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Msc terms.txtMaterial science is the field of engineering which deals or investigates the relationship between the structure ofmaterials at atomic or molecular scales and their macroscopic properties.

Metallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements,their intermetallic compounds, and their mixtures, which are called alloys. It is also the technology of metals: theway in which science is applied to their practical use

Material selection is a step in the process of designing any physical object. In the context of product design, themain goal of material selection is to minimize cost while meeting product performance goals.

deformation is a change in the shape or size of an object due to an applied force (the deformation energy in thiscase is transferred through work) or a change in temperature (the deformation energy in this case is transferredthrough heat). The first case can be a result of tensile (pulling) forces, compressive (pushing) forces, shear,bending or torsion (twisting). In the second case, the most significant factor, which is determined by thetemperature, is the mobility of the structural defects such as grain boundaries, point vacancies, line and screwdislocations, stacking faults and twins in both crystalline and non-crystalline solids.elastic deformationplastic deformationfatigue is the progressive and localized structural damage that occurs when a material is subjected to cyclicloading.

slip is the process by which a dislocation motion produces plastic deformation. An external force makes parts ofthe crystal lattice glide along each other, changing the material's geometry. Depending on the type of lattice,different slip systems are present in the material.

The positions of atoms or molecules occur on repeating fixed distances, determined by the unit cell parameters.However, the arrangement of atoms or molecules in most crystalline materials is not perfect. The regular patternsare interrupted by crystallographic defects.point defect-vacancy, interstitial defectline defect-edge defect

A physical property is any property that is measurable whose value describes a state of a physical system. The

changes in the physical properties of a system can be used to describe its transformations or evolutions betweenits momentary states.

Electrical properties

Dielectric constantDielectric strengthElectrical con ductivityPermeabilityPermittivityPiezoelectric constantsSeebeck coefficient

chemical proerties:

Hygroscopy is the ability of a substance to attract and hold water molecules from the surrounding environment.This is achieved through either absorption or adsorption

Metallic bonding constitutes the electrostatic attractive forces between the delocalized electrons, called conductionelectrons, gathered in an electron cloud, and the positively charged metal ions.

Examples of bcc include iron, chromium, tungsten, and niobium. Examples of fcc include aluminium, copper, goldand silver.

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Crystallites are small, often microscopic crystals that, held together through highly defective boundaries, constitutea polycrystalline solid. Metallurgists often refer to crystallites as grains.

Grain boundaries are interfaces where crystals of different orientations meet. A grain boundary is a single-phase

interface, with crystals on each side of the boundary being identical except in orientation. The term "crystalliteboundary" is sometimes, though rarely, used.

Grain boundary areas contain those atoms that have been perturbed from their original lattice sites, dislocations,and impurities that have migrated to the lower energy grain boundary

The addition of impurity atoms to a metal will result in the formation of a solidsolution.

A solid solution forms when, as the solute atoms are added to the host material,the crystal structure is maintained and no new structures are formed. Perhaps it isuseful to draw an analogy with a liquid solution. If two liquids, soluble in each other(such as water and alcohol) are combined, a liquid solution is produced as the molecules intermix, and itscomposition is homogeneous throughout. A solid solutionis also compositionally homogeneous; the impurity atoms are randomly and uniformly dispersed within the solid.

Impurity point defects are found in solid solutions, of which there are two types:substitutional and interstitial. For the substitutional type, solute or impurity atomsreplace or substitute for the host atoms

An example of a substitutional solid solution is found for copper and nickel.These two elements are completely soluble in one another at all proportions. Withregard to the aforementioned rules that govern degree of solubility, the atomic radiifor copper and nickel are 0.128 and 0.125 nm, respectively; both have the FCC crystal structure; and theirelectronegativities are 1.9 and 1.8 (Figure 2.7); finally, the

most common valences are 1 for copper (although it sometimes can be 2) and2 for nickel.

