Materials based on several components, which determines their operational and technological characteristics. Composites are based on a matrix based on metal, polymer or ceramic. Additional reinforcement is performed with fillers in the form of fibers, whiskers and various particles.

Are composites the future?

Plasticity, strength, wide scope of application - this is what distinguishes modern composite materials. What is this from a production point of view? These materials consist of a metallic or non-metallic base. To strengthen the material, flakes of greater strength are used. Among them we can highlight plastic, which is reinforced with boron, carbon, glass fibers, or aluminum, reinforced with steel or beryllium threads. If you combine the contents of the components, you can obtain composites of different strength, elasticity, and resistance to abrasives.

Main types

The classification of composites is based on their matrix, which can be metallic or non-metallic. Materials with a metal matrix based on aluminum, magnesium, nickel and their alloys gain additional strength due to fibrous materials or refractory particles that do not dissolve in the base metal.

Composites with a non-metallic matrix are based on polymers, carbon or ceramics. Among the polymer matrices, the most popular are epoxy, polyamide and phenol-formaldehyde. The shape of the composition is given by the matrix, which acts as a kind of binder. Fibers, strands, threads, and multilayer fabrics are used to strengthen materials.

Manufacturing composite materials is carried out on the basis of the following technological methods:

• impregnation of reinforcing fibers with matrix material;
• molding reinforcement tapes and matrix in a mold;
• cold pressing of components with further sintering;
• electrochemical coating of fibers and further pressing;
• deposition of the matrix by plasma spraying and subsequent compression.

What hardener?

Composite materials have found application in many areas of industry. We have already said what it is. These are materials based on several components, which are necessarily strengthened with special fibers or crystals. The strength of the composites themselves depends on the strength and elasticity of the fibers. Depending on the type of reinforcement, all composites can be divided:

• on fiberglass;
• carbon fiber composites with carbon fibers;
• boron fibers;
• organofibers.

Reinforcing materials can be laid in two, three, four or more threads; the more there are, the stronger and more reliable the composite materials will be in operation.

Wood composites

Wood composite is worth mentioning separately. It is obtained through a combination of raw materials different types, with wood being the main component. Each wood-polymer composite consists of three elements:

• particles of crushed wood;
• thermoplastic polymer (PVC, polyethylene, polypropylene);
• a complex of chemical additives in the form of modifiers - up to 5% of them in the material.

Most popular type wood composites- This is a composite board. Its uniqueness lies in the fact that it combines the properties of both wood and polymers, which significantly expands the scope of its application. Thus, the board is distinguished by its density (its indicator is influenced by the base resin and the density of wood particles), and good bending resistance. At the same time, the material is environmentally friendly, retains texture, color and aroma natural wood. Using composite boards is absolutely safe. Due to polymer additives, the composite board acquires high level wear resistance and moisture resistance. It can be used for finishing terraces, garden paths, even if they have a heavy load.

Production Features

Wood composites have a special structure due to the combination of a polymer base with wood. Among materials of this type we can note chipboards of different densities, oriented chipboards and wood-polymer composites. The production of composite materials of this type is carried out in several stages:

1. Wood is crushed. For this purpose crushers are used. After crushing, the wood is sifted and divided into fractions. If the moisture content of the raw material is above 15%, it must be dried.
2. The main components are dosed and mixed in certain proportions.
3. The finished product is pressed and formatted to obtain a marketable appearance.

Main characteristics

We have described the most popular polymer composite materials. What it is is now clear. Thanks to the layered structure, it is possible to reinforce each layer with parallel continuous fibers. It is worth mentioning separately the characteristics of modern composites, which differ:

• high value of temporary resistance and endurance limit;
• high level of elasticity;
• strength, which is achieved by reinforcing layers;
• Due to rigid reinforcing fibers, composites are highly resistant to tensile stress.

Metal-based composites are characterized by high strength and heat resistance, while they are practically inelastic. Due to the structure of the fibers, the speed of propagation of cracks, which sometimes appear in the matrix, is reduced.

