By using various combinations of binders and fillers, polymer composite materials (PCMs) with the necessary physical, mechanical and physical characteristics for use in different conditions. Often obtaining polymer composite materials and molding of products from them are combined into one process, which allows to significantly reduce the cost of products made from composites.

The optimal molding method for each specific PCM product is determined by a large number of factors, such as:

• design features of the product;
• the purpose of the resulting product (and the corresponding requirements - surface cleanliness, dimensional accuracy, etc.);
• properties and technological capabilities of the binding component;
• filler structure;
• economic factors (cost, productivity and service life of equipment, labor intensity, etc.)

Features of molding polymer composites based on thermoplastics

Productivity of extraction and processing methods polymer composites based is mainly determined by the speed of physical and physico-chemical processes occurring in the binder polymer during processing:

• melting;
• crystallization;
• heating;
• cooling;
• relaxation, etc.

The completeness and nature of these processes are largely determining factors for the quality of the finished product. In addition, the quality of finished products is also affected by destructive processes in the polymer, occurring at an increased speed as a result of thermal and mechanical effects on the material from the working parts of machines during the processing process.

The required shape can be given to a product from the development of highly elastic or plastic deformation. Due to the high viscosity of the material, the rate of deformation processes is low. Depending on the physical state of the polymer at the time of molding, varying degrees of nonequilibrium are achieved in the finished product due to incomplete relaxation of internal stresses. This imposes certain restrictions on the temperature range of operation of products obtained by various methods. An increase in the proportion of the highly elastic component of deformation leads to a decrease in the upper temperature limit down to the glass transition temperature of the polymer.

Features of molding polymer composite materials based on thermosets

The peculiarity of the methods for producing polymers is the combination of the physical processes of the molding itself with the chemical reactions of the formation of three-dimensional polymers (curing), and the properties of the products are determined by the speed and completeness of curing. Incomplete curing causes instability of the properties of products over time, as well as the occurrence of destructive processes in finished products.

Depending on the processing method, curing is combined with molding of the product (in the case of pressing thermosets, it occurs after the product is formed in the mold cavity (injection molding, thermoset injection molding) or when heat treatment molded blank (when molding large-sized products). Achieving the required completeness of curing of certain types of oligomers even in the presence of catalysts and at elevated temperatures requires considerable time (up to several hours). In this case, the final curing can be carried out outside the molding equipment, since shape stability is acquired long before the curing process is completely completed.

Some problems in the production of polymer composite materials

The presence of temperature differences across the cross-section of the product during processing leads to an increase in structural heterogeneity and the appearance of additional stresses associated with differences in the rates of cooling, crystallization, relaxation in different parts, as well as with varying degrees of hardening (in the case of thermosets). This causes heterogeneity in the properties of the material in the product, which is not always acceptable, and is the cause of many types of defects (warping, cracking, etc.). The existence of internal stresses, primarily orientational, also limits the operating temperature range. Some increase in the heterogeneity of the supramolecular structure and a decrease in internal stresses can be achieved through heat treatment of the finished product, but it is more effective to use methods of directed regulation of structures during the processing process.

When molding products from polymer composites possible significant change in structure, and consequently, the properties of the polymer. Therefore, materials and products obtained from the same polymer may vary significantly in characteristics if their technologies are different. The most important factors influencing the structure and properties of PCM are the processing process parameters:

• temperature,
• pressure,
• heating and cooling modes, etc.

Correct accounting and selection of all technological parameters allows us to achieve in the finished product:

• homogeneous structure,
• minimum level residual stresses(structural, shrinkage, thermal),
• high degree of completeness of the processes of hardening, crystallization,

to get high quality products.

I dedicated to history composite materials. I continue to spend my free time on this topic and today I want to talk a little about the terms and technologies of prototyping using polymer composites. If you have nothing to do for long winter evenings, then you can always make a snowboard, a motorcycle case, or a smartphone case from carbon fiber fabric. Of course, the process may end up being more expensive than buying a finished product, but it’s interesting to make something with your own hands.

Below the cut is a review of methods for manufacturing products from composite materials. I would be grateful if you add me in the comments so that the result is a more complete post.

A composite material is created from at least two components with a clear boundary between them. There are layered composite materials - for example, plywood. In all other composites, the components can be divided into a matrix, or binder, and reinforcing elements - fillers. Composites are usually divided according to the type of reinforcing filler or matrix material. You can read more about the use of composites in the post, and this post focuses on methods for making products from composites.

