JP2020105067A - Silicon carbide-containing article and method for producing the same - Google Patents

Abstract

To provide an article composed mainly of silicon carbide that has a sufficient mechanical strength while being produced by using the three-dimensional modeling technology.SOLUTION: An article, which comprises silicon carbide as main component, includes a metal boride having a melting point lower than the sublimation point of silicon carbide, and metallic silicon.SELECTED DRAWING: Figure 1

Description

The present invention relates to an article using a silicon carbide-based material having material characteristics such as high heat resistance, high heat conduction, and lightweight and high rigidity, particularly an article manufactured by a powder bed fusion bonding method which is an additive molding method, and manufacturing thereof. It is about the method.

Development of a three-dimensional modeling technique using a powder bed fusion bonding method is under way in order to produce a small number of various kinds and a metal part having a complicated shape. In this technique, a layer of powdered modeling material is scanned with an energy beam based on slice data generated from three-dimensional shape data of a modeling target, and the step of locally melting/solidifying the modeling material is performed in a plurality of layers. Is repeated to form a three-dimensional object. A laser beam, an electron beam, or the like is used as the energy beam.

Further, in recent years, using such a three-dimensional modeling technique, modeling of a ceramic material such as silicon carbide, which is difficult to process, has been studied. However, many ceramics such as carbides, borides, and nitrides do not melt but sublimate when rapidly given energy, or they become brittle without being crystallized during melting and solidification. There are technical challenges. Silicon carbide, which has excellent lightness, abrasion resistance, thermal shock resistance, chemical stability, etc. and is expected to be used in a wide range of fields, has no melting point at normal pressure and has a melting point of around 2545°C (temperature value of 2700°C, etc.). It is a material that will be sublimated under various theories). Patent Document 1 discloses a candidate of a powder that can be formed by utilizing transient liquid phase sintering such as eutectic or peritectic. As a powder candidate for forming a shaped article made of silicon carbide, a mixture of silicon carbide, aluminum oxide, a rare earth oxide and silica, a mixture of silicon carbide, aluminum nitride and a rare earth oxide, and a mixture of silicon carbide and metal germanium are exemplified. Has been done.

Japanese Patent Publication No. 2016-527161

The powder described in Patent Document 1 uses silica, aluminum nitride, or metal germanium as an essential material as a material mixed with silicon carbide to form a eutectic. However, silica decomposes into silicon monoxide and oxygen at 1900°C. Also, aluminum nitride sublimes at 2200°C. Even when germanium metal is heated at the same time as silicon carbide having a sublimation point of 2545° C. such as boiling at 2400° C. or less, it is highly likely that the silicon carbide is volatilized before melting. Moreover, although there is no disclosure about the strength of the shaped article, it is presumed that a shaped article having a low strength, in which the powders are partially bonded, will be formed.

The object of the present disclosure has been made in view of the above problems, and is to provide a shaped product containing silicon carbide as a main component, which has sufficient mechanical strength while being manufactured using a three-dimensional shaping technique. Moreover, it is providing the manufacturing method of such a molded article.

The article according to the present disclosure is characterized by containing silicon carbide, metal boride having a melting point lower than the sublimation point of silicon carbide, and metal silicon.

Further, in the method for manufacturing an article according to the present disclosure, a powder layer is formed by using a powder in which a powder containing silicon carbide and a powder containing metal boride having a melting point lower than the sublimation point of silicon carbide are mixed. And the step of melting and solidifying the powder by irradiating the formed powder layer with an energy beam based on the shape data of the object to be shaped and irradiating the shaped object And forming a formed article, and further impregnating the formed article with metallic silicon.

According to the features of the present invention described above, it is possible to provide a shaped article containing silicon carbide as a main component, which has sufficient mechanical strength while being manufactured by using the three-dimensional shaping technique.

It is a schematic diagram of the three-dimensional modeling apparatus used by the manufacturing method of this indication. It is a figure which shows the state at the time of impregnating a molded article with metallic silicon. It is a schematic diagram of the modeling thing created in the example of this indication. 3 is a SEM image of a cross section of Sample 1 manufactured according to the present disclosure. FIG. 5 is a diagram showing a three-dimensional structure in which only dark-colored regions in the cross-sectional SEM image of FIG. 4 are connected. It is a figure which shows the three-dimensional structure which joined only the light-colored area|region in the cross-section SEM image of FIG. 3 is an optical microscope image of a cross section of Sample 1 manufactured according to the present disclosure. 7 is a SEM image of a cross section of Sample 6 manufactured according to the present disclosure. 5 is an optical microscope image of a cross section of Sample 6 manufactured according to the present disclosure.

Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.

First, a modeling apparatus applicable to the manufacturing method of the present disclosure will be described with reference to FIG. 1. The modeling apparatus has a chamber 101 whose internal atmosphere can be controlled by a gas introduction mechanism 113 and an exhaust mechanism 114. Inside the chamber 101, a modeling container 120 for modeling a three-dimensional object, and a powder as a modeling material (hereinafter sometimes simply referred to as “modeling material” or “powder”) are spread over the modeling container 120. And a powder layer forming mechanism 106 for forming the powder layer 111.

The exhaust mechanism 114 may be provided with a pressure adjusting mechanism such as a butterfly valve in order to adjust the pressure, and is configured to adjust the atmosphere in the chamber due to the gas supply and the accompanying pressure rise (generally, blow replacement). Called).

The bottom of the modeling container 120 is configured by a modeling stage 107 whose position in the vertical direction can be changed by the elevating mechanism 108. The moving direction and the moving amount of the elevating mechanism 108 are controlled by a controller (not shown), and the moving amount of the modeling stage 107 is determined according to the layer thickness of the powder layer 111 to be formed. A structure (not shown) for installing the base plate 109 is provided on the modeling surface side of the modeling stage 107. The base plate 109 is a plate made of a meltable material such as stainless steel. When the first powder layer is melted and solidified, the surface of the base plate 109 is melted together with the molding material, and the molded object can be fixed to the base plate. Therefore, the position of the modeled object on the base plate 109 can be held so as not to shift during modeling. After the modeling is complete, the base plate 109 is mechanically separated from the modeled object.

The powder layer forming mechanism 106 has a powder container for containing the powder material and a supply mechanism for supplying the powder material to the modeling container 120. Further, either one or both of a squeegee and a roller for leveling the powder layer to a set thickness may be provided on the base plate 109.

The modeling apparatus further includes an energy beam source 102 for melting the modeling material, scanning mirrors 103A and 103B for scanning the energy beam 112 in two axes, and an optical system for condensing the energy beam on the irradiation section. It is equipped with 104. Since the energy beam 112 is irradiated from the outside of the chamber 101, the chamber 101 is provided with an introduction window 105 for introducing the energy beam 112 into the inside. The power density and the scanning position of the energy beam are controlled by the control unit according to the three-dimensional shape data of the modeling target and the characteristics of the modeling material acquired by the control unit (not shown). In addition, the positions of the modeling container 120 and the optical system 104 are adjusted in advance so that the beam diameter becomes an appropriate size by focusing near the surface of the powder layer 111. Since the beam diameter on the surface affects the modeling accuracy, it is preferably 30 to 100 μm.

Next, the manufacturing method of the present disclosure will be described. First, the base plate 109 is installed on the stage 107, and the inside of the chamber 101 is replaced with an inert gas such as nitrogen or argon introduced through the gas introduction mechanism 113. When the replacement is completed, the powder layer forming mechanism 106 forms the powder layer 111 on the base plate 109. The powder layer 111 is formed with a slice pitch of the slice data generated from the three-dimensional shape data of the modeling target, that is, a thickness corresponding to the stacking pitch.

The powder used for modeling in the present disclosure is mainly composed of powder of silicon carbide, and is a mixed powder with powder of metal boride having a melting point lower than the sublimation point of silicon carbide. It should be noted that powders of compounds other than the above may be included as long as the characteristics of silicon carbide are not significantly impaired. If the size of the powder particles of silicon carbide and metal boride is too small, the powder particles cannot be aggregated to form a powder layer having a uniform thickness, and if the size is too large, high energy is required to melt the powder layer, which makes modeling difficult. Therefore, a particle size of 3 μm to 100 μm is preferable, and a particle size of 5 μm to 50 μm is more preferable. Further, the thickness of each powder layer affects the modeling accuracy, and is therefore preferably about 30 to 100 μm.

Here, a method of measuring the particle size of the powder in the present disclosure will be described. The particle size contained in the powder has a distribution in a certain range, and the median value and the maximum particle size are defined. SiC is measured by the electrical resistance method according to JIS R 6001-2 "Grain size of grinding wheel abrasives" according to the particle size evaluation method already standardized in the industry. The particle size other than SiC, such as chromium monoboride and chromium diboride, is measured according to JIS Z 8832 "Particle size distribution measuring method-electric detection zone method".