For interstitial solid solutions, impurity atoms fill the voids or interstices amongthe host atoms (see Figure 4.2). For metallic materials that have relatively highatomic packing factors, these interstitial positions are relatively small. Consequently,the atomic diameter of an interstitial impurity must be substantially smaller thanthat of the host atoms. Normally, the maximum allowable concentration of interstitial impurity atoms is low (lessthan 10%). Even very small impurity atoms areordinarily larger than the interstitial sites, and as a consequence they introduce somelattice strains on the adjacent host atoms. Problem 4.5 calls for determination ofthe radii of impurity atoms (in terms of R, the host atom radius) that will just fitinto interstitial positions without introducing any lattice strains for both FCC andBCC crystal structures.

Carbon forms an interstitial solid solution when added to iron; the maximum

concentration of carbon is about 2%. The atomic radius of the carbon atom is muchless than that for iron: 0.071 nm versus 0.124 nm. Solid solutions are also possiblefor ceramic materials.

dislocation is a crystallographic defect, or irregularity, within a crystal structure

A dislocation is a linear or one-dimensional defect around which some of the atomsare misaligned

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Msc terms.txtInterfacial defects are boundaries that have two dimensions and normally separateregions of the materials that have different crystal structures and/or crystallographicorientations. These imperfections include external surfaces, grain boundaries, phaseboundaries, twin boundaries, and stacking faults

Another interfacial defect, the grain boundary, was introduced in Section 3.14 as the

boundary separating two small grains or crystals having different crystallographicorientations in polycrystalline materials.

Hardness is a measure of a materials resistance to localized plastic deformation.

The two most common hardness testing techniques are Rockwell and Brinell.Several scales are available for Rockwell; for Brinell there is a single scale.Brinell hardness is determined from indentation size; Rockwell is based onthe difference in indentation depth from the imposition of minor and majorloads.

theability of a metal to plastically deform depends on the ability of dislocations to move.

Virtually all strengthening techniquesrely on this simple principle:Restricting or hindering dislocation motion renders amaterial harder and stronger.

STRENGTHENING BY GRAIN SIZE REDUCTION:Because the two grains are of different orientations, a dislocation passing intograin B will have to change its direction of motion; this becomes more difficult as the crystallographicmisorientation increases.

Another technique to strengthen and harden metals is alloying with impurity atomsthat go into either substitutional or interstitial solid solution. Accordingly, this is

called solid-solution strengthening.High-purity metals are almost always softer andweaker than alloys composed of the same base metal. Increasing the concentrationof the impurity results in an attendant increase in tensile and yield strengths

cold working - Strain hardeningis the phenomenon whereby a ductile metal becomes harder andstronger as it is plastically deformed. Sometimes it is also called work hardening,or, because the temperature at which deformation takes place is cold relative tothe absolute melting temperature of the metal,cold working.Most metals strainharden at room temperature.Work hardening, also known as strain hardening or cold working, is the strengthening of a metal by plasticdeformation. This strengthening occurs because of dislocation movements and dislocation generation within thecrystal structure of the material.The working of metals below their recrystallisation temperature is known as cold working.

Most of the cold working processes are performed at room temperature. The cold working distortsthe grain structure and does not provide an appreciable reduction in size. It requires much higherpressures than hot working. The extent to which a metal can be cold worked depends upon its ductility. The higherthe ductility of the metal, the more it can be cold worked. During cold working, severestresses known as residual stresses are set up. Since the presence of these stresses is undesirable,therefore, a suitable heat treatment may be employed to neutralise the effect of these stresses. Thecold working is usually used as finishing operation, following the shaping of the metal by hot working. It alsoincreases tensile strength, yield strength and hardness of steel but lowers its ductility. Theincrease in hardness due to cold working is called work-hardening.

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Msc terms.txtIn general, cold working produces the following effects :1. The stresses are set up in the metal which remain in the metal, unless they are removed bysubsequent heat treatment.2. A distortion of the grain structure is created.3. The strength and hardness of the metal are increased with a corresponding loss in ductility.4. The recrystalline temperature for steel is increased.

