Modern Manufacturing - Introduction to structure and properties of materials by SupremeLord

VIEWS: 71 PAGES: 115

									           UEET 601
        Modern Manufacturing

Introduction to structure and properties
              of materials
                           Introduction
• What is manufacturing?
    – Conversion of a material from a primary form into a
      more valuable form - adding VALUE to a material
    – List examples of ANYTHING you know and how you
      think they were produced
    – Involves product
            • Design,
            • selection of Materials and
            • selection of Process




5/13/2011                   UEET 601 Modern Manufacturing   2
Manufacturing demands/trends:
• product design requirements, specs. and
  standards
• environmentally conscious and economic
  methods of manufacture
• Quality issues
• flexibility in manufacturing methods
  (Why?)
• New developments in materials, methods,
  CIM
• System dynamics, productivity
 5/13/2011     UEET 601 Modern Manufacturing   3
• Product design considerations:
   – product requirements and performance
   – design considered together with
     manufacturing
   – product design cycle and life cycle
     characteristics
   – CONCURRENT ENGINEERING - integrated
     product development and design:
        • CAD, CAM, CAE
        • Rapid prototyping
        • Design for manufacture and assembly

 5/13/2011           UEET 601 Modern Manufacturing   4
What materials?
• There are a wide variety of materials available
  today with diverse characteristics that suit
  various applications. They are:
   – Metals and alloys
        • Ferrous or non-ferrous (Examples?)
   – Plastics
        • Thermoplastics, Thermosets
   – Ceramics, glass and diamond
   – Composites
        • Engineered, Natural (examples?)
   – Nano-materials, shape memory alloys, armorphous
     alloys, superconductors

 5/13/2011               UEET 601 Modern Manufacturing   5
• Other considerations in the selection of
  materials:
    – Properties of Materials
         • Mechanical - how a material will respond to its
           service condition loading - strength, stiffness,
           hardness, e.t.c.
         • Physical properties - density, thermal, electrical
           and magnetic properties,
         • Chemical properties - oxidation, corrosion, toxicity,
           flammability
         • Manufacturing properties - machinability,
           weldability, formability, castability, heat treatment
• Cost and availability
• Appearance, service life and recyclability
 5/13/2011              UEET 601 Modern Manufacturing              6
What Process?
• A wide variety; usually a product goes through a
  combination of processes
• Choice depends on properties of material and
  product requirements, costs
   – casting - molten material allowed to solidify into
     shape in a mold cavity
   – forming and shaping - rolling, forging, extrusion,
     drawing, sheet forming, P/M, molding
   – machining - shape formed by removal of material
   – joining - welding, soldering, adhesive joining, brazing
   – Finishing operations - polishing, coating, e.t.c.
 5/13/2011          UEET 601 Modern Manufacturing        7
Structure of Materials
    The most important concept in
         materials science
Structure – Property Relationships

Composition

                 Structure       Properties

Processing


                             Useful applications
                          Compositionally Identical

                          Diamond
                          •hardest known material
                          •transparent to light
                          •electrically insulating
                          •highest thermal conduction of
                          any material known



                          Graphite
                          •one of the softest materials
                          known
                          •opaque
                          •electrically conductive (in the
                          basal plane)
                          •thermally conductive (in basal
                          plane)

Why? Processing, that’s why.
                    Structure of Materials
   States of Matter
   Gas – molecules are free to move, no definite shape, no definite
        volume  container determines volume
   Liquid - molecules are free to move but not as free as in a gas, definite
        volume, no definite shape  container determines the shape
   Solids – molecules cannot move freely, definite volume, definite shape
   Plasmas – high temperature, similar to a gas, but many electrons are
        free leaving many charged ions



While most industrial products are solids, liquids, or gasses, plasmas are
important for industrial processing.




*we’re going to forget about the Bose-Einstein condensate for this class.
            Structure of Materials
Bonding
Ionic – electron transfer from one atom to another, bonding is
     electrostatic, common in salts
Covalent – electrons are shared by nearby atoms, common in
     ceramics, semiconductors, and polymers
Metallic – electrons in the valence shells become delocalized and are
     shared by the now positively charged metal atoms, common in
     metals
Hydrogen bond – this is an electrostatic bond between an
     electronegative atom and a hydrogen atom bonded to nitrogen,
     oxygen, or fluorine, important for water and for nucleic acid and
     protein structures
Van der Waals bond – a relatively weak bond caused by electric
     dipoles, which in turn are caused by random motion of electrons,
     occurs in all materials, important for noble gases, colloids (paint,
     polishing and cutting formulations, etc.,)
Structure of Materials - Metals
The vast majority of metals are crystalline (atoms have a regular
    repeating spacing and orientation with respect to one another).

There are a number of different possible symmetries for atomic
    arrangement, some common ones:




  bcc                          fcc
        Structure of Materials - Metals

                                                                                            The 14 Bravais lattices

                                                                                            These represent the only
                                                                                            possible ways to stack hard,
                                                                                            uniform, spheres in 3-D
                                                                                            space. This is true for all
                                                                                            materials, not just metals.

                                                                                            Many more possibilities arise
                                                                                            when multiple atom types are
                                                                                            present.




* James F. Shackelford, Introduction to Materials Science for Engineers, Macmillan Publishing, 1988.
    Structure of Materials - Metals
 Consequences of crystal structure:
 FCC crystals have a close packed plane along the diagonal of the cube, it is
   relatively easy to shear parallel to this plane.

