RU2718682C2 - Method of making ceramics based on silicon carbide, reinforced with silicon carbide fibres - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method of producing ceramic composite from silicon carbide reinforced with silicon carbide fibre, which can be used for operation in acidic and aggressive media, in conditions of high temperatures and prolonged mechanical action. Method of producing ceramics involves mixing silicon carbide powder containing sintering additive in form of aluminium and yttrium oxides with silicone carbide fibres obtained by siliconisation. Dried mixture was added 3 wt. % of 10 % solution of polyvinylpyrrolidone is moulded preform bilateral cold uniaxial pressing, followed by sintering by hot pressing at 1850 °C with a maximum specific pressure of 30 MPa.

EFFECT: method allows to obtain densely sintered ceramic materials having strength up to 524 MPa, a fracture toughness K_IC = 6,1 MPa⋅m^1/2.

1 cl, 2 ex, 1 tbl, 2 dwg

Description

A method of manufacturing ceramics based on silicon carbide reinforced with silicon carbide fibers.

The invention relates to a method for producing ceramic composites - a silicon carbide composite reinforced with silicon carbide fiber having a combination of physical and mechanical properties, such as high strength and hardness, low coefficient of thermal expansion and wear resistance. This type of ceramic is designed to work in acidic and aggressive environments, at high temperatures and prolonged mechanical stress. The invention relates to a method for producing silicon carbide ceramics reinforced with a refractory filler.

A method of manufacturing a composite based on silicon carbide ceramics reinforced with silicon carbide fibers involves mixing components of a fine powder of Saint Gobain silicon carbide containing aluminum and yttrium oxides, which form yttrium aluminum garnet and sintered carbide, as a sintering agent silicon. The technical attractiveness of SiC fibers is due to the fact that they successfully combine a number of important operational characteristics, such as high melting point, chemical resistance, high strength, and elastic modulus. The introduction of silicon carbide fibers reinforces the structure of the material, increasing the flexural strength.

The invention relates to a technology for producing products based on silicon carbide ceramics reinforced with silicon carbide fibers.

Silicon carbide is a promising material with a combination of properties that can be widely used as electrical insulating and radio engineering products, magnetically permeable ceramics, armor ceramics, cutting tools, as well as sliding and rolling bearings. Over the past decade, Russia has conducted research on the development of composite materials based on carbon, carbide and silicon nitride, in which the above compounds can be both a matrix and a reinforcing filler in the form of continuous or discrete fibers, whiskers.

Known patent RU No. 2058964 published 04/27/1996 С04В 035/52, С04В 035/80, "A method for producing a composite material based on carbon fiber and silicon carbide", which describes a method for producing a composite material based on carbon fiber and silicon carbide with different contents of these components by the thickness of the material. The carbon preform for subsequent silicification is made of two layers: the main layer contains carbon fibers with reduced reactivity to silicon, and the surface layer is extremely high. The preform can be made by selecting carbon fibers with different densities or by manufacturing the surface layer of a carbon fiber preform with a barrier coating of pyrocarbon and / or silicon carbide and / or silicon nitride. The pores cannot be completely filled with silicon carbide and either filled with free silicon, which leads to excessive embrittlement and a decrease in the heat resistance of the material, or remain underfilled (when free silicon is removed at temperatures above 1850 ° C), which makes the working surface permeable to the oxidant that penetrates to the bearing layers of the product material. In addition, in the case of the use of a filler chemically active in silicon in the protective layers, the strength characteristics of the material (strength, wear resistance) are sharply reduced due to the degradation of the properties of the reinforcing filler.

In patent RU No. 2084425, published on 07.20.1997, С04В 035/52, С04В 035/83, С04В 035/56, “Method for producing products from carbon-carbide-silicon composite material and carbon-carbide-silicon composite material”, describes the production of products from carbon-silicon-silicon composite material, includes the manufacture of carbon fiber blanks based on carbon fiber and a thermosetting binder, its heat treatment to form a coke matrix reinforced with carbon fiber, saturation of the blank with pyrocarbon and siliconizing . A narrow range of operating temperatures significantly limits the scope of the material.

The closest is the method of producing the composite described in patent RU No. 2176628, publ. 12/10/2001 С04В 041/88, С04В 035/80, С04В 035/573 “Composite (options) and the method of its preparation, the method of processing fiber preform (options)”. The composite preparation method includes the following operations: using a fiber preform with fibers containing silicon carbide, infiltrating the fiber preform with a suspension containing from 97 to 99.9 weight. % silicon and from 0.1 to 3 weight. % of added carbon, and the impregnation of the workpiece containing silicon molten alloy at a temperature of from 1410 ° C to 1450 ° C. The proposed method for processing a fiber preform includes the following operations: using a preform that has from 20 to 80 vol. % coated fiber, and the fiber contains silicon carbide, and from 20 to 80 vol. % porosity, by impregnation, which contains ceramic particles, the preform pores are filled, which subsequently reduces porosity, and the ceramic particles are applied to the outer surface of the preform to form a monolithic layer on the surface of the preform. Other options for processing a fiber preform are a method comprising using a fiber preform containing silicon carbide, impregnating the preform with a suspension that contains a two-fraction mixture of silicon carbide particles, and infiltrating the preform with a matrix alloy containing silicon, and a method including using a non-oxide fiber preform ceramic fiber having at least one coating, said coating containing an element selected from the group formed by carbon Odom, nitrogen, aluminum and titanium, the fiber has a decomposition temperature in the range 1410 ° C to 1450 ° C, impregnating said preform slurry containing silicon carbide particles and 0.1 to 3 wt. % carbon, preparing a coating mixture, which includes an alloy containing a metal impregnating material, the specified element that is present in the coating composition, and a polymer, applying a coating mixture to at least one of the surface areas impregnated in step b) of the preform, heating coating mixture to a temperature in the range from 1410 ° C to 1450 ° C for melting the alloy, and the infiltration of the fibrous preform with molten alloy for a period of time from 15 to 240 minutes to obtain a reinforced ceramic fiber Mr. ceramic composite. The disadvantages of the methods are porosity (10-20%) and relatively low tensile strength of about 140-200 MPa.

