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Materials Science and Engineering

by: Tyree Funk

Materials Science and Engineering EGR 250

Marketplace > Grand Valley State University > Engineering and Tech > EGR 250 > Materials Science and Engineering
Tyree Funk
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This 42 page Class Notes was uploaded by Tyree Funk on Saturday September 26, 2015. The Class Notes belongs to EGR 250 at Grand Valley State University taught by Staff in Fall. Since its upload, it has received 4 views. For similar materials see /class/214379/egr-250-grand-valley-state-university in Engineering and Tech at Grand Valley State University.

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Date Created: 09/26/15
Engineer On 3 Disk Overview This note set is part of a larger collection of materials available at httpclaymoreengie neergvsuedu You are welcome to use the material under the license provided at httpclaye moreengineergvsuedueodglobalcopyrghthtml As always any feedback you can provide will be welcomed Copyright 199372001 Hugh Jack email jackhgvsuedu phone 616 77176755 fax 616 33677215 Copyright 19932001 Hugh Jack page 2 1 TABLE OF CONTENTS TABLE OF CONTENTS 2 MATERIAL PROPERTIES 4 TERMINOLOGY 7777777777777777777777777777777777777777777 A A 4 MICROSTRUCTURES 777777777777777777777777777777777777777 A A 4 IRONS AND STEELS 7777777777777777777777777777777777777777 A 78 NONFERROUS METALS AND ALLOYS 7777777777777777777777777 A A 15 HEAT TREATING 77777777777777777777777777777777777777777 A A 16 PAUL JOHNSON NOTES FOR EGR 250 7777777777777777777777777 A A 16 PRACTICE PROBLEMS 7777777777777777777777777777777777777 A A 43 page 3 Materials Information page 4 2 MATERIAL PROPERTIES 39 Ideally materials are a microscopic matrix of small balls that form a larger solid In reality the atoms that make of solids fall into local pockets of well organized matrices It is very rare to find a solid that is made up of a single structure 39 If solids were made of single well organized molecules they would be significantly stronger But small deformations and cracks weaken materials to the values we are more accustomed to 39 Material properties are a function of multiple factors Primarily chemistry determines what atoms are available to make up the structure Also the atoms are dispersed in a nonihomogei nous mix 39 Solids typically fail because cracks form and then quickly propagate through solids It is the chemistry and nonihomogenous structure that can slow or stop these cracks The composition of the solid also determines how stiff it is 21 TERMINOLOGY 39 A basic list of terms commonly used are Brittleness 7 the tendency of a material to break before it undergoes plastic deformation Ductility 7 the ability of certain materials to be plastically deformed without fracture pulli in Elasticity 7 The ability to deform and return to the undeformed shape This follows Hooke39s law Hardness 7 the resistance to deformation and forced penetration Malleability 7 the ability of a material to take a new shape when hammered or rolled Tensile Strength 7 the maximum tensile load that can be applied before a material fractures Toughness 7 The ability to withstand cracking as opposed to brittleness Yield Strength 7 The load at which the material stops elastically deforming and starts peri manently deforming 22 MICROSTRUCTURES 39 To consider materials properly we must start with the basic atomic structure and then look at the more macroscopic aspects and how they are related to the microscopic components page 5 221 Atomic Structures 39 In an atom there are some fundamental ratios 39 Each atom is understood to have a basic structure with a nucleus and orbiting electrons 39 The nucleus is a combination of neutrons and protons 39 The number of protons and neutrons in an atom are equivalent and these determine the atomic number If there are additional neutrons in the nucleus this is called an iso7 tope 39 The mass of the atom is determined by the sum of the neutrons and protons the electron mass is much smaller 39 In a mole of material there are 60231023 atoms 39 How these components fit together is described in models Bohr model 7 electrons have quantized energy levels 7 electrons are discrete and orbit the nucleus 7 a free electron has a negative energy level Wave7mechanic model 7 electron waves can behave like particles or waves 7 an electron is described as an electron cloud 7 electrons have energy levels including ground levels 7 valence electrons are the outermost and most likely to be removed first 39 The valences of electrons are determined with the 39spdf39 numbers 39 The basic atomic elements are listed in the periodic table This is in sequence of the atomic masses as well as proton counts It can also be used to determine similarities in properties by proximity in the table page 6 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 Rare Earth Sen 5 La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 13891 14012 14091 14424 145 15035 15196 15725 15892 16250 16492 16726 16893 17304 17497 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 Actinide Series Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lw 227 23204 231 23803 237 242 243 247 247 249 254 253 256 254 257 39 In the periodic table the metals are in the left hand side They have 1 to 3 valence electrons They tend to give up electrons when bonding 39 In the upper right hand of the periodic table are the nonimetals They typically are l to 3 valence electrons short of a full valence level As a result they tend to consume electrons when bondi ing These are He N O F Ne P S Cl Ar Br Kr l Xe At Rn 39 There is a band of semimetals 7 including semiconductors These often consume and give up electrons when bonding These are E O Si Ge As Se Te 221 Crystal Structures 39 Understanding crystal structures can help understanding of crystalline materials such as metals 39 Think of dropping balls into a box it can fall randomly but often it will fall into patterns This is like atoms in a solid 39 If all of the balls fall into a single organized pattern then we can say there is a single crystal page 7 39 Three of the basic structure types to consider are bcc 7 body centered cubic fcc 7 face centered cubic hcp 7 hexagonal close packed bcc fcc hcp 39 In a common solid there will be many regions in the crystal but there will also be boundaries where the crystal properties change These are known as boundaries 39 A common effect that can occur is slippage along one of the planes of the crystal An example is pictured below A shear force results in slippage along the slip plane 39 Different crystal structures will result in different possible slip planes bcc has 48 possible slip planes fcc has 12 possible hcp has 3 possible 39 Other slip structures are also possible page 8 23 IRONS AND STEELS 39 Irons and steels are the most popular metals in use today The production of iron was at one time a subject of mystic awe 39 Any engineer involved with modern engineering should have at least a passing knowledge of steels to understand many of the processes 231 Types of Steel 39 Various steel alloys are commonly identified with the SAEiAlSl numbers page 9 Steel Alloy Type Number Description Carbon 10XX plain 0057090 carbon steels llxx free cutting carbon steels Manganese 13XX 175 Mn Nickel Steels 23xx 350 Ni 25xx 500 Ni