Hand molding

In the case of producing single pieces, the most common method is hand molding. Gelcoat is applied to the prepared matrix - a material to obtain a good finish on the outer part of the reinforced material, which also allows you to select the color for the product. Then a filler is placed in the matrix - for example, fiberglass - and impregnated with a binder. We remove air bubbles, wait until everything cools down, and finish it with a file - cut it, drill it, and so on.

This method is widely used to create body parts for cars, motorcycles and mopeds. That is, for tuning in cases where it is not limited to sticking a “carbon-look” film.

Sputtering

Spraying does not require cutting the glass material, but instead requires the use of special equipment. This method is often used to work with large objects, such as boat hulls, vehicles, and so on. In the same way as in the case of hand molding, the gelcoat is applied first, then the glass material.

RTM (injection)

The method of injecting polyester resin into a closed mold uses equipment from a matrix and a counter mold - a punch. The glass material is placed between the matrix and the response mold, then a hardener - polyester resin - is poured into the mold under pressure. And, of course, finishing with a file after curing - to taste.

Vacuum infusion

The vacuum infusion method requires a bag in which a vacuum is created using a pump. The bag itself contains reinforcing material, the pores of which, after pumping out the air, are filled with a liquid binder.

An example of a method is for making a skateboard.

Winding

The method of winding composites makes it possible to make ultra-light cylinders for compressed gas, for which they use a PET liner pumped up to 2-5 atmospheres, as well as composite pipes used in the oil industry, chemical industry and in public utilities. From the name it is easy to understand that fiberglass is wound around a moving or stationary object.

The video shows the process of winding fiberglass onto a cylinder.

Pultrusion

Pultrusion is “broaching”. In this method, there is a continuous process of pulling the composite material through a pulling machine. The process speed is up to 6 meters per minute. The fibers are passed through a polymer bath, where they are impregnated with a binder, and then pass through a preforming device to obtain the final shape. The material is then heated in the mold to produce the final hardened product.

The process of producing sheet piles using pultrusion.

Direct pressing

Thermoplastic products are manufactured in molds under pressure. For this purpose, high-temperature hydraulic presses with a force from 12 to 100 tons and maximum temperature about 650 degrees. Plastic buckets, for example, are made this way.

Autoclave molding

An autoclave is necessary for carrying out processes under heat and pressure above atmospheric pressure in order to speed up the reaction and increase the yield of the product. Composite materials are placed inside the autoclave on special forms.

Composite Products

Composite materials are widely used in aircraft manufacturing. For example, built from them.

Automotive industry

Prostheses and orthoses.

If you have any additions, be sure to write about them in the comments. Thank you.

1. Composite or composite materials - materials of the future.

After modern physics of metals explained to us in detail the reasons for their plasticity, strength and its increase, intensive systematic development of new materials began. This will probably lead, already in the imaginable future, to the creation of materials with strength much greater than that of conventional alloys today. In this case, much attention will be paid to the already known mechanisms of steel hardening and aging of aluminum alloys, combinations of these known mechanisms with formation processes and numerous possibilities for creating combined materials. Combined materials reinforced with either fibers or dispersed solid particles offer two promising paths. The first to introduce the finest high-strength fibers of glass, carbon, boron, beryllium, steel or thread-like single crystals into an inorganic metal or organic polymer matrix. As a result of this combination, maximum strength is combined with a high elastic modulus and low density. These are the materials of the future that are composite materials.

Composite material is a structural (metallic or non-metallic) material that contains reinforcing elements in the form of threads, fibers or flakes of a stronger material. Examples of composite materials: plastic reinforced with boron, carbon, glass fibers, strands or fabrics based on them; aluminum reinforced with steel and beryllium threads. By combining the volumetric content of components, it is possible to obtain composite materials with the required values ​​of strength, heat resistance, elastic modulus, abrasive resistance, as well as create compositions with the necessary magnetic, dielectric, radio-absorbing and other special properties.

2. Types of composite materials.

2.1. Composite materials with a metal matrix.

Composite materials or composite materials consist of a metal matrix (usually Al, Mg, Ni and their alloys) reinforced with high-strength fibers (fibrous materials) or finely dispersed refractory particles that do not dissolve in the base metal (dispersion-strengthened materials). The metal matrix binds the fibers (dispersed particles) into a single whole. Fiber (dispersed particles) plus a binder (matrix) that make up one or another composition are called composite materials.

