KR101668556B1 - Mold Apparatus for the Fabrication of High Density Tube-shaped Silicon Carbide Fiber Reinforced Silicon Carbide Composites - Google Patents

Mold Apparatus for the Fabrication of High Density Tube-shaped Silicon Carbide Fiber Reinforced Silicon Carbide Composites Download PDF

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KR101668556B1
KR101668556B1 KR1020150041531A KR20150041531A KR101668556B1 KR 101668556 B1 KR101668556 B1 KR 101668556B1 KR 1020150041531 A KR1020150041531 A KR 1020150041531A KR 20150041531 A KR20150041531 A KR 20150041531A KR 101668556 B1 KR101668556 B1 KR 101668556B1
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silicon carbide
sic
preform
mold
pressure
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KR1020150041531A
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KR20160114967A (en
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윤당혁
유현우
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영남대학교 산학협력단
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B28—WORKING CEMENT, CLAY, OR STONE
    • B28B—SHAPING CLAY OR OTHER CERAMIC COMPOSITIONS; SHAPING SLAG; SHAPING MIXTURES CONTAINING CEMENTITIOUS MATERIAL, e.g. PLASTER
    • B28B1/00—Producing shaped prefabricated articles from the material
    • B28B1/52—Producing shaped prefabricated articles from the material specially adapted for producing articles from mixtures containing fibres, e.g. asbestos cement
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/64—Burning or sintering processes
    • C04B35/645—Pressure sintering

Abstract

The present invention relates to a mold apparatus for a tubular high-density silicon carbide fiber-reinforced silicon carbide composite (SiC f / SiC) which can not be produced by general powder molding or extrusion, and more particularly, (SiC f / SiC) capable of being used as a high-temperature heat exchanger, a spacecraft engine, and a structural material for a next-generation reactor, using a pressure sintering method and a mold apparatus according to the present invention. .

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a mold apparatus for a high-density tubular silicon carbide fiber reinforced silicon carbide composite,

The present invention relates to a mold apparatus for a high-density tubular silicon carbide fiber-reinforced silicon carbide composite (SiC f / SiC), and more particularly to a mold apparatus for preventing the breakage of a specimen during hot pressing and sintering, To a mold apparatus for producing a silicon fiber reinforced silicon carbide composite (SiC f / SiC).

Silicon carbide fiber reinforced silicon carbide composites (SiC f / SiC, silicon carbide fiber-reinforced silicon carbide composites) are materials that can be used in high temperature and extreme environments due to their excellent chemical, thermal and mechanical properties. Therefore, it is expected to be utilized not only as a structural material for high temperature heat exchangers and spacecraft engines but also as core materials for gas-cooled 4th generation reactors and inner wall materials of future fusion reactors.

Ceramics generally have many advantages such as high temperature stability, abrasion resistance and corrosion resistance, but they have weak defects in brittle fracture. It is therefore common practice to form fiber reinforced ceramic composites to overcome the limits of brittleness and to increase fracture toughness.

In particular, fiber-reinforced ceramic composites improve the fracture toughness of ceramics by absorbing energy when a matrix is subjected to stress and a weak interfacial phase existing between the fiber-matrix phases propagates. Therefore, pyrolytic carbon (PyC) having a thickness of 1 ㎛ or less is generally coated on the surface of the fiber to form a weak interfacial phase.

Silicon carbide (SiC) fibers currently commercially available are Sylamic TM fibers from Dow Corning of America, Hi-NiCalon TM fibers from Nippon Carbon Japan and Tyranno TM from Ube Japan, Fiber and so on. Among them, Tyranno TM -SA, which is a completely crystallized fiber prepared through modification of the precursor polymer, has a stoichiometric ratio of C / Si of 1.08 which is close to 1 and has high crystallinity. Therefore, stability is improved up to 1900 ° C in an oxygen- And is suitable for industrial fields such as aerospace and nuclear power where heat resistance is required.

The silicon carbide fiber reinforced silicon carbide composite (SiC f / SiC) can be prepared by depositing silicon carbide powder between the pores between the silicon carbide fibers woven in a one-direction or two-dimensionally and sintering the same. However, due to the strong covalent bonding force and low diffusivity between Si-C, silicon carbide is required to sinter at high temperature to apply pressure at a high temperature of 2000 ° C or higher in order to realize high density. However, since the silicon carbide fiber may be damaged at such a high temperature, a method of lowering the sintering temperature to 1800 ° C. or lower by adding a liquid phase sintering aid such as Al 2 O 3 -Y 2 O 3 is generally used Is used.

The matrix deposition method for producing silicon carbide fiber reinforced silicon carbide composite (SiC f / SiC) includes chemical vapor infiltration (CVI), polymer impregnation and pyrolysis (PIP), reaction sintering A method based on RS (reaction sintering), NITE (nano-infiltrated transient eutectoid) and electrophoretic deposition (EPD) has been developed. Among them, electrophoresis is a method in which the ceramic particles constituting the matrix, which is dispersed in the solvent, are moved to the opposite electrode under a direct electric field. The time required for the treatment is short and economical, and the preform ), Regardless of its shape.

