RU2544206C1 - Method of manufacturing products from ceramic-matrix composite material - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: matrix from thermostable fibres is made, filled with disperse filler and impregnated with coke-forming binding agent. As dispersive filler applied are refractory metals such as B, Si, Ti, Zr, Hf, in capsule from respective nitride or without one. Then, moulding of plastic workpiece and its thermal processing in nitrogen medium at temperature of carbide and/or carbonitrides of respective metals is realised. Obtained porous workpiece is siliconised by steam-liquid phase method by capillary condensation of silicon vapour, heated to 1700-1850°C and kept in the said interval of temperatures for 1-3 hours.

EFFECT: invention provides possibility of manufacturing bulky thin-walled products without application of mechanical processing, increased reliability of their work in oxidising media at high temperatures.

3 cl, 13 ex, 1 tbl

Description

The invention relates to the field of composite materials with a ceramic matrix, designed to work in an oxidizing environment and mechanical loading at high temperatures.

A known method of manufacturing products from carbon-carbide-silicon composite material (UKKM), including the formation of a skeleton of carbon fibers, compacting it by saturation with pyrocarbon and silicification [US patent No. 4397901, class. C23C 11/08, 1983].

With this method, a lot of free silicon remains in the material, which lowers the level of working temperatures of the product and increases the residual stresses in the material (due to the expansion of silicon during solidification), which leads to a decrease in its strength. In addition, the material does not have a sufficiently high content of silicon carbide, which reduces its stability when working in oxidizing environments at high temperatures.

The closest to the proposed technical essence and the achieved effect is a method of manufacturing products from ceramic composite materials, including the manufacture of a frame of heat-resistant fibers and filling it with a dispersed filler, followed by siliconizing the resulting workpiece.

In accordance with this method, graphite powder is used as a dispersed filler, and siliconization is carried out by the liquid-phase method by impregnating the preform with a molten silicon [1] L.N. Tuchinsky. Composite materials obtained by the method of impregnation, M.: Metallurgy, 1986 p.194. [2] V.N. Kostikov et al. - In the book. “Carbon-based structural materials. M .: Metallurgy, 1980, No. 15 p. 78-88.

The method can significantly increase the content of silicon carbide and reduce the content of free silicon in the ceramic composite material by reducing pore size and thereby to some extent increase its oxidative stability and strength.

The method does not provide the possibility of manufacturing large-sized thin-walled products without their mechanical processing. In addition, the composite material (KM) obtained by this method still has insufficient strength due to partial degradation of the properties of the reinforcing fibers, in particular, carbon fibers partially carbidize under the influence of silicon, and silicon carbide partially dissolve in the silicon melt (or vapor condensate) .

The objective of the invention is to provide the possibility of manufacturing large-sized thin-walled products without the use of mechanical processing, as well as improving the reliability of their work in oxidizing environments at high temperatures.

The problem is solved due to the fact that in the method of manufacturing products from a ceramic composite material, including the manufacture of a framework of heat-resistant fibers, filling it with a dispersed filler and siliconizing the resulting porous preform, in accordance with the proposed technical solution, refractory metals are used as a dispersed filler, such as B, Si, Ti, Zr, Hf, in a capsule of the corresponding nitride or without it, and the workpiece is siliconized by the vapor-liquid phase method by capillary molecular condensation silicon vapor, followed by heating to 1700-1850 ° C and holding at this temperature range for 1-3 ^hours; in this case, before carrying out the siliconization process, the framework of heat-resistant fibers filled with dispersed filler is impregnated with a coke-forming binder, a plastic preform is formed and it is heat treated in a nitrogen medium at the temperature of formation of carbides and / or carbonitrides of the corresponding metals.

In a preferred embodiment of the method, the encapsulation of the metal particles is carried out after filling the framework by heat treatment of the obtained porous preform in a nitrogen atmosphere.

In another preferred embodiment of the method of molding a plastic preform, it is carried out on the basis of a binder, which is a mixture of a coke-forming binder with a silicone binder.

The use of refractory metals such as B, Si, Ti, Zr, Hf as a disperse filler in the capsule of the corresponding nitride or without it creates the conditions for the formation of a certain part of the ceramic matrix and / or discrete hardening by its particles formed during the chemical transformation particulate filler particles.