2.2. Composite materials with a non-metallic matrix.

Composite materials with a non-metallic matrix have found wide application. Polymer, carbon and ceramic materials are used as non-metallic matrices. The most widely used polymer matrices are epoxy, phenol-formaldehyde and polyamide.
Coked or pyrocarbon carbon matrices are obtained from synthetic polymers subjected to pyrolysis. The matrix binds the composition, giving it shape. Strengtheners are fibers: glass, carbon, boron, organic, based on whisker crystals (oxides, carbides, borides, nitrides and others), as well as metal (wires), which have high strength and rigidity.

The properties of composite materials depend on the composition of the components, their combination, quantitative ratio and strength of bond between them.
Reinforcing materials can be in the form of fibers, strands, threads, tapes, multilayer fabrics.

The hardener content in oriented materials is 60-80 vol. %, in non-oriented (with discrete fibers and whiskers) - 20-30 vol. %. The higher the strength and elastic modulus of the fibers, the higher the strength and rigidity of the composite material. The properties of the matrix determine the strength of the composition under shear and compression and resistance to fatigue failure.

Based on the type of reinforcement, composite materials are classified as glass fibers, carbon fibers with carbon fibers, boron fibers and organofibers.

In layered materials, fibers, threads, tapes impregnated with a binder are laid parallel to each other in the laying plane. Flat layers are assembled into plates. The properties are anisotropic. For the material to work in a product, it is important to take into account the direction of the acting loads. It is possible to create materials with both isotropic and anisotropic properties.
Fibers can be laid at different angles, varying the properties of the composite materials. The flexural and torsional rigidities of the material depend on the order in which the layers are laid across the thickness of the package.

Reinforcers of three, four or more threads are used.
Most Applications has a structure of three mutually perpendicular threads. Reinforcers can be located in the axial, radial and circumferential directions.

Three-dimensional materials can be of any thickness in the form of blocks or cylinders. Bulky fabrics increase peel strength and shear resistance compared to laminated fabrics. A system of four threads is constructed by decomposing the reinforcement along the diagonals of the cube. The structure of four threads is equilibrium and has increased shear rigidity in the main planes.
However, creating four-directional materials is more difficult than creating three-directional materials.

3. Classification of composite materials.

3.1. Fiber composite materials.

Often the composite material is a layered structure in which each layer is reinforced with a large number of parallel continuous fibers. Each layer can also be reinforced with continuous fibers woven into a fabric that is the original shape, the width and length corresponding to the final material. Often the fibers are woven into three-dimensional structures.

Composite materials differ from conventional alloys in higher values ​​of tensile strength and endurance limit (by 50–10%), elastic modulus, stiffness coefficient and reduced susceptibility to cracking. The use of composite materials increases the rigidity of the structure while simultaneously reducing its metal consumption.

The strength of composite (fibrous) materials is determined by the properties of the fibers; the matrix should mainly redistribute stresses between the reinforcing elements. Therefore, the strength and elastic modulus of the fibers must be significantly greater than the strength and elastic modulus of the matrix.
Rigid reinforcing fibers perceive stresses arising in the composition during loading, giving it strength and rigidity in the direction of fiber orientation.

To strengthen aluminum, magnesium and their alloys, boron, as well as fibers from refractory compounds (carbides, nitrides, borides and oxides) having high strength and elasticity modulus, are used. Wire made from high-strength steels is often used as fibers.

For the reinforcement of titanium and its alloys, molybdenum wire, sapphire fibers, silicon carbide and titanium boride are used.

Increasing the heat resistance of nickel alloys is achieved by reinforcing them with tungsten or molybdenum wire. Metal fibers are also used in cases where high thermal and electrical conductivity are required. Promising strengtheners for high-strength and high-modulus fibrous composite materials are whiskers made of aluminum oxide and nitride, silicon carbide and nitride, boron carbide, etc.

Metal-based composite materials have high strength and heat resistance, while at the same time they have low plasticity. However, fibers in composite materials reduce the rate of propagation of cracks initiated in the matrix, and sudden brittle failure almost completely disappears. Distinctive feature Fibrous uniaxial composite materials are characterized by anisotropy of mechanical properties along and across the fibers and low sensitivity to stress concentrators.

The anisotropy of the properties of fiber composite materials is taken into account when designing parts to optimize properties by matching the resistance field with the stress fields.

Reinforcement of aluminum, magnesium and titanium alloys with continuous refractory fibers of boron, silicon carbide, titanium doboride and aluminum oxide significantly increases heat resistance. A feature of composite materials is the low rate of softening over time with increasing temperature.

The main disadvantage of composite materials with one- and two-dimensional reinforcement is the low resistance to interlayer shear and transverse breakage. Materials with volumetric reinforcement do not have this.

