Manufacturing method for fiber-reinforced silicon carbide-based composite material using reaction sintering method and manufacturing method for intermediate material

Abstract

To manufacture a product called a membrane-like prepreg sheet by impregnating ceramic-reinforced fibers with a slurry made from a mixture of powders of the raw materials: carbon, silicon, and silicon carbide, or to manufacture a preform by impregnating the reinforced fibers in a three-dimensional shape with the slurry, and to manufacture ceramic fiber-reinforced Si-based composite materials by heating them to 1420°C or higher.SOLUTION: Powdered raw materials are mixed together uniformly to create a slurry containing polymers or the like, which act as auxiliary agents for a film formation, and the slurry is then impregnated into ceramic fibers to manufacture a sheet material called a prepreg sheet. This sheet is then laminated and molded, and then heated at high temperatures to manufacture ceramic fiber-reinforced Si-based composite materials. Alternatively, the slurry is impregnated into reinforcing fibers with three-dimensional structure, and then heated at high temperatures to manufacture ceramic fiber-reinforced Si-based composite materials.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing a fiber-reinforced SiC-based composite material using a reaction sintering method, and relates to a production method in which the novel intermediate material (NIC method prepreg sheet) produced by the present invention is laminated (preformed) and heated, and a method in which reinforcing fibers are impregnated with the slurry used in the present invention and heated. [Background technology]

[0002] Ceramic fiber reinforced ceramic composites aim to improve the strength and ductility of ceramic materials by fiber reinforcement. For this reason, the integrity of the components, namely, fiber and matrix, is important. The fiber / matrix interface (F / M interface) is one of the important elements, and plays an important role in suppressing crack propagation from the matrix to the fiber and protecting the fiber.

[0003] Known methods for forming silicon carbide, the matrix of silicon carbide-based composite materials, include the chemical vapor deposition method (CVI method), polymer impregnation sintering method (PIP method), and nano powder impregnation transient liquid phase sintering method (NITE method). The NITE method is outstanding in terms of the excellent crystallinity and density of the SiC matrix, but it requires high temperature (1800°C or higher) and high pressure (20 MPa or higher) process conditions, and has the disadvantage of high process costs. At present, the reaction sintering method, which uses a liquid phase of silicon to form SiC by reacting it with carbon, is also called the liquid sintering method (liquid sintering method) and is in practical use most widely. The characteristics of this method are that it is an inexpensive process and can form a matrix with excellent airtightness and thermal conductivity properties. However, the remaining issues are that the C fiber is damaged by the reaction with high-temperature liquid Si, that the C layer that covers the fiber is damaged and its strength is reduced, and that the remaining Si phase liquefies at high temperatures, causing a significant deterioration in high-temperature strength. Many attempts have been made to address this issue, but the problems have not yet been solved.

[0004] Major problems with the reactive sintering method include process management for using large amounts of liquid silicon, the need to remove the silicon from the surface of the finished product after the process is complete, and the decrease in purity of silicon due to the dissolution of carbon, SiC, and other impurities from the reacting material, the preform (made of fibers and matrix precursors that will ultimately become SiC-based composite materials). These are obstacles to lowering the cost of the product.

[0005] The general preforms (mentioned above) used in the reaction sintering method vary in size and shape for each product, and are not suitable for manufacturing small quantities of a wide variety of products. There has long been a demand for intermediate materials that are easy to handle and can be used for a wide range of purposes. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2022-18980 [Non-patent literature]

[0007] [Non-Patent Document 1] Akiko Suyama, Yoshiyasu Ito, Toshiba Review Vol. 63, No. 2 (2008) P11-14. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention (hereinafter referred to as the NIC method) is a method for producing a sheet-like product called a prepreg sheet by impregnating a long fiber or fiber fabric as a reinforcing fiber with a slurry for impregnation, which is a mixture of carbon fine powder (Carbon Black, etc.) and Si submicron-class fine powder with SiC fine powder (add PCS, a precursor polymer that is the raw material of SiC, as necessary), and a film-forming material (mainly inorganic polymer) for forming into a film shape. This prepreg sheet is laminated to produce a quasi-product called a preform. This preform is heated, Si is liquefied, and reacted with carbon to provide a method for rapidly producing a ceramic fiber-reinforced SiC-based composite material with extremely low porosity, excellent airtightness, and excellent thermal conductivity, using only heat treatment. This method is a heating-only process that does not use liquid-phase Si. The remaining Si phase is extremely small in a single heating process, and the remaining Si phase is extremely fine, so it does not cause strength deterioration. The process can be simplified by manufacturing and using a membrane-like prepreg sheet, which is easy to handle and quality control, as an intermediate material. These simultaneously realize high performance products, high compatibility with a wide variety of products, and low prices. Figure 1 shows a conceptual diagram of the difference between the conventional reaction sintering method and the NIC method.