To date, conventional silicon carbide fiber reinforced silicon carbide composites (SiC f / SiC) prepared using this deposition method and hot press sintering method all have flat plate shapes. However, a technique for manufacturing a tubular SiC f / SiC composite, which is an optimum form for use as a structural material of a high temperature heat exchanger and a reactor, has not been developed yet. This is because the high-temperature sintering process in which the pressure is applied only in the upper and lower directions is suitable for manufacturing the flat SiC f / SiC composite, but is not suitable for manufacturing the tubular SiC f / SiC composite which requires the pressure in the necessary lateral direction. SiC < / RTI > f / SiC < RTI ID = 0.0 > complex. ≪ / RTI >

Therefore, in order to solve the above-mentioned problem, based on the results of the previous studies in which the present inventors participated (Patent No. 10-1101244 and No. 10-1179652), 1) two-dimensional woven TyrannoTM-SAS The SiC powder and Al2O3 And Y2O3 The sintering matrix is efficiently deposited using ultrasonic wave electrophoresis. 2) Since the pressure is applied only in one direction of the hot press sintering, a pressure transfer medium having fluidity that can not be sintered at a high temperature is used Tubular SiCf/ SiC composite, and 3) the pressure in the upward and downward directions is efficiently transferred to the tubular SiCf/ SiC composite is required to be produced.

It is an object of the present invention to find a condition to meet these requirements and to manufacture a mold apparatus for a high density tubular SiC f / SiC composite. For this purpose, two types (in-out and out-in type) of graphite molds are used to efficiently transfer the pressure to the outside and inside of the tubular SiC f / SiC composite during hot press sintering, And a high-density tubular SiC f / SiC composite having a density of 95% or more of an ideal density was produced, thereby completing the present invention.

Korean Patent No. 10-1179652 U.S. Published Patent Application 2013/0208848

The present invention uses a graphite powder which is not sintered at a high temperature as a pressure transmitting medium and uses a mold apparatus structure devised by the inventor. Provided is a mold apparatus for efficiently transferring the pressure applied in one direction in the up and down direction to the outer side of a tubular silicon carbide fiber reinforced silicon carbide composite in hot press sintering.

Further, the present invention relates to a method of manufacturing a ceramic fiber-reinforced ceramic composite material (SiC f / SiC) as well as a general ceramic long fiber-reinforced ceramic composites which are difficult to apply a molding or extrusion method To provide a mold apparatus capable of achieving this.

The present invention also provides a method for producing a high-density tubular silicon carbide fiber-reinforced silicon carbide composite (SiC f / SiC) by using an electrophoresis method and an ultrasonic wave treatment in combination, and a hot press-sintering method and a mold apparatus.

According to an aspect of the present invention for achieving the above object, a mold apparatus includes a tubular preform filled with a pressure transmitting medium and made of ceramic woven fiber, a pressure transmitting unit for transmitting a pressure at the time of hot pressing to the preform A top and bottom punch for transmitting the pressure to the side of the preform, and a graphite rod for maintaining the tube shape of the preform.

The pressure-transmitting medium may be an ovoid graphite powder which is not sintered at a high temperature during hot pressing and sintering.

The temperature in the hot press-sintering may be 1750 to 1950 ° C, and the pressure may be 10 to 20 MPa.

The upper and lower punches may be conical.

The in-out mold is filled with the pressure transfer medium inside the preform, and the pressure can be transferred from the interior to the exterior of the preform.

The out-in mold is filled with the pressure transmission medium outside the preform, and the pressure can be transferred from the outside to the inside of the preform.

The angle between the upper punch and the out-in mold bottom can be varied from 0 to 30 degrees.

According to an aspect of the present invention, a method for producing a silicon carbide fiber-reinforced silicon carbide composite (SiC f / SiC) comprises dissolving polyvinyl butyral (PVB) in ethanol in which a dispersant is added to prepare a binder solution (Step 1), dispersing SiC powder and 10 parts by weight of Al 2 O 3 -Y 2 O 3 sintering aid in a weight ratio of 1.5 to the binder solution to prepare a slurry (step 2) (Step 3) of uniformly depositing powder composed of the SiC and Al 2 O 3 -Y 2 O 3 auxiliary agent contained in the slurry in the pores of the preform in parallel with the electroforming method and the ultrasonic wave, (Step 4) of performing hot press-sintering on the deposited preform obtained in step 3 by using the mold apparatus according to any one of claims 1 to 7.

According to the mold apparatus for a high-density tubular silicon carbide fiber-reinforced silicon carbide composite of the present invention constituted as described above, the following effects can be obtained.

By designing the mold apparatus so that the tubular silicon carbide fiber reinforced silicon carbide composite has a density of up to 3.07 g / cm 3 (96.5% of the ideal silicon carbide fiber reinforced silicon carbide composite density), the high density tubular silicon carbide fiber reinforced carbide Silicon composite (SiC f / SiC).

When the hot-pressed sintered fiber according to the present invention is subjected to the electrodeposition and the ultrasonic treatment in combination with the high-temperature silicon carbide woven fiber, the tubular silicon carbide fiber reinforced composite (SiC f / SiC). The tubular silicon carbide fiber reinforced composite (SiC f / SiC) according to the present invention has improved density and mechanical strength of a sintered body and can be used as a structural material for gas turbines, aerospace and next generation nuclear reactors.

And it is possible to produce a general ceramic long fiber reinforced ceramic composite which is difficult to apply a molding or extrusion method in a stable tube form.