5. The surface finish is improved.6. The close dimensional tolerance can be maintained.

Hot working refers to processes where metals are plastically deformed above their recrystallization temperature.Being above the recrystallization temperature allows the material to recrystallize during deformation. This isimportant because recrystallization keeps the materials from strain hardening, which ultimately keeps the yieldstrength and hardness low and ductility high.[1] This contrasts with cold working.The advantages are:[1]

The working of metals above the *recrystallisation temperature is called hot working.Thistemperature should not be too high to reach the solidus temperature, otherwise the metal will burnand become unsuitable for use. The hot working of metals has the following advantages anddisadvantages :Advantages1. The porosity of the metal is largely eliminated.2. The grain structure of the metal is refined.3. The impurities like slag are squeezed into fibres and distributed throughout the metal.4. The mechanical properties such as toughness, ductility, percentage elongation, percentagereduction in area, and resistance to shock and vibration are improved due to the refinementof grains.Disadvantages1. It requires expensive tools.2. It produces poor surface finish, due to the rapid oxidation and scale formation on themetal surface.3. Due to the poor surface finish, close tolerance cannot be maintained

These properties and structures may revert back to the precold-worked states

by appropriate heat treatment (sometimes termed an annealing treatment). Suchrestoration results from two different processes that occur at elevated temperatures:recoveryand recrystallization,which may be followed by grain growth.

Recrystallization is a process by which deformed grains are replaced by a new set of undeformed grains thatnucleate and grow until the original grains have been entirely consumed. Recrystallization is usually accompaniedby a reduction in the strength and hardness of a material and a simultaneous increase in the ductility. Thus, theprocess may be introduced as a deliberate step in metals processing or may be an undesirable byproduct ofanother processing step. The most important industrial uses are the softening of metals previously hardened bycold work, which have lost their ductility, and the control of the grain structure in the final product.

recovery (where high angle grain boundaries do not migrate) and grain growth (where the driving force is only dueto the reduction in boundary area)

Recovery is a process by which deformed grains can reduce their stored energy by the removal or rearrangementof defects in their crystal structure. These defects, primarily dislocations, are introduced by plastic deformation ofthe material and act to increase the yield strength of a material. Since recovery reduces the dislocation density theprocess is normally accompanied by a reduction in a materials strength and a simultaneous increase in theductility. As a result recovery may be considered beneficial or detrimental depending on the circumstances

Grain growth is the increase in size of grains (crystallites) in a material at high temperature. This occurs whenrecovery and recrystallisation are complete and further reduction in the internal energy can only be achieved byreducing the total area of grain boundary. The term is commonly used in metallurgy but is also used in reference to

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Msc terms.txtceramics and minerals

hot rolling

Extrusion is a process used to create objects of a fixed, cross-sectional profile. A material is pushed or drawnthrough a die of the desired cross-section. The two main advantages of this process over other manufacturing

processes are its ability to create very complex cross-sections and work materials that are brittle, because thematerial only encounters compressive and shear stresses. It also forms finished parts with an excellent surfacefinish

Forging is a manufacturing process involving the shaping of metal using localized compressive forces.

Drawing is a metalworking process which uses tensile forces to stretch metal. It is broken up into two types: sheetmetal drawing and wire, bar, and tube drawing. The specific definition for sheet metal drawing is that it involvesplastic deformation over a curved axis. For wire, bar, and tube drawing the starting stock is drawn through a die toreduce its diameter and increase its length.

Rotary piercing is a hot working metalworking process for forming thick-walled seamless tubing. There are twotypes: the Mannesmann process and Stiefel process.

Corrosion is the gradual destruction of materials, usually metals, by chemical reaction with its environment. In themost common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such asoxygen. Rusting, the formation of iron oxides, is a well-known example of electrochemical corrosion. This type ofdamage typically produces oxide(s) or salt(s) of the original metal. Corrosion can also occur in materials other thanmetals, such as ceramics or polymers, although in this context, the term degradation is more common. Corrosiondegrades the useful properties of materials and structures including strength, appearance and permeability toliquids and gases.