Next, the energy beam 112 is scanned according to the slice data, and the powder in a predetermined region of the powder layer 111 is irradiated with the energy beam 112 to be melted. As the energy beam source 102, it is preferable to use an energy beam source capable of outputting energy having a wavelength having a high absorptance of 50% or more. In particular, it is preferable to use an energy beam in the wavelength range in which the metal boride has a high absorptivity because the molten metal boride wraps around the silicon carbide during shaping. When the modeling material is chromium diboride, a semiconductor fiber laser having a wavelength of 1000 to 1120 nm is suitable.

It is preferable that the energy beam 112 has an energy intensity at a level at which the powder in the area irradiated with the energy beam is melted and solidified within a few msec and the particles are bonded to each other. When the powder layers are laminated, not only the powder layer located on the outermost surface on the irradiation side of the energy beam 112 but also the powder layer immediately below the powder layer irradiated with the energy beam 112 can be melted and solidified to some extent. , It is necessary for modeling. If the powder layer immediately below is insufficiently melted, the modeling tends to peel off layer by layer, resulting in a molded article having low strength. When the first powder layer laid directly on the base plate 109 is melted and solidified, the irradiation condition of the energy beam is adjusted in consideration of the heat capacity and heat conduction of the base plate 109 so that the surface of the base plate 109 is melted at the same time.

Subsequently, the elevating mechanism 108 lowers the modeling stage 107 by the stacking pitch, and then spreads the powder on the layer scanned with the energy beam to form a new powder layer, and the energy beam 112 is scanned and irradiated. To do. As described above, when the new powder layer is irradiated with the energy beam 112, a part of the layer scanned by the energy beam 112 (specifically, the part in contact with the new powder layer) is melted and solidified again. To be done. When the region of the new powder layer immediately below the region irradiated with the energy beam 112 is the region already melted and solidified, the beam irradiation region of the new powder layer is a part of the region previously melted and solidified. It mixes with the material, solidifies, and bonds to each other. By repeating these operations, it is possible to form the modeled article 110 in which the regions melted and solidified for each layer by the energy beam 112 are integrated.

Since the molded article 110 is bonded to the base plate 109, it is taken out of the chamber 101 together with the base plate. After that, the base plate 109 and the modeled article 110 are cut and separated by a wire saw or a disc blade to which abrasive grains such as diamond are attached, whereby the modeled article 110 can be obtained.

Next, an example of the step of including metallic silicon in the modeled article will be described with reference to FIG. Even if the melting point of metal silicon (1414° C.), a heat-resistant spherical material 202 having a uniform particle size is laid on the bottom of a crucible 201 made of a material such as graphite that does not volatilize or deteriorate so that the thickness does not exceed two layers. The model 110 is placed on top. The heat-resistant spherical material 202 has an effect of forming a gap so that the crucible 201 and the molded article 110 are not strongly fixed to each other by the solidified product of metallic silicon that has exuded from the molded article 110 during the impregnation step.

Further, the porosity of the modeled article 110 is derived in advance from the shape and mass, and the metallic silicon powder 203 is placed on the modeled article in an amount larger than the amount corresponding to the voids. Then, the crucible 201 is placed in a vacuum heat treatment furnace, the atmosphere in the furnace is replaced with argon, the pressure is appropriately reduced, and heating is performed from room temperature to a temperature higher than 1414° C. which is the melting point of metallic silicon, for example, 1500° C. The liquefied metallic silicon exceeding the melting point penetrates into the voids of the modeled object. After that, when cooled to room temperature, dry air is introduced to bring it to atmospheric pressure, and the crucible is taken out of the vacuum heat treatment furnace. At the time of cooling, at a temperature near the melting point of metallic silicon, the rate of temperature change is reduced in order to prevent distortion and stress that occur due to different solidification timing depending on the location. The heat-resistant spherical material 202 adhering to the surface of the modeled object can be removed by the solid substance of metallic silicon exuded from the modeled object 110, and the shape and surface can be further adjusted by grinding, polishing or the like to obtain a desired article.

[Powder Material Used in the Present Disclosure]
In the present disclosure, a powder of silicon carbide and a powder of metal boride having a melting point lower than the sublimation point of silicon carbide, which forms eutectic or hypoeutectic with silicon carbide, are mixed to form a modeling powder. By using such a modeling powder to fabricate a modeled product containing a eutectic or a hypoeutectic of silicon carbide and metal boride, a modeled product having a strength approaching that of silicon carbide is realized.

Here, the eutectic/hypoeutectic will be described below.

In the case of the mixture of the material X and the material Y such as metal, there is a material ratio in which the melting point is lower than the melting point of each material. At that time, the material ratio when the melting point becomes the lowest is called the eutectic composition, and the melting point is called the eutectic temperature.