Figure 1 (a) SiC powder and (b) scanning electron microscopy (SEM) of Al 2 O 3 -Y 2 O 3 powder mixture constituting the sintering auxiliary picture, (c) the Tyranno TM SA Grade3 of fiber diameter 7.5 ㎛ (D) is a scanning electron microscope (SEM) photograph taken on an enlarged scale of the structure of (c); Fig. 5 (b) is a cross- (E) and (f) are scanning electron microscope (SEM) images showing pyrolytic carbon (PyC) layers coated at 400 nm on the surface of silicon carbide fibers at different magnifications,
FIG. 2 is an electrophoresis apparatus structure for placing a gaseous phase on the pores of a tubular silicon carbide woven fiber preform using an electrophoresis method;
FIG. 3 is a graph showing the zeta potential behavior of β-SiC, Al 2 O 3 and Y 2 O 3 powders, respectively, as a composition on a substrate in accordance with pH in an ethanol slurry,
FIG. 4 is a scanning electron micrograph of 1, 3, and 5 layers after depositing the matrix by electrophoresis in a tubular silicon carbide woven fiber preform in which Tyranno TM -SA woven fibers were wound in five layers,
5 (a) and 5 (b) are a schematic view showing a sintering process of a tubular silicon carbide woven fiber preform by applying a cylindrical graphite rod to a central portion of a mold, which is generally used in hot-
6 (a) to 6 (d) are graphs showing the relationship between the presence or absence of a green tape and the sintering temperature and pressure of the Tyranno TM -SA tubular silicon carbide fiber reinforced Density table and physical inspection of silicon carbide composites,
FIG. 7 is a structural view of an in-out mold to which an ovoid graphite powder is applied in order to efficiently apply the pressure of the hot press-sintering to the outer side surface of the tubular silicon carbide woven fiber preform;
Figs. 8 (a) and 8 (b) show the mill scale and actual counts of the silicon carbide fiber-reinforced silicon carbide composite subjected to hot press-sintering for 2 hours at a sintering temperature of 1750 o C and a pressure of 20 MPa using the mold of Fig. ,
FIG. 9A is a structural view of an in-out mold obtained by deforming upper and lower punches into a conical shape using the mold of FIG. 7, and FIG. 9B is a cross-sectional view of a tubular silicon carbide woven fabric The actual inspection of the mold having the preform,
10 (a) and 10 (b) are graphs depicting the density of the silicon carbide fiber-reinforced silicon carbide composite subjected to hot pressing and sintering at a sintering temperature of 1750 ° C. and a pressure of 20 MPa for 2 hours using the mold of FIG. And due diligence,
11 (a) and 11 (b) illustrate the out-in mold structure of the out-in mold designed using the mold of FIG. 9 to minimize the specimen swelling and failure phenomenon of the silicon carbide fiber- And due diligence,
Figs. 12 (a) to 12 (c) are cross sectional views showing the presence or absence of a green tape, which is the same as the matrix composition of a tubular silicon carbide fiber-reinforced silicon carbide composite subjected to hot pressing and sintering for 2 hours at a sintering temperature of 1750 o C And density table according to change of pressure,
13 (a) and 13 (b) are cross-sectional views of the mold apparatus of FIG. 11,
(A) of Fig. 14 Fig. 14 is 2 eseo 1750 o C by application of 20 MPa pressure the matrix made winding the same green tape and the matrix composition using a mold of 11 to 20 layers of the tubular silicon carbide woven fiber preform (B) shows the result of polishing the surface of the tubular silicon carbide fiber-reinforced silicon carbide composite subjected to the hot-pressing for 10 hours, and polishing the surface of (a) to obtain a tubular silicon carbide fiber reinforced with a diameter of 20 mm, a height of 50 mm and a thickness of 15 mm Physical examination of silicon carbide complex,
15 (a) to (c) are SEM micrographs showing the microstructure of the tubular silicon carbide fiber-reinforced silicon carbide composite produced using the mold of FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of a mold apparatus for a high-density tubular silicon carbide fiber-reinforced silicon carbide composite (SiC f / SiC) according to the present invention will be described in detail with reference to the drawings.

First, the present invention relates to a process for preparing a binder solution by dissolving polyvinyl butyral (PVB) in ethanol to which a dispersant is added (step 1), adding SiC powder and 10 parts by weight of Al 2 O 3 -Y 2 O 3 sintering aid in a weight ratio of 1.5 to prepare a slurry (step 2). The electroforming method and the ultrasonic wave are simultaneously performed on the tubular preform according to claim 1 to prepare a slurry (Step 3) of uniformly depositing powder composed of SiC and Al 2 O 3 -Y 2 O 3 sintering aids in the pores of the preform, and a step (step 3) of using the mold apparatus according to any one of claims 1 to 7 (SiC f / SiC, hereinafter referred to as 'tubular composite') comprising a step (step 4) of subjecting the deposited preform obtained in step 3 to hot pressing and sintering (step 4).

1 (c) and 1 (d) show a preform structure in which Tyranno ™ SA Grade 3 fibers (Ube, Japan) having a diameter of 7.5 μm are woven in 0/90 ° and 2-dimension by 1600 strands. Using the preforms, nano-sized SiC powder and Al 2 O 3 -Y 2 O 3 were added to the vacancies between fine crevices and fiber bundles between the silicon carbide woven fibers By depositing a matrix phase composed of a sintering aid, it is possible to provide a tubular composite (SiC f / SiC) having a densified structure with few pores. However, since deposition using only ceramic (SiC) powder is difficult, it is preferable to prepare a slurry in which a ceramic powder is dispersed in a binder solution and deposit it.

