-dimensional model were measured. This measured value is referred to as Comparative Example 3.
Next, heat treatment was applied to the three-dimensional structure. The heat treatment conditions are a reduced pressure atmosphere (10 Pa), a heating temperature of 1500° C., and a heating time of 2 hours (continuous). After the heat treatment, the relative density (%), Rockwell hardness (HRA), and transverse rupture strength (MPa) of the three-dimensional structure were measured. This measured value is referred to as Comparative Example 4.

Next, hot isostatic pressing (HIP) was applied to the three-dimensional structure after the heat treatment. The HIP conditions are a pressurized atmosphere (100 MPa) of argon (Ar) gas, a heating temperature of 1380° C., and a heating time of 4 hours (continuous). After HIP, the relative density (%), Rockwell hardness (HRA), and transverse rupture strength (MPa) of the three-dimensional structure were measured. This measured value was used as the evaluation result of Example 2.
(evaluation)
Table 3 shows the evaluation results of Example 2 and Comparative Examples 3 and 4.

As shown in Table 3, even when the raw material powder contains tungsten carbide (WC) powder and cobalt (Co) powder but does not contain titanium carbide (TiC), HIP is applied to the three-dimensional model after heat treatment. It was confirmed that the Rockwell hardness was increased when the coating was applied. It was confirmed that the three-dimensional modeled article after HIP (Example 2) has a higher Rockwell hardness than those after modelling and heat treatment.
FIG. 4 is an SEM image showing an enlarged cross section of the three-dimensional structure (Example 2) after HIP. In FIG. 4, the white parts are tungsten carbide (WC) and the black parts are cobalt (Co). In Example 2, a large amount of tungsten carbide is uniformly distributed, and the overall hardness is high.

10 modeling area 11 wiper 12 stock 13 solidifying means 14 elevating table 20 powder material 21 powder solidified layer

Claims (6)

A step of forming a three-dimensional shaped object by sintering the powder material by irradiating it with a laser beam or an electron beam using a powder material for layered manufacturing containing tungsten carbide and cobalt;
a step of heat-treating the modeled object in a reduced-pressure atmosphere;
and a step of subjecting the heat-treated shaped article to hot isostatic pressing. The method of claim 1, wherein the powder material comprises titanium carbide. 3. The method of manufacturing a shaped article according to claim 2, wherein the content of said titanium carbide in said powder material is 1% by mass or more and 20% by mass or less. The method for manufacturing a shaped article according to any one of claims 1 to 3, wherein the heating temperature of the hot isostatic pressing is 1200°C or higher and 1400°C or lower. The method for manufacturing a modeled object according to any one of claims 1 to 4, wherein the pressurizing pressure in the hot isostatic press working is 50 MPa or more and 180 MPa or less. The method for manufacturing a modeled object according to any one of claims 1 to 5, wherein the processing time of the hot isostatic pressing is 1 hour or more and 5 hours or less.

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