Composites

segregated reinforcement

reinforcement particles are not in direct contact, they do not create their own infrastructure, reinforcement is a discontinuous phase

What are single Structured Composites?

systems with one matrix and one or more added phases

What are two or multi-structured composites

systems with two or more matrices, where each may contain one or more added stages A multistructure usually provides the significantly better properties of composites.

Three basic groups of matrices

· Metal/Metallic · (Polymer) Macromolecule and inorganic - polymeric, bitumen · (Ceramic) Mineral - based on inorganic binders, ceramic, glass, carbon

List common fiber materials

· natural · glass · graphite and carbon · polymer - aramid, nylon · ceramic · metal · fiber single crystals/monocrystals (whiskers)

What are the three general reinforcement phase geometries?

· particulate (dispersion) · fibre · skeletal

Metals used for the matrix

Aluminum, Titanium, Silver, Copper, Iron, Nickel

Choosing components in composites

The basis is selection in accordance to the desired/required mechanical, physical and chemical properties. It is necessary to insure contact of the two components, therefore: · the matrix must wet the reinforcing phase · the matrix must withstand a surrounding often aggressive environment · it must have the ability to deform under load · it must restrict the development of cracks

What affect do large particles have on the strength of the matrix?

Large particles can no longer effectively prevent the movement of dislocation, but will take part of the load from the matrix. The optimal particles are of a few mm, where the amount in a matrix should be of 25% (but not more than 50%) so that the reinforcement is noticeable. For armoring usually solid brittle particles are used - very often ceramic.

disjugated systems

bonds between phases are so weak that the system has only limited consistency (loose materials, earth/soil) - not a composite

aggregated reinforcement-

the individual particles are in direct contact, they can create their own infrastructure - they are somehow arranged, reinforcement is a continuous phase

What are the primary constituents of a composite?

A composite material is composed primarily of a matrix, i.e. a continuous phase, which is armored with a reinforcement (reinforcement is a secondary phase), which is usually the discontinuous phase.

What is a Type 1 composite?

A system that does not contain pores. This system is composed of matrices and fillers and their mutual relationship is that the filler particles are segregated, i.e. they do not touch. It is a system where there is not too much of a filler. An example of composite type I is a polymeric matrix with added particles such as ash, without pores. A second common example is the glass matrix composite, non-porous again. Two-component system: Vk = Vm + Vf

Composites Type II

A system, that is already three-phase, consisting of a matrix, filler and pores. In such a system there are little pores, less matrix, and it contains mostly filler. As the filler takes up most of the whole system, it is aggregated. And because the system contains little pores, they are segregated. An example of composite type II is concrete. Three-component system: Vk = Vm + Vf + Vv

What are Aramid fibers?

Aramid is a synthetic poly-amide polymer with long chain-like molecules that are highly oriented along the fiber axis. This molecular structure produces remarkable tensile strength and impact resistance that is beneficial in demanding applications. Lightweight and flexible, with a high strength-to-weight ratio, aramid fibers are commonly used in armor and ballistic protection applications, and in other high impact applications. Aramid can be molded using a number of processes including pultrusion.

Ceramic and glass Matrix properties / common materials used

Ceramics is inorganic non-metallic heterogeneous material consisting of crystalline substances of varying composition and configuration. Ceramic materials generally have good chemical resistance, lows thermal conductivity, a high melting point, high hardness and compression strength and are electrically non-conductive. The main disadvantage is the considerable brittleness, poor workability, and high sensitivity to internal defects. They are suitable for use at high temperatures. Glass is an amorphous substance, which was formed by the solidification of the melt without crystallization. The properties of glass and ceramics are close

What is a composite?

As composites can be considered material composed of two or more components (phases), where at least one of them is solid, reaching the properties which cannot be provided by any of the components separately or not even by their mere sum. The properties of composites are achieved by cooperation the individual phases called the synergistic effects.

What is gas-phase infiltration

At the gas-phase infiltration the reinforcement (of continuous fibers) is saturated by vapours arising from the thermal decomposition of chemical compounds - so-called matrix precursor. There is a condensation of saturated vapour on the reinforcement (fibers) and a solid phase forms.