Referring to the scanning electron microscopic photographs of FIGS. 1 (a) and 1 (b), the SiC powder and the Al 2 O 3 -Y 2 O 3 sintering assistant of step 2 according to the present invention are characterized in that (a) (B) of about 0.5 to about 4.0 with respect to the particle size of the? -SiC powder, which is a sintering aid for Al 2 O 3 -Y 2 O 3 . That is, when the average particle size of the SiC powder is 50 nm, the average particle size of the Al 2 O 3 -Y 2 O 3 auxiliary agent is more preferably 200 nm or less. The relative weight ratio of the Al 2 O 3 -Y 2 O 3 sintering aid is Al 2 O 3 / Y 2 O 3 = 1.5 is preferable for forming a liquid phase with a sintering auxiliary agent. The weight ratio of the Al 2 O 3 -Y 2 O 3 sintering aid added to the SiC powder is preferably 8 to 12 wt%.

1 (e) and 1 (f) are Pyrolytic carbon (PyC) layers coated on a silicon carbide fiber surface at 400 nm. The silicon carbide woven fiber for use in step 3 is preferably coated with a pyrolytic carbon layer (PyC) to a thickness of 200 to 1,000 nm for imparting fracture toughness to the tubular composite (SiC f / SiC).

The binder solution used for the slurry is preferably polyvinyl butyral (PVB) having a molecular weight of 50,000 to 60,000 g / mol, and the binder solution is 0.5 to 1.0% by weight of the solvent desirable. The amount of the binder solution added to the SiC powder contained in the slurry is preferably adjusted to 4 to 8 wt%, more preferably 5 wt%. The solvent used for the binder solution is preferably anhydrous ethanol.

It is preferable to add a dispersant to the binder solution according to the present invention. The dispersant is preferably a polymer of a polyester / polyamine copolymer series. For example, a trade name Hypermer KD 1 may be used. At this time, the dispersant is preferably used in an amount of 1 to 5 wt% based on the SiC powder.

In general, silicon carbide (SiC, ceramic) nanopowders have a high specific surface area, and thus have a very high tendency to agglomerate. Therefore, they have an excellent dispersibility capable of being deposited in fine crevices between silicon carbide fibers. The mechanism of dispersion is as follows: 1) electrostatic repulsion using the repulsive force by the surface charge of the SiC powder and 2) steric mechanism of dispersing by dispersing the dispersant composed of the polymer on the surface of the SiC powder .

1) In the electrostatic repulsion mechanism, the absolute value of the zeta potential, which is the surface charge value of the SiC powder, is preferably 30 mV or more. On the other hand, (2) in the steric hindrance mechanism, it is preferable to use the polymer dispersant to be added which gives a repulsive force to the SiC powder because of its excellent surface adsorption.

In addition, the slurry of Step 2 was mixed with SiC powder and Al 2 O 3 -Y 2 O 3 After the addition of the sintering aid, it is preferable to further ball mill to increase dispersibility of the powders. At this time, the ball milling is preferably carried out for 24 to 48 hours using a 6 mm SiC ball. If a universal ZrO 2 ball is used in place of a SiC ball, it is preferable to use a SiC ball because the hardness of SiC is larger than ZrO 2 to cause zirconium (Zr) contamination.

2 is a structural view of an electrophoresis apparatus for depositing SiC powder and Al 2 O 3 -Y 2 O 3 sintering aids contained in slurry in pores (spaces) between tubular silicon carbide woven fiber preforms by electrophoresis. The experimental apparatus is made of stainless steel which is an electric conductor, and the cylindrical chamber in which the slurry is contained can be made to have a diameter of 5 to 30 cm, preferably 20 cm. The cylindrical chamber is connected to the (+) side of the DC power supply unit and serves as an anode. At the center of the cylindrical chamber, a 5 to 20-fold wrapped silicon carbide woven fiber preform may be placed on a cylindrical graphite rod having a diameter of 2 cm. The graphite rod is connected to (-) of the DC power supply unit to serve as a cathode. The outside of the cylindrical chamber made of stainless steel is made of Teflon, which is an electric insulator, so that the flow of current can be cut off.

The electrophoresis method of step 3 is preferably performed under a direct current voltage of 10 to 30 V for 30 to 120 minutes. In the embodiment of the present invention, by applying a DC voltage of 20 V and conducting electrophoresis for 60 minutes, the SiC powders contained in the slurry having a positive (+) surface charge are mixed with the silicon carbide woven fabric It is deposited on the preform.

When the matrix is deposited on the pores between the fibers of the preform by electrophoresis, it is difficult to deposit the matrix on the surface of the pores because the matrix is preferentially deposited on the surface of the pores. do. When such a surface sealing phenomenon occurs, pores are continuously present in the tubular composite (SiC f / SiC). Therefore, it is necessary to minimize the density of the tubular composite (SiC f / SiC) because of porosity.

In order to solve such a problem, the present invention preferably further includes an ultrasonic wave generator in step 3 as shown in Fig. In the preferred embodiment of the present invention, an ultrasonic wave having a power of 10 W was applied at a cycle of 1 second for the initial 50 minutes to perform the electrophoresis, and only the electrophoresis was performed for 10 minutes before the ultrasonic wave was removed. That is, the ultrasonic wave applied at a constant period desorbs the matrix that is preferentially adsorbed on the surface of the pores, and the driving force by the electrophoresis method increases the efficiency because the desorbed matrix is deposited deep inside the microcavities of the SiC fibers, that is, the pores.