In the eutectic composition, both the material X and the material Y are in a liquid phase at a temperature equal to or higher than the melting point, and the material X and the material Y are simultaneously precipitated at a temperature lower than the melting point. Therefore, the material X and the material Y are composed of a fine precipitation phase, and become a eutectic body having a layered structure called lamella and having a high strength.

Next, consider a case where the mixture of the material X and the material Y contains more material X than the eutectic composition. In this case, the material is in a liquid phase above the melting point, but when it falls below the melting point, the material X first solidifies and the material X precipitates (called primary crystal) up to the eutectic temperature. When the temperature falls to the eutectic temperature, the liquid phase portion excluding the precipitated crystal of the material X has a eutectic composition. Precipitates at the same time. In other words, compared with the case where the eutectic composition is originally used, the structure in which the crystals of which the crystal grows large as much as the precipitation of the material X starts earlier is mixed. When the material Y is more than the eutectic composition, the crystal of the material Y grows large. Those states are called hypoeutectic. The eutectic and hypoeutectic can be confirmed by observing the cross section of the shaped article with a scanning electron microscope.

The present inventors have examined conditions such as a powder composition and a particle size capable of obtaining a eutectic state or a state of a large eutectic crystal of silicon carbide in order to obtain physical properties close to those of silicon carbide.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. The present invention is not limited to the following examples unless it exceeds the gist.

(Powder 1)
As silicon carbide, a silicon carbide powder (manufactured by Taihei Random Co., Ltd., trade name NC#800) having a median particle diameter of 14.7 μm was prepared. As the chromium boride to be mixed, chromium diboride powder having a melting point of 2200° C. (manufactured by Nippon Shinkin Co., Ltd., trade name CrB2-O, median particle diameter is about 5 μm) was prepared. These powders were mixed at a molar ratio of silicon carbide:chromium diboride=7:3 so as to form a composition powder in which a eutectic crystal or a hypoeutectic crystal was formed, and mixed by a ball mill to obtain powder 1. .. The method for determining the molar ratio and the method for mixing are the same for the other powders. The median value of the particle size as used herein has the same meaning as the median size, and means the particle size at which the cumulative frequency of the powder is 50%. The particle size distribution can be measured by a well-known laser diffraction method or scattering method.

(Powder 2)
A silicon carbide powder similar to that of Powder 1 and vanadium diboride powder having a melting point of 2400° C. (median particle diameter of about 4 μm, manufactured by Nippon Shinkin Co., Ltd., trade name VB2-O) were used. Powder 2 was prepared by mixing at a molar ratio of vanadium boride=1:1 and mixed to obtain powder 2.

(Powder 3)
The same silicon carbide powder as powder 1 and chromium monoboride powder having a melting point of 2100° C. (manufactured by Nippon Shinkin Co., Ltd., trade name CrB-O, median particle size of about 9 μm) are carbonized at a molar ratio. Silicon:chromium monoboride=3:1 was prepared and mixed to obtain powder 3.

(Powder 4)
Silicon carbide powder similar to powder 1 and titanium diboride powder having a melting point of 2920° C. (manufactured by Nippon Shinkin Co., Ltd., trade name TiB2-N, median particle diameter of about 4 μm) were used as silicon carbide: Powder 4 was prepared by mixing and mixing titanium oxide at a molar ratio of 1:1.

(Powder 5)
Silicon carbide powder similar to powder 1 and zirconium diboride having a melting point of 3200° C. (manufactured by Nippon Shinkin Co., Ltd., trade name ZrB2-O, median particle diameter of about 5 μm) were used as silicon carbide: diboride. Powder 5 was prepared by mixing and mixing zirconium at a molar ratio of 1:1.

Table 1 summarizes the composition of each powder.

[Manufacturing of shaped object using powder material]
Modeling was performed using the above powders 1 to 5 as materials and the modeling apparatus shown in FIG. Specifically, for each powder, four rectangular parallelepiped shaped objects having a bottom area of 4 mm×40 mm were manufactured on a stainless steel base plate 109. FIG. 3 shows a perspective view of the four modeling objects 110 and the base plate 109 after the completion of modeling.

As the energy beam source 102, a semiconductor fiber laser having a wavelength of 1070 nm was used, and the powder layer was irradiated with a laser power of 100 W and an irradiation pitch of 50 μm. Further, since the irradiation energy suitable for modeling differs depending on the type of powder material, the scanning speed was set in advance between 100 mm/sec and 1000 mm/sec, and the optimum scanning speed was set for each material. An attempt was made to form 300 layers with a powder layer thickness (lamination pitch) of 30 μm.

