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  • ESERCIZIO: calcolare quanti atomi ci sono in un cm 3 di Cu. (m.a Cu = 63.54; d Cu = 8.96 g/cm 3 )
  • 01 introd

    1. 1. Scienza e Tecnologia dei Materiali2011 - M.Ferraris1The aim of this course:• The aim of this course is to provide Mechanical andAutomotive Engineering students basic knowledge ondifferent classes of materials• Relationship between structure of materials and theirproperties (Materials Science)• Structure of materials = chemical-physicalstructure, (chemical bonds, composition, …)• To design/choose materials (Materials Engineering)• Choice of materials, production process,structure-properties, performances, cost, lifecycle
    2. 2. Scienza e Tecnologia dei Materiali2011 - M.Ferraris2MATERIALS OF INTEREST INENGINEERING• Metals and alloys• polymers• composites• glasses• ceramics(fuels, lubricants, paints, …....)
    3. 3. 3http://helios.augustana.edu/physics/301/periodic-table-fix.jpg
    4. 4. Scienza e Tecnologia dei Materiali2011 - M.Ferraris4OVERVIEW ON METALS ANDALLOYS• ELEMENTS (Fe, Ti, Al, Mg, Cu,…)• Heath and electricity• Prepared by melting• Can be machined• All solids at room temperature• Can form alloys• Corrosion and oxidation issues• Density ranging between 2,7 and 8 g/cm3
    5. 5. Scienza e Tecnologia dei Materiali2011 - M.Ferraris5OVERVIEW ON CERAMICS• Compounds (oxydes, carbides, nitrides, ..)(Al2O3,SiC, Si3N4,…)(density ranging between 3 and 5 g/cm3)• hard and brittle, difficult to be machined• Insulators (heat and electricity)• High melting point• Prepared by sintering or other processes, nevermelting• examples: bricks, concrete, tiles, porcellains, ….
    6. 6. Scienza e Tecnologia dei Materiali2011 - M.Ferraris6OVERVIEW ON POLYMERS• Organic macro-molecules,natural or synthetic• Prepared by organic synthesis• Low density, less than 1g/cm3• Easy to machine• Insulators (sound, heat and electricity)• Low thermal and mechanical properties• examples: tyres, adhesives, paints, bitumen,..
    7. 7. Scienza e Tecnologia dei Materiali2011 - M.Ferraris7OVERVIEW ON GLASSES• Prepared by melting of oxides(SiO2, Na2O, CaO, Al2O3, K2O,...)• Hard, brittle, can be deformed only at suitabletemperature, cannot be machined• insulators (heat and electricity)• Density of about 2,5 g/cm3• examples: window and car glasses, opticalfibers
    8. 8. Scienza e Tecnologia dei Materiali2011 - M.Ferraris8OVERVIEW ON COMPOSITES• TWO PHASES:MATRIX and SECOND PHASE• Classified according to the matrix:• Metal matrix composites• Polymer matrix composites• Ceramic matrix composites• Glass and glass-ceramic matrix composites• examples: wood, reinforced concrete, bones,bamboo,….