3.2. Dispersion-strengthened composite materials.

Unlike fibrous composite materials, in dispersion-strengthened composite materials the matrix is ​​the main load-bearing element, and dispersed particles inhibit the movement of dislocations in it.
High strength is achieved with a particle size of 10-500 nm with an average distance between them of 100-500 nm and their uniform distribution in the matrix.
Strength and heat resistance, depending on the volumetric content of strengthening phases, do not obey the law of additivity. The optimal content of the second phase varies for different metals, but usually does not exceed 5-10 vol. %.

The use of stable refractory compounds (oxides of thorium, hafnium, yttrium, complex compounds of oxides and rare earth metals) that are insoluble in the matrix metal as strengthening phases allows maintaining the high strength of the material up to 0.9-0.95 T. In this regard, such materials are often used as heat-resistant. Dispersion-strengthened composite materials can be obtained on the basis of most metals and alloys used in technology.

The most widely used aluminum-based alloys are SAP (sintered aluminum powder).

The density of these materials is equal to the density of aluminum, they are not inferior to it in corrosion resistance and can even replace titanium and corrosion-resistant steels when operating in the temperature range of 250-500 ° C. In terms of long-term strength, they are superior to wrought aluminum alloys. Long-term strength for alloys SAP-1 and SAP-2 at 500 °C is 45-55 MPa.

Nickel dispersion-strengthened materials have great prospects.
Nickel-based alloys with 2-3 vol. have the highest heat resistance. % thorium dioxide or hafnium dioxide. The matrix of these alloys is usually a solid solution of Ni + 20% Cr, Ni + 15% Mo, Ni + 20% Cr and Mo. The alloys VDU-1 (nickel strengthened with thorium dioxide), VDU-2 (nickel strengthened with hafnium dioxide) and VD-3 (Ni + 20% Cr matrix, strengthened with thorium oxide) are widely used. These alloys have high heat resistance. Dispersion-strengthened composite materials, just like fibrous ones, are resistant to softening with increasing temperature and duration of exposure at a given temperature.

3.3. Fiberglass.

Fiberglass is a composition consisting of a synthetic resin, which is a binder, and glass fiber filler. Continuous or short glass fiber is used as filler. The strength of fiberglass increases sharply with a decrease in its diameter (due to the influence of inhomogeneities and cracks that occur in thick sections). The properties of fiberglass also depend on the alkali content in its composition; The best performance is found in alkali-free glasses of aluminoborosilicate composition.

Non-oriented glass fibers contain short fiber as filler. This allows you to press parts of complex shapes using metal reinforcement. The material is obtained with isotopic strength characteristics much higher than those of press powders and even fibers. Representatives of this material are AG-4V glass fibers, as well as DSV (metered glass fibers), which are used for the manufacture of power electrical parts, mechanical engineering parts (spool valves, pump seals, etc.). When using unsaturated polyesters as a binder, premixes PSC (pasty) and prepregs AP and PPM (based on glass mat) are obtained. Prepregs can be used for large-sized products of simple shapes (car bodies, boats, instrument bodies, etc.).

Oriented glass fibers have a filler in the form of long fibers, arranged in oriented individual strands and carefully glued together with a binder. This ensures higher strength of fiberglass.

Fiberglass can operate at temperatures from –60 to 200 °C, as well as in tropical conditions, withstand large inertial overloads.
When aging for two years, the aging coefficient K = 0.5-0.7.
Ionizing radiation has little effect on their mechanical and electrical properties. They are used to produce high-strength parts with reinforcement and threads.

3.4. Carbon fibers.

Carbon fibers (carbon fibers) are compositions consisting of a polymer binder (matrix) and reinforcing agents in the form of carbon fibers (carbon fibers).

High Energy S-S connections carbon fibers allows them to maintain strength at very high temperatures(in neutral and reducing environments up to 2200 ° C), as well as at low temperatures. Fibers protect from surface oxidation protective coatings(pyrolytic). Unlike glass fibers, carbon fibers are poorly wetted by a binder
(low surface energy), so they are etched. At the same time, the degree of activation of carbon fibers in terms of the content of the carboxyl group on their surface increases. The interlayer shear strength of carbon fiber reinforced plastics increases by 1.6-2.5 times. Viscerization of TiO, AlN and SiN filamentary crystals is used, which results in an increase in interlayer rigidity by 2 times and strength by 2.8 times. Spatially reinforced structures are used.

The binders are synthetic polymers (polymer carbon fiber); synthetic polymers subjected to pyrolysis (coked carbon fiber); pyrolytic carbon (pyrocarbon carbon fibers).