Nickelichromium 31xx 125 Ni and 065 Cr 33xx 350 Ni and 157 Cr 303xx Corrosion and heat resisting Molybdenum 40xx 025 Mo carbonimolybdenum 41xx 095 Cr chromiumimolybdenum Nickelichromiumimoldb 43xx 182 Ni 050 Cr 025 Mo 47xx 105 Ni 045 Cr 020 Mo 86xx 055 Ni 050 Cr 020 Mo 87xx 055 Ni 050 Cr 025 Mo 93xx 325 Ni 120 Cr 012 Mo 98xx 100 Ni 080 Cr 025 Mo Nickelimolybdenum 46xx 157 Ni 020 Mo 48xx 350 Ni 025 Mo Chromium 50xx 0277050 Cr low chromium 51xx 0807105 Cr low chromium 51xxx 102 Cr medium chromium 52xxx 145 Cr high chromium 514xx corrosion and heat resisting Chromiumivanadium 61xx 095 Cr 015 V Siliconimanganese 92xx 0657087 Mn 0857200 Si Boron XXBXX Leaded XXLXX 39 Typical applications for plain steels based on the SAEiAlSl numbers are Number Properties page 10 Applications LOW 1006712 soft and plastic Carbon 1015 722 soft and tough 1023732 medium 103540 Medium b0 1052755 1060770 shock resistant Hig 1074780 tough and hard carbon 1084795 2311 Alloying Elements Sheets stripping tubes welding rivets screws wire structural shapes pipes gears shafts bars structural shapes large section parts forged parts shafts axles rods gears heat treated parts shafts axles gears spring wire heavy duty machine parts gears forgings dies rails set screws shear blades hammers wrenches chisels cable wire cutting tools dies milling cutters drills taps etc 39 A Short list of elements is given below page 1 l Element Effect Boron hardenability slight improvement of machinability and formability Calcium deoxidant toughens slight improvement of machinability and forming Carbon hardenability strength hardness wear resistance lower ductility weld7 Cerium ability toughness Chromium controls inclusions toughens deoxidant Cobalt toughens hardenability wear and corrosion resist high temp strength aid Copper carburization Lead high temperature strength and hardness Magnesium strengthens resist air corrosion reduces high temp workability and sur7 Manganese face quality Molybdenum embrittles machinability Nickel like cerium Niobium hardenability strength abrasion resist machinability deoxidant lower Phosphorous weldability Selenium hardenability wear resist toughness high temp strength creep resist Silicon hardness Sulfur strengthens toughness corrosion resist hardenability Tantalum fine grains strengthens toughness lower transition temp lower harden7 Tellurium ability Titanium strengthens hardenability corrosion resist machinability lower ductility 39 Typical elements that are left over from the manufacturing processes leave behind detrimental elements 7 antimony 7 arsenic 7 hydrogen 7 nitrogen 7 oxygen 7 tin 232 Making Steels 39 The basic process is 1 Iron ore is mined and crushed At this point in contains iron carbon oxygen and a variety of other minerals Z The ore is heated in a blast furnace with coke This removes some of the elements nota7 bly oxygen Pig iron remains and has high levels of carbon 3 A refining furnace is then used to burn off the excess carbon leaving a good quality page 12 steel 2321 The Ores 39 The ores come in a number of forms 7 taconite 7 7hermatite 7 iron oxide mineral 7 limonite 7 iron oxide and water 39 The ores are crushed to ease handling and speed melting 39 After crushing iron rich ore can be separated using magnets 39 the resulting ore is formed into pellets of about 65 iron 2322 Coke 39 The classic recipe for Coke begins with bituminous coal It is then heated to 2100 F and then cooled with water 39 Coke will 7 generate higher level of heat during steel making 7 generate carbon monoxide which reacts with oxygen in iron oxide and leaves iron 2323 Flux Slag 39 Some materials are used as a ux and to create slag 7 limestone 7 dolomite 39 By adding a ux material it will react with impurities causing them to ow 39 After the ux dissolves the impurities it reacts with them to form a solid called slag This oats to the top of the melt where it is removed 233 The Blast Furnace How To Make Pig Iron page 13 39 These furnaces are large heated vessels and they are lined with bricks of refractory materials 39 lron pellets limestone and coke are mixed together and dumped into the top of the furnace 39 Air is preheated to 2000 F and this is used to blast39 the mixture into the furnace The coke ignites and elevates the temperature of the mixture to 3000 F This results in a reduction of the iron oxides and separation of the slags 39 After some period of time a few hours the furnace is tapped and the iron is drawn off to large ladles This pig39 iron typically has a impurity contents of 4 C 15 Si 1 Mn 004 S 04 P 234 How To Make Steel 39 Making steel is a process of reducing the following impurities in pig iron 7 manganese 7 silicon 7 carbon 7 phosphorous 7 sulphur 7 etc 39 This operation is commonly done in one of three furnaces 7 open hearth 7 flames are directly applied to the metal and can be seen from the open hearth 7 electric 7 basic oxygen 7 a blast of pure oxygen reacts with impurities 39 The basic procedures with all of these furnaces is 1 Charge pour in scrap iron 2 Pour in molten pig iron 3 Add lime 4 Run the furnace 5 Tap the furnace to remove the steel 7 care must be used not to pour the slag on the sur7 face 6 Pour off the slag off 39 Any oxygen left in the steel when solidified will combined with carbon The result is small voids that are actually pockets of carbon monoxide gas A killed steel will have all oxygen removed page 14 2341 Electric Furnaces 39 There are two basic types 7 induction 7 arcing 39 In induction furnaces large coils are wound around the crucible AC current is applied and this induces heat in the metal inside Vacuum can be applied to the melt to increase purities of the final steel 39 Arcing furnaces use carbon electrodes at high potentials to create arcs These act to heat the metal 39 The furnaces reach temperatures up to 3500 F 235 Forming The Steel 39 There are options after the steel has been processed 7 ingots 7 the steel is poured into ingots and stored to be formed later 7 continuous casting 7 the steel is poured and immediately formed to bars rolls etc 39 Continuous casting uses a slow pour that when running smoothly 1 Is liquid at the top where it is being poured 2 It solidifies still at forming temperatures and typically moving at 5 fpm A pulling action keeps a continuous rate 3 It is rolled bent formed and cut 39 The result of continuous casting is a single process that produces final steel sections without any of the intermediate problems that result from remelting ingots 236 Stainless Steel 39 These steels use a high Chromium content10 to 12 to form a protective layer of chromium oxide over the surface of the work that is resistant to many forms of corrosion 39 General families of stainless steels include Austenitic ZXX 3XX 7 Ferritic 4XX 7 Martensitic 4XX and 5XX 7 Precipitation Hardened PH 7 page 15 Duplex 7 24 NONFERROUS METALS AND ALLOYS 241 Aluminum 242 Titanium 39 silver colored 39 close packed hexagonal structure alpha phase 39 above 885 C the material undergoes beta phase transition to body centered cubic arrangements 39 four commercial grades ASTM 174 Properties Chemistry Grade UTS YS ksi Elong N 00 C H 00 Fe 02 00 l 35 25 24 003 010 0015 020 018 2 50 40 20 003 010 0015 030 025 3 65 55 18 005 010 0015 030 035 39 melts at 1800 C 39 resistance to corrosion 39 twice steels strength to density 39 high affinity for carbon page 16 39 soft and