The implementation before the silicification process of forming a plastic preform based on a coke-forming binder and heat treatment in a nitrogen medium at the temperature of formation of carbides and / or carbonitrides of the corresponding metals allows the workpiece to be given the desired shape and size before its material becomes difficult to machine, and also into in conjunction with the above feature - to implement the conditions necessary for the partial formation of a ceramic matrix (i.e., even before the process silicification) or, at least, for dispersed hardening of a ceramic matrix by carbides and / or carbonitrides of refractory metals.

In this case, the heat treatment in nitrogen increases the likelihood of the formation of metal carbonitrides.

And yet: as a result of the chemical interaction of coke (carbon) with metals such as B, Si, Ti, Zr, Hf (including those having a capsule of the corresponding nitrides), part of the coke is consumed. This facilitates the conversion of the remainder of the coke to silicon carbide during the siliconization process.

It is even more facilitated — during the siliconization process — the processing of coke into silicon carbide if the plastic preform is formed on the basis of a binder, which is a mixture of a coke-forming binder with a siloxane binder. This is due to the fact that during the interaction of siloxane groups with coke, volatile compounds are formed, namely: silicon monoxide (SiO) and carbon monoxide (CO), which leads to the formation of an additional open porosity in the workpiece material (before the siliconizing process).

In addition, the implementation before the siliconizing process of forming a plastic preform based on a coke-forming binder and heat treatment in a nitrogen environment at the temperature of formation of carbides and / or carbonitrides of the corresponding metals can significantly reduce the access of silicon to the surface of the reinforcing fibers. This is achieved both by covering part of their surface with a partially formed ceramic matrix, and by reducing the size of pores, which (in an already smaller amount) contain silicon, which is forced (moreover) to primarily interact with more active than reinforcing fibers coke.

Siliconizing a porous preform by the vapor-liquid-phase method by capillary condensation of silicon vapors allows silicon to be introduced into pores of arbitrarily small sizes (even into pores smaller than 3 μm into which silicon melt does not penetrate) and even into pores whose surface is covered with coke active against silicon, and get silicon carbide after their interaction.

Continuing further heating to 1700-1850 ° C and holding in that temperature range for 1-3 ^hours allows complete carbidization silicon and thus - the formation of the ceramic matrix.

In the new set of essential features, the object of the invention has a new property: the ability to give the product from KM the desired shape and size without the use of mechanical processing, as well as to ensure a high content of KM ceramic matrix with the exception of the degradation of the properties of the reinforcing fibers.

The new property allows us to solve the problem, namely: it provides the ability to manufacture large-sized thin-walled products from ceramic composite materials without the use of mechanical processing, and also improves the reliability of their work in oxidizing environments at high temperatures.

The method is as follows.

The frame is made of heat-resistant fibers such as carbon and silicon carbide fibers. Then the frame is filled with dispersed filler. In this case, refractory metals, such as B, Si, Ti, Zr, Hf in a capsule of the corresponding nitride or without it, are used as a dispersed filler. In a preferred embodiment of the method, the encapsulation of the metal particles is carried out after filling the framework by heat treatment of the obtained porous preform in a nitrogen atmosphere.

Then carry out the molding of the plastic blank. For this, the fiber preform is impregnated with a coke-forming binder (and in a preferred embodiment of the method, it is impregnated with a binder, which is a mixture of a coke-forming binder with a siloxane binder), cured under pressure at the curing temperature of the binder.

After receiving a plastic preform (with the required shape and size), heat treatment is carried out in nitrogen at a final temperature equal to the temperature of formation of carbides and / or carbonitrides of the corresponding metals (it may differ for different nitrides).

Then, the obtained porous preform obtained after heat treatment is siliconized by the vapor-liquid-phase method by capillary condensation of silicon vapors. In this case, silicon enters the pores of arbitrarily small sizes. This is done at relatively low temperatures (not more than 1500 ° C). Thereafter, heating was continued up to 1700-1850 ° C, producing an extract in this temperature range for 1-3 ^hours to complete the carbonization silicon. During this period, a partial chemical interaction of silicon with metal carbides and / or carbonitrides of metals can also occur with the formation of Novotny triple phases (such as Ti ₅ Si ₃ C and the like) and silicides of the corresponding metals with high oxidation resistance.

Then the workpiece is cooled.

The following are examples of a specific implementation of the method of manufacturing products from KM with a ceramic matrix.

Examples 1, 1a, 1b.