List carbon and graphite fiber basic properties

Basic characteristics of these fibers: · ten times higher rigidity and half the density (1.8 to 2 g.cm -3, contains 90 - 95 % pure carbon) over the glass fibers · elongation at a rupture is smaller than with glass fibers · tensile strength at room temperature is lower than that of the glass or aramids, but it does not decrease with temperature up to 1000 °C · excellent thermal properties, if they are protected against oxidation, stable and chemically inert to 1000 °C, with protection against oxidation stable to 2000 °C · minimal thermal expansivity, sometimes even contractility · unlike glass high fatigue resistance · electrical conductivity · double up to a hundred times more expensive than glass · they are very strongly anisotropic · often have poor adhesion to the matrix, therefore, it is necessary to modify the surface The fibers can contain various amounts of graphite, accordingly, they are referred to as: Carbon - with a predominance of amorphous carbon Graphite - with a predominance of crystalline graphite Preparation methods: · pyrolysis of polymers - the most common method today - synthetic polymers - polyacrylonitrile (PAN), natural polymers - different pitches · Pyrolysis of hydrocarbons - even nanofiber formation is possible · evaporation from the arc discharge between carbon electrodes - the positive pressure of argon - whiskers

Production of boron fibers

Boron fibers are prepared by the CVD method (Chemical Vapor Deposition). This method is based on reducing the gas mixture (H2 a BCl3) that is fed into the reactor due to high temperature. The substrate is a thin tungsten filament. Boron trichloride is reduced with a hydrogen forming elemental boron, which is deposited on the substrate surface.

Casting

Casting technology (e.g. pressure) is used mainly in the manufacture of metal composites with short fibers (possibly with whiskers) or polymer composites.

list common ceramic fibers and their properties

Ceramic based fibers are characterised by a relatively low weight, high strength and high modulus of elasticity. These include primarily boron fibers, carbon fibers, and further carbide, nitride and oxide fibers. Boron is one of the substances that are very difficult to make malleable and is highly reactive, so for use in a metal matrix a thin layer of SiC is applied on the fibers. Carbon fibers are the most important among ceramic fibers. They are produced in the form of carbon or graphite fibers, which varies in the final processing temperature. In the first case, carbonization ends at a temperature of 900 - 1500 °C, in the second case, graphitization is carried out at a temperature of 2600 - 2800 °C. Graphitization increases the modulus of elasticity while the strength decreases. The advantage of carbon fibers is their very low density. Other types of ceramic fibers are simple compounds, most commonly oxides (MgO, ZnO2, TiO2, Al2O3, and SiO2), mixed oxides (mullite 3Al2O3.2SiO2 or spinel MgO. Al2O3), carbides (SiC, TiC, B4C), nitrides or metal compounds. Basic characteristics of ceramic fibers: · high thermal resistance and stability · used in composites with metal and ceramic matrices for high temperatures · high rigidity · lower density than metals, but higher than plastics or carbon fibers · low thermal expansion · low dependence of strength on the temperature · unlike carbon, glass and aramid they withstand even greater pressure (more than fibers they often approximate needles or rods - have considerable bending stiffness) · usually have only a very small slenderness ratio - are relatively short SiC fibers, as one of the most abundant, have two basic methods of production according to whether they were to be continuous or short.

Production of SiC fibers

Continuous SiC fibers are produced, like boron fibers using the CVD method. The source of silicon and carbon are gaseous alkylsilanes (CH3SiCl3), which are reduced in the reactor with hydrogen. Silicon carbide settles on the carbon substrate. Short fibers of SiC - whiskers are produced for example from rice hulls, which are annealed in an inert atmosphere, wherein there is the decomposition of organic substances and the conversion of SiO2 present in the shells into SiC.

Compare dispersion reinforced composites to precipitation reinforced metal alloys. Additionally describe the strengthening mechanism of dispersion particulates in a matrix

Dispersion strengthened composites resemble precipitation-reinforced metal alloys (hardening). They differ as follows: At low temperatures, the listed alloys have better properties (a higher increase in strength) than dispersion strengthened composites - the reason is better adhesion. However, at higher temperatures, the precipitate may partially dissolve or coagulate, thereby deteriorating the properties of these alloys. In dispersion-reinforced composites the properties are very little dependent on temperature. The particles are selected so that when increasing the temperature they will neither dissolve nor coagulate. Dispersion efficiently eliminates the movement of dislocations and thus limits the plastic deformation of the composite (increase in young's modulus). Dispersion increases primarily ultimate tensile stress and yield stress and suppresses any creep of the matrix.