ductile when annealed 25 HEAT TREATING 26 PAUL lOHNSON NOTES FOR EGR 250 39 These notes in this section were copied from Paul Johnson39s web site and placed here 261 Atomic Bonding and Structure 2611 Atomic Structure AFundamental Concepts lAtomic number 7 of protons in nucleus ZAtomic mass 7 sum of protons and neutrons 3Atomic weight 7 weighted average of atomic masses of natural isotopes 4Atomic mass unit amu 7 1 12th the mass of 12C 5Mole 7 Avogadro39s Number 6023 x 1023 units atoms or molecules of a substance BAtomic Models 1Bohr model aQuantized energy levels for electrons in atom bDiscrete particle like electrons in an orbital cEnergy levels are negative with respect to zero energy for a free electron ZWave7Mechanical model aWave is neither wave nor particle but can act like either in certain situations bElectron described as an electron 39cloud39 cEnergy levels divided into subshells with discrete states for each pair of electrons given by quantum numbers lPrincipal quantum number n 1 Z 3 4 5 6 7 Zan quantum number subshell l s p d f 33rd quantum number energy states in subshell mi 1s 3p 5 7f 44th quantum number spin moment ms 12 712 dGround state 7 all electrons in atom filling lowest energy level states eValence electrons 7 electrons in highest energy shell in ground state page 17 2612 Periodic Table AMetallic elements 11 to 3 valence electrons 2Electropositive 7 tend to give up electrons in bonding BNon7metals 11 to 3 electrons short of full valence level 2Electronegative 7 tend to add electrons in bonding Clntermediate elements 1Metallic and non7metallic characteristics 2lncludes semiconductors 3May gain or lose electrons in bonding lllAtomic Bonding ABonding Reactions lBonding forces aAttractive force due to bond bRepulsive force due to electron clouds cEquilibrium when net force is zero 2Bonding Energy 7 Equilibrium when energy is minimum BPrimary Strong Bonding llonic aTransfer of electrons from electropositive to electronegative atoms bCoulombic attraction between ions 2Covalent aSharing of electrons between 2 or a few atoms bNumber of bonds are those needed to fill valence level cBonds between atoms with similar electronegativities 3Metallic aSharing of electrons among many atoms bValence electrons 39free39 to move cWeak Secondary Bonding 4lnduced Dipole aTemporary short term shifts in charge creating dipoles bCoulombic attraction between dipoles 5Polar Molecules aPermanent dipoles bLarge differences in attraction for electrons cCoulombic attraction between dipoles 6Hydrogen Bonding aSpecial case of polar molecule bonding bDipoles formed between Hydrogen and highly electronegative atoms eg H20 262 Ideal Crystal Structure page 18 lCrystal Structure Fundamentals ACrystal structure 7 atoms arranged in regular repeating pattern over large distances compared to atomic size BSolid sphere model of atoms CLattice 7 37dimensional array of points arranged in a regular repeating periodic structure DUnit cell 7 the smallest portion of a lattice which represents the symmetry and structure of the entire lattice EEquivalent sites 7 points in a lattice which are indistinguishable from other points in the lattice 7 in a real crystal each equivalent site is associated with an identical atom or group of atoms FLattice geometry lCrystallographic axes 7 X y z ZCrystallographic angles 7 a b g 3Unit cell dimensions ain X direction bin y direction c in z direction llCrystal Systems and Structures ACubic Crystal System labcabg90 ZSimple Cubic SC al equivalent site per unit cell bno crystals with only 1 atom per equivalent site 3Face7Centered Cubic FCC lattice a4 equivalent sites per unit cell bcommon metals with 1 atom per equivalent site include 7 Al Cu Ni 4Body7Centered Cubic BCC lattice aZ equivalent sites per unit cell bcommon metals with 1 atom per equivalent site include 7 Fe Cr W BHexagonal Crystal System lab1cab90 g 120 21 equivalent site per unit cell 3Face7Centered Hexagonal FCC aZ atoms per equivalent site with close packed arrangement bcommon metals with HCP structure include 7 Zn Mg Ti CTetragonal Crystal System ab1cabg90 D Orthorhombic Crystal System a1b1cabg90 ERhombohedral Crystal System abcabg190 FMonoclinic Crystal System a1b1cag90 1b GTriclinic Crystal System a1b1ca1b1g190 lllCrystal Geometry page 19 APoints in a crystal lSet origin for crystal system ZPoints identified by translation from the origin BDirection vectors lMove origin to tail of vector or draw parallel vector from origin ZDetermine translation to tip point 3May also use tip minus tail to find translation 4Convert indices obtained to lowest integer form 5Place indices into brackets in form uvw 6Negative indices indicated by a bar over the number CPlane indices lFind intercepts of plane with the three crystallographic axes Zlf plane includes the origin move either the plane or the origin 3lnvert intercept values obtained 4Convert reciprocals to lowest integer form 5Place indices in parentheses in form hkl 6Negative indices indicated by a bar over the number DFamilies of directions and planes lFamilies refer to directions or planes in a crystal which have exactly the same arrange7 ment and spacing of equivalent sites and atoms ZFamilies of directions have the same atomic spacing 3A family of directions is indicated by placing the indices for any one member of the fam7 ily in pointed brackets in the form ltuvwgt 4Families of planes have the same planar arrangement of equivalent sites and atoms 5A family of planes is indicated by placing the indices for any one member of the family 1n braces in the form hkl ELinear and Planar densities lLinear density aFraction or of a vector which passes through atoms bVector must pass through the center of the atom for the atoms to be counted ZPlanar density aFraction or of the plane which is covered by the atoms spheres bOnly atoms whose center lies on the plane are counted 3Close packed crystals aDensest possible packing of identical size spheres bFCC and HCP structures for metals are close packed cStacking of close packed layers of atoms lFCC 7 ABCABCABC ZHCP 7 ABABABAB FStructure variations lSingle crystals 7 some materials can exist as large macroscopic single crystals aSi in semiconductors bTurbine blades page 20 ZPolycrystalline 7 most materials exist as a set of contiguous small crystals Grain boundary 7 interface between individual crystals 3lsotropic vs anisotropic alsotropic materials have randomly oriented polycrystals 7 thus physical properties are the same in all directions bAnisotropic materials have non7random orientations of the crystallographic axes 7 thus physical properties vary with direction in the material 4Amorphous materials 7 no long range orientation of the atoms to each other 5Polymorphic and Allotropic Materials 263 Crystal Imperfections lPoint Defects 7 crystal structure irregularities at a single point AVacancies lAtom missing from crystal lattice ZLattice distortions around the vacancy BSelf7interstitials lExtra atom squeezed into interstice of the lattice ZVery rare in normal densely packed structures 3Extreme lattice distortions around the extra atom CSolid Solutions 7 alloys containing two or more different types of atoms llnterstitial Solid Solution aSmall solute atoms in some of the interstices of the larger solvent atoms bVery dilute solutions due to large stresses involved ZSubstitutional Solid Solution aAtoms on solvent