JP7249811B2 - METHOD FOR MANUFACTURING METAL POWDER MATERIAL - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a metal powder material, and more particularly, to a method for producing a metal powder material suitable for producing a three-dimensional modeled object by irradiating an energy beam such as a laser beam in an additive manufacturing method. .

As a new technique for manufacturing a three-dimensional model, additive manufacturing (AM) has developed remarkably in recent years. As one type of additive manufacturing technology, there is an additive manufacturing method that utilizes the solidification of powder materials by irradiation with energy beams. As the layered manufacturing method using metal powder materials, there are two representative methods: a powder layered melting method and a powder deposition method.

Specific examples of the powder layered melting method include selective laser melting (SLM) and electron beam melting (EBM). In these methods, a metal powder material is supplied onto a base material to form a powder bed, and based on three-dimensional design data, a laser beam, an electron Irradiate energy rays such as rays. Then, the powder material in the irradiated portion solidifies by melting and re-solidifying to form a shaped body. A three-dimensional model is obtained by repeating the supply of the powder material to the powder bed and the modeling by the irradiation of the energy beam, and successively laminating the modeled body in layers.

On the other hand, a specific example of the powder deposition method is laser metal deposition (LMD). In this method, a metal powder is sprayed from a nozzle onto a position where a three-dimensional structure is to be formed, and a laser beam is simultaneously irradiated to form a three-dimensional structure having a desired shape.

When manufacturing a three-dimensional modeled object made of metal materials using the additive manufacturing method as described above, the resulting three-dimensional modeled object has a structure in which the distribution of constituent materials is uneven, such as voids and defects. There is It is desirable to suppress the generation of such a non-uniform structure as much as possible. For example, in Patent Document 1, in the SLM method or the like, when a metal powder layer is irradiated with an energy beam, a static magnetic field is applied perpendicularly to the surface of the metal powder layer. We are trying to reduce the defects that have occurred.

JP 2017-25401 A

In the production of a three-dimensional modeled object by the additive manufacturing method using a metal material, the cause of the uneven distribution of the constituent materials inside the three-dimensional modeled object is the energy described in Patent Document 1. There can be many factors in addition to the phenomenon that occurs when the radiation is applied. Among them, the state of the powder material before irradiation with the energy beam can also have a great influence on the state of the three-dimensional structure to be obtained.

For example, in the powder layered melting method, by smoothly supplying the powder material to the powder bed and stably forming the powder bed in which the powder material is evenly spread, it is easy to obtain a three-dimensional model with high homogeneity. In addition, the higher the density of the powder material in the powder bed, the less likely solidification shrinkage will occur in the three-dimensional structure obtained by irradiating the energy beam. Also in the powder deposition method, a three-dimensional structure can be stably formed by smoothly supplying the powder material without clogging the nozzle. Thus, in layered manufacturing using powder materials as raw materials, it is important to control the properties of the powder materials used.

The problem to be solved by the present invention is to provide a method for producing a metal powder material that can produce a metal powder material suitable for producing a three-dimensional model in the additive manufacturing method.

In order to solve the above problems, the method for producing a metal powder material according to the present invention includes a raw material production step of producing a raw material body composed of metal particles by an atomizing method, and mechanically aggregating the metal particles in the raw material body. and a disaggregation step of dissolving into , are performed in this order, and in the disaggregation step, the agglomerates of the metal particles are sheared by an air flow, and a shearing force is applied to the agglomerates by a forced vortex.

The metal particles are preferably made of titanium alloy, nickel alloy, cobalt alloy, or iron alloy.

In the method for producing a metal powder material according to the above invention, the raw material is produced by the atomization method, and the raw material contains a certain amount of aggregates (secondary particles) of metal particles. However, in the pulverization step, by eliminating the agglomeration of the metal particles in the agglomerate, the circularity of the constituent particles of the raw material can be increased.