    9. 9. Scienza e Tecnologia dei Materiali2011 - M.Ferraris9OVERVIEW ON COMPOSITES• Can be classified according to the secondphase morphology:• Fiber reinforced composites (long fibers, shortfibers)• Particle reinforced composites• The second phase can be: metal, polymer,ceramic, glass
    10. 10. Scienza e Tecnologia dei Materiali2011 - M.Ferraris10STRUCTURE OF MATERIALS• CRYSTALLINE ORDERED– metals, ceramics• AMORPHOUS DISORDERED• glass, polymers
    11. 11. Scienza e Tecnologia dei Materiali2011 - M.Ferraris11EXCEPTIONS….• Glass-ceramics, polymers, composites::• Amorphous in some zones, crystalline inothers
    12. 12. Scienza e Tecnologia dei Materiali2011 - M.Ferraris12CORRELATION STRUCTURE-PROPERTIES….• …the aim of Materials Science• CRYSTALLINE STRUCTURE– Melting Temperature• AMORPHOUS STRUCTURE– They don’t have melting temperature,but progressive softening
    13. 13. Scienza e Tecnologia dei Materiali2011 - M.Ferraris13CRYSTALLINE STRUCTURE:MELTING TEMPERATURE• Melting temperature = Solid to liquid (Tm)• directly proportional to the material bondstrength
    14. 14. 14MELTING TEMPERATURETm(°C)Tm(°C)Tm(°C)W 3410 Mg 651 Al2O3 2045Ti 1675 Pb 270 SiO2 1730Fe 1536 Sn 232 MgO 2800Ni 1453 Al 660 CaCO3 1339Cu 1083
    15. 15. Scienza e Tecnologia dei Materiali2011 - M.Ferraris15CRYSTALLINE STRUCTURE• Chemical bond and crystalline structure:atoms, ions or molecules in crystallinestructures are in ordered positions incrystalline cells• atoms, ions or molecules are at the equilibriumdistance between attraction and repulsionforces : bond length or bond distanceibchem.com
    16. 16. Scienza e Tecnologia dei Materiali2011 - M.Ferraris16CRYSTALLINE STRUCTURE• “CRYSTALLINE materials: ordered positioningof atoms (ex: metals), or ions (ex: ceramics) ormolecules (ex: polymers)”• CRYSTALLINECELL• a,b,c0,1-0,26 nmVideo
    17. 17. Scienza e Tecnologia dei Materiali2011 - M.Ferraris17CRYSTALLINE CELLSa,b,c cell parametersα,β,γ cell angles• identify the structure of crystalline materialsby cell parameters• a,b,c about 0,1-0,26 nm at room T and withoutexternal applied forces
    18. 18. Scienza e Tecnologia dei Materiali2011 - M.Ferraris18CRYSTALLINE CELLS• a,b,c changes with T and applied forces• At zero K they are at the equilibrium distance• When T increases, vibration around theequilibrium distance cause thermal expansion,then melting.
    19. 19. Scienza e Tecnologia dei Materiali2011 - M.Ferraris19SEVERAL CRYSTALLINE CELLSa = b = c α = β = ϒ = 90° CUBICa = b ≠ c α = β = ϒ = 90° TETRAGONALa ≠ b ≠ c α = β = ϒ = 90° ORTOROMBICa = b = c α = β = ϒ ≠ 90° ROMBOEDRICa = b ≠ c α = β = 90° , ϒ = 120° HESAGONALa ≠ b ≠ c α = β = 90° ≠ ϒ MONOCLINEa ≠ b ≠ c α ≠ β ≠ ϒ ≠ 90° TRICLINE
    20. 20. 20Crystalline cells
    21. 21. 21Es: Cu, Al, Ag, AuEs: Fe, W, CrEs: Mg, Ti, ZnHexagonal compact
    22. 22. Scienza e Tecnologia dei Materiali2011 - M.Ferraris22• Lattice plane: 3 atoms (or ions or molecules) in a cell, define one latticeplane• COORDINATION NUMBER:
    23. 23. Materiali per l’IngegneriaM.Ferraris23http://amscampus.cib.unibo.it/archive/00001824/01/5-Silicio_web.dochttp://www.diee.unica.it/~vanzi/Origami.PDFhttp://www.lnf.infn.it/esperimenti/rap/docs/silicio.pdf
    24. 24. Materiali per l’IngegneriaM.Ferraris24Gold (Au)nanocluster,embedded inamorphoussilica matrix(SiO2)Ausilica, SiO2, amorphousJ. Morgiel, Cracovia
    25. 25. Materiali per l’IngegneriaM.Ferraris25http://ceramics.org/video/individual-carbon-atoms-in-motion/
    26. 26. 26X-ray diffraction (XRD)XRD of a crystallinematerial (Au)XRD of amorphous silicaand silica crystalline (SiO2)
    27. 27. 27Electromagneticradiation spectrumE=hνλ= 1 / νΕ= energyν = frequencyλ= wavelengthEnergy, frequencywavelengthHigh Energy, highfrequency, shortwavelengthLow Energy, lowfrequency, longwavelength
    28. 28. Scienza e Tecnologia dei Materiali2011 - M.Ferraris28X ray diffractionn λ = 2 d sinθ(Bragg law)n= number, 1, 2, 3…
    29. 29. 29X-ray diffraction (XRD): to detect anamorphous or crystalline materialXRD of a crystallinematerial (Au)XRD of amorphous silicaand silica crystalline (SiO2)
    30. 30. Materiali per l’IngegneriaM.Ferraris30Examples ofXRD
    31. 31. Scienza e Tecnologia dei Materiali2011 - M.Ferraris31CRYSTALLINE STRUCTURE:POLYMORPHISM• A crystalline solid melts when heated• Polymorphism: change of crystalline structureduring heating (solid state reaction)• examples: Ti, Fe, SiO2• Polymorfism and variation of materialsproperties : (V, α, k, E, d,….)