[0009] A method in which the above-mentioned impregnation slurry is directly impregnated into a fiber structure having a 3D structure and then heated may also show economic advantages in the manufacture of single-shape mass-produced products, and such a method also belongs to the present invention as an advanced form. [Means for solving the problem]

[0010] The present invention relates to a manufacturing method characterized by the production of a sheet-like product called a prepreg sheet by impregnating a slurry prepared by mixing carbon powder, Si powder, and SiC nanopowder (including the addition of PCS, a precursor polymer that is the raw material for SiC), with a film-forming material (mainly inorganic polymer) for molding into a film shape, into a long fiber or fiber fabric that serves as a reinforcing fiber.

[0011] The present invention relates to a manufacturing method characterized in that a preform obtained by laminating and molding the prepreg sheet of the present invention is heated in a vacuum or in an inert atmosphere to produce ceramic fiber-reinforced Si-based composite materials of various sizes and shapes.

[0012] Various inorganic materials can be used for the reinforcing ceramic fibers of the present invention. Specifically, carbon fibers, silicon carbide fibers, silicon nitride fibers, boron fibers, etc. can be used alone or in combination. The substrate must have a heat resistance at least higher than the reaction temperature. For example, silicon carbide fibers with high crystallinity and near stoichiometric composition that do not contain impurity oxygen, such as Hi-Nicalon Type S or Tyranno SA, are silicon carbide fibers with a heat resistance of 1800°C, and the heating temperature during processing can be increased to nearly 1800°C.

[0013] The raw material powder carbon, Si, and SiC used in the manufacturing method of the present invention are fine particles, flakes, fine particles, ultrafine particles (nano powder), nanotubes, etc., and the purity has a degree of freedom depending on the application, and basically a purity of 95% or more is acceptable, excluding harmful impurities. The raw material for SiC also includes the addition of PCS, a precursor polymer.

[0014] The reinforcing ceramic fibers used in the manufacturing method of the present invention may be in the form of long fibers, various woven fabrics such as plain weave fabrics, satin weave fabrics, three-dimensional weave fabrics and string weave fabrics, or in the form of felt or nonwoven fabric.

[0015] The treatment temperature in the manufacturing method of the present invention is 1420°C or higher. If the treatment temperature is lower than 1420°C, sufficient liquid phase Si is not formed in a short time, and it is difficult to form SiC by reaction with carbon. There is no particular upper limit to the treatment temperature, but it must be adjusted according to the heat resistance of the fiber to be treated. In general, 1450 to 1800°C is preferable. The setting of the heating profile and the maintenance time at the maximum temperature are determined by the shape, dimensions, and use (corresponding to the product specifications) of the product to be manufactured. The cooling profile after heating is also determined by the shape, dimensions, and use (corresponding to the product specifications) of the product.

[0016] The atmosphere inside the furnace in the manufacturing method of the present invention is basically a vacuum, although an inert gas atmosphere (e.g., Ar, He, etc.) may be used depending on the product specifications.