FIG. 3 is a graph of the zeta potential behavior of β-SiC, Al 2 O 3, and Y 2 O 3 powders, respectively, in the base phase composition according to pH in an ethanol slurry. By controlling the zeta potential according to the pH of the SiC (ceramic) powders constituting the slurry of step 2, it is possible to maximize the dispersion due to the electrostatic repulsion force. It is known that when the zeta potential is at least 30 mV, the dispersibility due to electrostatic repulsion is secured.

The pH of the slurry is adjusted using NH 4 OH and HCl aqueous solution. As the pH increases, the zeta potential decreases from positive (-) value to all - ceramic powder, which is known to be due to the increase of OH - concentration with increasing pH.

Referring to Figure 3 β-SiC, Al 2 O 3 and Y 2 O 3 The isoelectric point (IEP) of the powder was pH = 6.3, 10.0, and 8.3, respectively. Therefore, when the electrophoresis is carried out in an alkali region having a pH of the slurry of > 10, all of the powders (? SiC, Al 2 O 3 and Y 2 O 3) have a negative zeta potential, Calm occurs. However, in this case, Al 2 O 3 There arises a problem that the driving force for the electrophoresis method is lowered under the electric field due to the low zeta potential of the powder. Further, in the region where the slurry has pH < 6, all of the powders have a positive zeta potential. Particularly, since the zeta potential of all the above-mentioned powders is more than +40 mV in the acidic region of the pH <3 of the slurry, the driving force for electrostatic repulsion and electrophoresis is very large.

Therefore, the electrophoresis method of the present invention maximizes the dispersibility from the viewpoint of the electrostatic repulsive force and maximizes the driving force of the electrophoresis method by adjusting the pH of the slurry to 3. At pH = 3, there is a difference in mobility due to the difference in the zeta potential of each of the β-SiC, Al 2 O 3 and Y 2 O powders. However, nonuniform deposition is caused by adding the binder solution to the slurry It can be solved by increasing the viscosity.

A mold apparatus for a tubular composite (SiC f / SiC) according to a preferred embodiment of the present invention includes a tubular preform filled with a pressure transmitting medium and made of ceramic woven fiber, a pressure during hot press sintering A mold for transferring the preform to a side of the preform, an upper and lower punch for transmitting the pressure to the side of the preform, and a graphite rod for maintaining the tube shape of the preform.

5 (a) and 5 (b) are a structural view and an actual view of sintering a tubular silicon carbide woven fiber preform by applying a cylindrical graphite rod to a central portion of a mold generally used in hot press-sintering. This shows a structure in which a pressure is applied to the outside of the tubular preform wound on the cylindrical graphite rod by using hot press-sintering which applies pressure only in one up and down directions.

7 is a structural view of an in-out mold to which ovoid graphite powder is applied in order to efficiently apply the pressure of the hot press-sintering to the outer side surface of the tubular silicon carbide woven fiber preform. This shows the structure of the mold that transfers pressure to the outside of the tubular preform more efficiently than the mold of FIG. In order to transfer pressure to the outside of the tubular preform in hot press-sintering, in which the pressure is transferred only in one up and down direction, fluid ovoid graphite powder should be used. Accordingly, by injecting the ovoidly-formed graphite powder into the tubular preform, pressure was efficiently transferred to the side of the tubular preform.

FIG. 9A is a structural view of an in-out mold obtained by deforming upper and lower punches into a conical shape using the mold of FIG. 7, and FIG. 9B is a cross-sectional view of a tubular silicon carbide woven fabric It is the actual inspection of the mold equipped with the preform. The mold structure of Fig. 9 is a mold apparatus designed to improve the problem of the mold structure of Fig. By placing the conical punch at the upper and lower portions of the tubular preform filled with the ovoid graphite powder, it was attempted to transfer the upward and downward pressure to the outside of the tubular preform more efficiently.

In the present invention, the mold structure shown in Figs. 7 and 9 is named as an in-out mold because pressure is externally applied inside the tubular silicon carbide woven fiber preform.

However, in the case of using the in-mold type mold shown in Figs. 7 and 9, frequent breakage occurred in the sintering process of the tubular silicon carbide fiber-reinforced silicon carbide composite. An out-in mold designed to solve this problem is shown in Fig. 11 (a) and 11 (b) illustrate the out-in mold structure of the out-in mold designed using the mold of FIG. 9 to minimize the specimen swelling and failure phenomenon of the silicon carbide fiber- And due diligence.

The out-of-die mold structure of Fig. 11 places graphite powder on the outside of a tubular silicon carbide woven fiber preform wound on a graphite rod, as opposed to an in-situ mold in which an ovoidized graphite powder is packed inside a tubular silicon carbide woven fiber preform. Further, by varying the angle of the upper punch and the lower out-of-doll mold from 0 to 30 degrees, it was attempted to effectively transfer the upward and downward pressure to the outside of the tubular preform.

Therefore, a high-density tubular silicon carbide fiber-reinforced silicon carbide composite can be manufactured through the above-described manufacturing method of the silicon carbide fiber-reinforced silicon carbide composite, the electrophoresis apparatus and the molding apparatus.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples are illustrative of the present invention, and the present invention is not limited to the following examples.

