Engineering materials and metallurgy -Ferrous and Non Ferrous metals 1

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Ferrous and Non Ferrous metals Limitations of plain carbon steels  Cannot be strengthened above 690 MN/m2 without loss of ductility and impact resistance.  The depth of hardening is limited.  Must be quenched very rapidly to obtain a fully martenstic structure leading to the possibility of quench distortion and cracking.  Have poor impact resistance at low temperatures.  Alloy steels containing a number of alloying elements have been developed to overcome these deficiencies. Dr.K.RaviKumar Dr.N.G.P.Institute of Technology

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ALLOY STEELS A homogeneous mixture or solid solution of two or more metals the atoms of one replacing or occupying interstitial positions between the atoms of the other. The principal alloying elements used are : Manganese Mn nickel Ni chromium Cr molybdenumMo tungsten W vanadium V cobalt Co silicon Si boron B copper Cu titanium Ti and niobium Nb.  Low Alloy steel Alloying elements8  High Alloy steel Alloying elements8

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Effect of alloying elements Carbon  Carbon is the primary hardening element in steel.  Hardness and tensile strength increases as carbon content increases.  Ductility and weld-ability decreases with increasing carbon. Manganese  Beneficial to surface quality especially in resulfurized steels.  Manganese contributes to strength and hardness but less than carbon.  The increase in strength is dependent upon the carbon content.  Increasing the manganese content decreases ductility and weldability but less than carbon.

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Phosphorus  Increases strength and hardness and decreases ductility and notch impact toughness of steel.  Higher phosphorus is specified in low-carbon free-machining steels to improve machinability. Sulphur  Decreases ductility and notch impact toughness especially in the transverse direction.  Weldability decreases with increasing sulphur content. Sulphur is found primarily in the form of sulfide inclusions.  The only exception is free-machining steels where sulphur is added to improve machinability.

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Silicon  Is one of the principal deoxidizers used in steelmaking.  Silicon is less effective than manganese in increasing as-rolled strength and hardness.  Increases magnetic properties Copper  Is beneficial to atmospheric corrosion resistance when present in amounts exceeding 0.20.  Copper 0.10 to 0.50 in significant amounts is detrimental to hot-working steels.  Copper negatively affects forge welding but does not seriously affect arc or oxyacetylene welding.  Copper can be detrimental to surface quality.

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Lead  Is virtually insoluble in liquid or solid steel.  Lead is sometimes added to carbon and alloy steels by means of mechanical dispersion during pouring to improve the machinability. Boron  Is added to improve hardenability.  Boron-treated steels are produced to a range of 0.0005 to 0.003.  Improves machinablity and cold forming capacity Chromium  Is commonly added to steel to increase corrosion resistance and oxidation resistance  Also increases the hardenability and improves high-temperature strength.

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Nickel  Is a ferrite strengthener.  Nickel does not form carbides in steel.  It remains in solution in ferrite strengthening and toughening the ferrite phase.  Nickel increases the hardenability and impact strength of steels. Molybdenum  Increases the hardenability of steel.  Molybdenum may produce secondary hardening during the tempering of quenched steels.  It enhances the creep strength of low-alloy steels at elevated temperatures Aluminum  Is widely used as a deoxidizer.  Aluminum can control austenite grain growth in reheated steels and is therefore added to control grain size.  Aluminum is the most effective alloy in controlling grain growth prior to quenching.

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Titanium zirconium and vanadium  Are also valuable grain growth inhibitors but there carbides are difficult to dissolve into solution in austenite.  Vanadium increases the yield strength and the tensile strength of carbon steel.

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High strength low alloy steels HSLA  Not hardened by heat treatments  Yield strength 289-482 Mpa tensile strength 414 – 621 Mpa.  Microstructure will be in the form of ferrite-pearlite  Low carbon content less than 0.2 1.0 Mn and less than 0.5 of other alloying elements  Provides increased strength to weight ratio.  Especially preferable for thinner sections.  Superior in weldablity formablity toughness strength compared to plain carbon steels.  They can be annealed normalized or stress relieved. Applications  Trucks construction equipment off-highway vehicles mining equipment and other heavy-duty vehicles use HSLA sheets or plates for chassis components buckets all type Structural works.  Applications such as offshore oil and gas rigs single-pole power- Transmission towers railroad cars and ship construction.

