An Brief Introduction to Materials Science and EngineeringElaine D. Haberer

History of Materials Science & Engineeringmaterials closely connected our culturethe development and advancement of societies are dependent on the available materials and their useearly civilizations designated by level of materials development

initially natural materialsdevelop techniques to produce materials with superior qualities (heat treatments and addition of other substances)

MATERIALS SELECTION!

Materials Science and Engineeringstructurepropertiesmaterial characteristicresponse to external stimulusmechanical, electrical, thermal, magnetic, optical, deteriorative performancebehavior in a particular applicationarrangement of internal componentssubatomicatomicmicroscopicmacroscopic (bulk)characterization

Classification of MaterialsMetalsgood conductors of electricity and heatlustrous appearancesusceptible to corrosionstrong, but deformableCeramics & Glassesthermally and electrically insulatingresistant to high temperatures and harsh environmentshard, but brittlePolymersvery large moleculeslow density, low weightmaybe extremely flexible

Classification of Materials: A Few Additional CatagoriesBiomaterialsimplanted in human bodycompatible with body tissuesSemiconductorselectrical properties between conductors and insulatorselectrical properties can be precisely controlledCompositesconsist of more than one material typedesigned to display a combination of properties of each componentIntel Pentium 4fiberglass surfboardship replacement

Why study materials?applied scientists or engineers must make material choicesmaterials selectionin-service performancedeteriorationeconomics

BUTreally, everyone makes material choices!aluminumglassplastic

Choice of Mediummedium: woodWood is a natural material that ties the indoors to the outdoors when it is usedA project is a creative 3 dimensional design processYou don't need a huge shop space or heavy duty metal working machine tools. George J. Haberermedium: pastelsI love this rather dirty, dusty medium. Most important factor is that I keep the work behind my bedroom door and in the trunk of my car. Where could I have put all the canvases??? Jacqueline M. Haberer

structurepropertiesperformanceprocessing

Levels of StructureSTRUCTURE (length scale)< 0.2 nm

MetalsMetallic Bondone, two, or three valence electronsvalence electrons free to drift through the entire material forming a sea of electrons surrounding net positive ionic coresnon-directional bondPropertiesgood conductors of electricity and heatlustrous appearancesusceptible to corrosionstrong, but deformable

Ceramics and GlassesIonic Bondcomposed of metallic and non-metallic elementsmetallic elements give up valence electrons to non-metallic elementsall atoms have filled inert gas configurationionic solidnon-directional bondCoulombic bonding forceCeramics & Glassesthermally and electrically insulatingresistant to high temperatures and harsh environmentshard, but brittle

PolymersCovalent Bondelectrons are shared between adjacent atoms, each contributing at least one electronshared electrons belong to both atomsdirectional bondPolymersvery large moleculeslow density, light weight materialsmaybe extremely flexible

Levels of Structure

Atomic Arrangement: Ordered vs. DisorderedCrystalline: atoms are arranged in a 3D, periodic array giving the material long range orderstacking can effect properties (i.e. ductility)anisotropic materialsNon-crystalline or amorphous: atoms only have short-range, nearest neighbor order

viscous materials (generally complex formulas) or rapid coolingisotropic materials

Levels of Structure

MicrostructureSingle Crystalthe periodic arrangement of atoms extends throughout the entire sampledifficult to grow, environment must be tightly controlledanisotropic materialsPolycrystallinemany small crystals or grainssmall crystals misoriented with respect to on anotherseveral crystals are initiated and grow towards each otheranisotropic or isotropic materials

Levels of Structure

Bulk PropertiesMechanical: elastic modulusshear modulushardnessElectrical:conductivityresistivitycapacitanceOptical:reflectivityabsorbanceemissionThermal:thermal expansionheat capacitythermal conductivity

Processing Structure Properties PerformancePerformance Goal: increased strength from a metallic materialIn actuality, crystals are NOT perfect. There are defects!In metals, strength is determined by how easily defects can move!