The product in the form of a plate measuring 100 × 400 × 3.6 mm was made as follows. A carbon-piercing framework 4.3 mm thick was formed from carbon fabric of the TMP-4 brand (having a pyrocarbon coating on the fibers). The framework was filled with a fine filler, for which a suspension was prepared on the basis of silicon powder (example 1) or silicon in a capsule of silicon nitride (example 1a) with a particle size of not more than 5 μm and impregnated to it under vacuum with superposition of ultrasound onto the suspension. Then, the obtained porous preform was impregnated with a coke-forming binder, namely phenol-formaldehyde grade BZH-3. After that, the plastic preform was molded under a pressure of 6 kgf / cm ² at a final temperature of 150 ° C. Received a plastic blank of size 100 × 400 × 3.5 mm Then, the plastic billet was heat-treated in argon (example 1) and in highly pure nitrogen (examples 1a and 1b) at a final temperature of 1300 ° C. During this period, the formation of coke from the polymer matrix and the interaction of some of it with silicon (Example 1) or silicon encapsulated in a nitride silicon shell occurred. In this case, silicon carbide and / or silicon carbonitride was formed. After this, the obtained preform was placed in a retort (located in the reactor of the vacuum unit) together with crucibles filled with silicon. Then the billet and crucibles with silicon were heated at a reactor pressure of 27 mm Hg. up to a temperature of 1750 ° C. Moreover, after the workpiece reached a temperature of 1400 ° C, a higher temperature was set on crucibles with silicon (in the specific case 1500 ° C) due to their additional heating, and exposure was performed at the indicated temperatures for 8 hours. During this period, the process of capillary condensation of silicon vapors was realized, which allowed filling the pores of the material with silicon. Then it was heated to 1750 ° C and held at 1750-1800 ° C for 2 hours in the absence of a temperature difference between the silicon vapor and the workpiece. During this period, most of the coke remaining unreacted after interaction with a finely divided silicon powder was carbidized due to interaction with a silicon vapor condensate. After that, the workpiece was cooled. As a result, in accordance with example 1, a KM plate was obtained with preservation of its shape and dimensions obtained after molding a plastic preform. CM had an apparent density of 1.72 g / cm ³ and an open porosity of 0.6%. The content of silicon carbide and free silicon in it amounted to 39.6% and 11.8%, respectively.

Examples 2, 2a, 2b, 2c.

A plate with a size of 100 × 400 × 3.5 mm was made of KM, analogously to Example 1. The difference was that titanium (or rather titanium hydride, was used as a dispersed filler, since titanium powder very actively absorbs gases and is also very pyrophoric) (example 2), boron powder (example 2a), zirconium powder (example 2b), hafnium powder (example 2c) with particle sizes of not more than 5 microns. The properties of the obtained material are given in the table.

Example 3

A plate with a size of 100 × 400 × 3.5 mm was made of KM, analogously to Example 1. The difference was that as a binder in the molding of a plastic blank, a mixture of a coke-forming binder (phenol-formaldehyde grade BZh-3) with a polysiloxane binder (organosilicon resin K-9 brand) was used. The properties of the obtained CM are shown in the table.

Example 4

A plate with a size of 100 × 400 × 3.5 mm was made of KM, analogously to Example 1. The difference was that carbon fiber fabric of the UT-900 brand was used as a reinforcing filler.

The properties of the obtained material are given in the table.

Example 5

A plate with a size of 100 × 400 × 3.5 mm was made of KM, analogously to Example 1. The difference was that as a reinforcing filler, a fabric made of Nikalon carbide-silicon fibers was used. Material properties are given in the table.

Example 6 of a specific implementation of the method, as well as examples 1, 1a, 1b, 2a-2c, 3-5 in a more concise summary, but with an indication of some properties of the CM, are shown in the table. Here are examples 7 and 8 of the manufacture of products from KM in accordance with the prototype method.

Based on the analysis of the table, the following conclusions can be drawn:

1. The manufacture of products from KM with a ceramic matrix in accordance with the claimed method allows to obtain KM:

a) with a sufficiently high content of ceramic matrix, a relatively low content of free silicon and carbon;

b) with higher strength in comparison with the prototype (compare examples 1, 2, 3 with example 8, and examples 4, 6 with example 7), which is due to less degradation of the properties of the reinforcing filler under the influence of silicon.

2. Depending on the medium and temperature of processing the plastic billet, refractory metals turn into the corresponding carbides and / or carbonitrides of metals (carbonitride is conventionally designated as MeC × MeN, Me is metal). When siliconizing, they partially transfer to metal silicides.