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High alloy steels Stainless steel  In metallurgy stainless is defined as an iron-carbon alloy with a minimum of 11.5 wt chromium content.  Stainless steels are High alloy steels and have superior corrosion resistance because they contain relatively large amount of chromium Selecting a Stainless Steel  Corrosion resistance  Magnetic properties  Resistance to oxidation and sulfidation  Ambient strength  Ductility  Resistance to abrasion and erosion  Toughness  Elevated temperature strength  Cryogenic strength  Thermal conductivity  Electrical resistivity etc

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Types of Stainless steel  Austenitic grades  Ferrite grades  Martensitic  Precipitation-hardening martensitic stainless steels  Duplex stainless steels Austenitic grades –Features  Compostion:0.15 carbon16 -26Chromium nickel-8-24 Magnese-15  Retain austenitic structure  Austenitic steels have Face Centered Cubic structure.  Non magnetic in the annealed condition and can be hardened only by cold working.  Possess excellent cryogenic properties and high temperature strength.

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Ferritic grades  Highly corrosion-resistant but less durable than austenitic grades.  Compostion-less than 0.2carbon and 16 – 20 chromium and very little nickel molybdenum some aluminum or titanium.  Common ferritic grades include 18Cr-2Mo 26Cr-1Mo 29Cr-4Mo and 29Cr-4Mo-2Ni.  Ferritic grades are chromium containing alloys with bcc crystal structure  The ferritic alloys are Ferro magnetic  They can have good ductility and formablity but high temperature strength are relatively poor compared to austenitic grades

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Martensitic grades  Compostion:1.2 carbon12 -18 Chromium  Martensitic stainless steels are not as corrosion-resistant as the other two classes  Extremely strong and tough as well as highly machinable.  Heat treatable.  Body centered cubic crystal structure in the hardened condition.  Resistant to corrosion only in the mild environment  Excess carbides present to increase wear resistance or to maintain cutting edges Precipitation –hardening martenstic stainless steels  Precipitation hardening stainless steels are chromium-nickel alloys.  PH most common grade17chromium 4nickel.  Precipitation hardened to get higher strengths than the other martensitic grades  Precipitation-hardening stainless steels may be either austenitic or martensitic in the annealed condition.

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Duplex stainless steels  Duplex stainless steels are a mixture of BCC ferrite and FCC austenite crystal structures.  The percentage in each phase is a dependent on the composition and heat treatmentmostly 40 – 60 .  Most Duplex stainless steels are intended to contain around equal amounts of ferrite and austenite phases in the annealed condition.  The primary alloying elements are chromium and nickel.  Duplex stainless steels generally have similar corrosion resistance to austenitic alloys.  Duplex stainless steels also generally have greater tensile and yield strengths but poorer toughness than austenitic stainless steels. Stainless steel grades  200 Series—austenitic chromium-nickel-manganese alloys  300 Series—austenitic chromium-nickel alloys  400 Series—ferritic and martensitic chromium alloys  500 Series—heat-resisting chromium alloys  600 Series—martensitic precipitation hardening alloys

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Tool steels  Tool steel refers to a variety of carbon and alloy steels that are particularly well-suited to be made into tools .  Tool steels contain more alloying elements than normal alloy steels.  Hardness resistance to abrasion ability to hold a cutting edge and/or their resistance to deformation at elevated temperatures are the major features.

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Types of tool steels

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Defining property AISI grade Significant characteristics Water-hardening W Cold-working O Oil-hardening A Air-hardening medium alloy D High carbon high chromium Shock resisting S Tungsten base High speed T Tungsten base M Molybdenum base Hot-working H H1-H19: chromium base H20-H39: tungsten base H40-H59: molybdenum base Plastic mold P Special purpose L Low alloy F Carbon tungsten

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Water-hardening grades  W-grade tool steel is water quenched tool .  W-grade steel is essentially high carbon  This type of tool steel is the most commonly used tool steel because of its low cost compared to other tool steels.  They work well for small parts and applications where high temperatures are not encountered above 150 °C 300 °F it begins to soften to a noticeable degree.  Hardenability is low so W-grade tool steels must be quenched in water. These steels are rather brittle. Typical applications for various carbon compositions are:  0.60—0.75 carbon: machine parts chisels setscrews  0.76—0.90 carbon: forging dies hammers and sledges.  0.91—1.10 carbon: drills cutters and shear blades.  1.11—1.30 carbon: small drills lathe tools razor blades

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Cold-working grades Grade-O refers to oil hardening and grade-A refers to air hardening.  The toughness of O-grade and A-grade tool steels are increased by alloying with silicon Manganese Silicon Chromium.  These tool steels are used on larger parts  More alloying elements are used in these steels as compared to water-hardening grades.  These alloys increase the steels hardenability and thus require a less severe quenching process. These steels are also less likely to crack.  D-grade tool steels contain between 10 and 18 chromium and carbon from 1.50- 2.35 . These steels retain their hardness up to a temperature of 425 °C 800 °F. Common applications for these grade of tool steel is forging dies die-casting die blocks and drawing dies.