lattice replaced by solute atoms of a different type bSolubility limits dependent on lAtomic size 7 must be similar for large solubility ZCrystal structure 7 greatest solubility if same lattice 3Electronegativity 7 similar or intermetallic or ceramic may form 4Valence 7 solute with same or higher valence than solvent for highest solubility 3Composition specifications aAtomic 7 fraction or of atoms for each component present bWeight 7 fraction or of the weight of each component cConversions between wt and at llLinear Defects 7 crystal structure irregularities in one dimension AEdge dislocation l39Extra39 half plane of atoms in crystal ZBurger39s Vector perpendicular to line of dislocation 3Movement of dislocation leads to crystal offset equal to Burgers vector BScrew dislocation lHelical arrangement of atoms around the dislocation line ZBurger39s Vector parallel to line of dislocation page 21 3Movement of dislocation leads to crystal offset equal to Burgers vector CMixed dislocation 7 most real dislocations in materials lRegions with edge screw and mixed screw7edge character ZMovement of dislocation leads to crystal offset equal to Burgers vector llllnterfacial Defects 7 crystal structure irregularities in two dimensions AExternal surfaces lAtoms on surface have smaller coordination number than atoms in bulk ZCoordination number 7 number of nearest neighbors BGrain boundaries lRegion between individual crystals with less perfect bonding than in bulk of crystal ZLower coordination number 7 depends on degree of mismatch between crystals CTwin boundaries lSimilar to a grain boundary but occurring within grains ZLattice on opposite sides of boundary are mirror images lVBulk or Volume Defects 7 crystal structure irregularities in three dimensions 7 cracks voids porosity inclusions VMetallography APolish surface of metal to mirror finish BEtch to preferentially erode atoms with lowest coordination number weakest bonding CExamine microscopically to see grain structure 264 Diffusion lDiffusion Processes ASelf7diffusion lRandom motion of atoms within a 39pure39 material ZMeasurable only by radioactive isotope diffusion Blnterdiffusion lRandom motion of atoms in an alloy ZNet flux down a concentration gradient 3Homogenization of alloy llDiffusion Mechanisms AVacancy Diffusion lThermal vibration leading to motion ZMovement of surrounding atom into vacancy 3Energy to move in lattice directed toward vacancy Blnterstitial Diffusion lThermal vibration leading to motion ZMovement of atom from interstice to interstice 3Energy to move in lattice 4At low concentrations neighboring interstice usually empty lllSteady State Diffusion AFlux and concentration gradient assumed NOT to change with time page 22 BFick39s First Law 7 1 7 net flux of atoms down the concentration gradient 7 2D 7 diffusivity depending on energy required to move atoms in lattice and thermal exci7 tation 7 3dCdx 7 concentration gradient 7 CDiffusivity 7 lD0 7 pre7exponential diffusivity 7 an empirical constant for a given diffusion couple ZQd 7 average energy required to get atom to move in lattice 3R 7 gas constant in units appropriate to the energy 4T 7 temperature in absolute units 7 usually degrees kelvin lVNon7teady State Diffusion AConcentration gradient and flux are a function of time most real situations BFick39s second law 7 VFactors Affecting Diffusion AAtomic packing BTemperature CAtomic size DDiffusion path lBulk diffusion ZGrain boundary diffusion 3Surface diffusion 265 Mechanical Properties of Metals lStress and Strain AStress 7 the loading of a specimen BStrain 7 the response of the system CTensile Testing lAxial loading of a specimen ZUniform round or rectangular cross7section 3Stress 7 4Strain 7 aLinear 7 bCross7sectional 7 DCompression Testing l39Squat39 specimens needed to avoid bending ZFor brittle materials 3For materials used under heavy compressive loads EShear and Torsion Testing lStress 7 ZStrain 7 page 23 lllElastic Behavior AHooke39s Law lStress proportional to strain in elastic region ZFollowed to considerable extent by most metals 3 4E modulus of elasticity or Young39s modulus BNon7linear materials lTangent modulus Slope of stress7strain curve at point of interest ZSecant modulus Slope of stress strain from origin to some point on the line CAnelasticity lTime dependent strain under load ZNot significant for metals 3High hysteresis for many polymers pseudoplastic behavior DPoisson39s Ratio lRelation between strain in direction of applied stress and strain in transverse directions 2 where the applied stress is in the z direction 3n 05 indicates no net change in volume lVPlastic Behavior AOnset of plastic deformation 7 lWhen dislocations begin moving in most metals ZViscous flow in amorphous materials 3Twinning in some metals BYielding 7 lElastic limit 7 point at which deformation just begins 7 not easily determinable ZProportional limit 7 point at which Hooke39s law no longer is followed 3Yield point phenomenon 7 abrupt onset of dislocation movement for solute 39pinned39 dis7 locations 402 Yield Strength 7 stress at 0002 strain CTensile Strength Ultimate Tensile Strength lMaXimum Engineering Stress Level reached ZBased on starting cross sectional area DFracture Strength lStress at point of sample separation ZVariable and not often used in engineering design EDuctility l elongation 7 Z reduction in area 7 FToughness lAmount of energy absorbed up to fracture ZEqual to area under plastic portion of stress7strain curve GResilience lEnergy absorbed by a specimen in elastic deformation ZEqual to area under elastic portion of stress7strain curve page 24 HTrue Stress and Strain lBased on actual cross sectional area rather than original area ZHigher values of stress and strain due to nonfuniform deformation in neck VHardness AHardness measurement concepts lResistance to plastic deformation of surface aMetals bCeramics cMost polymers ZResistance to elastic deformation of surface aElastomers bSome other polymers BHardness testing lMoh39s hardness scale 7 hardness relative to naturally occurring minerals ZRockwell hardness scales aRelative depth of indentation of indenter into surface bPreiload of indenter to penetrate surface scale and irregularities cLoads from 60 kg soft materials to 150 kg hard materials 3Superficial Rockwell hardness scales aRelative depth of indentation into surface bLight loads 15 to 45 kg to measure surface properties 4Brinell hardness scale alndentation of hardened ball into surface bLoads from 500 to 3000 kg 5Vickers and Knoop microhardness scales aVery small diamond indenter blndented into surface features using microscope on metallographic specimen cHardness of individual phase regions of sample 6Hardness conversions aConversions between hardness scales not generally possible since different materials react differently to different types of testing bConversion scales available for specific material types VlVariability of Material Properties ARepeat testing necessary to determine material properties BRange of values often used to report strength or hardness in order to represent variability VllSafety Factors Almpossible to perfectly analyze stresses and material properties in any design problem BSafety factor used to account for unknowns in design parameters CRange of safety factors lLow safety factor when overidesign may make product unusable aSelect materials with small