 In general fcc metals are more ductile, and have lower melting points than bcc
     metals.

                        fcc – planes can slip easily


                           bcc – large corrugations, slippage is more difficult



Crystal structure also plays a very significant role in electronic properties, very
important for semiconductors.
        Structure of Materials - Metals
   Formation of crystals:
   During cooling from a molten state crystal growth starts (nucleates) in
   many different places, these nuclei grow until they run into one another.

                                                                Since the crystals nucleate in random
                                                                orientation, when they meet there will
                                                                be a boundary. These crystals are
                                                                called grains.

                                                                Most metals are polycrystalline,
                                                                production of single crystals is possible
                                                                in many cases but requires specialized
                                                                processing.



* http://chemical-quantum-images.blogspot.com/2007/03/shaping-copper.html
  Structure of Materials - Metals
Defects in Crystals:
Point
         - Impurity (present in all materials)
         - Thermally Generated
                  vacancies – a missing atom
                  interstitial – an atom in a position that isn’t supposed to
                  have one
Line
         - dislocations
Planar
         - twins
         - grain boundaries
 Structure of Materials - Ceramics
  Most are crystalline (except for glasses) and often polycrystalline, with
  many grains like metals.

  The difference is in bonding, covalent (or ionic) instead of metallic.
  Much more difficult for dislocations to move, low ductility/brittle.
  Consider Al and Al2O3:

Al                                          Al2O3
Melting point 660 °C                        Melting point 2054 °C
Mohs hardness 2.75                          Mohs hardness 9 (about 100X harder)
Electrical resistivity 2.65 x 10-6 Ωcm      Electrical resistivity 2.0 x 1013 Ωcm



 Semiconductors are generally similar in bonding, but with greater ease of freeing
 an electron.
           Structure of Materials -
              Semiconductors
                     Silicon is FCC with two atoms per lattice
                     point, this is the same as diamond and
                     germanium. Diamond is not considered a
                     semiconductor because it requires too much
                     energy to free an electron.

                     In most applications semiconductors are used
                     in single crystal form (no grain boundaries).




* wikipedia.org
            Structure of Materials -
               Semiconductors
Conductivity of Semiconductors is modified by controlling defect populations.



                                                Adding small quantities of an
                                                element with one too many
                                                electrons makes that extra
                                                electron very easy to free.

                                                Adding small quantities of an
                                                element with too few
                                                electrons makes a missing
                                                bond in the structure, this is
                                                also easy to move.


 * wikipedia.org
   Structure of Materials - Glass
Sometimes classified as a ceramic. A covalently bonded network that
does not have a well defined repeating structure, it is amorphous.

•Generally formed by cooling a melt of mostly silica (SiO2) containing
other glass formers, intermediates, and modifiers (B2O3, P2O5, Na2O,
CaO, Al2O3, PbO, etc.) fast enough that it cannot order itself into
crystals. Unlike in metals this is not difficult to achieve.
•While there is no long range order there is typically short range order,
Si atoms are mostly bonded to four O atoms.
•Melting point is not as well defined as in other materials, glass
transition temperature.
Structure of Materials - Polymers
Covalently bonded chains, made from repeating monomer units –
polymerization


                                                              •Covalently bonded within
                                                              the chain, but with the
                                                              ability to twist.
 H    H                            H     H    H       H       •Between chains bonding
           Catalyst, heat, light                              can range from Van der
 C    C                            C     C    C       C       Waals to covalent cross-
                                                              linking
 H    H                            H     H    H       H


                                                          n

ethylene                               polyethylene
Structure of Materials - Polymers
Huge variety of polymer types
Addition – polyethylene, PVC, pAA, pAMPS, polystyrene, etc.
Condensation – polyurethane, nylon, polycarbonate, silicones, etc.




 Can also be co-polymers (mixed monomer types, block or random, cross-
 linked or not, etc.
Mechanical, Physical, and
Manufacturing Properties of
        Materials
       Mechanical Properties
• Manufacturing often involves application of
  external forces.
• The response of a material to external
  forces is important for its use in different
  applications
          Types of Forces
• Tension
• Compression
• Torsion
• Bending
• Shear
Tensile testing is a common way to evaluate
the strength of a material, though other
types of testing are also done.
                          Tension Test
• A material loaded in tension will stretch.
                                                         F
                                          A

                                 L0
                 F
    stress       units are force per area [Mpa, psi]
                 A
                 L
    strain e       Dimensionless, expressed as in/in or %
                 L0



What is the relationship between stress and strain? It depends on the material.
                          Stress – Strain Curves




*http://irc.nrc-cnrc.gc.ca/images/cbd/157f02e.gif
                          Stress – Strain Curves

                                                                                       Proportional, Hook’s law,
                                                                                       Young’s modulus, E=/e




*http://www.mech.uwa.edu.au/unit/MECH2402/lectures/hot_cold_working/degarmo_17-7.gif
                    Ductility
The extent to which plastic deformation
takes place before fracture:
Elongation L f  Li
                       *100%
               Li

Percent reduction in cross sectional area
             Ai  Af
                       *100%
               Ai
                        Hardness
Ability to resist permanent indentation from a
scratch.
The result depends both on the material and on the shape of the
indenter, it is not a fundamental material property.