Epoxyphenol carbon fiber reinforced KMU-1l, reinforced with carbon tape, and KMU-1u on a rope, viskerized with whiskers, can operate for a long time at temperatures up to 200 °C.

Carbon fiber fibers KMU-3 and KMU-2l are produced using an epoxyaniline-formaldehyde binder; they can be used at temperatures up to 100 °C; they are the most technologically advanced. Carbon fiber KMU-2 and
KMU-2l based on a polyimide binder can be used at temperatures up to
300 °C.

Carbon fibers are distinguished by high statistical and dynamic fatigue resistance and retain this property at normal and very low temperatures (the high thermal conductivity of the fiber prevents self-heating of the material due to internal friction). They are water and chemical resistant. After exposure to air, X-rays and E almost do not change.

The thermal conductivity of carbon fiber reinforced plastics is 1.5-2 times higher than the thermal conductivity of fiberglass reinforced plastics. They have the following electrical properties: = 0.0024-0.0034 Ohm cm (along the fibers); ? = 10 and tg =0.001 (at a current frequency of 10 Hz).

Carbon fiberglass contains glass fibers along with carbon, which reduces the cost of the material.

3.5. Carbon fiber with carbon matrix.

Coked materials are produced from conventional polymer carbon fibers subjected to pyrolysis in an inert or reducing atmosphere. At a temperature of 800-1500 °C, carbonized ones are formed, at 2500-3000 °C, graphitized carbon fibers are formed. To obtain pyrocarbon materials, the hardener is laid out according to the shape of the product and placed in a furnace into which gaseous hydrocarbon (methane) is passed. Under a certain regime (temperature 1100 °C and residual pressure 2660 Pa), methane decomposes and the resulting pyrolytic carbon is deposited on the reinforcement fibers, binding them.

The coke formed during the pyrolysis of the binder has high adhesion strength to carbon fiber. In this regard, the composite material has high mechanical and ablative properties and resistance to thermal shock.

Carbon fiber with a carbon matrix of the KUP-VM type is 5-10 times higher in strength and impact strength than special graphites; when heated in an inert atmosphere and vacuum, it retains strength up to 2200
°C, oxidizes in air at 450 °C and requires a protective coating.
The coefficient of friction of one carbon fiber composite with a carbon matrix is ​​high (0.35-0.45), and wear is low (0.7-1 microns for braking).

3.6. Boron fibers.

Boron fibers are compositions of a polymer binder and strengthener – boron fibers.

Boron fibers are characterized by high compressive, shear and shear strength, low creep, high hardness and elastic modulus, thermal conductivity and electrical conductivity. The cellular microstructure of boron fibers provides high shear strength at the matrix interface.

In addition to continuous boron fiber, complex boron glass nitrates are used, in which several parallel boron fibers are braided with glass fiber, which imparts dimensional stability. The use of boron glass threads facilitates the technological process of manufacturing the material.

Modified epoxy and polyimide binders are used as matrices for producing boron fiber nitrates. Boron fibers KMB-1 and
KMB-1k are designed for long-term operation at a temperature of 200 °C; KMB-3 and KMB-3k do not require high pressure during processing and can operate at temperatures not exceeding 100 °C; KMB-2k is operational at 300 °C.

Boron fibers have high fatigue resistance and are resistant to radiation, water, organic solvents and lubricants.

3.7. Organofibers.

Organofibers are composite materials consisting of a polymer binder and reinforcers (fillers) in the form of synthetic fibers. Such materials have low mass, relatively high specific strength and rigidity, and are stable under the action of alternating loads and sudden changes in temperature. For synthetic fibers, the loss of strength during textile processing is small; They are insensitive to damage.

For organofibers, the values ​​of the elastic modulus and temperature coefficients of linear expansion of the strengthener and binder are close.
Diffusion of binder components into the fiber and chemical interaction between them occurs. The structure of the material is defect-free. Porosity does not exceed 1-3% (in other materials 10-20%). Hence the stability of the mechanical properties of organofibers under sharp temperature changes, impact and cyclic loads. Impact strength is high (400-700 kJ/m²). The disadvantage of these materials is their relatively low compressive strength and high creep (especially for elastic fibers).

Organic fibers are resistant to aggressive environments and humid tropical climates; dielectric properties are high and thermal conductivity is low. Most organofibers can operate for a long time at a temperature of 100-150 °C, and those based on a polyimide binder and polyoxadiazole fibers - at a temperature of 200-300 °C.

In combined materials, along with synthetic fibers, mineral fibers (glass, carbon fiber and boron fiber) are used. Such materials have greater strength and rigidity.