Protection from corrosion [edit]

US Army shrink wraps equipment such as helicopters to protect it from corrosion and thus save millions of dollars.

Surface treatments [edit]Applied coatings [edit]Main article: Galvanization

Galvanized surfacePlating, painting, and the application of enamel are the most common anti-corrosion treatments. They work byproviding a barrier of corrosion-resistant material between the damaging environment and the structural material.Aside from cosmetic and manufacturing issues, there are tradeoffs in mechanical flexibility versus resistance toabrasion and high temperature. Platings usually fail only in small sections, and if the plating is more noble than thesubstrate (for example, chromium on steel), a galvanic couple will cause any exposed area to corrode much morerapidly than an unplated surface would. For this reason, it is often wise to plate with active metal such as zinc orcadmium. Painting either by roller or brush is more desirable for tight spaces; spray would be better for largercoating areas such as steel decks and waterfront applications. Flexible polyurethane coatings, like Durabak-M26

for example, can provide an anti-corrosive seal with a highly durable slip resistant membrane. Painted coatingsare relatively easy to apply and have fast drying times although temperature and humidity may cause dry times tovary.

Reactive coatings [edit]If the environment is controlled (especially in recirculating systems), corrosion inhibitors can often be added to it.These form an electrically insulating or chemically impermeable coating on exposed metal surfaces, to suppresselectrochemical reactions. Such methods obviously make the system less sensitive to scratches or defects in thecoating, since extra inhibitors can be made available wherever metal becomes exposed. Chemicals that inhibit

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Msc terms.txtcorrosion include some of the salts in hard water (Roman water systems are famous for their mineral deposits),chromates, phosphates, polyaniline, other conducting polymers and a wide range of specially-designed chemicalsthat resemble surfactants (i.e. long-chain organic molecules with ionic end groups).

Anodization [edit]Main article: Anodizing

This climbing descender is anodized with a yellow finish.Aluminium alloys often undergo a surface treatment. Electrochemical conditions in the bath are carefully adjustedso that uniform pores several nanometers wide appear in the metal's oxide film. These pores allow the oxide togrow much thicker than passivating conditions would allow. At the end of the treatment, the pores are allowed toseal, forming a harder-than-usual surface layer. If this coating is scratched, normal passivation processes takeover to protect the damaged area.

Anodizing is very resilient to weathering and corrosion, so it is commonly used for building facades and otherareas that the surface will come into regular contact with the elements. Whilst being resilient, it must be cleanedfrequently. If left without cleaning, panel edge staining will naturally occur.

Biofilm coatings [edit]A new form of protection has been developed by applying certain species of bacterial films to the surface of metalsin highly corrosive environments. This process increases the corrosion resistance substantially. Alternatively,antimicrobial-producing biofilms can be used to inhibit mild steel corrosion from sulfate-reducing bacteria.[6]

Controlled permeability formwork [edit]Main article: Controlled permeability formworkControlled permeability formwork (CPF) is a method of preventing the corrosion of reinforcement by naturallyenhancing the durability of the cover during concrete placement. CPF has been used in environments to combatthe effects of carbonation, chlorides, frost and abrasion.

Cathodic protection [edit]Main article: Cathodic protectionCathodic protection (CP) is a technique to control the corrosion of a metal surface by making that surface the

cathode of an electrochemical cell. Cathodic protection systems are most commonly used to protect steel, water,and fuel pipelines and tanks; steel pier piles, ships, and offshore oil platforms.

Sacrificial anode protection [edit]

Sacrificial anode in the hull of a ship.For effective CP, the potential of the steel surface is polarized (pushed) more negative until the metal surface hasa uniform potential. With a uniform potential, the driving force for the corrosion reaction is halted. For galvanic CPsystems, the anode material corrodes under the influence of the steel, and eventually it must be replaced. Thepolarization is caused by the current flow from the anode to the cathode, driven by the difference inelectrochemical potential between the anode and the cathode.