[0017] When the furnace atmosphere in the manufacturing method of the present invention is an inert gas, it is possible to utilize the effect of hot isostatic pressing by increasing the gas pressure. Effect of the Invention

[0018] The manufacturing method of the present invention is characterized by optimizing the component ratio of the fine raw material powder, mixing it as uniformly as possible, and impregnating it between and within the fiber bundles, which promotes fine dispersion of the residual Si and overcomes the disadvantages of the conventional reactive sintering method (RS method). [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 illustrates the difference in concept between the method of the present invention and the conventional reactive sintering method. [Diagram 2] FIG. 2 shows a comparison of the characteristics and microstructures of the method of the present invention and the conventional reactive sintering method. (Example 1) [Diagram 3] FIG. 3 illustrates the difference in the amount of residual Si and dimensions of SiC produced by the NIC method with different ratios of C, Si, and SiC (Example 2). [Figure 4] FIG. 4 shows the appearance of the prepreg sheet to the finished SiC / SiC plate (Example 3). [Diagram 5] FIG. 5 is a comparison of the microstructure of the SiC / SiC composite material of Example 3 between the matrix SiC and the SiC fiber bundle (Example 3). Example 1

[0020] SiC plates without fibers (only matrix components) were manufactured by the conventional reaction sintering method and the method of the present invention, and bending strength tests and thermal conductivity characteristic tests were carried out. Reaction sintering method: Si powder with an average particle size of 1μm and carbon powder with a size of 100nm are mixed in a solution of water and dispersant under the condition of C / SiC=0.5 to create a slurry. The slurry is pressure cast and dried at room temperature to create a solid preform. This preform is placed in a heating container, 300nm fine Si powder is poured in from above, and heated at 1450℃ for 2 hours to create a SiC plate. The present invention's method (NIC method): Si powder with an average particle size of 1 μm, carbon powder with a size of 100 nm, and Si powder with a size of 300 nm are mixed in a ratio of C:Si:SiC=3:8:5, and mixed into a mixed solution of ethanol, PVB (B60H) powder, and PEG (#400) liquid to create a slurry. This slurry is made into a green sheet membrane using a sheet casting method. The green sheets are stacked into a shape of 60x60x20 mm, and a preform is created by applying a pressure of 4 MPa at room temperature. This preform is heated in a vacuum at 1450°C for 2 hours to create a SiC plate. Figure 2 shows a comparison of the microstructure, bending strength, and thermal conductivity of the SiC plate created. Example 2

[0021] A slurry is made by mixing Si powder with an average particle size of 1 μm, carbon powder with a size of 100 nm, and Si powder with a size of 300 nm in different ratios and mixing them into a mixed solution of ethanol, PVB (B60H) powder, and PEG (#400) liquid. This slurry is made into a green sheet membrane using the sheet casting method. The green sheets are stacked into a shape of 60 x 60 x 20 mm, and a preform is made by pressing them at room temperature at a pressure of 4 MPa. This preform is heated in a vacuum at 1450 °C for 2 hours to make a SiC plate. Figure 3 compares the microstructure, residual Si amount, and average diameter of residual Si of SiC plates made by changing the C:Si:SiC mixture ratio. By changing the dimensions and mixture ratio of the raw powder and changing the heating conditions according to the application, SiC suitable for the purpose can be made. The film thickness and production speed can be changed by appropriately adjusting the mixture ratio of ethanol, PVB (B60H) powder, and PEG (#400) liquid to make the green sheet and the prepreg sheet impregnated with reinforcing fibers. Example 3

[0022] Using the slurry used to manufacture the green sheet in Example 2, a SiC / SiC prepreg sheet was manufactured by two-stage impregnation of a SiC plain weave fabric with a low-viscosity slurry and a standard-viscosity slurry, a preform was formed by laminating and molding the prepreg sheet, and a SiC / SiC plate was manufactured by subjecting the preform to a high-temperature heat treatment at 1450°C for 2 hours. The appearances of each of these are shown in Figure 4. A typical example of the internal microstructure is shown in Figure 5.

Claims

1. Carbon fine powder (Carbon Black, etc. This method involves impregnating long fibers or woven fiber fabrics with a slurry made by mixing submicron-class Si fine powder with SiC fine powder (including PCS, the precursor polymer that forms SiC), and a film-forming material (mainly inorganic polymers) to be molded into a film shape, to produce a sheet-like product known as a prepreg sheet.

2. This method involves heating a semi-finished product called a preform, which is made by laminating prepreg sheets, to produce a ceramic fiber reinforced Si-based composite material.

3. A method for producing a ceramic fiber-reinforced Si-based composite material by heating a semi-product called a preform, in which three-dimensional reinforcing fibers are impregnated with the slurry of claim 1.

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