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Shock resisting grades  S-grade tool steel are designed to resist shock at both low and high temperatures.  A low carbon content is required for the necessary toughness approximately 0.5 carbon. High speed grades  T-grade and M-grade tool steels are used for cutting tools where strength and hardness must be retained at temperatures up to or exceeding 760 °C 1400 °F.  M-grade tool steels were developed to reduce the amount of tungsten and chromium required.  T also known as 18-4-1 is a common T-grade alloy. Its composition is 0.7 carbon 18 tungsten 4 chromium and 1 vanadium.

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Hot-working grades  H-grade tool steels were developed for strength and hardness during prolonged exposure to elevated temperatures.  All of these tool steels use a substantial amount of carbide forming alloys.  H1 to H19 are based on a chromium content of 5  H20 to H39 are based on a tungsten content of 9 to 18 and a chromium content of 3 to 4  H40 to H59 are molybdenum based. Special purpose grades  P-grade tool steel is short for plastic mold steels. They are designed to meet the requirements of zinc die casting and plastic injection molding dies.  L-grade tool steel is short for low alloy special purpose tool steel. L6 is extremely tough.  F-grade tool steel is water hardened by substantially more wear resistant than W-grade tool steel.

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 Maraging Steels  Maraging steel is essentially free of carbon which distinguishes it from most other types of steel. The result is a steel which Possesses high strength and toughness.  A special class of low carbon ultra-high strength steels which derive their strength not from carbon but from precipitation of inter-metallic compounds.  Maraging steels are carbon free iron-nickel alloys with additions of cobalt molybdenum titanium and aluminium.  Cobalt is added in percentages up to 12 to accelerate the precipitation reactions.  The term maraging is derived from the strengthening mechanism which is transforming the alloy to martensite with subsequent age hardening . Applications  Aerospace e.g. undercarriage parts and wing fitting Tooling machinery e.g. extrusion press rams and mandrels in tube production gears and fasteners.  They are suited to engine component applications such as crankshafts

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Non ferrous alloys The more common non-ferrous materials are the following metallic elements and their alloys:  Copper  Aluminium  Magnesium  Lead  Nickel  Tin  Zinc  Cobalt etc.

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COPPER The main grades of raw copper used for cast copper base alloys are  High conductivity copper electrolytic having min 99.9 Cu. The oxygen content may be of the order 0.40 Pb and Fe less than 0.005 Ag 0002 and Bi less than 0.001. Electrolytic copper is used for electrical purposes.  Deoxidized copper having min 99.85 Cu less than 0.05As 003 Fe and 0.003 Bi. Other elements may be of the 0.05 P 0.01 Pb 0.10 Ni 0.003 and 0.005 Ag and Sb respectively.  Arsenical deoxidized copper having 0.4 As 0.04 P and remaining copper. It is used for welded vessels and tanks.  Arsenical touch pitch copper containing 0.4 As 0.065 oxygen0.002 Pb 0.15 Ni 0.006 Ag 0.01 Sb and less than 0.005 BI less than 0.020 Fe and remaining copper.  Oxygen free copper contains 0.005 Pb 0.001 Ni 0.001 Ag and less than 0.0005 and 0.001 Fe and Bi respectively. It is melted and cast in non-oxidising atmosphere

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Properties and applications of Copper : Properties  Excellent resistance to corrosion.  Non-magnetic properties.  Easy to work it is ductile and malleable.  Moderate to high hardness and strength.  High thermal and electrical conductivity. .  It can be easily polished plated and possesses a pleasing appearance.  Resistance to fatigue abrasion and corrosion.  It can be soldered brazed or welded.  Very good machinability. .  Ease of forming alloys with other elements like Zn Sn AI Pb Si Ni etc. Applications  i Electrical parts  ii Heat exchangers  iii Screw machine products  iv For making various copper alloys such as brass and bronze

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Copper Alloys  High strength and corrosion resistance a combination desirable for marine applications.  Possess excellent corrosion resistance electrical and thermal conductivities and formability.  High wearing properties hardness.  Some copper alloys are selected for decorative applications because of appearance.  Elements such as aluminium zinc tin beryllium nickel silicon lead etc. form alloys with copper. Classification of Copper alloys : High copper alloys - contains 96.0 to 99.3 copper.  Possess enhanced mechanical properties due to the addition of small amounts of alloying elements such as chromium zirconium beryllium and cadmium. A few typical high copper alloys are:  i Cu1 Cd ii Cu 0.8 Cr iii Cu 0.12-0.30 Zr iv Cu 1.5-2.0 Be  Used for electrical and electronic components resistance welding electrodes wire conductors diaphragms .