Wear resistance is related and sometimes tested
also with a sliding stylus or indenter.
               Hardness Tests
Brinell Hardness (BHN) – uses a hard ball
indenter
Multiple different sizes and materials can be used for the
ball
Vickers Hardness – uses a diamond
pyramid indenter
Knoop (KHN) – also uses a diamond
pyramid
A microhardness test, for thin sheets
Rockwell – multiple types of tests
                 Fatigue
• Components may undergo cyclic or
otherwise fluctuating loads that may cause a
part to fail at lower stresses than if under a
static load.
• Its cause is the movement of dislocations
that eventually form small cracks which
weaken the material.
• Fatigue failure is responsible for the
majority of failure of mechanical
components.
                          Creep
 Permanent elongation over time under a
static load.
• caused by disslocation slipping, grain boundary sliding, and
diffusional flow
•often worse at elevated temperature but that is material
dependent (W > 1000 °C, ice even at sub-zero temps),
typically 30% of melting temp for metals and 40-50% for
ceramics (glass does NOT creep near room temperature)
• very important for high temperature applications – nuclear
plants, turbine blades, steam power plants, etc
• also important for more mundane applications – paper
clips, light bulbs
          Impact Resistance
The ability to withstand impact loads. It is a
 function of both ultimate tensile strength
 and ductility (the area under stress-strain
 curve)
               Physical Properties
 Other physical properties are also improtant in
material selection and manufacturing decisions.
(examples)

•Density
•Melting point
•Heat capacity
•Thermal expansion
•Thermal conductivity
•Electrical conductivity
•Magnetic properties (permittivity, magnetoresistance, magnetorestriction
•Other dielectric properties (dielectric constant, breakdown strength)
•Chemical compatibility/corrosion resistance
•Optical properties
     Specific properties are a
    convenient way to compare
             materials
Material     UTS   Specific Stiffness Specific
             (Mpa) Strength (E, Gpa) Stiffness

Steel        450   58       210      27
(SG = 7.8)

Aluminum     150   56       70       26
(SG =2.7)
                                 Density
                              m
Mass per unit volume                    [g/cm3, lb/ft3]
                              V
Important for transportation. Strength (of the type required) per weight is
another way to look at this one.




                          Melting Point
 Important for casting, refractories, others…
                        Heat Capacity
                            Q
 Energy required to    cp              [cal/g°C, J/g°C, cal/lb°F]
 change temperature         mT
Important for machining, forming, and thermal management, why?




                 Thermal Expansion
Dimensional change         1  L 
                           L 
                             
                          T  i 
per unit temperature                       [1/°C]
                                  
  Important for stress management, expansion joins, glass metal seals, shrink
  fits, thermal fatigue, etc.
                 Thermal Conductivity
 Rate at which a                Q  1  x
                           k                  [W/mK]
 material can transport         t  A   T
 heat.
Important for machining, thermal management (extrusion, microelectronics, etc.)




                Electrical Conductivity
Ability of a material to       l
carry electrical                             [1/ Ωcm]
current, inverse of           RA
resistivity.

  Important for electrical applications, examples?
            Chemical Compatibility
This is a major issue that needs to be considered along with all of the other
physical properties.

Examples: Corrosion in transportation (air, sea, land), refractories, bridges and
buildings, …



                   Dielectric strength
Amount of applied electric field before failure. [V/cm]

Important in integrated circuits (driving away from SiO2 gates), electrical
insulation.
                Magnetic properties
Important in hard disk industry, transformers, RF processing, others?




                    Other properties
Piezolectric, ferroelectric, thermoelectric, magnetorestriction,
magnetoresistance. What might these be useful for?
  Changing Properties of
Metals, Heat Treatment and
 Strengthening Processes
                Structure of Alloys
Alloy = composed of two or more types of
atoms, at least one of which must be a
metal. Both solid solutions and intermetallic
compounds are alloys.




 Steel – the most famous class of alloys
            Solid Solutions
What it sounds like, analogous to a solution
of liquids.
The solvent must maintain its original crystal
structure. Either because the solute can
occupy the same sites (with about 15% of
the same size), or because the solute can
occupy interstices.
     Intermetallic Compounds
Compounds that form between metals.
Rather than a solution in the same structure
a new structure is formed. Many are hard
and brittle. Fe3C is the most famous of
these.
              Phase Diagrams
• In pure metals solidification takes place at constant
temperature
• Mixtures solidify over a range of temperature.
• Phase diagrams show the EQUILLIBRIUM situation,
kinetics are not considered




                       * http://www.sv.vt.edu/classes/MSE2094_NoteBook/96ClassProj/sciviz/html/clicktuta.html
                        The Iron-Carbon System
                                          Polymorphic transformation
                                          BCC to FCC (austenite)




                                            Partial transformation to
                                            ferrite (ductile and soft)




                                           Transformation to ferrite
                                           and pearlite (alternating
                                           layers of cementite and
                                           ferrite)




* Materials Science and Metallurgy,
4th ed., Pollack, Prentice-Hall, 1988
    General classes of steels
• Low carbon (mild steels) <0.3% C - high
ductility, low strength, for general use,
sheets, plate.
• Medium carbon steel 0.3-0.6% C – higher
strength, higher hardness, less ductility,
gears, axles, railroad, etc.
• High carbon steels >0.6% C – hard, strong,
brittle, tool steel, springs, cutting tools
               Heat Treatments
Both microstructure and composition affect
a material’s properties. Heat treatment is
one way to manipulate microstructure.
 These changes to microstructure are caused by phase
transformations and changes in grain size. These effects are
both thermodynamically and kinetically driven.
Ferrous Alloys
    Pearlite – has a laminar structure which
    can be coarse or fine depending on the
    rate of cooling through the eutectoid
    temperature. Finer structures are
    generated by faster cooling.