However, in the modeling using the powder 4 containing titanium diboride and the modeling using the powder 5 containing zirconium diboride, the molded part begins to come off during the formation of the powder layer, and the modeling cannot be continued. I ended it at that point because it ended. As for the shaping using the powder 1, the powder 2, and the powder 3, a rectangular parallelepiped having a height of about 9 mm was obtained.

Next, as a cutting device, a wire saw CS-203 (trade name) manufactured by Musashino Electronics Co., Ltd. was used, and the modeled object 110 and the base plate 109 were separated with a wire saw of φ0.4 mm to which diamond abrasive grains were attached.

Here, a modeled object using the powder 1 as the material powder is a sample 1 (Comparative example 1), a modeled object using the powder 2 as the material powder is sample 2 (Comparative example 2), and a modeled object using the powder 3 as the material powder is a sample. As 3 (Comparative Example 3), 4 samples each were obtained. The modeling using the powder 4 as the material powder and the modeling using the powder 5 as the material powder were not completed as described above. However, as the numbering, the sample 4 is assigned as the comparative example 4 and the sample 5 is assigned as the comparative example 5. It was

In Samples 1 to 5, the contained elements were identified by energy dispersive X-ray analysis (EDX), and the molecular structure was identified by X-ray diffraction (XRD). Although Sample 1 had some oxides that are expected to be caused by the oxidation of the surface, it was found that it was composed of the raw material powders of silicon carbide and chromium diboride if they were ignored. Similarly, Sample 2 was found to be composed of silicon carbide and vanadium diboride.

Further, it was examined by FIB-SEM how silicon carbide and metal boride were distributed in the member. FIB-SEM is a sample structure in which the exposed sample surface or cross section is repeatedly observed with a SEM (scanning electron microscope) while the sample is being drilled with a FIB (focused ion beam), and the SEM image group is processed by a computer. It is a system that can observe 3D in three dimensions.

FIG. 4 shows an SEM image of a cross section of Sample 1. The darkest portion 10 was a void, the lightest colored region 12 was composed of chromium diboride, and the darkened region 11 between the regions 10 and 12 was composed of silicon carbide. .. The boundary between the silicon carbide region 11 and the chromium diboride region 12 had a complicated shape, and it could be inferred that at least one material was molten. Further, it was confirmed from the distribution of the silicon carbide region 11 and the chromium diboride region 12 observed in the SEM image that a eutectic/hypoeutectic crystal was formed.

In the SEM image group obtained for the sample 1, the region was identified by the density of this color, and the three-dimensional structure in which the regions 11 made of silicon carbide were connected was shown in FIG. A three-dimensional structure in which the regions 12 made of chromium diboride are connected together is shown in FIG.

From FIG. 5 and FIG. 6, it can be understood that the silicon carbide and the chromium boride in Sample 1 each have a three-dimensional network structure and are intricately entwined with each other. The range in which the three-dimensional network structure was confirmed using FIB-SEM was 60 μm×45 μm×160 μm, which was much larger than the median value of the particle diameters of the raw materials silicon carbide and chromium diboride. The material was suspected to have melted and connected during shaping.

Next, the voids included in the modeled article 110 were calculated. Except for the edges of the modeled object, the joints with the plate, and the outermost surface, the heat conduction did not differ greatly, so it was considered that the voids were contained on average. Therefore, for the porosity, an optical microscope image of a portion having an average void except for an end portion of a modeled object, a joint portion with a plate, and an outermost surface in a certain cross section is obtained, and the void ratio is 2.44 mm×1.63 mm. In the visual field corresponding to the region, the dark-colored portion corresponding to the voids was taken as the ratio occupied in the visual field. FIG. 7 shows an optical microscope image of a region having an average void in a cross section of Sample 1. For each of a plurality of places (10 or more) that are assumed to have an average porosity, a threshold value is set for the density, and a portion having a density higher than the threshold value is judged to be a void by image analysis, and the area of the entire area. When the porosity was calculated by the ratio and they were averaged, it was calculated that about 30% was the porosity.

[Process of including metallic silicon in the manufactured model]
Next, the molded article 110 was made to contain metallic silicon. As shown in FIG. 2, a 1-mm diameter alumina spherical body 202 was laid on the bottom of a crucible 201 made of graphite so as not to have a thickness of two or more layers, and one shaped article 110 was placed thereon.

Further, 1.5 times the volume of the metal silicon powder 203 (specific gravity 2.33, particle size ~45 μm) corresponding to the porosity calculated above was placed on the model 110.