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BRASSES  Brasses contain zinc as the principle alloying element. Brasses are subdivided into three groups  i Cu-Zn alloys  ii Cu-Pb-Zn alloys or leaded brasses and  iii Cu-Zn-Sn alloys or tin brasses.  Zinc in the brass increases ductility along with strength.  Brass has high resistance to corrosion and is easily machinable also acts as good bearing material.  Brass possesses greater strength than copper however it has lower thermal and electrical conductivity. Various types of brasses are discussed below:  1 Gilding metal  Range from 5 to 15 Zn balance Cu and possess shades of colour from the red of copper to a brassy yellow.  They are supplied mainly in the form of sheet strip and wire for jewellery and many other decorative purposes.  Like copper gilding metal is hardened and strengthened by cold work.  Gilding metal is used making coins medals tokens fuse caps etc.

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2 Cartridge brass -contains 70 Cu and 30 Zn.  In the fully annealed condition it has a tensile strength of over 300 N/mm2.  Greater elongation and tensile strength  cold deformation in presses and by spinning or other means  Used for cupped articles like the caps of electric lamp bulbs door furniture etc.  Cartridge brass work hardens when deformed in the cold and must be annealed if many successive operations are to be performed. 3 Admiralty brass  Admiralty brass contains Cu 71 Zn 28 and Sn 1.  The small amount of tin added to brass improves its resistance to certain types of corrosion.  Used exacting conditions of marine condensers.  widely used for the tubes and other parts of condensers cooled by fresh water and for many other purposes.  For such applications the modern alloy contains about 0.04. Arsenic which improves resistance to a penetrative form of corrosion known as dezincification.

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4 Aluminium brass -contains 76 Cu 22 Zn and 2 Al a little arsenic is added to inhibit dezincification.  In contact with sea water a protective film builds up on the surface of this alloy in the early stages of corrosion and prevents further attack.  Moreover if the film is damaged by the abrasive action of sand particles for instance it is self-healing. 5 Basis brass -contains copper 61.5-64 the remainder being zinc.  Basis brass is used for press work where a relatively cheap material is required  The main commercial forms are sheet strip and wire. 6 Muntz metal or yellow metal - contains 60 of copper and 40 of Zn  Essentially a hot working material.  It is manufactured in the form of hot rolled plate and hot rolled rod or extruded sections in a great variety of shapes and sizes.  Yellow metal is frequently used as a brazing alloy for steel.  Other applications of muntz metal are as: Ship sheathing Perforated metal Valve stems Condenser tubes Architectural work etc.

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7Leaded 60 : 40 brass - is the chief material fed to automatic lathe and similar machines usually in the form of extruded bar .  Lead is added to Cu-Zn alloy to promote machinability  The lead content ranges from about 0:5 to as much as 3.5.  60:40 brass tends to improve the weldability ductility and impact strength.  used for: Keys Lock-parts Gears Clock parts Valve parts Pipe unions. 8 Nava1 brass -contains Cu 60 Zn 39.25 and Sn 0.75.  The purpose of tin is to Improve the resistance to corrosion.  Used for structural applications and for forgings especially in cases where contact with sea water  Naval brass is obtainable as hot-rolled plate particularly for marine condenser plates and in the form of extruded rod for the production of machined or hot forged components.  Other applications of naval brass are: Propeller shafts Valve stems Pump impellers etc. 9 Admiralty brass -contains 71 Cu 28 Zn and 1 Sn.  It is used for decorative and architectural applications screw machine products heat exchanger components pump impellers

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BRONZE  Bronze is basically an alloy of copper tin and elements other than nickel or zinc .  Bronze possesses superior mechanical properties and corrosion resistance than brass.  Bronze is comparatively hard and it resists surface wear.  Bronze can be shaped or rolled into wire rod and sheets. Types of bronzes i Phosphor Bronze -deoxidized with phosphorus during the refining process and hence are known as phosphor bronze.  The amount of phosphorus may range from a trace to about 0.35 or even higher in some special grades.  In amounts greater than 1.0 phosphorus causes excessive brittleness  A phosphor bronze containing approximately 4 each of tin lead and zinc has excellent free-cutting characteristics.  Standard Phosphor bronze for bearing applications contains 90 Cu 10 Sn min and 0.5 P min.  It has a tensile strength of 220-280 N/mm2  Phosphor bronze for gears contains 88 Cu 12 Sn 0.3 max Zn 0.50 max Pb and 0.15 min P.  It has a tensile strength of 220-310 N/mm2. This alloy is also utilised for general bearings where its rigidity is of advantage.