          Martensite – a supersaturated solid
          solution of carbon in iron, achieved by very
          rapid cooling (quenching) from austenite.
          has a laminar structure which can be
          coarse or fine depending on the rate of
          cooling through the eutectoid temperature.
          Finer structures are generated by faster
          cooling.
             •http://info.lu.farmingdale.edu/depts/met/met205/tttdiagram.html
             •http://www.matter.org.uk/steelmatter/metallurgy/7_1_2.html
         Ferrous Alloys (cont.)
 Spheroidize anneal – pearlite heated to just below
the eutectoid temperature for a long period of time (1
day) will transform the cementite laminar stuctures to
spheres – less stress concentration better ductility
and toughness
Tempering – martensite is reheated to an
intermediate temperature <650 C and some is
converted to ferrite and cementite. This relieves
stress and restores some ductility. (note that this is
NOT what tempering in glass means)
Alloying – Other elements can be added to shift the
TTT curve to the right. Allows martensite formation
at lower cooling rates.
          Other Heat Treatment
               Processes
Annealing – Used widely to restore ductility in cold worked
materials or in castings. Material is heat soaked to a specific range
of temperature for a period of time and allowed to cool slowly either
in a furnace or in still air.
In full annealing, there is microsturctural change due to
recystallization, in a stress relief anneal the material is heated to a
lower temperature to reduce internal stresses.
Case Hardening – a process where carbon is introduced to the
surface only, allows the underlying material to retain ductility and
toughness.
            Non-Ferrous Alloys