Nickel and nickel based composites

Dispersion strengthening is done by oxides ThO2, HfO2, ZrO2. Dispersion strengthened nickel alloys are stronger and more stable to higher temperatures. It is a refractory material for operation in a temperature range 650-1650 °C. They are mainly used in aviation and space technology. The reinforcement should be selected so as to avoid chemical reactions.

List particulate (dispersion) reinforcement geometries, common materials used and what is the affect of particulates clustering at the grain boundaries of the matrix?

Dispersion's usually consist of powders with particles of various shapes (spherical, pyramidal, lamellar, etc.) and various sizes. As particulate dispersion's (filler powder) there are usually used powders of inorganic compounds such as oxides (MgO, ZnO, BeO, Al2O3, ZrO2, etc.), carbides (SiC, TiC, B4C, Al4C3, etc.), nitrides (Si3N4, BN), borides, or silicates (kaolin, mica, glass beads, etc.). Glass is often used for weight reduction in the form of solid or hollow glass beads Clustering of the particles at the grain boundaries of the matrix (a risk especially within a metal) during the solidification of the matrix is very undesirable, and causes embrittlement.

What are the general characteristics of fibers typically used in composites?

Fibers are stronger than the same compact (dense/thick) materials. Fibre strength depends mainly on its cross-section. With decreasing cross-section the fiber strength increases (due to applying the strengthening processes, depending on the degree of deformation). Fibers usually have a circular cross-section and a diameter in a wide range. To compare, a human hair has a diameter of 0.05 mm and spider fibers have 0.015 mm.

Effect of fibers in matrix

For fiberous composites the units of reinforcement (fibers) in one direction are significantly larger than in other directions. Synergistic interaction (synergy) between solid and rigid fibers with a ductile or brittle matrix allows for the construction of composites with high strength, stiffness and toughness. These composites have the widest range of application.

Forming

Forming technologies are suitable for the production of shaped parts, profiles, panels, etc. The oldest technology is a hot pressing. More recent technologies include extrusion and injection moulding.

List glass fiber general properties

Glass fibers are mainly used to reinforce polymer matrices. They have relatively high strength but a comparatively low modulus of elasticity and are fragile. They mostly occur in the form of various fabrics. Their basic characteristics are: · density of about 2.5 g.cm -3 · toughness (stiffness/firmness) roughly as aluminium - 1/3 steel firmness, E = 80 to 100 GPa · small fatigue strength · thermal conductivity is less than half that of steel · thermal expansion is less than half of the thermal expansion of steel Glass fibers rank among traditional fibers, which are produced by rapid drawing from the melt. Due to their relatively simple manufacturing glass fibers are cheaper compared to others.

What are the general characteristics of a granularly reinforced composite?

Granular reinforcement is based on separate particles of different sizes and their different volume share in the matrix. Optimum strengthening occurs at approximately the same particle size and their even distribution. Such composites are used particularly to obtain specific combinations of performance and not only to increase their strength. A concrete system with a crushed aggregate can be given as an example of granular reinforcement.

Production of graphite and carbon fiber

Graphite and carbon fiber are mainly made of fibers of PAN (polyacrylonitrile fibers), and from novoloid fibers (phenol-aldehyde fibers). The production of PAN fibers has three basic steps: · stabilization - 200-300 °C, an oxidizing atmosphere, and the fiber is under mechanical stress, it will cross-link macromolecules with oxygen bridges; fiber turns black and becomes infusible. · carbonization - 1200-1500 °C, an inert atmosphere N2, the decomposition of macromolecules, hydrogen removal, the reduction of oxygen and nitrogen, 80-95%mass is carbon; fiber achieves the highest strength · graphitization - 1800-3000 °C, an inert atmosphere of N2 and Ar, a further increase of the carbon content, the similar conversion of the recrystallization of a given graphite is taking place; the increase of fiber stiffness; due to the growth of the graphite crystals and the increase of defectiveness, fiber strength decreases Carbon fibers are protected against abrasion (they are more fragile than glass, and in order to reduce adsorption of the gases on their surfaces) by using polymeric coatings. It is also necessary to increase surface reactivity towards binding agents, of the matrix and therefore it is necessary to roughen the surface of the fibers by etching for example.