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 Leaded phosphor bronze contains 87 Cu 7.5 Sn 2.0 max Zn 3.5 Pb 0.3 min P and 1.0 max Ni.  It has a tensile strength of 250 N/mm2  This material is satisfactory for many bearing applications. Properties of phosphor bronze  a has high strength and toughness  b is resistant to corrosion  c has good load bearing capacity and  d has low coefficient of friction. Applications  a bearing applications  b making pump parts linings springs diaphragms gears clutch discs bellows etc. ii Aluminium bronzes – contains Cu -89-91 Al 6-8 Fe 1.5 -3.5 Sn 0.35 Mn 1max Properties of Aluminium bronzes : Good strength High corrosion resistance Good heat resistance Good cold working properties etc Used in-Bearings Valve seats Gears Propellers Slide valves Cams Imitation jewellery Pump parts etc. iii Silicon bronzes – contains Si 1-4 Fe 0.5-1.0 Mn 0.25-1.25 and balance Cu  Lead when added as 0.5 improves machinability. Used in: Bearings Roll mill sleepers Screwdown nuts Boiler parts Die cast parts etc. 

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GUN METAL  Gun metal is an alloy of copper tin and zinc.  Zinc cleans the metal and increases its fluidity.  A small amount of lead may be added to improve cast ability and machinability. Types Admirality gun metal contains 10 Sn 2 Zn 1.5 max Ni and balance Cu.  It has tensile strength of 260-340 N/mm2.  It is used for pumps valves and miscellaneous castings. Leaded gun metal contains 7 Sn 2.25 Zn 0.3 Pb 5.5 and balance copper. It has a tensile strength of 430-480 N/rr.m2. Nickel gun metal contains 5 Sn 5 Zn 5 Pb 2.0 max Ni. It has a tensile strength of 200-270 N/mm2. This is among the most widely used grades particularly where high pressure is required. In general gun metal is used for Bearings Steam pipe fittings Hydraulic valves and gears etc

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Cupronickel or copper-nickel  Is an alloy of copper that contains nickel and strengthening elements such as iron and manganese.  Cupronickel is highly resistant to corrosion in seawater.  It is used for piping heat exchangers and condensers in seawater systems as well as marine hardware and sometimes for the propellers crankshafts etc.  A more familiar common use is in silver-coloured modern circulation coins. A typical mix is 75 copper 25 nickel and a trace amount of manganese.  It is used in thermocouples and the 55 copper/45 nickel alloy constantan is used to make resistors thermocouples and rheostats  Monel metal is a nickel-copper alloy containing minimum 63 nickel and 31.5 percent copper with small amounts of iron manganese carbon and silicon.  Stronger than pure nickel  Monel alloys are resistant to corrosion by many agents including rapidly flowing seawater. They can be fabricated readily by hot- and cold-working machining and welding.

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BEARING MATERIALS  Bearings support moving parts such as shafts and spindles of a machine or mechanism.  Bearings may be classified as  RoIling contact i.e. Ball and roller bearings.  Plain bearings. Copper-based alloys  Bronze covers a large number of copper alloys with varying percentages of Sn Zn and Pb.  Bronze is one of the oldest known bearing materials.  Typical compositions of bearing bronze arc:  Cu-80 Sn -10 Pb -10  Cu-85 Sn -15  Bronze 10 to 14 tin remainder copper is used in the machine and engine industry for bearing bushes made from thin walled drawn tubes.  Copper-based alloys are employed for making bearings required to resist heavier pressures such as in railways.

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ALUMINIUM AND ITS ALLOYS  Aluminium is a silvery white metal and it has the following characteristics:  i It is a light metal with a density about a third that of steel or brass.  ii Aluminium is a very good conductor of electricity.  iiiAluminium has a higher resistance to corrosion than other metals but film of oxide may forms on its surface.  iv Aluminium is a good conductor of heat.  v Aluminium is very ductile.  . vi Aluminium is non-magnetic.  vii Melting point of pure aluminium is about 650 0 C  Although pure aluminium is not particularly strong it forms strength alloys with other metals such as CU Cr Ni Fe Zn Mn Si and Mg.  i Some of these aluminium alloys are more than 4 times strong as the same weight of mild steel.  ii They are malleable and ductile.  iiiThey exhibit toughness and become stronger at temperaturebelow the ordinary atmospheric range.  ivThey do not work well at temperatures of the order of 300-4OO O C.  v Aluminium and its alloys can be a Cast b Forged c Welded d Extruded e Rolled etc.

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Uses of AI and Al-alloys  i Transportation industry-structural frame-work engine parts trim and decorative features hardware doors window frames tanks furnishing and fittingstrains trucks buses automobile cars and aeroplanes use many component parts made up of aluminium alloys.  ii Overhead conductors and heat exchanger parts.  iii In food industry aluminium alloys find applications as food preparation equipmentspans etc. refrigeration storage containers bakery equipment shipping containers etc.  iv In architectural field aluminium alloys find uses such as window farmes doors hardware roofing coping sills railings fasteners lighting fixture solar shading grills etc.  v Cryogenic applications.  vi As heavy duty structures such as travelling cranes hoists conveyor supports bridges etc.  vii In process industries parts made up of aluminium and its alloys are used to handle organic chemicals petrochemicals and drugs. Tanks pipes heat exchangers gratings smoke-stacks precipitators centrifugal valves fittings etc. are produced from aluminium alloys.