Non-ferrous alloys and some stainless
steels have completely different phase
diagrams from normal steels, thus they use
different heat treatments and mechanisms to
alter properties.
Precipitation hardening – a 2-phase alloy is heated until it is
above its solubility limit and is then slowly cooled or held at
an intermediate temperature, precipitates will form in the
solid solution, these can interfere with slip propogation.
Non-ferrous Alloys
             Introduction
• Covers a very wide range of alloys
• In general, more expensive than Ferrous
  alloys but have other advantages
• We will examine the most common
  categories
           Aluminum and its Alloys
General properties               Relevant Applications
• very high specific strength
                                 • transport industry, structural
  and stiffness                    parts (B747 = 82% Al)
• good corrosion resistance,     • containers and packaging
  good formability                 (cans, foils, etc), aerospace
• easily formed into shape       • cookware, aircraft skin
• good electrical conductivity   • overhead power lines,
                                   electrical applications
• good thermal conductivity        (integrated circuits)
                                 • heat exchanger tubes,
                                   radiators
Alloys
• Two categories: WROUGHT and CAST
Wrought:
• formed into shape. Also has two categories:
   – Those strengthened by heat treatment
   – Those strengthened by cold working
• Major applications: formed products, fittings, tubes, sheet
  metal, rivets (Al/4%Cu - ages naturally)
Cast:
• final component produced by a pouring molten metal into
  a mold
• Most popular are the Al-Si alloys. Si promotes fluidity
  during casting.
• Used mainly for Aluminum castings of components e.g
  engine parts (cylinder head), general Al castings
      Magnesium and its Alloys
• Magnesium - the lightest metal for general engineering
  applications; possesses good vibration damping
  characteristics
• Cast or wrought
• Typical applications in aircraft and missile components,
  materials handling equipment, portable power tools,
  ladders, luggage racks, sporting accessories (weight),
  textile and printing (lower inertial effects)
• Pure Mg has low strength - alloyed to improve
  performance Main alloying elements are Zn and Al
• Good castability, formability and machinability
      Copper and its Alloys
• Commercially pure Cu generally contains
  very little alloying (e.g Phosphorous,
  sulfur and oxygen)
• Good thermal and electrical conductivity -
  electrical applications, heat exchangers
• Good formability - rivets, rolls, nails,
  gaskets
Alloys
Brass - Copper + Zinc; good ductility, corrosion
  resistance and thermal conductivity. Used for
  radiators, ammunition catridges, plumbing, gears
Tin Bronze - Copper and tin. Good formability and
  castability. Castings
Phosphor Bronze – Cu + Sn + Phosphorous.
  Phosphorous protects the melt from oxidation.
  High toughness and low coefficient of friction.
  Bearings, bushes, valves, clutch disks, springs.
Cupro-nickels: Copper + nickel; ornamental
  applications, coins, heat exchangers
Others - Aluminum bronze, beryllium bronze
          Nickel and its Alloys
• Ni is ferromagnetic
• Major element that imparts strength, toughness and
  corrosion resistance -used extensively in stainless
  steels
• High melting point (1455oC), high resistance to
  oxidation at elevated temperatures
• Generally used for high temperature applications
  (superalloys) such as jet engine components, rocket
  parts, nuclear reactor parts, chemical plants, coins,
  marine applications, solenoids
• Nickel alloys exhibit high strength and corrosion
  resistance at elevated temperatures especially
  when alloyed with Chromium, Molybdenum and
  Cobalt.
• Examples: Monel alloy - Ni + Cu, used for
  chemical applications, coins, pump shafts;
  Inconel - Ni + Cr; very high UTS (1400
  MN/m2); used in gas turbines, nuclear reactors;
  Hastelloy - Ni+Cr+Mo; high corrosion
  resistance at elevated temperatures; gas
  turbines; jet engines; Nichrome - Ni + Cr + Fe;
  high electrical resistance and resistance to
  corrosion; used for electrical elements; Invar
  alloys - Ni +Fe; Low thermal expansion
             Superalloys
• Important in high temperature applications;
  HEAT RESISTANT or HIGH
  TEMPERATURE alloys
• High corrosion resistance, high UTS and
  fatigue strength at elevated temperatures,
  good thermal shock resistance
• Most have a service temperature up to
  1000oC
• General applications - jet engines, rocket
  engines, dies for metal working, chemical
  plants, tools, nuclear reactors
A) Iron-base superalloys:
• generally contain 32 - 67% Fe + Cr, Ni.
  Example - Incoloy
B) Cobalt-base superalloys:
• 35 - 65% Co + Cr, Ni. Not as strong as Ni
  base
C) Nickel-base superalloy:
• Most widely used. Contains 38 - 76% Ni +
  Cr, Mo, Co, Fe (See Ni and alloys)
       Titanium and Alloys
• Expensive. High specific strength, high
  corrosion resistance even at elevated
  temperatures. Properties very sensitive to
  alloying elements
• General applications - aircraft parts, jet
  engines, racing cars, chemical, marine,
  submarine components, biomaterials
  (bone implants)
• Major alloying elements in decreasing
  order: Aluminum, Vanadium, Molybdenum,
  Manganese
       Refractory Metals and Alloys
• Principal property is very high melting point
• Molybdenum :
  – Very high melting point.
  – Main alloying elements: Ti and Zr
  – Applications - solid-propellant rockets, jet engines,
    honeycomb structures, heating elements, dies
• Niobium:
  – Good ductility and formability, good resistance to
    oxidation
  – Applications - rockets and missiles, nuclear and
    chemical plants, superconductors
• Tungsten:
  – Highest melting point (3410oC), high strength at
    elevated temperatures, high density, low resistance
    to oxidation
  – Applications - Welding electrodes, spark plugs,
    dies, circuit breakers, throat liners in missiles, jet
    engines
• Tantalum:
  – High melting point, good ductility, oxidation
    resistant, high resistance to corrosion at low
    temperatures
  – Applications - electrolytic capacitors, acid-resistant
    heat exchangers, diffusion barriers
    (microelectronics)
Beryllium
• High specific strength. Toxic if inhaled, dust from
  machining etc.
• Pure Beryllium used in rocket nozzles, space and
  missile structures, aircraft disc brakes
• Widely used as an alloying element e.g with Cu -
  springs, non sparking tools
Zirconium
• Good strength, ductility and corrosion resistance at
  elevated temperatures
• Used in electronic components, nuclear reactor
  parts. Widely used as an alloying element
Low Melting Point Alloys
 Lead:
   – High density, good resistance to corrosion, soft. Fairly
     toxic. Good vibration damping.
   – Applications - radiation shielding, vibration and sound
     damping, weights, ammunition, chemical plants
   – Alloying with Antimony and Tin enhances properties
     and makes it suitable for production of collapsible
     tubes, bearing alloys, lead-acid storage batteries
   – Extensive applications in solders when alloyed with tin
   – Toxicity is causing it to be largely removed from
     consumer electronics solders
•   Zinc:
    – 4th most widely used metal.
    – Used for galvanized iron sheets
    – Main alloying base for die-casting alloys - fuel pumps and grills for
      cars, household components
    – Major alloying elements: Al, Cu and Mg
    – Also suitable for superplastic applications
• Tin:
    – Main application of pure tin is in coating of steel sheets for food cans.
    – Tin-base alloys - WHITE METAL - contain copper, antimony and lead
      - used for journal bearings (Babbit metal)
    – Tin is an important alloying element for dental alloys, for bronze and
      for solders (with lead)
    – Low melting point (232 C) makes it suitable for float glass process
 Precious Metals
• Gold - ductile, good corrosion resistance.
  Applications: jewelry, ornaments, electroplating,
  coinage
• Silver: ductile, highest electrical conductivity.
  Applications : jewelry, coinage, electroplating,
  electrical applications, photographic film, solders
• Platinum: ductile, good corrosion resistance.
  Applications: electrical contacts, spark-plug
  electrodes, catalysts, jewelry, dental applications,
  thermocouples
Others
Shape Memory alloys:
• When deformed plastically at room temperature will
  return to original shape upon application of heat.
• Example 55%Ni/45%Ti.
• Applications - antiscald valves in hot water systems,
  eye glass frames, connectors


