Classification OF Materials PDF

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Lecture on Ckassification of materials...

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CLASSIFICATIONOF ENGINEERING MATERIALS -Metal -Ceramic -Polymer -Composite

Classification It is the systematic arrangement or division of materials into groups on the basis of some common characteristic 1. According to General Properties 2. According to Nature of Materials 3. According to Applications

1. Metals -Metals are the most commonly used class of engineering material. Metal alloys are especially common, and they are formed by combining a metal with one or more other metallic and/or non-metallic materials. -The combination usually occurs through a process of melting, mixing, and cooling. The goal of alloying is to improve the properties of the base material in some desirable way. Metal Alloys

Carbon Steel 0Carbon steels are basically just mixtures of iron and carbon.

Low Carbon Steel -has less than about 30% carbon.It is characterized by low strength but high ductility. -cold working not heat treatment -very weldable and inexpensive to produce -use for wire,structural shapes,machine parts, and sheet metal. Medium-Carbon Steel -Medium-carbon steel contains between about 0.30% to 0.70% carbon. It can be heat treated to increase strength, especially with the higher carbon contents. Medium-carbon steel is frequently used for axles, gears, shafts, and machine parts. High-Carbon Steel High-carbon steel contains between about 0.70% to 1.40% carbon. It has high strength but low ductility. Common uses include drills, cutting tools, knives, and springs.

Low-Alloy Steel

-These are metals and alloys containing a high proportion of the element iron. -strongest materials(high strength)

Low-alloy steels, also commonly called alloy steels, contain less than about 8% total alloying ingredients. Low-alloy steels are typically stronger than carbon steels and have better corrosion resistance.

Ferrous Alloys

Tool Steel

1.1 Ferrous metals

-have iron as the base element. -are the most common alloys in use due to the abundance of iron, ease of production, and high versatility of the material. The biggest disadvantage of many ferrous alloys is low corrosion resistance.

-Tool steels are primarily used to make tooling for use in manufacturing, for example cutting tools, drill bits, punches, dies, and chisels. Alloying elements are typically chosen to optimize hardness,wear resistance, and toughness.

Stainless Steel Carbon is an important alloying element in all ferrous alloys. In general, higher levels of carbon increase strength and hardness, and decrease ductility and weldability.

-have good corrosion resistance due to addition of chromium. (11%) -passivation

Cast Iron

1.2 Non – ferrous metals

-is a ferrous alloy containing high levels of carbon,generally greater than 2%. -have a low melting temperature which makes them well suited to casting.

•These materials refer to the remaining metals known to mankind. •The pure metals are rarely used as structural materials as they lack mechanical strength. •They are mainly used with other metals to improve their strength.

Gray Cast Iron Gray cast iron is the most common type. The carbon is in the form of graphite flakes. Gray cast iron is a brittle material and its compressive strength is much higher than its tensile strength. -A very good property of grey cast iron is that the free graphite in its structure acts as a lubricant. (sliding) -Nodular cast iron has good strength, ductility, and machinability.Common uses include crankshafts, gears, pump bodies, valves, and machine parts.

White Cast Iron -cabide(knoen as cementite) -It has a high tensile strength and low compressive strength. Since it is hard, therefore, it cannot be machined with ordinary cutting tools but requires grinding as shaping process. White cast iron is primarily used for wear-resisting components as well as for the production of malleable cast iron.(nozzle)

Malleable Cast Iron -Malleable cast iron is produced by heat treating white cast iron. The heat treatment improves the ductility of the material while maintaining its high strength. -hubs of wagon wheels,door hinges,locks etc.

Wrought iron -It is the purest iron which contains at least 99.5% iron but may contain up to 99.9% iron. The wrought iron is a tough, malleable and ductile material. It cannot stand sudden and excessive shocks. It can be easily forged or welded. -chains,crane hooks

They are used where their special properties such as corrosion resistance, electrical conductivity and thermal conductivity are required. The non-ferrous metals are usually employed in industry due to the following characteristics : 1. Ease of fabrication (casting, rolling, forging, welding and machining), 2. Resistance to corrosion, 3. Electrical and thermal conductivity, and 4. Weight

Aluminum -white metal -It is a light metal having specific gravity 2.7 and melting point 658°C. The tensile strength of the metal varies from 90 MPa to 150 MPa. In its pure state, the metal would be weak and soft for most purposes, but when mixed with small amounts of other alloys, it becomes hard and rigid. -It is extensively used in aircraft and automobile components where saving of weight is an advantage.

Aluminum Alloys -The aluminium may be alloyed with one or more other elements like copper, magnesium, manganese, silicon and nickel. The addition of small quantities of alloying elements converts the soft and weak metal into hard and strong metal, while still retaining its light weight. The main aluminium alloys are : 1. Duralumin. It is an important and interesting wrought alloy. This alloy possesses maximum tensile strength (up to 400 MPa) after heat treatment and age hardening. 2. Y-alloy.copper-aluminium alloy.