As a result, the obtained metal powder material can be suitably used for layered manufacturing. That is, when forming the powder bed used in the powder layered melting method, the high fluidity of the metal powder material makes it possible to stably supply the metal powder material. Moreover, it becomes easy to form a powder bed with high uniformity. It also facilitates higher packing density in the powder bed. In the powder deposition method as well, the high fluidity of the metal powder material suppresses clogging of the nozzle, making it easier to stably form a model.

Here, the pulverization step is to shear the aggregates of the metal particles by the air flow, and by applying a shearing force to the aggregates by the forced vortex, the aggregation of the metal particles can be efficiently dissolved. can. In addition, the metal particles can be classified at the same time as or after the agglomeration is eliminated by using the same apparatus as that used for eliminating the agglomeration of the metal particles.

When the raw material is made of any one of titanium alloy, nickel alloy, cobalt alloy, and iron alloy, the metal powder material obtained by this manufacturing method is preferred over those alloys that are in great demand for manufacturing using the additive manufacturing method. It can be suitably used as a raw material for a three-dimensional structure.

(a) and (b) are diagrams for explaining the dropping of the powder material from the hopper, and the dropping of the powder material progresses in the order of (a) and (b). (c) is a diagram for explaining the spreading of the powder material. It is a figure explaining the pulverization process using a forced vortex type air classifier. It is a test result showing the particle size distribution and circularity of metal particles before pulverization (#1) and after pulverization (#2). It is a particle image for evaluation of particle shape, and (a) shows the state before pulverization and (b) shows the state after pulverization in the case of a particle size of 70 μm. It is an SEM image of metal particles, (a) shows the state before pulverization, and (b) shows the state after pulverization. It is a test result showing the effect of pulverization, (a) shows the evaluation result of the internal friction angle (φ), and (b) shows the evaluation result of the bulk density (ρ).

A method for producing a metal powder material according to one embodiment of the present invention will be described in detail below. A method for producing a metal powder material according to an embodiment of the present invention produces a powder material that can be used as a raw material for producing a three-dimensional modeled object by irradiating an energy beam in an additive manufacturing method.

[Outline of method for producing metal powder material]
In a method for producing a metal powder material according to an embodiment of the present invention, first, a raw material producing step of producing a raw material body composed of metal particles by an atomizing method is carried out. The manufactured raw material often contains agglomerates (secondary particles) in which metal particles, which are primary particles, are agglomerated. Particle agglomeration is mechanically resolved. By eliminating agglomeration in the pulverizing step, a metal powder material having a higher degree of circularity than the original raw material can be obtained.

A metal powder material composed of metal particles with a high degree of circularity manufactured in this way is more suitable for manufacturing a three-dimensional model by the additive manufacturing method than a metal powder material composed of a raw material itself with a low degree of circularity. It has characteristics suitable for Therefore, before describing in detail the manufacturing method of the metal powder material according to the present embodiment and the metal powder material obtained by the method, the properties required for the powder material for additive manufacturing will be described.

[Characteristics required for powder materials for additive manufacturing]
The inventors have clarified what characteristics are important in powder materials for stably manufacturing a three-dimensional modeled article by the layered manufacturing method and obtaining a three-dimensional modeled article of good quality.

Among the layered manufacturing methods, in the powder layered melting method such as the SLM method and the EBM method, as shown in FIG. form the floor. The obtained powder bed is irradiated with an energy beam such as a laser beam or an electron beam in a predetermined pattern, causing the powder material P to melt and re-solidify, thereby producing a model A. By alternately repeating the supply of the powder material P and the irradiation of the energy beam, the modeled object A can be laminated in layers to manufacture a three-dimensional modeled object.

As shown in FIGS. 1(a) and 1(b), the hopper 1 for supplying the powder material P has a cylindrical powder supply path 11 at the bottom of the container 10, and the powder material P filled in the container 10. is forced out of the powder feed channel 11 by gravity and fed for powder bed formation. At this time, it is important to stably flow out the powder material P from the hopper 1 in order to stably form a highly uniform powder bed.

Several processes are involved in the outflow of the powdered material P from the hopper 1 . First, at the initial stage of outflow, as shown in FIG. 1(a), the powder material P positioned directly above the shaded powder supply path 11 flows from the container 10 filled with the powder material P into the empty powder. It falls toward the supply channel 11 (movement M1).