Impregnation of the reinforcement by a matrix in the liquid state

It is used in the production of composites based on thermoset (polymers), thermoplastic and metal matrices. The principle is based on (comprises) the saturation of a shaped reinforcement (fibers, fabrics, mats) with a corresponding liquid matrix in the form and subsequent solidification (thermosets by hardening, thermoplastics by solvent evaporation and metals by crystallization).

Metallic fibers

Metal fibers are among the cheapest, but they are relatively heavy. They are used to reinforce the metal matrices. Due to their specific weight (density) they are not too preferred. The main role in the preparation of the composite metal-metal is played by the compatibility of the fibers and the matrix. For reinforcement of metal matrices for temperatures up to 300°C fibers of carbon steel are used. For the reinforcement of metal matrices for a high temperature, fibers made of heat resistant metal are used, for example tungsten or molybdenum. Specifically, these are the most commonly used fibers: · steel - often strengthening aluminium alloys · tungsten - for strengthening heat resistant materials, but they are very heavy · boric - very light, yet rigid and solid; their production is relatively difficult; typical representative - Borsic fibers: where a layer of boron is applied on a thin tungsten wire by a chemical deposition of BCl3 vapour and its surface is protected against oxidation (or any boron diffusion into the matrix) by a thin layer of SiC · recently, extensive research into the fibers of the metallic glasses has been carried out

Metal Matrix properties / what metal matrices are commonly used?

Metallic matrices have good electrical and thermal conductivity, are malleable, have good wear and heat resistance, and also provide the possibility of coating and bonding. The most widely used metallic matrices are aluminium, magnesium, titanium and their alloys and for very high temperature nickel-based alloys, for electrical purposes matrices of copper or silver are used

What are the propertied of Natural Fibers?

Natural fibers may have surprisingly good properties. For example, a spider fiber with a diameter of 0.02 - 7 mm has a tensile strength of 1140 MPa and an elongation of 31%. Natural fibers have often a very complex fiber structure - e.g. cotton fibers. Among natural fibers are not only those of the spider and cotton, but also flax, jute, hemp, coconut, and more. The basis of all these fibers is cellulose. Most of these fibers is biodegradable. Contemporary (modern) tendencies are represented by the production of cellulose nanofibers by the fiberization of wood.

What is the primary function of hollow particles in a composite? What are the two most common materials used as hollow particles?

Often, especially in composites with a plastic matrix the excessive density of particles disturbs the density of the matrix. Where the weight of the composite is decisive, we begin to use hollow spheres instead of the ordinary particles. Because of a particle size of dozens up to hundreds of mm they are among armoring particles. They are often made of glass, sometimes of corundum as well.

Effect of particulates in composites

Particles as a reinforcing phase are dispersed in a matrix and do not own an aggregate structure. They may have a spherical, lamellar, rod or irregular shape where one dimension of such a reinforcement unit does not significantly exceed the dimensions of others. A metal, polymeric, or ceramic matrix is used. The most often used particles are: oxides, nitrides, carbides and borides. Particles in the composite limit the development of the plastic deformation in the matrix material, and participate in the transmission of stress, but to a much lesser extent than the fibers in the fibrous composites. Particle reinforcement (filler) is used to improve the properties of matrix materials, for example to modify thermal and electrical conductivity and the behavior at high temperatures, to reduce friction, increase wear resistance, improve machinability, increase hardness, and reduce contraction. Generally speaking, from the mechanical point of view, the particles in the matrix of the composite cause strengthening

What is the process of Plasma injections in the production of composites

Plasma injections are used for the production of composites with a metal or ceramic matrix. Reinforcing fibers are covered in layers by plasma spraying and the resulting layers are subsequently connected by pressing (ceramic matrix), or hot forming in a vacuum (a metal matrix).