Amorphous alloys
• Are not crystalline, made by rapid solidification. High
  strength, low loss from magnetic hysteresis. Cores
  for transformers, generators.
Nanomaterials
• Materials having sizes in the order of 1 -
  100 nm.
• Currently under very active research
• Microelectromechanical devices, medical
  applications
Ceramics, Glass, Graphite,
  Composite Materials
                  Ceramics
• Compounds of metals and non-metals
  – traditional - bricks, clay, tiles
  – engineered - made for specified applications
    such as automotive, aircraft, e.t.c.
Structure
• Bonding normally covalent or ionic
• usually high hardness, thermal, and
  electrical resistance.
                  Ceramics, Glass, Composite       76
                          Materials
       Mechanical Properties
• Aluminum oxide strength in compression
  2100 MPa, flexural strength 500 Mpa
• Ceramics are much stronger in
  compression than in tension, why?
• Stress concentration, by grains, defects,
  design.
• High strength requires small grain size
• Creates opportunities for composites for
  some applications
Oxide Ceramics
• Alumina (Al2O3) – spark plugs, electrical insulators, porcelain
• Zirconia (ZrO2) – fake diamond, oxygen sensors (YSZ)
• Used in emery clothes/paper, abrasive tool materials, heat engine
   components (Zirconia)
• MgO – used in refractories
• Calcium silicates (3CaO·SiO2, 2CaO·SiO2) – portland cement
Other ceramics
• Carbides - used in tools and die materials
    – usually carbides of Ti, Si, Tungsten
• Nitrides - generally also used as tool materials
    –   Cubic born nitride (second hardest material known)
    –   Titanium nitride (used as a coating material - low friction, high hardness)
    –   silicon nitride (cutting tools, diffusion barrier in microelectronics)
    –   aluminum nitride good thermal conductivity and thermal expansion match to Si


                               Ceramics, Glass, Composite                      78
                                       Materials
• Cermets - combinations of a ceramic phase bonded with
  metal. (composite!)
   – High temperature applications: tools, jet engine nozzles, aircraft
     brakes
• Silica: -polymorphic material abundant in nature. Bricks,
  glasses, quartz. SiO2 hard - tool materials.
• Nanophase ceramics and composites: ductility improve
  by reducing particulate size (e.g. by gas condensation)
   – important parameters: particulate size, distribution and
     contamination
   – Better ductility than conventional ceramics, easier to fabricate.
   – Used for auto and jet engine components (e.g. valves, rocker
     arms, cylinder liners)




                         Ceramics, Glass, Composite                      79
                                 Materials
General properties
• generally brittle, hard and strong, especially at high temperatures.
• Maintain their strength and stiffness at high temperatures
• low toughness, low thermal expansion
• low electrical conductivity
• high wear resistance
• thermal conductivity varies
• in general, have lower specific gravity than metals but higher
  melting points and higher elastic moduli
• Phase transitions, ion conduction, and symmetry, can be important
  for applications
• Properties are the result of chemistry and structure (what makes
  something piezoelectric, ferroelectric, insulating, etc.?)




                         Ceramics, Glass, Composite                      80
                                 Materials
Applications
• electrical and electronic industry – insulators, capacitors
• sanitary ware (e.g. porcelain)
• high temperature applications (cylinder liners, bushings,
  seals, bearings)
• coating on metals - to reduce wear, prevent corrosion,
  thermal barrier (e.g titanium nitride coating on tungsten
  carbide tool inserts; tiles in space shuttle to provide
  thermal barrier on re-entry/exit to atmosphere)
• low density and high stiffness - ceramic turbochargers
• strength and inertness - bioceramics (e.g. bone
  implants) aluminum oxide, silicon nitride
• Microelectronics – insulators, diffusion barriers, gate
  dielectrics, capacitors, sensors
                      Ceramics, Glass, Composite            81
                              Materials
                Symmetry and Crystallography are
               important for many of the electronic
                    applications of ceramics
                                                 Perovskite structure,
                                                 symmetric – no net
                                                 electric field




       BaTiO3, PbTiO3, etc.
       exhibit this behavior

                                          Distorted structure –
                                          net electric field




* http://vpd.ms.northwestern.edu/members/Zixiao/Perovskite.jpg
Glass
• amorphous solid, supercooled at a rate so high that
  crystals do not form
• has no distinct melting/freezing point - glass transition
  temperature, Tg
• contains at least 50% silica (glass former); composition
• generally resistant to chemical attack; have special
  significant applications in optics (CRT’s, LCD’s, TV’s,
  lighting, containers, cookware, microelectronics –
  especially chalcogenide glasses)




                      Ceramics, Glass, Composite              83
                              Materials
                                           Structure of Glass
                                                                         SiO44- tetrahedral
                                                                         building blocks –
                                                                         give short range
                                                                         order, but there is
                                                                         no long range
                                                                         order.




                                                  Modifiers can also
                                                  change the structure

* http://www.ohsu.edu/research/sbh/results.html
• properties of the glass (but not strength) can be modified
  by adding various types of oxides –MODIFIERS
• what does modify the strength?
• Properties of glasses: - elastic but brittle, high strength,
  low thermal conductivity and expansion, high electrical
  resistance
• glass ceramics – starts as a glass, but is partially
  crystallized by heat treatment (usually 70+%
  crystallized). The crystalline component has a negative
  coefficient of thermal expansion, the glass has a positive
  CTE  excellent thermal shock resistance




                      Ceramics, Glass, Composite            85
                              Materials
                         Glass Modifiers
•   Na – lowers melting
    point, but increases        Modifiers can alter properties to suit different
    water solubility            applications.
•   Ca – improves water
    resistance
•   B – thermal properties
•   Pb – refractive index
•   Fe – color (brown)
•   Co – color (deep blue)
•   Ce – UV absorption
•   P – diffusion barrier for
    sodium
    (microelectronics)
          Tensile failure in glass

              H2O
                                                        H HO
                                                       O
           Si O Si                                Si             Si
                                              O         O             O
                                                  Si        Si




