Structural materials of new generation

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STRUCTURAL MATERIALS OF NEW GENERATION

КОНСТРУКЦИОННЫЕ МАТЕРИАЛЫ НОВОГО ПОКОЛЕНИЯ

Demidov D.N.

Vladimir State University named after

Alexander and Nikolay Stoletovs, Russia

There are, more than 50,000 materials available to the engineer. Breakthroughs in materials science and engineering are needed to enable these new capabilities. Such research can improve energy productivity and manufacturing processes, reduce waste, and lead to numerous highly functional, high-performance materials technologies.

There are many metals which you are familiar with - copper pipes and wire, aluminium saucepans and cast iron stoves. Metals may be mixed with other elements especially other metals to produce alloys which will have improved properties. Heat treatment can also be used to change the properties of alloys e.g. hardening and tempering of high carbon steel.

All metals are good conductors of heat and electricity. Copper is a particularly good conductor but is not very strong, it is also fairly dense. Aluminium is a good conductor has a low density and when alloyed has a high tensile strength. Some alloys such as pewter and zinc alloys have a low melting point and can be easily formed by casting or moulding but they have a low tensile strength.

Metals in common use are corrosion resistant except iron and steel which rust quickly. Corrosion resistance is achieved by electroplating to add a layer of corrosion resistant material such as chromium or zinc, painting, plastic coating, and coating with an oil or grease. The alloy stainless steel is very rust resistant.

When choosing a metal for a particular job the properties must be carefully considered. For example aluminium could be used for overhead power lines as its lower density and good tensile strength offset its slightly lower electrical conductivity.

In my article I would like to discussed about the classification of engineering materials. Basically Engineering Materials Can be classified into two categories: Metals and Non-Metals. Metals are polycrystalline bodies which are having number of differentially oriented fine crystals. Normally major metals are in solid states at normal temperature. However, some metals such as mercury are also in liquid state at normal temperature. All metals are having high thermal and electrical conductivity. All metals are having positive temperature coefficient of resistance. Means resistance of metals increase with increase of temperature. Examples of metals - Silver, Copper, Gold, Aluminum, Iron, Zinc, Lead, Tin etc.

Also metals can be further divided into two groups:

Ferrous Metals - All ferrous metals are having iron as common element. All ferrous materials are having very high permeability which makes these materials suitable for construction of core of electrical machines. Examples: Cast Iron, Wrought Iron, Steel, Silicon Steel, High Speed Steel, Spring Steel etc.

Non-Ferrous Metals- All non-ferrous metals are having very low permeability. Example: Silver, Copper, Gold, Aluminum etc. Non-Metal materials are non-crystalline in nature. These exists in amorphic or mesomorphic forms. These are in both solid & gases forms at normal temperature. Normally all non-metals are bad conductor of heat and electricity. Examples: Plastics, Rubber, Leathers, Asbestos etc.

As these non-metals are having very high resistivity which makes them suitable for insulation purpose in electrical machines.

I would like to say a few words about ceramics. This class of material includes plates and cups, bricks, earthenware pots, engineering ceramics, glasses [glasses are non-crystalline and not normally classed as ceramics], and refractory (furnace) materials. Ceramics are made by heating together materials such as silica, chalk and clays. Other chemicals may be included to act as flux and to change colour etc. Engineering Ceramics Include: Silicon carbide, Zirconia, Silicon nitride, Diamond, Cubic boron nitride, Tungsten Carbide.

Engineering ceramics are ideally suited for high performance applications where a combination of properties such as wear resistance, hardness, stiffness and corrosion resistance are important. In addition to these properties, engineering ceramics have relatively high mechanical strength at high temperatures. They are good electrical insulators, They often have a close thermal expansion coefficient to metals (they can be bonded to metals - e.g. carbide tipped tools).Ceramics have been regarded as hard but brittle, however modern ceramics have been developed which are viable alternatives to metals and their alloys in many applications - engineering ceramic parts and components are more durable and have longer life-spans under given operational conditions. Ceramic cutting tools, for instance, require less sharpening or replacement due to wear, and will last at least 60 to 100 times longer than steel blades.

Engineering ceramics are chemically resistant to most acids, alkalis and organic solvents and can withstand high temperatures. Metals weaken rapidly at temperatures above 816 degrees C while engineering ceramics retain a good degree of their mechanical properties at much higher temperatures.

Mechanical components include wear plates and thermal barriers, bearings for high speed and high stiffness spindles, bushes, gears. Process components include pump shafts, seats, bearing surfaces, gears and even complete pump bodies, valve guides and seats. Ceramics are used for cutting tools including razor blades for film and tape cutting to 300mm diameter circular slitters for the paper industry. Ceramic turbine blades are used in most turbochargers providing lighter units than the steel alternatives allowing improved performance at higher temperatures.

Composite are mixtures of materials which give improved properties. One of the materials is the matrix or binding chemical and the other is the reinforcer. A good example is GRP - glass reinforced polyester(plastic) resin. where the glass fibres increase the strength of the polyester resin. Carbon fibre reinforced epoxy resin is stronger and lighter than steel. Concrete is a composite (the cement is the matrix and the gravel and steel rods are the reinforcer) as are bricks made from clay reinforced with straw. Natural composites include wood, shell and bone.

Car bodies - especially sports cars, F1 racing cars, boat hulls, lightweight struts and supports in bridge building and the construction industry. Aerospace - use of carbon fibre composites as well as high tech ceramic parts has revolutionized this industry.

So, innovative materials that are more durable in high-temperature environments than traditional materials will improve productivity, avoid down time, and increase energy productivity. The goal is to increase service life tenfold, decreasing the energy intensity of the materials and components.

In conclusion I would like to say, that in order to meet the design requirements and expanding demands in various engineering fields, it is essential to incorporate new technological improvements in material sciences into existing processes and applications. This involves engineering new material systems and improving existing ones towards higher strength, toughness and wear resistance.

construction material innovative ceramics

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