After that, the crucible 201 was placed in a vacuum heat treatment furnace (not shown), and the inside of the furnace was replaced with argon. Then, the temperature was raised from room temperature to 1000° C. at a temperature increase rate of 300° C./h and kept for 2 hours. Then, the temperature was increased to 1200° C. at a temperature increase rate of 300° C./h while the pressure was reduced to an absolute pressure of 1.5 kPa in 40 minutes, and subsequently, the temperature increase rate was increased to 120° C. to 1500° C. and maintained for 2 hours.

After that, the temperature was lowered at 120° C./h to 1424° C. just above the melting point of the metallic silicon, and then gradually cooled to 1400° C. at 6° C./h.

Then, it cooled at 300 degreeC/h, and when it became 70 degreeC or less, dry air was introduce|transduced and it was set as atmospheric pressure and the crucible 201 was taken out from the vacuum heat treatment furnace.

By the above-mentioned method, metallic silicon was included in two pieces of sample 1, two pieces of sample 2, and two pieces of sample 3 in total. Sample 1 containing metal silicon was sample 6 (Example 1), sample 2 containing metal silicon was sample 7 (Example 2), sample 3 was containing metal silicon. 8 (Example 3).

Further, in the step of including the metallic silicon in the shaped article, the alumina spheres adhering to the surface of the shaped article 110 are detached, the shape and surface are adjusted by polishing, and an article containing metallic silicon having a size of about 4 mm×40 mm×9 mm. Got

[Characteristics of goods]
Next, sample 1, sample 2, sample 3, sample 6, sample 7, and sample 8 were subjected to a three-point bending test in accordance with the JIS standard fine room temperature bending strength test method (JIS R 1601). .. Further, the fracture surface of each of these samples was polished, and the porosity was calculated from the optical microscope image of the polished cross section.

The SEM image of Sample 6 is shown in FIG. When the composition analysis was performed, among the parts occupying a certain area, the darkest region 11 was silicon carbide, the thinnest region 12 was chromium diboride, and the region 13 having an intermediate concentration between them was metallic silicon. there were. Further, the black portions 10 that are slightly island-shaped between the respective materials are voids. In the same manner as in Sample 1, the porosity was calculated from the optical microscope image in the cross section of Sample 6. FIG. 9 shows an optical microscope image of a cross section of Sample 6 having an average porosity, which was used for calculating the porosity. A threshold value was set based on the density, and a portion having a higher density than the threshold value was judged to be a void by image analysis, and the void ratio was calculated by the area ratio with the entire area. Further, in the same manner as in Sample 1, it was determined from the SEM image whether eutectic/hypoeutectic was formed.

The porosity of the other samples was calculated in the same manner as in Samples 1 and 6, and it was determined whether or not eutectic/hypoeutectic crystals were formed. The results are shown in Table 2.

As a comprehensive judgment, a product having a shape of 4 mm×40 mm×9 mm that could not be formed was designated as “C”. In addition, what was able to be molded but had a porosity of about 30% and could not obtain sufficient bending strength was designated as "B". Even such a thing can be considered to be used as a filter or the like. In addition, a material obtained with a bending strength (100 MPa or more) similar to that of sintered ceramics is considered to be used for various purposes, and thus is designated as “A”.

Next, the reason why the sample 1, the sample 2, and the sample 3 could be modeled and the reason why the samples 4, 5 could not be modeled will be considered.

First, consideration will be given to the reason why the modeled product was obtained from Sample 1, which was molded with a mixed powder of silicon carbide and chromium diboride (melting point 2200° C.) having a lower melting point than the sublimation point (2545° C.) of silicon carbide. .. When the mixed powder of silicon carbide and chromium diboride is irradiated with a laser beam and the temperature is raised, the chromium diboride first reaches the melting point and melts. Then, it is presumed that the surface of the particles of silicon carbide is covered with the molten chromium diboride. It is considered that silicon carbide sublimes as a simple substance but melts at the interface between two substances, and the melting of silicon carbide progresses from the interface between the silicon carbide and the melt of chromium diboride. Even if the temperature rises and reaches the sublimation point of silicon carbide, it is presumed that the volatilized silicon carbide dissolves in the molten chromium diboride to suppress volatilization. Therefore, even if the laser beam irradiation raises the temperature beyond the sublimation point of silicon carbide, the molten state of silicon carbide and chromium diboride is maintained. After that, when the irradiation time of the laser beam was finished and the temperature of the irradiation region started to drop, it was presumed that silicon carbide and chromium diboride began to precipitate, respectively, and both substances were mixed without any gap, resulting in the state of FIG. It It is considered that the same applies to Sample 2 using a mixed powder of silicon carbide and vanadium diboride and Sample 3 using a mixed powder of silicon carbide and chromium monoboride.