Polymeric fiber basic properties

Polymeric fibers are usually designed for polymeric matrices. The disadvantage of all polymeric fibers is higher temperature sensitivity, as well as their poor wettability. The reason is the low surface energy of the fibers and therefore they require modification of the surface (surface treatment). The basic properties of polymer fibers: · low density of about 1 g.cm -3 · medium-high strength · low stiffness · usually a relatively large elongation at a fracture · in principle, chemically resistant, attacked only by strong acids and lyes · degrading effect of UV radiation in the presence of oxygen A typical representative of this type of fiber is KEVLAR (aramid - aromatic polyamide), its basic characteristics are: · strength of about 2.8 GPa · at a density of 1.44 g.cm-3 excellent relative strength - five times that of steel · deformation at a fracture slightly smaller than in glass, but larger than graphite · during long-term heating above 175 °C Kevlar fibers degrade · the negative coefficient of thermal expansion

Describe polymeric Matrix properties and common materials used

Polymeric matrices are the most common type in production. In comparison with metals they have low weight, high strength, are corrosion resistant, do not require surface treatment, absorb vibrations and have low thermal and electrical conductivity. The mechanical properties vary according to the type of polymer, whether it is a thermoplastic, thermoset or elastomer. For the production of composites all three types of polymers are used. Thermoplastics are mostly chemically resistant and tougher than thermosets, while for elastomers, the dominant feature is its elongation. Due to their low density, they are most widely used in aircraft design. The disadvantage is the low thermal stability of polymers. The most important composites have a thermoset matrix.

What is a Prepreg composite?

Pre-preg is "pre-impregnated" composite fibers where a thermoset polymer matrix material, such as epoxy, or a thermoplastic resin is already present. The fibers often take the form of a weave and the matrix is used to bond them together and to other components during manufacture. The thermoset matrix is only partially cured to allow easy handling; this B-Stage material requires cold storage to prevent complete curing. B-Stage pre-preg is always stored in cooled areas since heat accelerates complete polymerization. Hence, composite structures built of pre-pregs will mostly require an oven or autoclave to cure. Pre-preg allows one to impregnate the fibers on a flat workable surface, or rather in an industrial process, and then later form the impregnated fibers to a shape which could prove to be problematic for the hot injection process. Pre-preg also allows one to impregnate a bulk amount of fiber and then store it in a cooled area (below 20°C) for an extended period of time to cure later. The process can also be time consuming in comparison to the hot injection process and the added value for pre-preg preparation is at the stage of the material supplier.g.

Production of particulate composites

Production of particulate composites is considerably simpler, grains are not as sensitive and therefore intensive manual mixing can be used. It is necessary to ensure complete coating of all grains by a matrix, force out the air and ensure maximum homogeneity of a mixture, and further to prevent particle sedimentation, while the viscosity of the matrix is important (as well). In some cases, sedimentation is used especially when we want to obtain a material with a graduated percentage of filler.

Skeletal reinforcement

Skeletal reinforcement is one in which the matrix and secondary phase creates skeletal formations which are mutually mechanically penetrated. In this case we distinguish a matrix and armoring skeleton. The technology of preparation consists of the infiltration of the matrix skeleton by a liquid substance (a low-melting metal or polymer) which solidifies in the pores of the matrix and creates the armoring skeleton. A master skeleton is a porous body of metal, ceramics or graphite prepared by powder metallurgy techniques.

How are glass fibers produced?

The base of glass fibers is carbon SiO2. In a glass furnace, fresh molten glass is produced from a batch, or rather glass beads or frits are melted. The glass is then drawn (becoming fibrous) by nozzles located in the bottom of the furnace. The fiber diameter is typically 1 mm, but it can be regulated by stretching the glass stream flowing from the furnace. The final diameter of the fiber is given by the difference between the flow speed of molten glass and the speed of extracting the individual fibers. After removal from the furnaces, monofilaments are surface-treated with lubricants, grouped into strands and wound onto a coil. Before use, they are usually spun using one of textile technologies into the desired shape.

List and describe the structures (super structure, infrastructre etc) within a composite

The composite as a whole is formed by a superstructure. The structure of the individual phases, which are contained in the composite is called an infrastructure. The term microstructure is designed to describe the structure of the individual substances that are contained in each phase of the composite. Specifically cement concrete. This means the structural arrangement of cement concrete as a system is described by a superstructure, which is formed by the infrastructure of the binder, liquid phase (pores) and fillers. The binder is composed of a variety of minerals and each mineral has its own microstructure. The same is obviously true for every grain of the filler. The third infrastructure (pores) may be formed by a gas or liquid. Cement concrete = superstructure - the main determining factor of the composite, which tells us how many distinct phases are there in the system, how are they arranged, etc. Aggregate, binder and pores = infrastructure speaks about the shapes of individual phases, their sizes, and how they touch. Minerals in the binders, liquids and gases in the pores = microstructure says for example, from what the molecules of individual minerals are in phases, what is the nature of those minerals.