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 Types of aluminium alloys Aluminium alloys  Al-Mn  Al-Mg  Al-Mg-Mn  Al-Mg-Si  Al-CU-Mg  Al-Cu-Si  Al-CU-Mg-Pb  Al-Mg-Si-Pb  Al-Zn-Mg-Cu Aluminium alloys can be classified as follows: a Wrought alloys b Cast alloys c Heat-treatable alloys d Non-heat-treatable alloys.

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Nickel Alloys  Nickel alloys are used extensively because of their corrosion resistance high temperature strength and their special magnetic and thermal expansion properties. The major alloy types that are used are:  Iron-Nickel-Chromium alloys  Stainless Steels  Copper-Nickel alloys and Nickel-Copper alloys  Nickel-Chromium and Nickel-Chromium-Iron alloys  Low Expansion Alloys  Magnetic Alloys

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Nickel Copper Alloys  These nickel copper alloys are sometimes referred to as MONEL or NICORROS and contain nickel with copper and small amounts of iron and manganese.  This nickel copper alloys contains 63 nickel minimum 28-34 copper and a maximum of 2 manganese and 2.5 iron. There are also a small number of impurities kept at limited values to ensure the metals properties are not harmed.  These nickel copper alloys are used where a higher strength is required compared to pure nickel.  Nickel copper alloys have a wider range of environments where they resist corrosion but in some specialised applications such as strong alkali contaminant nickel or commercially pure nickel would be superior.  Nickel copper alloys find wide application in oil refining and marine applications where long corrosion-free life is required.  Because of good thermal conductivity of nickel copper alloys they are frequently are used for heat exchangers where sea water is one of the fluids concerned.

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Nickel Chromium Base Alloys  These nickel chromium base alloys are used extensively in applications where heat resistance and/or corrosion resistance is required. In some members of the group where conditions are less demanding some nickel is replaced by iron to decrease the overall cost.  Metals fail at high temperatures by both oxidation scaling and through a loss in strength. Alloys in this class are designed to resist failure from both of these mechanisms. Nickel alloys are not suitable for high temperature sulphur rich environments.  Where corrosion resistance is significant molybdenum is used as an alloying addition in nickel chromium based alloys.

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Magnesium Alloys  Magnesium has a density two-thirds that of aluminum and only slightly higher than that of fiber-reinforced plastics and possesses excellent mechanical and physical properties.  In metal casting process magnesium alloys better wettability. Advantages of Magnesium  Magnesium alloy properties can provide a casting designer with several advantages over other lightweight alloys.  Weight —The lightest of all structural metals magnesium preserves the light weight of a design without sacrificing strength and rigidity.  Damping Capacity —Magnesium is unique among metals because of its ability to absorb energy.  Impact Dent Resistance —The elastic energy absorption characteristics of magnesium result in good impact and dent resistance and energy management.

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 High Stiffness-to-Weight Ratio —This characteristic is important where resistance to deflection is desired in a lightweight component.  Improved Die Life —Unlike molten aluminum molten magnesium does not react with tool steels resulting in longer die life and increased productivity.  Machining —Magnesium is recognized as the easiest of structural metals to machine and is the standard of the cutting tool industry when comparing machinability of metals.

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Alloy Families  Magnesium alloys can be used in multiple applications but they easily can be divided into two groups: sand casting alloys and diecasting alloys.  Alloys also can be classified as general purpose high- ductility and high-temperature alloys.  Most magnesium alloys are produced as high-purity versions to reduce potential corrosion problems associated with higher levels of iron nickel and copper. Sand casting alloys often are produced with a fine grain structure due to small additions of zirconium  Common applications of Mg alloys include: hand-held devices like saws tools automotive parts like steering wheels seat frames electronics like casing for laptops camcoders cell phones etc.

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Titanium alloys  Titanium alloys are metals that contain a mixture of titanium and other chemical elements.  They are light in weight have extraordinary corrosion resistance and the ability to withstand extreme temperatures.  However the high cost of both raw materials and processing limit their use to military applications aircraft spacecraft medical devices highly stressed components such as connecting rods on expensive sports cars and some premium sports equipment and consumer electronics.

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Properties The attributes of titanium alloys of prime importance to the design engineer are:  Outstanding corrosion resistance  Excellent erosion resistance  High heat transfer capability  Superior strength-to-weight ratios Titanium alloys are also used because of their:  Low thermal expansion co-efficient  Non-magnetic character  Fire resistance  Short radioactive half life Commercially pure titanium and alpha alloys of titanium are non-heat treatable and are genarally very weldable . They have:  Low to medium strength  Good notch toughness  Reasonably good ductility  Excellent mechanical properties at cryogenic temperatures

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Applications  Ti 6Al-4V may be considered in any application where a combination of high strength at low to moderate temperatures light weight and excellent corrosion resistance are required.  Some of the many applications where this alloy has been used include aircraft turbine engine components aircraft structural components aerospace fasteners high- performance automotive parts marine applications medical devices and sports equipment.