Polymer materials

Polymer composites are presented in a variety of options, which opens up great opportunities on their use in various fields, from dentistry to the production of aircraft. Composites based on polymers are filled with different substances.

The most promising areas of use can be considered construction, oil and gas industry, production of automobile and railway transport. It is these industries that account for about 60% of the volume of use of polymers. composite materials.

Thanks to its high stability polymer composites to corrosion, a smooth and dense surface of products obtained by molding, increases the reliability and durability of the final product.

Let's look at popular types

Fiberglass

Glass fibers formed from molten inorganic glass are used to reinforce these composite materials. The matrix is ​​based on thermoactive synthetic resins and thermoplastic polymers, which are distinguished by high strength, low thermal conductivity, and high electrical insulating properties. Initially, they were used in the production of antenna radomes in the form of dome-shaped structures. IN modern world Fiberglass plastics are widely used in the construction industry, shipbuilding, production of household equipment and sports items, and radio electronics.

In most cases, fiberglass is produced on the basis of spraying. This method is especially effective in small- and medium-scale production, for example, hulls of boats, boats, cabins for road transport, railway cars. Spraying technology is convenient and economical, since there is no need to cut the glass material.

Carbon fiber reinforced plastics

The properties of polymer-based composite materials make it possible to use them in a wide variety of fields. They use carbon fibers as a filler, obtained from synthetic and natural fibers based on cellulose and pitches. The fiber is thermally processed in several stages. Compared to fiberglass plastics, carbon fibers have a lower density and a higher density while being light and strong. Due to their unique performance properties, carbon fiber reinforced plastics are used in mechanical and rocket engineering, the production of space and medical equipment, bicycles and sports equipment.

Boroplasty

These are multicomponent materials based on boron fibers introduced into a thermosetting polymer matrix. The fibers themselves are represented by monofilaments, strands, which are braided with an auxiliary glass thread. The high hardness of the threads ensures the strength and resistance of the material to aggressive factors, but at the same time, boron plastics are fragile, which complicates processing. Boron fibers are expensive, so the scope of boron plastics is limited mainly to the aviation and space industries.

Organoplasty

In these composites, the fillers are mainly synthetic fibers - tows, threads, fabrics, paper. Among the special properties of these polymers are low density, lightness compared to glass and carbon fiber plastics, high tensile strength and high resistance to impacts and dynamic loads. This composite material is widely used in such areas as mechanical engineering, shipbuilding, automobile construction, in the production of space technology, and chemical engineering.

What is the effectiveness?

Due to their unique composition, composite materials can be used in a variety of fields:

• in aviation in the production of aircraft parts and engines;
• space technology for the production of power structures of devices that are subject to heating;
• automotive industry to create lightweight bodies, frames, panels, bumpers;
• mining industry in the production of drilling tools;
• civil engineering for the creation of bridge spans, elements of prefabricated structures in high-rise buildings.

The use of composites makes it possible to increase the power of engines and power plants, while reducing the weight of machinery and equipment.

What are the prospects?

According to representatives of the Russian industry, composite materials belong to a new generation of materials. It is planned that by 2020 the volume of domestic production of products in the composite industry will increase. Pilot projects aimed at developing new generation composite materials are already being implemented across the country.

The use of composites is advisable in a variety of fields, but it is most effective in industries related to high technology. For example, today not a single aircraft is created without the use of composites, and some of them use about 60% of polymer composites.

Thanks to the possibility of combining various reinforcing elements and matrices, it is possible to obtain a composition with a certain set of characteristics. And this, in turn, makes it possible to use these materials in a variety of fields.

composite material sudlal, composite material impex
Composite material(KM), composite- an artificially created heterogeneous continuous material consisting of two or more components with a clear interface between them. In most composites (with the exception of layered ones), the components can be divided into a matrix (or binder) and reinforcing elements (or fillers) included in it. In composites for structural purposes, reinforcing elements usually provide the necessary mechanical characteristics of the material (strength, rigidity, etc.), and the matrix ensures the joint operation of the reinforcing elements and their protection from mechanical damage and aggressive chemical environments.