4. Economic efficiency of using composite materials.

The areas of application of composite materials are not limited. They are used in aviation for highly loaded parts of aircraft (skin, spars, ribs, panels, etc.) and engines (compressor blades and turbines, etc.), in space technology for components of power structures of devices subject to heating, for stiffeners, panels , in the automotive industry to lighten bodies, springs, frames, body panels, bumpers, etc., in the mining industry (drilling tools, parts for combines, etc.), in civil engineering (bridge spans, elements of prefabricated structures of high-rise buildings, etc.) etc.) and in other areas of the national economy.

The use of composite materials provides a new qualitative leap in increasing the power of engines, energy and transport installations, and reducing the weight of machines and devices.

The technology for producing semi-finished products and products from composite materials is quite well developed.

Composite materials with a non-metallic matrix, namely polymer carbon fibers, are used in the shipbuilding and automotive industries (car body, chassis, propellers); Bearings, heating panels, sports equipment, and computer parts are made from them. High-modulus carbon fibers are used for the manufacture of aircraft parts, equipment for the chemical industry, X-ray equipment and others.

Carbon fibers with a carbon matrix replace various types of graphite. They are used for thermal protection, aircraft brake discs, and chemically resistant equipment.

Products made from boron fiber are used in aviation and space technology (profiles, panels, compressor rotors and blades, propeller blades and helicopter transmission shafts, etc.).

Organofibers are used as an insulating and structural material in the electrical and radio industry, aviation technology, and automotive industry; They are used to make pipes, containers for reagents, coatings for ship hulls, and more.

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1. Ceramic composites

When creating a new generation of aircraft engines, lightweight and very resistant fire-resistant materials - ceramic composites - are used to reduce weight, reduce fuel consumption and reduce harmful emissions.

On Figure 1 diagram presented technological process, developed by NASA for the production of composites Melt Infiltrated Ceramic Matrix Composites.

First, a fabric is made from silicon carbide fibers (trade name Sylramic), a workpiece of a given shape and size is formed from it, then the workpiece is saturated with molten silicon carbide and fired.

Fibers can be used to make a composite Sylramic or Sylramic with boron nitride coating. Such composites can withstand heating up to 1200 o C.

A similar technology is used in the manufacture of composite oxide materials, where the fabric is made from Nextel 720(containing 85% Al 2 O 3 and 15% SiO 2) is saturated in the melt of aluminosilicates.

Composite materials have a layered structure (see. rice. 2).

Compared to monolithic ceramic materials (for example, Si 3 N 4), composite ceramics are not as brittle and have increased impact resistance (see Fig. rice. 3 and 4).

Ceramic composite materials are widely used in the construction of hypersonic vehicles. aircraft(orbital UAV X37, rocket X51A WaveRider (see. rice. 5 and 6).

When flying at a speed of 68 Mach, the temperature of the surfaces of the leading edges of the planes can reach 2700 o C, and the temperature in the combustion chamber of a ramjet engine with a supersonic combustion chamber (scramjet) can reach 3000 o C.

To ensure thermal protection and high strength characteristics of the structure during aerodynamic heating, multilayer sandwich structures are used Ceramic Matrix Composite/Foam Core (ceramic matrix composite with an inner layer of porous ceramics).

A composite sandwich panel with a density of about 1.06 g/cm 3 has high strength and rigidity. Coefficient thermal expansion, ceramic composite cladding material and porous ceramic material the cores are selected in such a way as to ensure a temperature gradient on the outer and inner surfaces of the sandwich panel of about 1000 o C without delamination and cracking.

Having a density of about 1.06 g/cm, it has high strength and rigidity. The coefficient of thermal expansion, ceramic composite cladding material and porous ceramic core material are selected in such a way as to ensure a temperature gradient on the outer and inner surfaces of the sandwich panel of about 1000C without delamination and cracking.

The scramjet combustion chamber uses ceramic composites based on high-temperature ceramics. Such ceramics, consisting of zirconium diboride and silicon carbide, are sintered using high-frequency electric spark discharges (the so-called SparcPlasma Sintering method). Compared to the hot isostatic pressing method, SparcPlasma Sintering allows you to obtain a more dense structure (see. Fig.7 and 8).

In addition, for the combustion chamber they are developing "self-healing" ablative materials, in which substitution of the substance is ensured at the micro level. These are the so-called “secondary polymer layered impregnated tiles” ( SPLIT) (laminated slabs impregnated with recycled polymer) having a heterogeneous composition. The term "secondary" is used because each plate element contains at least two polymer layers, the secondary endothermic reaction between which absorbs a significant amount of heat, helping to prevent overheating of the material behind the heat shield.