    32. 32. Scienza e Tecnologia dei Materiali2011 - M.Ferraris32POLYMORFISM
    33. 33. Materiali per l’IngegneriaM.Ferraris33
    34. 34. Scienza e Tecnologia dei Materiali2011 - M.Ferraris34CRYSTALLINE STRUCTURE:DEFECTS• Crystalline structure is not completelyordered….LATTICE DEFECTS:• MONODIMENSIONAL DEFECTS• BIDIMENSIONAL DEFECTS• TRIDIMENSIONAL DEFECTS
    35. 35. 35MONODIMENSIONAL DEFECT:INTERSTITIAL
    36. 36. 36MONODIMENSIONAL DEFECTS:SUBSTITUTIONAL
    37. 37. 37MONODIMENSIONAL DEFECTS:SUBSTITUTIONAL
    38. 38. Scienza e Tecnologia dei Materiali2011 - M.Ferraris38MONODIMENSIONAL DEFECTS(or POINT DEFECTS)• Vacancies (lack of one atom or ion ormolecule in the lattice)• interstials• substitutionalsvacancysubstitutionainterstitial
    39. 39. Scienza e Tecnologia dei Materiali2011 - M.Ferraris39ARE POINT DEFECTS«DEFECTS»…?• ALLOYS and in general solid solutions arepossible because of interstitials andsubstitutionals defects• presence of substitutional impurities arenecessary for in semiconductor science….
    40. 40. Scienza e Tecnologia dei Materiali2011 - M.Ferraris40Solid solutions: substitutional alloys• Metal alloys are solid solutions :– up to 15% atoms as substitutional defects different fromthose of the main lattice– Es: Cu/Ni– RNi = 1.25Å, RCu = 1.28Å– both CFC– Same electronegativity– valence Ni +2, Cu +1, +2– Atoms with similar radius, crystalline cell, electronegativityand valence
    41. 41. Scienza e Tecnologia dei Materiali2011 - M.Ferraris41Solid solutions: interstitial alloys– Atoms as interstitial defects different from those ofthe main lattice– Only small atoms can enter a metallic cell asinterstitial defects (max 10%)– Ex.: carbon is an interstitial defects in the ironlattice in steels, up to about 2%– RFe = 1.24Å, RC = 0.71Å
    42. 42. Scienza e Tecnologia dei Materiali2011 - M.Ferraris42BIDIMENSIONAL DEFECTS:DISLOCATONS• Edge and screw dislocations: responsible ofplastic deformation of materials• (video)• Commercial metal or alloy (ex. Cu) about 108dislocations per cm3
    43. 43. Scienza e Tecnologia dei Materiali2011 - M.Ferraris43Dislocations in nature….!• Dislocation: one lattice plane more….Solfuro di rame (CuS)cactus!
    44. 44. Scienza e Tecnologia dei Materiali2011 - M.Ferraris44Edge dislocationshttp://www.uet.edu.pk/dmems/EdgeDislocation.gif
    45. 45. 45350ÅNitruro di gallio(GaN)Screw dislocations
    46. 46. Scienza e Tecnologia dei Materiali2011 - M.FerrarisMateriali per l’IngegneriaM.Ferraris46Dislocation motionVedi moto dislocazioni.ppt123456
    47. 47. Scienza e Tecnologia dei Materiali2011 - M.Ferraris47DISLOCATION AND PLASTICDEFORMATION• Dislocation motion means fracture of a bond andformation of another one in a different nearbylattice position• dislocations are present in ALL crystalline materials(metals, ceramics,…)• In ceramics, it is NOT possible to form a new bond ina different nearby lattice position due to the ionic orcovalent nature of bonds. No plastic deformation (atroom T)• In metals, it IS possible to form a new bond in adifferent nearby lattice position due to the metalnature of bonds. Plastic deformation.