The mechanical behavior of the composition is determined by the relationship between the properties of the reinforcing elements and the matrix, as well as the strength of the bonds between them. The characteristics and properties of the created product depend on the choice of initial components and the technology of their combination.

When reinforcing elements and a matrix are combined, a composition is formed that has a set of properties that reflect not only the original characteristics of its components, but also new properties that individual components do not possess. For example, the presence of interfaces between the reinforcing elements and the matrix significantly increases the crack resistance of the material, and in compositions, unlike homogeneous metals, an increase in static strength does not lead to a decrease, but, as a rule, to an increase in fracture toughness characteristics.

To create the composition, a variety of reinforcing fillers and matrices are used. These are getinax and textolite (laminated plastics made of paper or fabric glued with thermosetting glue), glass and graphite plastic (fabric or wound fiber made of glass or graphite, impregnated with epoxy adhesives), plywood. There are materials in which thin fibers made of high-strength alloys are filled with aluminum mass. Bulat is one of the oldest composite materials. In it, the thinnest layers (sometimes threads) of high-carbon steel are “glued” together with soft low-carbon iron.

Materials scientists are experimenting with the goal of creating materials that are more convenient to manufacture, and therefore more efficient. cheap materials. Self-growing crystalline structures glued into a single mass with polymer glue (cements with the addition of water-soluble adhesives), thermoplastic compositions with short reinforcing fibers, etc. are being studied.

• 1 Classification of composites
• 2 Advantages of composite materials
• 3 Disadvantages of composite materials
  • 3.1 High cost
  • 3.2 Anisotropy of properties
  • 3.3 Low impact strength
  • 3.4 High specific volume
  • 3.5 Hygroscopicity
  • 3.6 Toxicity
  • 3.7 Low serviceability
• 4 Applications
  • 4.1 Consumer goods
  • 4.2 Sports equipment
  • 4.3 Medicine
  • 4.4 Mechanical engineering
    • 4.4.1 Characteristics
    • 4.4.2 Technical specifications
    • 4.4.3 Technical and economic advantages
    • 4.4.4 Areas of application of the technology
  • 4.5 Aviation and astronautics
  • 4.6 Weapons and military equipment
• 5 See also
• 6 Notes
• 7 Literature
• 8 Links

Classification of composites

Composites are usually classified according to the type of reinforcing filler:

• fibrous (reinforcing component - fibrous structures);
• layered;
• filled plastics (reinforcing component - particles)
  • bulk (homogeneous),
  • skeletal (initial structures filled with a binder).

Composites are also sometimes classified according to the matrix material:

• composites with a polymer matrix,
• composites with ceramic matrix,
• metal matrix composites,
• oxide-oxide composites.

Advantages of composite materials

The main advantage of CM is that the material and structure are created simultaneously. The exception is prepregs, which are semi-finished products for the manufacture of structures.

It is worth immediately stipulating that CMs are created to perform these tasks, and accordingly cannot contain all possible advantages, but when designing a new composite, the engineer is free to give it characteristics that are significantly superior to the characteristics of traditional materials when fulfilling a given purpose in a given mechanism, but inferior to them in any other aspects. This means that CM cannot be better than traditional material in everything, that is, for each product the engineer carries out all the necessary calculations and only then chooses the optimum between materials for production.

• high specific strength (strength 3500 MPa)
• high rigidity (elastic modulus 130…140 - 240 GPa)
• high wear resistance
• high fatigue strength
• It is possible to manufacture dimensionally stable structures from CM
• ease

Moreover, different classes of composites may have one or more advantages. Some benefits cannot be achieved simultaneously.