Processing Structure Properties Performancesingle-crystal(transparent)polycrystalline,fully dense(translucent)polycrystalline, 5% porosity(opaque)Aluminum Oxide (Al2O3)

Characterization TechniquesSTRUCTURE (length scale)< 0.2 nm1 nm = ?0.2-10 nm1-1000 mm> 1 mmcharacterization

Optical Microscopylight is used to study the microstructureopaque materials use reflected light, where as transparent materials can use reflected or transmitted light

Electron Microscopybeams of electrons are used for imagingelectrons are accelerated across large voltagesa high velocity electron has a wavelength of about 0.003 nmthe electron beam is focused and images are formed using magnetic lensesreflection and transmission imaging are both possibleTransmission Electron Microscopy (TEM)an electron beam passes through the materialthin samplesdetails of internal microstructure observed1,000,000x magnification possibleScanning Electron Microscopy (SEM)an electron beam scans the surface and the reflected (backscattered) electrons are collectedsample must be electrically conductivematerial surface is observed200,000x magnification possible

Scanning Probe Microscopy (SPM)SPM image of a butterfly wing. 3D topographical map of material surfaceprobe brought into close proximity of material surfaceprobe rastered across the surface experiencing deflection in response to interactions with the material surfaceuseful with many different types of materialsSPM image of silica coated gold nanoparticles.SPM image of 70 nm photoresist lines.

X-ray DiffractionBraggs Law: 2d sin q = nlx-rays are a form of light that has high energy and short wavelengthwhen x-rays strike a material a portion of them are scattered in all directionsif the atoms in the material is crystalline or well-ordered constructive interference can order

Case Studies

Clayaluminosilicate: combination of alumina (Al2O3) and silica (SiO2) that bind watermelting temperature of alumina > silicalayered crystalline structure: kaolinite (Al2Si2O5(OH)4)water fits between layersclay has three main ingredients: (1) clay(2) quartz (cheap filler material)(3) flux (lowers melting temperature)Forming:hydroplastic formingslipcastingDrying:shrinkagematerial becomes brittle

Clay (cont.)Firing:firing temperature, 900-1400oC (1650-2550oF)permanent physical and chemical changesfuses or melts over large temperature rangedesired shaped is retainedshrinkage due to removal of bound waterSintering:bonds start to form between particlesparticles are fused into a very porous solidmelting has not yet occuredVitrification:flux lowers quartz melting temperaturequartz particles begin to melt and pull silica out of clay matrixsilicates form increasing the viscosity of the meltremaining alumina rich clay particles have higher melting temperaturefinal structure: alumina rich particles in silicate glass matrix

Polymer Clay (Sculpey, FIMO)polyvinyl chloride (PVC)long chain or high molecular weight polymerthermoplastic: polymer that melts to a liquid when heated and freezes to a brittle, glassy state when cooledas-purchased a plasticizer is added to keep clay malleableheating the clay decomposes the plasticizer hardening the claywithout plasticizer: polymer clay is brittle at room temperaturewith plasticizer: polymer clay is malleable at room temperature- the plasticizer acts as a lubricant putting space between chains and allowing them to slide passed each other

Metal Foil Embossingpolycrystalline metal sheetrelatively isotropic in-planeductile materialembossing process: plastic or non-recoverable, permanent deformationduring embossing bonds are broken with original neighboring atoms and reformed with new neighborsyield strength: stress required to produce a very slight deformationmetals a can generally only support 0.5% elongation before plastic deformation occursmaterials choice important

Metal AlloyYield Strength (MPa)Aluminum35Copper69Iron130Steel180Titanium450

Summarystructurepropertiesperformanceprocessingmetalceramicpolymerwoodpastels

Needs some pictures. Too many words.Animate. Interactive?interactiveinteractiveinteractiveinteractiveinteractiveinteractive, 1- PETE polyethylene terathalate, 2- high density polyethylene Dont forget to mention which types of material (metals, ceramics, or polymers) form crystalline versus non-crystalline material. But, mention even metallic glasses are possible given the proper processing.