Impressed current cathodic protection [edit]

For larger structures, galvanic anodes cannot economically deliver enough current to provide complete protection.Impressed current cathodic protection (ICCP) systems use anodes connected to a DC power source (such as acathodic protection rectifier). Anodes for ICCP systems are tubular and solid rod shapes of various specializedmaterials. These include high silicon cast iron, graphite, mixed metal oxide or platinum coated titanium or niobiumcoated rod and wires.

Anodic protection [edit]Main article: Anodic protectionAnodic protection impresses anodic current on the structure to be protected (opposite to the cathodic protection).

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Msc terms.txtIt is appropriate for metals that exhibit passivity (e.g., stainless steel) and suitably small passive current over awide range of potentials. It is used in aggressive environments, e.g., solutions of sulfuric acid.Anodizing (also spelled "anodising", particularly in the UK) is an electrolytic passivation process used to increasethe thickness of the natural oxide layer on the surface of metal parts.

The process is called "anodizing" because the part to be treated forms the anode electrode of an electrical circuit.

Anodizing increases corrosion resistance and wear resistance, and provides better adhesion for paint primers andglues than does bare metal.

types of corrosion:

Pitting is another form of very localized corrosion attack in which small pits or holesform. They ordinarily penetrate from the top of a horizontal surface downward ina nearly vertical direction

ATMOSPHERIC: Atmospheric corrosion and its severity is essentially determined by four variables:1. air pollution (both man made and natural such as volcanic gases)2. airborne salt spray or droplets3. temperature4. and moisture.GALVANIC: When dissimilar metals are connected in the presence of an electrolyte a galvanic corrosion reactionoccurs. Both the presence of an electrolyte solution and a bi-metallic coupling is required for this type of corrosionto occur.CREVICE CORROSION: Crevice corrosion occurs in sheltered, localized areas such as crevices, joints, boltedand threaded parts and under existing corrosion deposits. It is the result of concentration of salts, acids andmoisture which results in the formation of an occluded corrosion cell in such sheltered areas. A small anode iscreated in the crevice with the remainder of the body acting as a large cathode so corrosion at the crevice is highlyaccelerated as well as concentrated.

Ferrous Metalsferrous metals are those which have iron as their main constituent. The ferrous metals commonly used inengineering practice are cast iron, wrought

iron, steels and alloy steels. The principal raw material for all ferrous metals is pig iron which isobtained by smelting iron ore with coke and limestone, in the blast furnace. The principal iron oreswith their metallic contents are shown in the following table :Table 2.2. Principal iron ores.Iron ore Chemical formula Colour Iron content (%)

Magnetite Fe2O3 Black 72Haematite Fe3O4 Red 70Limonite FeCO3 Brown 6065Siderite Fe2O3(H2O) Brown 48

The cast iron is obtained by re-melting pig ironwith coke and limestone in a furnace known as cupola.It is primarily an alloy of iron and carbon. The carbon

contents in cast iron varies from 1.7 per cent to 4.5 percent. It also contains small amounts of silicon,manganese, phosphorous and sulphur. The carbon in acast iron is present in either of the following two forms:1. Free carbon or graphite, and 2. Combined carbon or cementite.Since the cast iron is a brittle material, therefore,it cannot be used in those parts of machines which aresubjected to shocks. The properties of cast iron whichmake it a valuable material for engineering purposes

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Msc terms.txtshape.The wrought iron is a tough, malleable and ductile material. It cannot stand sudden and excessiveshocks. Its ultimate tensile strength is 250 MPa to 500 MPa and the ultimate compressive strength is300 MPa.It can be easily forged or welded. It is used for chains, crane hooks, railway couplings, waterand steam pipes.

Many items, before they came to be made of mild steel, were produced from wrought iron, including rivets, nails,wire, chains, rails, railway couplings, water and steam pipes, nuts, bolts, horseshoes, handrails, straps for timberroof trusses, and ornamental ironwork

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