In the hopper 1, when the powder material P positioned directly above the powder supply path 11 drops, a gap is generated in the area occupied by the dropped powder material P, as shown in FIG. 1(b). Then, the surrounding powder material P crumbles toward the gap and fills the gap (movement M2). At this time, the filling of the voids and subsequent dropping of the powder material P proceeds stably and with high uniformity when the surrounding powder material P is more likely to crumble. An internal friction angle (φ) can be used as an index indicating how easily the powder material P collapses.

The internal friction angle (φ) is the coefficient of proportionality to the applied pressure of the shear stress generated in the direction that intersects the pressure when pressure is applied to the powder material P, and is expressed by the friction angle. , indicates that the aggregate of the powder material P is likely to crumble and spread. That is, the smaller the internal friction angle (φ), the easier it is for the powder material P to collapse and fill the voids generated in the hopper 1 . The internal friction angle (φ) is obtained by, for example, measuring the shear stress (τ) generated when a pressure (σ) is applied to the powder material P, and plotting σ on the horizontal axis and τ on the vertical axis. It can be obtained as the angle of the approximate straight line with respect to the axis (tan φ=τ/σ). The internal friction angle (φ) is, for example, preferably 22° or less, more preferably 18° or less. The angle of repose can be substituted for the angle of internal friction (φ).

Then, powder is supplied by dropping (motion M1) of the powder material P positioned directly above the powder supply path 11 shown in FIG. When the powder material P is supplied to the path 11, the powder material P flows out of the hopper 1 through the powder supply path 11 (movement M3). The higher the flow rate (FR) of the powder material P at this time, the higher the fluidity of the powder material P, and the more the powder material P can flow stably. The flow velocity (FR) of the powder material P is a quantity having a strong correlation with the internal friction angle (φ) described above, and the smaller the internal friction angle (φ), the larger the flow velocity (FR) tends to be. There is

As described above, in the powder material P, the smaller the internal friction angle (φ), the more excellent the fluidity of the powder material P, and the more stable the supply of the powder material P from the hopper 1 to the powder bed. Moreover, it can be advanced with high uniformity. As a result, the powder bed can be stably formed in layered manufacturing by the powder layered melting method.

The powder material P supplied from the hopper 1 onto the base material 2 is smoothed by a recoater (blade) 3 and spread over the base material 2 and the already formed lower-layer shaped body A. is considered a powder bed. At this time, the distribution of the powder material P is made uniform by sweeping the recoater 3 horizontally over the surface of the substrate 2 (movement M4) so as to spread the powder material P dropped from the hopper 1 . In order to easily disperse the powder material supplied from the hopper 1 onto the base material 2 and onto the model A, and to facilitate spreading of the powder material P by the recoater 3, the powder material P It is preferable that the aggregate is easily collapsed (Movement M5). As explained above, when the internal friction angle (φ) is small, the powder material P is likely to crumble, making it easier to form a highly uniform powder bed.

In addition, in the powder bed on which the powder material P is spread, the more densely the powder material P is filled, the easier it is to form a homogeneous three-dimensional model through the irradiation of the energy rays. This is because when the powder material P is melted by the irradiation of the energy beam and re-solidified, deformation due to solidification shrinkage and defects due to residual gas are less likely to occur. As the powder material P, the higher the bulk density (ρ) is used, the more densely the powder material P can be packed in the powder bed. The bulk density (ρ) is preferably 2.5 g/cm ³ or more. The bulk density (ρ) may be measured using, for example, a known density measuring instrument. In this specification, apparent density (AD) is assumed as bulk density, but tap density (TD) may be used as an index instead. As another index, a filling rate (%) that indicates the proportion of particles in the bulk volume of the granular material layer can be used. In this case, the filling rate is preferably 55% or more.

