UEET 601

1
UEET 601

• Modern Manufacturing
• Introduction to structure and properties of
  materials

2
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

3

• 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

4

• 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

• 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

6

• 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

7

• 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.

8
Structure of Materials
9
The most important concept in materials science

• Structure Property Relationships

Composition
Properties
Structure
Processing
Useful applications
10

• 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, thats why.
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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.
were going to forget about the Bose-Einstein
condensate for this class.
12
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.,)
13
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
14
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.
15
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.
16
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
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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 isnt
  supposed to have one
• Line
• - dislocations
• Planar
• - twins
• - grain boundaries

18
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 Melting point 660 C Mohs hardness
2.75 Electrical resistivity 2.65 x 10-6 Ocm
Al2O3 Melting point 2054 C Mohs hardness 9
(about 100X harder) Electrical resistivity 2.0 x
1013 Ocm
Semiconductors are generally similar in bonding,
but with greater ease of freeing an electron.
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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
20
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.
21
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.

22
Structure of Materials - Polymers

• Covalently bonded chains, made from repeating
  monomer units polymerization

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

H
H
H
H
H
H
Catalyst, heat, light
C
C
C
C
C
C
H
H
H
H
H
H
n
ethylene
polyethylene
23
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.
24
Mechanical, Physical, and Manufacturing
Properties of Materials
25
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

26
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.

27
Tension Test

• A material loaded in tension will stretch.

F
A
L0
stress
units are force per area Mpa, psi
strain
Dimensionless, expressed as in/in or
What is the relationship between stress and
strain? It depends on the material.
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Stress Strain Curves
http//irc.nrc-cnrc.gc.ca/images/cbd/157f02e.gif
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Stress Strain Curves
Proportional, Hooks law, Youngs modulus, Es/e
http//www.mech.uwa.edu.au/unit/MECH2402/lectures
/hot_cold_working/degarmo_17-7.gif
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Ductility

• The extent to which plastic deformation takes
  place before fracture
• Elongation
• Percent reduction in cross sectional area

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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.

32
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

33
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.

34
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 gt 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

35
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)

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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

37
Specific properties are a convenient way to
compare materials
38
Density
Mass per unit volume
g/cm3, lb/ft3
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
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Heat Capacity
Energy required to change temperature
cal/gC, J/gC, cal/lbF
Important for machining, forming, and thermal
management, why?
Thermal Expansion
Dimensional change per unit temperature
1/C
Important for stress management, expansion joins,
glass metal seals, shrink fits, thermal fatigue,
etc.
40
Thermal Conductivity
Rate at which a material can transport heat.
W/mK
Important for machining, thermal management
(extrusion, microelectronics, etc.)
Electrical Conductivity
Ability of a material to carry electrical
current, inverse of resistivity.
1/ Ocm
Important for electrical applications, examples?
41
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.
42
Magnetic properties
Important in hard disk industry, transformers, RF
processing, others?
Other properties
Piezolectric, ferroelectric, thermoelectric,
magnetorestriction, magnetoresistance. What
might these be useful for?
43
Changing Properties of Metals, Heat Treatment and
Strengthening Processes
44
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
45
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.

46
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.

47
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/96
ClassProj/sciviz/html/clicktuta.html
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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
49
General classes of steels

• Low carbon (mild steels) lt0.3 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 gt0.6 C hard, strong,
  brittle, tool steel, springs, cutting tools

50
Heat Treatments

• Both microstructure and composition affect a
  materials 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.

51
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/tt
  tdiagram.html
• http//www.matter.org.uk/steelmatter/metallurgy/7_
  1_2.html

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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 lt650 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.

53
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.
54
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.

55
Non-ferrous Alloys
56
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

57
Aluminum and its Alloys

• General properties
• very high specific strength and stiffness
• good corrosion resistance, good formability
• easily formed into shape
• good electrical conductivity
• good thermal conductivity

• Relevant Applications
• transport industry, structural parts (B747 82
  Al)
• containers and packaging (cans, foils, etc),
  aerospace
• cookware, aircraft skin
• overhead power lines, electrical applications
  (integrated circuits)
• heat exchanger tubes, radiators

58

• 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/4Cu - 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

59
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

60
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

61

• 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

62
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

63

• 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
  - NiCrMo 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

64
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

65

• 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)

66
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

67
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

68

• 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)

69

• 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

70
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

71

• 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

72
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

73
Others

• Shape Memory alloys
• When deformed plastically at room temperature
  will return to original shape upon application of
  heat.
• Example 55Ni/45Ti.
• 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.

74

• Nanomaterials
• Materials having sizes in the order of 1 - 100
  nm.
• Currently under very active research
• Microelectromechanical devices, medical
  applications

75
Ceramics, Glass, Graphite, Composite Materials
76
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.

77
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

78

• 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 (3CaOSiO2, 2CaOSiO2)
  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

79

• 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)

80

• 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.?)

81

• 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

82
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/Pe
rovskite.jpg
83

• 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
  (CRTs, LCDs, TVs, lighting, containers,
  cookware, microelectronics especially
  chalcogenide glasses)

84
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
85

• 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

86
Glass Modifiers

• Na lowers melting point, but increases water
  solubility
• 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)

Modifiers can alter properties to suit different
applications.
87
Tensile failure in glass
H2O
H
H
O
O
Si
Si
O
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
88

• 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

89

• 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

90
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

91

• 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

92

• 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

93

• 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

94

• 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

95

• 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)

96

• 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?

97
Polymers Structure and Properties
98

• 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

99

• 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

100

• 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

101

• 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

102

• Example formation of polyethylene form ethylene

103

• 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

104

• 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

105

• 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 propertieseffects 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)

106
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

107
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

108

• Thermosetting polymers -The polymerization bonds
  in these materials are set and permanentthus,
  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 temptwo
  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

109
Silicones

• Contain silicon, carbon, hydrogen, and oxygen,
  and sometimes others.

polydimethyle siloxane

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

110
Polyurethane

• Depending on R groups useful for foams,
  insulation, adhesives, tires, furniture,
  sealants, coatings.

111
Epoxies
112
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113
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.

114

• 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)

115
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