    48. 48. 48Interaction betweendislocations and pointdefectsMechanicalhardening, coldworkingVideo
    49. 49. 49Dislocations interact withthemselves: mechanicalhardening of alloys
    50. 50. Scienza e Tecnologia dei Materiali2011 - M.Ferraris50INTERACTION DISLOCATION ANDPOINT DEFECTS• DISLOCATIONS INTERACT with themselves (cold working,hardening).• Dislocations interact with point defects: dislocation motion isslower (VIDEO) in alloys than in pure metals• Better mechanical properties of alloys vs pure metals• Without dislocations, the plastic deformation of metals cannotbe explained• Dislocations can be seen with Scanning or Transmissionelectron Microscopy (SEM, TEM).
    51. 51. 51Dislocation motion
    52. 52. Materiali per l’IngegneriaM.Ferraris52Interaction dislocation substitutionaldefect and influence on mechanicalproperties of alloys vs pure metals
    53. 53. 53Interaction dislocation/substitutionaldefect and influence on mechanicalproperties of alloys vs pure metals
    54. 54. 54Preferential sliding planes fordislocationsLow density plane High density plane
    55. 55. Scienza e Tecnologia dei Materiali2011 - M.Ferraris55TRIDIMENTIONAL DEFECTS• surface is a defect : reactivity of atoms orions or molecules at the surface. Lowercoordination number, higher reactivity• GRAIN BOUNDARIES (gb)
    56. 56. Scienza e Tecnologia dei Materiali2011 - M.Ferraris56http://www.numis.northwestern.edu/Research/Projects/3x1.shtml
    57. 57. Scienza e Tecnologia dei Materiali2011 - M.Ferraris57• GRAIN BOUNDARIES:distorted bonds at the boundary between twograins in a polycrystalline materialTRIDIMENTIONAL DEFECTS
    58. 58. Scienza e Tecnologia dei Materiali2011 - M.FerrarisMateriali per l’IngegneriaM.Ferraris58SOLIDIFICATION OF A LIQUID AND ITS STRUCTURE1425 °Cor SiO2a 1730 °CSLOW SPEEDSOLIDIFICATIONMONOCRYSTALLINESTRUCTUREMEDIUM SPEEDSOLIDIFICATIONPOLYCRYSTALLINESTRUCTUREHIGH SPEEDSOLIDIFICATIONAMORPHOUSSTRUCTURELIQUIDGRAINand GB
    59. 59. Scienza e Tecnologia dei Materiali2011 - M.FerrarisMateriali per l’IngegneriaM.Ferraris59Nucleation andgrowth,formation of GBinpolycrystallinematerials
    60. 60. Scienza e Tecnologia dei Materiali2011 - M.Ferraris60CRYSTALLINE STRUCTURE• MONOCRYSTALS: crystalline cells all orientedin the same (ex. Silicon for microelectronics)• POLYCRYSTALS: crystalline cells oriented inthe same way ONLY inside grains:solidification too quick to allow sameorientation in entire lattice (ex .metals, alloys,ceramics)
    61. 61. Scienza e Tecnologia dei Materiali2011 - M.Ferraris61Monocrystal (a) …. polycrystal(b)
    62. 62. 62Monocrystals• Difficult to obtain compared topolycrystalline materials• Silicon for electronics– Extra slow molten silicon solidification(1-10 µm per second)– About 1.5m length silicon cylinders300 mm diameter, sliced as wafers– About 10 defects/ cm 2http://www.csc.fi/elmer/examples/czmeltflow/growth.gifhttp://www.ami.bolton.ac.uk/courseware/mdesign/ch2/SingleCrystalSiliconIngot.jpg
    63. 63. 63http://www.ingegneriadelsole.it/celle_silicio_cristallino.htm
    64. 64. 64Polycristalline materials• Natural solidification from a liquid metal gives apolycrystalline metal• Several grains, same cell orientation inside thegrain, grains separated by grain boundaries(gb)http://mimp.mems.cmu.edu/~ordofmag/alumina.jpghttp://www.mse.nthu.edu.tw/jimages/Beuty/Steel1.jpgGrains inAl2O3Grainsin steel