As described above, by using the powder material P that has a small internal friction angle (φ) and is easily crumbled, a highly uniform powder bed can be formed from the powder material P supplied from the hopper 1. . Further, by using a powder material P having a large bulk density (ρ), it is possible to improve the homogeneity of the three-dimensional structure to be manufactured. As described above, in combination with the effect of using the powder material P that can be stably discharged from the hopper 1 with high uniformity, in the layered manufacturing by the powder layered melting method, the entire layered manufacturing process can be stably performed. You can proceed smoothly. In addition, it becomes easier to obtain a three-dimensional model of good quality.

Even in layered manufacturing by a powder deposition method such as the LMD method, by using the powder material P having excellent fluidity as described above, the step of supplying the powder material P to the nozzle can be stably executed. can. Furthermore, even in the process of injecting the powder material P from the nozzle toward the part to be modeled along with the airflow, blockage of the nozzle can be suppressed and the model can be stably advanced.

[Means for improving properties of metal powder material]
Next, the means for improving the properties of the metal powder material so as to be suitable for additive manufacturing as described above, that is, the means for increasing the fluidity and bulk density of the metal powder material will be described.

The shape of the metal particles that make up the metal powder material has a great effect on the fluidity and filling properties of the metal powder material. If the metal particles have a shape close to a sphere with high symmetry, the internal friction angle (φ) in the metal powder material becomes smaller due to the effect of the shape. As a result, the easiness of collapsing of the aggregate of the metal powder material is improved, and the fluidity of the metal powder material is increased. As a result, in layered manufacturing, the metal powder material can be stably discharged from the hopper or the like, and the metal powder material can be easily spread as a powder bed. Moreover, when the metal particles have a shape close to a sphere, the metal particles can be densely packed due to the effect of the shape, and the bulk density (ρ) of the metal powder material increases. As a result, it is possible to form a dense powder bed and improve the quality of the three-dimensional structure.

From the viewpoint of sufficiently obtaining the effects as described above, the circularity of the metal particles is preferably 0.80 or more at least in a region smaller than the average particle diameter. Its circularity is more preferably 0.85 or more, more preferably 0.90 or more. Here, the degree of circularity of a metal particle is an index indicating the degree of proximity to a perfect circle of a two-dimensional figure (projection figure) obtained by projecting the three-dimensional shape of the metal particle onto a plane.

The circularity of the metal particles can be calculated as [perimeter of a circle having the same area as the projected figure]/[total length of contour of the projected figure]. When the metal particles are perfectly spherical, that is, when the projected figure is a perfect circle, the degree of circularity is 1. Analysis of the degree of circularity may be performed based on microscopic images obtained by an optical microscope, an electron microscope (SEM), or the like. The above circularity is preferably obtained as an average value of a statistically sufficient number of metal particles whose particle diameter can be regarded as equal to the average particle diameter. For example, it is preferable to analyze the circularity of metal particles having a particle size in the range of ±5 μm around a certain particle size, and adopt the average value as the circularity for that particle size. When the metal particles are agglomerated by attractive force, the circularity of the agglomerates (secondary particles) as a whole is evaluated.

Increasing the circularity of the metal particles contributes to the improvement of the fluidity of the metal powder material not only by the effect of the height of the circularity itself but also by reducing the amount of water adsorption. This is because the higher the degree of circularity, the smaller the specific surface area of the metal particles, and the smaller the area where water can be adsorbed. As a result, the attractive force acting between the metal particles can be reduced by the liquid bridge via water, and the shear adhesion force between the metal particles can be reduced.

[Details of manufacturing method of metal powder material]
Here, the details of the method for producing a metal powder material according to one embodiment of the present invention will be described. As described above, in the method for producing a metal powder material according to the present embodiment, the fluidity and bulk density of the metal powder material are increased by performing the pulverization step on the raw material body produced in the raw material preparation step. be able to.

(1) Raw Material Preparing Step First, it is necessary to prepare a raw material, which is the raw material of the metal powder material. The raw material is made of metal particles. Some of the metal particles may be aggregated by mutual attraction to form aggregates (secondary particles). It is preferable that the metal particles, which are the primary particles, mainly consist of particles having a particle size on the order of microns, for example, an average particle size (D50) of 10 μm or more. Here, the particle size with an average particle size of 10 μm or more is based on the particle size of metal particles generally employed as a raw material for layered manufacturing.