To protect composite ceramics based on silicon carbide from reactions with fuel combustion products in the combustion chamber and water vapor, nanocomposite corrosion-resistant coatings.

2. Structural nanocomposite materials

Metal-ceramic nanocomposite alloys

Aluminum and magnesium alloys reinforced with ceramic nanoparticles are used as lightweight structural materials.
The main problem when casting such alloys is the uniform distribution of ceramic nanoparticles in the volume of the casting. Due to the poor wettability of nanoparticles in the melt, they agglomerate and do not mix. The University of WisconsinMadison (USA) has developed a technology for mixing nanoparticles in a melt using ultrasonic waves, which create microbubbles in the melt. When such microbubbles collapse, microshock waves are formed. Intense micro-shock waves effectively disperse nanoparticles throughout the molten metal volume.

Ceramic nanocomposite materials

The addition of carbon nanotubes and fullerns (including carbon nanowhiskers) to the ceramic matrix improves the mechanical properties of the ceramic (providing increased ductility and reduced fragility).

On rice. 9 micrographs of carbon nanotubes in an alumina matrix are shown. The development of a microcrack is visible; carbon nanotubes (CNT), being a reinforcing element, prevent the development of a crack.

In addition to carbon nanotubes, inorganic fullerene-like materials (multilayer nanospheres or nanotubes of tungsten, titanium, niobium and molybdenum bisulfides) are used as reinforcing elements in nanocomposite ceramics.

It has been experimentally confirmed that inorganic fullerene-like materials are resistant to dynamic loads up to 210 tons/cm 2 (compared to 40 tons/cm 2 for high-strength steel), which makes it a very promising material for fillers in polymer or ceramic composites used as light armor.

Ceramics is a very promising material for use in various industries. MAXphases (Mn+1AXn phases)– polycrystalline nanolaminated ternary nitrides, carbides or borides of transition metals.

Depending on the composition of these materials, they can have completely unique multifunctional properties: be durable, at the same time easy to process, withstand high temperatures, have high thermal conductivity, and a very low coefficient of friction. Figuratively speaking, this is ceramics that can be cut with a regular hacksaw.

MAXphase materials were discovered by the American researcher Prof. M. Barsoum (Drexel University - USA) in 1996

were discovered by the American researcher Prof. M. Barsoum (Drexel University - USA) in 1996

Areas of application: energy (high electrical conductivity, ability to withstand high mechanical loads, high temperature), gas and steam turbines(has a low coefficient of friction at high temperatures), aviation and astronautics. On rice. 10 a micrograph of a nanolaminant structure is presented MAXphase ceramics.

Processing of composite materials

The emergence of new composite materials with improved properties imposes new requirements on the development of technologies and tools for their processing. Used abroad A complex approach: metal and ceramics processing technologists are involved in projects to develop new materials. In particular, specialists from the Army Research Laboratory and the US Air Force Laboratory participate in NASA projects.

For example, to drill holes in plates and panels made of composite ceramics, tools with polycrystalline diamond inserts are used, as well as solid carbide tools with nanocomposite multilayer coatings.

Special solders are used to join parts made of high-temperature ceramics based on zirconium diboride.

In particular, AgCuTi alloys (trademark CusilABA And Ticusil), as well as alloys based on palladium - cobalt and palladium nickel (trademark Palco And Palni) provide reliable connection of such ceramics with structural materials made from refractory molybdenum alloys.

A.V. Fedotov
Director of Development
NPF "ElanPraktik"

Composite materials – artificially created materials that consist of two or more components that differ in composition and are separated by a pronounced boundary, and which have new properties designed in advance.

The components of the composite material are different geometrically. A component that is continuous throughout the entire volume of a composite material is called matrix. A discontinuous component separated within the volume of a composite material is called fittings. The matrix gives the required shape to the product, influences the creation of the properties of the composite material, and protects the reinforcement from mechanical damage and other environmental influences.

Organic and inorganic polymers, ceramic, carbon and other materials can be used as matrices in composite materials. The properties of the matrix determine technological parameters the process of obtaining the composition and its: density, specific strength, operating temperature, resistance to fatigue failure and exposure to aggressive environments. Reinforcing or strengthening components are evenly distributed in the matrix. They, as a rule, have high , and in these indicators they significantly exceed the matrix. Instead of the term reinforcing component, the term filler can be used.

Classification of composite materials

According to the geometry of the filler, composite materials are divided into three groups:

• with zero-dimensional fillers, the sizes of which in three dimensions are of the same order;
• with one-dimensional fillers, one of the sizes of which is significantly larger than the other two;
• with two-dimensional fillers, two sizes of which are significantly larger than the third.