Briefly describe process of hot rolling fibers

The fibers are inserted between two metal foils which pass between the pressure rollers at elevated temperatures

Production of fiber composites primary issues / problems

The main problem is to insert the fibers into the matrix avoiding mechanical damage and to maintain the uniform distribution, directionality and coherence of fibers. Fibers may be relatively easy to break (mechanically) during each manipulation, especially non-metallic fibers (glass, ceramics) are sensitive as their strength depends greatly on the surface integrity. With fiber bundles we need to ensure wetting of each fiber, e.g. by means of wetting agents.

What is the purpose of the matrix?

The matrix combines the individual particles of reinforcement, protecting them against external influences and prevents their violation. The basic function of the matrix is to transmit the external load onto the reinforced phase. For the matrix, a good bond strength with the reinforcing phase material (i.e. perfect wettability without chemical interaction at the interface of the matrix and reinforcement) is required. Among other requirements for the matrix, a low weight is commonly included. In comparison with the reinforcement phase, a matrix has generally lower strength and greater plasticity.

Properties required for the production of composites with a matrix in the liquid state

The methods of producing composites with a liquid matrix are the most commonly used. The basic condition for producing and obtaining the optimal properties of composites are: · good wettability of reinforcement by a matrix material · minimum development of chemical reactions at the interface of the matrix - reinforcement · impregnation of the reinforcement-matrix liquid · infiltration-gas phase

List the types of glass fibers and their applications

The most commonly/frequently used types of glass for fiber production: · E glass (borosilicate) - electrical insulation · S glass (silica-magnesium glass) - high-strength composites · A glass (contains SiO2, K2O, CaO, MgO a Al2O3) - thermal insulation · C glass (pyrex) - chemical applications

What affect does the orientation of fibers in the reinforcement phase have on the properties of the composite?

The orientation of the reinforcing phase affects the isotropy of the system. If the reinforcing particles have the shape and dimensions in all directions about the same (for example powders), the composite behaves basically as an isotropic material, therefore its properties are the same in all directions. On the contrary systems reinforced with cylindrical reinforcement (fibers) show an anisotropy of properties.

What is the purpose of the reinforcement?

The reinforcement phase handles the bulk of the external loads. It is expected to have high strength and a modulus of elasticity E (E is about one order higher than that of the matrix), as well as a small deformation at a fracture with a high proportion of elastic deformation. Regarding the tensile behaviour of the composite it is given by the shape, concentration and orientation of reinforcement.

What shapes are used to compose the reinforcement phase?

The shape of reinforcement particles can be considered approximately as a sphere (the powder form of reinforcement) or as a cylinder (fibers). Their size and distribution then determine the texture of the composite.

Silver and silver based composite properties

They are characterized by good electrical conductivity, have a high melting point and therefore are used primarily in electronics for electrical contacts of different relays, switches and circuit breakers. These composites are reinforced by dispersion strengthening with the particles of refractory compounds, particularly Al2O3, CdO, SnO2 and others.

Iron and iron based composites

They are most often reinforced with oxide particles, but normally ferrous alloys are not strengthened since most of the produced steel are (already) sufficiently resistant to stress at higher temperatures. Dispersion strengthening in materials based on iron oxides is done by admixing oxides in terms of resistance to embrittlement in the field of neutron devices.

Copper and copper based composites

They are strengthen with oxides Al2O3, BeO, ThO2, SiO2 and TiO2, which increase heat resistance and thermal stability while maintaining high electrical conductivity. For the reinforcement, particles of carbides, nitrides and refractory compounds are used. Dispersion strengthened copper-based materials are used in electrical engineering and electronics as electrical contacts, motor forces, and in the welding technology for manufacturing electrodes (spot welding galvanized sheet metal), etc.

Aluminum and aluminum based composite properties

They are the most widely used metal matrices, mainly for their price and variability. Aluminum is lightweight, does not corrode, malleable at low temperatures and affordable. There are many modifying alloys, (with) resistance up to 600 °C. The resulting composites have a good strength to density ratio, therefore, they are often used in aeronautics and the automotive industry and also have a good thermal and electrical conductivity. Due to the high activity of aluminum to oxygen the reinforcing phases mainly are oxides Al2O3, carbides Al4C3 and SiC.