The raw material body is a constituent material of the three-dimensional modeled article, and is made of a metal material having a component composition desired for the three-dimensional modeled article. The type of metal material is not particularly limited, but suitable examples include titanium alloys, nickel alloys, cobalt alloys, and iron alloys. This is because there is a great demand for manufacturing a three-dimensional modeled object using these alloys as raw materials by the additive manufacturing method. In particular, titanium alloys and nickel alloys are in great demand for members having special shapes that are difficult to manufacture by other processing methods. Examples of titanium alloys include Ti-Al alloys such as Ti-6Al-4V alloy. Examples of nickel alloys include Inconel (registered trademark). Moreover, various tool steels can be exemplified as iron alloys.

The raw material is manufactured by the atomizing method. In the atomization method, fine metal particles are obtained by solidifying a molten alloy in the form of fine droplets. Specifically, the gas atomization method generates minute droplets by injecting molten alloy into a vacuum and blowing an inert gas onto the injected molten alloy. , a disc atomization method that generates fine droplets by centrifugal force can be applied. In the atomization method, metal particles having a particle size on the order of microns can be efficiently obtained. Also, the atomization method can be applied to various alloy compositions. In particular, the gas atomization method is suitable from the viewpoint of production efficiency of metal particles, simplicity, and the like.

(2) Cracking Step In the raw material obtained by the atomization method, the circularity of the metal particles as primary particles is relatively high. However, these metal particles tend to agglomerate, and the circularity of the entire raw material containing the agglomerated structure is low. Therefore, by subjecting the raw material obtained by the atomizing method to a pulverizing step, the agglomeration is eliminated and the circularity of the raw material as a whole is increased.

In the pulverization step, agglomeration of metal particles in the raw material is mechanically dissolved. That is, by applying a physical stimulus to the agglomerate with a solid substance, a fluid substance, or the like, the mutually agglomerated metal particles are separated. The details of the disaggregation process are to sufficiently eliminate the agglomeration of the metal particles, while suppressing the impact on the metal particles themselves as primary particles, that is, the pulverization and damage of the metal particles themselves to the extent that they can be ignored for the elimination of agglomeration. It is not particularly limited as long as it can be used. Typical pulverization methods include shearing of aggregates by air flow and pulverization of aggregates by collision with an impactor.

(Shearing of aggregates by air flow)
In the case of shearing aggregates by air flow, shear flow is generated in the gaseous substance and the raw material is introduced into it. Then, the shear flow eliminates the shear adhesion between the metal particles. Shear flow can be generated, for example, by forced eddies. By arranging two plates facing each other in parallel and rotating one plate against the other at high speed about an axis perpendicular to the plate surface, centrifugal force creates a gap between the two plates. Shear flow occurs in the flowing fluid. In this state, a raw material containing agglomerates of metal particles is passed through the space between the plate members together with a gas such as an inert gas, whereby a shearing force is applied to the agglomerates and the agglomerates are sheared.

A forced vortex type air classifier can be given as a specific example of a device capable of shearing aggregates using shear flow. As the forced vortex type air classifier, for example, the one disclosed in Japanese Patent Application Laid-Open No. 2003-145052 can be used. FIG. 2 shows a schematic cross section of the configuration of such a forced vortex air classifier 5. As shown in FIG. The classifier 5 is provided with a casing 51 and a rotor 52 which is accommodated in the casing 51 and rotates about the rotation axis R at high speed. Blades 53 are provided on the upper plate 52 a of the rotor 52 facing the inner surface of the upper plate 51 a of the casing 51 .