Example 1: Tubular high density silicon carbide fiber reinforced silicon carbide composite ( SiC f / SiC )

The weight ratio of Al 2 O 3 / Y 2 O 3 = 1.5, the mixed powder Al 2 O 3 -Y 2 O 3 a sintering aid in a high energy mill rotating at 3,000 rpm, 0.4 mm milling the average particle size by milling for 2 hours using ZrO 2 balls having a diameter of less than 200 nm Respectively.

Thereafter, 0.625 parts by weight of a polyvinyl butyral (PVB) binder of 55,000 g / mol was added to 100 parts by weight of an ethanol solvent, and 3 parts by weight of Hypermer KD 1 as a dispersant was added to 100 parts by weight of SiC powder.

SiC powder having an average particle size of 50 nm and Al 2 O 3 -Y 2 O 3 sintering aid powder having an average particle size of 200 nm or less were added to the binder solution prepared as described above. Al 2 O 3 - Y 2 O 3 The amount of the sintering aid is 10 parts by weight based on 100 parts by weight of the SiC powder. The slurry was prepared by performing ball milling with a SiC ball of 6 mm for 24 hours so that the weight ratio of the binder solution to the SiC powder was 0.05. NH 4 OH or HCl was added as a pH controller to adjust the pH of the slurry to 3 and to have a zeta potential of greater than 40 mV.

The slurry was introduced into the electrophoresis apparatus shown in FIG. 2, and a Tyranno ™ SA Grade 3 tubular silicon carbide woven fiber preform coated with a 400 nm pyrolytic carbon layer was placed in the center of the cylindrical chamber as a cathode.

A DC voltage of 20 V was applied, and an ultrasonic wave of 10 W output was applied for 1 second in the initial 50 minutes of performing the electrophoresis. Only 10 minutes before the end of the electrophoresis, only the electrophoresis was performed with the ultrasonic wave removed. As a result, the SiC powder and Al 2 O 3 -Y 2 O 3 The sintering aid powder is densely deposited on the tubular preform.

The SiC and Al 2 O 3 -Y 2 O 3 The tubular preforms in which the sintering aid powder was deposited were heated to 350 ° C at a rate of 1 ° C per minute in air and held at this temperature for 2 hours and then cooled to room temperature at a rate of 1 ° C per minute The polyvinyl butyral binder solution was removed. The tubular silicon carbide woven fiber preform in which the polyvinyl butyral binder solution was removed was used in the mold of FIG. 5 which is generally used in hot pressing and sintering.

FIG. 8 (a) and 8 (b) show the results of the rolling and sintering of the silicon carbide fiber-reinforced silicon carbide composite subjected to the hot press-sintering for 2 hours at a sintering temperature of 1750 ° C and a pressure of 20 MPa using the mold of FIG. to be. This is the result of sintering and density measurement according to the presence of the same green tape as the matrix composition. In order to increase the sintered density of the low-tubular composite (SiC f / SiC), hot-press-sintering was carried out using an in-out mold capable of filling graphite powder as a pressure transmitting medium, f / SiC) was measured.

The mold of FIG. 9 was used to solve the problem of low density and specimen destruction of the tubular composite (SiC f / SiC) which occurs when the mold of FIG. 7 is used.

10 (a) and 10 (b) are graphs depicting the density of the silicon carbide fiber-reinforced silicon carbide composite subjected to hot pressing and sintering at a sintering temperature of 1750 ° C. and a pressure of 20 MPa for 2 hours using the mold of FIG. And real world view. This is a result of measuring the density of the tubular composite after performing the hot press-sintering using the mold of FIG. 9, that is, the in-mold with the conical upper and lower punches.

Out-in molds shown in Figs. 11 and 13 were fabricated to solve the problem of specimen destruction that continuously appeared even when the improved in-mold shown in Fig. 9 was used. The high-density tubular silicon carbide fiber-reinforced silicon carbide composite (SiC f / SiC) shown in Fig. 14 can be produced by performing hot press-sintering on the tubular silicon carbide fiber-reinforced plastic fiber preform using the mold of Fig.

Experimental Example 1: Hot pressing sintering  Pre-silicon carbide Of junk fibers Analysis of internal deposition degree

In Example 1, ultrasonic waves were treated by electrophoresis using a tubular silicon carbide woven fiber preform in which 5 layers of silicon carbide woven fabric were wound, and the degree of deposition in the silicon carbide woven fiber was analyzed.

FIG. 4 is a scanning electron microscope (SEM) image of a 1, 3, and 5 layer after depositing a matrix by electrophoresis on a tubular silicon carbide woven fiber preform that is formed by winding five layers of Tyranno TM- SA silicon carbide woven fiber. In FIG. 4, it can be seen that the gaseous phase is very densely packed in the pores (voids) between the silicon carbide woven fibers in the first, third, and fifth layers of the tubular silicon carbide woven fiber preform. It can be seen that the electrophoresis method using ultrasonic wave is very effective for deposition on the base.

Comparative Example 1: During hot pressing sintering  Normally Mold  Density Analysis of Sintered Tubular Silicon Carbide Fiber Reinforced Silicon Carbide Composites

6 (a) to 6 (d) are graphs showing the relationship between the presence or absence of a green tape and the sintering temperature and pressure of the Tyranno TM -SA tubular silicon carbide fiber reinforced Density silicon carbide complexes. 6 is a tubular silicon carbide fiber reinforced silicon carbide composite sintered using a general mold when hot-pressing and sintering a tube-shaped silicon carbide woven fiber preform prepared in Experimental Example 1 in which the matrix was deposited.