Titanium and (titanium) based composite properties

They are used mostly for fiber composites. Among the features are the variability of the alloys, a strength similar to steel, low corrosion and a higher price. Such composites have about twice the density of aluminum, but the ratio of strength to density for titanium composites is even higher than for aluminum, and moreover they can withstand much higher temperatures. They are usable up to 1000 - 1200 °C, compared to aluminum. Titanium alloys are very reactive at increased temperatures and therefore prone to react with fibers or other fillers during production. As a reaction, a brittle interfacial zone occurs that reduces the material strength. The most frequently used alloys are Ti6Al14V, Ti3Al25V or pure titanium.

Describe Powder Method of composite production

This method is applied in the production of composites with metal, ceramic and polymeric matrices. The base is the application of the powder metal, ceramic or polymer matrix onto reinforced fibers (by electrostatic forces, in water suspension, etc.), compaction into a shape and then the subsequent sintering at high pressures and temperatures. Whiskers (metallic or ceramic) may be mixed into a powder matrix. The most important application of a powder method is in the production of composites with ceramic matrices. It is the basis for the production of composites with a skeletal matrix.

Composites Type III

This system is again a three-phase, therefore it contains a matrix, filler and pores. In this case it is again a little matrix, but a lot of filler and pores. Both the filler and the pores are aggregated. These pores are even and continuous. If the pores are completely continuous, the system is inconsistent. It follows that it is a material with good insulating properties, such as plasterboard. Three-component system: Vk = Vm + Vf + Vv

Describe the pressing / press forming process of composites

While pressing, the reinforcement (of fibers) is placed between the metal foils and inserted between heated press boards, where due to the action of pressure and temperature both components connect diffusively. Pressing takes place in a vacuum or in a protective (modified) atmosphere. By the compression of several single-layer parts of the multi-layer composite are formed

Whiskers description and properties

Whiskers are special thin crystals with a minimal amount of defects within the structure. Whiskers with its properties exceed other reinforcing phases. These are single crystals/monocrystals whose characteristics depend mainly on the conditions of growth, and the perfection of the surface and diameter. It is necessary to distinguish whiskers from monocrystal fibers of the same chemical composition - those have a number of free, moving dislocations. The most important characteristic of whiskers is a high modulus of elasticity. Basic properties of whiskers: · the diameter of less than 1 mm, length of 3 - 4 mm, a slenderness ratio above 1000 - they usually behave as long discontinuous fibers · there should always be a special type of cultivation - so they contain only one screw dislocation in the middle · they can be obtained from a variety of substances by the condensation of vapour within the vacuum · the strength is about 1/10 E, up to this value a whisker deforms only flexibly, after exceeding this value, it deforms as a regular monocrystalline fiber

conjugated systems

by chemical and physical forces at the interface the material remains rigid even under external forces; by the phase that reinforces the system are those further divided as: o granular - axial dimensions of the particles are not very different (aggregate) o fibrillar - where there is one dimension prevailing (fiber) o lamellar - one dimension is suppressed compared to the other two (plate)

Typical use of dispersive strengthening

is typical primarily for the metal matrix composites - such a composite has a greater tensile modulus, higher thermal stability and reduced contraction.

List fiber classes based on their diameter

nanofibers - to 100 nm · microfibers - 0.1 to 1 mm - whiskers · middle-sized fibers - 1 to 10 mm - carbon, glass, textile · coarse (rough) fibers - over 10 mm - B, SiC, etc.

Methods for the production of composites with a matrix in the solid state

pressing/press forming and hot rolling · plasma injection · powder methods

Parameters and requirements during designing the product

· the selection of individual (most suitable) components with regard to their future performance · determining the compatibility of components - each phase in the composite must maintain its positive qualities, ingredients (components) must not damage each other · finding an appropriate geometrical form for each phase - stronger parts to be elongated (fibers, strips, belts etc.), while the weaker phase should be wrapping the stronger one and bring individual fibers together into a single structure · phases in the composite should be distributed so that they can work together · conditions in which the future composite will function - temperature, abrasion, etc.