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CERAMICS  Ceramics are inorganic non metallic materials which are formed by the action of heat. The most important of these were the traditional clays made into pottery bricks tiles and the like along with cements and glass. Mechanical properties  Ceramic materials are usually ionic or covalent bonded materials and can be crystalline or amorphous.  Has less tensile strength  High hardness due to brittility  High compressive strength  Poor toughness  wear-resistant  thermal insulators  electrical insulators  nonmagnetic  oxidation resistant  prone to thermal shock and  chemically stable.

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Classification of ceramics  Ceramics can also be classified into  Oxides : Alumina zirconia .  Non-oxides: Carbides borides nitrides silicides . Carbides  It is a compound of carbon with a less electronegative element. For example Fe 3 C cementite is formed in steels to improve their properties.  Examples  Calcium carbide Silicon carbide SiC Tungsten carbide Cementite Boron carbide Tantalum carbide Titanium carbide Silicon carbide Silicon carbide SiC carbarundum  It is a compound of silicon and carbon bonded together to form ceramics.

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Properties of carbides  High strength  Low thermal expansion  High thermal conductivity  High hardness  High elastic modulus  Excellent thermal shock resistance  Superior chemical inertness

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Applications of SiC  Fixed and moving turbine components  Suction box covers  Seals bearings  Ball valve parts  Hot gas flow liners  Heat exchangers  Semiconductor process equipment  Abrasives  Disc brake  Diesel particulate filter  Cutting tools  Coarse to fine grit sandpapers

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Aluminum Oxide Al2O3 Alumina  Aluminium oxide is of aluminium with the chemical formula Al 2 O 3. Being very hard it is used as an abrasive. Having a high melting point it is used as a refractory material. Key Properties  Hard wear-resistant  Excellent dielectric properties  Resists strong acid and alkali attack at elevated temperatures  Good thermal conductivity  Excellent size and shape capability  High strength and stiffness  Aluminium oxide is an electrical insulator  But has a relatively high thermal conductivity 40 W/m K.  In its most commonly occurring crystalline form called corundum or α-aluminium oxide  As a component in cutting tools. 3

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Applications  Gas laser tubes  Wear pads  Seal rings  High temperature electrical insulators  High voltage insulators  Furnace liner tubes  Thread and wire guides  Electronic substrates  Abrasion resistant tube and elbow liners  Laboratory instrument tubes and sample holders  Instrumentation parts for thermal property test machines  Grinding media  Over 90 of which is used in the manufacture of aluminium metal.  Health and medical applications include it as a material in hip replacements  It is widely used as a coarse or fine abrasive including as a much less expensive substitute for industrial diamond.  Many types of sandpaper use aluminium oxide crystals.  Aluminium oxide is widely used in the fabrication of superconducting devices

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Partially stabilized Zirconia PSZ ZrO 2 Tensile strength higher than alumina Toughness and fracture toughness is better than other ceramics High elavated temperature strength Applications of ZrO 2  Precision ball valve balls and seats  High density ball and pebble mill grinding media  Rollers and guides for metal tube forming  Thread and wire guides  Hot metal extrusion dies  Deep well down-hole valves and seats  Powder compacting dies  Marine pump seals and shaft guides  Oxygen sensors  High temperature induction furnace susceptors  Fuel cell membranes  Electric furnace heaters over 2000°C in oxidizing atmospheres

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NITRIDES  Nitride is a compound of nitrogen with a less electronegative element.  Silicon nitride Si 3 N 4 is a hard solid substance that can be obtained by direct reaction between silicon and nitrogen .  For machining of steel it is usually coated by titanium nitride .  Cubic boron nitride is used in grinding wheel in the form of abrasive. APPLICATIONS The largest market for silicon nitride components is in reciprocating diesel and spark ignited engines for combustion components and wear parts.  glow plugs for faster start-up  Precombustion chambers  turbocharger  exhaust gas control valve for increased acceleration.  fixtures in induction heating and resistance welding exploit the electrical insulation wear resistance low thermal conductivity and thermal shock resistance of the material.  Nozzles thermocouple sheats and melting crucibles for handling molten aluminium zinc tin and lead alloys.  Arc welding nozzles for high strength electrical resistance and thermal shock resistance of the material.