Then, hot press sintering was performed for 2 hours under Ar (argon) while changing the sintering temperature to 1750 to 1950 o C and the pressure to 10 MPa or 20 MPa Respectively. As a result, the sintered density of the tubular composite sintered using the general mold was 1.77 to 2.05 g / cm 3 . However, the density results are in the ideal range of 55.7 to 64.5% of the theoretical density 3.18 g / cm &lt; 3 &gt;, making it impossible to produce high density tubular silicon carbide fiber reinforced silicon carbide composites.

Experimental Example 2: In-out type Mold  And Sintering of Tubular Silicon Carbide Fiber Reinforced Silicon Carbide Composite Using Graphite Powder as Pressure Transmission Medium

As shown in Comparative Example 1, the tubular silicon carbide fiber reinforced silicon carbide composite (SiC f / SiC) using a general mold showed a low sintered density after hot pressing and sintering. This is because the pressure applied in the lateral direction of the tubular composite body (SiC f / SiC) due to the hot press-sintering process in which the pressure is applied only in the upward and downward directions is absent. Therefore, a pressure transmission medium was used to transfer the upward and downward pressure to the side of the tubular composite (SiC f / SiC). The pressure transmission medium used was a graphite powder which was not sintered at a high temperature, and the mold of FIG. 7 capable of filling the graphite powder was devised and manufactured. Therefore, the mold of FIG. 7 was used to transmit the pressure in one direction to the outside of the tubular composite (SiC f / SiC) through the flowable graphite powder.

The 5-ply tubular silicon carbide woven fiber preform with the matrix deposited thereon was subjected to calcination at 350 ° C. for 2 hours and hot sintering at 1750 ° C. and 20 MPa for 2 hours. The results are shown in FIG. FIG. 8 (a) and 8 (b) show the results of the rolling and sintering of the silicon carbide fiber-reinforced silicon carbide composite subjected to the hot press-sintering for 2 hours at a sintering temperature of 1750 ° C and a pressure of 20 MPa using the mold of FIG. to be. The density of the tubular silicon carbide fiber reinforced silicon carbide composites (SiC f / SiC) was 2.74 g / cm 3 (86.2%) and 2.92 g / cm 3 (91.8%), respectively, Respectively. This shows that the pressure applied to the side of the tubular silicon carbide fiber reinforced silicon carbide composite (SiC f / SiC) was efficiently performed due to the graphite powder used as the pressure transmission medium. Therefore, the result of Experimental Example 2 was improved in density compared to the use of the general mold of Comparative Example 1. [ However, there is still a problem that the tubular silicon carbide fiber reinforced silicon carbide composite (SiC f / SiC) after sintering is broken, and the density result of Experimental Example 2 has a problem that 95% of the target density can not be satisfied.

In order to increase the density of the tubular composite (f SiC / SiC) to be applied pressure more efficiently on the side of the outside of the tubular composites (SiC f / SiC). Thus, by changing the upper and lower punches to a conical shape, the mold structure of FIG. 9 was designed and manufactured, and then subjected to hot pressing and sintering. The results are shown in FIG. 10 (a) and 10 (b) are graphs depicting the density of the silicon carbide fiber-reinforced silicon carbide composite subjected to hot pressing and sintering at a sintering temperature of 1750 ° C. and a pressure of 20 MPa for 2 hours using the mold of FIG. And due diligence. The density of the tubular silicon carbide fiber-reinforced silicon carbide composite (SiC f / SiC) was 2.85 g / cm 3 (89.6%) and 2.98 g / cm 3 (93.7%) Respectively. This shows that the upper and lower punches are efficiently applied to the side surface of the tube-shaped composite body (SiC f / SiC), as compared with the case of using the mold of FIG. 7. However, there is still a problem that the tubular silicon carbide fiber reinforced silicon carbide composite (SiC f / SiC) is broken after sintering, and the target density of 95% is not satisfied. Such a breakage problem is caused by densification of removing the pores of the tubular silicon carbide woven fiber preform during the sintering process, and the phenomenon that the tubular preform shrinks inside occurs, and the pressure generated in the mold is in the opposite direction Which is caused by the fact that it acts as an external force.

The mold structure of FIGS. 7 and 9 is referred to as an in-out mold because pressure is externally applied to the inside of a tubular silicon carbide fiber-reinforced silicon carbide composite (SiC f / SiC).

Experimental Example 3: out - in )brother Mold alc  Density Analysis of Sintered Tubular Silicon Carbide Fiber Reinforced Silicon Carbide Composite Using Graphite Powder as Pressure Transmitting Medium

The problems shown in the above Experimental Examples 1 and 2 are that when the pressure is applied to the outer side of the tubular silicon carbide fiber reinforced silicon carbide composite (SiC f / SiC), which is inefficient, and in the opposite direction to the shrinkage of the tubular composite (SiC f / SiC) In the direction of pressure applied. Therefore, the inventors devised and manufactured the mold structure of Fig. This is an out-in mold structure that allows pressure to be applied from the outside to the inside of the tubular silicon carbide fiber-reinforced silicon carbide composite (SiC f / SiC) during hot press sintering.

The mold of FIG. 11 was made to fill graphite powder, which was a pressure-transmitting medium, outside the tubular silicon carbide woven fiber preform, and gave an angle change of 0 to 30 degrees to the upper punch and the lower mold. The results are shown in FIG.