According to the arrangement of fillers, three groups of composite materials are distinguished:

• with a uniaxial (linear) arrangement of filler in the form of fibers, threads, whiskers in the matrix parallel to each other;
• with a biaxial (planar) arrangement of reinforcing filler, mats of whiskers, foil in a matrix in parallel planes;
• with a triaxial (volumetric) arrangement of the reinforcing filler and the absence of a preferential direction in its location.

According to the nature of the components, composite materials are divided into four groups:

• composite materials containing a metal or alloy component;
• composite materials containing a component from inorganic compounds oxides, carbides, nitrides, etc.;
• composite materials containing a component of non-metallic elements, carbon, boron, etc.;
• composite materials containing a component of organic compounds, epoxy, polyester, phenolic, etc.

The properties of composite materials depend not only on the physicochemical properties of the components, but also on the strength of the bond between them. Maximum strength is achieved if the formation of or occurs between the matrix and the reinforcement.

In composite materials with zero-dimensional filler The metal matrix is ​​most widely used. Metal-based compositions are strengthened by uniformly distributed dispersed particles of varying dispersion. These materials are different.

In such materials, the matrix absorbs the entire load, and dispersed filler particles prevent the development of plastic deformation. Effective hardening is achieved with a content of 5...10% filler particles. Particles of refractory oxides, nitrides, borides, and carbides serve as reinforcing fillers. Dispersion-strengthened composite materials are produced by powder metallurgy methods or by introducing reinforcing powder particles into a liquid molten metal or alloy.

Composite materials based on aluminum oxide (Al 2 O 3) reinforced with particles have found industrial application. They are produced by pressing aluminum powder followed by sintering (SAP). The advantages of SAP appear at temperatures above 300 o C, when aluminum alloys soften. Dispersion-strengthened alloys retain the hardening effect up to a temperature of 0.8 T pl.

SAP alloys are satisfactorily deformed, easily machined, welded, etc. SAP produces semi-finished products in the form of sheets, profiles, pipes, and foil. Blades of compressors, fans and turbines, and piston rods are made from them.

In composite materials with one-dimensional fillers Strengtheners are one-dimensional elements in the form of whiskers, fibers, and wires, which are held together by a matrix into a single monolith. It is important that the strong fibers are evenly distributed in the plastic matrix. For the reinforcement of composite materials, continuous discrete fibers with dimensions of cross section from fractions to hundreds of micrometers.

Materials reinforced with whisker-like monocrystals were created in the early seventies for aircraft and space structures. The main method for growing whiskers is to grow them from supersaturated steam (PC process). To produce particularly high-strength whisker crystals of oxides and other compounds, growth is carried out according to the P-J-C mechanism: directed growth of crystals occurs from a vapor state through an intermediate liquid phase.

Whiskers are created by drawing liquid through dies. The strength of crystals depends on the cross-section and smoothness of the surface.

Composite materials of this type are promising as... To increase the efficiency of heat engines, gas turbine blades are made of nickel alloys reinforced with sapphire threads (Al 2 O 3), this makes it possible to significantly increase the temperature at the turbine inlet (the tensile strength of sapphire crystals at a temperature of 1680 o C is above 700 MPa).

Reinforcement of rocket nozzles from tungsten and molybdenum powders is carried out with sapphire crystals both in the form of felt and individual fibers, as a result of which it was possible to double the material at a temperature of 1650 o C. Reinforcing the impregnating polymer of fiberglass laminates with thread-like fibers increases their strength. Cast metal reinforcement reduces it in structures. Strengthening glass with non-oriented whiskers is promising.

To reinforce composite materials, metal wire made of different metals is used: steel of different compositions, tungsten, niobium, depending on the operating conditions. Steel wire is processed into woven meshes, which are used to produce composite materials with reinforcement oriented in two directions.

For the reinforcement of light metals, boron and silicon carbide fibers are used. Especially valuable properties possess carbon fibers, they are used for reinforcing metal, ceramic and polymer composite materials.

Eutectic composite materials– alloys of eutectic or close to eutectic composition, in which the strengthening phase is oriented crystals formed during the process of directional crystallization. Unlike conventional composite materials, eutectic ones are obtained in one operation. A directional oriented structure can be obtained on ready-made products. The shape of the resulting crystals can be in the form of fibers or plates. Directed crystallization methods are used to produce composite materials based on cobalt, niobium and other elements, therefore they are used in a wide temperature range.