Next, in the case of the sample 4 formed with the mixed powder of silicon carbide and titanium diboride (melting point 2920° C.), which is a metal boride having a melting point higher than the sublimation point of silicon carbide, the desired shaped object was not obtained. Examine the reason. When the temperature is raised by irradiating the mixture of silicon carbide and titanium diboride with the laser beam, the sublimation point of silicon carbide is reached before the melting point of titanium diboride. Therefore, sublimation of silicon carbide starts first, and then titanium diboride starts to melt. On the surface of the silicon carbide particles, contact between the molten titanium diboride and the silicon carbide powder is hindered by the sublimation gas, and the contact between them is very limited. Then, while the titanium diboride is melted, the silicon carbide also continues to sublime, so that the contact area between the two substances does not increase. In this way, the melting of silicon carbide is very limited and hardly precipitates even when cooled. Therefore, the eutectic or hypoeutectic like sample 1 to 3 is not a densely entangled modeled product, and the bond at the boundary between silicon carbide and titanium diboride is weak, resulting in a brittle modeled product. It is thought that it has gone.

Based on the above hypothesis and the above experimental results, when modeling is performed with a powder material containing silicon carbide powder and metal boride powder having a melting point lower than the sublimation point of silicon carbide, a eutectic or hypoeutectic crystal is formed. It is considered that the entanglement was made without any gaps, and the bond at the boundary was strongly modeled.

Next, samples 1, 2, and 3 and samples 6, 7 and 8 in which they are made to contain metallic silicon will be considered. By including metallic silicon in the voids included in the modeled article 110 immediately after the modeling, the void ratio of about 30% was almost eliminated (1% or less). Therefore, most of the voids in the modeled article 110 immediately after modeling It is presumed that they were communicating three-dimensionally.

Further, the bending strength was improved about 20 to 30 times, which was higher than the bending strength of metallic silicon (generally said to be about 200 MPa). Since it is considered that the three-dimensional structure of metallic silicon itself occupies about 30% of the volume of the article, the improvement in bending strength due to the inclusion of metallic silicon is estimated to be about 200 MPa×30%=60 MPa. However, actually, the bending strength in the as-molded state was increased from 5 MPa to 230 MPa, and the strength was improved by 225 MPa. This is because the three-dimensional structures of silicon carbide, chromium diboride (or vanadium diboride, chromium monoboride), and metallic silicon are in contact with each other and are entangled three-dimensionally. It is surmised that it has realized a bending strength that cannot be foreseen. Moreover, it can be inferred that the fact that the occurrence and development of cracks is prevented by filling the voids with metallic silicon also contributes to the improvement in strength.

[Mixing ratio of powder of silicon carbide and powder of metal boride]
Next, using a powder obtained by mixing a powder of silicon carbide and a powder of chromium diboride, a mixing ratio of silicon carbide and chromium diboride suitable for a molded article was examined. As the powder of silicon carbide and the powder of chromium diboride, the same powder as powder 1 was used.

The total content of the mixed powder of silicon carbide and chromium diboride is 100%, and the chromium diboride powder is contained in a molar ratio of 7.0%, 10%, 30%, 50%, 65% and 70%, respectively. Were designated as powders 6 to 11, respectively. Samples 9 to 14 in which articles were manufactured using these powders in the same manner as the molding using powders 1 to 5 were Comparative Examples 6 to 11, respectively.

With respect to the powder 6 having a large proportion of silicon carbide, when 30 layers were formed, the previous powder layer, that is, the uppermost layer was peeled off when the next powder layer was formed. Although the modeling could be continued, the same phenomenon occurred each time a new powder layer was formed, and as a result, modeling could not be continued. On the other hand, the powder 11 having a large ratio of chromium diboride has a ball-shaped projection on the surface during modeling, and the roller comes into contact with the projection during the formation of the powder layer, and the uppermost layer is peeled off. It was possible. Later analysis of the ball-shaped protrusions revealed that chromium diboride was the main component. It is considered that this is because the purity of the molten chromium diboride increased, so that the surface tension of the droplets formed on the surface increased and aggregated to increase the diameter, which solidified.