variability of properties higher cost blncrease inspections to detect incipient failures ZHigh safety factor when safety is of ultimate concern and high cost and inspection are not practical page 25 266 Dislocations and Strengthening Mechanisms lDislocation Slip ADislocation on closest packed plane moving in close packed direction BBurger39s vector offset 7 1 inter7atomic spacing CDislocation density 1Usually 105 to 106 dislocations per cmZ cm dislocations per cm3 ZCold worked materials up to 1010 cmZ 3Dislocation formation due to interaction of dislocations with each other and other defects in the material DSlip systems 1Closest packed or nearly so planes ZClose packed directions lying in the plane 3Number and orientation of slip systems determines ductility ESingle crystal slip 1Resolved shear stress 7 2 f angle between applied force and normal to slip plane 1 angle between applied force and slip direction 3Critical Resolved Shear Stress CRSS 7 t crss 7 stress on dislocation required to make it move 4Minimum applied stress when f l 45 FPolycrystalline slip 1Grain deformation constrained by contiguity with adjoining grains ZStress level in each grain not the same 3Distortion of grain shape due to deformation 4Crystal 39texture39 due to grain rotation 5 Deformation by twinning GStrengthening mechanisms 1Grain size reduction ZSolid solution strengthening 3Strain hardening aCold workin bCW A07AdA0 x 100 cHot working llRecrystallization AElimination of effects of cold work by heat treatment BStages 1Recovery aReduction in strain energy bElimination of some point defects c1mproved conductivity page 26 Z Recrystallization aNucleation and growth of new more perfect grains bGrain refinement cRecovery of ductility and toughness dStrength reduced from CW39d state but higher than before CW 3Grain Growth alncrease in grain size to eliminate grain boundary defects bReduction of strength 267 Phase Diagrams llntroduction ATerminology lPhase 7 a homogeneous portion of a system that has uniform chemical and physical char7 acteristics 7 ie the same crystal structure throughout with no discontinuous changes in composition or dimensions ZComponent 7 the chemical elements or occasionally compounds which compose an alloy 3Solvent 7 the component of a solution present in the greatest amount 4Solute 7 the component of a solution present in a minor amount note that the distinction between solute and solvent is sometimes blurred 5Solubility Limit 7 the maximum concentration of solute which can be dissolved in a sol7 vent 6Equilibrium 7 a system in its most stable or lowest energy configuration 7 reaching equi7 librium may take a very long time BSugar 7 Water Phase Diagram llSolid State Phase Diagrams ABinary lsomorphous Systems Cu7Ni lContain a single solid phase ZMelting point range for all but pure components 3Phase compositions in 2 phase regions 7 given by solubility limits of each phase 4Phase amounts in 2 phase regions 7 given by position along tie line 5lnverse Lever Arm Rule aAmount of given phase proportional to the length of tie line on opposite side of line bCalculated from phase compositions at solubility limits and composition of overall alloy 6Equilibrium melting and solidification 7Non7equilibrium solidification aCoring 7 varying composition of solid phase s bSuppression of melting point page 27 8Mechanical properties aSolid solution strengthening due to solute addition bDuctility reduction usually but not always occurs with strengthening BBinary Eutectic Systems Eutectic 7 having a low melting point lEutectic point invariant point 7 melting at a specific temperature ZThree phases in equilibrium at eutectic point compositions and temperature 3L U a b aWritten as a cooling reaction bPhase compositions and temperatures included 4 Terminology aTerminal solid solutions 7 phases containing the pure components bHypoeutectic 7 having a composition less than eutectic cHypereutectic 7 having a composition greater than eutectic dProeutectic phases 7 form before higher T eutectic eLiquidus 7 line above which all of alloy is liquid fSolidus 7 line below which all of alloy is solid gSolvus 7 boundaries between solid phase regions 5 Eutectic microstructures aEutectic alloys 7 often lamellar bPrecipitation from terminal solid solutions cHypo7 and Hypereutectic alloy structures CPhase Diagrams with lntermediate or lntermetallic Phases lPhases present other than terminal solid solutions alntermediate phases 7 solid solutions at intermediate compositions blntermetallic compounds 7 stoichiometric phases with very small range of solubility ZEutectoid reaction Eutectic like aa U b g bCools from one solid phase to two different solid phases 3Peritectic reaction aa L U b bCools from a mixture of liquid and a solid phase to a different solid phase 4 Peritectoid reaction aa b U g bCools from a mixture of two solid phases to a different solid phase 5 Congruent transformations aL U a or a U b bA transformation with no change in composition of the phases DGibb39s Phase Rule lDetermines the number of degrees of freedom of an alloy system with a certain number of phases in equilibrium ZP F C N P number of phases in equilibrium F number of degrees of freedom C number of components in the alloy system page 28 N number of non7compositional variables e g temperature and pressure llllron7Carbon Alloys Fe7Fe3C phase diagram APhases lFerrite 7 a iron ZAustenite 7 g iron 3Delta ferrite 7 d iron 4Cementite lron Carbide 7 Fe3C Blnvariant reactions lEutectic transformation 7 L g Fe3C ZEutectoid transformation 7 g a Fe3C 3Peritectic transformation 7 d L g CEutectoid microstructures lPearlite from eutectoid composition alloy ZHypoeutectoid alloys 7 proeutectoid ferrite 3Hypereutectoid alloys 7 proeutectoid carbide 4Rapidly cooled alloys aBainite bMartensite 268 Phase Transformations lNucleation and Growth Transformations ANucleation time 7 slow transformation as nuclei form BGrowth time 7 rapid growth initially followed by slowing growth Fig 101 CRate of reaction generally taken as r lt05 DNucleation process 7 fastest when old phase s most unstable EGrowth rate 7 fastest at higher temperatures diffusion FReactions on heating 7 faster as T increases GReactions on cooling lNucleation faster as T decreases ZGrowth rate faster as T increases llFe7Fe3C Transformations APearlite transformation lRate increases as T decreases 7 down to about 550 C ZHigher nucleation rate at lower T gives finer Pearlite 3lsothermal Transformation Diagrams 7 transformation from austenite to ferrite and car7 bide when held at constant T BBainite transformation lHomogeneous nucleation at lower T produces Bainite ZTransformation rate decreases as T decreases due to slower growth 3Rapid cooling required to form Bainite CSpheroidite production page 29 lCoarse carbide particles in a ferrite matrix ZNOT produced directly from austenite 3Reheating of some other ferrite and carbide structure to coarsen carbides DMartensite lRapid cooling of austenite to temperature where austenite is very unstable but transfor7 mation rate to ferrite and carbide is very slow ZBody centered tetragonal lattice produced BCC ferrite with supersaturation of carbon 3Athermal transformation 7 not time dependent 4Degree of transformation dependent on temperature Ms 8 Mf ETempered Martensite lProduced by reheating of Martensite ZMartensite transforms to very fine ferrite