Scratches intensify stresses  reduces strength
Water attacks Si-O-Si bonds  reduces strength
Flame polishing removes scratches  increases strength
HF polishing removes scratches  increases strength
Like other ceramics glass is much stronger in compression than in tension
Unlike other ceramics glass lends itself to tempering
Graphite
• Crystalline form of carbon
• lower frictional properties - used as SOLID LUBRICANT e.g.
  in metal forming
• brittle; strength and stiffness vary with temperature
• Amorphous C is used as a pigment (black soot) and rubber
  additive (carbon black)
• high electrical and thermal conductivity, good resistance to
  thermal shock at high temperatures - used in electrodes,
  heating elements, motor brushes, furnace parts
• low resistance to chemical attack - filters for corrosive fluids
• graphite fibers - used to reinforce composites




                        Ceramics, Glass, Composite                   88
                                Materials
Diamond
• 2nd principal form of carbon
• Hardest substance known, brittle - used for tool
  materials, polishing, grinding, etc.
• polycrystalline diamond – ornaments and abrasives
• synthetic diamond - can also be made into particles
  - used in abrasive cutting wheels
• other uses - dies for very small diameter wire
  drawing; coatings for cutting tools and dies
• Diamond Like Carbon (DLC) – can be produced as
  a thin film for wear resistance – hard disks



                   Ceramics, Glass, Composite       89
                           Materials
         Composite Materials
• A major development and one of the most
  important classes of engineering materials.
  These materials are referred to as
  ENGINEERED MATERIALS (c.f. Natural
  composites - wood.)
• Composites consist of the MATRIX - base
  material and the REINFORCING material
  usually fibers
• Widely used in aerospace and structures

                  Ceramics, Glass, Composite    90
                          Materials
Reinforced Plastics
• Matrix is a polymer or plastic
• Reinforcement consists of various types of fibers
  such as glass, graphite, boron, or aramids
• Fibers are strong and stiff in tension but brittle, and
  can degrade. Property depends material and
  method of processing
• Matrix - tough
• Reinforced plastic will contain the advantage of the
  two
• % of fibers by volume in the composite for reinforced
  plastics varies between 10 and 60
                     Ceramics, Glass, Composite      91
                             Materials
• Reinforcing fibers: -
   – Glass - most widely used and least expensive. (Glass fiber
     reinforced plastics - GFRP) glass should be weak in tension, why
     does this work?
   – Graphite - more expensive than glass but low density, high strength
     and stiffness (Carbon fiber reinforced plastics -CFRP)
   – Conductive graphite - are a recent development to enhance the
     electrical and thermal conductivity of CFRP. Fibers coated with metal.
     Used in electromagnetic and radio frequency shielding, and lighting
     protection
   – Aramids - among the toughest fibers. E.g. KEVLAR. But hygroscopic,
     complicates their use
   – Boron - fibers deposited by chemical vapor deposition onto tungsten
     fibers. High strength and stiffness, resistance to high temperatures.
     Heavy and expensive
   – Others - nylon, silicon carbide, aluminum oxide, steel; whiskers
   – Fibers can be short or long, continuos or discontinuous

                          Ceramics, Glass, Composite                  92
                                  Materials
• Matrix materials:
   – have three functions:-
      • support fibers in place and transfer the stresses to them
        while they carry the most load
      • protect fibers against physical damage or environment
      • reduce propagation of cracks in the composites - ductile
   – Are usually thermoplastics or thermosets

Properties
• mechanical and physical properties depend on the kind,
  shape and orientation of fiber
• long fibers offer more effective reinforcement
• bonding between matrix and fiber is very critical - weak
  bonds give rise to delaminations, and fiber pullouts
  especially under adverse environmental conditions
                       Ceramics, Glass, Composite                   93
                               Materials
• Highest stiffness obtained when fibers are aligned in the direction of
  tensile load
• Fiber can be re-arranged in reinforced composites to give the part a
  specific service condition. For instance if the part is subjected to
  forces in different directions, either the fibers can be crisscrossed in
  different directions or the layers of fibers can be built up into
  laminate having improved properties in more than one direction
Applications
• Formica (table tops).
• Reinforced plastics typically used in military and commercial aircraft
  (B777 - 9% composites), rocket components, helicopter rotor
  blades, automobiles (e.g. bumpers), leaf springs, drive shafts,
  pipes, tanks, pressure vessels, boats




                          Ceramics, Glass, Composite                     94
                                  Materials
Metal Matrix composites
• higher stiffness than polymer matrix composites
• posses better properties at higher temperatures than
  polymer matrix composites
• BUT higher density and difficulty in processing
• matrix materials - aluminum, magnesium, aluminum-
  lithium, copper, titanium, and superalloys
• fiber materials - graphite, aluminum oxide silicon
  carbide, boron molybdenum and tungsten
• boron fibers in aluminum - space shuttle structural
  beams ( high specific stiffness and strength, high
  thermal conductivity)
• hypersonic aircraft (under development)

                     Ceramics, Glass, Composite          95
                             Materials
Ceramic-matrix composites
• matrix is ceramic
• have high temperature resistance and resistance to
  corrosive environments
• matrix materials - silicon carbide, silicon nitride,
  aluminum oxide, carbon
• fibers - carbon, aluminum oxide
• applications - jet and automotive engines, deep sea
  mining, cutting tools, dies.
• Reinforced concrete – very widespread use, steel
  has a corrosion problem, why does this work?