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Sialon  It is a silicon nitride ceramic with a small percentage of aluminum oxide added.  It is highly thermal shock resistant strong and is not wet or corroded by aluminum brass bronze and other common industrial metals. Properties  Excellent thermal shock resistance  Not wetted or corroded by nonferrous metals  High strength  Good fracture toughness  Good high temperature strength  Low thermal expansion  Good oxidation resistance  Retain tensile strength upto 1400OC Application  Thermocouple protection tubes for nonferrous metal melting  Machining nickel based alloys  Immersion heater and burner tubes  Degassing and injector tubes in nonferrous metals  Metal feed tubes in aluminum die casting  Welding and brazing fixtures and pins

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Cermets  A cermet is a composite material composed of ceramic cer and metallic met materials.  The metal is used as a binder for an oxide boride or carbide. Generally the metallic elements used are nickel molybdenum and cobalt.  They are used in such applications for turning grooving and milling  Cermets are used instead of tungsten carbide in saws and other brazed tools due to their superior wear and corrosion properties.  Titanium nitride Titanium carbonitride titanium carbide and similar can be brazed like tungsten carbide if properly prepared however they require special handling during grinding.

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COMPOSITE MATERIALS  Composite is a mixture of two or more distinct constituent or phases  Both constituents have to be present in reasonable property say 5.  The constituent that is continuous and is often but not always present in the greater quantity in the composite is termed as matrix.  The second constituent is referred to as the reinforcing phase or reinforcement as it reinforces the mechanical properties of matrix. The reinforcement is harder stronger and stiffer than matrix in most causes. Functions of Matrix Material:  It takes the load and transfers it to the reinforcement.  It binds or holds the reinforcement and protects the same from mechanical or chemical damage that might occur by abrasion of their surface in particular with fibers.  It also separates the individual fibers and prevents brittle cracks from passing completely across the section of the composite. Functions of Reinforcing Material:  The major load on the composite is carried by the reinforcing phase.

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Advantages of composite materials  High strength to weight ratio  High stiffness  Low density  High young’s modulus tensile strength  Increase in the toughness Types of composites  Metal Matrix composites  Ceramic Matrix composites  Polymer Matrix composites Metal Matrix compositesMMC  Matrix - Aluminium Copper Nickel based alloys Iron etc  Reinforcement – Carbon Silicon CarbideSiCAluminium oxideAl 2 O 3 Tungsten carbide etc.

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Applications of Al/SiC MMC: Automotive -Reciprocating and static engine components braking systems Aerospace -Struts undercarriage guided weapons satellites Rail Engineering -Engine and braking components Military -Gun barrel overwraps missiles aerofoils and fins bodies and blast pipesmilitary diesel components. Electronic -Substrates and packaging thermal management racking power sources and storage Marine -Propellers impellers pressurized hulls marine diesel components Industrial -Reciprocating and high speed machinery precision equipment Sport/Leisure -Rackets cycles and frames motor racing golf clubs

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Ceramic Matrix compositesCMC:  In case of CMC ceramic materials are used as matrix. Some of the ceramic materials used are  Silicon carbide  Alumina  Glass ceramics  Carbon Advantages:  Co efficient of thermal expansion of ceramics is low  Thermal and electrical conductivity is less than MMC  CMC can withstand high temperature and can provide high strength than MMC Disadvantages:  CMC can withstand very high temperature only if the reinforcement is a high temperature withstanding material  After processing the thermal stress in MMC can be relieved from plastic deformation whereas it is not possible in CMC

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 Types of CMCs:  Alumina matrix composites  SiC whisker reinforced CMC-Used for cutting tools and manufacturing industries  Zirconia toughened alumina  Glass ceramic matrix composites  Carbon-carbon composites Applications of CMCs: Applications:  Aerospace -After burners brakes heat shields nozzles  Automobile - Brakes  Manufacturing- Thermal insulation cutting tools wire drawing dies  Medical - Fixation plates

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POLYMER MATRIX COMPOSITES: Types of polymers:  Thermosets  Thermo plastics-Crystalline and Non-crystalline  Rubber Advantages:  Low strength  Low strength than MMC CMC  Low fracture toughness Disadvantage:  Low working temperature  Low coefficient of thermal expansion  Dimensional instability Commercial PMCs:  Fibre reinforced epoxies  Carbon-fiber reinforced plastic or CFRP  Glass-fiber reinforced plastic or GFRP also GRP.  Aramid fibre reinforced plastic

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Applications:  Industrial -Solar collectors Electrostatic precipitation plates Fan blades Water tanks  Recreational - Television antennas Snow mobiles  Construction -Seating bath tabs roof sections bus shelters  Aerospace -Wing ribs helicopter blades landing gears cockpit hatch covers escape doors  Automobile -Crash members leaf springs car bodies  Electrical -Panels housings switch gear  Chemical -Pipes tanks pressure vessels hoppers valves pumps

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