and carbide 3Structure similar to Bainite but easier to produce 4Potential for warping and cracking in quench FProeutectoid phase formation lPhases form only at higher temperatures where diffusion is fast ZProeutectoid ferrite for hypoeutectoid alloys 3Proeutectoid carbide for hypereutectoid alloys llllsothermal Transformation Diagrams AApplicability lDescribe only the transformation of austenite when held at a fixed temperature ZAfter austenite has been transformed lT diagram no longer applies 3Reheating will not reverse the transformation 41T diagrams apply to aa specific alloy composition ba specific austenitizing temperature and time ca specific austenite grain size BPlain Carbon Steel Alloys lEutectoid Steel lT aPearlite produced at higher temperatures 7 becomes finer as transformation T decreases bBainite produced at medium temperatures 7 becomes finer as transformation T decreases cMartensite produced when quenched ZHypoeutectoid Steel IT a Proeutectoid ferrite produced if transformed above or just below eutectoid T bAt lower T39s no proeutectoid regions 3Hypereutectoid Steel lT aProeutectoid carbide produced if fully austenitized and transformed above or just below eutectoid T 7 NOT desirable bAt lower T39s no proeutectoid regions 4 Martensite transformations aMs 8 Mf decrease as carbon content increases bHigher carbon gives more strained M lattice page 30 CAlloy Steels lAlloying elements used to slow transformations more diffusion required ZPearlite transformation slowed more than bainite 3Slower cooling and bainite formation possible lVContinuous Cooling Transformation Diagrams ACCT diagrams shifted to right and down from IT diagrams BRepresent more realistic cooling in manufacturing VMechanical Behavior AEffect of carbon content on mechanical properties lHigher C 7 higher strength and hardness ZHigher C 7 lower ductility and toughness BEffect of microstructure on mechanical properties lFiner distribution of carbide 7 higher strength and hardness ZFiner distribution of carbide 7 lower ductility and toughness 269 Metal Alloys lFabrication Processes AForming Operations lCold working 7 deformation at temperature where a deformation structure is created ZHot working 7 deformation at temperature where dynamic recrystallization can occur 3Forging 7 forcing metal to take the shape of a die by applying high pressure 4Rolling 7 passing metal through restricted rollers to reduce thickness andor produce a shape 5Extrusion 7 pushing metal through a restricted opening to change its dimensions andor shape 6Drawing 7 pulling metal through a die to change its dimensions andor shape BCasting Operations lSand casting 7 pouring molten metal into a caVity formed by packing sand around a pat7 tern ZDie casting 7 forcing molten metal under pressure into a permanent caVity in a metal mold 3lnvestment casting lost wax process 7 pouring molten metal into a caVity created by a wax pattern surrounded by a ceramic shell 4 Continuous casting 7 casting of a continuous 39ingot39 strand 7 not normally used to produce a finished product CPowder Metallurgy lPowdered metal compacted under high pressures to produce a 39green39 compact ZGreen compact is sintered heated to produce fusion of the metal powder llFerrous Alloys ASteels 7 up to approximately 14 C lLow alloy page 31 aLow carbon lt 025 C lPlain carbon aLow carbon steels 7 not heat treatable as is blnexpensive and easily formable ZHigh strength low alloy aSmall amounts of alloying elements to increase strength blmproved corrosion resistance cHigher cost bMedium carbon 025 to 060 C lPlain carbon aDifficult to harden except for small parts ZLow alloy aAlloying elements added to improve hardenability bGenerally quenched and tempered or cooled to form bainite cHigh carbon gt 060 C lPlain carbon aLow cost tool steels bHardened only by severe quenching cSoften easily in high speed cutting ZAlloy tool steels aAlloying elements added to form stabile carbides bHardened by moderate quenching cHold edge at high speeds ZHigh alloy aStainless steels lAustenitic aFCC stabilized by Ni andor Mn additions bNot hardenable ZFerritic aBCC stabilized by Cr additions bLow carbon not hardenable 3Martensitic aFCC and BCC lattices possible bC sufficient to form martensite 4Precipitation Hardenable PH aAlloy precipitate formed bNot hardenable by eutectoid transformation BCast lrons 7 carbon content in eutectic region lGray lron a25 7 40 wt C and 10 to 30 wt Si bGraphite akes formed on solidification cHigh damping capability dWeak in tension eAlloy matrix lferrite Zpearlite page 32 ZDuctile Nodular lron aCraphite spheres formed on solidification bAdditions of Mg or Rare Earths to change surface tension of C cMore ductile than gray iron dAlloy matrix lferrite Zpearlite 3martensite tempered 3White lron aBased on metastable Fe7Fe3C phase diagram bLow Si lt1 and moderate C to alloy metastable Fe7Fe3C alloy cHigh hardness and wear resistance brittle lllNonferrous Alloys ACopper and Alloys lCopper nominally pure aHigh conductivity bSoft and malleable ZBrass aCu7Zn alloys balpha7brass lsingle phase FCC lattice Zsoft and ductile cbeta7brass lmixture of alpha and beta prime ordered beta phase phases ZheaVily strengthened by presence of hard beta prime39 phase 3Bronze aCu alloyed with Sn Al Si andor Ni bStrong with good corrosion resistance 4Precipitation hardened Be7Cu alloys aHigh strength and tough bReasonably good conductors cElectrical contacts and springs dHigh strength tools and parts BAluminum and Alloys lWrought alloys aDesigned to be formed by working processes bHeat treatable alloys can form a precipitate cNon7heat treatable alloys strengthened by solid solution only ZCast alloys aDesigned to be formed only by casting 7 generally brittle if deformed bHeat treatable alloys are precipitation hardened 3Temper designations aDescribe heat treatmentcold work processes bF7 as fabricated CH 7 strain hardened do 7 annealed softened page 33 eT 7 hardened 7 various subtypes indicating combinations of cold work and aging COther Nonferrous Alloys lMagnesium alloys aUsed for their light weight bChemically reactive corrode easily ZTitanium alloys aHigh strength low weight alloys bCorrosion resistant cHigh cost 3Refractory metals aHigh strength strongly bonded metals bTemperature resistant but oxidize readily at high temperatures cUsed primarily as alloying elements 4 Superalloys aAlloys based on Fe Ni or C0 bHigh strength corrosion resistance and temperature resistance cOften include 10 or more other alloying elements 5Noble metals aExpensive corrosion resistant metals such as Au Ag Pd Pt etc bUsed for jewelry catalysts etc 2610 Ceramics lCeramic Structures Alonic ceramics llonic character based on difference in electronegativity ZCharge neutrality required 3Coordination number based on radius ratios of ions 4AX Crystals aRock salt NaCl CN 6 bCsCl CN 8 cZnS CN 4 5AmXp Crystals CaFZ 6AmBnXp Crystals BaTi03 BSilicate ceramics lTetrahedral bonding 7 highly covalent ZCrystalline SiOZ 3Silica glasses 7 amorphous CCarbon polymorphs lDiamond 7 cubic crystal ZGraphite 7 ordered structure in 27D layers page 34 3Fullerenes 7 quotbuckyballsquot 7 complex 37D structures llDefects in Ceramics ASchottky defect 7 ion pair vacancy BFrenkel defect 7 cation vacancycation interstitial pair CVacancies in crystals with polyvalent ions eg FeO with FeZ and Fe3 Dlnterstitial solute E Substitutional