When the rotor 52 is rotated, a shear flow is generated in the gap between the upper plate 51 a of the casing 51 and the upper plate 52 a of the rotor 52 and the blades 53 . When the raw material M obtained by the atomizing method in the raw material manufacturing process is introduced from the powder inlet 54, the raw material M undergoes pulverization while passing through the gap (movement m1). The raw material M has a structure in which a plurality of metal particles P1 having a particle size desired to be finally collected as a metal powder material are agglomerated, or has a particle size smaller than such metal particles P1 and is finally removed. It includes a structure in which the desired fine particles P2 are attached to the metal particles P1, but undergoes fragmentation due to shear flow, and the multiple aggregated metal particles P1 are separated from each other, and the fine particles P2 are separated from the metal particles P1. In this manner, a metal powder material P in which the metal particles P1 are separated from other metal particles P1 and fine particles P2 can be obtained.

As the name suggests, the forced vortex air classifier 5 is originally used for classifying powder. During the passage (movement m1') it undergoes classification, ie fractionation according to particle size. The blades 53 provided on the upper plate 52a of the rotor 52 are originally intended to spatially disperse the powder introduced from the powder inlet 54 as a pre-classification stage. However, by adjusting the operating conditions such as the speed of the airflow for introducing the powder and the rotation speed of the rotor 52, it can be used for breaking up the raw material M produced by the atomization method as described above. .

Furthermore, as described above, since the forced vortex type air classifier 5 is a device capable of classifying powder, it is also possible to perform pulverization and classification of the raw material M in a single operation. That is, the particles pulverized in the space between the upper plate 51a of the casing 51 and the upper plate 52a of the rotor 52 and the blades 53 provided thereon are put on the airflow as they are, and passed through the classifying blades 55a and 55b to the rotor. It can be introduced into the cavity 52b of 52 and classified (movement m1'). Due to differences in operating conditions of the classifier 5 between pulverization and classification, even if they are not performed in one operation, they can be performed using the same apparatus.

As described above, when the disaggregation process is carried out by shearing aggregates by air flow using a forced vortex air classifier or the like, the metal powder material obtained contains Since the agglomeration of the agglomerates is eliminated, the circularity of the constituent particles is higher than that of the raw material. For example, by pulverization, the circularity of the metal powder material after pulverization can be improved to 1.1 times or more, or 1.2 times or more, that of the raw material before pulverization. Here, since the elimination of agglomeration by pulverization is performed mechanically, while avoiding the denaturation of metal particles that may occur when using a chemical method or a thermal method, a simple apparatus can be used to obtain circular particles. degree improvement can be made.

The pulverization process may be carried out by either shearing by air flow or pulverization by impact. Since the shearing by airflow is due to the dispersing mechanism, it is preferable to use the shearing by airflow from the viewpoint that the pulverizing device can be used in common with the classification device. On the other hand, from the viewpoint of the efficiency of pulverization and the simplicity of the apparatus, it is preferable to use pulverization by collision. Both methods of pulverization can also be used together. By using them together, the certainty of pulverization can be enhanced. In that case, it is preferable to crush the aggregates by collision and then shear the aggregates by air flow. This is because, as described above, classification can be performed by the same device as used for shearing, such as a forced vortex type air classifier.

In addition, after the raw material manufacturing process and/or after the pulverization process, the particle groups may be appropriately classified. Classification can be performed by airflow classification or sieve classification. By performing classification, relatively large-diameter metal particles P1 having a desired particle size as a metal powder material are separated from smaller-diameter fine particles P2 and agglomerates remaining without being sufficiently pulverized. can be separated. Among the metal particles P1, those having a particle size within a desired narrow range can be fractionated. As described above, when the classification is performed after the crushing process, especially when the crushing is performed using a forced vortex air classifier, the same equipment as in the crushing process is used, simultaneously with or after the crushing process. , can be classified. Further, chemical treatment or the like may be applied to the raw material body after the raw material manufacturing process or the metal powder material after the pulverizing process. Further, the obtained metal powder material may be appropriately mixed with another kind of powder material or the like and used for lamination molding.