    65. 65. Materiali per l’IngegneriaM.Ferraris65GRAIN BOUNDARIES• Irregular bonds, impurities,dislocations, atoms withlower coordination number,…• High reactivity• Observable by opticalmicroscopy and chemicaletching• (file micr_acciai_ghise; video crystalline cells, video mechproperties)
    66. 66. Materiali per l’IngegneriaM.Ferraris66
    67. 67. Materiali per l’IngegneriaM.Ferraris67Optical and electronMicroscopy• Optical microscopy (2000x)• Scanning Electron Microscopy (SEM)(104x)• Transmission Electron Microscopy(TEM) (106x)
    68. 68. Materiali per l’IngegneriaM.Ferraris6820 µmTiTi2(Co,Ni)Ti(Co,Ni)TiCoSEM and compositionalanalysis (EDS)
    69. 69. 69Atomic Force Microscopy (AFM) (109x)
    70. 70. Scienza e Tecnologia dei Materiali2011 - M.FerrarisMateriali per l’IngegneriaM.Ferraris70SOLIDIFICATION OF A LIQUID AND ITS STRUCTURE1425 °Cor SiO2a 1730 °CSLOW SPEEDSOLIDIFICATIONMONOCRYSTALLINESTRUCTUREMEDIUM SPEEDSOLIDIFICATIONPOLYCRYSTALLINESTRUCTUREHIGH SPEEDSOLIDIFICATIONAMORPHOUSSTRUCTURELIQUIDGRAINand GB
    71. 71. Materiali per l’IngegneriaM.Ferraris71
    72. 72. Scienza e Tecnologia dei Materiali2011 - M.Ferraris72AMORPHOUS MATERIALS• Disordered structure, no melting point• glasses, polymers• Short range order (few nm) (ex: Si4+and O--ions are situated in tetrahedra in silicateglasses
    73. 73. 73• Local, short range order;bond angle and length arevariable• No order after fewnanometers• “Undercooled liquids”• Quick solidification of a liquid• “No time to obtain acrystalline structure” !http://www.research.ibm.com/amorphous/figure1.gifAmorphous silicaAMORPHOUS MATERIALS
    74. 74. Scienza e Tecnologia dei Materiali2011 - M.Ferraris74Amorphous materials: silica glassesSi4+O--tetrahedron amorphous structure of silica:tetrahedra chains
    75. 75. Scienza e Tecnologia dei Materiali2011 - M.Ferraris75Crystalline and amorphous silica (SiO2)
    76. 76. Scienza e Tecnologia dei Materiali2011 - M.Ferraris76AMORPHOUS MATERIALS• Amorphous materials are notthermodynamically stable:• They become crystalline if suitable heated• All liquids can be solidified quickly enough toobtain amorphous solids• All liquids can be solidified slowly enough toobtain poly- or mono-crystalline solids
    77. 77. Scienza e Tecnologia dei Materiali2011 - M.Ferraris77• Ex: silica glass: bond angles, force andlength differ in different tetraedra• No melting temperature• Viscosity vs temperature• The opposite than with crystalline materials !AMORPHOUS MATERIALS
    78. 78. Scienza e Tecnologia dei Materiali2011 - M.Ferraris78VISCOSITY• Viscosity is a measure of a fluidsresistance to flow.• It describes the internal friction of a movingfluid (i.e. tetrahedra chains in a silica glass).
    79. 79. Scienza e Tecnologia dei Materiali2011 - M.Ferraris79VISCOSITY• Viscosity Unit : Poise10 Poise = 1 Pa∙s = 1 (N/m2)∙s• Example of viscosity:H2O (room T) η= 1 x 10-3Pa sSiO2(silica) (1720°) η= 1 x 106Pa s
    80. 80. Scienza e Tecnologia dei Materiali2011 - M.Ferraris80VISCOSITY : AMORPHOUS andCRYSTALLINE materialsViscosity decreasescontinuosly foramorphous materials.This is not the case forcrystalline materialsAl2O3Glasses, polymers
    81. 81. Scienza e Tecnologia dei Materiali2011 - M.Ferraris81VISCOSITYannealingsofteningWorking pointMelting point
    82. 82. Scienza e Tecnologia dei Materiali2011 - M.FerrarisMateriali per l’IngegneriaM.Ferraris82Viscosity curve of a glass
    83. 83. Viscosity for glass and glass-ceramics83glassGlass-ceramic

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