The results of measuring the geometry of the plate blanks in the redistribution indicate the fundamental possibility of their preservation in the manufacture of large-sized thin-walled products by the proposed method.

Table No. p / p Type and grade of filler Type of particulate filler Type and grade of binder used in the molding of plastic preforms Heat treatment temperature ° C, reactor pressure, medium The maximum temperature during silicification, ° C KM Properties Density, g / cm ³ Open porosity,% Structure Content, wt.% The content of free carbon / silicon, wt.% Tensile Strength, MPa Ceramic matrix ** one 2 3 four 5 6 7 8 9 10 eleven 12 one TMP-4 low-modulus carbon fabric silicon Phenol-formaldehyde grade БЖ-3 1300, P _atm , argon 1800 1.72 0.6 SiC + C + Si 39.6 11.8 / 7.9 43,4 1a - // - silicon in a capsule of Si ₃ N ₄ ^* - // - 1400, P _atm , nitrogen - // - 1.71 0.7 Si ₃ N ₄ × SiC + SiC + C + Si 40,2 10.3 / 8.5 48.9 1b - // - silicon - // - 1400, P _atm , nitrogen - // - 1.70 0.6 - // - 40.8 9.7 / 8.3 45.6 2 - // - titanium hydride - // - 1400, P _atm , argon - // - 1.83 1.4 TiC + C + SiC + Si 50.9 7.0 / 3.8 50.1 2a - // - boron - // - - // - - // - 1,66 0.8 B ₄ C + SiC + C + Si 43.9 9.8 / 4.1 - 2b - // - zirconium - // - - // - - // - 1.86 1.7 ZrC + SiC + C + Si 50,0 8.1 / 4.3 - 2c - // - hafnium - // - - // - - // - 1.90 1.4 HfC + SiC 51.8 7.5 / 3.9 -

one 2 3 four 5 6 7 8 9 10 eleven 12 3 TMP-4 low-modulus carbon fabric silicon A mixture of phenol-formaldehyde binder grade K-9 1300, P _atm , argon 1800 1.76 0.8 SiC + C + Si 43.9 9.6 / 6.8 40.1 four UT-900 brand carbon fabric - // - Phenol-formaldehyde binder grade BZH-3 - // - - // - 1.88 5.9 SiC + C + Si 47.4 8.5 / 6.9 105.9 5 Fabric made of silicon carbide fibers such as "Nikalon" - // - - // - - // - - // - 2.45 2.0 SiC × Si ₃ N ₄ + SiC + C + Si 31.7 6.5 / 5.0 164.7 6 UT-900 brand carbon fabric - // - - // - 1300, P _atm , nitrogen 1700 1.92 4.8 SiC × Si ₃ N ₄ + SiC + C + Si 50.1 7.1 / 6.4 108.3 7 UT-900 high modulus carbon fabric graphite with particle size ≤5 μm - - 1750 1.94 6.0 SiC 55,2 9.8 / 7.5 69.1 8 TMP-4 low-modulus carbon fabric graphite with particle size ≤5 μm - - 1750 1.78 0.4 SiC 51.3 9.4 / 7.7 34.5 * encapsulation of silicon particles in the framework, carried out by heating from 800 ° C at P _atm in especially pure nitrogen with extracts at 1000, 1100, 1200, 1300, 1400 ° C for 2 hours. ** excluding the content of free C and Si.

Claims (3)

1. A method of manufacturing products from a ceramic composite material, including the manufacture of a frame of heat-resistant fibers, filling it with a dispersed filler and siliconizing the resulting porous preform, characterized in that refractory metals such as B, Si, Ti, Zr, Hf are used as a dispersed filler , in a capsule of the corresponding nitride or without it, and the workpiece is siliconized by the vapor-liquid phase method by capillary condensation of silicon vapor, followed by heating to 1700-1850 ° C and holding in the specified temperature range for 1-3 ^x hours; in this case, before carrying out the siliconization process, the framework of heat-resistant fibers filled with dispersed filler is impregnated with a coke-forming binder, a plastic preform is formed and it is heat treated in a nitrogen medium at the temperature of formation of carbides and / or carbonitrides of the corresponding metals. 2. The method according to claim 1, characterized in that the encapsulation of the metal particles is carried out after filling the frame by heat treatment of the obtained porous preform in nitrogen. 3. The method according to claim 1, characterized in that the molding of the plastic preform is carried out on the basis of a binder, which is a mixture of coke-forming binder with a siloxane binder.