-increases its strength and machinability. 3. Magnalium. It is made by melting the aluminium with 2 to 10% magnesium.Due to its light weight and good mechanical properties, it is mainly used for aircraft and automobile components. 4. Hindalium. It is an alloy of aluminium and magnesium with a small quantity of chromium.

was made for casting guns. It is extensively used forcasting boiler fittings, bushes, bearings, glands, etc.

Lead -bluish grey metal -It is so soft that it can be cut with a knife.

Tin Nickel Alloys -Nickel alloys have high temperature and corrosion resistance. Common alloying ingredients include copper, chromium, and iron. -Monel is a group of nickel alloys, primarily composed of nickel (from 52 to 67%) and copper, with small amounts of iron, manganese, carbon, and silicon. -Inconel is a nickel-chromium alloy that is classified as a superalloy because of its highperformance qualities and resistance to corrosion and oxidation. -Hastelloy is a nickel-molybdenumchromium superalloy with an addition of tungsten designed to have excellent corrosion resistance in a wide range of severe environments.

Copper It is one of the most widely used non-ferrous metals in industry. It is a soft, malleable and ductile material with a reddish-brown appearance. -It is a good conductor of electricity. The copper alloys are broadly classified into the following twogroups : 1. Copper-zinc alloys (Brass). The most widely used copper-zinc alloy is brass. 2. Copper-tin alloys (Bronze). The alloys of copper and tin are usually termed as bronzes.

Gun Metal -It is an alloy of copper, tin and zinc. It usually contains 88% copper, 10% tin and 2% zinc. This metal is also known as Admiralty gun metal. The zinc is added to clean the metal and to increase its fluidity. -The metal is very strong and resistant to corrosion by water and atmosphere. Originally, it

-It is brightly shining soft,malleable and ductile.

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Zinc Base Alloys -The most of the die castings are produced from zinc base alloys. These alloys can be casted easily with a good finish at fairly low temperatures. -These alloys are widely used in the automotive industry and for other high production markets such as washing machines, oil burners, refrigerators, radios, photographs, television, business machines, etc. -high mechanical strength properties, corrosion resistance. 1. Monel metal. It is an important alloy of nickel and copper. -It is used for making propellers, pump fittings, condenser tubes, steam turbine blades, sea water exposed parts, tanks and chemical and food handling plants. 2. Inconel-It is used for making springs which have to withstand high temperatures and are exposed to corrosive action. It is also used for exhaust manifolds of aircraft engines. 3. Nichrome. It consists of 65% nickel, 15% chromium and 20% iron. It has high heat and oxidation resistance. It is used in making electrical resistance wire for electric furnaces and heating elements. 4. Nimonic. It consists of 80% nickel and 20% chromium. It has high strength and ability to operate under intermittent heating and cooling conditions. It is widely used in gas turbine engines.

2. Non – metallic materials 2.1 Synthetic materials These are non – metallic materials that do not exist in nature, although they are manufactured from natural substances such as oil, coal and clay. -They combine good corrosion resistance with ease of manufacture by moulding to shape and relatively low cost. -Synthetic adhesives are also being used for the joining of metallic components even in highly stressed applications. 2.2 Natural materials Such materials are so diverse that only a few can be listed here to give a basic introduction to some typical applications. -Wood: This is naturally occurring fibrous composite material used for the manufacture of casting patterns. -Rubber :This is used for hydraulic and compressed air hoses and oil seals. Naturally occurring latex is too soft for most engineering uses but it is used widely for vehicle tyres when it is compounded with carbon black. -Glass : This is a hardwearing, abrasion-resistant material with excellent weathering properties. It is used for electrical insulators, laboratory equipment,optical components in measuring instruments etc and,in the form of fibers, is used to reinforce plastics. It is made by melting together the naturally occurring materials : silica (sand), limestone (calcium carbonate ) and soda (sodium carbonate) -Emery : This is a widely used abrasive and is a naturally occurring aluminum oxide. Nowadays it is produced synthetically to maintain uniform quality and performance. -Ceramic: These are produced by baking naturally occurring clays at high temperatures after moulding to shape. They are used for high – voltage insulators and high – temperature – resistant cutting tool tips. -Diamonds: These can be used for cutting tools for operation at high speeds for metal finishing where surface finish is greater importance. For example, internal combustion engine pistons and bearings. They are also used for dressing grinding wheels. -Oils : Used as bearing lubricants, cutting fluids

and fuels. -Silicon : This is used as an alloying element and also for the manufacture of semiconductor devices.