The objective of the invention is to increase the strength characteristics by reinforcing with silicon carbide fibers, which will help expand the scope and increase the service life of the final product.

The technical result consists in increasing the strength characteristics by reinforcing the material with silicon carbide fibers.

The technical result is achieved by the fact that the method of manufacturing ceramics based on silicon carbide involves mixing a powder of silicon carbide with a sintering additive and with SiC fibers in an isopropanol medium in a planetary mill. Drying the resulting mixture, adding 3 wt.% 10-% aqueous solution of polyvinylpyrrolidone. Shaping of blanks and sintering in an argon medium according to the invention. Preforms are formed by cold uniaxial double-sided pressing in a steel mold at a pressure of 100 MPa. Subsequent sintering is carried out by hot pressing in a graphite mold at a temperature of 1850 ° C with a maximum specific pressure of 30 MPa.

The introduction of reinforcing fibers into ceramics has a positive effect on increasing the complex of its basic properties, including strength. This is due, firstly, to the level of physicomechanical properties of modern fibrous reinforcing fillers, as well as to the implementation of a more complex, in comparison with monolithic ceramics, fracture mechanism of a ceramic composite, which is especially true for impact loads.

The difference from the prototype is that at the mixing stage, ready-made silicon carbide fibers obtained by silicification are used. Sintering is carried out by hot pressing, which reduces the porosity of the product.

Products from the proposed ceramic material are obtained as follows.

As the starting material, an industrial granular powder of silicon carbide of the Saint Gobain Sika Densitec-L brand with a dispersion of up to 1 μm was used (Figure 1). Silicon carbide powder with a sintering additive and silicon carbide fibers (Figure 2), taken in the required quantities, are mixed in a planetary mill for 30-60 minutes in an alcohol medium. The dried mixture is wiped through a sieve and pressed by double-sided pressing in a metal mold with a pressure of 100 MPa. The obtained raw materials are subjected to hot pressing in a graphite mold at 1850 ° C for 1 h in a protective medium of argon, the pressing pressure is 30 MPa. Table No. 1 presents the properties of the obtained ceramic materials based on silicon carbide with different content of silicon carbide fibers.

Example 1. Prepare a mixture of the following composition: silicon carbide with sintering additive - 97 wt. %; silicon carbide fiber - 3 wt. %

The components are mixed in a planetary mill for 60 minutes. As grinding bodies, balls of zirconium dioxide with a diameter of 5 mm are used. The dried mixture is wiped through a 063 sieve, weigh the required amount of charge, introduced into the charge 3 wt. % 10-% aqueous solution of polyvinylpyrrolidone and carry out preliminary bilateral pressing in a metal mold. The resulting raw material is hot pressed in a graphite mold at 1850 ° C for 1 h in argon. The resulting ceramic material has a bending strength at room temperature of 455 MPa, a density of 3.18 g / cm ³ .

Example 2. Prepare a mixture of the following composition: silicon carbide with sintering additive - 95 wt. %; silicon carbide fiber - 5 wt. %

The components are mixed in a planetary mill for 60 minutes. As grinding bodies, balls of zirconium dioxide with a diameter of 5 mm are used. The dried mixture is wiped through a 063 sieve, weigh the required amount of charge, introduced into the charge 3 wt. % 10% aqueous solution of polyvinylpyrrolidone and carry out preliminary bilateral pressing in a metal mold. The resulting raw material is hot pressed in a graphite mold at 1850 ° C for 1 h in argon. The resulting ceramic material has a bending strength at room temperature of 471 MPa, a density of 3.19 g / cm ³ .

Claims (1)

A method of manufacturing a silicon carbide ceramic reinforced with silicon carbide fibers, comprising mixing silicon carbide powder with a sintering additive and with silicon carbide fibers in an isopropanol medium in a planetary mill, drying the resulting mixture, adding 3 wt.% 10% aqueous solution of polyvinylpyrrolidone, forming blanks and sintering in an argon medium, characterized in that silicon carbide fibers obtained by the method of siliconization are used as the reinforcing component; preforms are formed by preliminary cold dnym bilateral uniaxial pressing in a steel mold under a pressure of 100 MPa, followed by sintering by hot pressing in a graphite mold at 1850 ° C with a maximum specific pressure of 30 MPa.

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