solute lllPhase Diagrams Components often stable compounds lVMechanical Behavior AFlexure testing BBrittle fracture CViscous flow in amorphous ceramics creep Chapter 15 7 Polymer Structures lHydrocarbons and Polymers ASaturated Hydrocarbons CnHZnZ lCovalent bonds in molecules ZWeak van der Waals bonds between molecules 3Melting point and strength increase with molecule size Blsomers 7 same chemical formula but different structure llThermoplastic vs Thermosetting AThermoplastic polymers lLarge molecules bonded to each other with weak bonding forces ZSoften on heating BThermosetting polymers 137D network of strong usually covalent bonds throughout polymer structure ZSmaller molecules may be trapped in the 37D network 3Will NOT soften on heating once 37D structure is created lllCommon Polymers AVinyls lPolymers based on mer CZHSX ZPolyethylene 3Polyvinyl chloride 4 Polypropylene 5 Polystyrene BVinylidenes 7 Polymethyl methacrylate CTeflon 7 PTFE DBakelite Phenyl7formaldehyde 7 thermoset EOther thermoplastics lNylon 66 ZPET 3Polycarbonate lVPolymerization AMonomer 7 basic building block of the polymer page 35 BMer 7 the smallest repeating unit of a polymer CAddition polymerization lActive radical such as HO breaks bond in monomer ZActive site breaks bond in additional monomer and adds it to chain VMolecular Weight APolymer properties partially based on average molecular weight B7 the number average molecular weight C7 the weight average molecular weight DDegree of polymerization 7 average number of mers per molecule VlPolymer Structures A39Random walk39 arrangement for linear polymer mers able to rotate freely BBranched polymers CCrosslinked polymers vulcanized DNetwork polymers thermosets Elsomers lStereoisomers 7 same bonds but different positioning of side groups on adjoining mers aisotactic batactic csyndiotactic ZGeometrical isomers 7 side groups bonded to same atoms but different positions within the mer acis7isoprene lnatural rubber Zelastic material due to 39arched39 mer btrans7isoprene lgutta percha Zhard brittle material due to linear mer FCopolymers 7 more than one mer in a linear polymer lRandom 7 random arrangement of mers in chain ZAlternating 7 alternating arrangement of mers in chain 3Block 7 blocks of each type of mer in chain 4Graft 7 backbone of one mer and chains of other mer grafted into backbone G Crystallinity lMers must have a regular arrangement in linear chain ZRegions of crystallinity 7 never completely a crystal 2611 Electrical Properties lElectrical Conductivity AOhm39s Law 7 V IR BResistivity Conductivity 7 CConduction by electrons or by ions llBand Structures in Solids page 36 ADiscrete energy levels in isolated atoms BEnergy bands for valence electrons as the atoms come close together and bond CValence band 7 energy band containing valence electrons in lowest energy state DConduction band 7 energy band with next highest energy levels beyond valence band 7 no electrons at lowest energy state EFermi energy 7 highest filled energy state at UK lowest energy state FEnergy band gap 7 energy difference between energy of highest energy electron at UK and the next empty state lllConduction Models AMetallic Materials lVery small energy band gap 7 highest filled state and next state adjacent to each other ZPartially filled valence band 30verlapping valence and conduction bands Blnsulators lStrong ionic or covalent bonding holds electrons tightly ZLarge energy band gap between filled valence band and conduction band 3High amount of activation energy required to boost electron from valence to conduction band CSemiconductors lWeaker covalent bonding ZSmall energy band gap between filled valence band and conduction band 3Small amount of activation energy required to boost electron from valence to conduction band DMobility lAbility of an electron to move under the force of an applied electric field ZConductivity given by number of carriers charge of carrier and mobility of carrier 7 EElectrical Resistivity lMetallic materials aTemperature effects lResistivity increases with temperature ZChange approximately linear for metals in normal temperature range of application bAlloying effects lAdding alloying elements to a pure material increases resistivity ZMultiphase materials have net resistivity approximately proportional to resistivity and amount of each phase cDeformation effects 7 Cold work increases resistivity due to distorted lattice lVSemiconduction Alntrinsic Semiconduction lConduction due to excitation of valence electrons into conduction band ZEqual number of electron carriers in conduction band and empty sites holes in valence band page 37 3Hole 7 treated as a positive carrier with charge magnitude same as electron electrons actually move 4Conductivity due to sum of conductivity of electrons and holes 7 where n p for intrinsic conduction BExtrinsic Semiconduction lConduction primarily due to either electrons or holes Zn7type extrinsic semiconduction aAddition of impurity with extra valence electron bDonor electron will have energy close to conduction band cn gtgt p at operating temperatures 3p7type extrinsic semiconduction aAddition of impurity with one less valence electron bAcceptor site will have energy close to valence band cp gtgt n at operating temperatures CEffects of Temperature on Conduction lElectron mobility decreases with temperature ZNumber of carriers increases with temperature in a semiconductor 3lntrinsic semiconductors aEqual numbers of n and p carriers bCarriers increase faster than mobility decreases 4 Extrinsic semiconductors ap7type semiconductors lmore holes than electrons Zsaturation level for normal operation bn7type semiconductors lmore electrons than holes Zexhaustion level for normal operation VHall Effect AMoving carriers subjected to a magnetic field BPositive and negative carriers deflected in opposite directions CVoltage induced perpendicular to current flow VlSemiconductor Devices ADiodes lp7n junction Zmovement of charge carriers from junction leads to rectification aforward bias 7 carriers pushed to junction region and combine breverse bias 7 carriers pulled away from junction 7 few carriers to combine and carry current 3l7V characteristics of a diode alarge forward current bsmall reverse current cbreakdown at high reverse voltages BTransistors lBipolar Junction Transistors BJT39s page 38 a3 semiconducting regions 7 NPN or PNP bemitter7base junction forward biased cbase7collector junction reverse biased dpnp operation lnarrow base region allows holes to pass from emitter to collector through the base Zsmall base7emitter current controls larger emitter7collector current enpn operation lnarrow base region allows electrons to pass from emitter to collector through the base Zsmall base7emitter current controls larger emitter7collector current ZMetal Oxide Silicon Field Effect Transistor MOSFET asingle charge carrier active but controlled by a narrow channel which carriers must pass through bvery small gate current can control large source7drain current high input impedance cp7channel FET lpositive charge on gate will reduce hole carriers in p7type Si Znegative charge on gate will allow passage of holes dn7channel FET lnegative charge on gate will reduce electron carriers in n7type Si Zpositive charge on gate will allow passage of electrons VllConductivity in Ceramics and Polymers Alonic Ceramics lConduction