Disadvantages of composite materials

Composite materials have enough a large number of disadvantages that hinder their spread.

High price

The high cost of CM is due to the high knowledge intensity of production, the need to use special expensive equipment and raw materials, and therefore developed industrial production and the country's scientific base. However, this is only true when replacing simple rolled products made of ferrous metals with composites. In the case of lightweight products, products of complex shapes, corrosion-resistant products, high-strength dielectric products, composites are the winner. Moreover, the cost of composite products is often lower than analogues made of non-ferrous metals or stainless steel.

Anisotropy of properties

Anisotropy is the dependence of CM properties on the choice of measurement direction. For example, the modulus of elasticity of unidirectional carbon fiber along the fibers is 10-15 times higher than in the transverse direction.

To compensate for anisotropy, the safety factor is increased, which can offset the advantage of CM in specific strength. An example of this is the experience of using CM in the manufacture of the vertical tail of the MiG-29 fighter. Due to the anisotropy of the used CM, the vertical tail was designed with a safety factor that was a multiple of the standard aviation coefficient of 1.5, which ultimately led to the fact that the composite vertical tail of the Mig-29 turned out to be equal in weight to the structure of the classic vertical tail made of duralumin .

However, in many cases, property anisotropy is useful. For example, pipes operating under internal pressure experience twice the breaking stress in the circumferential direction compared to the axial direction. Therefore, the pipe should not be of equal strength in all directions. In the case of composites, this condition can be easily achieved by doubling the reinforcement in the circumferential direction compared to the axial one.

Low impact strength

Low impact strength also causes the need to increase the safety factor. In addition, low impact strength causes high damage to CM products and a high probability of hidden defects that can only be detected by instrumental testing methods.

High specific volume

High specific volume is significant drawback when using CM in areas with strict restrictions on the occupied volume. This applies, for example, to the field of supersonic aviation, where even a slight increase in the volume of the aircraft leads to a significant increase in wave aerodynamic drag.

Hygroscopicity

Composite materials are hygroscopic, that is, they tend to absorb moisture, which is due to the discontinuity of the internal structure of the CM. During long-term operation and repeated temperature transitions through 0 Celsius, water penetrating into the CM structure destroys the CM product from the inside (the effect is similar in nature to the destruction highways in the off-season). To be fair, it should be noted that this drawback applies to the first generation of composites, which had insufficiently effective adhesion of the binder to the filler, as well as a large volume of cavities in the binder matrix. Modern types composites with high adhesion of the binder to the filler (achieved by the use of special lubricants), obtained by vacuum molding methods with a minimum amount of residual gas cavities, are not subject to this drawback, which makes it possible, in particular, to build composite ships, produce composite reinforcement and composite supports for overhead power lines.

However, CM can absorb other liquids with high penetrating ability, for example, aviation kerosene or other petroleum products.

Toxicity

During operation, CMs can emit fumes that are often toxic. If CM is used to make products that will be located in close proximity to humans (the composite fuselage of the Boeing 787 Dreamliner may serve as such an example), then additional research into the effects of CM components on humans is required to approve the materials used in the manufacture of CM.

Low operational efficiency

Composite materials may have low manufacturability, low maintainability and high operating costs. This is due to the need to use special labor-intensive methods (and sometimes manual labor), special tools for the modification and repair of objects made of CM. Often products made from CM are not subject to any modification or repair at all.

Areas of use

Consumer goods

• Reinforced concrete is one of the oldest and simplest composite materials
• Fishing rods made of fiberglass and carbon fiber
• Fiberglass boats
• Car tires
• Metal composites

Sport equipment

Composites have firmly established themselves in sports: high achievements require high strength and low weight, and price does not play a special role.

• Bicycles
• Equipment for skiing- poles and skis
• Hockey sticks and skates
• Kayaks, canoes and oars for them
• Body parts for racing cars and motorcycles
• Helmets

Medicine

Material for dental fillings. The plastic matrix serves for good filling, the glass particle filler increases wear resistance.