Ceramics Ceramics are solid compounds that may consist of metallic or nonmetallic elements. The primary classifications of ceramics include glasses, cements, clay products, refractories, and abrasives. Characteristic of ceramics: • Brittleness • High thermal and electrical resistance • High resistance to corrosion • Opaque • High temperature stability

Glass Glasses are common materials and are seen in applications including windows, lenses, and containers. Glasses are amorphous,whereas the other ceramics are mainly crystalline. Primary advantages of glasses include transparency and ease of fabrication. The base element of most glasses is silica, and other components can be added to modify its properties. Common processes used to form glass include: • heating until melting, then pouring into molds to cast into useful shapes • heating until soft, then rolling • heating until soft, then blowing into desired shapes

Cements Cements are materials that, after mixing with water, form a paste that then hardens. Because of this characteristic, cements can be formed into useful shapes while in paste form before they harden into rigid structures. Plaster of paris is one common cement. The most common cement is called Portland cement, which is made by mixing clay and limestone and then firing at high temperature. Portland cement is used to form concrete, which is made by mixing it with sand, gravel, and water. It can also be mixed with sand

and water to form mortar. Like other ceramics, cements are weak in tension but strong in compression. Cement is very inexpensive to produce, and it used widely in the construction of buildings, bridges, and other large structures.

Clay Products Clay is a very common ceramic material. It can be mixed with water, shaped, and then hardened through firing at high temperature. The two primary classifications of clay products include structural clay products and whitewares. Structural clay products see applications including bricks, tiles, and piping. Whitewares see applications including pottery and plumbing fixtures.

Refractories Refractory ceramics can withstand high temperatures and extreme environments. They can also provide thermal insulation. Brick is the most common refractory ceramic.

Abrasives Abrasive ceramics are hard materials that are used to cut, grind, and wear away other softer materials.Typical properties of abrasives include high hardness,wear resistance, and temperature resistance. Abrasives can either be bonded to a surface (e.g. grinding wheels and sand paper), or can be used asloose grains (e.g. sand blasting). Common abrasives include cemented carbide, silicon carbide, tungsten carbide, aluminum oxide, and silica sand. Diamond is also an excellent abrasive, but it is expensive. Factors affecting materials properties: 1. Heat treatment This is the controlled heating and cooling of metals to change their properties to improve their performance or to facilitate processing. 2. Processing Metal is hot worked or cold worked depending upon the temperature at which it is flow formed to shape . These temperatures are not easy to define - for instance , lead hot works at room temperature and can be beaten into complex

shapes without cracking. 3. Environmental reactions The properties of materials can also be effected by reaction with environment in which they are used. -For example Resting of steel Unless steel structures are regularly maintained by rest neutralization and painting process, resting will occur. The rest will eat into the steel, reduce its thickness and,therefore, its strength. In extreme cases an entire structure made from steel may be eaten away. 4.Dezincification of brass Brass is an alloy of copper and zinc and when brass is exposed to a marine environment for along time, the salt in the sea water pray react with the zinc content of the brass so as remove it and leave it behind on spongy, porous mass of copper. This obviously weakness the material which fails under normal working conditions. 5.Degradation of plastic Many plastic degrade and become weak and brittle when exposed to the ultraviolet content of sunlight. Special dyestuffs have to be incorporated into the plastic to filter out these harmful rays.

Polymers Polymers are materials that consist of molecules formed by long chains of repeating units. They maybe natural or synthetic. Many useful engineering materials are polymers, such as plastics, rubbers,fibers, adhesives, and coatings. Polymers are classified as thermoplastic polymers, thermosetting polymers (thermosets), and elastomers.

Thermoplastic Polymers The classification of thermoplastics and thermosets is based on their response to heat. If heat is applied to a thermoplastic, it will soften and melt. Once it is cooled, it will return to solid form. Thermoplastics do not experience any chemical change through repeated heating and cooling (unless the temperature is high enough to break the molecular bonds). They are therefore very well suited to injection molding.

Thermosetting Polymers Thermosets are typically heated during initial processing, after which they become permanently hard. Thermosets will not melt upon reheating. If the applied heat becomes extreme however, the thermoset will degrade due to breaking of the molecular bonds. Thermosets typically have greater hardness and strength than thermoplastics. They also typically have better dimensional stability than thermoplastics, meaning that they are better at maintaining their original dimensions when subjected to temperature and moisture changes.

Elastomers Elastomers are highly elastic polymers with mechanical properties similar to rubber. Elastomers are commonly used for seals, adhesives, hoses, belts,and other flexible parts. The strength and stiffness of rubber can be increased through a process called vulcanization, which involves adding sulfur and subjecting the material to high temperature and pressure. This process causes cross-links to form between the polymer chains....