primarily due to ion motion ZGenerally insulating materials until at or near melting BPolymers lGenerally insulating due to covalently bonded electrons ZConduction possible by doping with appropriate compounds sometimes filled with con7 ducting elements VlllDielectric Behavior ADielectric Materials 7 insulators with internal dipoles capable of aligning with an external field BCapacitance lRelative ability of a device to store charge C QV units of farads or coulombsvolt ZParallel plate capacitor C e Al ae is the permittivity of the material between the plates bA is the area of the plates Cl is the distance between the plates 3 Permittivity ain avacuum 7 e 0 885 x 10712 Fm brelative permittivity dielectric constant 7 e r e e 0 cdielectric strength 7 resistance to breakdown in presence of an electric field page 39 2612 Thermal Properties lBackground for interest in thermal properties AThermal expansion variations in circuit parts BThermal conductivity for energy removal from circuits CComponent property variation with temperature llHeat Capacity AMeasure of the amount of thermal energy which can be absorbed lC dQdT in Jmol7K ZSpecific heat equals heat capacity per unit mass Ukg7K 3May be measured as heat capacity at constant volume Cv or heat capacity at constant pressure Cp For solids they are approximately equal BVibrational Heat Capacity 1Quantized vibrational energy in atoms electrons ZPhonon 7 quantum of vibrational energy 3Scattering of electrons due to vibration CTemperature Dependence lCv ATS at low temperatures ie increases rapidly with temperature up to the Debye temperature ZCv approximately constant at higher temperatures Cv 3 R 25 Jmol7K above q d Debye Temperature DOther Factors lElectron excitation 7 small contribution by free valence electrons ZRandomization of electron spins at Curie temperature lllThermal Expansion ALinear Thermal Expansion Coefficient 1D 110 a l D T where a l is the thermal expansion coefficient at room temperature usu7 ally about 25 C ZThermal expansion varies slightly with temperature 7 correction needed far from room temperature 3Related to average atomic spacing as temperature increases 7 refer to atomic bonding curves BBqu Thermal Expansion Coefficient a v 3 al lVThermal Conductivity ASteady State Heat Flux 7 1Analogous to diffusion 7 flow of heat from high temperature region to low temperature region ZFlux proportional to temperature gradient BConduction mechanisms 1Lattice vibration waves phonons 7 primarily in insulators ZElectron motion 7 primarily in conductors 3Thermal conductivity k related to electronic conductivity in metals by Wiedemann7 Franz Law 7 k Ls T page 40 VThermal Stresses AStresses can be created by thermal expansion contraction of a restrained object BStresses can be created by differential thermal expansion contraction CThermal shock lStresses due to rapid temperature change ZResistance improved by aHigh fracture strength bHigh thermal conductivity cLow moduli of elasticity dLow thermal expansion coefficients often at odds with c 2613 Magnetic Properties of Materials lMagnetic Induction AMagnetic field induced by electrical current lMagnetic Field Strength 7 H 7 magnetic field strength amperesmeter N 7 number of turns in coil 1 7 current in coil 1 7 length of coil ZMagnetic Flux Density 7 indicates response of material subjected to a Magnetic Field B 7 Magnetic Flux Density teslas 7 weberssquare meter m 7 magnetic permeability WbA7m 3Magnetic Field Strength in a vacuum given by where m 0 is the permeability of a vacuum 4p x1077 Hm 4Relative permeability 7 indicates the relative ability of a material to be magnetized by an external magnetic field 5Magnetization 7 M 7 represents the magnetic field strength contributed by the magneti7 zation of the medium in the magnetic field or where c m is the magnetic susceptibility which is also given by c m m r 7 l BMaterial Response to a Magnetic Field lDiamagnetism aNo permanent magnetic dipoles blnduced magnetic dipoles in atoms align in a direction opposite to the applied field cThe magnetic flux density is thus slightly less than it would be in a vacuum m r lt l ZParamagnetism aPermanent magnetic dipoles randomly arranged when no field applied 7 thus no mag7 page 41 netism observable bMagnetic dipoles in atoms align in the same direction as the applied field cThe magnetic flux density is thus slightly greater than it would be in a vacuum m r gt 3Ferromagnetism aStrong permanent magnetic dipoles bM gtgt H thus B mOM cAtomic dipoles tend to align over relatively large areas even without an applied field magnetic domains dSaturation magnetization Ms occurs when all dipoles align with external field eContribution of individual atoms to magnetization sums to total Ms 4 Antiferromagnetism aPermanent magnetic dipoles naturally align in opposing orientations bNo net magnetic moment results 5 Ferrimagnetism aCeramics may exhibit permanent magnetization bMagnetization depends on crystallographic orientation of atoms in lattice llTemperature and Magnetization ASaturation magnetization decreases with increased temperature BCurie Temperature 7 Tc 7 temperature at which ferromagnetism ceases 768 C for iron lllMagnetic Domains and Hysteresis ADomains lMagnetic dipoles in a domain aligned ZDipole arrangement varies from domain to domain 3Domains usually smaller than grain size 4Dipole orientation transition across domain wall boundary 5Random domain orientation gives unmagnetized material BHysteresis lMagnetization curve aApplied H field causes domains to align bReducing H field to zero leaves permanent magnetization in ferromagnetic material Remanence 7 Br cH field required to reduce B to zero is the Coercivity Hc dEnergy absorbed in cycling through hysteresis loop 7 proportional to area inside curve eDemagnetization by cycling hysteresis curve from large amplitude down to zero CSoft vs Hard Magnetic Materials lHard magnetic materials aHigh Remanence and Coercivity large hysteresis bDifficult to demagnetize cHigh energy loss in cyclic field dGood for permanent magnets ZSoft magnetic materials aLow Remanence and Coercivity small hysteresis bEasy to demagnetize cLow energy loss in cyclic field page 42 dGood for motor and solenoid cores 2614 Optical Properties of Materials lElectromagnetic Radiation ASpectrum lRadio ZMicrowave 3lnfrared 4Visible 5 Ultraviolet 6X7rays 7g 7rays BPropagation lWave Model aElectric field component bMagnetic field component cSpeed of propagation 3x108 msec in a vacuum 1e 0 7 electric permittivity of a vacuum Zm 0 7 magnetic permeability of a vacuum dRelationship of frequency n and wavelength 1 7 c l n ZParticle Model aQuantized photons of energy b where h Planck39s constant lllnteractions with Matter AElectron excitation lPhoton energy transferred to electron if change of energy D E puts the electron at an allowable energy state 2D E hn BReemission of photon lExcited electron will fall back to lower energy state with emission of photon ZEmission in visible range can be created by excitation from electron or other particle CRT Clnteraction with semiconductors lElectron 7 hole pair created if hn gt Eg ZRecombination of electron and hole emitting photon of radiation lllApplications in Electrical Devices ALuminescence lExcited electrons dropping back to a lower energy state emitting photon of light


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