Mechanical engineering

In mechanical engineering, composite materials are widely used to create protective coatings on friction surfaces, as well as for the manufacture of various engine parts internal combustion(pistons, connecting rods).

Characteristic

The technology is used to form additional protective coatings on surfaces in steel-rubber friction pairs. The use of technology makes it possible to increase the duty cycle of seals and shafts of industrial equipment operating in an aquatic environment.

Composite materials consist of several functional excellent materials. The basis of inorganic materials is magnesium, iron, and aluminum silicates modified with various additives. Phase transitions in these materials occur at fairly high local loads, close to the ultimate strength of the metal. In this case, a high-strength metal-ceramic layer is formed on the surface in an area of ​​high local loads, due to which it is possible to change the structure of the metal surface.

Polymer materials based on polytetrafluoroethylene are modified with ultrafine diamond-graphite powders obtained from explosive materials, as well as ultrafine powders of soft metals. Plasticization of the material is carried out at relatively low (less than 300 °C) temperatures.

Organometallic materials derived from natural fatty acids contain significant amounts of acidic functional groups. Thanks to this, interaction with surface metal atoms can be carried out in a resting mode. Friction energy accelerates the process and stimulates the appearance of cross-links.

Specifications

Depending on the composition of the composite material, the protective coating can be characterized by the following properties:

• thickness up to 100 microns;
• shaft surface cleanliness class (up to 9);
• have pores with sizes of 1 - 3 microns;
• friction coefficient up to 0.01;
• high adhesion to metal and rubber surfaces.

Technical and economic advantages

• A high-strength metal-ceramic layer is formed on the surface in the area of ​​high local loads;
• The layer formed on the surface of polytetrafluoroethylene has a low coefficient of friction and low resistance to abrasive wear;
• Metal-organic coatings are soft, have a low coefficient of friction, a porous surface, and the thickness of the additional layer is a few microns.

Areas of application of technology

• application to work surface seals in order to reduce friction and create a separating layer that prevents rubber from sticking to the shaft during the rest period.
• high-speed internal combustion engines for automobile and aircraft construction.

Aviation and astronautics

In aviation and aerospace, there has been a pressing need for strong, lightweight, and durable structures since the 1960s. Composite materials are used for the manufacture of load-bearing structures aircraft, artificial satellites, thermal insulating coatings of shuttles, space probes. Increasingly, composites are used for the manufacture of air and spacecraft, and the most loaded power elements.

Weapons and military equipment

Due to their characteristics (strength and lightness), CMs are used in military affairs for the production various types armor:

• body armor (see also Kevlar)
• armor for military equipment

Until the 4th century. BC e. were widely used in bows as weapons.

see also

• Composite reinforcement
• Hybrid material

Notes

1. J. Lubin. 1.2 Terms and definitions // Handbook of composite materials: 2 books = Handbook of Composites. - M.: Mechanical Engineering, 1988. - T. 1. - 448 p. - ISBN 5-217-00225-5.

Literature

• Kerber M. L., Polymer composite materials. Structure. Properties. Technologies. - St. Petersburg: Profession, 2008. - 560 p.
• Vasiliev V.V., Mechanics of structures made of composite materials. - M.: Mechanical Engineering, 1988. - 272 p.
• Karpinos D.M., Composite materials. Directory. - Kyiv, Naukova Duma

Links

• Journal of Mechanics of Composite Materials and Structures
• “Composites from Science City” TV story
• "Black Wing Technology" TV story

composite material impex, composite material sudlal, composite materialism, compositional materials science

Composite Material Information About

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 of inorganic compounds of 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 aluminum oxide 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.

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. Composite materials are precisely such materials of the future.

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 organ fibers 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 organ fibers 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 boron nitride coated. 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 aircraft (X37 orbital UAV, X51A WaveRider rocket (see below). 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 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 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 substance substitution 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 the 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"