Figs. 12 (a) to 12 (c) are cross sectional views showing the presence or absence of a green tape, which is the same as the matrix composition of a tubular silicon carbide fiber-reinforced silicon carbide composite subjected to hot pressing and sintering for 2 hours at a sintering temperature of 1750 o C And the density table and actual inspection according to the change of the pressure. As a result of using the mold of Fig. 11, there was no problem of specimen destruction that occurred when using an in-mold type mold. When the pressure was 10 MPa, the density was 2.31 g / cm 3 (72.6%) as shown in FIG. 12 (a). When the pressure was increased to 20 MPa, And a high density of 3.07 g / cm 3 (96.5%). The result of the reproducibility test is shown in Fig. 12 (c), which shows the same density as (b).

Thus, the out-of-die mold of FIG. 11 can be used to efficiently produce tubular silicon carbide fiber-reinforced silicon carbide composites (SiC f / SiC) having a density of about 95% of the ideal theoretical density.

Of Figure 14 (a) is a 20 MPa pressure the matrix made winding the same green tape and the matrix composition using a mold of 11 to 20 fold rather than 5 fold in a tubular silicon carbide woven fiber preform under application to 1750 o C (B) is a photograph of the tubular silicon carbide fiber-reinforced silicon carbide composite subjected to hot press-sintering for 2 hours, and (b) This is due diligence of the reinforced silicon carbide complex. The density of the tubular silicon carbide fiber-reinforced silicon carbide composite (SiC f / SiC) at this time was 3.05 g / cm 3 (95.9%), which is higher than the target density of 95% in the present invention.

Experimental Example 4: Tubular silicon carbide fiber reinforced silicon carbide Microstructure analysis after sample polishing of composite

The tubular silicon carbide fiber reinforced silicon carbide composite (SiC f / SiC) prepared in Experimental Example 3 was polished and observed with a scanning electron microscope. The surface was first polished using SiC abrasive paper (sandpaper) # 300, 600, 1200, and then abrasive liquid in which diamond powder having a particle size of 6 or 1 占 퐉 dispersed was sequentially rotated at 200 rpm. . Then, the tubular composite body (SiC f / SiC) was polished using the friction between the test piece and the abrasive plate to prepare a specimen having a smooth surface.

15 (a) to (c) are SEM micrographs showing the microstructure of the tubular silicon carbide fiber-reinforced silicon carbide composite prepared using the mold of FIG. (a) and (b) show a very dense microstructure in which all the pores of the tubular composite (SiC f / SiC) produced by the electrophoresis and the ultrasonic treatment are completely deposited on the base. (C) shows that the pyrolytic carbon layer is still present even after hot sintering at 1750 ° C and that the silicon carbide woven fiber retains the original circular pattern.

As described above, in the embodiment of the present invention, the matrix is deposited on the tubular silicon carbide woven fiber preform in parallel with the electrophoresis method and the ultrasonic wave, and the tubular silicon carbide fiber reinforced silicon carbide (SiC f / SiC). The high density tubular silicon carbide fiber reinforced silicon carbide composites (SiC f / SiC) produced according to this example exhibited a high density of up to 3.07 g / cm 3 (96.5% of the ideal theoretical density) with minimal specimen failure.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It will be apparent that modifications, variations and equivalents of other embodiments are possible. Therefore, the true scope of the present invention should be determined by the technical idea of the appended claims.

Claims (8)

A tubular preform filled with a pressure delivery medium and made of ceramic woven fibers;
A mold for transferring pressure at the time of hot pressing to the preform;
An upper and lower punch for transmitting the pressure to a side surface of the preform; And
And a graphite rod mounted on the inside of the preform to maintain a tube shape of the preform against a pressure transmitted from the mold to the preform.
The method according to claim 1,
Wherein the pressure-transmitting medium uses an ovoid graphite powder which is not sintered at a high temperature during hot press-sintering.
The method according to claim 1,
Wherein the temperature during the hot press-sintering is 1750 to 1950 占 폚, and the pressure is 10 to 20 MPa.
The method according to claim 1,
Wherein the upper and lower punches have a conical shape.
The method according to claim 1,
Wherein the mold is filled with the pressure transfer medium inside the preform and transfers the pressure from the inside to the outside of the preform.
The method according to claim 1,
Wherein the out-in mold is filled with the pressure transmission medium outside the preform, and the pressure is transferred from the outside to the inside of the preform.
The method according to claim 6,
Wherein the angle between the upper punch and the bottom of the out-in mold is varied from 0 to 30 degrees.
A step of dissolving polyvinyl butyral (PVB) in ethanol to which a dispersant is added to prepare a binder solution (step 1);
Dispersing SiC powder and 10 parts by weight of Al 2 O 3 -Y 2 O 3 sintering aid in a weight ratio of 1.5 to the binder solution to prepare a slurry (step 2);
The step of uniformly depositing a powder composed of the SiC and Al 2 O 3 -Y 2 O 3 auxiliary agents contained in the slurry in the pores of the preform in parallel to the tubular preform according to claim 1 by electrophoresis and ultrasonic wave ); And
A method for manufacturing a silicon carbide fiber-reinforced silicon carbide composite (1), comprising: (a) performing hot press-sintering on a deposited preform obtained in step (3) using the mold apparatus according to any one of claims 1 to 7 SiC f / SiC).


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