[Metal powder material to be manufactured]
As described above, the metal powder material produced through pulverization of the raw material consists essentially of metal particles having the same composition and primary particle size as those of the raw material. The agglomerated structure is eliminated, and the degree of circularity is higher than that of the raw material. That is, it is composed of particles having a more symmetrical shape and a smoother surface than the raw material. The average particle size of the metal particles after pulverization is preferably 10 μm or more from the viewpoint of suitability as a raw material for layered manufacturing. Furthermore, the average particle size is preferably in the range of 30 μm or more to 80 μm or less. As described above, the circularity of the metal particles is preferably 0.80 or more, more preferably 0.85 or more, or 0.90 or more, at least in a region smaller than the average particle diameter.

In the manufacturing method according to the present embodiment, the raw material body is subjected to a pulverization step to obtain a metal powder material with improved circularity, so that the internal friction angle (φ) is greater than that of the original raw material body. become smaller. Also, the bulk density (ρ) increases. As a result, the ease of crumbling of the metal powder material is improved, thereby improving the fluidity. In addition, the fillability of the metal powder material is also improved. In this way, by using a metal powder material with excellent fluidity and filling properties in the additive manufacturing method, the metal powder material can be uniformly and stably supplied and spread when forming a powder bed. can be done. The packing density of the powder bed is increased, and the homogeneity of the three-dimensional structure obtained is also improved. For example, by pulverizing the raw material body, the internal friction angle (φ) can be reduced to 80% or less of the initial value in terms of tanφ. On the other hand, the bulk density (ρ) can be increased by 1.2 times or more.

EXAMPLES The present invention will be described in more detail below using examples. Here, tests were conducted on the state and characteristics of the metal powder material obtained by subjecting the raw material to the pulverization process.

(Preparation of sample)
Metal particles made of Ti-6Al-4V alloy (alloy containing 6% by mass of Al and 4% by mass of V, with the balance being Ti and unavoidable impurities; Ti-64) were prepared by gas atomization. Then, classification was performed at 45/105 μm to prepare sample #1.

In addition, the metal particles prepared by the gas atomization method were also pulverized using a forced vortex type air classifier. Then, using the same device, classification was performed at 45/105 μm to prepare sample #2.

(Evaluation of state and properties of metal particles)
First, each of sample #1 and sample #2 was evaluated for particle shape using a particle image analyzer. Then, based on the particle shape, the particle size distribution was evaluated, and the circularity was measured for each 10 μm particle size.

Then, the internal friction angle (φ) and bulk density (ρ) were evaluated for each of sample #1 and sample #2. The internal friction angle (φ) is measured in accordance with JIS Z 8835 using a rotating cell type shear tester to measure the shear stress (τ) generated when pressure (σ) is applied to the powder material. I went by Plotting σ on the horizontal axis and τ on the vertical axis, the slope of the approximation straight line was set to tanφ, and the internal friction angle (φ) was obtained. In addition, the bulk density (ρ) was measured using a metal powder bulk specific gravity meter in accordance with JIS Z 2504. Each measurement was performed under conditions of an air temperature of 23° C. and a relative humidity of 26% RH.

(Evaluation results)
<State of metal particles>
FIG. 3 shows the particle size distribution of sample #1 (before pulverization) and sample #2 (after pulverization) (indicated by solid and broken lines). It shows that sample #1 and sample #2 have similar particle size distributions in median and width. In addition, Table 1 below shows parameters related to the particle size distribution. Each of these parameters also has a similar value between sample #1 and sample #2. In other words, the desired particle size distribution was obtained for both samples #1 and #2 by classification. It is confirmed that it is not due to

FIG. 4 shows an example of a particle image obtained for a particle size of 70±5 μm. (a) shows the observation results of the sample #1, and (b) shows the observation results of the sample #2. Looking at those images, most of the particles in sample #1 have distorted shapes that deviate greatly from circular shapes. Among them, there are many particle shapes in which small-diameter particles adhere to large-diameter particles. In contrast, in sample #2, all particles have a shape that is fairly close to circular.

Further, based on the particle images in FIG. 4, the circularity of the metal particles was calculated and averaged to 0.71 for sample #1. On the other hand, a numerical value close to 1, which is 0.91, was obtained for sample #2.