In addition, samples 15 to 18 were manufactured by performing a step of including metallic silicon in each of the samples manufactured similarly to the samples 10 to 13. The step of incorporating metallic silicon could be performed without any problems. Samples 15 to 18 were designated as Examples 4 to 7, respectively. Further, for each of the formed samples, the three-point bending test and the porosity were calculated in the same manner as in the above example.

The results are shown in Table 3. In the column of molar ratio, the value of (mol% of silicon carbide)/(mol% of chromium diboride) is shown.

It was found that a powder having a molar ratio of silicon carbide to chromium diboride in the range of silicon carbide:chromium diboride=90:10 to 35:65 is suitable for modeling, with the entire mixed powder being 100%. It was That is, it was found that a mixed powder having a molar ratio of silicon carbide and chromium diboride in the range of 0.54≦silicon carbide/chromium diboride≦9.00 was suitable for modeling. Furthermore, it was confirmed that the bending strength of the article obtained by including metallic silicon in the shaped article was improved more than expected.

In the above-mentioned embodiments, the two-component system such as silicon carbide and chromium diboride, silicon carbide and chromium monoboride, silicon carbide and vanadium diboride, etc. were investigated. It does not depart from the present case to appropriately add various boron-containing substances such as lanthanum and boron carbide within a range that does not change the main characteristics. In some cases, it is effective to reduce the specific gravity and increase the strength, and it can be used appropriately.

Further, in the above-mentioned examples, a powder having a median particle diameter of 5 μm was used for chromium diboride, and a powder having a median particle diameter of 9 μm was used for chromium monoboride. The use of powder does not limit the use of other particle sizes. However, the metal boride to be mixed is preferably smaller than the particle size of silicon carbide and has a particle size of 10 μm or less so that it is easily melted.

Further, in the above-mentioned embodiment, the molding was performed by the powder bed fusion bonding method using the laser, but the present invention is not limited to this method, and can be applied to other methods of the three-dimensional modeling method that undergoes similar thermal history. For example, it can be applied to a powder bed fusion bonding method using an electron beam, and also to a directed energy deposition method in which a gas and a material powder are simultaneously ejected and melted by a laser.

Further, in the above-mentioned embodiment, in the step of including the metallic silicon in the shaped article, the metallic silicon powder was placed on the shaped article and melted, but instead of the metallic silicon powder, a metallic silicon wafer, metallic silicon pellets, etc. It may be used, and further, a method called a MI method in which a shaped article is dipped in a metal silicon melt and then pulled up may be used.

It becomes possible to form silicon carbide, which has been difficult by the conventional three-dimensional modeling method. For example, by using a eutectic shaped product of silicon carbide and metal boride, it can be used for heat exchangers, engine nozzles, stages, etc., which have the advantages of high heat resistance, high thermal conductivity, and high physical strength. It is possible.

101 Chamber 102 Energy Beam Source 103A, 103B Scanning Mirror 104 Optical System 105 Introducing Window 106 Powder Layer Forming Mechanism 107 Modeling Stage 108 Elevating Mechanism 109 Base Plate 110 Modeling Object 111 Powder Layer 112 Energy Beam 113 Gas Injecting Mechanism 120 Modeling Container 201 Crucible 202 heat-resistant spherical material 203 metal silicon powder

Claims (8)

An article comprising silicon carbide, a metal boride having a melting point lower than the sublimation point of silicon carbide, and metallic silicon. The article according to claim 1, wherein the metal boride is at least one selected from the group consisting of chromium diboride, vanadium diboride, and chromium monoboride. The metal boride is chromium diboride, and the molar ratio with silicon carbide is in the range of silicon carbide:chromium diboride=90:10 to 35:65. Goods. The article according to claim 1 or 2, wherein the metal boride has a three-dimensional network structure. The article according to any one of claims 1 to 4, which has a porosity of 1% or less. Forming a powder layer using a powder obtained by mixing powder containing silicon carbide and powder containing metal boride having a melting point lower than the sublimation point of silicon carbide;
By simultaneously scanning and irradiating the formed powder layer with an energy beam based on the shape data of a molding target, the powder containing the silicon carbide and the boride having a melting point lower than the sublimation point of the silicon carbide are formed. A step of melting and solidifying powder containing metal,
Formed by repeating the process,
Furthermore, the manufacturing method of the article characterized by including the process of including metallic silicon in the said modeling thing. The method for producing an article according to claim 6, wherein the metal boride is at least one selected from the group consisting of chromium diboride, vanadium diboride, and chromium monoboride. 8. The metal boride is chromium diboride, and the molar ratio with the silicon carbide is in the range of silicon carbide:chromium diboride=90:10 to 35:65. Manufacturing method of article.