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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

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ueet 601

UEET 601

Modern Manufacturing

Introduction to structure and properties of materials

introduction
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

UEET 601 Modern Manufacturing

slide3
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

UEET 601 Modern Manufacturing

slide4
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

UEET 601 Modern Manufacturing

slide5
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

UEET 601 Modern Manufacturing

slide6
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

UEET 601 Modern Manufacturing

slide7
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.

UEET 601 Modern Manufacturing

the most important concept in materials science
The most important concept in materials science

Structure – Property Relationships

Composition

Structure

Properties

Processing

Useful applications

slide10

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 materials11
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 materials12
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
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 metals14
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 metals15
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 metals16
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 metals17
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
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 10-6Ωcm

Al2O3

Melting point 2054 °C

Mohs hardness 9 (about 100X harder)

Electrical resistivity 2.0 x 1013Ωcm

Semiconductors are generally similar in bonding, but with greater ease of freeing an electron.

structure of materials semiconductors
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 semiconductors20
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
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
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

structure of materials polymers23
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 properties
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
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
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.

stress strain curves
Stress – Strain Curves

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

stress strain curves29
Stress – Strain Curves

Proportional, Hook’s law,

Young’s modulus, E=s/e

*http://www.mech.uwa.edu.au/unit/MECH2402/lectures/hot_cold_working/degarmo_17-7.gif

ductility
Ductility

The extent to which plastic deformation takes place before fracture:

Elongation

Percent reduction in cross sectional area

hardness
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
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
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
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
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
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
density
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…

heat capacity
Heat Capacity

Energy required to change temperature

[cal/g°C, J/g°C, cal/lb°F]

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.

thermal conductivity
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/ Ωcm]

Important for electrical applications, examples?

chemical compatibility
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
Magnetic properties

Important in hard disk industry, transformers, RF processing, others?

Other properties

Piezolectric, ferroelectric, thermoelectric, magnetorestriction, magnetoresistance. What might these be useful for?

structure of alloys
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
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
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
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
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
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
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
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
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
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

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.

introduction56
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

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

Aluminum and its Alloys
slide58
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 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
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
slide61
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
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
slide63
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
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
slide65
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
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
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
slide68
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)
slide69
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
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
slide71
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
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
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.
slide74
Nanomaterials
  • Materials having sizes in the order of 1 - 100 nm.
  • Currently under very active research
  • Microelectromechanical devices, medical applications
ceramics
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 Materials

mechanical properties77
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
slide78
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 Materials

slide79
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 Materials

slide80
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 Materials

slide81
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 Materials

symmetry and crystallography are important for many of the electronic applications of ceramics
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

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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 Materials

structure of glass
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

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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 Materials

glass modifiers
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.

tensile failure in glass
Tensile failure in glass

H2O

H

H

O

O

Si

Si

Si

O

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

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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 Materials

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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 Materials

composite 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 Materials

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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 Materials

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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 Materials

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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 Materials

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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 Materials

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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 Materials

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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 Materials

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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 and Applications

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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 and Applications

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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 and Applications

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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 and Applications

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Example: formation of polyethylene form ethylene

Polymers - Structure, Properties and Applications

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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 and Applications

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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 and Applications

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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 and Applications

teflon
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
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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
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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 and Applications

silicones
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
Polyurethane
  • Depending on R groups – useful for foams, insulation, adhesives, tires, furniture, sealants, coatings.
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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.
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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 and Applications