Similar to the evaluation of the circularity corresponding to the particle size of 70 μm based on the particle image in FIG. The evaluation results are shown in FIG. 3 together with the particle size distribution (indicated by plotted points and straight lines). According to FIG. 3, the circularity of sample #2 is higher than that of sample #1 for all grain sizes. In both samples #1 and #2, the degree of circularity is high, especially on the small diameter side, but sample #2 has a wider range of particle diameters with high degree of circularity.

From the above evaluation results, it can be seen that the circularity of sample #2, which has undergone pulverization, is significantly higher than that of sample #1, which has undergone only classification, and metal particles that are nearly spherical are obtained. . In other words, by pulverization, the circularity of the metal particles can be increased, and the metal particles can be made to have a nearly spherical shape.

Furthermore, FIG. 5 shows the results of SEM observation of metal particles. In FIG. 5(a), the particles of sample #1 are shown. It can be seen that a large number of small particles having a diameter of about 10 μm or less adhere to the surface of large particles having a diameter of several tens of μm. Aggregates of these large-diameter particles and small-diameter particles correspond to the distorted particle image with low circularity obtained in FIG. 4(a).

On the other hand, in FIG. 5(b), in which the particles of sample #2 were observed at the same magnification, the proportion of aggregates in which smaller particles adhered to the surface of particles several tens of μm in diameter was small. It's becoming In other words, it can be seen that in sample #2, the agglomeration of the metal particles is eliminated and the symmetry of the shape of the particles as a whole is improved by undergoing pulverization. This agrees with the circularity analysis result shown in FIG. 3 and the particle image in FIG.

<Characteristics of metal powder material>
FIG. 6(a) shows the measurement results of the internal friction angle (φ). According to this, the internal friction angle (φ) in sample #2, which has undergone pulverization, is 80% or less in terms of tanφ compared to sample #1, which has undergone only classification.

Furthermore, FIG. 6(b) shows the measurement results of the bulk density (ρ). According to this, the bulk density (ρ) of the sample #2 that has undergone pulverization is 1.2 times greater than that of the sample #1 that has undergone only classification.

As described above, by pulverizing the raw material obtained by the atomization method, the internal friction angle (φ) of the metal powder material is decreased and the bulk density (ρ) is increased. All of these are due to the improved circularity of the constituent particles.

The embodiments and examples of the present invention have been described above. The present invention is not particularly limited to these embodiments and examples, and various modifications are possible.

1 Hopper 10 Container 11 Powder Supply Path 2 Substrate 3 Recoater 5 Forced Vortex Air Classifier A Modeled Body M Raw Material P Powder Material P1 Metal Particle P2 Fine Particles

Claims (7)

a raw material manufacturing step of manufacturing a raw material body composed of metal particles by an atomizing method;
and a pulverization step of mechanically eliminating agglomeration of the metal particles in the raw material, and
In the pulverization step, the agglomerates of the metal particles are sheared by an air flow, and a shearing force is applied to the agglomerates by a forced vortex ,
A method for producing a metal powder material , wherein the circularity of the metal particles is increased by 1.1 times or more by the pulverizing step . 2. The method of manufacturing a metal powder material according to claim 1, wherein the metal particles are made of one of titanium alloy, nickel alloy, cobalt alloy and iron alloy. 3. The method for producing a metal powder material according to claim 1, wherein the bulk density of the metal powder material composed of the metal particles is increased by 1.2 times or more by the pulverizing step. 4. The pulverization step reduces the internal friction angle φ of the metal powder material made of the metal particles to 80% or less in tan φ. A method for producing a metal powder material. After performing the pulverization step with a forced vortex air classifier,
5. The production of the metal powder material according to any one of claims 1 to 4, wherein the metal particles are classified using the same forced vortex air classifier used in the pulverization step. Method. 6. The method for producing a metal powder material according to any one of claims 1 to 5, wherein the pulverization step improves the circularity of the metal particles by 1.2 times or more. 7. The method according to any one of claims 1 to 6, wherein the circularity of the metal particles becomes 0.90 or more at least in a region smaller than the average particle diameter by the pulverizing step. A method for producing the described metal powder material.

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