                   Ceramics, Glass, Composite        96
                           Materials
Polymers: Structure and
      Properties
Why Polymers?
• Easily formed into shape with less energy and
  fewer finishing operations
• Low density
• High corrosion resistance
• Low electrical and thermal conductivity
• Cheaper than metals and ceramics
• But some limitations:- low strength/stiffness, low
  service temperature, some polymers degrade
  with time in sunlight

                   Polymers - Structure, Properties    98
                         and Applications
Formation of Polymers
• Short hydrocarbon chains – monomers –
  form into long chains - Polymerization
• Synthesis of polymers can be initiated by:
  •    Heat or catalyst – addition polymerization
  •    monomers reacting together when mixed –
      condensation polymerization. By products such as
      water are ―condensed‖ out.
• Polymer chains formed can be:
  •    linear
  •   branched
  •   cross linked
  •   networked

                     Polymers - Structure, Properties    99
                           and Applications
• In most cases the structure is amorphous
  although some crystallization may occur
• Both of these affect the density and
  properties
• The degree to which they occur (degree of
  crystallinity) can be controlled in the
  polymerization process
• The degree of crystallinity affects the
  mechanical and physical properties:
     • higher crystallinity implies higher density, higher
       stiffness, less ductile, more resistant to solvents and
       temperature




                    Polymers - Structure, Properties             100
                          and Applications
• Molecular weight (MW) - sum of the
  molecular weights of the mers in a
  representative chain. The higher the
  MW the greater the average chain
  length. (i.e chain lengths vary)
  • MW has a strong influence on the properties -
    tensile strength, toughness and viscosity increase
    with chain length. Typical values ~104 to 107
• Degree of Polymerization - ratio of the MW of
  polymer to the MW of the mer.
  • Example PVC: MW of mer = 62.5
  • DP of PVC with MW of 50,000 = 50,000/62.5= 800


                 Polymers - Structure, Properties        101
                       and Applications
Example: formation of polyethylene form
  ethylene




               Polymers - Structure, Properties   102
                     and Applications
• Glass Transition Temperature
• Amorphous polymers do not have a
  specific melting point but undergo a
  distinct change in behavior over a
  specific temperature range
• This is known as the glass transition
  temperature, Tg
• Below Tg – hard, rigid and brittle
• Above Tg – rubbery and leathery
• Tg important in service considerations
  and production
               Polymers - Structure, Properties   103
                     and Applications
Additives
• To improve characteristics below Tg polymers can
  be blended.
• Several types:
   Fillers – solid or fibrous, improve mechanical
     performance
   Plasticizers – e.g. elastomer, lowers Tg and
     improves toughness
   Colorants – dies and pigments, impart required
     color; carbon provides protection against UV
     radiation
   Others – flame retardants, lubricants (reduce
     friction during forming process), cross-linking
     agents
                  Polymers - Structure, Properties   104
                        and Applications
Types
Three basic types of polymers:
Thermoplastics – Polymers which can be raised to
  temps above their Tg and cooled (softened and
  hardened) without modifying any of their original
  material properties—effects of heating are
  reversible
   Examples: Nylons, Fluorocarbons (Teflon), PVC,
  Polystyrenes
   If temp of thermoplastic is raised above Tg,
  becomes a viscous fluid (not definite melting
  temperature, softens over range of temp)
  Repeated heating and cooling cycles produces
  thermal degradation (thermal aging)
                 Polymers - Structure, Properties   105
                       and Applications
                              Teflon
                 Poly(tetrafluoroethene)




•Very non-reactive – non-stick coatings for cookware, hardened munitions,
etc.
•Discovered accidentally during refrigerant research
•Tends to creep at room temperature – can be both good and bad depending
on design
                                  PVC
                   Polyvinyl chloride (polychloroethene)




•Huge number of uses – plumbing, magnetic stripe cards, hoses, flooring,
electrical insulation (fire retardant)
•Plasticizers enabled use and processing
•Can be further chlorinated with chlorine gas and UV to replace some of the
hydrogen (CPVC) – increases TG
Thermosetting polymers -The polymerization bonds
  in these materials are set and permanent—thus,
  the curing reactions are irreversible (unlike
  thermoplastics); "non-recyclable" material, cannot
  be melted (will decompose first)
   Examples: Epoxies, Silicones, Polyesters,
  Urethane (some are thermoplastic)
   No well defined glass transition temp—two stage
  curing process:
  (1)mix molecules to partially polymerize into linear chains
    and
  (2) set molecular structure by heating, forming and cooling
    processes
   Better mechanical properties in general than
  thermoplastics Polymers - Structure, Properties        108
                         and Applications
                  Silicones
• Contain silicon, carbon, hydrogen, and
  oxygen, and sometimes others.


             polydimethyle siloxane



• Good temperature stability, chemical
  resistance, electrically insulating, non-
  toxic, somewhat gas permeable
            Polyurethane




• Depending on R groups – useful for
  foams, insulation, adhesives, tires,
  furniture, sealants, coatings.
Epoxies
                 Epoxies
• Three dimensional cross linked polymers
• Usually applied in two parts
• Useful for coatings and as matrix for
  composites.
• Properties can be tailored by adjusting R
  groups.
Elastomers – Exhibit large elastic deformations, low
  Tg, soft, show hysteresis loss effects during
  unloading - differences in curves represents
  energy loss (vibration dampening and sound
  absorbing)
  Elastomers can be "thermoset" by vulcanization
  and cross-linking of polymer chains occurs at high
  temperatures can also be thermoplastics
   Examples: tires; hoses; tennis shoe soles; tooling
  (esp. urethanes)



                  Polymers - Structure, Properties   114
                        and Applications
Polymers - Structure, Properties   115
      and Applications

								
To top